Talkback Comp Build Thread

[Joe Malone]

Fit all parts to pcb except one marked zener.
*10R are 10R if powering with 36vdc and have 18v zeners fitted to the PCB. Or if using any +/-12v to +/-18v with no 18v zeners fitted.

BOM for Talkback Comp at this link https://jlmaudio.com/TalkbackComp/BOM%20Talkback%20Comp%20170505.pdf
Use step by step build map at this link https://jlmaudio.com/builds/maps/talkbackcompmap.html

Either link zener with wire or short wires in threshold connector together to enable comp.
Turn both trim pots fully counterclockwise.
Power up with +/-18vdc
Send in 1k tone of -10dBu or less into input XLR so comp is not compressing at all.
Adjust VR2 clockwise until you drop the signal at the XLR output of the comp by 1dB.
Done.

You can now set RV1 for whatever mic gain you need.
The jumper beside the output XLR can be set for 18v phantom power or none.
Enjoy.

JLM STBUS 10pin output (Same as on AMP HEAD, Stereo IO kit etc)
Pin 1 Left +
Pin2 Left -
Pin 3 & 4 V+
Pin 5 & 6 0v
Pin 7 & 8 V-
Pin 9 Right -
Pin 10 Right +

Comp is mono so Left and Right BALIO & XLR Out are all linked together.

To stop crosstalk when talkback not being used Out + & - signals are shorted togehter by relay and comp locked fully down by relay.

Pressing Talkback button removes short on comp and output.

[kante1603]

Hello Joe,

hope you‘re fine and had a good time at the AES.Seems some beautifull things are coming (I loved the 500 series VUPPM and the FX processor announcements!).

For the Talkback Comp:

1.:I‘d like to have full phantom power because I use condenser type microphones which need full +48vdc.Can I do it by classic feeding it via two 6K81 (matched) resistors to input pins 2 & 3?
I guess I can leave the +18vdc (jumper PP) disabled?


2.:For talkback use I‘d like to have a simple hpf on it,a first order fixed frequency (say 90 to 100Hz) would be o.k. for me.Possible?


3.:I see we can adjust threshold and mic gain.What‘s the output level,are we talking about line level around 0dBu?


4.:The TB-switch switches the relay,right? Would be easy to extend it to a jack for a footswitch,no?


Thank you in advance,

best regards from munich,

Udo.

[Joe Malone]

Hello Joe,

hope you‘re fine and had a good time at the AES. Seems some beautiful things are coming (I loved the 500 series VUPPM and the FX processor announcements!).

HI Udo great to hear from you. Yes several things coming soon

For the Talkback Comp:

1.:I‘d like to have full phantom power because I use condenser type microphones which need full +48vdc.Can I do it by classic feeding it via two 6K81 (matched) resistors to input pins 2 & 3?
I guess I can leave the +18vdc (jumper PP) disabled?

Talkback PCB has the 2 x 6k8 resistors already with 10uF smoothing cap. Just feed 48v into PP terminal for 48v phantom power. Do not fit any jumper to the other 2 pins.

2.:For talkback use I‘d like to have a simple hpf on it,a first order fixed frequency (say 90 to 100Hz) would be o.k. for me.

Change C4 & C5 from 10uF to 1.5uF each to HPF -3dB @ 90Hz. Must be 50v or more when using 48v phantom power.

3.:I see we can adjust threshold and mic gain.What‘s the output level,are we talking about line level around 0dBu?

Just add a resistor or pot across output XLR pin 2 & 3 to pad output. Output is driven by 2 x 270R resistor so it can be shorted by the relay.

4.:The TB-switch switches the relay,right? Would be easy to extend it to a jack for a footswitch,no?

Yes will work but needs to be a fully floating TS jack as it cannot connect to 0v.

[kante1603]

Thank you very much Joe,

ordered some stuff some minutes ago.
Will you send the schematics (watermarked as always) with the Talkback Compressor kit?

Have a nice day,

best regards,

Udo.

[Joe Malone]

Thank you very much Joe,

ordered some stuff some minutes ago.
Will you send the schematics (watermarked as always) with the Talkback Compressor kit?

