1176 rev.D - Hairball Mnats- Preamp works well but no comp...?! (solved)

[hugo]

Hi all,
I just finished 2 rev.D 1176, and during the calibration process i was in trouble...the same on both unit
Input and output are working well, the signal is passing normaly. I made the first step of calibration, many many times... full CCW, send 1hz 0.775vac, etc.. and made this -1db reduction with the Qbias trimmer. But the problem is : Bypass, ratio, attack release do not affect the dynamic of the signal...the level stay always the same. the pin is correctyl on normal position, closest to q13..
Did someone had the same problem ?.. May i change Fets or something ?

Thanks all for your support.

 

[RuudNL]

If you can get a 1 dB level drop with the Qbias trimpot, the FET is working.
I would check the wiring.
Check if you measure a DC voltage at higher input levels at the junction of the two diodes connected to the attack pot.
(The DC voltage should vary with the input level.)

 

[hugo]

i do not have a good understanding of what you mean, sorry i do not see diodes...i checked the wiring, all ok...but still no compression at all..

 

[rainton]

i do not have a good understanding of what you mean, sorry i do not see diodes...i checked the wiring, all ok...but still no compression at all..

Hey Hugo,
sorry to crash in here but I tried to reach you several times via PM regarding the Pultec chassis group buy. Can you please check your PMs and get back to me as soon as possible?

Thank you
Martin

 

[RuudNL]

Measure here.

 

[hugo]

Thanks for your time,
I putted my multimeter on DC, and put the black pin to the input ground, and the red pin on cr2, at the side of the wall..
When i turn the input knob, it does not mae any variation of this DC voltage...

The 2 units have the same problem, so i think the soldering is good, the wiring has been double checked..
i trusted Mouser for resistances values, did not check them before soldering, but as the preamp and line output are working well, i can not find why the compression does not want to be in...i thin about suicide, 2 days searching the solution.
thanks all for your support

 

[RuudNL]

From what I understand from your previous post, you don't get any varying DC at the output of the sidechain amplifier.
This could mean two things:

- The sidechain amplifier is getting no input signal
- There is a fault in the sidechain amplifier.

To check this, test if there is an input (audio) signal at the negative side of C17 (referred to ground)
You could use and amplifier and speaker, or a Hi-z pair of headphones to check the input signal.
If you get a signal, the problem is in the sidechain amplifier.
If you don't get a signal, there may be a fault in the wiring of the ratio switch PCB.
If there is an input signal, check all component values in the sidechain amplifier carefully, check if the transistors are inserted the right way, etc.

 

[hugo]

Hi,
Thanks a lot, R37 was wrong, units both ok ! thanks

 

[RuudNL]

Look, compare and check.
(No way of telling you without seeing the PCB...)

But more important: do you have audio at the input of the side chain amplifier?
(You can't measure this with a multimeter!)

 

[hugo]

Hi,
Thanks so much Rudd, R37 was wrong, units both ok ! thanks

 

[RuudNL]

Good to read that you have them working now!