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Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: Dds on June 15, 2021, 11:03:21 AM

Title: CP4500 second channel (PCB B) low gain
Post by: Dds on June 15, 2021, 11:03:21 AM
Hello,

I built my CP4500 kit, and the first channel is just working fine, but not the second one (PCB B). When I feed the unit with a 2VAC, 1kHZ signal, the max output level i get when the "in" control is engaged si about 1,5VAC at maximum. This level is also not affected by the "thresold" or "makeup gain" controls, contrary to the first channel.

I checked the solder and cleaned the whole PCB in an isopropyl dip since it seems to be a frequent issue. Nothing changed for now. All the ICs seem to be in the good spots and in the right directions.

Here are the results i measured  following the troubleshooting procedure .

Channel 2

Step.....ConditionsResult
1Mix = 100%
Ratio = 10
Attack = 0.1
Release =1.2
IN button pressed
HF lift, 100Hz, 50Hz buttons released
Negative meter probe on 0V
  • V+ =+15 to +16VDC, +16VDC
  • V-  =-15 to -16VDC),   -16VDC
  • +12V = +11.1 to +12.9VDC, don't know  where to measure it
  • -12V  = -11.1 to -12.9VDC  same
2Step 1 conditions plus:
Input signal = 0V
Threshold on +15
Makeup on 0		TP6, TP7, TP8, TP9 = 0VDC  0VDC
3input signal = 3VAC
Threshold on +15
Makeup on 0		Signal level (VAC) on
  • TP6=1.5VAC,  1.16VAC
  • TP7=1.5VAC,   2.02 VAC
  • TP8=1.5VAC,   1.16 VAC
  • TP9=0.06VAC  1,09 VAC
DC voltage (VDC) on
  • pin 1 of U16 (white dot) = 0V.  -0.023 VDC
4input signal = 3VAC
Threshold on -15
Makeup on +20		Signal level (VAC) on
  • TP6=1.5VAC,   1.16VAC
  • TP7=0.4VAC,   2.02 VAC
  • TP8=1.5VAC,   1.16 VAC
  • TP9=0.2VAC    1.09 VAC
DC voltage (VDC) on
  • pin 1 of U16 (white dot) = +0.2V  -0.023 VDC


Thank you guys,
Title: Re: CP4500 second channel (PCB B) low gain
Post by: JPK on June 15, 2021, 06:55:33 PM
Are the voltage on TP12 and TP13 from the channel 1 test steps 3 and 4 still OK after you connect the channel 2?
Title: Re: CP4500 second channel (PCB B) low gain
Post by: Dds on June 16, 2021, 12:14:58 AM
Ok, I just checked the measurments you ask, and it seems the first channel doesn't work properly after all (see my measurments in red). I got these results without the PCB B connected.

Channel 1

Step.....ConditionsResult
1Mix = 100%
Ratio = 10
Attack = 0.1
Release =1.2
IN button pressed
HF lift, 100Hz, 50Hz buttons released
Negative meter probe on 0V
  • V+ =+15 to +16VDC, +16 V
  • V-  =-15 to -16VDC),  -16V
  • +12V = +11.1 to +12.9VDC,  +11.9V
  • -12V  = -11.1 to -12.9VDC  -11.9 V
2Step 1 conditions plus:
Input signal = 0V
Threshold on +15
Makeup on 0		TP1, TP2, TP3, TP4, TP11, TP12 = 0VDC  OVDC for all
3Step 1 conditions plus:
Input signal = 0V
Threshold on +15
Rotate Makeup from 0 to +20		TP12 goes from 0 to -2.3VDC  ok, -2,3VDC
4Input signal = 0V
Makeup on 0
Rotate Threshold from -15 to +15		TP13 goes from -1.8V to +2.8VDC ok
5Input signal = 3VAC
(measured between output XLR pins 2&3
with compressor bypassed)
Makeup on 0
Threshold goes from +15 to -15
  • TP4 goes from 0.060VAC to 0.190VAC  0.11 VAC to 0.24 VAC
  • TP5 goes from +0.35VDC to a negative value ok
  • TP11 goes from 0VDC to -3.5VDC  0V to 0V
  • TP12 goes from 0VDC to +3.5VDC  0V to 4V
6input signal = 3VAC
Threshold on +15
Makeup on 0		Signal level (VAC) on
  • TP1=1.5VAC,  3VAC
  • TP2=1.5VAC,  3VAC
  • TP3=1.5VAC,  3VAC
  • TP4=0.06VAC 0.11 VAC
DC voltage (VDC) on
  • pin 1 of U6 (white dot) = 0V. 0V
7input signal = 3VAC
Threshold on -15
Makeup on +20		Signal level (VAC) on
  • TP1=1.5VAC,  3VAC
  • TP2=0.4VAC,  0.5VAC
  • TP3=1.5VAC,  3VAC
  • TP4=0.2VAC    0.24VAC
DC voltage (VDC) on
  • TP11=-3.5VDC,    0VDC
  • TP12=+1.2VDC,  +1.6VDC
  • TP13=+1.7VDC    +2.1VDC

