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Project Specific Discussions => Filters/Equalizers => Topic started by: ruffrecords on January 09, 2013, 05:14:38 PM

Title: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 09, 2013, 05:14:38 PM
I was recently asked if I could design an EQ that worked like the 'pop' and 'classic' EQ plug ins that used to be used in the REDD47 consoles and predecessors. Using the curves published in 'Recording The Beatles' I came up with a circuit based on a stripped down and modified Helios 69 EQ with a switch to selec 'pop' or 'classic'. I was then asked if I could not make it so both the the 'pop' and 'classic EQ curves were available at the same time. In doing this, a very strange thought occurred to me. The Helios treble EQ is virtually identical to the EMI 'classic' EQ curves (the frequency, step size and gain range are identical) as is the bass cut except for the frequency it works at. The bass boost is very nearly the same but tweaked from a shelf to a bell curve. The clincher is that the 'pop' 4.7KHz peaking EQ is a stepped version of one of the Helios 69 mid boost frequencies.

I then realised that Dick Swettenham, who designed the Helios 69 EQ, had previously worked at Abbey Road studios in the service and design departments so he must surely have had a deep understanding of the innards of the REDD EQ.

I am sure you can now see where I am going with this. Is the Helios 69 EQ simply a modified and expanded version of the REDD EQ?

I simulated a cut down version of the Helios 69 EQ (pic attached)  and it is surprisingly easy to get curves very close to those of the REDD EQ.

What do you think/know??

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: dissonantstring on January 09, 2013, 05:21:16 PM
ian, very nice observation.  thanks!
best,
grant
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Dylan W on January 09, 2013, 08:50:11 PM
Fascinating, Ian, had no idea Swettenham worked at Abbey Road. You know, I was just thinking about something yesterday.. I love the Abbey Road RS 127 plugin (a model of the outboard Brilliance Box, apparently used as an extension to the Pop/Classic board eq). It is a +/- 10dB boost/cut in 2dB steps, frequency selectable at 2.7K, 3.5K, and 10K. It's apparently another passive design. My Christmas copy of Recording the Beatles is still in the mail somewhere, so I don't know if the curves are in there, but it would be unbelievable to have a couple of these.

Dylan
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on January 10, 2013, 07:06:53 AM
To add the Brilliance in the circuit may be a great idea. I know the RS127 plugin and I find it amazing!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 10, 2013, 08:09:16 AM
Funny you should mention the RS127 because as soon as I sent my outline design to the guy who asked about the REDD EQ, the first thing he said was could I add the RS127.

I'll look into it.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: letterbeacon on January 10, 2013, 05:16:33 PM
I would also be very interested in this!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: alexc on January 10, 2013, 11:15:45 PM
At least!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on January 11, 2013, 01:57:42 AM
I am interested, too!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 11, 2013, 05:36:05 AM
I am in two minds about doing an RS127. One the one hand it is little more than three boost/cut frequencies on the Helios EQ, albeit with switched boost/cut on a single control so in that sense it is already available.  On the other hand, from reading Recording The Beatles, it seems the RS127 was used a lot as a passive balanced lossy stand alone outboard EQ so we could contemplate replicating that. Or we could do a brand new EQ which incorporates the REDD EQ and the RS127 in one.

Thoughts/preferences?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: bernbrue on January 11, 2013, 06:25:36 AM
Or we could do a brand new EQ which incorporates the REDD EQ and the RS127 in one.
Thoughts/preferences?

Cheers

Ian

A combo of both would be fantastic! Excellent observation!!
regards
Bernd
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: alexc on January 11, 2013, 06:27:24 AM
Brand new combo with the reddeq and rs filter done Ian style  :)

(please!)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on January 11, 2013, 07:34:13 AM
My vote is for a new EQ which incorporates the REDD EQ and the RS127 in one
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Holger on January 11, 2013, 07:48:05 AM
My vote is for a new EQ which incorporates the REDD EQ and the RS127 in one

preferably on a 100 x 160 mm euro card
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on January 11, 2013, 08:12:13 AM
My vote is for a new EQ which incorporates the REDD EQ and the RS127 in one, too

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 11, 2013, 09:57:00 AM
Damn, that was quick AND decisive. I think we have a consensus!! OK, so my next EQ project is a REDD EQ with incorporated RS127.

The only real question is this. The RS127 had boost/cut  frequencies either side of the 4.7KHz 'pop' boost in the REDD EQ so it effectively just extended the range of frequencies the REDD had from one to four. In theory, with a REDD EQ followed by the RS127, you could boost at 4.7KHz with the REDD and boost/cut at another frequency with the RS127 at the same time. Do we want to be able to do that or can I incorporate the 4.7KHz in with the RS127 frequencies which means that although you can only boost/cut one frequency at a time you are not limited to just boosting at 4.7KHz?

I have a strong suspicion they selected a single frequency depending on the material and rarely if ever boosted at two frequencies simulataneously - but who knows?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on January 11, 2013, 10:47:51 AM
An option may be: 10khz control (High), 100 hz (bass) and to include the 5khz in the middle with the others values of the RS127 (2,7khz, 3,5khz, 5khz)

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: nille on January 11, 2013, 10:59:21 AM
They talk about centre frequencies being shifted by the interfacing transformer on page 10 in the Abbey Road plugin manual.
Perhaps something to consider.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on January 11, 2013, 01:33:54 PM
I know the RS127 is a passive circuit ... the REDD Eq is passive, too?
Anyway a passive circuit may be a good choice so each one can decide to put a tube or discrete makeup amp
I am building some REDD 47 preamplifiers and it may be amazing to have a complete channel strip of the REDD 51 Console
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: letterbeacon on January 11, 2013, 02:09:25 PM
Yes, it would be great to use the REDD47 as the make up gain stage after the EQ and then there's also Ian's tube make up gain PCB to choose from too.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on January 11, 2013, 02:38:07 PM
+1 for passive circuit
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 11, 2013, 03:30:04 PM
Yes, it would be great to use the REDD47 as the make up gain stage after the EQ and then there's also Ian's tube make up gain PCB to choose from too.

Are you thinking of using a complete REDD 47 channel as gain make up i.e. going in at the mic transformer?? If you are then that would mean the passive EQ would have to be 600 in and 600 out. Truer to the spirit of the EMI days but is it practical for the present day?

The alternative is 10K bridging input followed by an regular op amp or tube gain make up.

Cheers

ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: letterbeacon on January 11, 2013, 06:19:16 PM
I think the best thing would be to make it as universal as possible -I was just thinking out loud about using the REDD47 as a make up stage.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 11, 2013, 06:38:01 PM
I think the best thing would be to make it as universal as possible -I was just thinking out loud about using the REDD47 as a make up stage.

OK, I will start with the basic Helios topology as that seems to have been derived from the EMI EQ and see what I can come up with. So we have a 10K bridging input and your choice of gain make up afterwards.

Cheers

ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on January 12, 2013, 01:30:58 AM
I agree for a passive circuit and it may be useful to design the pcb as small as possible so it can be adapted in a blank API module (for example)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 12, 2013, 06:34:50 AM
I agree for a passive circuit and it may be useful to design the pcb as small as possible so it can be adapted in a blank API module (for example)

Yes, that is a problem with the current Helios PCB; it's too big to fit into a 500 series module. One option would be to do a PCB similar to the universal EQ where all the controls are off PCB.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on January 12, 2013, 06:53:29 AM
A circuit where all the controls are off the pcb may be the right solution for all
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on January 12, 2013, 07:30:38 AM
To put all the controls off the pcb it is a good idea, but ... have you plans to use single inductors or multi tapped ones?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 12, 2013, 09:19:20 AM
To put all the controls off the pcb it is a good idea, but ... have you plans to use single inductors or multi tapped ones?

Probably multi-tapped. The bass inductor looks like being 7 Henries. The presence and treble boost could be a multi-tap. The classic top cut/boost is identical to the Helios 10KHz cut/boost and so would be RC only.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 13, 2013, 11:17:57 AM
I have drawn up a schematic of a combined REDD EQ and RS127. I am not 100% sure the  presence switch works but I was trying to avoid having another 2 pole 11 way switch as is needed for the bass. I need to do some simulations to see if this is going to work as expected. At the moment there are just four switched controls: bass, treble and presence boost/cut plus presence frequency select.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/MK1cicuitscaled.jpeg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/MK1cicuitscaled.jpeg)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on January 13, 2013, 12:14:28 PM
Considering this circuit do you think it's possible to keep the controls on a pcb compatible with API dimensions?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 13, 2013, 03:49:32 PM
Considering this circuit do you think it's possible to keep the controls on a pcb compatible with API dimensions?

Yes, I think that would be possible. It has a couple of inductors just like the Helios EQ I did. It uses the identical treble boost/cut circuit and the same bass boost/cut switching. The mid boost/cut frequency selection is much the same as the Helios and the mid  gain pot plus boost/cut toggle has been replaced by a single pole 12 way switch. The Helios I managed to get into a PCB 100mm by 100mm with three of the switches on the PCB and I see no reason why this EQ should not be the same.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Marc Duchesne on January 13, 2013, 06:50:47 PM
Though about a 500 (51X) board dimension Ian...
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 14, 2013, 04:21:41 AM
Though about a 500 (51X) board dimension Ian...

Good question. 500 series is very popular. For my other EQ designs I have left the choice of enclosure and gain make up amp up to the DIYer. This provides the maximum flexibility and at the moment I see no reason to change that.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 14, 2013, 12:30:13 PM
I have just finished simulating the initial presence control design and it appears to work OK. We can get the same centre frequencies as the RS127 using the Carnhill VTB9044 inductor ( or the Chrion equivalent) and appropriate taps/caps. I have tweaked it so it has the same boost Q as indicated by the 4.7KHz curve in 'Recording The Beatles' (about 0.5). I am assuming the Q is the same at each of the four presence frequencies.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/presencesim.png (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/presencesim.png)

The cut works using the same LC pairs as for boost and so, just like the Helios, the cut Q is several times the boost cut at about 2.5.

Now, I have no way of knowing if EMI use the same LC pairs for cut or a completely different set to keep the Q the same. In the absence of actual curves for the RS127 presence control it is impossible to know. So, does anyone have such a set of curves or could someone create them using the RS127 plug-in??

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: bernbrue on January 14, 2013, 12:53:10 PM
http://www.gearslutz.com/board/music-computers/216773-abbey-road-brilliance-pack-4.html

A guy over at gearslutz did some measurements.
regards
Bernd
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: TimS on January 15, 2013, 02:38:29 AM
Yet another cool project!

I do hope the Universal Passive EQ is still in the works, though - I've got all sorts of ideas for what I want to do with that thing.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 15, 2013, 06:15:52 AM
Yet another cool project!

I do hope the Universal Passive EQ is still in the works, though - I've got all sorts of ideas for what I want to do with that thing.

Yes, I am still working on that. I recently created a new footprint that allows you to fit either Car hill or Chrion inductors on the PCB. I have also tweaked a lot of the tracking to make it a single sided PCB suitable for home etching.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 18, 2013, 06:40:13 AM
Dylan has kindly made some excellent measurements of the available plugins. From these it is clear that the cut Q is the same as the boost Q which means I need to rethink the cut - probably needs its own inductor.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on January 19, 2013, 11:20:33 AM
 8)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on January 21, 2013, 12:09:52 PM
Hi Ian, any news about this fantastic project?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 21, 2013, 03:47:59 PM
Hi Ian, any news about this fantastic project?

Squeezing it in between the EZTube MIxer, the universal EQ and switch PCBs for the same!!

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: leadbreath on January 22, 2013, 10:33:36 AM
hey ian i love u man.... :-*
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 23, 2013, 03:43:08 PM
Following the information provided by Dylan concerning the actual shape of the Brilliance boost and cut curves, I have redesigned the circuit to use separate inductors for the brilliance boost and cut so as to keep the Q the same for both. This unfortuantely means another 2 pole 11 way switch is needed but I cannot see a way to avoid it. I have yet to work out all the component values but hereis the MKII circuit:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/MKIIcircuit.jpg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/MKIIcircuit.jpg)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: dissonantstring on January 23, 2013, 04:08:21 PM
hi ian,
liking this project's progression.  thank you very much kind sir for all your time and energies.  i also like the way you arc the switch position connections in your schem.   :D 
best,
grant
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 24, 2013, 05:58:11 PM
I have done some simulations of the new design which confirms the brilliance boost and cut Q can be made the same and I have  worked out an initial set of capacitor and inductor values. It looks like the brilliance boost can be done with a VTB9044 inductor but there seems to be no standard one that will do the brilliance cut. This needs values of 10, 20, 32 and 40mH. Looks like on for Chrion.

I also discovered an error in the bass cut circuit which I have fixed hopefully. Pic of simulation circuit with notes attached.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Dylan W on January 24, 2013, 06:14:28 PM
I have done some simulations of the new design which confirms the brilliance boost and cut Q can be made the same and I have  worked out an initial set of capacitor and inductor values. It looks like the brilliance boost can be done with a VTB9044 inductor but there seems to be no standard one that will do the brilliance cut. This needs values of 10, 20, 32 and 40mH. Looks like on for Chrion.

I also discovered an error in the bass cut circuit which I have fixed hopefully. Pic of simulation circuit with notes attached.

Cheers

Ian

Glad to see this is coming along. How sharp did you decide to go for the brilliance Q in general?

Dylan
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 24, 2013, 06:46:53 PM
I have done some simulations of the new design which confirms the brilliance boost and cut Q can be made the same and I have  worked out an initial set of capacitor and inductor values. It looks like the brilliance boost can be done with a VTB9044 inductor but there seems to be no standard one that will do the brilliance cut. This needs values of 10, 20, 32 and 40mH. Looks like on for Chrion.

I also discovered an error in the bass cut circuit which I have fixed hopefully. Pic of simulation circuit with notes attached.

Cheers

Ian

Glad to see this is coming along. How sharp did you decide to go for the brilliance Q in general?

Dylan


I have not measured the actual Q yet. I simply adjusted it to be visually the same as the ones you provided for me. Next job is to do that and and create a set of curves.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 25, 2013, 11:41:15 AM
I spent a few hours struggling with LTspice trying to get it to step through the pot values for brilliance boost and cut  at 4.7KHz and finally bullied the  bl...y thing into submission. The results are attached. The cut is not quite the mirror of the boost but it is close. Perhaps Dylan, you would like to compare them with the plots you made of the plug-ins.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on January 29, 2013, 01:59:51 AM
Hi Ian, any progress?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 29, 2013, 05:38:23 AM
Hi Ian, any progress?

Dylan has checked my sims against his plugin measurements and reported that the 2.7 and 10KHz curves are not symmetrical but other than that they look good.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on January 29, 2013, 06:03:41 AM
Thank you Ian for what you are doing for us
Fab
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 29, 2013, 12:39:27 PM
I have now beaten LTspice into submission and it now prints out the plots just as I want them. The following links take you to pics of the set of curves for 2.7KHz, 3.5KHz, 4.7KHz and 10KHz respectively:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/2k7plot.jpg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/2k7plot.jpg)

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/3k5plot.jpg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/3k5plot.jpg)

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/4k7plot.jpg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/4k7plot.jpg)

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/10kplot.jpg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/10kplot.jpg)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 30, 2013, 05:13:04 PM
I have now compared the plots from the LTspice simulation with those of the plug-ins made by Dylan. The curves are not identical but they are within half a dB at the extremes of the curves and spot on in the middle (except for the 10KHz plot where the plug-in seems to peak at 9KHz.

I think that is close enough so the next step is to update the schematic and begin a PCB layout.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: buildafriend on January 30, 2013, 05:58:06 PM
oh man, my orange 86 project just got cooler.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 31, 2013, 06:03:24 AM
oh man, my orange 86 project just got cooler.

I can't seem to find a schematic for the orange 86. How are you intending to incorporate this EQ?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ethervalve on January 31, 2013, 09:55:21 AM


I can't seem to find a schematic for the orange 86.


Charlie's site seems to be down. I just put my copy on dropbox: https://dl.dropbox.com/u/5567562/Orang86schematics.pdf
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: buildafriend on January 31, 2013, 03:09:21 PM
my assumption was that I could throw this post output transformer as a passive second stage within the same chassis. if you dont mind my asking, was the redd47 eq implimented differently than the way I am imagining?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 31, 2013, 03:54:47 PM
my assumption was that I could throw this post output transformer as a passive second stage within the same chassis. if you dont mind my asking, was the redd47 eq implimented differently than the way I am imagining?

The REDD47 EQ was implemented exactly as you imagine but it does have an insertion loss which was often made up by following it with another REDD47. Also it was 200 ohms balanced in and out.

My version is like the Helios and Pultec EQs I designed earlier in that it is intended for a 10K bridging input and needs to be followed by a dedicated gain make up amplifier. If you wanted it to be an 100% passive, no gain make up, 600 in, 600 out equaliser then that could be done by adjusting the component values but it would have about 15dB insertion loss.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: drask on January 31, 2013, 04:06:39 PM
Hi Ian,

Do you know wich amp is in the RS127? Tube? Germanium? Transistor?

Thank's
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: buildafriend on January 31, 2013, 07:16:01 PM
my assumption was that I could throw this post output transformer as a passive second stage within the same chassis. if you dont mind my asking, was the redd47 eq implimented differently than the way I am imagining?

The REDD47 EQ was implemented exactly as you imagine but it does have an insertion loss which was often made up by following it with another REDD47. Also it was 200 ohms balanced in and out.

My version is like the Helios and Pultec EQs I designed earlier in that it is intended for a 10K bridging input and needs to be followed by a dedicated gain make up amplifier. If you wanted it to be an 100% passive, no gain make up, 600 in, 600 out equaliser then that could be done by adjusting the component values but it would have about 15dB insertion loss.

Cheers

Ian

So a poor mans tube gain make up stage might be wise.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 01, 2013, 07:55:15 AM
Hi Ian,

Do you know wich amp is in the RS127? Tube? Germanium? Transistor?

Thank's

It did not have an amp. It was 100% passive. It did not contain a gain make up amp and so it had an insertion loss, probably around 10 to 15dB. In those days everything was 600 ohms in and 600 ohms out (or 200 in the case of EMI) and they were just plugged together and a REDD47 pre added at the end to restore the gain.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 01, 2013, 07:58:43 AM
So a poor mans tube gain make up stage might be wise.

Yes!

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 01, 2013, 12:36:37 PM
I have finished updating the schematic and filled in all the values as well as correcting the bass cut circuit error. Next I will begin the PCB layout.I am going to start with a Eurocard sized PCB so it is compatible with the EZ Tube Mixer.

Cheers

Ian

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on February 02, 2013, 02:22:14 AM
Hi Ian,
have you plans to realize the circuit with all the controls off PCB so it si possible to adapt the board in API module?
Have a nice weekend!
Fab
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 02, 2013, 08:20:29 AM
Hi Ian,
have you plans to realize the circuit with all the controls off PCB so it si possible to adapt the board in API module?
Have a nice weekend!
Fab

I don't know. It would be nice if it could be used in a variety of places;  EZ Tube Mixer, 500 series or 19inch racks.

I am not sure how mounting the controls off the PCB would help that. At the moment I have the bass, brilliance and treble level controls on the PCB (Grayhills) and the brilliance frequency select off board. You could easily wire an off board switch to the Gray hill pads.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on February 02, 2013, 10:39:22 AM
In a API 500 format I am sure it becomes a best seller!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: buildafriend on February 02, 2013, 12:32:44 PM
I would like as much as possible to be on the PCB, I also prefer the grayhill switches. Small enough to fit in 500 format is a great idea. 
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 02, 2013, 04:53:21 PM
The PCB is currently 100mm tall and a 500 series card is about 114mm high so this PCB will definitely fit in a 500 format. The only question is how will you do the input and gain make  parts?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on February 03, 2013, 02:36:33 AM
Hi Ian,
what do you think about the possibility to include in the PCB a small stage for gain with 2 or 3 transistors (es. BC184) similar to Neve output stage?

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 03, 2013, 01:34:06 PM
Hi Ian,
what do you think about the possibility to include in the PCB a small stage for gain with 2 or 3 transistors (es. BC184) similar to Neve output stage?

To be honest I am very reluctant to do that because all my designs are vacuum tube based. I don't do transistor designs any more and I don't really want to go back to them. Unfortunately the 500 series format does not really lend itself to vacuum tubes (I have looked into it in some detail) so there is little incentive for me to develop 500 series boards. I know the 500 series is very popular and if my designs appeared in a 500 format they would probably be very popular but I am not in it for popularity or money - I do it because it is fun.

A lot of people have built my EQ designs into rack mounting units and that is fine because there are plenty of available gain make up amps you can use in that format but it is not so easy for 500 series. I am happy to do them in eurocard height format and these should fit into a 500 series module but you will have to sort out your own gain make up.

