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Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: Xavier on April 22, 2023, 08:04:11 PM

Title: CP4500 setup issue
Post by: Xavier on April 22, 2023, 08:04:11 PM

Hi everybody,

I have some issue during the setup procedure. 
When I check the voltage at the step 1.4, i only can go from +0.7 to +2.8VDC when i turn the threshold knob (steps 1.1 to 1.3 are OK)
May be this is the reason why I can't trim the channel 1 level and i have 6dB more at the output when the compressor is IN condition

If you have any idea to fix this problem, your help would be very appreciated ;D

Thanks !

Title: Re: CP4500 setup issue
Post by: JPK on April 24, 2023, 04:18:54 PM

Check that the left pin of R95 goes from 12VDC to +12VDC when you rotate the threshold from +15 to -15.
Check the value and solder joints of R95, to R99 and U21.

Title: Re: CP4500 setup issue
Post by: Xavier on April 24, 2023, 10:25:29 PM

Thank you for your answer but unfortunatly it doesn't work
R95 to R99 are the good one and are correctly soldered
U21 is the good one too and with the right orientation. I tried to replace U21 by U18 but it didn't change anything
I have the correct voltage at the left pin of R95 between -11.77 and + 12.00VDC

Title: Re: CP4500 setup issue
Post by: JPK on April 25, 2023, 03:18:02 PM

Can you report the DC voltages on the 8 pins of U21 for the 2 extreme positions of the Threshold?

(https://www.soundskulptor.com/prodimages/debug/ic8pins.png)

Title: Re: CP4500 setup issue
Post by: Xavier on April 25, 2023, 09:30:28 PM

When the threshold is +15 
pin 1 = 0
pin 2 = 0
pin 3 = 0
pin 4 = -15.82
pin 5 = 0
pin 6 = 0
pin 7 = + 2.84
pin 8 = +16.01

When the threshold is -15
pin 1 = -2.52
pin 2 = -2.52
pin 3 = -2.52
pin 4 = -15.82
pin 5 = 0
pin 6 = 0
pin 7 = +0.72
pin 8 = +16.01

Title: Re: CP4500 setup issue
Post by: JPK on April 26, 2023, 03:16:52 PM

The issue is pin 1-2-3 = -2.52V when the threshold is at -15. It should remain at 0 when there is no input signal.
Is it the same if you remove U9?

Title: Re: CP4500 setup issue
Post by: Xavier on April 26, 2023, 07:17:17 PM

Sorry i made a mistake (it was too late maybe ::)) the measure was done with the signal IN and the compressor bypassed
So during the step 1.4, with the correct initial conditions, TP13 goes from -1.8 to +2.8 VDC

With no signal U21 pin 1, 2 and 3 are 0 indeed

Then i tested the others conditions and :

step 1.5
TP4 goes from 0.053 --> 0.185 VAC
TP5 goes from 0.36 --> -1.17 VDC
TP11 goes from 0 --> -3.46 VDC
TP12 goes from 0 --> +3.47 VDC

step 1.6
TP1 is +1.48 VAC
TP2 is +1.62 VAC
TP3 is + 1.5 VAC
TP4 is + 0.054 VAC
pin 1 U6 is 0 VDC

step 1.7
TP1 is 1.48 VAC
TP2 is 0.45 VAC
TP3 is 1.49 VAC
TP4 is +0.18 VAC
TP11 is -3.47 VDC
TP12 is +1.14 VDC
TP13 is +1.66 VDC

Even the values seem not so bad, i still have 6dB more when the compressor is IN

Title: Re: CP4500 setup issue
Post by: JPK on May 03, 2023, 08:07:24 AM

Your values are good.
Try swapping U7 with the one from the other channel, in case it is damaged.