dmp

Re: 525 build thread
« Reply #620 on: December 03, 2019, 12:49:10 PM »
Can you  measure for the control voltage?
If you feed a audio wave to the unit and measure the DC voltage at the attack pot, you should see the control voltage go up as you increase the signal level feeding the unit.


duantro

Re: 525 build thread
« Reply #621 on: December 05, 2019, 12:37:16 PM »
I swapped out a fresh vcr2n, and no difference. DMP are you saying measure the dc voltage at the attack pot, while increasing signal level?

dmp

Re: 525 build thread
« Reply #622 on: December 05, 2019, 01:40:35 PM »
Yes - I would start out measuring on the attack pot (the side that faces the VCR2N) for the control voltage.  You probably will not have any voltage there. If you don't, then work your way back through the sidechain to see where things are getting messed up.
The basic operation is an audio signal goes to the ceiling control, which sends a signal to the sidechain (the ceiling changes a dual voltage divider to adjust the threshold and output together) . The signal to the sidechain  is amplified and rectified to a DC control voltage. That voltage changes the resistance of the FET (VCR2N) in the first 2520 amp circuit, to modify the gain of the amp.

duantro

Re: 525 build thread
« Reply #623 on: December 16, 2019, 06:53:28 PM »
Thanks so much DMP, for the detail explanation. I was sick over the weekend and now am backed up with work, but will check this asap!

duantro

Re: 525 build thread
« Reply #624 on: January 07, 2020, 06:00:18 PM »
I finally got around to looking at this. Spent about 5 hours searching for components and retracing wiring, etc. Still the same results. I'm not getting any dc voltage at the att connection on the meter board. I am getting between -2vdc to -12vdc on the top lead of r50 depending on how hard I send input audio. I double checked the wiring and solder joints going to the release time board. Input pot changes the meter reduction, but does nothing to the sound. Output pot is working, but when it is ccw there is still like 30 % audio coming through. Sw5 just makes out put gain hotter as turned cw. So frustrating...

dmp

Re: 525 build thread
« Reply #625 on: January 08, 2020, 11:09:19 AM »
You have a negative control voltage on R50 but not on the attack pot???
Which side of R50: CR5 or CR12/CR11?

duantro

Re: 525 build thread
« Reply #626 on: January 08, 2020, 12:42:26 PM »
You have a negative control voltage on R50 but not on the attack pot???
Which side of R50: CR5 or CR12/CR11?
On the CR11/CR12 side. I'm wondering if I should just jumper a wire from R50 to the inside att/c3 junction on the meter board, as it seems to die en route somewhere. The previous owner attempted a few repairs, perhaps a solder trace got too hot.

dmp

Re: 525 build thread
« Reply #627 on: January 08, 2020, 12:48:12 PM »

From the schematic the R50/CR11/CR12 node should connect to the Attack pot / C3  - so yeah something seems funny
I don't remember what the routing looks like and I don't have one of mine with me to look at now, so can't be much help.

duantro

Re: 525 build thread
« Reply #628 on: January 08, 2020, 12:59:31 PM »
That fixed the side chain! Compression at last! ....However, I'm still getting around 20-30% signal passing through, with the output pot turned off. Time to search for that and calibrate.

dmp

Re: 525 build thread
« Reply #629 on: January 08, 2020, 01:08:23 PM »
Nice!

The ceiling also attenuates the signal


duantro

Re: 525 build thread New
« Reply #630 on: January 08, 2020, 01:18:04 PM »
Nice!

The ceiling also attenuates the signal
Right. I'm talking about the output pot itself. Regardless of the ceiling control position, I still get signal with output off. I think it might be time to double check the calibration now. Thinking of making sure R7 isn't way off.
Also, i need to do the mounting screw mod to disconnect gold finger 5 and 13 from each other. Does this image look correct to cut the red line?
Edit: i cut that and the same section from pin 13.
« Last Edit: January 09, 2020, 01:50:04 PM by duantro »


 

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