On the other hand, this is a bit of a special case because I don't think there is a 500 module available with this EQ. I guess it deoends on just how many people would want a 500 series card with this EQ.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: mylesgm on February 04, 2013, 04:08:03 AM
I would be happy to do this eq in 500 and I'm sure there are many more people interested too.  The easiest way would be to create the eq board in such a way that it can use an existing interface like this: http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=128

Then the builders can decide what opamps/tx they wish to use or can create their own interface if there is enough space left in the 500 footprint.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on February 04, 2013, 07:20:06 AM
It seems the right solution ;)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: buildafriend on February 04, 2013, 11:07:19 AM
if it is made as a 500 series card :'(, I would greatly appreciate some terminal block pads for input and output so that it can be integrated in a normal rack mount chassis, as you had originally intended.

thanks regardless
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Biasrocks on February 04, 2013, 01:41:48 PM
http://classicapi.com/catalog/product_info.php?cPath=84_86&products_id=147

if it is made as a 500 series card :'(, I would greatly appreciate some terminal block pads for input and output so that it can be integrated in a normal rack mount chassis, as you had originally intended.

thanks regardless
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 04, 2013, 04:21:06 PM
I would be happy to do this eq in 500 and I'm sure there are many more people interested too.  The easiest way would be to create the eq board in such a way that it can use an existing interface like this: http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=128

Then the builders can decide what opamps/tx they wish to use or can create their own interface if there is enough space left in the 500 footprint.

That looks to be an interesting option. Does anyone have exact dimensions for this PCB?? I printed off the bare PCB from the web site and guestimated its depth as 68mm. Given the 500 series total depth if 150.8 mm that leaves about 82mm in which to squeeze the EQ which is half the depth of a Eurocard and rather tight.

The other thing I am not clear about is what do you use for metalwork if you don't buy a kit?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on February 05, 2013, 04:56:14 AM
Another solution may be this one

http://www.audiomaintenance.com/acatalog/blank_pcbs.html

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: shabtek on February 05, 2013, 07:34:53 AM
whoa there Strawties;

 ;Dnobody would know what to do with that (;D cheeky)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on February 05, 2013, 10:35:49 AM
You can mount the circuit on the 500 Board and then build a small gain preamplifier on the remaining part (the Neve circuit in this page may be a good example)
The JLM Audio circuit is really nice, but for a loss of 10/15 dB perhaps it is too  ;D
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 05, 2013, 05:48:46 PM
It seems there is a range of options for those keen to put this into a 500 series module. What I will do is keep it 100mm high with standard 3U module fixing holes, but also try to keep it as shallow as possible so 500 series fans can use it too.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on February 06, 2013, 01:50:43 AM
Ian, have you found the 7h inductor for bass?
I have made a little search but for those values I have seen inductors similar to transformers
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 06, 2013, 06:13:43 AM
Ian, have you found the 7h inductor for bass?
I have made a little search but for those values I have seen inductors similar to transformers

Yes, there is a Carnhill inductor with a 7H tap, the VTB9043. It is the very small values I am having trouble finding.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on February 06, 2013, 01:59:48 PM
Great Ian, I can't wait to see this circuit!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on February 07, 2013, 01:14:56 AM
In the last schematic posted by Ian there are 3 multi tapped inductors (considering that the 7H one is in a multi tapped inductor) ... not really cheap ... but if it sounds like I expect ...
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 07, 2013, 08:46:16 AM
Several people have asked about using the REDD EQ with the REDD 47 mic preamp. Like my other passive EQs, this one does need some gain make up and there is no easy way to fit the EQ within the existing REDD 47 circuit because it is all tied together via negative feedback. So you really need a separate gain make up stage.

One way to solve this is to remove the output transformer and drive the EQ direct from the output of the E88CC then add another E88CC stage for gain make up after the EQ (you will need to modify it to increase its gain). You can then fit the output transformer here instead of after the first E88CC.

Or you could use the poor man's tube gain make up stage or something similar.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: baadc0de on February 07, 2013, 10:12:06 AM
Hi Ian. The additional E88CC would probably be easier to do as it could run off the identical power supply or lightly modified?

Cheers,
Bojan.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 07, 2013, 11:20:43 AM
Hi Ian. The additional E88CC would probably be easier to do as it could run off the identical power supply or lightly modified?

Cheers,
Bojan.

Yes, that is true. There is only a small increase in HT and heater currents.

I checked out the REDD 47 schematic and the E88CC stage as it is has a gain of about 13dB so it is almost ready to use (the REDD EQ has an insertion loss of about 15dB). The 330K that goes to the anode of the EF86 would instead go via a capacitor to the output of the EQ. A 1uF 400V orange drop would be fine.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 07, 2013, 12:27:23 PM
In the last schematic posted by Ian there are 3 multi tapped inductors (considering that the 7H one is in a multi tapped inductor) ... not really cheap ... but if it sounds like I expect ...

There are 3 inductors in this design and the values are rather non-standard so I think I will ask Chrion to do a quote for a set.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 11, 2013, 05:59:53 PM
I am making good progress with the PCB layout. I have arranged the three main level switches Treble, Brilliance and Bass on one inch centres on the PCB. The frequency select switch for the Brilliance control will be off board and connected via a 10 way header.

At the moment I am assuming all three inductors will be Carnhil/Chrion types/sizes. However, the ones for the Brilliance cut are quite small in value, ranging from 12mH to 47mH and not available in any of the standard Carnhill types. So I have started a separate thread in the drawing board asking if anyone has had experience of using small leaded inductors in EQ circuits:

http://www.groupdiy.com/index.php?topic=51380.msg652961#msg652961 (http://www.groupdiy.com/index.php?topic=51380.msg652961#msg652961)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on February 12, 2013, 12:17:54 AM
Great work Ian!
I have not experiences with these small inductors but I know someone used them for Pultec eq with good results
Eventually it works, you could use a small single inductor for the bass instead of the big one that is more expensive (it may be good for those like me who want to realize more channels)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 12, 2013, 05:25:08 AM
Great work Ian!
I have not experiences with these small inductors but I know someone used them for Pultec eq with good results
Eventually it works, you could use a small single inductor for the bass instead of the big one that is more expensive (it may be good for those like me who want to realize more channels)

The trouble with the bass inductor is that it is 7 Henries and you can only get that amount of inductance in something fairly large. However, I am sure Chrion would be able to make one for a lot less than the Carnhill price.

Cheers

ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 18, 2013, 04:37:18 AM
I have just had delivery of some small inductors to try in the brilliance cut part of the EQ. I'll build a test circuit and see how it performs. If it works OK I'll build it into the PCB layout.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on February 19, 2013, 05:17:34 AM
 :)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 22, 2013, 03:04:08 PM
I just lashed up the 10KHz brilliance cut circuit using a small 10mH inductor and measured the response. I did not have the exact resistor values to hand so the cut is only just over 8dB but the response looks about right to me. I will try the other frequencies next.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 28, 2013, 06:22:10 PM
I bought some more small  inductors, worked out the values needed to be wired in series to get the values we want, calculated the correct cap values and how to make them with paralleled pairs and built the brilliance cut EQ around a Lorlin switch. I then tested all four frequencies on my Lindos test set. The results are here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/swtests/ (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/swtests/)

Click on any .htm files to get the results in your browser. I did not change the pot values so we still have 8dB cut rather than 10 but it is the same for all four frequencies which is encouraging.

I am happy with these results. The Q seems right as does the overall shape of the plots so I am going to start the PCB layout on the basis of using this circuit and these values. I'll tweak the resistor values on the bench to get the right cut values.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 04, 2013, 06:02:45 PM
I have just about finished the PCB layout for the REDD EQ using the small leaded inductors made by EDCOR for the Brilliance cut. It is fairly tidy and I have checked the ground plane integrity so any changes now would be mostly cosmetic like moving component idents. I need to check it thoroughly against the schematic and then it will be ready to be made. I am expecting the Helios PCBs made by Iteastudio any day now and if these are good I'll most likely get 10 of the RED EQ boards made by them as well as their prices are very reasonable - unless it turns out lots of people want one.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: baadc0de on March 05, 2013, 10:20:19 AM
Well, this is shaping up to be pretty awesome! One small inquiry / request though, since probably a few of us will be using this to augment our existing REDD47 preamps, would an extra PCB that does the E88CC makeup section be feasible? If small enough, maybe that could be added as an extra section that you can opt to use or not on the existing EQ PCB? Sorry for chiming in so late with this idea.. just thought to throw it out and see if anyone likes it!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Marc Duchesne on March 05, 2013, 12:12:23 PM
As I realised, this is not 51X compatible. Will there be a 51X design available.
Thanks !
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 05, 2013, 06:25:10 PM
As I realised, this is not 51X compatible. Will there be a 51X design available.
Thanks !

It is at least partially 51X compatible. It is only 100mm high so it will fit inside a 51X slot but is does not have a 51X connector or input and gain make up circuits. There are ways of doing this that were discussed earlier in the thread using readily available parts.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 05, 2013, 06:32:49 PM
Well, this is shaping up to be pretty awesome! One small inquiry / request though, since probably a few of us will be using this to augment our existing REDD47 preamps, would an extra PCB that does the E88CC makeup section be feasible? If small enough, maybe that could be added as an extra section that you can opt to use or not on the existing EQ PCB? Sorry for chiming in so late with this idea.. just thought to throw it out and see if anyone likes it!

I am trying to keep the number of versions to a manageable number, preferably one!! The current format is ideal for builders of the EZTubeMixer and can also, with a little effort be built into a 51X compatible module. It is also fine for rack mounting module builders as you can use any gain make up you fancy. If you want a tube gain make up stage then you could always use my poor man's tube gain make up stage which uses an E88CC either as a mu follower or SRPP stage. I gues what you would really like it to be the same as the E88CC stage in the REDD47. Let me have a look at the current poor man's tube make up PCB layout and see if it can be built as the REDD 47 E88CC stage.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Marc Duchesne on March 05, 2013, 07:16:32 PM
It is at least partially 51X compatible. It is only 100mm high so it will fit inside a 51X slot but is does not have a 51X connector or input and gain make up circuits. There are ways of doing this that were discussed earlier in the thread using readily available parts.

Cheers

Ian

........

Cool, I can then manage to fit it in a 51X, do you happen to know if anybody designed a 500 front panel already...
Thanks Ian

-marc
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: baadc0de on March 06, 2013, 04:08:09 AM
I totally missed the poor man's makeup. Yeah, if that can be rewired to be similar / same as in the REDD, I'm a happy camper :)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 06, 2013, 06:03:01 AM
Cool, I can then manage to fit it in a 51X, do you happen to know if anybody designed a 500 front panel already...
Thanks Ian

-marc

As far as I know there are no front panel designs at all right now.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: jplebre on March 06, 2013, 09:55:39 AM
So discrete inductors will be the way to go for the small values?

Not a cheap build and not seeing myself able to save any time soon as I need tons of iron for current ongoing projects.

Hey Ian take your time on this one :P "slow makes perfect" and all that :)

Couple of Q if you can spare the time:
Any special considerations if planning on interfacing the O/p with a BA283?
Wouldn't the input have to be balanced? you said you were going to do 10k bridging just want to understand if this would be just something setting the impedance or dealing with the balanced in as well? (hope I'm making sense).

Cheers!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Dylan W on March 06, 2013, 01:49:36 PM
Ian, which inductors did you decide to use? I can't find any small value parts on Edcor's site.

I'll be in for a pair of boards.

Dylan
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 06, 2013, 02:59:18 PM
Ian, which inductors did you decide to use? I can't find any small value parts on Edcor's site.

I'll be in for a pair of boards.

Dylan

My apologies, I must have had well known inductor manufacturers on the brain. The small value inductors are made by EPCOS. - the EPCOS - B82145A Series RF Chokes.

http://tinyurl.com/bz9dbct (http://tinyurl.com/bz9dbct) Edit: fixed URL

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 06, 2013, 03:55:39 PM
So discrete inductors will be the way to go for the small values?

From the few tests I have done so far they seem to work fine. I was feeding levels of +10dBu or more into the test circuit so I could get a 0dBu output so they were getting realistic levels. With +15dBu fed in and maximum cut at 2.7KHz the 1KHz distortion at this level was 0.01%
Quote
Couple of Q if you can spare the time:
Any special considerations if planning on interfacing the O/p with a BA283?
Wouldn't the input have to be balanced? you said you were going to do 10k bridging just want to understand if this would be just something setting the impedance or dealing with the balanced in as well? (hope I'm making sense).

Should be OK - I assume you are talking about the output section of the BA283. Its input impedance should be high enough hot to load the EQ.

The EQ as a whole is unbalanced just like the Helios EQ on which is is based. The input can be run balanced or unbalanced. You can use it unbalanced just like the Helios EQ in the EZTubeMixer or you can balance its input with a 10K:10K bridging transformer or an op amp circuit.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 07, 2013, 05:32:07 PM
I totally missed the poor man's makeup. Yeah, if that can be rewired to be similar / same as in the REDD, I'm a happy camper :)

I have worked out how to modify the poor man's tube gain make up PCB so as to build the REDD 47 E88CC output stage on it. it is not pretty but it's not messy either. Attached pdf document describes how to do it. let me know if you think it is practical or not.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: baadc0de on March 08, 2013, 05:09:38 AM
Perfectly serviceable. Thanks! Put me down for two PCBs of each :)

I totally missed the poor man's makeup. Yeah, if that can be rewired to be similar / same as in the REDD, I'm a happy camper :)

I have worked out how to modify the poor man's tube gain make up PCB so as to build the REDD 47 E88CC output stage on it. it is not pretty but it's not messy either. Attached pdf document describes how to do it. let me know if you think it is practical or not.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Marc Duchesne on March 09, 2013, 06:46:27 PM
Ian, do you think this buffer board could be supplied with something like the G9 (51X format) high voltage converter like Gemini86 built.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 16, 2013, 12:52:02 PM
Ian, do you think this buffer board could be supplied with something like the G9 (51X format) high voltage converter like Gemini86 built.

I think it could. It only consumes about 5mA from the HT supply so it should be fine.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on March 24, 2013, 02:16:51 AM
Hi Ian,
how is the progress of the circuit?
Cheers
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 24, 2013, 07:39:37 AM
Hi Ian,
how is the progress of the circuit?
Cheers

Nearly done. I have been busy with other things just lately. I just need to put the last minute touches to the PCB. Then it's just a matter of guaging the level of interest before ordering some PCBs.

Cheersian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on March 24, 2013, 08:04:40 AM
Thank you Ian
have you already defined the size of the pcb?
Have a nice day
Fab
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 24, 2013, 02:19:51 PM
Thank you Ian
have you already defined the size of the pcb?
Have a nice day
Fab

Pretty much. I made it 100mm  high with 3U fixing holes so it can be used in the EZTubeMixer project and so it would also fit in a 500 series module. The PCB is currently 100mm by 100mm. Attached is a pic of the current layout.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on March 24, 2013, 02:43:39 PM
Thank you Ian!
I have read that the frequency select switch for the Brilliance control will be off board
Do you think it is possible to put all the controls in a API front panel keeping the other switches on board?
Eventually, do you have plans to realise a lorlin off board adapter?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 24, 2013, 07:52:26 PM
Thank you Ian!
I have read that the frequency select switch for the Brilliance control will be off board
Do you think it is possible to put all the controls in a API front panel keeping the other switches on board?
Eventually, do you have plans to realise a lorlin off board adapter?

I have just done a modification to the PCB layout so the brilliance frequency selector uses the same header that we use on the Universal EQ to mate with the off board Grayhill switch PCB. As several people requested it I also did a pin compatible Lorlin board. Both are now available in the Universal EQ group buy:

http://www.groupdiy.com/index.php?topic=51131.msg649433#msg649433 (http://www.groupdiy.com/index.php?topic=51131.msg649433#msg649433)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 27, 2013, 07:18:12 PM
Here is the latest version of the OCB. I corrected some minor and one major error and tidied up all the competent idents. The only thing I need to think about now is whether to include a bypass switch - the original did not have one - you just set the switches to 0dB for a flat response.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Holger on March 28, 2013, 03:02:45 AM
A bypass switch would be nice. Sometimes it is better to improve things.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 28, 2013, 06:19:25 AM
A bypass switch would be nice. Sometimes it is better to improve things.

I think what I will do is include the 'pad' I used in the Pultec EQ then people can use any off board switch they like.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 02, 2013, 01:08:56 PM
Do you think to realize a "pro" PCBs like your other projects or only the gerber files?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 02, 2013, 01:54:30 PM
Do you think to realize a "pro" PCBs like your other projects or only the gerber files?

Actually, I am quite intrigued by this EQ. Once I am happy with the layout I will definitely have some made. Then, if there is enough interest I will make them available here.

One reason I am intrigued by it is that, on the journey that led to the final circuit, I had a design that quite neatly made a fully switched Helios 69 EQ - not a pot in sight. It occurred to me that stereo version of that would make quite a good mastering EQ.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 02, 2013, 02:30:57 PM
Do you know if there are differences between the Chrion inductors and the Carnhill ones?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 02, 2013, 04:15:58 PM
Do you know if there are differences between the Chrion inductors and the Carnhill ones?

I am sure there are differences but I guess you mean any differences that affect the sonics. The answer is I do not know as so far I have only used Carnhill ones.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 03, 2013, 12:13:21 PM
I can't wait to see this circuit  :D
In the meantime, it is possible to know the value of the components?
So we can begin to search them!
Best
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 03, 2013, 04:05:10 PM
I can't wait to see this circuit  :D
In the meantime, it is possible to know the value of the components?
So we can begin to search them!
Best

The current circuit is here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/MKIIV2circuitscaled.jpg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/MKIIV2circuitscaled.jpg)

Most but not all of the component values are correct. I am in the process of putting together a BOM for it.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 04, 2013, 05:04:08 AM
If the values are not definitive, I think it's better to wait you complete the project
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 04, 2013, 06:06:38 AM
If the values are not definitive, I think it's better to wait you complete the project

They were only uncertain when I drew that circuit. The main uncertainty was around the capacitor values in the brilliance boost/cut and the inductor values in the brilliance cut circuit. Now that I have selected the brilliance cut inductors and built and tested that part of the circuit, those values are firm.

So, I have put together a preliminary BOM which you can find here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/AssyIns.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/AssyIns.pdf)

It will at least help you to identify the long lead time items. There may be minor resistor and capacitor value changes after I test the first PCB.


I am more concerned about the PCB layout. I have checked it three times now and each time found a major error/omission so that is what I am going to concentrate on.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 04, 2013, 06:42:28 AM
I have seen in the schematic that there is a 10khz filter in the brilliance control, too
It has a different shape or it is the same of the High control?

Do you think to realize an adaptor to use Lorlin switches instead of Grayhill?
The Lorlin are chaeper and I use them from many years without problems
This mod may be useful for those who want to realize more modules (8 or 16) for a custom mixer
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 04, 2013, 10:53:03 AM
I have seen in the schematic that there is a 10khz filter in the brilliance control, too
It has a different shape or it is the same of the High control?

Yes, the 10KHz brilliance boost is the same shape as the 'Pop' EQ in the REDD 47 - in other words it is a peaking response. The treble control is shelving at 10KHz just like the 'Classic' EQ in the REDD 47. So you can have either with this EQ.

Quote
Do you think to realize an adaptor to use Lorlin switches instead of Grayhill?
The Lorlin are chaeper and I use them from many years without problems
This mod may be useful for those who want to realize more modules (8 or 16) for a custom mixer

The problem with that is that two of the switches are 2 pole 12 way types and as far as I know Lorlin does not make one like that. The treble control is a 1 pole 12 way so a Lorlin could be used there. The brilliance switch is not on the PCB. I have brought its connections out to a 16 way header which is compatible with the Lorlin and Grayhill adapter PCBs I have designed for the Unversal EQ. So you can already use a Lorlin for that switch. You could also use it for the 1 pole 12 way treble switch by wring from the Lorlin adapter board direct to the Grayhill pads on the PCB.

The Lorlin adapter PCb first appeared here:  http://www.groupdiy.com/index.php?topic=50484.msg650062#msg650062 (http://www.groupdiy.com/index.php?topic=50484.msg650062#msg650062)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 07, 2013, 06:57:30 PM
I have added the pad to the PCB to facilitate EQ IN/OUT switching and done a few more tweaks and changes. I think it is just about there now. I will check it once more then commit to production of some prototypes probably at the end of the week.


Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 11, 2013, 04:35:08 AM
Hi Ian,
I am considering that using the Lorlin switch with your adapter may be difficult in a API format project.
It is possible for you to post the way to connect the leads directly to the pins of the Lorlin switch?
In this way it is possible to save precious space on the front panel
Thank you
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 11, 2013, 06:02:42 AM
Hi Ian,
I am considering that using the Lorlin switch with your adapter may be difficult in a API format project.
It is possible for you to post the way to connect the leads directly to the pins of the Lorlin switch?
In this way it is possible to save precious space on the front panel
Thank you

I am assuming you mean for the frequency selection switch. I will draw and post a sketch.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 11, 2013, 06:45:35 AM
Yes, the switch that is out from the board
Any comment about how is the sound in your tests?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 11, 2013, 11:53:43 AM
Yes, the switch that is out from the board
Any comment about how is the sound in your tests?

