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Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: brinporter on January 12, 2021, 06:39:41 AM

Title: Signal loss when CP4500 is on
Post by: brinporter on January 12, 2021, 06:39:41 AM

Hi, I've just finished populating my CP4500, and am having some calibration issues. Right off the bat My V+ and V- are reading a little hot (and cold) at +/-16.3ish V. I don't know if this is a big deal, but the guide says it should be between 15-16.

The part I'm really stumped at is getting my output signal to read the same when the compressor is IN or not. Ive got a 3.0VAC reading while the comp is off (with the 1Khtx signal through my DAW), but I cant seem to get any more signal out of my T1 trimmer resistor no matter how much I turn it. I've cleaned the PCB's thoroughly, checked the polarity of all my caps and diodes, made sure that the T1 resister was working properly by isolating it with the DMM, but I cant get the signal up to where it should be.

Any suggestions?

Thanks in advance
-Brin

Title: Re: Signal loss when CP4500 is on
Post by: JPK on January 12, 2021, 04:30:09 PM

My V+ and V- are reading a little hot
No problem here, it is your lunchbox which is a little hot.

Can you do the voltage checks shown here (https://www.soundskulptor.com/forum/index.php?topic=3.msg3#msg3) and report the ones which are wrong?

Title: Re: Signal loss when CP4500 is on
Post by: brinporter on January 12, 2021, 07:58:48 PM

Alright, so I found some readings that were a little off

Test 6
TP2 1.35

Test 7
TP4 0.18

I should also mention that the T1 max's out at 0.4 VAC when the compressor is IN

Cheers

Title: Re: Signal loss when CP4500 is on
Post by: JPK on January 13, 2021, 11:30:25 AM

Check that the VCA's (THAT2180A) are well inserted into their socket. Sometimes a bad contact on one of them creates this kind of problem.

Try to use a 100Hz sinus signal instead of 1kHz, in case your meter is not fast enough.

Did you test the conductivity of your solder residues? In case it does conduct, a simple clean won't be enough. You will need to immerse the 3 PCB in a bath of isopropyl alcohol for 10mn.

Title: Re: Signal loss when CP4500 is on
Post by: brinporter on January 14, 2021, 01:16:28 AM

Checked all the VCA's, tried the 100Hz signal, and soaked all the PCBs in iso with another good scrub. I did all the tests again to make sure nothing changed, and the problem is consistent.

any other suggestions?

Title: Re: Signal loss when CP4500 is on
Post by: brinporter on January 14, 2021, 07:31:51 AM

I figured it out!

I had 2 THAT 1646 IC's on PCB 1, and 2 THAT 1246 IC's on PCB 2. There should have been one of each on both PCB's.

Well... Everyone's gotta start somewhere. Thank you for your help. This thing sounds great!