SSL "Talkback" Listen Compressor

[geetar_king]

Hopefully, this is the way it turned out. Otherwise, follow these clarified instructions.

Thanks jd, yes I followed your instructions and I understand the biasing. It worked well. Everything to do with the talkback board is okay for now, except the input stage being less than 20dB by a bit, i think it was 15.1dB....  

Matching up to the blend is the next part i'm working on. Matching the clean signal up to the blend board is working no prob, but i'm having problems with the input with makeup gain for the 'wet' compressed signal. I tried to use the pot setup suggested by SSLtech in a previous post, but couldn't get it to work, so I put the pot on the feedback arm of the opamp and changed some resistor values to make it work.

Still have to tweak the blend board. It seems that after the input on the blend, the signal comes out weak at the output. Might have to play with the 10K and 39K resistors around the blend pot or maybe the last 5532 on the chain needs tweaking. Seems like ratio of the input to output on the blend board is very low. I'm trying to set it all up for unity gain.

 

[geetar_king]

Changing the 39K resistors before the output SSMs fixes the drop through the blend board. I changed these to 10R resistors.

In attempts to understand why the input gain on the talkback board was only about 15dB gain I made a few simulations and played around.  It seems that the 470nF capacitor on the inverting input of the opamp lowers the ratio...  I double checked the original talkback board to see if the 470nF cap is in series or parallel with R22, the resistor on the inverting input.  Yes, its in series.  Does anyone know why they would have put this cap in there? What does it do to the signal besides changing the gain?

I simulated the input opamp with the 470nF in series like the schematic and original board, as well as in parallel with the resistor on the inverting input.

(sorry for the large photo, may have to scroll over to view it...)

Results:
Series -> gain is 15.4dB
Parallel -> gain is 19.8dB


Since I want 20dB gain, is it okay to put the 470nF in parallel??  Will this change the sound of the input or frequency response or something...?

If anyone can suggest what else to change to get 20dB out of that input please let me know.  If I had a different potentiometer for the input then that would be easy... but I'm trying to work with the 10K pot that I have...

 

[geetar_king]

Apparently the 470nF cap is a filter for high frequency noise. So as long as there are no noise issues, it sounds like it should be safe to leave it out.  Many op-amp designs don't have a cap there anyways.

 

[geetar_king]

Okay... done the dual mono talkback with the blend option! 

It has selectable input between line or mic input and phantom power is available when in mic mode.  I used 1:4 Sowter 3811f transformers on the input. Power is off of the 9K PSU board. Front panel is by FPE, racked in a par-metal case.

I had to make a few tweaks to the previously posted schematics, and so i will upload the new schematics once I make the revisions.

It sounds great! No hum issues at all. In the future, I'd like to build another one with controls to vary the time constant.  The release on this baby is huge!  I'd also like to mesh the blend and talkback boards into one to make this easier to wire up.  Maybe have the talk-n-blend board with a control board or something.

I'd like to thank Livingnote and everyone in the thread here for helping out and for staying interested along the way.  The original SSL talkback card has been passed along to peterc, so don't bug me for the card!

-gK

 

[danjpiscina]

Okay... done the dual mono talkback with the blend option!  

It has selectable input between line or mic input and phantom power is available when in mic mode.   I used 1:4 Sowter 3811f transformers on the input. Power is off of the 9K PSU board. Front panel is by FPE, racked in a par-metal case.

I had to make a few tweaks to the previously posted schematics, and so i will upload the new schematics once I make the revisions.

It sounds great! No hum issues at all. In the future, I'd like to build another one with controls to vary the time constant.  The release on this baby is huge!  I'd also like to mesh the blend and talkback boards into one to make this easier to wire up.  Maybe have the talk-n-blend board with a control board or something.

I'd like to thank Livingnote and everyone in the thread here for helping out and for staying interested along the way.  The original SSL talkback card has been passed along to peterc, so don't bug me for the card!

-gK

awesome! are you selling any boards?

 

[Whoops]

Amazing work,
this is a really interesting project and thanks a lot GK for your interest in making this possible.

Your ideas were also quite good, and I'm happy to see the first built unit.
everything looks really neat

How did you make the PCB's? are you thinking in offering them??

 

[geetar_king]

awesome! are you selling any boards?

No, not yet anyways.

I'll combine the blend and the talkback board into one talk-n-blend board, and then I'll see how much interest there is. The board layouts I put together were dual layer. I had these fab'd pretty cheap. Dual layer let me condense the board size by about half.

If anyone wants the layouts they are welcome to have them, but to reduce the wiring between boards it would be pretty easy to combine the boards into one layout.