Here you go:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/LorlinWiringscaled.jpeg (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/LorlinWiringscaled.jpeg)

I have not built the complete EQ so I have not made any listening tests yet. I plan to order some prototype PCBs this week and build one when they arrive.

Edit: here's what I hope is the final PCB layout:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/REDDEQApril11th.png (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/REDDEQApril11th.png)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 11, 2013, 01:29:55 PM
Thank you!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 15, 2013, 10:30:01 AM
I just the order for some prototype PCBs.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 15, 2013, 11:59:45 AM
I think there are many people (like me) that are waiting to know how it sounds :)
have you made modifications in the component list?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 15, 2013, 03:46:01 PM
I think there are many people (like me) that are waiting to know how it sounds :)
have you made modifications in the component list?

I am going to build one when the PCBs arrive and listen to it. Then I will decide if I think any components need to be changed.

I started this thread because the Helios 69 EQ, designed by Dick Swettenham, has a lot of similarities with the EMI EQ and Dick worked at EMI before he designed the Helios EQ.

The brilliance boost is very very similar to the Helios mid boost and I know that sounds really good. The brilliance cut is like the Helios mid cut but arranged for a much gentler Q so I expect it will sound quite different. The top cut/boost is again very similar to the Helios 10KHz cut/boost - the only difference is the cut is shelving whereas the Helios is not. So again I expect it to sound similar but gentler.  The bass cut is again similar to the Helios but it is shelving whereas the Helios is not, so once more it should be gentler.The bass boost is quite different to the Helios so I have not heard that yet but it is a shelving EQ rather than a peaking one as in the Helios.

Overall I guess I expect it to sound gentler all round which could be rather interesting.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 20, 2013, 09:01:20 AM
Hi Ian, any progress?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 20, 2013, 09:49:33 AM
Hi Ian, any progress?

PCB has gone to manufacture. I am trying out a new PCB company. They are a Chinese family living in England who still have a factory in China. Boards should be here in a couple of weeks.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on April 20, 2013, 11:00:50 AM
you are referring to the prototype PCBs or definitive?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 20, 2013, 06:31:34 PM
you are referring to the prototype PCBs or definitive?

Prototype.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 02, 2013, 06:22:15 AM
The prototype REDD EQ PCBs arrived in the post this morning. I am trying a new PCB supplier Quick-Teck. They are a UK based Chinese family with a PCB factory back in China. An initial visual inspection of the PCBs indicates they are of good quality.

I will build and test one over the next couple of weeks.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on May 02, 2013, 11:47:34 AM
Great!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: buildafriend on May 02, 2013, 01:08:35 PM
YEEEHAWWW!!!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 06, 2013, 05:44:32 PM
I have got the prototype REDD EQ basically working. There are three errors on the PCB but the workarounds are easy. I had to rationalise some of the resistor values either to standard values or the nearest I had to hand but the errors should result only in small fractions of a dB change in response. At the moment bass boost works as advertised. Treble boost and cut max at 9dB rather than 10 as do the brilliance boosts and cuts. There's something wrong with the bast cut which seems to go in 1dB steps instead of 2dB steps.

The minor errors are the PAD 0V is not connected to 0V and one end of R11 is also not connected top 0V. A couple of links fix these. The other error is I used the wrong size footprint for the brilliance boost inductor (VTB9044). Fortunately I used one that was too big so as a workaround I have glued the inductor to the PCB up side down and wired it to the PCB pads. If you decide to use a Chrion inductor then this is not a problem.

The 1dB error on max boost/cut is probably due to resistor rationalisation so I need to revisit that. Bass cut problem I am not sure about.

Pic attached.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: baadc0de on May 06, 2013, 05:58:54 PM
Looking good Ian!

Will you be making another run with the errors fixed?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on May 07, 2013, 01:19:27 AM
Ian said that this board is a prototype, so he can fix the problems before to realize the definitive PCBs
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 07, 2013, 04:25:50 AM
Looking good Ian!

Will you be making another run with the errors fixed?

Yea, I will. I did get quite a few prototypes made because getting 10 made is as cheap as getting 3 made.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on May 07, 2013, 05:06:25 AM
Hi Ian, have you made any sound test?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 07, 2013, 10:09:30 AM
Hi Ian, have you made any sound test?

Not yet. I will do that once I am confident it is working correctly.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on May 08, 2013, 01:47:28 AM
Hi Ian, it is possible to know when the definitive PCBs will be avaible?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 08, 2013, 04:07:59 AM
Hi Ian, it is possible to know when the definitive PCBs will be avaible?

I am retired now so I no longer work to schedules.!! However, I expect to have all the prototype board problems solved in the next couple of weeks. Allow another couple of weeks for the new version of PCB to be made so lets say about a month in total.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on May 08, 2013, 08:35:49 AM
Thank you. Keep us informed!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 08, 2013, 05:53:45 PM
Good news. The bass cut problem was a test kit set up problem that is now resolved, bass cut works as advertised. I have now measured every single setting of each of the three controls. All the boosts are close but a bit high at the last two settings. All the mid boosts are a little short on the max cut. If you are interested in the rew resuslts they are here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/prototests/redd/ (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/prototests/redd/)

Click on any of the .htm files - each graph is labelled.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 10, 2013, 05:44:06 AM
I have now tweaked a couple of resistor values in the brilliance cut and the cut now reaches 10dB (it is a little more at 10KHz because of the lower total series resistance due to the inductors). Also, the EQ was designed to be fed from a 10K fader in the EZTubeMixer and so was designed with a 2.5K source resistance. When this resistance is added in series with the input the boost hits 10dB on the nose too. So I am now happy with the response. If you omit this resistance the boosts are increased by a dB and are slightly sharper which is much the same as what is reported to happen in the real thing. Next step is to fix the PCB layout. In the meantime I might pass some music through it to see what it sounds like.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on May 10, 2013, 11:59:17 PM
Yes, let us know something about the sound!
Cheers
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 11, 2013, 07:05:13 AM
Yes, let us know something about the sound!
Cheers

I am going to run a track through it and record the result, perhaps with a commentary about the EQ settings on another track. I'll try posting a wav of the result to dropbox.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 11, 2013, 09:16:59 AM
Hopefully, here is a link to a wav file of a test of the REDD EQ. The left channel is the track via the REDD EQ and the right is me saying what the EQ setting is at each point. I have normalised the track to take out the EQ loss.

http://dl.dropboxusercontent.com/u/65071114/reddeqtestnormalised.wav (http://dl.dropboxusercontent.com/u/65071114/reddeqtestnormalised.wav)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on May 11, 2013, 10:20:33 AM
It is my impression ... or this equalizer sounds really cool?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Junction on May 11, 2013, 11:20:38 AM
nice work Ian, sounds vintagely awesome  ;)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: jplebre on May 11, 2013, 06:25:50 PM
HOLY!
Like.... where's the "really like" button?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: bruce0 on May 11, 2013, 09:21:17 PM
Ian, with custom inductors can I use the Universal EQ board to make this EQ?  I guess I wouldn't get a dip?  I have taken a look at the schematic but I am a little confused by schematic style (I was introduced to electronics after paper!).

Anyway, how universal is the universal, and is it a different animal from this?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 12, 2013, 08:29:38 AM
Ian, with custom inductors can I use the Universal EQ board to make this EQ?  I guess I wouldn't get a dip?  I have taken a look at the schematic but I am a little confused by schematic style (I was introduced to electronics after paper!).

Anyway, how universal is the universal, and is it a different animal from this?

It's hard to draw the universal EQ in any kind of normal schematic style simply because it is a collection of parts that can be put together in lots of different ways. However, looking at the PCB schematic I think I could draw a new version of that which gives a better idea of how the parts could fit together. I am in the middle of writing up how to work out the RC values and I think it would be a good idea to include a description of how it all basically fits together. Having said that, it is still a collection of circuits blocks and the EQ you make with it is limited only by what you can build with these parts. I don't want to say 'this is how it all goes together' and have people think that is the only way it can be built.

Having said that, you probably could build the REDD EQ using the universal EQ PCB but it would be a bit of a bodge.  The switching on the REDD EQ is rather unique so many of the components would have to be mounted directly to the switches. If you really want to try the REDD EQ I would be happy to send you one of the prototype PCBs free of charge - it just needs a couple of links adding under the PCB plus the brilliance boost inductor needs to be glued on upside down and wired in by hand.  A lot less work than modding the universal EQ PCB.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: bruce0 on May 12, 2013, 03:22:42 PM
Thanks! Sent postage via paypal with my address. 

Prototype would be great!  After all what is DIY without straps and trace cuts anyway?  And the inductor is no problem I am building my own - I will build brilliance as RM8 like chrion.

I will order some switches and build some inductors.
Looking at schematic "shorting MBB" would transition quieter on Brilliance boost/cut, wouldn't it?

FYI… Neither Mouser nor Digikey stock the EPCOS inductors. Farnell/Element 14 charge a "special" to ship those inductors to US. I ordered some axial Fastron VHBCC series ones Equivalent Q and current Current, slightly higher DCR and a bit longer case. Do you think these would work as well?


Mouser Part           MFG     Inductance   Imax   DCR     Min Q

434-VHBCC-102J-01 -   Fastron        1mH   400mA  4.2     70
434-15-222J -         Fastron      2.2mH   250mA   10     65
434-VHBCC-332J-01 -   Fastron      3.3mH   220mA   12     50
434-VHBCC-103J-01 -   Fastron       10mH   120mA   40     60


http://www.fastrongroup.com/image-show/25/VHBCC.pdf?type=Complete-DataSheet&productType=series

On Uni-EQ - Thank-you … I finally get it, the sections are building blocks... they don't connect.  (I looked at the boards and they really don't   ::)  Light dawns on Marble Head!)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 13, 2013, 09:55:49 AM
@Bruce,

The Fastron types look pretty close to the EPCOS. DCR is only about 10% higher and Q and current rating are fine so I would say they will be OK.

RM8 core will be fine. The VTB9044 inductor I use is also on an RM8 core.

MBB as a rule should be quieter but I used a BBM on the prototype (Lorlin) and I could not detect any switch clicks on the test recording.

I sent you an email asking for your shipping address because it did not come through with the Paypal payment. Once I have that I can ship your PCB.

Cheers

Ian

Cheer
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 15, 2013, 05:53:55 PM
I have checked the new inductor footprint and it looks fine. I have made some other mods to the PCB layout such as adding provision for a series input resistor if a low  impedance source is used, added the usual PAD circuit and a couple of extra mounting holes. I have also spread out the capacitors in the treble boost/cut circuit to allow sightly larger types to be fitted.

I have updated the assembly instructions with the final component values and added the new ones:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/AssyInsV2.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/AssyInsV2.pdf)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on May 17, 2013, 01:36:47 AM
Great work Ian!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on May 20, 2013, 04:21:52 AM
Hello Ian, do you think to add this pcb in your emporium?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 20, 2013, 06:05:50 AM
Hello Ian, do you think to add this pcb in your emporium?

Yes, I will. The V2 PCB layout is now done. I just need to check it one more time before committing to manufacture. I expect to place the order later this week with PCBs arriving a couple of weeks after. PCB price will be around 11GBP.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on May 20, 2013, 06:43:40 AM
A little more expensive than the Helios?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 20, 2013, 07:24:21 AM
A little more expensive than the Helios?

Correct. The Helios I got right first time (apart from a very minor silk screen error). The REDD EQ needs a re-layout so I have to pay tooling charges again. Just trying to recover my costs. I have some of the original prototype PCBs which will work perfectly well if you are prepared to make the necessary mods to correct the errors.  You can have one for the cost of shipping if you wish.

Edit. What the hell. I was never in this for money. I'll keep the REDD EQ price the same as the Helios.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 28, 2013, 06:00:28 AM
I have ordered the V2 PCBs for the REDD EQ. Should be here in a couple of weeks.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 03, 2013, 05:54:52 PM
You may remember that the REDD EQ is based on the topology of my Helios 69 EQ design- in fact the first version was little more that a Helios with a switched attenuator for the boost/cut. For some time I have been thinking about a mastering EQ and the Helios lends itself quite well to modifying into one as it already has a stepped Hi boost/cut. From the REDD EQ work I worked out how to step the Helios mid boost/cut (and eliminate the boost/cut switch) and the bass is quite easy to convert to a switched pot.

So, I have put together a document that shows how to work out the resistor values for stepped switching of the Helios mid boost/cut and any similar attenuator based EQ as well as how to mod the Helios bass boost EQ to stepped operation. The mods are quite simple so the existing PCBs can be used. You basically replace the two pots with stepped switched and disable the cut/boost and EQ in/out switches.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 03, 2013, 08:06:29 PM
Hi Ian,
You do not fool around do you :-*
 ;)


You write that the large inductor may have significant resistance that one should " measure the dc resistance of the inductor and subtract this value from the value of the resistor connected to the input."

This would be the 1864ohm resistor. Yes ? 

I've got some switches to draw up :)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 04, 2013, 03:18:12 AM
Hi Ian,

This would be the 1864ohm resistor. Yes ? 

I've got some switches to draw up :)

Yes, that's the one.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 04, 2013, 02:15:37 PM
I'm doing a bit of shopping for switches on my downtime today.
I'll need some quiet time to diagram that switch. 

For the benefit of everyone who's following the thread and gets a chance to look at the PDF
I'll ask for clarification on some things as I move along.

The stepped cut boost (for 12steps each of cut and boost) requires 2 decks 24 poles right? 
The ELMA at the audiomaintenance store is 66GBP
OTOH there are a lot of chinese 2p24T MBBs on ebay for cheep.  I might go there.

where did you get the 2P12W series71 (2 gang switch)?
I can't find that one anywhere in the US, although I can special order at Digikey.
audiomaintenance has a 1P12W (1gang) and a 3p12w (3gang) and the alternative would be to re-assemble those 2 into a pair of 2gang switches.

Thanks
Kelly
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 04, 2013, 06:22:10 PM
@Kelly

The stepped cut boost (for 12steps each of cut and boost) requires 2 decks 24 poles right?

Yes, it you want to do this on the mid band of the REDD EQ. To do it on the Helios mid band requires only a 1 deck 24 pole switch.

where did you get the 2P12W series71 (2 gang switch)?

I got them on special order via a UK distributor. I could not find them anywhere either.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 04, 2013, 07:35:55 PM
Have you shipped many of those Helios boards to the US?
Maybe I'll see if Hairball or Classic API would be interested in stocking up on a few... they both carry the 1p12
Do you recall what the minimum was?

1 Deck for the Helios mid...  aaahh   OK  glad I asked
I've had a few glances at the drawing, enough to confuse myself.
I'll have to draw it when I can focus.

Kelly
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: bruce0 on June 04, 2013, 11:07:34 PM
I got my switches at Digikey, expensive but in stock.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 05, 2013, 02:51:31 AM
Thanks Bruce, I checked there this morning and they had a lead time out into August...
That was for the 71 BF30 02 1 12S

But  I just searched again and I found a different part number 71BDF30-02PAJN   
with the D and the AJ standing for adjustable stops.   In stock.  ;D
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 05, 2013, 05:26:06 AM
Have you shipped many of those Helios boards to the US?
Maybe I'll see if Hairball or Classic API would be interested in stocking up on a few... they both carry the 1p12
Do you recall what the minimum was?

1 Deck for the Helios mid...  aaahh   OK  glad I asked
I've had a few glances at the drawing, enough to confuse myself.
I'll have to draw it when I can focus.

Kelly

On the Helios, the 2 bank 12pole is for the bass switch. This really needs to be a shorting type and that is the one that is not readily available. You can probably get away with the regular non-shorting type of which the the 71BDF30-02PAJN is one version that is readily available.

The REDDEQ uses a similar bass circuit so it also needs a 2 deck 12 way switch there. It also needs a two deck 12 way for the mid boost/cut.

I have sold a lot of Helios boards the the US. In fact I have run out of the original design and only have a few of the 3U ones left. Looks like its time to order some more.

If I can get time I'll draw a quick circuit of how the Helios would look fully switched.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: bruce0 on June 05, 2013, 10:41:19 AM
@Sleeper and Ian:

I too wanted the shorting and found them unavailable at digikey.  So I took the non shorting, which is what I think Ian used in the prototype.

Pretty much I "never" track with an EQ (if I need EQ I fix mic placement). And in mixing a small bump here and there doesn't get recorded.

(I am still drilling faceplates, so can't test yet.  I don't know the extent of the bump, or if there is one.)

I tried going direct to Grayhill and they sent me the attached email.  If you are in the US, the distributors listed may help and if you are up for for a grayhill "group buy" I would be up for it, though I only need a couple I could stock a few.  And with these little switches $500 comes up pretty fast so the minimum order is not so high really (and I have to use all these nice little grayhill cards from Ian!) so we could probably cobble together a minimum order (they quote 8 weeks, but if we are a small order in a standard range of products, I would guess they have stock lying around).

Quote
Bruce,

   Hello, please note in order to purchase direct you must be an OEM
account, and we have a $500.00 order minimum.

   If you can not meet this dollar minimum requirement, you may buy thru
an authorized Grayhill distributor such as, Sager,

   Future, Allied, Arrow, Avnet or Digi- Key.

         71BDF30-02-1-AJS        1-24 pcs      $27.02 each

         71BDF30-01-1-AJS        1-24 pcs      $19.69 each

               Lead time for both switches is approximately
8 weeks ARO
               and are non-cancellable non-returnable

            Terms Net 30 Days FOB LaGrange, IL
               Quotation Valid For 90 Days
                   Quote Subject To Grayhill
                     Terms And Conditions
            **** Minimum Order $500.00 ****


I bought switches for a stereo version, so 6 switches, plus a couple of extra, so I was in for $180 plus shipping.  If you do decide to go direct, I would be on for a couple of shorting versions.
Title: NAPIS Mastering EQ
Post by: ruffrecords on June 05, 2013, 12:22:44 PM
I attach an outline schematic showing the mid section of the Helios EQ implemented with a stepped pot - it is only 12 way as that's all I could fit on the paper but it serves to illustrate the way it is wired. I also included the wiring for the stepped bass pot. Again, to save space I just did 6 steps but with a bigger switch you could do 12. There are no component values.

Conscious of the problems people are having getting hold of 2 deck 12 way Grayhill shorting switches I have shown the bass section split into two separate switches; one for the HPF and the other for the bass boost so you could use a pair of Lorlin 6 or 12 way BBM (shorting) switches instead. It also means you can do HPF and bass boost at the same time should you feel the need.

As there is not a pot in sight, I have christened this EQ the NAPIS.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 05, 2013, 12:29:09 PM
Hi Ian and Bruce
I've sent some inquiries out to distributors, If that works, we're on, if not than maybe we'll group buy.. .
Kelly

edit
Jeez Ian, are you sure you didn't retire because you were bored that no one could keep up with you...
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 05, 2013, 03:34:08 PM
Jeez Ian, are you sure you didn't retire because you were bored that no one could keep up with you...

I know what you mean. I had a great career but was always doings things other people wanted me to do. Now I am retired I just do the things that interest me and I just don't seem to be able to stop. Anyway, I am enjoying myself.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 05, 2013, 04:34:39 PM
The postman just delivered my boards!
Thanks for that drawing.
It looks like I'm going to slow up for a tad, as I've got a lot of parts in transit.   
Onward...

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on June 07, 2013, 12:00:27 AM
Hello Ian, considering the high price of the Gryhill switch, is it possible to use some pots?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 07, 2013, 01:44:11 AM
Ian and I have recently been discussing a mastering version, all switches...
the original has 3 switches and 2 pots
but
No.
Check the schematic... the different frequencies and the bass boost do their thing by switching in different LC filters.
You could make it work with 3 dollar switches, like lorlins, but you would have to hand wire it to the board. 
That's a lot more work. less money though
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Gearsix on June 07, 2013, 04:05:55 AM
I think you are speaking about the Helios.
I am asking for the Redd Eq where at least for two switches the Lorlin can't be used
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 07, 2013, 06:58:50 AM
I think you are speaking about the Helios.
I am asking for the Redd Eq where at least for two switches the Lorlin can't be used

As you will probably know from the very first post, the REDD EQ was designed at the request of a client. The idea was to make it as close to the original. The original used switches so this design does too.

I am of the view that the Helios was derived from the REDD design. One thing that was changed was the mid and bass boost switches were replaced by pots. So in that sense the Helios is the answer to your question.

The other unique feature of the REDD EQ is that the Q of the mid boost/cut is the same for cut as it is for boost. To achieve this requires a 2 pole switch for the mid boost/cut control. In the Helios they let the  boost Q and cut Q be different which meant you only needed a 1 pole switch. Then they replaced that with a pot and a boost/cut toggle switch which also saves on inductors. So again, the Helios is sort of the answer to your question.

The harder question is can you build the REDD EQ PCB with pots replacing some of the switches?

Starting at the top end, the 10KHz boost/cut is a switch just like the Helios. The design does not lend itself to replacing this with a pot. The mid frequency switch is off board and could be a cheap Lorlin so that's not an issue. The stepped level pot is a 2 pole 12 way Grayhill. This could be replaced by a pot and a boost cut switch effectively turning it into a Helios mid but you lose the boost/cut Q being the same. At the low end the bass switch works much like the Helios and is a 2 pole 12way Grayhill. You could hard wire a cheap Lorlin into the bass cut pads and replace the stepped boost by a pot to save using the Grayhill. This would give you separate bass cut and boost controls.

