Talkback Combiner PCB'S

[Igor]

Hi Ben, yes, all these caps are 100uF. In any case, 224=220 nf, 100u=100U=100m=100microfarad.

 

[plumsolly]

Hi Ben, yes, all these caps are 100uF. In any case, 224=220 nf, 100u=100U=100m=100microfarad.

Thanks Igor - that's what I had assumed, but when I looked up farad on wikipedia it said:

1F = 1000 mF = 1,000,000 μF = 1,000,000,000 nF = 1,000,000,000,000 pF
1μF = 1,000 nF = 1,000,000 pF

and then on this calculator:
http://www.translatorscafe.com/cafe/units-converter/electrostatic-capacitance/calculator/nanofarad-%5BnF%5D-to-farad-%5BF%5D/ It also says that mf = millifarad
That's where i got confused. Thanks again and I'll post pictures soon of a completed crm!!
Best, Ben

 

[Igor]

That's cool. Will be happy to see pictures!

 

[crisotop]

To connect the tb combiner to CRM, use tb_on terminal on CRM audio pcb. They have same pinout.
100r resistors usen in case something shorted from outside, just to save expensive A6833 relay driver.

Have't had the chance to include the Talkback Combiner to my CRM, but either I'm completely blind, or I have a different CRM motherboard, because I can't find any "tb_on" terminal on the CRM audio pcb?

Thanks
Christoph

 

[Igor]

There were 2 revisions. On older version,
pin1 of 9-pin connector should be connected to tb_on1 on talkback combiner pcb;
pin 6 of 9 pin connector should be connected to tb_on2 on talkback combiner pcb.

 

[Sylvain D.]

Hi Igor,

I am running the TC as a "stand alone" unit and after assembly it is passing audio at slightly lower than unity gain. But the real  problem I am having is that the "talkback" does not seem to engage.  So, no audio dimming, no LED and no mic audio.  (I assume that I am doing this correctly by shorting "TB ON" pins 1 and 2 to engage TB?) Do you have any suggestions? :-\

Sylvain

 

[Sylvain D.]

So Igor,

Following my previous post regarding "talkback engage"...

Upon further reading of "page 1" of this TC discussion, am I to understand that in order to engage "talkback on", I must apply  +/- 5V at the "TB_ON" terminal?

Is this correct?

Sylvain

 

[Igor]

Yes, to engage talkback, apply 5V to "tb_on" terminal. See schematic.
If you run talkback combiner from +/-15V, without dc/dc converter,
change R36, 37, 38 to 3k6....4k7, tb_on2 goes to -15V, tb_on1 goes thru switch to +15v.
To get exact unity gain, change R16, R29.

 

[Sylvain D.]

Thanks Igor,

That's much clearer to me now.

Sylvain 8)

 

[Sylvain D.]

Hi all,

With the help and clariffications from Igor, my TC now works.
However, when I engage the mic, I get a loud hum...
(Other than that, it seems to work well.)

Any thoughts anyone?

Sylvain

 

[Igor]

Check for ground loops. Is this hum only or hum "over" the mic signal?
Microphone should be connected with shielded cable. Maybe microphone got "second earth"?

 

[Sylvain D.]

Hi Igor,

The hum was there over the mic and also without the mic connected.

I've checked that it is not a ground loop by feeding the input with an Ipod and feeding the output directly with headphones.

N.B. -> there is no hum when just passing audio without talkback engaged. It runs clean that way.
(If the hum was there always I would suspect the power supply. But that is not the case)

But what I did find is that replacing C3 with a much higher value like 1000mf , the hum becomes negligible. (I tried 100mic, 220mic, 470mic and 1000mic seemed to do the trick).

It's hard for me to believe that your value for C3 would be "so much" off. So I think that maybe something is wrong somewhere else...

What do you think.  Should I just stick with the big cap at C3? It seems to work well that way.


Sylvain

 

[Igor]

Ahemmm....How do you feed power to TB combiner? Just check how much mV AC do you have on +/-15V....

 

[Sylvain D.]

I am feeding the tc with a stand alone(wall wart) ps with +/-12Vdc output at 200ma. (mesuring 17Vdc - no load)
I am getting 1.6Vac at+/-15Vdc. Could that be it?

Sylvain

 

[Igor]

Cool.

1.6Vac  at+/-15Vdc

This is the answer
Just use stabilized PS. The DC/DC converter is not installed on PCB?

 

[Sylvain D.]

Yes. DC/DC is installed.
I also changed  R36, 37, 38 to 4k3 as you recomended...

 

[Sylvain D.]

Igor,
Success! ;D

I tried a different power supply(switching supply) and it's all good! No more hum.
I guess I had a bad (cheap) power supply...

Thanks for your help Igor.

Sylvain

 

[Igor]

Sylvain, you don't need DC/DC converter in case you use external power supply (+/-15v).
Othervise...Cool!

 

[dtonthept]

Hello all,

I absolutely hate asking this question... but... does anyone have a mouser link to a trimpot that fits the PCB?

Thanks,

D

 

[dtonthept]

And... Oh goodness here we go!! I've been trawling the web trying to find anyone who has the NSL-32SR2 optocouplers in stock, no joy yet, does anyone know who might have some?