Author Topic: Unbalanced channels + + +

December 07, 2023, 09:49:24 PM
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Dolbah

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So, this is a continuation of thread: https://www.soundskulptor.com/forum/index.php?topic=419.msg2349#msg2349
Just to politely not weddingcrash the other users questions.

So:
I have unbalanced output after a couple of years.

My issue is that whn i start calibrating the unit from start, i can not get T1 on channel one to match the 3.0 VAC signal that is present when i standby. T1 only manages to increase the voltage to 2.595 VAC.

Edit: and on channel two board i can't get T2 og T3 down to 2.595.

-----------------------------------------------------------------------------------------------------


@Dolbah
Do you get TP1=1.5VAC with 3VAC at the input?
Are the VCA's socketed or SMC?


@JPK



3.0 VAC source signal gives me 1,492 VAC on TP1.

With T1 turn on max, it gives me  2.709 VAC on the unit output.


My VCAs are in sockets

EDIT:
I realized now, that when testing with only board 1 powered, i get the above results. As soon as i power both boards, board/channel 1 suddenly gets a bump and is suddenly outputting 2.95 VAC
When removing board 2, it goes down to 2.7 VAC.

EDIt 2:
I had a bunch of OPA2134PAs laying around, so startet switching them. When replacing U21, i finally was able to match the bypass and active signal. But i have no chance of getting T4 to trimm the meter to 12 dB attenuation (worked yesterday).
Also noen of the trimmers on board 2 is reacting. And i feel the threshold is very sensitiv.
« Last Edit: December 07, 2023, 09:51:20 PM by Dolbah »

December 07, 2023, 11:07:34 PM
Reply #1

Dolbah

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So, something has really happened to this unit now.

Watch this video, thisn is not normal. This is only happening on left ch. (pcb A)
https://www.dropbox.com/s/zk0808316bocxha/IMG_6345.MOV?dl=0

When hooking it up with both pcbs the right ch. does not loose the sound like this.

any ideas?

December 08, 2023, 11:48:35 AM
Reply #2

JPK

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i can not get T1 on channel one to match the 3.0 VAC
With board 1 only, try removing the VCA's, one at a time. It should reduce the output level by 0.75V. If one of the VCA's doesn't reduce the output, it can be a defective VCA or a bad slot.
JPK

December 11, 2023, 12:50:56 PM
Reply #3

Dolbah

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i can not get T1 on channel one to match the 3.0 VAC
With board 1 only, try removing the VCA's, one at a time. It should reduce the output level by 0.75V. If one of the VCA's doesn't reduce the output, it can be a defective VCA or a bad slot.
Do you mean U2, U3, U4, U5?

  • With 3.75 VAC on output: 
  • When Removing U5, reduces output to 1.875 VAC,
  • Then Removing U2 = 1.875 VAC.
  • Then Removing  U3 = 1.880 VAC
  • Removing U4 =  Silence

So, no 0,75 VAC reduction


But, i tried the follwing to, to try to identify if one is acting weird:

  • 1 VCA always in slot U5
  • the other 3 VCA put in U2 one by one 
  • All VCA say 3,75 VAC except one of them which only give 1.875 VAC

So, can we conclude one of them is gone bad?



 


December 11, 2023, 05:14:50 PM
Reply #4

JPK

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Do you mean U2, U3, U4, U5?
Yes

So, no 0,75 VAC reduction
Were you configured as in step 4 of the setup guide?

All VCA say 3,75 VAC except one of them which only give 1.875 VAC
This is possible. 
Does the result depends on the slot? If true the issue could be the slot.
Do you get good results if you replace the suspect VCA by one from the other board?
JPK

December 12, 2023, 03:59:18 PM
Reply #5

Dolbah

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Do you mean U2, U3, U4, U5?
Yes

So, no 0,75 VAC reduction
Were you configured as in step 4 of the setup guide?

All VCA say 3,75 VAC except one of them which only give 1.875 VAC
This is possible.
Does the result depends on the slot? If true the issue could be the slot.
Do you get good results if you replace the suspect VCA by one from the other board?

Were you configured as in step 4 of the setup guide? = Yes

Does the result depends on the slot? If true the issue could be the slot. = No, result does not seem to depend on slot.

But, today the following happened:

As i told, i replaced all OPAs with some others i had laying around, same brand and model. 
The CP4500 was laying on top of my 19" rack, connected to my luchbox via the extender. Powered on.
When i reached to pick it up, i only touched the corner of the front plate.. and BOOM! I saw the small fire in the electrical blast between my finger and the unit.
One of the OPAs blew so hard a piece of the plastic is gone.