To be honest I am not sure whether it is worth it or not.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on June 12, 2013, 05:50:35 AM
Hi Ian, any new from the pcb side?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: anjing on June 12, 2013, 07:47:10 AM
I think Ian took a week off.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on June 13, 2013, 11:25:03 AM
Great  :)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 18, 2013, 12:59:44 PM
I am back from holiday in Sherwood Forest. While I was away the post man delivered the new REDD EQ PCBs so if you want one please email me.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 22, 2013, 06:36:09 PM
16 of the 20 boards are spoken for and shipped. Only 4 left.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 25, 2013, 12:46:41 AM
Hi Ian,
I'm waiting to hear back from Hairball Audio.  He's contacted Grayhill, so we'll see if those switches become available in the states...

I've got some inductor questions.
No matter what, Chrion, Carnhill or Cinemag, I'm paying a good bit for the inductors and a lot of that is either shipping or design... 

David at Cinemag can wind the inductors for me, but he had a question to which I have no answer...

Quote
The Carnhill inductor called out in the schematic (VTB9042) probably is on a P2616 core.  That part number refers to the size of the core, which is important for the maximum signal level it can handle.  For this tapped 1H core, there are tradeoffs between inductance tolerance (+3% vs +5%) and the dcr of the windings and, hence, the Q (quality factor).  Note that Carnhill specifies +10%.  I need to know which characteristic is most important for this application.

I have cinemags in my pultecs and they sound great. 

Maybe I can save a bit on the 10H
I've been looking at the inductor threads, mostly pultec stuff, that's around...
as well as looking at specs from Sowter and seeing that the 10H has a DCR of 1000r
I found a thread which measured the Carnhill DCR at 738r
Don't Q and DCR combine to make the shape of the filter curve...   


The reason I ask is that I may have found some much cheaper alternatives for the 10H
most of these guys are under 10USD.
Maybe the DCR makes them unsuitable?
I recall reading you tested a bunch of Epcos B8214 inductors.
Did you like them?

This? http://www.mouser.com/ds/2/28/S4924-5105.pdf (http://www.mouser.com/ds/2/28/S4924-5105.pdf)
the 106K has a min.Q  .25     DCR  137ohm     Current   54ma

And then there is something like this Hammond 157H    it's big, but
10H with a DCR at 470 ohm     
http://www.mouser.com/ds/2/177/EDB157H-222270.pdf (http://www.mouser.com/ds/2/177/EDB157H-222270.pdf)

This Triad specs about the same.     10H dcr 500 
http://www.mouser.com/ds/2/410/C-3X-222148.pdf (http://www.mouser.com/ds/2/410/C-3X-222148.pdf)

Thanks
Kelly
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 25, 2013, 05:36:09 AM
@Sleeper

I guess you are talking about the Helios EQ because the REDD EQ does not use a 9042 inductor! - it uses the 9044.

Tee P2616 core looks about right to me for the 9042 (the 9044 is smaller). Although the Carnhill inductors are specified at 10% the ones I have measured are much better than that. I suggest you ask Dave at Cinemag for 5%. The DCR of the inductor defines the maximum possible Q. In an equaliser, the DCR plus the intentional circuit resistance defines the actual Q. What you want is for the circuit to determine the Q, not the inductor so you generally arrange for the DCR to be a small fraction of the circuit resistance hence my advice to go for the lesser tolerance which presumably means lower DCR.

10H inductor. The Hammond and Triad are not suitable. They have iron cores intended to work at 100/120Hz only. They are no good for audio unfortunately.

The ones from Mouser are surface mount types and their values are in the micro Henry range. They might be suitable substitutes for the EPCOS 8214  in the REDD EQ (which incidentally sound fine - they were used in the prototype REDD EQ) but they get nowhere near 10H.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: tomas1808 on June 26, 2013, 01:25:15 PM
What are the dimensions of the REEDEQ board?

Thanks!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 26, 2013, 05:07:02 PM
What are the dimensions of the REEDEQ board?

Thanks!

It is 100mm by 100mm (just under 4 inches square).

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on June 26, 2013, 05:57:43 PM
Quote
but they get nowhere near 10H
Can I borrow a couple of those hundreds... I need more zeros.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on July 09, 2013, 05:00:13 AM
The second batch of REDD EQ PCBs arrived in the post this morning. I'll be shipping outstanding orders over the next couple of days.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: eparg on July 10, 2013, 07:28:33 PM
Hi Ian,
I'm waiting to hear back from Hairball Audio.  He's contacted Grayhill, so we'll see if those switches become available in the states...

Any updates from Hairball?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on July 12, 2013, 01:46:05 AM
Hi All,
He got prices back and doesn't want to do it.
I also got swamped with tons of work. (Yay! ) but I don't have time to do a group buy.

So the options are,
Something like $27 each and an 8-10 week lead time from digi key

That's not for me... I'll lose interest. ???

Or  -since I'm making a stereo pair
from audiomanitenance
5, 1p12t  and 1, 3p12t     
then
disassemble the 3p and make it a 2p and
add the leftover deck to a 1p  to make a 2P

BUT  I haven't tried to disassemble one of these, but I'll bet it isn't to difficult.
I've dis-assembled coles and davens and leaf switches and they aren't too bad.
I'm only guessing for now.

OR   make Ian's mastering version that's all switches.
I'm going this route.
BTW I'm referring to the Helios PCB  (I don't know about the Redd)
Then,
use 1p switches in all 3 slots. 
Add 3 lorlins - 1 for each of the pots to make it stepped for mastering
and 1 for the 50hz low pass       
the drawing that shows you how to do this is on the previous page of the thread.

I've figured out how to do this on the board but it's hard to describe.
My switches are on order now and I'll share a photo when I'm all done.
Kelly
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on July 12, 2013, 12:05:56 PM
I am tempted to realize a couple of these equalizers, but the grayhill switches are really expensive.
It is possible that someone has found the way to use other 2 pole 12 positions switches?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on July 12, 2013, 12:33:21 PM
This was discussed earlier. RTTD

You can use Lorlins or Alphas at about 3 bucks each but you have to solder 12 wires between the board and the switches. 
The 2 pole grayhill can be wired as 2 separate switches  and once again you have to solder 12 wires between the board and the switches.

The single pole grayhills are about 16 dollars vs about 3 for the Lorlins.
But the lorlins will take much longer to mount

I haven't found any other PC mount rotary switches and you do need to use the grayhills if you are going to build this into a 500 series format. 
If not, do what you like.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: eparg on July 12, 2013, 11:25:59 PM
Well I pulled the trigger on ordering the rest of the components. Carnhill inductors from audio maintenance, grayhill's from digikey. Digikey estimated a 4 week lead time which for me isn't too bad. I'll report back when I actually receive them (hopefully 2 weeks).
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on July 13, 2013, 01:03:32 AM
I'm kind of into the way Ian redrew the low end though.
Now instead of either a 50hz cut OR a boost at 30, 60, 120, 240, 400
it's a cut AND a boost.  I'll bet that's going to sound cool    sometimes.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Fablab on July 13, 2013, 03:10:22 AM
Strawtles, the only solution to save money with these switches is if someone will do a group buy
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: eparg on July 26, 2013, 11:28:23 PM
I placed an order for the Grayhill switches from Digikey and they were delivered two weeks after the order. Digikey estimates a 4 week lead time but it was much faster for me. So any of you who are hesitant about ordering from Digikey because of a long lead time you need not fear!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on July 28, 2013, 06:31:28 AM
Hi Eparg, what's the code you used to order the 2 way 12 positions switch from Digikey?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: eparg on July 28, 2013, 07:22:28 PM
Hi Eparg, what's the code you used to order the 2 way 12 positions switch from Digikey?

Hey,

I ordered these switches: 71BDF30-02PAJN

Direct link: http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=gh7107-nd

Seems that they now have 41 in stock!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Strawtles on July 29, 2013, 12:36:26 AM
Thank you eparg!
I have seen that for large quantities the price goes down
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: leadbreath on July 30, 2013, 11:39:51 AM
hi ian,

i cant seem to find these pcb's in your emporium?
will you be updating, as i need to place a multiple pcb order ?

cheers
mick
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on July 30, 2013, 01:28:58 PM
hi ian,

i cant seem to find these pcb's in your emporium?
will you be updating, as i need to place a multiple pcb order ?

cheers
mick

Sorry about that. I updated the forum page but not the web page. Both should have the REDDEQ listed now.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on August 31, 2013, 08:27:21 PM
I'm kind of into the way Ian redrew the low end though.
Now instead of either a 50hz cut OR a boost at 30, 60, 120, 240, 400
it's a cut AND a boost.  I'll bet that's going to sound cool    sometimes.

So I've been busy, but I'm back to it.
I' believe I've got all the switching sorted out:  this is diagrammed in the document here.
http://www.groupdiy.com/index.php?topic=51030.msg671466#msg671466 (http://www.groupdiy.com/index.php?topic=51030.msg671466#msg671466)

Ian, can you confirm something for me?
I'm 99% sure, but as it involves lopping off the pole/leg on that center grayhill mid freq switch.
I shouldn't have soldered it, but I also don't have a spare board to look at to be 100% sure.
As we've all just discussed, the grayhills aren't cheap, so I'm playing it safe.

My midrange switch (center) pole should attach to the grayhill's switch (center) pole and nothing else yes?

Here are some images.
(http://mob939.photobucket.com/albums/ad239/takeit2m/2013-08-31151032_zps85c14bde.jpg?t=1377992706)(http://mob939.photobucket.com/albums/ad239/takeit2m/2013-08-31151052_zps0529309d.jpg?t=1377992700)
I'll post more pics of the implementation once I'm sure it works :-X
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on September 01, 2013, 06:03:48 AM

My midrange switch (center) pole should attach to the grayhill's switch (center) pole and nothing else yes?


Yes, the mid range switched pot centre pole goes only to the centre pole of the mid range grayhill and nowhere else.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: sine_wave on September 12, 2013, 05:15:21 PM
Just curious... Has anyone done a panel mockup for this yet? I've been trying to but haven't got any results worth mentioning yet. I'm trying to figure out a way of having the cut/boost dB numbers as well as the frequency numbers and not have it look cluttered, etc. I thought if I saw what some of you other guys are doing it might help get the old creative juices flowing. :)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on September 12, 2013, 05:46:22 PM
Here's one side of a helios Mastering version - all stepped controls.
Although I normally like my high-end on the right and my low on the left, I prefer not to mount my boards from the roof.
Not sure about the redd, but the Helios also presents the dilemma of having a midrange control that steps over the high boost/cut - but for me the mid is the most important feature.

I don't find that a polar array of the text elements ever really looks right.  you have to nudge things around a bit to get it to look proper.  I use the array in the center to mark my switch steps and to give me a drilling center, it's not in the final print.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on September 13, 2013, 05:42:24 AM
Here's one side of a helios Mastering version - all stepped controls.
Although I normally like my high-end on the right and my low on the left, I prefer not to mount my boards from the roof.

Nice layout. Am I correct in assuming left and right have separate controls? Is that an advantage for mastering or is it simply to simplify the switching.

Cheers

ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on September 13, 2013, 03:40:35 PM
left and right have separate controls? Is that an advantage for mastering or is it simply to simplify the switching.

Cheers

ian

Yes, there is a copy of this left and right.
I do track (as well as master) through my 1-2 so I want independence. But the switches (and my resistor tolerances) give me left right matching.   

Assuming it all works. I've got my makeup amps burning in.  Time to test over the weekend.
:)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on September 13, 2013, 04:44:47 PM
left and right have separate controls? Is that an advantage for mastering or is it simply to simplify the switching.

Cheers

ian

Yes, there is a copy of this left and right.
I do track (as well as master) through my 1-2 so I want independence. But the switches (and my resistor tolerances) give me left right matching.   

Assuming it all works. I've got my makeup amps burning in.  Time to test over the weekend.
:)

That's handy, so you can use it as two mono channels for tracking and as a close matching pair for mastering. Neat.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: buildafriend on September 24, 2013, 08:42:53 PM
Hey Ian,

I have a few bucks for a the REDDEQ boards now. Since my REDD47/orange86 parts have mostly been acquired I think I should get on top of implementing this. Man I'm so excited! 8) How should I go about paying (if they are available)? I might pick up a Poor Man's Gain make up stage PCB too.

Thanks.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on September 27, 2013, 04:29:50 AM
Hey Ian,

I have a few bucks for a the REDDEQ boards now. Since my REDD47/orange86 parts have mostly been acquired I think I should get on top of implementing this. Man I'm so excited! 8) How should I go about paying (if they are available)? I might pick up a Poor Man's Gain make up stage PCB too.

Thanks.

Go here:

http://www.ianbell.ukfsn.org/EzTubeMixer/ (http://www.ianbell.ukfsn.org/EzTubeMixer/)

and follow the instructions at the top.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: sine_wave on October 19, 2013, 09:38:58 PM
Thanks Sleeper, but I should have mentioned; I'm referring to the REDD EQ.

Here are my thoughts so far... I'm thinking of taking inspiration from EMI/Abbey Road and housing this EQ in one of BUD's portacabs or whatever they're called (à la RS127). Will be like having my own little "Presence Box". Of course these boards go way beyond just a RS127 though since they also include the Treble and Bass from the REDD Console.
In fact, The REDD Console EQ part of this project tempted me to integrate it somehow into the REDD47 preamp that I'll be building soon, but I'm pretty sure I've ruled that out. Doing it that way requires a lot more thought, because in a way one is pretty much creating a "REDD Channel Strip". I've already spent lots of time on my REDD47 panel and to include this amazing little EQ would mean a complete (or close to it) re-design. Pretty sure I'm gonna use the BUD boxes. I'm interested in hearing from anyone else who bought the REDD EQ. What do you plan?

Here's one side of a helios Mastering version - all stepped controls.
Although I normally like my high-end on the right and my low on the left, I prefer not to mount my boards from the roof.
Not sure about the redd, but the Helios also presents the dilemma of having a midrange control that steps over the high boost/cut - but for me the mid is the most important feature.

I don't find that a polar array of the text elements ever really looks right.  you have to nudge things around a bit to get it to look proper.  I use the array in the center to mark my switch steps and to give me a drilling center, it's not in the final print.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Bonsaimaster on October 22, 2013, 10:30:53 AM
So starting to build the REDD EQ stereo mono pair. Newbie at this type of build so will be asking lots of questions and ask for advice. Here is the front panel design for the project.

Daniel
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on October 22, 2013, 05:13:40 PM
Nice panel layout.Love the logo - somehow it reminds me of Popeye - no idea why.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on October 22, 2013, 05:41:19 PM
I'm certain popeye goes to a pirate island...
It's the logo off of Wimpy's tricorner hat ;)

I had success with the Helios all stepped EQ.
It sat for a while because my scope was on the fritzz.
It's burning in with 2520 make up gain amplifiers. 
So far so good. Can't wait to crank it through my real monitors.  8)

Thanks again Ian.

BTW
I just put a couple of extra grayhill 2deck switches on blackmarket.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Bonsaimaster on October 22, 2013, 06:09:06 PM
Studio is named after my son who is called stinky monkey.

We have Stinky Monkey Records

and

Monkey Dungeon Studios - our moto "You don't get out till the music is right!"
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on October 23, 2013, 07:36:20 AM
I'm certain popeye goes to a pirate island...
It's the logo off of Wimpy's tricorner hat ;)

I had success with the Helios all stepped EQ.
It sat for a while because my scope was on the fritzz.
It's burning in with 2520 make up gain amplifiers. 
So far so good. Can't wait to crank it through my real monitors.  8)

Thanks again Ian.

BTW
I just put a couple of extra grayhill 2deck switches on blackmarket.

Can you email me some pics for the gallery. Pierre is running this. We can also put a link to your studio website if you wish.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on October 31, 2013, 11:15:18 PM
Ian, I sent you some pics directly. Hope you got them.
Here's one for your listeners ;D
2 channels of Ruff Helios EQ mastering version all stepped controls.   
Solid State Pultec output circuit- 2520 opamp with a quadfilar transformer.
Run a few mixes with it.
Beautiful
Recycled rack case - decals mounted on 12 gauge aluminium front panel.
good enuf.
Thanks for the great project.
Kelly
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on November 01, 2013, 07:15:20 AM
Ian, I sent you some pics directly. Hope you got them.

Yes, thanks, they arrived safely. I will be forwarding them to Pierre to add to the gallery. Do you want us to include a link to your studio?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Bonsaimaster on January 17, 2014, 09:00:46 AM
Ok I just got the transformers from Sowter and wired everything up. A nubbie questions. Can you tell me the procedure to setup the trip pots on the PAD and direct signals? Also I have a dual mono version and want to know how to match these trim settings. Any info would be appreciated.

Bonsaimaster
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 18, 2014, 06:10:49 AM
Ok I just got the transformers from Sowter and wired everything up. A nubbie questions. Can you tell me the procedure to setup the trip pots on the PAD and direct signals? Also I have a dual mono version and want to know how to match these trim settings. Any info would be appreciated.

Bonsaimaster

The procedure is quite simple and applies to just about all of my passive EQs:

1. Set the EQ controls to lfat - no boost or cut
2. Set the EQ in/out swtich to EQ in.
3. Feed a 0dBu signal into the EQ and adjust the gain of the gain make up amp for 0dBu output.
4. Set the EQ in/out switch to out.
5. With the same input signal. adjust the pad pot for 0dBu at the output

If you adjust both channel of a dual mono system they should be quite closely matched.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Bonsaimaster on February 08, 2014, 05:41:05 PM
Finally got the transformers and finished the project. Sounds great! Thanks Ian for all the help and tolerating the stupid questions.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: kogstudio on February 17, 2014, 04:39:41 PM
Hey there those in the know,

As a quick (and highly subjective question)to answer primarily aimed for those who have used both.
If you were choosing one option re the REDD or Helios 69 EQ which would you go for and why?
How do people compare things like e.g. -
Mid range similarities/differences
Applicability to particular styles or instruments
Anything else that they think might be relevant to consider...
Also for the REDD EQ, any particular recommended make up amps over any others? (i.e. suitability, cost effectiveness etc) e.g. Poor mans tube make up, REDD Pre etc (or should I just use one of my e.g. 1950's style tube line amps, Neve, manley, API etc)

Any info/wisdom much appreciated :)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 17, 2014, 06:14:34 PM
As I mentioned right at the beginning of this thread, Dick Swettenham, who designed the Helios 69, previously worked at EMI where the REDD EQ was developed. it is clear there are a lot of topological similarities between the two EQs and my guess is Dick saw his own EQ as an improvement on the REDD. The top boost/cut are identical. The Helios bass cut is a HPF whereas the REDD is shelving. The Helios bass boost is peaking whereas the REDD is shelving (but both use inductors for bass boost). The Helios uses the same inductor for mid  boost as for  mid cut which makes its cut curves much sharper than its boost curves. The REDD EQ uses different inductors for cut to keep the overall curve shape for cut the same as for boost.

Those are the technical differences. You will see many references on the net the the 'musicality' of the Helios EQ, not just by recording engineers but by musicians. I don't think there are any hardware versions of the REDD EQ except for mine and a few originals secreted away somewhere so most of the net based comments you see on the REDD EQ are based on the software plug ins.

I did a test recording of my REDD EQ in action which you can listen to here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/sounds/REDDEQ/reddeqtest%2005.wav (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/sounds/REDDEQ/reddeqtest%2005.wav)

To me the inductor based bass boost is nicely fat despite being a shelving type. The mid frequency peaks and shapes seem well chose to bring out individual instruments without distorting them. The treble is capable of adding a nice 'air'.

I am biased but I would recommend using my Twin Line Amp for gain make up.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: kogstudio on February 18, 2014, 02:35:58 AM
Cool thanks Ian :)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: mus1k_freak on March 02, 2014, 06:25:08 PM
what did everyone do for the 18uf and 68uf caps in the helios eq? seems like i cant find anything that small with that rating, at least not at mouser, also couldnt find n56 and 4n3   maybe not standard values in the US?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sleeper on March 02, 2014, 08:47:33 PM
I got all my stuff at mouser or from my parts bin. If you look at my post on the previous page you can see I mixed it up a little bit... They aren't all exactly the same style.  I couldn't get one value, so I just used 2 caps in parallel. this won't necessarily work with the WIMA box type caps, you need a bit longer leg because the parallel caps have to sit up off of the board somewhat...  you could always make a longer leg from resistor off-cuts.

I feel like 68uf seems a little big. be careful that you are reading it right...
maybe that's correct.
I'm pretty sure that a couple of the largest caps in the project did require a little bit of lead forming, in other words, shaping the legs like hockey sticks so they would fit the hole spacing on the pcb. nothing extreme.
Good luck
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 03, 2014, 05:00:59 AM
There are no caps as big as 68uF in the Helios EQ. There is a 68nF and the biggest is a 680nF. For just about all the capacitors in this EQ I use ones made by Panasonic that are available from Farnell and its clones.