Have a nice day,

best regards,

Udo.

HI Udo Yes I will send you the schematic now so you can study it before the kit arrives.

[kante1603]

Thanks a lot Joe,

looking forward to receive the schematics,will definetely make things clearer for me.

Best regards,

Udo.

[kante1603]

Hi Joe,

thank you for the schematics!
So D9 (Zener) can be omitted,yes?
It‘s also not in the BOM.
Shorting it out enables the compressor whether by closing/switching the threshold connector or directly by wire.
If we don‘t need the comp. we just leave it open (meaning omit D9)?

Can we bring the gain pot to a front panel? If yes which taper is prefered?

Thank you in advance,

Udo.

[Joe Malone]

Hi Joe,

thank you for the schematics!
So D9 (Zener) can be omitted,yes?
It‘s also not in the BOM.
Shorting it out enables the compressor whether by closing/switching the threshold connector or directly by wire.
If we don‘t need the comp. we just leave it open (meaning omit D9)?

Can we bring the gain pot to a front panel? If yes which taper is prefered?

Thank you in advance,

Udo.

D9 is optional to raise the threshold level. You can use a series string of diodes and zeners to have switchable threshold levels.
Normally you would just short the threshold pins together to enable the comp
Gain pot for best control on front panel use is a 10k rev log pot.

If using for talkback you will be amazed at how set and forget it can be and work with constant output no matter what input level.

[kante1603]

Hi Joe,

if I‘m right then first things first:HAPPY BIRTHDAY!!!
(I‘m in the same „league“)

Have built it today,looking good so far.
Am I right that the output is quite hot?
Can you tell us a rough gain range for Rgain (from ccw to cw) with the compressor disabeled?

The compressor bias went well,although I found a more usefull starting point at about -15dBu on my generator to set the -1dB point.
For now I only have a generator (close to 0 ohms output imp.) and a receiver (100k on input),so measured values will change a bit I think.
Will do a real world test in the studio next week with some microphones (50 to 200ohms) into a DAW interface or active speakers (10k to 20k inputs) and report back.
Looks promising!

Best regards,

Udo.

[Norikazu]

Hello Joe,

The package arrived the other day.
Thank you very much.

If possible, could you send me a schematic for the Talkback Compressor kit and the Dsub 4 kit?

Best regards,

[Joe Malone]

Hello Joe,

The package arrived the other day.
Thank you very much.

If possible, could you send me a schematic for the Talkback Compressor kit and the Dsub 4 kit?

HI Norikazu
Yes send an email to me at joe@jlmaudio.com and I will send it when I am on the workshop computer

[mrclunk]

Is there anyway to add very simple GR metering on this? Doesn't need to be accurate. I've VU buffer pcb's handy if that simplify things?
thanks
Paul

[Joe Malone]

Is there anyway to add very simple GR metering on this? Doesn't need to be accurate. I've VU buffer pcb's handy if that simplify things?
thanks
Paul

A high brightness led across the threshold plug wires will give a compression threshold led. A uA meter across the same wires may be able to be calibrated to be like a SSL GR meter but haven't experimented with this.

[mrclunk]

So i couldn't find a high brightness LED that would work so i made a little TL072 buffer circuit to drive an GR LED. Works well.

Next question..

How would i go about powering an Electret (TB) mic with this circuit?

Can i just remove one of the 6K8 resistors and put a 9V zener across the PP to ON jumper terminals.
My PSU Desk psu is +/- 17VDC

Think that should work...
thanks
paul

[Joe Malone]

So i couldn't find a high brightness LED that would work so i made a little TL072 buffer circuit to drive an GR LED. Works well.

Next question..

How would i go about powering an Electret (TB) mic with this circuit?

Can i just remove one of the 6K8 resistors and put a 9V zener across the PP to ON jumper terminals.
My PSU Desk psu is +/- 17VDC

Think that should work...
thanks
paul

HI Paul Sorry missed this post. Do you have a link to the Electret mic you are going to use and I will draw up the best way to use it.