So put all the the original opas back now, just in case i bought a bad batch...

When tunring on, it works as before. Samme issues, no more no less.

So..


Good idea crossswapping VCAs:

What i did was to put all the VCAs from board 2 into board 1. And this actually seemed to work, at least the threshold went smoother again, i just visualized on the meter and heard if the sine diaapears quickly.

So i started changing one after an other to see if any of the board 1 VCA was the culprit. And i actually experienced one VCA working from board ione and the rest not, but when i started round 2 and testet the first working VCA again, suddenly it did not work. So i have a hard time recreating anything, as the issue seem to be random.

I then checked all...
...the board 1 VCAs in Board 2 = did not work - Nor same issuen tho. I have a constant sine that does not get affected by the threshold
...The board 2 VCA on Board 1 = did not work - Same issue as before
...the board 1 VCAs in board 1 = did not work - Same same
back in ...the bord 2 VCA back in Board 2= works fine

This again seem to confirm that there might be something with both board 1 VCAs and something else on board 1.

The funny thing is, the unit worked fine. I only had maybe 1-2dB unbalance on one channel, but all this trouble started the moment i tried readjusting the balance.





« Last Edit: December 13, 2023, 01:46:35 PM by Dolbah »

December 14, 2023, 11:14:53 AM
Reply #6

JPK

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99% of the reported issues are caused by bad solder joints.
I would recommend starting by reviewing all you solder joints and reflowing all suspect looking ones.
Don't be shy on heating until the solder flows nicely, as long as your iron is thermally regulated.
JPK

December 16, 2023, 09:10:16 PM
Reply #7

Dolbah

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99% of the reported issues are caused by bad solder joints.
I would recommend starting by reviewing all you solder joints and reflowing all suspect looking ones.
Don't be shy on heating until the solder flows nicely, as long as your iron is thermally regulated.
The unit has worked fine since i buildt it, as i said something happened when i started adjusting the balance that was off-
I have looked over the olders joints, they all look ace but i did reflow any mildly suspicious ones and i did redo the ones around the trimmers though, as these are the only parts i touched when this all started to happen, but there was nothing visiblywrong with these joints.
I do not beleive this is caused by any bad soldering.

I have also Switched all socketed parts from Board 2 into board 1 with same result.

So i have backtracked to the measuring tests and found something (green is ok, red is not, blue is not sure)



1.1

Mix = 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,
• V-  =-15 to -16VDC),
• +12V = +11.1 to +12.9VDC,
• -12V  = -11.1 to -12.9VDC



1.2
Step 1 conditions plus:
Input signal = 0V
Threshold on +15
Makeup on 0
TP1, TP2, TP3, TP4, TP11, TP12 = 0VDC



1.3
Step 1 conditions plus:
Input signal = 0V
Threshold on +15
Rotate Makeup from 0 to +20
TP12 goes from 0 to -2.3VDC



1.4
Input signal = 0V
Makeup on 0
Rotate Threshold from -15 to +15
TP13 goes from -1.8V to +2.8VDC



1.5
Input 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
• TP5 goes from +0.35VDC to a negative value
• TP11 goes from 0VDC to -3.5VDC
• TP12 goes from 0VDC to +3.5VDC

When testing TP11 and TP12, my meter starts meassuring around 0.5 VAC and the meter starts decreasing in value unbtil it hits 0 VAC. Thishappen both with Threshold on -15 and +15

1.6
input signal = 3VAC
Threshold on +15
Makeup on 0
Signal level (VAC) on
• TP1=1.5VAC,
• TP2=1.5VAC,
• TP3=1.5VAC,
• TP4=0.06VAC
DC voltage (VDC) on
• pin 1 of U6 (white dot) = 0V.


1.7
input signal = 3VAC
Threshold on -15
Makeup on +20
Signal level (VAC) on

• TP1=1.5VAC
• TP2=0.4VAC = 0,26
• TP3=1.5VAC,
• TP4=0.2VAC

DC voltage (VDC) on
• TP11=-3.5VDC,
• TP12=+1.2VDC,
• TP13=+1.7VDC





« Last Edit: December 16, 2023, 09:29:51 PM by Dolbah »

December 18, 2023, 06:12:09 PM
Reply #8

JPK

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When testing TP11 and TP12, my meter starts meassuring around 0.5 VAC and the meter starts decreasing in value unbtil it hits 0 VAC. Thishappen both with Threshold on -15 and +15
Here we are measuring DC voltage, not AC.