Here is an 18nF:

http://uk.farnell.com/panasonic/ecqv1h183jl/cap-film-pet-18nf-50v-rad/dp/1669203 (http://uk.farnell.com/panasonic/ecqv1h183jl/cap-film-pet-18nf-50v-rad/dp/1669203)

and here is a 68nF:

http://uk.farnell.com/panasonic/ecqv1h683jl/cap-film-pet-68nf-50v-rad/dp/1744827 (http://uk.farnell.com/panasonic/ecqv1h683jl/cap-film-pet-68nf-50v-rad/dp/1744827)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: mus1k_freak on March 03, 2014, 08:38:29 AM
That make sense on the silk screen there was a u68 and a u18 everything else  was n. So I'm guessing that's 680?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 03, 2014, 10:19:00 AM
That make sense on the silk screen there was a u68 and a u18 everything else  was n. So I'm guessing that's 680?


That's right. There's only room for three characters  on the silk screen so u68 is used for 0.68uF por 680nF. u18 is 0.18uF or 180nF.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ForthMonkey on June 05, 2014, 09:42:49 AM
How can i combine Redd eq with Redd mic pre to building mixer with line input?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 06, 2014, 05:27:41 AM
How can i combine Redd eq with Redd mic pre to building mixer with line input?

I am not sure what you mean. Do you no longer need the mic input?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ForthMonkey on June 06, 2014, 07:26:50 AM
How can i combine Redd eq with Redd mic pre to building mixer with line input?

I am not sure what you mean. Do you no longer need the mic input?

Cheers

Ian

Now i'm designing solid state recording/mixing console.I've converted Redd pre to fet preamp.It's working really good.I breadboarded it and i liked sound.I want to use this redd eq or only low&high bands with this preamp(It has mic&line inputs).With no transformers.But I can't figure it out how can i add eq?

Circuit like this;

Mic&Line Balanced Input Module->FetRedd Preamp->Balanced Output Module
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 06, 2014, 03:39:54 PM
URL="http://www.mediacollege.com/audio/processing/limiter/"]http://www.mediacollege.com/audio/processing/limiter/[/URL]

Now i'm designing solid state recording/mixing console.I've converted Redd pre to fet preamp.It's working really good.I breadboarded it and i liked sound.I want to use this redd eq or only low&high bands with this preamp(It has mic&line inputs).With no transformers.But I can't figure it out how can i add eq?

Circuit like this;

Mic&Line Balanced Input Module->FetRedd Preamp->Balanced Output Module

OK, now I understand. Post a schematic of what you have showing where you want to put the EQ and I'll see if I can help.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ForthMonkey on June 06, 2014, 04:16:21 PM
PMed
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: goetzmd on June 07, 2014, 07:09:37 AM
Please excuse me if this is a stupid question but I'm pretty new to electronics. :)

Have I got this right?
This is a passive EQ which means I could hook it up directly to my +4dBu line input and output of my audio-interface and it will work without any power supply. The downside would be the non-symetrical in- and output and a 10dB loss.

Cheers,
Goetz
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 07, 2014, 10:13:13 AM
Please excuse me if this is a stupid question but I'm pretty new to electronics. :)

Have I got this right?
This is a passive EQ which means I could hook it up directly to my +4dBu line input and output of my audio-interface and it will work without any power supply. The downside would be the non-symetrical in- and output and a 10dB loss.

Cheers,
Goetz

Basically yes, but it is not ideal. Driving it direct with +4dBu from a regular audio interface is no problem. Feeding its output into a regular 10K bridging input is not ideal. The REDD EQ output impedance is a nominal 5K ohms but it varies over a wide range depending on the EQ settings. It works best when loaded by a high impedance input like a tube or FET op amp.

By all means try it but you will find all the boosts are increased, the top cut and mid cut will be reduced. The bass cut will be unaffected. The extra boost is caused by the loading. This also increases the loss in the EQ.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: goetzmd on June 08, 2014, 07:10:15 AM
Thanks Ian!

I'm going to order 2 pcbs and read up more in impedance and opamps! :)

Would it be a quick and dirty fix to hook up the output to the hi-z input of an audio interface?

Thanks and all the best,
Goetz
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 08, 2014, 10:12:00 AM
Thanks Ian!

I'm going to order 2 pcbs and read up more in impedance and opamps! :)

Would it be a quick and dirty fix to hook up the output to the hi-z input of an audio interface?

Thanks and all the best,
Goetz

Yes, that would be fine.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: goetzmd on June 17, 2014, 03:27:04 PM
I received my boards (thanks Ian) and ordered all switches and the single value inductors from Farnell. They were all in stock for EU shipping but pretty expensive.

Since I'm building a 500 series version I have limited space for extras. I'd love to have a transformer – but there's only room for one. What would be the historically correct transformer or something similar that's available today? Also, would make more sense - an input or output transformer?

For example a blue Carnhill VTB 9071 10k:10k as input transformer has the right dimensions…

FYI: I also want to add a fet opamp to match the level and output impedance, a bypass switch and a +- 10dB output trim. (At least I think that this makes sense…  :o )

I'm a real newbie so any suggestions are highly appreciated!  :)

Cheers,
Goetz
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 17, 2014, 04:37:38 PM
I received my boards (thanks Ian) and ordered all switches and the single value inductors from Farnell. They were all in stock for EU shipping but pretty expensive.

Since I'm building a 500 series version I have limited space for extras. I'd love to have a transformer – but there's only room for one. What would be the historically correct transformer or something similar that's available today? Also, would make more sense - an input or output transformer?

For example a blue Carnhill VTB 9071 10k:10k as input transformer has the right dimensions…

FYI: I also want to add a fet opamp to match the level and output impedance, a bypass switch and a +- 10dB output trim. (At least I think that this makes sense…  :o )

I'm a real newbie so any suggestions are highly appreciated!  :)

Cheers,
Goetz


The individual inductors are quite cheap, the only problem is that you have to buy at least 5 of each from Farnell but at least you need 3 of the 10mH ones. perhaps REDD EQ builders could pass on their spare inductors to others??

The Carnhill 10K:10K will be fine as an input transformer. the original would have had a 200:200 transformer or it might have been balanced throughout in which case it would not have needed a transformer at all. Either way, my version is intended to be fed from a 10K:10K transformer and Carnhill is about as good as you can get.

FET OPA for gain make up and trim sounds fine to me. Bypass can be done with a DPDT switch. You can wire it up much the same way as it was done for the PMEQP1A:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png)

Just substitute the REDDEQ where is says PMEQP1A. The pad is already on the REDD EQ PCB. The 470K was nedded for the PMEQP1A. You can leave it out for a FET OPA and just use the OPA gain setting to get the overall gain right.

Cheers

Ian

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: goetzmd on June 19, 2014, 07:23:33 AM
The individual inductors are quite cheap, the only problem is that you have to buy at least 5 of each from Farnell but at least you need 3 of the 10mH ones. perhaps REDD EQ builders could pass on their spare inductors to others??
The individual inductors are in fact cheap – I'll offer the additional ones I've bought when they arrive. I meant  that the switches are expensive, especially since I had to substitute the Lorlin with another Grayhill to fit it all into a single 500 modul.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png)
Thank you Ian! That helps a lot!!  :)

Any particular reason why you trim the bypassed signal and not the actual eqed signal?

Also, do you have any suggestions regarding the output. I'm pretty sure I can't fit a full size output transformer in.
This is an option but I'd rather use not an IC:
http://store.diyrecordingequipment.com/balanced-output-building-block/
Or would this be a sensible option:
http://www.neutrik.com/en/accessories/transformers/nte1

Cheers,
Goetz
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 19, 2014, 06:37:23 PM
The individual inductors are quite cheap, the only problem is that you have to buy at least 5 of each from Farnell but at least you need 3 of the 10mH ones. perhaps REDD EQ builders could pass on their spare inductors to others??
The individual inductors are in fact cheap – I'll offer the additional ones I've bought when they arrive. I meant  that the switches are expensive, especially since I had to substitute the Lorlin with another Grayhill to fit it all into a single 500 modul.

Ah, now I understand. Yes , the Grayhill switches are not cheap but they are very good quality.
Quote
Any particular reason why you trim the bypassed signal and not the actual eqed signal?

So it is universally applicable. Each EQ has a different insertion loss. To set it up you set the controls to flat and then adjust the gain make up for overall unity gain. Then you swtich in the pad to bypass the EQ and adjust the pad for the same output. This works with any passive EQ no matter what the insertion loss.
Quote
Also, do you have any suggestions regarding the output. I'm pretty sure I can't fit a full size output transformer in.
This is an option but I'd rather use not an IC:
http://store.diyrecordingequipment.com/balanced-output-building-block/
Or would this be a sensible option:
http://www.neutrik.com/en/accessories/transformers/nte1

Cheers,
Goetz

Semiconductors are not my area. There are lots of options and I am sure there are others here much better qualified to make recommendations.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: goetzmd on June 21, 2014, 04:34:16 AM
So it is universally applicable. Each EQ has a different insertion loss. To set it up you set the controls to flat and then adjust the gain make up for overall unity gain. Then you swtich in the pad to bypass the EQ and adjust the pad for the same output. This works with any passive EQ no matter what the insertion loss.
That totally makes sense! Thanks, Ian!

For the output I'm looking into really small transformers...
http://www.neutrik.com/en/accessories/transformers/nte1

All the best,
Goetz
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 21, 2014, 05:26:56 AM
For the output I'm looking into really small transformers...
http://www.neutrik.com/en/accessories/transformers/nte1

All the best,
Goetz

The trouble with small transformers is they cannot take high signal levels. The NTE one you linked to for example is specified for a maximum level of  -3 dBu (@ 50 Hz, 1% THD). Not much good if you want a +4dBu output level. The obvious way to save space if you are using a semiconductor gain make up stage is to make it electronically balanced. The trouble with the 500 series format is that by the time you have fitted and input and output transformer there's not much room left for anything else.

Have you thought about making it a double width module?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: goetzmd on June 21, 2014, 06:17:19 AM
The trouble with small transformers is they cannot take high signal levels. The NTE one you linked to for example is specified for a maximum level of  -3 dBu (@ 50 Hz, 1% THD). Not much good if you want a +4dBu output level. The obvious way to save space if you are using a semiconductor gain make up stage is to make it electronically balanced. The trouble with the 500 series format is that by the time you have fitted and input and output transformer there's not much room left for anything else.

Have you thought about making it a double width module?

Thank you for pointing that out Ian! Neutrik has another small transformer which I already used in building the Studer EQ: http://www.neutrik.com/en/accessories/transformers/ntl1  It can do 5V (@30 Hz, 1% THD) which should be around +16 dBu… at least if my math is correct.  ;D I simply was looking for an alternative since this one is 50 € a piece….

I thought about a double width module but I feel that part of the 500 format charm is the limited space. Also my rack is nearly full…  :'(   ;)

Cheers,
Goetz
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 21, 2014, 01:38:27 PM
The Neutrik specifications are confusing  to say the least. It says "NTL1 is a line transformer intended to balance amplifier outputs for line driving up to +24 dBm". The it says it can drive 6V rms into 600 ohms at 30Hz which is just over 17dBu. The strange thing is the primary inductance is a whopping 150 Henries and the primary dc resistance is 100 ohms. YThis says to me that this is really intended as a 10K:10K line input transformer.

I am definitely not a transformer expert but for a line output transformer driven by an op amp you need a lot less primary inductance so you can use a lot fewer turns and hence have a larger signal level before saturating the core. A 15 Henry inductance has an impedance of 1884 ohms at 20Hz which would be more than OK.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 22, 2014, 05:46:56 AM
I am down to the last two REDD EQ PCBs. If it looks like there is a demand I will order another batch.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: goetzmd on June 22, 2014, 08:23:51 AM
The Neutrik specifications are confusing  to say the least. It says "NTL1 is a line transformer intended to balance amplifier outputs for line driving up to +24 dBm". The it says it can drive 6V rms into 600 ohms at 30Hz which is just over 17dBu. The strange thing is the primary inductance is a whopping 150 Henries and the primary dc resistance is 100 ohms. YThis says to me that this is really intended as a 10K:10K line input transformer.

Thanks, Ian. I checked: on the Studer EQ this things is the input transformer…

Has anybody another idea for a small size output transformer?

Mouser-BOM
This contains all resistors and capacitors for 2 units:
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=58a092f82a

Cheers,
Goetz
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 22, 2014, 11:28:05 AM
Jensen and Cinemag both do a smallish (just over one inch cube sized) 600:600 output transformer but it is only good to about +8dBu.

edcor do the PC600/600 which will do 5V rms which i +16dBu but I cannot download the data sheet to se how big it is.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: goetzmd on June 24, 2014, 02:33:50 PM
Thanks, Ian! The Edcor looks good. I'm slowly getting the basic parts. I'll build your boards first and go from there…

Since Farnell sells the single value inductors only in bags of 5 I have some spare parts to give away:

If you're building a stereo pair, live in Europe and send me a pm, you'll get for free:
2 x 1 mH
2 x 2.2 mH
2 x 3.3 mH

Already gone – we have a winner! :)

Cheers,
Goetz
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on July 04, 2014, 06:02:57 AM
Thanks, Ian! The Edcor looks good. I'm slowly getting the basic parts. I'll build your boards first and go from there…

Cheers,
Goetz

I just found these little gems:

http://www.triadmagnetics.com/catalog_template.php?productCategoryId=47 (http://www.triadmagnetics.com/catalog_template.php?productCategoryId=47)

They are available from Farnell. I just bought some of the 10K:10K 0.1W types for use in a VU meter buffer. When I tested them their primary inductance was over 30 Henries at 100Hz and their response was just 0.5dB down at 20Hz. 1KHz distortion at +18dBu was just 0.05%. And the are really small.

For your application the 600:600 one might be more appropriate:

http://uk.farnell.com/triad-magnetics/ty-145p/transformer-audio-0-1w/dp/1610411 (http://uk.farnell.com/triad-magnetics/ty-145p/transformer-audio-0-1w/dp/1610411)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: letterbeacon on July 23, 2014, 09:06:03 AM
I'm also thinking about squeezing a REDD EQ in a 500 format. I would like to use a DOA to make up the gain after the EQ. Is it as simple as taking the gain stage and surrounding resistors and capacitors from the circuit below and using it after the EQ?

I plan to use the triad OT recommend in the post above.

Any help would be much appreciated!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: letterbeacon on July 23, 2014, 02:08:35 PM

I just found these little gems:

http://www.triadmagnetics.com/catalog_template.php?productCategoryId=47 (http://www.triadmagnetics.com/catalog_template.php?productCategoryId=47)

They are available from Farnell. I just bought some of the 10K:10K 0.1W types for use in a VU meter buffer. When I tested them their primary inductance was over 30 Henries at 100Hz and their response was just 0.5dB down at 20Hz. 1KHz distortion at +18dBu was just 0.05%. And the are really small.

For your application the 600:600 one might be more appropriate:

http://uk.farnell.com/triad-magnetics/ty-145p/transformer-audio-0-1w/dp/1610411 (http://uk.farnell.com/triad-magnetics/ty-145p/transformer-audio-0-1w/dp/1610411)

Cheers

Ian

It's more than likely me misunderstanding the specs, but don't they only go down to 200Hz?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on July 24, 2014, 02:34:50 AM

It's more than likely me misunderstanding the specs, but don't they only go down to 200Hz?

You are right, the spec says they only go down to 200Hz. that's why I was only considering using it for a VU buffer. They are so cheap I thought it was worth buying a couple just to try out. I was pleasantly surprised at their measured performance. In particualr, they have a nice high inductance which is the main determinant of low frequency response. At 30 Henries, this represents an impedance of  3770 ohms at 20Hz which, even with a 600 ohm source gives a 20Hz loss of only 1 dB.

Cheers

IAn
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: letterbeacon on October 22, 2014, 05:57:47 PM
Ian, I sent you some pics directly. Hope you got them.
Here's one for your listeners ;D
2 channels of Ruff Helios EQ mastering version all stepped controls.   
Solid State Pultec output circuit- 2520 opamp with a quadfilar transformer.
Run a few mixes with it.
Beautiful
Recycled rack case - decals mounted on 12 gauge aluminium front panel.
good enuf.
Thanks for the great project.
Kelly

Is there anywhere I can see the other pics that Kelly sent? I'm planning something similar and would love to see how he's laid out the inside of the unit.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: anjing on October 22, 2014, 06:26:10 PM
You can find a gallery of different projects build from Ian's pcb'shere:
http://theworldin35mm.com/projectgallery/
 (http://theworldin35mm.com/projectgallery/)Kelly's Eq is there.

Regards,
Pierre
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: letterbeacon on October 22, 2014, 06:27:40 PM
Perfect, thank you!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on December 24, 2014, 02:51:04 AM
Hey all,
So im collecting parts for a stereo or dual mono helios 69 in a 1u using Ian's pmtgmu and ht-350 supply. I will be using 6gc7 tubes as well as the antec toroidal ive read others have used.
I have just a few questions I'd like some clarity on.
Thanks in advance.
So I'm probably doing a stepped gain switch using 1 pole 12 pos lorlins in place of the pots and using grayhills like they were intended and was wondering if the non-shorting type were okay to use?  Its all they have at digikey and I am trying to somewhat consolidate my purchases (and yes I know capi carries them).
I was also hoping on using edcor 10k/10k in and the 600/600 ohm output xfmrs and would like to hear some opinions on how they are since they seem to get mixed reviews.  Maybe sowter in and edcor out or vice versa?
And finally concerning inductors are there single inductor alternatives to the Carnhill vtb 9042 and 9043?
If the carhill inductors are a necessary component for the helios 'sound' id rather not diminish anything and will just suck it up but if I could save a buck or two that would be pretty helpful.

Ive pretty much gotten everything laid out using the wealth of info over on the poor man's pultec thread and parts are just beginning to come in so id really appreciate your thoughts.
Oh and Ian thank you very much for designing and supplying these boards.  Your contributions to this community are inspiring. You're a genius man.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on December 24, 2014, 11:25:26 AM
So I'm probably doing a stepped gain switch using 1 pole 12 pos lorlins in place of the pots and using grayhills like they were intended and was wondering if the non-shorting type were okay to use?  Its all they have at digikey and I am trying to somewhat consolidate my purchases (and yes I know capi carries them).

Non-shorting Lorlins for the variable resistors should be OK. There is not possibility of switching capacitor charged with dc voltages at that point in the circuit so shorting is not required. If you are really concerned you can put a 4M7 resistors from the wiper to each end of the Lorlin to ensure there is always a dc connection path. For the Grayhills, non-shorting are OK for the Hi amd Mid controls. The Lo control really should use a shorting type for the low cut part of the circuit as the capacitors in the part of the circyuit have no independent dc path to discharge them. Again, if you are really concerned about this you can wire 4M7 resistors between all successive pairs of contacts on the lo cut section.

Quote
I was also hoping on using edcor 10k/10k in and the 600/600 ohm output xfmrs and would like to hear some opinions on how they are since they seem to get mixed reviews.  Maybe sowter in and edcor out or vice versa?

The output transformer is the more critical one. The input transformer can probably be any 10K:10K type provided it is driven by a low impedance source. The main limitation of the poor man's tube gain make up stage is its relatively high output impedance. This means it need a good quality 600:600 output transformer with a high primary inductance in order to give good performance.  Edcors tend to have lower primary inductance that Sowter. If you want to save money use an Edcor at the input and a Sowter at the output.
Quote
And finally concerning inductors are there single inductor alternatives to the Carnhill vtb 9042 and 9043?
If the carhill inductors are a necessary component for the helios 'sound' id rather not diminish anything and will just suck it up but if I could save a buck or two that would be pretty helpful.

I am in contact with one of the original designers of the Helios 69. The Helios 'sound' is in part due to the properties of the surplus inductors they used in the early builds; inductors that they bought over the counter in the Tottenham Court Road. Needless to say these inductors are no longer available. Carnill make inductors for many classic designs including Neve (in fact one of the original factories used for making Neve transformers and inductors has been part of the Carnhill group for many years) so their quality is very good. Whether the sound they produce in my design is the same as the 'Helios' sound is not for me to say. You need to judge that for yourself. groupdiy member Chrion did make alternative lower cost inductors for a time but I have not seem him around for some time.


Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on December 24, 2014, 02:27:48 PM
Thanks for chiming in Ian. I have used Carnhills in a few builds (1290, 1084, etc..) and can certainly attest to them being the Rolls Royce of xfmrs so imagine they probably have a significant enough impact so will stop screwing around and just use them. 
Edcor in and Sowter out sounds good to me.
Thanks again
Dylan
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on December 25, 2014, 02:25:55 PM

One last inquiry (for awhile anyway);
Do you (or anyone) see any problems using Carnhills vtb 2281?
The specs seem right.
Might as well
btw happy xmas everyone.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on December 29, 2014, 05:08:19 PM
Uhhmmg
So Antek is currently out of the 05t240.  Bummer. They do have:

[url]http://www.antekinc.com/as-1t250//[url]
Which is overkill but fine I guess.
Anyone else know of a US or affordable source for the toroidal for this project?
I found this toroidal at Don Audio for you guys in Europe:
[url]http://www.don-audio.com/Toroidal-Transformer-Mila-sec-250vct-63vct-48V/url]
Which if all else fails(if not just overkill) is fine right?

