REDD EQ, Helios 69 and Dick Swettenham

[ruffrecords]

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

 

[letterbeacon]

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.

 

[ruffrecords]

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

 

[Strawtles]

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)

 

[ruffrecords]

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

 

[Fablab]

A circuit where all the controls are off the pcb may be the right solution for all

 

[Strawtles]

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?

 

[ruffrecords]

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

 

[ruffrecords]

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

Cheers

Ian

 

[Strawtles]

Considering this circuit do you think it's possible to keep the controls on a pcb compatible with API dimensions?

 

[ruffrecords]

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

 

[Marc Duchesne]

Though about a 500 (51X) board dimension Ian...

 

[ruffrecords]

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

 

[ruffrecords]

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

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

 

[bernbrue]

http://www.gearslutz.com/board/music-computers/216773-abbey-road-brilliance-pack-4.html

A guy over at gearslutz did some measurements.
regards
Bernd

 

[TimS]

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.

 

[ruffrecords]

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

 

[ruffrecords]

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

 

[Fablab]

8)

 

[Strawtles]

Hi Ian, any news about this fantastic project?