REDD EQ, Helios 69 and Dick Swettenham

[Rocinante]

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  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?

 

[ruffrecords]

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  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

 

[Rocinante]

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. 

 

[ruffrecords]

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

Cheers

Ian

 

[Rocinante]

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

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
and eliminating the switch (as well as the A and B section) of the PMTGMUsm here:
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


 

 

[ruffrecords]

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

 

[Rocinante]

Thanks Ian, yes that helped a ton and is quite simple.
Cheers
Dylan

 

[Rocinante]

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

 

[ruffrecords]

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

 

[Rocinante]

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

 

[ruffrecords]

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

 

[Rocinante]

Voila!  Here is a nice gut shot for you.  I'll take some more glamor pics later.

  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.

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

 

[ruffrecords]

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

 

[thomasdf]

Hey Ian
Do you still have a PCB for this one?
Thomas

 

[ruffrecords]

Hey Ian
Do you still have a PCB for this one?
Thomas

Yes I do. four in stock right now.

Cheers

Ian

 

[jona]

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

 

[ruffrecords]

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

 

[jona]

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.

 

[ruffrecords]

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

 

[Jeremy.Starseed]

Any boards available?

Interested in 4