Also; I've been in touch with cinemag and David had some suggestions for the output xfmr; CMLI-600, that im more than likely gonna try.
Thanks in advance
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on December 30, 2014, 11:27:26 AM

One last inquiry (for awhile anyway);
Do you (or anyone) see any problems using Carnhills vtb 2281?
The specs seem right.
Might as well
btw happy xmas everyone.

VTB2281 will do fine and nice and cheap too.

Happy New Year

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on January 01, 2015, 12:28:21 PM
Happy New Year!!!

Okay so I am beginning to wire up the Helios and am following Dave's
really great wiring diagram made for the Poor Man's Pultec
and have a question regarding the eq bypass.  I am using the PMTGMU which
in Dave's diagram has the boards connected to the eq via the DPDT in/out
switch.  But...  the Helios has a provision on the board for an eq bypass
as well.  Now a clever man might add both to one DPDT switch but I read
somewhere (which I can't find now and it's driving me crazy ) where it was
suggested to use just the Helios bypass in/out.  I imagine then that I would
just go directly to the PMTGMU from the Helios in and outs.  Am I on the
right track?

Thanks
Dylan
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 01, 2015, 12:51:50 PM
Yes. The Helios  is unique for one of my EQs in that the bypass switch is built in - I literally copied it from the original - so you do not need the DPDT bypass used in the poor man's EQP1A. You can just go straight into In and IG (ground) from the Helios EQ out. You do not need to fit VR2 either or the 470 and 10K resistors next to it.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on January 01, 2015, 01:49:46 PM
Yes. The Helios  is unique for one of my EQs in that the bypass switch is built in - I literally copied it from the original - so you do not need the DPDT bypass used in the poor man's EQP1A. You can just go straight into In and IG (ground) from the Helios EQ out. You do not need to fit VR2 either or the 470 and 10K resistors next to it.

Cheers

Ian

Thanks Ian.
Good to know.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on January 06, 2015, 11:51:36 PM
Hey
  So the Antek 05t240 is out of stock and I am having some trouble finding a multiple winding transformer that is 1u (as well as won't cost me an arm and a leg).   I found this guy:  http://www.ampmaker.com/store/240V-6.3V-toroid-power-transformer.html (http://www.ampmaker.com/store/240V-6.3V-toroid-power-transformer.html)  but I am not sure if it will handle the two 6cg7's.  The price and size is certainly right.  When I emailed them they believed it would be close.  Maybe to close to call?
Anybody have any thoughts?


 
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 07, 2015, 05:39:55 AM
Hey
  So the Antek 05t240 is out of stock and I am having some trouble finding a multiple winding transformer that is 1u (as well as won't cost me an arm and a leg).   I found this guy:  http://www.ampmaker.com/store/240V-6.3V-toroid-power-transformer.html (http://www.ampmaker.com/store/240V-6.3V-toroid-power-transformer.html)  but I am not sure if it will handle the two 6cg7's.  The price and size is certainly right.  When I emailed them they believed it would be close.  Maybe to close to call?
Anybody have any thoughts?

This transformer is made by Carnhill. One limitation of toroids is that if you take much more than the rated current from them they can easily saturate which is not a good thing.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on January 07, 2015, 12:03:45 PM
Thanks Ian.  Don Audio it is.  Hey...  good dude to support.  Plus IIRC I get a real nice Elma pen as an extra surprise whenever I order something.
Okay so I am seeing that several people are only connecting the middle and first leg of the 50k lo "gain" potentiometer and tying the middle and third leg together.  Why?  Isn't that how we are tapping the vtb 9043?
I am just awaiting a few tiny more things (Like a power xfmr- ha) but nearly everything is here and beginning to come together.
I also just finished a front panel and will post it up here for people to use. 
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 07, 2015, 06:58:47 PM
Thanks Ian.  Don Audio it is.  Hey...  good dude to support.  Plus IIRC I get a real nice Elma pen as an extra surprise whenever I order something.
Okay so I am seeing that several people are only connecting the middle and first leg of the 50k lo "gain" potentiometer and tying the middle and third leg together.  Why?  Isn't that how we are tapping the vtb 9043?

I am confused. if you tie the middle and first legs together then connect the middle and third together you end up with all three shorted together??

You need only  to short the first and middle together. This is because this pot acts as a rheostat (variable resistor) rather than as a potential divider. See the schematic near  the end of this document:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Helios69EQ/Helios3bandDocV1.2.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Helios69EQ/Helios3bandDocV1.2.pdf)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on January 08, 2015, 10:55:17 AM

I am confused. if you tie the middle and first legs together then connect the middle and third together you end up with all three shorted together??

You need only  to short the first and middle together. This is because this pot acts as a rheostat (variable resistor) rather than as a potential divider. See the schematic near  the end of this document:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Helios69EQ/Helios3bandDocV1.2.pdf (http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Helios69EQ/Helios3bandDocV1.2.pdf)

Cheers

Ian

I believe my description was unclear and I apologize.  I understand now though.  I tried to wrap my head around that part of the schematic for awhile but obviously wasn't understanding it correctly.   Although this isn't my first project I'm still pretty green. 
I feel pretty clear on how most of the circuit ties in together (which is really clever by the way) but am still a little shaky on the Pin and Pout section.  The PG I understand is the ground for the Pin and Pout. 

Using the system diagram here:
 http://www.ianbell.ukfsn.org/pics/EQSystem.png (http://www.ianbell.ukfsn.org/pics/EQSystem.png)
and eliminating the switch (as well as the A and B section) of the PMTGMUsm here:
http://www.ianbell.ukfsn.org/pics/PMTGMsm.jpeg (http://www.ianbell.ukfsn.org/pics/PMTGMsm.jpeg)
 am I right in thinking I should run the input xfmr to the Pin and the Helios in (as well as corresponding shields; PG) and Pout runs to the output xfmr along with PG?

I can't thank you enough Ian


   
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 09, 2015, 06:06:55 AM
Hooking up the Helios EQ PCB is quite simple. Your input goes (via a 10K:10K transformer) to the pad labelled IN and the one labelled 0V next to it. Your output comes from the pad labelled OUT and the one labelled 0V next to it. The EQ IN/OUT switch is wired to the three pads labelled COM, BY and EQ which stand for switch common, bypass and EQ in. You just need to connect a single pole double throw switch to these three pads.

If you are using the poor man's tube gain make up PCB (PMTGMU) for gain make up then all you need to to is connect the OUT and 0V pads of the Helios EQ straight to the pads labelled In and IG on the PMTGMU and fit VR1. You do not need to fit VR2 or the 10K and 470 ohm resistors and you do not need to use the pads labelled Pin, Pout and PG.

Hope that helps.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on January 09, 2015, 10:03:15 AM
Thanks Ian, yes that helped a ton and is quite simple.
Cheers
Dylan
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on January 21, 2015, 01:56:27 AM
Ian,
  So I was doing some more leisurely research the other day that ended up becoming a several days long Helios bender.  I am nearly done (all wired up just need some damn time) and the front panel design is just a keystroke away from going 'express' and I was wondering how hard would it be to implement the high pass filter switch at 40 and 80hz that is found on the newer models? 
I read somewhere that you actually had this as a template on one of your ez tube mixer channels and was hoping...

and of course; thank you.
I think I'll have time to fire it up tomorrow.
Dylan
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 21, 2015, 06:28:20 AM
Unfortunately the HPF in the Helios 69 uses a separate additional buffer amplifier which completely decouples it from the main 3 band passive EQ. So, to do it properly you need an additional unity gain buffer. If you are using a semiconductor gain make up stage then this is relatively easy to do as it is little more than one more op amp. Can be done with tubes but needs an extra one.

You might be able to do a passive one between the Helios EQ out and its gain make up amp so long as the make up amp has a high enough input impedance. For example the original Helios 69 discrete gain make up has an input impedance of about 300K and the EQ output impedance is close to 5K. We can load 5K with 91K without significantly upsetting the operation of the EQ. A 22nF  series cap with a 91K load turns over at 479.5Hz and 44nF turns over at  39.75Hz. Helios used a clever scheme using a single pole double throw toggle switch with a centre off which switch in either one or two capacitors for the two frequencies. Later I think they used two separate toggles. Here's a sketch of the design above. Please note I have not built or tested this.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on January 26, 2015, 08:38:51 PM
It's alive.  And sounds great!  I haven't calibrated it or busted out my scope, but boy does that mid boost just do great things.  I'm gonna use this a lot i can tell. Just sent in my order to FPE so it'll be a week before that'll go on. I have it housed in a temporary front panel while i worked on the design.  Currently it is using the variable resistors and pots but I've got a feeling im gonna throw some grayhill or elma 1 pole 12 positions in there instead.
Ian; Thank you!
Great project, great support,  and great outcome. 
Learned a lot of cool stuff   (including a little history of EMI), as well as gained another myopic obsession regarding the type 69.
I'll post pics when the front panel arrives.
Cheers
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on January 27, 2015, 04:23:02 AM
I am pleased it is working and that you like it. Gotta love that inductor based modest Q mid boost - something special about that.

Pierre hosts a gallery of pics of projects of my designs built by others. When you have some pics I would be happy to pass them on to him for inclusion in the gallery if you wish.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Rocinante on February 13, 2015, 12:58:57 PM
Voila!  Here is a nice gut shot for you.  I'll take some more glamor pics later.

(http://i.imgur.com/GuQEKJ9l.jpg)

   What else could one possibly desire really?  Grayhills and Elma knobs.  Carnhill output transformers and inductors.  Nos tubes!!!!  I played around with various kinds of caps as well.  I am still calibrating it a little but it seems this was designed for acoustic guitar.  It puts that 'wooliness' into it that can be perfect.  I am just loving the high and mid bands.  This can really add a brightness that is smooth more than sharp but present nevertheless.  I betcha this will do incredible things to twelve string guitars and accordions.  I'll soon find out.

(http://i.imgur.com/j7ou2Edb.jpg)

(http://i.imgur.com/0iM9qKYl.jpg)

(http://i.imgur.com/DL92hdIl.jpg)

The front panel pays respect to the original. 
I know I've said it before but; thanks for the great project Ian. 
Cheers

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 13, 2015, 02:00:20 PM
Great photos! Nice, nest, professional looking build. Front panel is first class. If you would like to email full res pics to me I'll pass them on to Pierre for inclusion in the gallery. My email address is in my profile.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: thomasdf on April 30, 2015, 10:02:11 AM
Hey Ian
Do you still have a PCB for this one?
Thomas
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on April 30, 2015, 02:18:15 PM
Hey Ian
Do you still have a PCB for this one?
Thomas

Yes I do. four in stock right now.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: jona on May 03, 2015, 04:21:03 AM
hey,

i built a 2 channel version with external psu and have  a small problem with my eq.. i used a 470k potentiometer on the front panel to adjust  gain.
there is some hum audible until i dial in full gain on the pot.. then the hum is completely gone..
i used shielded 2 conductor cable to connect the pot. i connected the shield to IG and pin 3 on the pot, wiper to grid and input to pin 1 on the pot..  what could be the problem?

thanks
 

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 03, 2015, 07:12:44 AM
hey,

i built a 2 channel version with external psu and have  a small problem with my eq.. i used a 470k potentiometer on the front panel to adjust  gain.
there is some hum audible until i dial in full gain on the pot.. then the hum is completely gone..
i used shielded 2 conductor cable to connect the pot. i connected the shield to IG and pin 3 on the pot, wiper to grid and input to pin 1 on the pot..  what could be the problem?

thanks

Do you also have a screened cable from the EQ output to the pot?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: jona on May 03, 2015, 08:25:31 AM
thanks for your reply ian..
do you mean eq out to gain makeup ? i used the same 2 conductor with shield. shield and one conductor tied together to 0V on both sides and the other conductor for the signal.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 04, 2015, 04:26:37 AM
thanks for your reply ian..
do you mean eq out to gain makeup ? i used the same 2 conductor with shield. shield and one conductor tied together to 0V on both sides and the other conductor for the signal.

OK I am getting confused. I imagined your signal went EQ out ---> pot --> gain make up. If that is the case then you need to use screened cable for both connections.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Jeremy.Starseed on May 10, 2015, 09:34:57 AM
Any boards available?

Interested in 4  :)

Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on May 11, 2015, 12:56:14 PM
Any boards available?

Interested in 4  :)

Two versions of the board are available - the original and the 3U version.

The original is about 125mm by 75mm and has provision for PCB mounted pots as well as the three frequency selection pots.  The peak/trough and EQ in/out switches are mounted off board. I have four of this type of board in stock

The 3U version, as its name suggests, is intended to be able to fit vertically in a 3U enclosure and measures 100mm by 100mm. The three frequency switches are closer together and the two pots, the peak/trough and EQ in/out switches are mounted off board. I have six of these in stock.

Both boards are priced at £9. For instructions on how to order go here:

http://groupdiy.com/index.php?topic=48986.msg619033#msg619033 (http://groupdiy.com/index.php?topic=48986.msg619033#msg619033)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on December 18, 2015, 06:51:36 PM
should i use shortig or non shorting switches for the redd eq? cheers
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on December 19, 2015, 05:57:38 AM
should I use shorting or non shorting switches for the redd eq? cheers

For the REDD EQ non-shorting should be fine.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ding on December 22, 2015, 01:50:57 AM
http://www.digikey.com/product-detail/en/71BDF30-02PAJN/GH7107-ND/98682 (http://www.digikey.com/product-detail/en/71BDF30-02PAJN/GH7107-ND/98682)
Is this the right switch for the redd?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on December 22, 2015, 02:40:50 AM
http://www.digikey.com/product-detail/en/71BDF30-02PAJN/GH7107-ND/98682 (http://www.digikey.com/product-detail/en/71BDF30-02PAJN/GH7107-ND/98682)
Is this the right switch for the redd?

I think that is the right switch for S1 and S2. I am not quite sure why digikey uses that particular version of the part number. The correct part number, which is in the assembly guide, is 71BDF 30-02-1-AJN. For S3 you need 71BDF 30-01-1-AJN

CHe Grayhill part number are in the assembly documentation which you can find in the REDDEQ folder under the DIY tab at my web site:

www.customtubeconsoles.com (http://www.customtubeconsoles.com)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ding on February 20, 2016, 10:00:01 PM
What are the distances between the switches on both the helios and redd?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 21, 2016, 11:36:51 AM
What are the distances between the switches on both the helios and redd?

On the 3UHelios and the 3UREDDEQ, the switches are one inch apart.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ding on February 21, 2016, 07:49:57 PM
What are the distances between the switches on both the helios and redd?

On the 3UHelios and the 3UREDDEQ, the switches are one inch apart.

Cheers

Ian

I was trying to fit some .9 inch mini chicken head knobs but I guess that would be too tight. How about the regular helios pcb? I also see that you have only one in stock. Are you planning on getting more or are these being phased out for your new makeup gain version?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ding on February 21, 2016, 07:51:12 PM
double post!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on February 22, 2016, 02:14:16 AM
What are the distances between the switches on both the helios and redd?

On the 3UHelios and the 3UREDDEQ, the switches are one inch apart.

Cheers

Ian

I was trying to fit some .9 inch mini chicken head knobs but I guess that would be too tight. How about the regular helios pcb? I also see that you have only one in stock. Are you planning on getting more or are these being phased out for your new makeup gain version?
They are further apart in the original version because there is a pot between them. I don' recall the exact dimension. I'll fire up the PCB package and measure it for you.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ding on March 01, 2016, 04:26:05 PM
For anyone that needs the helios69 (NOT the "3U version") distances. The distances of the pots and switches, from the left hand end of the PCB are:

1. Hi switch, 0.5 inches
2. Mid pot, 1.5 inches
3. Mid switch, 2.5 inches
4. Lo pot, 3.5 inches
5. Lo switch,  4.4 inches
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 01, 2016, 06:46:49 PM
For anyone that needs the helios69 (NOT the "3U version") distances. The distances of the pots and switches, from the left hand end of the PCB are:

1. Hi switch, 0.5 inches
2. Mid pot, 1.5 inches
3. Mid switch, 2.5 inches
4. Lo pot, 3.5 inches
5. Lo switch,  4.4 inches

And I am expecting a fresh batch of this version of the Helios any day now.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 03, 2016, 05:31:49 AM
The new batch of the original Helios EQ boards arrived yesterday. They the V2 version. It has been updated to include Molex connectors for input and output and the pads for the mid boost/cut switch have been rearranged to make it simpler to wire up. I will update the emporium.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ding on March 04, 2016, 02:28:53 PM
Hey Ian, where did you get those caps on the Helios 69 image in your website? I have been having a hell of a time finding some of the caps of the right width on mouser or digikey. Most of the poly's (PP) are too wide to fit and some I can't even find in 5mm lead spacing.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 04, 2016, 04:23:56 PM
Hey Ian, where did you get those caps on the Helios 69 image in your website? I have been having a hell of a time finding some of the caps of the right width on mouser or digikey. Most of the poly's (PP) are too wide to fit and some I can't even find in 5mm lead spacing.

The brown looking ones are by Panasonic:

http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000005410&st=PANASONIC%20ELECTRONIC%20COMPONENTS%20CAPACITORS&pageSize=25&beginIndex=1&showResults=true&pf=110141064,110141066,110141074,110162379,110183064,110202702 (http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000005410&st=PANASONIC%20ELECTRONIC%20COMPONENTS%20CAPACITORS&pageSize=25&beginIndex=1&showResults=true&pf=110141064,110141066,110141074,110162379,110183064,110202702)

but it looks like they are being phased out. So now I tend to get the liltte box shaped ones by EPCOS and KEMET:

http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000005410&pageSize=25&showResults=true&pf=110141064,110141066,110141074,110162379,110183064,110202702 (http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000005410&pageSize=25&showResults=true&pf=110141064,110141066,110141074,110162379,110183064,110202702)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ding on March 04, 2016, 07:32:55 PM
Ah, ok. I've been trying to stick to polypropylene so it's been a little more difficult for me. I guess there is a wider verity of polyester. I'll just have to manage which ones go below and which ones go above. Thanks.

Alain
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 05, 2016, 02:42:28 AM
Ah, ok. I've been trying to stick to polypropylene so it's been a little more difficult for me. I guess there is a wider verity of polyester. I'll just have to manage which ones go below and which ones go above. Thanks.

Alain

Yes, polypropylene are much harder to find in 5mm spacing. You don't really need to worry too much about the dielectric type of the caps as long as they are film types and rated at at least 50V. Most of the 'sound' of the Helios EQ is due to the iron .

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on March 22, 2016, 06:01:07 PM
After some email conversations with a current builder of the REDD EQ I have updated the build documentation to clarify and expand a few areas. New document is called REDDEQManul0.2.pdf and is in the REDDEQ folder of the DIY tab of my web site:

http://www.customtubeconsoles.com/diy (http://www.customtubeconsoles.com/diy)

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on June 30, 2016, 07:04:00 PM
Almost done. Took a pic before closing this thing.
4ch reddd using marinair on inputs, mullard caps throughout, dons Induktors for mid cut and carnhills on the outputs. This Unit has an output impedance of around 200ohms and gain makeup will be done with Telefunken v72 preamps. Sorry for the Bad pic. Cheers Jakob
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on June 30, 2016, 07:16:27 PM
Fitting the mustards was a b€tch..... Oh and ian is the the greatest guy ever. Thanks so much mate! 8ch pultec coming very soon. All caps (Pios in that case)  are matched. My girlfriend loves playing with the lrc bridge and matched them perfectly with exell sheets.  Best Girl for any tech 😀
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on June 30, 2016, 07:39:03 PM
Best Girl ever. This is a fraction of what she did. she literally matched hundreds of them.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on July 01, 2016, 05:22:14 PM
Jakob, can you send me some full resolutions pics of this build so I can get Pierre to add them to his gallery of my projects?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on July 01, 2016, 05:31:24 PM
Jakob, can you send me some full resolutions pics of this build so I can get Pierre to add them to his gallery of my projects?

Cheers

Ian

problem is my camera. this is high resolution mode :) but i have some friends over for the match tomorrow night and im certain that one of them has a smartphone with better cam. ill send you some pics then.  unless im too devestated in case italy kicks us out of the tournament - as usual :)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on July 06, 2016, 03:18:38 PM
these sound amazing. especially with a v72 as gain makeup. i tried neves and gmls as well and while i like it, there is something really special when powering them with the old telefunkens. the high end is pure butter.
i do have a slight hum issue which i have to trace down. i did use the output transformers unshielded wire - ill replace that first.

edit; i think i chased it down. looks like i miswired the marinairs - fed 0v to a wrong pin. its clean now.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on July 07, 2016, 04:44:17 PM
I see Italy AND Wales both got kicked out. Will France beat Germany tonight???

Alons y!!