There's a bunch of possibilities with this board. You could add in a high pass filter board. I'll look into adding a switchable time constant too.

 

[fucanay]

Wow, this looks really cool. I'd love to build one once you have a finalized board.

So, you have it setup as Mic/Line. Does that mean it has actual mic pres in there? Maybe similar to the 9k pres?

Anyway, I like original and quirky stuff more than clones of old studio standard gear. Even if I use them less.

Matt

 

[geetar_king]

So, you have it setup as Mic/Line. Does that mean it has actual mic pres in there? Maybe similar to the 9k pres?

Thanks Matt.  Yep the original talkback card had a simple gain stage using a 5534. I left this gain stage accessible in line input mode as well. In line mode, a few relays just reverse the 1:4 input traffo and it seems to work well for line levels.  It'll probably get more use in 'line' but it was easy enough to add a few relays to the board to have the original mic option too.

 

[Whoops]

Can't wait for the new board layout,
it would be great if there was enough people interested in the boards.

 

[rvlt]

Superb work!!

I would definitely be interested in one board, or two..

btw, do you think you could post some audio examples?

 

[Matthew Jacobs]

Awesome work! a true beauty...

I've been silently following this thread, and just wanted to say that I would definitely be interested is a couple of boards. I'm sure there would be many more.

J

 

[geetar_king]

Thanks guys.

I'll try to post a few clips. Maybe put it on some drums and something else

 

[idylldon]

Thanks guys.

I'll try to post a few clips. Maybe put it on some drums and something else

Excellent build!  Congrats on bringing this one to the finish line. 

Cheers,
--
Don

 

[Whoops]

Thanks guys.

I'll try to post a few clips. Maybe put it on some drums and something else

Definitely,
I would be great to listen to some sound clips of drums  being smashed but this compressor.

 

[geetar_king]

New Talk-N-Blend schematic is attached.

Let me know if there are any glaring errors before I make a layout.

The compressor and blend will be molded into one mono board, then you can just add more boards for more channels. I'm not making a PSU board but the SSL 9K PSU board works for at least 2 channels, that's what I used. You'll need at least +18V and -18V and 48V for phantom power if you want it.

I have changed some resistor values in the schematic to the values I have used in my build. The signal chain should be the same though.

I also added a header to connect a power switch. This way you can run power to your board from the power supply, then hook up a 3PDT switch. Or you can just run power to the switch then to the board, which is what I did in my build. This should be a little cleaner though.  There is a 3u3 cap on the 48V rail that is on the original card. I will be including this on the board. You can leave it out if your 48V supply is okay but it wouldn't hurt to have it. (unless you aren't going to use the mic setup, then you dont even need 48V.)


On my build, i'm still getting 3dB increase at 50% mix. I don't know how to remedy this, but please suggest if you know. It's annoying. I think maybe adding resistors on the legs going to 1 and 3 on the 10K blend pot? I know pan law says you'll get 3dB with uncorrelated signals but I believe there was a way...

 

[livingnote]

Yeeeeahhh there we go Lord I love it when stuff gets working )))

 

[Whoops]

New Talk-N-Blend schematic is attached.

Let me know if there are any glaring errors before I make a layout.

The compressor and blend will be molded into one mono board, then you can just add more boards for more channels. I'm not making a PSU board but the SSL 9K PSU board works for at least 2 channels, that's what I used. You'll need at least +18V and -18V and 48V for phantom power if you want it.

I have changed some resistor values in the schematic to the values I have used in my build. The signal chain should be the same though.

I also added a header to connect a power switch. This way you can run power to your board from the power supply, then hook up a 3PDT switch. Or you can just run power to the switch then to the board, which is what I did in my build. This should be a little cleaner though.  There is a 3u3 cap on the 48V rail that is on the original card. I will be including this on the board. You can leave it out if your 48V supply is okay but it wouldn't hurt to have it. (unless you aren't going to use the mic setup, then you dont even need 48V.)


On my build, i'm still getting 3dB increase at 50% mix. I don't know how to remedy this, but please suggest if you know. It's annoying. I think maybe adding resistors on the legs going to 1 and 3 on the 10K blend pot? I know pan law says you'll get 3dB with uncorrelated signals but I believe there was a way...

You are doing an amazing work,
congratulations.

I feel bad that I don't have enough knowledge to help.

maybe someone can give some input.

Are you around Keith?
people always seem to need some valuable help from SSLTech

 

[Whoops]

Hi Geetar_king,
how is it going?

Did you have any time to combine the blend and the talkback into one board?

it would be great to hear some sound samples of a drum kit going thorugh it, if you have the time to do so.

Thanks

 

[shuchoco]

i'd definitely buy a couple of these boards!