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Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: Gian on August 04, 2025, 09:04:21 AM

Title: CP4500 Cannot level match and incorrect voltages in step 1.6
Post by: Gian on August 04, 2025, 09:04:21 AM

Hi, having trouble on Step 7 of the set up guide. I cannot get enough voltage when setting T1, it only goes up to +1.754 and I am trying to get to 2.00 when aiming for no level change.

PCB is Rev 1.4
Here are my voltages:

This starts to go wrong in step 1.6
Step 1.1
V+=+16.06
V-=-16.21
+12=+11.74
-12=-11.71

Step 1.2
TP1 = -0.006
TP2 = -0.003
TP3 = -0.014
TP4 = 0.000
TP11 = 0.005
TP12 = -0.004

Step 1.3
TP12 goes from -0.005 to -2.292 VDC

Step 1.4
TP13 goes from -1.764 to +2.808

Step 1.5 (with input of +3.003VAC)
TP4 goes from 0.080 to 0.199VAC
TP5 goes from +0.335 to -1.785VDC
TP11 goes from 0.005 to -3.669VDC
TP12 goes from -0.005 to +3.665VDC

Step 1.6
Here is where things are not correct
TP1 = 1.954VAC
TP2 = 0.039VAC
TP3 = 1.959VAC
TP4 = 0.199VAC
DC voltage at pin 1 of U6 = 0.213VDC

Step 1.7
TP1 = 1.954VAC
TP2 = 0.487VAC
TP3 = 1.959VAC
TP4 = 0.199
TP11 = -3.669
TP12 = +1.377
TP13 = +1.905

Thanks

Gian

Title: Re: CP4500 Cannot level match and incorrect voltages in step 1.6
Post by: JPK on August 05, 2025, 10:11:42 AM

In Voltage Checks step 1.2, please report the DC voltages on  each pin of U6.
Same question in step 1.6 ?

(https://i.imgur.com/riRh8YL.png)

Title: Re: CP4500 Cannot level match and incorrect voltages in step 1.6
Post by: Gian on August 06, 2025, 11:38:32 AM

Hi, thanks for your help on this. It is very much appreciated.

for step 1.2 (comp engaged)
DC voltages on U6
Pin 1:  0.000 VDC 
Pin 2:   0.000 VDC
Pin 3:   0.001 VDC
Pin 4:   -16.20 VDC
Pin 5:   0.000 VDC
Pin 6:   -0.001 VDC
Pin 7:   -0.001 VDC
Pin 8:   +16.03 VDC

for step 1.6 (comp disengaged)
DC voltages on U6
Pin 1: 0.000 VDC
Pin 2:  -0.001 VDC
Pin 3:  0.000 VDC
Pin 4:  -16.20 VDC
Pin 5:  0.000 VDC
Pin 6:  -0.001 VDC
Pin 7:  -0.001 VDC
Pin 8:  +16.05

Title: Re: CP4500 Cannot level match and incorrect voltages in step 1.6
Post by: JPK on August 06, 2025, 12:19:45 PM

Was that done in step 1.2 or 1.6 ?
I would need the measurements in both cases.

Title: Re: CP4500 Cannot level match and incorrect voltages in step 1.6
Post by: Gian on August 06, 2025, 01:40:48 PM

hi, apologies. I have now updated my previous message (above) with step 1.2 and 1.6 voltages

Title: Re: CP4500 Cannot level match and incorrect voltages in step 1.6
Post by: JPK on August 06, 2025, 04:59:42 PM

There is something wrong with the measurements:
In a previous message, you reported DC voltage at pin 1 of U6 = 0.213VDC for step 1.6 and now it is 0.000 ?

Title: Re: CP4500 Cannot level match and incorrect voltages in step 1.6
Post by: Gian on August 07, 2025, 12:56:30 AM

Hi, yes I reported +0.203VDC at pin 1, 2, 3. But I think I had incorrect front panel settings that were not 1.2 conditions.

Conditions:
Mix 100%, Ratio 10, Attack 0.1, Thresh +15, Makeup 0
For step 1.2 (no input, compressor IN), for step 1.6 (input of 3VAC, compressor OUT)
My values are the same for step 1.2 and 1.6
Pin 1: -0.001
Pin 2: -0.001
Pin 3: 0.000
Pin 4: -16.22
Pin 5: 0.000
Pin 6: -0.001
Pin 7: -0.001
Pin 8: +16.05

Title: Re: CP4500 Cannot level match and incorrect voltages in step 1.6
Post by: JPK on August 07, 2025, 11:40:14 AM

ok, wrong lead.

Step 1.6
Here is where things are not correct
TP1 = 1.954VAC
Please double check that the input voltage is correct at 3VAC

TP2 = 0.039VAC
Check the value and solder joints of trimmer T1 and R54.
Make sure all 2180A's are properly inserted into the sockets and that JMP1 is in place.

TP4 = 0.199VAC
Do you confirm this value ?