Cheer

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: UffeK on October 03, 2016, 02:40:22 PM
Would the G-Pultec gainstage be suitable as gainstage for the REDD EQ?

http://www.gyraf.dk/gy_pd/pultec/gy_pd_sch.gif

Thanks

UffeK
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on October 03, 2016, 06:30:40 PM
Would the G-Pultec gainstage be suitable as gainstage for the REDD EQ?

http://www.gyraf.dk/gy_pd/pultec/gy_pd_sch.gif

Thanks

UffeK

Yes it will. You might need to add a preset pot between the EQ output and the amp input to set the overall gain to unity - a 470K pot will do it - but otherwise it should be ideal.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: UffeK on October 05, 2016, 04:28:43 AM
Thanks Ian
I really appriciate this.
 
I consider building the EQ as a stereo pair, and consider the pros and cons with tube vs transistors as booster.
No doubt the tubes will have a small say on the sound, but here we are only looking for the flavor from the filters(chokes caps and resistors), right?

I consider two alterternatives for step one:
1) - Simply use my EF86 based Ampex MX 10 as booster
         https://www.gearslutz.com/board/attachments/geekslutz-forum/148250d1260800659-post-xformer-pad-mx10-ampex_mx-35_schematic.gif
 
2) - Do a stereo version of the the TL072 amp you also suggest.
        Here I was wondering if this simple little amp based on the TL072 would be a suitable MKI alternative:
        http://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k2572_rev2.pdf
        Perhaps modded with an OPA2604 for a more tubey sound.

Could I have your thoughts, please?

Thank you, Sir

UffeK


 
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on October 05, 2016, 01:20:10 PM

I consider two alterternatives for step one:
1) - Simply use my EF86 based Ampex MX 10 as booster
         https://www.gearslutz.com/board/attachments/geekslutz-forum/148250d1260800659-post-xformer-pad-mx10-ampex_mx-35_schematic.gif

This has more than enough gain but unfortunately the EF86 has no drive capability so as soo as you connect it to a 10K line input you will lose a lot of level and distortion will become significant. If you want a single tube gain make up you could use my poor man's tube gain make up stage.
Quote

2) - Do a stereo version of the the TL072 amp you also suggest.
        Here I was wondering if this simple little amp based on the TL072 would be a suitable MKI alternative:
        http://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k2572_rev2.pdf
        Perhaps modded with an OPA2604 for a more tubey sound.

For the correct high impedance input and best noise performance you need to use a non inverting op amp configuration. The  little amp you refer to is configured as an inverting type which is not really suitable. I guess you could cut tracks and wire link it to convert it but it is a lot of trouble to go to. Perhaps there is something similar which is non inverting? The circuit you need is not complex so you could always build it on Veroboard.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: UffeK on October 25, 2016, 01:14:17 PM
Thanks Ian.
Sometime during the reading on REDD EQ and RS127, I found an article on the Siemens W295B.
I also got the this plugin from Soundtoys for free:
http://www.soundtoys.com/product/sie-q/ (http://www.soundtoys.com/product/sie-q/)
-which is modeled after the W295B.
Comparing the functionality + the fact that the W295B has both the input and output transformers as well as the booster amp, got me thinking that this might be an alternative not too far from the real EMI thing.
Long story short; I found a fine set of these for sale locally for less that the BOM I made for the EMI project, and I decided to buy.

These old Siemens EQs sound absolutely fantastic, especially the high shelving is really nice. No harshness at all.
Comparing the Plugin to the real deal, I must say that they did a really good job at capturing the sound of the hardware, but the hardware has more of the hard to describe pleasing the ears factor, which is probably because of the the transfomers.

Here is a diagram for comparison:
http://audio.kubarth.com/rundfunk/getfile.cgi?f=H%2C30W-S0Q-%234Y.5%5DW%2BW-I96UE%3BG-%3F%3DS%28Y-6%29%3F%3CV-H96UA%3D%26EC%2BG%21D9%40%60%60%0A (http://audio.kubarth.com/rundfunk/getfile.cgi?f=H%2C30W-S0Q-%234Y.5%5DW%2BW-I96UE%3BG-%3F%3DS%28Y-6%29%3F%3CV-H96UA%3D%26EC%2BG%21D9%40%60%60%0A)

Thanks
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on October 25, 2016, 07:02:53 PM
The W295B is interesting but quite different to the Helios and REDD EQ. Looking at the W295B schematic it is clear that the treble and bass boost/cut are straightforward Baxandall style EQs that rely on negative feedback. The topology of the mid EQ is very similar to one of the API EQs. I uses a passive circuit for cut and a negative feedback one for boost.

Both the Helios and REDD EQs are passive thoughout and just need a gain make up amplifier to restore the insertion loss.

The fact that you like the sound may mean that the exact topology is not important as you might think.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: tommypiper on November 19, 2016, 08:15:36 PM

...4ch reddd using marinair on inputs, mullard caps throughout, dons Induktors for mid cut and carnhills on the outputs. ...Cheers Jakob

Nice build!  Can you share how you are wiring the transformers?  Which carnhills are you using on the outputs?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: surfkat on November 23, 2016, 01:26:07 PM
Did anyone ever build this board into a 500 module? I read through the thread but did not see any. That is what I want to do, with a DOA make-up amp and transformer I/O. Just wanted to see if anyone else had managed to get all that into a 500 slot.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on November 23, 2016, 05:14:10 PM
Did anyone ever build this board into a 500 module? I read through the thread but did not see any. That is what I want to do, with a DOA make-up amp and transformer I/O. Just wanted to see if anyone else had managed to get all that into a 500 slot.

The standard board is too tall to fit in a 500 series module but the 3U version is only 100mm square so it should fit in OK. I am sure someone added a JLM 500 series interface board to one to make it into a 500 series module but I cannot remember who it was.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: tommypiper on November 23, 2016, 05:26:05 PM
Ian, I believe you mentioned that both these EQs need to be loaded 100k.  I'm thinking to build them stand-alone, and plug in outboard make-up gain amps from other boxes via XLRs.  What kind of transformers would I use to allow the EQs to interface with the outside world?  And what types of amps will create the correct load?  (I have Neve type Marinair / Carnhills, if you want to explain how to wire those, as an example...  ) thanks much.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on November 24, 2016, 04:09:54 AM
Ian, I believe you mentioned that both these EQs need to be loaded 100k.  I'm thinking to build them stand-alone, and plug in outboard make-up gain amps from other boxes via XLRs.  What kind of transformers would I use to allow the EQs to interface with the outside world?  And what types of amps will create the correct load?  (I have Neve type Marinair / Carnhills, if you want to explain how to wire those, as an example...  ) thanks much.

On the input you need any good 10K:10K input transformer. Something like the Carhnhill VTB9071 would do. Its data sheet shows how to wire it up.

The output needs to be loaded as lightly as possible and anything above 100K should be OK. If you want to use an external gain make up amplifier then perhaps the safest approach is to add a DI transformer like the Carhnill VTB9072 wired  144K:250R. Again, the Carnhill data sheet shows how to wire it like this.

This will give you balanced inputs and outputs. The EQ loss is about 15dB and the DI transformer loss is about 27dB giving a total loss of 42dB to be made up by your external amplifier.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: tommypiper on November 24, 2016, 02:03:45 PM
... the DI transformer loss is about 27dB giving a total loss of 42dB to be made up by your external amplifier.

Cheers

Ian

That's a steep loss on the output transformer just to have it balanced. 

What is the input impedance into the second tube on your Classic mu follower?   (I believe it's 1M, based on the grid resistor?)  So I could insert the EQ there.

To make a world-facing Line In on that second stage, what transformer would you suggest?  Since we already have very high impedance...   Thanks!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on November 25, 2016, 02:54:25 AM
That's a steep loss on the output transformer just to have it balanced. 
It is but that's because the EQ is not designed to be used that way
Quote
What is the input impedance into the second tube on your Classic mu follower?   (I believe it's 1M, based on the grid resistor?)  So I could insert the EQ there.
Yes, that is just the sort of input to load the EQ with. The input impedance will be close to 1M
Quote
To make a world-facing Line In on that second stage, what transformer would you suggest?  Since we already have very high impedance...   Thanks!
I am not sure I understand the question - I thought you wanted to connect the output of the EQ to it.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: tommypiper on November 25, 2016, 03:35:35 AM
Right, I understand putting the EQ in its own box not ideal...

I am not sure I understand the question - I thought you wanted to connect the output of the EQ to it.

Cheers

Ian

Was still thinking if I had the EQ in its own box, without the DI transformer, will it work to connect to the Classic?  Keep in mind there would be the 10k attenuator there, so does that change the load from 1M to 10k?  And what kind of Line Input transformer do I need -- does the 10k attenuator change that? 

I would need a Line In transformer on the Classic to be able to interface other line inputs... could you please link to the Carnhill transformer?  My browser can't get past their splash page to see any products.

Another option I'm thinking... add the BA 283AM output stage on the EQ.  Do you know what the input impedance is on that output stage, by chance? 
Thanks!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on November 25, 2016, 12:32:36 PM
Right, I understand putting the EQ in its own box not ideal...

Was still thinking if I had the EQ in its own box, without the DI transformer, will it work to connect to the Classic?  However I would need a Line In transformer on the Classic to be able to interface other line inputs... could you please link to the Carnhill transformer?  I can't get past their splash page.
You could add a switch to connect the input of the second stage of the classic either to the EQ output or to a line input transformer. The EQ input would then be unbalanced high impedance (just what the EQ likes) and the line in would be 10K balanced.

You can download the Carnhill Design Guide from audiomaintenance:

http://www.audiomaintenance.com/acatalog/Input_Transformers.html (http://www.audiomaintenance.com/acatalog/Input_Transformers.html)

Quote
Another option I'm thinking... add the BA 283AM output stage on the EQ.  Do you know what the input impedance is on that output stage, by chance? 
Thanks!

No I am afraid I don't know that but it is probably not high impedance enough.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: tommypiper on November 25, 2016, 01:35:00 PM
You could add a switch to connect the input of the second stage of the classic either to the EQ output or to a line input transformer. The EQ input would then be unbalanced high impedance (just what the EQ likes) and the line in would be 10K balanced.

Excellent, that's what I was thinking.  Will the Classic 10k attenuator and HPF work with both the line input (with input transformer) and the unbalanced EQ input?  Does that change the load on the EQ from 1M to 10k?

And no problem connecting the EQ to Classic with unbalanced cable...?  Use screened cable, screen connected to one end...?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on November 25, 2016, 02:12:52 PM
Nice build!  Can you share how you are wiring the transformers?  Which carnhills are you using on the outputs?

i wont comment since it doesnt work at this point. i use a 15k:600 carnhill. in theory it makes the output look like 200ohms in order to feed it into a micpre. but it picks up crazy amounts of hum at this point. i have not found a solution so far. i just ordered a mu metal can for the output xformer. i hope it helps. otherwiese im out of luck and will most likely have to fit some internal makeup.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on November 25, 2016, 06:51:44 PM
Excellent, that's what I was thinking.  Will the Classic 10k attenuator and HPF work with both the line input (with input transformer) and the unbalanced EQ input?  Does that change the load on the EQ from 1M to 10k?

No, it will work with the input transformer because as you have guessed it changes the EQ load to 10K which is not what we want.
Quote
And no problem connecting the EQ to Classic with unbalanced cable...?  Use screened cable, screen connected to one end...?

Screened cable should be fine provided it is no too long (say 1 metre or less). Connect screen at both ends to 0V.

Cheers

ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: tommypiper on November 25, 2016, 07:31:31 PM
No, it will work with the input transformer because as you have guessed it changes the EQ load to 10K which is not what we want.

I meant, will it work without an input transformer in the Classic, but with the 10k attenuator... I believe the answer is the 10k attenuator will create a 10k load.  So, how do I control gain there without loading the EQ?  Can we use a 100k attenuator? 

Since the circuit load is 1M, would it make sense to make a 250k attenuator?  And incidentally, will the Classic HPF (in your instructions which needs a 10k load) work ok with the higher Z?

thanks!

BTW:  AML is not listing one of the Helios inductors:  VTB9042.  Is there another source?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on November 26, 2016, 05:19:06 AM
I meant, will it work without an input transformer in the Classic, but with the 10k attenuator... I believe the answer is the 10k attenuator will create a 10k load.  So, how do I control gain there without loading the EQ?  Can we use a 100k attenuator? 
100K should be OK. It is high enough not to load the EQ but low enough not to br particularly susceptible to interference.
Quote
Since the circuit load is 1M, would it make sense to make a 250k attenuator?  And incidentally, will the Classic HPF (in your instructions which needs a 10k load) work ok with the higher Z?
I think there would be no additional benefit in going to 250K. If you use 100K then you will need to use different capacitors for the HPF. Since 100K is 10 times 10K, the capacitors need to be reduced 10 times for the frequencies to remain the same.
Quote
BTW:  AML is not listing one of the Helios inductors:  VTB9042.  Is there another source?

That's very odd. I do not know of another source other than Carnhill themselves. I will ask Colin.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on November 26, 2016, 08:24:10 AM
BTW:  AML is not listing one of the Helios inductors:  VTB9042.  Is there another source?

i might have some for sale. pm me if needed
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on November 29, 2016, 03:21:02 AM

BTW:  AML is not listing one of the Helios inductors:  VTB9042.  Is there another source?

I asked Colin at AML about this. Apparently someone bought all his stock of these. He has more on order but they won't be available for four weeks.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: salomonander on November 29, 2016, 10:43:47 AM
i have 7 for sale in case someone needs them
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on July 05, 2019, 12:20:47 PM
Hey All,

Reviving this thread because I just built a REDD EQ and have a few questions. I'm planning to build it into a channel strip with an ADM-1668 card (Schematic attached). I'm curious if anyone has any recommendations as to where I should wire it in this signal path. I'm still trying to wrap my head around how and why impedances changes in circuits and I know it's important for this EQ to have a high impedance source.

The input xfo is a UTC 0-8 and is wired secondary to primary, so the input is 500 ohms and the output is 15k.

My stupid question is as follows: Does this mean that the impedance is 15k until it hits the output xfo? Or does it change with every component in the circuit? If so, should I add something to get the optimal impedance for this EQ?

I'm of course very interested in a simple answer of where I should insert the EQ in the signal path, but I'd also like to learn a little so I don't have to bug y'all in the future. :) Thanks in advance.

Cheers,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on July 05, 2019, 04:13:22 PM
Hey All,

Reviving this thread because I just built a REDD EQ and have a few questions. I'm planning to build it into a channel strip with an ADM-1668 card (Schematic attached). I'm curious if anyone has any recommendations as to where I should wire it in this signal path. I'm still trying to wrap my head around how and why impedances changes in circuits and I know it's important for this EQ to have a high impedance source.
It is important for my REDDEQ design to have a high impedance load (100K or higher if possible). It also works best with a source impedance of around 2500 ohms but it will work with any source impedance lower than this.
Quote
The input xfo is a UTC 0-8 and is wired secondary to primary, so the input is 500 ohms and the output is 15k.
I am not sure why you are using this at the input. The O-8 is an output transformer.
Quote
My stupid question is as follows: Does this mean that the impedance is 15k until it hits the output xfo? Or does it change with every component in the circuit? If so, should I add something to get the optimal impedance for this EQ?

I'm of course very interested in a simple answer of where I should insert the EQ in the signal path, but I'd also like to learn a little so I don't have to bug y'all in the future. :) Thanks in advance.

Cheers,
Erik

My REDDEQ looks like a load of between 5K and 10K depending on the setting of the controls and the frequency. The input transformer will reflect this impedance to the primary and hence the input. My REDDEQ is designed to be fed via a 10K:10K transformer so its input impedance is reflected more or less intact to the primary. Any professional audio source will then drive this input. So in this instance the input transformer really should be changed to a 10K:10K type. The EQ itself should be placed between the output of the transformer and the input of the op amp.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on July 05, 2019, 05:43:37 PM
Thanks so much for the info!

It is important for my REDDEQ design to have a high impedance load (100K or higher if possible). It also works best with a source impedance of around 2500 ohms but it will work with any source impedance lower than this.
So it will work with anything, but works best 25k. What does "best" mean in this case? The curves will be closer to the original?

I am not sure why you are using this at the input. The O-8 is an output transformer.

Thats the way the card came. I attached the promotional material for the product.

My REDDEQ looks like a load of between 5K and 10K depending on the setting of the controls and the frequency. The input transformer will reflect this impedance to the primary and hence the input. My REDDEQ is designed to be fed via a 10K:10K transformer so its input impedance is reflected more or less intact to the primary. Any professional audio source will then drive this input. So in this instance the input transformer really should be changed to a 10K:10K type. The EQ itself should be placed between the output of the transformer and the input of the op amp.

I inserted it between the xfo pin 7 and R9 and it seems to be working well except the brilliance setting doesn't appear to be doing anything. I'm going to double check all my work, but I'm curious if this could have something to do with not having the ideal 25k source.

Regarding the 10K:10K: xfo, would you recommend that I add one to this circuit on the input of the REDDEQ?


Cheers,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on July 06, 2019, 11:31:45 AM
Thanks so much for the info!
So it will work with anything, but works best 25k. What does "best" mean in this case? The curves will be closer to the original?
It will work with any source impedance from zero to 2500 ohms. At 2500 ohms the curves will be closest to the original. The reason for this is the EQ is designed to be used in a mixer directly after a 10K fader. The source impedance of such a fader typically varies from zero to 2500 ohms. In a stand alone EQ, where the source impedance is likely to be close to zero, there is provision on the PCB to add a series resistor to raise this to 2500 ohms. This is covered in the documentation for the EQ.
Quote
Thats the way the card came. I attached the promotional material for the product.
Unfortunately the promotional info makes no mention of the transformers. It seems odd that the input transformer  position should be fitted with an output type, particularly as that type is also intended for use in tube output stages.
Quote
I inserted it between the xfo pin 7 and R9 and it seems to be working well except the brilliance setting doesn't appear to be doing anything. I'm going to double check all my work, but I'm curious if this could have something to do with not having the ideal 25k source.
That looks OK to me. Any wrong impedances are likely to affect all bands in much the same way. However,
Quote
Regarding the 10K:10K: xfo, would you recommend that I add one to this circuit on the input of the REDDEQ?

Cheers,
Erik
I do. I think you should replace the existing input transformer with a 10K:10K type.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Winston O'Boogie on August 12, 2019, 06:10:57 AM
I was recently asked if I could design an EQ that worked like the 'pop' and 'classic' EQ plug ins that used to be used in the REDD47 consoles and predecessors. Using the curves published in 'Recording The Beatles' I came up with a circuit based on a stripped down and modified Helios 69 EQ with a switch to selec 'pop' or 'classic'. I was then asked if I could not make it so both the the 'pop' and 'classic EQ curves were available at the same time. In doing this, a very strange thought occurred to me. The Helios treble EQ is virtually identical to the EMI 'classic' EQ curves (the frequency, step size and gain range are identical) as is the bass cut except for the frequency it works at. The bass boost is very nearly the same but tweaked from a shelf to a bell curve. The clincher is that the 'pop' 4.7KHz peaking EQ is a stepped version of one of the Helios 69 mid boost frequencies.

I then realised that Dick Swettenham, who designed the Helios 69 EQ, had previously worked at Abbey Road studios in the service and design departments so he must surely have had a deep understanding of the innards of the REDD EQ.

I am sure you can now see where I am going with this. Is the Helios 69 EQ simply a modified and expanded version of the REDD EQ?

I simulated a cut down version of the Helios 69 EQ (pic attached)  and it is surprisingly easy to get curves very close to those of the REDD EQ.

What do you think/know??

Cheers

Ian

Hey Ian,
I only just saw this.  Well done.  I did similar a few years back after plugging the original REDD eq schematics into spice and tweaking things to match using a similar topology to yours.
The original is a very well designed circuit but it isn't really practicable or necessary to use the original topology of two 400 ohm constant impedance stacked circuits for a  200 ohm with 10dB total loss -  rather than the usual (at the time) 10dB loss per band (+20dB total). 
For the 'Pop' presence and the brilliance controls, using a Pultec/Helios type circuit, I found it necessary to adjust the Q slightly for each step to match the original topology but I doubt it made much difference to what was heard/ perceived.

Regarding Dick Swettenham and EMI, I'm not sure there is any connection with the circuits.  The approach is very different, even if similar results can be obtained by manipulating things.  The REDD eqs were based on an earlier EMI desk eq that had  2OdB insertion loss which, in turn, was pretty much based on original research by Alan Blumlein and others.   
The Helios EQ was simply a lesser expensive to build passive LCR EQ when constant impedance wasn't needed.  It was quite commonly used before everyone adopted Peter Baxendall's feedback type EQ.   The Sound Techniques original A Range desks at Trident et al.  used a similar EQ to the Helios before switching to Baxendall type for the System 12 etc. 

That's all I can think of at the moment.
Cheers.


Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 12, 2019, 01:15:57 PM
That looks OK to me. Any wrong impedances are likely to affect all bands in much the same way.