Title: Re: CP4500 second channel (PCB B) low gain
Post by: Dds on June 17, 2021, 09:53:05 AM
Hello again,

What do you thin could be the cause of the TP11 voltage not following the Threshold pot ? I am a bit confused here.
Title: Re: CP4500 second channel (PCB B) low gain
Post by: JPK on June 18, 2021, 06:46:53 PM
It is weird because TP12 is working and it is based on TP11.
Check directly on U21 pin1 which is connected to TP11.
Check The solder joint on TP11.

TP1=1.5VAC,  3VAC
This also seems impossible. Make sure you have the correct voltage at the input, measured between pins 2&3 on the XLR.
Title: Re: CP4500 second channel (PCB B) low gain
Post by: Dds on June 19, 2021, 11:45:13 AM
Thank you for your answer. I did double check my first channel measurments, because they seemed illogical to me also. So finally, the first channel seems perfectly right ( I did the measurments too late in the evening, and they were not good at all).
However, I can confirm the measurments on the second channel : everything seems right, except the TP7, TP9 and pin 1 of U16 which all have fixed, wrong values that never change.

I also checked, the connexion on the second channel doesn't affect the TP 12 and Tp 13 voltage from the channel 1 test steps 3 and 4 after I connect the channel 2. They are still ok ( about 2 % change in value when PCB B connected).
Title: Re: CP4500 second channel (PCB B) low gain
Post by: JPK on June 21, 2021, 09:12:16 AM
What is the revision number of your PCB?
Check your components value and solder joints around U19 and U20, R65...R69.
Is the DC voltage on R65 (left pin if REV1.4, bottom pin if REV1.3) changing when you turn the threshold pot?
Title: Re: CP4500 second channel (PCB B) low gain
Post by: Dds on June 21, 2021, 11:15:23 AM
The PCB is revision 1.4. I'll reflow all the solders in the area you described. All seems to be in order however ( solders, component values), i'll double check this evening.

I confirm the DC voltage on R65 (left for if REV1.4) doesn't change when thresold pot is moved. I measure a fixed -0.29 VDC with 3VAC, 1kHz signal in and thresold pot turning from -15 to +15, and a fixed 0.48 VDC with no signal in and the thresold pot turning from -15 to +15.


Title: Re: CP4500 second channel (PCB B) low gain
Post by: JPK on June 21, 2021, 12:07:00 PM
Check if you get a DC voltage change on the connector CN3A pins 9-10 when you move the threshold pot.
If not, check the solder joints on CN1B pin 15 and CN3B pin 10.
The pin numbering on the connectors starts from the square pad and goes like this:
1  2
3  4
5  6
7  8
...
Title: Re: CP4500 second channel (PCB B) low gain
Post by: Dds on June 21, 2021, 01:33:46 PM
Thank you for your answer, I have a fixe value of 0.48 VDC (same as on R65) on CN3A pins 9-10 independently of  the thresold pot moving, with no signal in.
Title: Re: CP4500 second channel (PCB B) low gain
Post by: JPK on June 21, 2021, 02:57:53 PM
Try to follow the threshold control voltage:
It goes from TP13
to CN1A pin 15
to CN1B pin 15
to CN3B pin 9-10
to CN3A pin 9-10
to R65.
Title: Re: CP4500 second channel (PCB B) low gain
Post by: Dds on June 21, 2021, 08:04:17 PM
Thank you for your answers and your time. It is finally working. The issue was the connection between PCB A and one of the XT500 extenders which was not stable, don't know why. All seems better now.