I'm still having issues with the Brilliance band. High and Low bands are working great, but the brilliance has an extremely wide Q on all frequencies. They're so wide they pretty much just turn up/down the entire signal. I've double-checked all cap and resister values, beeped out each signal path to ensure I'm getting signal everywhere it's supposed to be and everything looks normal. I haven't tried the 10k:10k transformer yet, but everything else seems to be working great so I'm not sure that's the issue. I'm wondering if the inductor could potentially be bad...? Is there is simple way to test this and is it possible to do without pulling it out of the circuit?

I'm using the wire link instead of a 2k4 resistor for R35 because my transformer coming into it is high impedance. I believe that I'm thinking about this correctly. The manual mentions If a low impedance source is used and R35 is a wire link, then the Q of the brilliance curves will be sharper and the maximum boost and cut will be increased.. I have very wide Q's, so I'm not exactly sure how to proceed here.

Thanks again for all the help!
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 12, 2019, 05:09:20 PM
I'm still having issues with the Brilliance band. High and Low bands are working great, but the brilliance has an extremely wide Q on all frequencies. They're so wide they pretty much just turn up/down the entire signal. I've double-checked all cap and resister values, beeped out each signal path to ensure I'm getting signal everywhere it's supposed to be and everything looks normal. I haven't tried the 10k:10k transformer yet, but everything else seems to be working great so I'm not sure that's the issue. I'm wondering if the inductor could potentially be bad...? Is there is simple way to test this and is it possible to do without pulling it out of the circuit?

I'm using the wire link instead of a 2k4 resistor for R35 because my transformer coming into it is high impedance. I believe that I'm thinking about this correctly. The manual mentions If a low impedance source is used and R35 is a wire link, then the Q of the brilliance curves will be sharper and the maximum boost and cut will be increased.. I have very wide Q's, so I'm not exactly sure how to proceed here.

Thanks again for all the help!

The Brilliance band does have a wide Q. The Q is approximately one. So on the 2K7 band for instance the -3dB points will be about 1K3 and 4K respectively. Attached is the plots for the 2K7 band as obtained from the official EMI plug in which is what I attempted to emulate in hardware.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Winston O'Boogie on August 14, 2019, 10:45:46 AM
The Brilliance band does have a wide Q. The Q is approximately one. So on the 2K7 band for instance the -3dB points will be about 1K3 and 4K respectively. Attached is the plots for the 2K7 band as obtained from the official EMI plug in which is what I attempted to emulate in hardware.

Cheers
Ian

And those curves look pretty much "spot on" 😊

DCR of EWalter's  inductor could be widening  Q maybe?

Side note: in the early iterations of the EMI 'pop" EQ, the dcr of the low end inductor had been neglected in the design,   There was a production modification note added later which advised changing the lower end values of the bridge-T resistive networks to correct for it.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 14, 2019, 04:12:40 PM
Ok - I'm making some serious headway. I don't have any great analysis tools, so I've been struggling a bit up until now. I've been using pink noise and a spectrum analyzer which has been difficult to tell exactly what is going on, but today I used Plugin Doctor's linear analysis and got some very informative readings!

The Brilliance band does have a wide Q. The Q is approximately one. So on the 2K7 band for instance the -3dB points will be about 1K3 and 4K respectively. Attached is the plots for the 2K7 band as obtained from the official EMI plug in which is what I attempted to emulate in hardware.


So at this point everything is looking pretty spot on and inline with all of the plots included with the instructions, however the 2k7 band is still being problematic. It has an extremely wide boost and a very narrow cut  :'(

Everything else is looking fantastic - this is my last hurdle.

Below is a link to the screenshots of the measurements I got for the 2k7 cut/boost. I couldn't overlay them into one image, so I had to include a separate shot of each switch position:
https://imgur.com/a/mIAZVnk (https://imgur.com/a/mIAZVnk)

Thanks again for all the help!


DCR of EWalter's  inductor could be widening  Q maybe?

This is a little over my head, but lemme know if the screenshots might set off any light bulbs. If there is something I should test on the inductor, I'm game!

Cheers,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Winston O'Boogie on August 14, 2019, 06:10:19 PM

This is a little over my head, but lemme know if the screenshots might set off any light bulbs. If there is something I should test on the inductor, I'm game!

Cheers,
Erik

The birth father of this project - Ian - would be a better person than I am to answer specifics regarding q etc & I'm sure he'll be along soon. 
I don't have his latest/last revision schematic on hand but, looking at the boost plots you made @2K7, is it possible there's a short on the last winding of your inductor? 
I'm not exactly sure why the cut would be off in Q, it's using a different inductor than boost and is located as a shunt reactance.   But it could be widened by inserting some resistance in series with that particular tap of the inductor.  Maybe wait for Ian before changing anything there though. 
Check the boost inductor tap for problems there in the meantime.
Persevere, you're almost there!  😊
Whereabouts can I find Ian's up to date schematic?


Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 14, 2019, 06:32:57 PM
Several points:

1. You should use white noise rather than pink to look at EQ spectra.
2. The brilliance boost and cut Q should be virtually identical. The circuit uses separate LC circuit for boost and cut in order to do this
3. The Q of the circuit depends on the characteristic impedance which is made up of various circuit resistances and the dcr of the inductor.  The recommended inductors are chosen such that the contribution of the inductor dcr to Q is largely swamped by that of the other circuit resistances. The fact you are getting a sharper Q for cut compared to boost indicates one of them is wrong somewhere. I don't know if you are using one of my PCBs but it you are you should makes sure the resistor ladder values are correct and the frequency band select switch is wired correctly.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Winston O'Boogie on August 14, 2019, 07:48:45 PM
The recommended inductors are chosen such that the contribution of the inductor dcr to Q is largely swamped by that of the other circuit resistances. The fact you are getting a sharper Q for cut compared to boost indicates one of them is wrong somewhere.

I always assumed your design was 100% spot on Ian and you'd accounted for everything.  Hope it didn't sound like I thought otherwise.
I figured it was an issue with a wrong resistor value, and short or wiring issue on the boost inductor etc. 

Good luck EWalter 👍
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 15, 2019, 04:42:32 AM
I always assumed your design was 100% spot on Ian and you'd accounted for everything.  Hope it didn't sound like I thought otherwise.
No, you didn't sound like that. Back in the day, inductor dcr might well have been an issue because they did not have or use the high AL materials available today so basically you are right. Even today, dcr is important for the bass inductor (7 Henries) and you need to compensate for it in the design. Mid section you can more or less ignore it.
Quote
I figured it was an issue with a wrong resistor value, and short or wiring issue on the boost inductor etc. 

Good luck EWalter 👍
I agree, that is the most likely reason.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Winston O'Boogie on August 15, 2019, 01:51:32 PM
...dcr is important for the bass inductor (7 Henries) and you need to compensate for it in the design. Mid section you can more or less ignore it.
OK got it.  I plan on using your scheme in a squalid-state pre I'm working on for my son, full credit will be given to the designer of course 🌝
I may incorporate active mids from Neve 1081 type, not sure yet, but I always thought that the high end lift on the Helios, Sound Techniques etc.  was sweeter sounding than a Baxendall high shelf.  Some of my fav.  sounding records recorded on Sound Techniques at Trident etc.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 15, 2019, 04:22:30 PM
OK got it.  I plan on using your scheme in a squalid-state pre I'm working on for my son, full credit will be given to the designer of course 🌝
I may incorporate active mids from Neve 1081 type, not sure yet, but I always thought that the high end lift on the Helios, Sound Techniques etc.  was sweeter sounding than a Baxendall high shelf.  Some of my fav.  sounding records recorded on Sound Techniques at Trident etc.

Of all the EQs I have designed I like the REDD the best. To my ears it is certainly the most musical. Despite the very broad mid boost it is remarkable how it can bring out individual instruments in a mix. Second place of course goes to the Helios.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Winston O'Boogie on August 15, 2019, 05:13:17 PM
Of all the EQs I have designed I like the REDD the best. To my ears it is certainly the most musical. Despite the very broad mid boost it is remarkable how it can bring out individual instruments in a mix. Second place of course goes to the Helios.

Cheers

Ian

Oh without doubt, that mid boost is great!  My comments were more about the high end shelf of Helios or EMI 'Classic' as incorporated in yours being a really sweet sounding one compared to a typical Baxendall of a decade later which would be imparted with the sonic attributes of the amps the tone control enclosed which, sometimes, weren't the best at being linear upat the top end to be honest.
But having the mid of the 'Pop' too is fantastic.  To look at the curves of the original EMI which were plotted for each implementation of boost and cut and the responses available as they reacted with each in boost and/or cut, you realise that a lot was possible with just two bands available on the desk.
I don't think the 'Classic' cassettes were ever employed in the Studio 2 REDD.51 desk and, possibly, neither were they in the Studio 3 one.
Classical was a Studio one thing with its REDD.37, and also the REDD.37 in Kingsway Hall which was used by both EMI and Decca.

Anyway, 👍
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Winston O'Boogie on August 15, 2019, 05:28:05 PM
P.S.  To follow up on my thoughts re.  Dick Swettenham and the EMI EQ connection postulate, it seems he left Abbey Road just before they took delivery of the REDD.37 desks which incorporated the Pop and Classic EQ.  If there were any REDD desks there before he left, it would have been the REDD.17 with a similar, but not identical classic type tone control.
I think he took the Pultec basic scheme and scaled it up in impedance, adding bits of his own based on what he'd found out were useful while being a maintenance engineer.   We will never know for sure though so... 
Cheers.
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 16, 2019, 03:50:35 AM
P.S.  To follow up on my thoughts re.  Dick Swettenham and the EMI EQ connection postulate, it seems he left Abbey Road just before they took delivery of the REDD.37 desks which incorporated the Pop and Classic EQ.  If there were any REDD desks there before he left, it would have been the REDD.17 with a similar, but not identical classic type tone control.
I think he took the Pultec basic scheme and scaled it up in impedance, adding bits of his own based on what he'd found out were useful while being a maintenance engineer.   We will never know for sure though so... 
Cheers.

Ah,  hoisted by the timeline petard. If he left before the 37s arrived he would have known much less. I am not sure about Pultec with scaled up impedance. I did that with my poor man's EQP1A project. The topology is somewhat different to the Helios but an interesting thought nonetheless. After all, they all consist of a pot divider with frequency selective components on each arm.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 16, 2019, 11:58:48 AM
I don't have his latest/last revision schematic on hand but, looking at the boost plots you made @2K7, is it possible there's a short on the last winding of your inductor? 
I'm not exactly sure why the cut would be off in Q, it's using a different inductor than boost and is located as a shunt reactance.   But it could be widened by inserting some resistance in series with that particular tap of the inductor.  Maybe wait for Ian before changing anything there though. 
Check the boost inductor tap for problems there in the meantime.
Persevere, you're almost there! 
Whereabouts can I find Ian's up to date schematic?

Here is all the info on the build: https://drive.google.com/drive/folders/0B_n67A1hN3qtfjNQX0Z3Y1V3UTFYelRJZWp6UXQ5dmhWcXVXOFZ3Z0VtOWotemNjbHo3dnM (https://drive.google.com/drive/folders/0B_n67A1hN3qtfjNQX0Z3Y1V3UTFYelRJZWp6UXQ5dmhWcXVXOFZ3Z0VtOWotemNjbHo3dnM)

I checked all of the inductors in the cut path and they all check out just fine. L9 is the only one that is unique to the 2k7 circuit and it measured at 10.44mH. The rest of the inductors checked out, and are all used on other bands that don't have this same problem.


I figured it was an issue with a wrong resistor value, and short or wiring issue on the boost inductor etc. 



I agree, that is the most likely reason.


I checked all resistors and there were a couple that were slightly off do to my having different values. R12 is 390 and I had put in a 419 & R17 is 5k6 and I had put in 6k2. I've since replaced these with the correct values but I'm it didn't solve anything. I believe these are being used in the cut circuit of all frequencies, so I'm not sure this was the issue seeing as though all other bands are working well.

I also double-checked the caps on the 2k7 band cut and they're all correct values. I even pulled them out and tested them to be sure and they checked out.

I also beeped through the entire signal path on the 2k7 switch and didn't find any issues.

I'm hitting some walls here, but I want to say that this EQ sounds amazing! I'd be more than happy with it as-is at this point, I just want to see if I can get this last bit sorted out. I'm really happy with the way this little channel strip project has turned out so far and will post some pics once I get it wrapped.

Cheers,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 16, 2019, 12:13:56 PM
HI Erik, just to be clear, the only part you now have a problem with is the 2K7 Hz cut - is that right? And you are using my PCBs?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 16, 2019, 12:19:19 PM
Hey Ian,

That's correct! And yes, I'm using your PCB.

Thanks,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 16, 2019, 06:15:26 PM
Hey Ian,

That's correct! And yes, I'm using your PCB.

Thanks,
Erik

OK, does the 2K7 cut work at all?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 17, 2019, 08:33:05 AM
OK, does the 2K7 cut work at all?

Cheers

Ian

Hey Ian,

It does work, it’s just extremely narrow while the boost is extremely wide.

Thanks,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 17, 2019, 05:28:50 PM
Hey Ian,

It does work, it’s just extremely narrow while the boost is extremely wide.

Thanks,
Erik

Is this true of all cut frequencies or just the 2K7?

Cheers

ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 19, 2019, 11:24:57 AM
Is this true of all cut frequencies or just the 2K7?

Cheers

ian

It is only the 2k7 that has this problem. All others are fine.

Thanks,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 21, 2019, 03:55:30 AM
OK, this is puzzling. If you look at the schematic, the only thing the 2K7 cut position changes is adding 10mH of inductance in series with other inductors and it changes the capacitance to 78nF. I can see no simple fault that would explain making the 2K7 cut very sharp. The only thing I can think of that might do that is if that switch position somehow had a low impedance path to 0V. Perhaps a solder bridge near the two caps making up the 78nF?

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 22, 2019, 04:38:22 PM
OK, this is puzzling. If you look at the schematic, the only thing the 2K7 cut position changes is adding 10mH of inductance in series with other inductors and it changes the capacitance to 78nF. I can see no simple fault that would explain making the 2K7 cut very sharp. The only thing I can think of that might do that is if that switch position somehow had a low impedance path to 0V. Perhaps a solder bridge near the two caps making up the 78nF?

I just measured the capacitance across these caps and got 77nF. The inductor that’s unique to the 2k7 cut is reading 10mH. 

Regarding the switch position having a low z path to 0V, I’m not sure how I’d check this, but am happy to do so.

I guess my question would be; could it have something to do with the fact that the boost seems extra wide? Once again, I’m not finding any issues with any values of any of the components in the cut or boost paths, just trying to spitball some ideas.

One good thing is that I don’t really see myself using that band much, so if this is the way it is, I wouldn’t be very upset. I can always look at the bright side of having a surgical cut band in an often harsh frequency range! Additionally I don’t mean to take up all of your time with tedious troubleshooting.

Cheers,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 22, 2019, 05:07:50 PM
Hi Erik,


The boost frequency selectively shorts out the top of the pot divider and the cut shorts out the bottom of it. So if one of them has a fault it could possibly affect the other. One test you could do it to remove the 10mH cut inductor that the 2K7 band adds in. You should then get a flat response.

Also try this test. With the cut/boost control a zero, check the insertion loss of the EQ for each of the three mid frequencies. If the one part 2K7 band is messing with something you should see it here.

Can you post a pic of the PCB showing the wiring to the mid frequency select switch?

Cheers

ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 23, 2019, 05:05:18 PM
Can you post a pic of the PCB showing the wiring to the mid frequency select switch?
ian


Hey Ian,

I just figured it out! Mine didn't come with the Lorlin header PCB (not sure if it was supposed to come with or if it's an add on), so I just used a different switch and wired it point-to-point. I found that I had reversed the boost and cut on the 2k7 :FACEPALM: even after tracing these down half a dozen times or so... My sincere apologies for the goose chase and thank you very much for all of your help. This EQ is fantastic - I'm thinking about getting 2 more to build a stereo box for my 2 bus!

I've included some images of the final build below (just realized that I don't really have any good ones of the top side of the REDD though!). This is basically my first build, so it's not as pristine as I'd like it to be, but I think it turned out alright. I'm also planning to add more to this box since there's a lot of room, but haven't decided on what it will be yet. I'll definitely include a selectable HPF and potentially some kind of compressor kit or something. There are also some cosmetic things that bum me out a bit - most notably the knobs on the REDD pots are slightly crooked due to the flat end on the Greyhill switches being off center.

Details:
ADM 1668 Mic/Line card
 - API/Melcor type op amp
 - UTC 0-8 input xfo
 - ADM custom output XFO

REDD EQ
 - 3 pos switch for Brilliance freq (I didn't use all 4 frequencies cause this was the switch I had)
 - Blue LED indicator light for EQ bypass (I'm a geek and this is really exciting to me)

Five Fish PSU2448 Power Supply

Functions:
Mic/Line
+48V
Polarity Reverse
Output pad

(https://i.imgur.com/gjYH6S2.jpg?3)
(https://i.imgur.com/zfksJmP.jpg?1)
(https://i.imgur.com/vGcIfSC.jpg?1)

Thanks again for all the help! Now on to the next project!

Cheers,
Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on August 23, 2019, 05:57:36 PM
Hey Erik, result man! It is so gratifying when you finally get it to work.

There may have been a Lorlin adaptor PCB in the distant past but most people just hard wire the Lorlin so I have not made any for years and I have no stock.

Enjoy

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 23, 2019, 09:26:52 PM
There may have been a Lorlin adaptor PCB in the distant past but most people just hard wire the Lorlin so I have not made any for years and I have no stock.

Ah! I figured as much and just went for it with a switch I had laying around.

Thanks!

-Erik
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Winston O'Boogie on August 24, 2019, 09:27:12 PM
Hey, glad you got it sorted Erik, nice one.
Easy mistake to make.  I haven't turned on a piece of gear I made yet that failed to amaze me when audio comes out the other end.
Down some wires. 
Cool 👍
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: EWalter on August 26, 2019, 04:01:26 PM
Hey, glad you got it sorted Erik, nice one.
Easy mistake to make.  I haven't turned on a piece of gear I made yet that failed to amaze me when audio comes out the other end.
Down some wires. 
Cool 👍

It really does sound so much better when you make it yourself!  ;)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: Sorr on September 20, 2019, 11:02:05 PM
Ian,
You wrote in post 285, "Hooking up the Helios EQ PCB is quite simple. Your input goes (via a 10K:10K transformer) to the pad labelled IN "
I thought it required a low I/P driving Z, such as 600 ohms?
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on September 21, 2019, 03:16:57 AM
Ian,
You wrote in post 285, "Hooking up the Helios EQ PCB is quite simple. Your input goes (via a 10K:10K transformer) to the pad labelled IN "
I thought it required a low I/P driving Z, such as 600 ohms?

Transformers do what it says on the tin - they transform. The input impedance of the EQ is about 10K so I recommend a 10K:10K transformer to successfully reflect this input impedance to its primary. It looks like a regular line input to the outside world. The EQ is designed to work from a source impedance of no more than 2500 ohms. This is so it can be used directly after a 10K fader in a mixer. If you drive it from a low impedance source you can add a series resistor (there's a place on the PCB for this) to raise the soirce impedance to 2500 ohms. You don't have to do this though - if you drive from a low impedance source without the extra resistor, all that happens is the maximum boost and cut is increased by about a dB.

Bottom line is for a bakanced input you need a 10K:10K transformer but you can drive it from a low impedance source.

Cheers

Ian
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: letterbeacon on June 03, 2020, 04:27:13 AM
I'm looking forward to  building a couple of your Helios EQs - thanks again for making them open source.

I think you've answered this above, but just to confirm - I have some 600:600 input transformers lying about. I know the circuit is designed with a 10k:10k in mind, but if I read your above post correctly, I can use a 600:600 but the maximum boost and cut is increased by a dB. Is that correct?

My other question is that I would like to use the 2128 amp circuit for make-up gain that was used in the original desks for the same purpose. Would the 2128 amp work with your circuit?

Here's a link to a doc with the 2128 in: https://groupdiy.com/index.php?topic=58393.msg948059#msg948059 (https://groupdiy.com/index.php?topic=58393.msg948059#msg948059)
Title: Re: REDD EQ, Helios 69 and Dick Swettenham
Post by: ruffrecords on June 03, 2020, 06:12:00 AM
I'm looking forward to  building a couple of your Helios EQs - thanks again for making them open source.

I think you've answered this above, but just to confirm - I have some 600:600 input transformers lying about. I know the circuit is designed with a 10k:10k in mind, but if I read your above post correctly, I can use a 600:600 but the maximum boost and cut is increased by a dB. Is that correct?

My other question is that I would like to use the 2128 amp circuit for make-up gain that was used in the original desks for the same purpose. Would the 2128 amp work with your circuit?

Here's a link to a doc with the 2128 in: https://groupdiy.com/index.php?topic=58393.msg948059#msg948059 (https://groupdiy.com/index.php?topic=58393.msg948059#msg948059)

Yes, a 600:600 input transformer will be fine. Its lower source impedance may give you an extra dB of boost. Cut should be relatively unaffected.

The 2128 amp is perfect for gain make up.

Cheers

Ian