You always have the option to send us your your unit for a check. In this case, please contact us here.
JPK

December 18, 2023, 10:53:49 PM
Reply #9

Dolbah

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When testing TP11 and TP12, my meter starts meassuring around 0.5 VAC and the meter starts decreasing in value unbtil it hits 0 VAC. Thishappen both with Threshold on -15 and +15
Here we are measuring DC voltage, not AC.

You always have the option to send us your your unit for a check. In this case, please contact us here.
My bad, these values checks out on VDC too.

Meaning the unit is paasing all tests, and there is no real reason it should not work as excpected?

Not to keen on spending $$ sending the unit to France. If we can
I've buildt over 20 pc. of 500 units from various brands, only the SS TS 500 Tape module has been the one i/we gave up on.
As i said, this one worked well until i adjusted T1, T2, T3 and T4 to get it back in perfect stereo balance, then it started fritzing. Could it be that one of the trimmers have gone bad? Did you watch the video i linked?


December 18, 2023, 11:02:43 PM
Reply #10

Dolbah

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When testing TP11 and TP12, my meter starts meassuring around 0.5 VAC and the meter starts decreasing in value unbtil it hits 0 VAC. Thishappen both with Threshold on -15 and +15
Here we are measuring DC voltage, not AC.

You always have the option to send us your your unit for a check. In this case, please contact us here.
My bad, these values checks out on VDC too.
Meaning the unit is passing all tests, and there is no real reason it should not work as excpected?

Not to keen on spending $$ sending the unit to France. If we can't fix this one remotley, it will sadly be discarded and put in a dusty corner. To bad, as i really really like this one.
I've buildt over 20 pc. of 500 units from various brands, only the SS TS 500 Tape module has been the one i/we gave up on.

As i said, this one worked well until i adjusted T1, T2, T3 and T4 to get it back in perfect stereo balance, then it started fritzing. Could it be that one of the trimmers have gone bad?

I tried adjusting T3 with a sine going through, and when my screwdriver touched the metal trimmerhead the audio slightly changed volume. I tried wiggelig a little and at one point the wiggeling actualy seemed to improve the issue. Both channeles now responded almost the same when adjusting threshold.
So i desoldered the T3 and inspected it. Looked fine!... and then resoldered it again = the main issue still persists, but the audio is now stable when my screwdriver hits the trimmer, and wiggeling does not help. This is all to confusing. Could it be that the trimmer is gone bad on T3? This is the trimmer i adjustet very first in the process.

I made a new video showing the issue in stereo:

https://www.dropbox.com/s/aa10nuih14c7ysq/IMG_6421.MOV?dl=0
« Last Edit: December 18, 2023, 11:04:17 PM by Dolbah »

December 19, 2023, 05:53:39 PM
Reply #11

JPK

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My bad, these values checks out on VDC too.
Meaning the unit is passing all tests, and there is no real reason it should not work as excpected?


I don't think so:
TP11 goes from 0VDC to -3.5VDC
TP12 goes from 0VDC to +3.5VDC
This should happen when the threshold changes from +15 to -15. Is that the case?

Could it be that the trimmer is gone bad on T3?
Possible. You can check it by measuring the resistance between the 2 side pins. It should vary from 0 to 200 ohms (remove U22 before checking)3
JPK

December 19, 2023, 07:08:01 PM
Reply #12

Dolbah

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My bad, these values checks out on VDC too.
Meaning the unit is passing all tests, and there is no real reason it should not work as excpected?


I don't think so:
TP11 goes from 0VDC to -3.5VDC
TP12 goes from 0VDC to +3.5VDC
This should happen when the threshold changes from +15 to -15. Is that the case?

Could it be that the trimmer is gone bad on T3?
Possible. You can check it by measuring the resistance between the 2 side pins. It should vary from 0 to 200 ohms (remove U22 before checking)3


Ok, i will check.

But could you give a feedback on what you see in the video i linked?

Does the behaviour of channel 1 tell you anything about what this can be?  Threshold mutes the audio in a very steep fashion, instad of compressing it. 
This also happens when only board 1 is active, is that normal?  If not, the chances are slim that T3 is the culoprit, as is it not even installed in the unit when testing board 1 alone.

(Edit: checked all trimmers, and they respond ok)
« Last Edit: December 19, 2023, 10:26:38 PM by Dolbah »

December 20, 2023, 05:32:09 PM
Reply #13

JPK

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Does the behaviour of channel 1 tell you anything about what this can be?
Sorry, no.

Threshold mutes the audio in a very steep fashion, instad of compressing it.
The signal on TP12 is the side chain signal which  directly controls the VCA's. So we need to know what is going on TP11 and TP12.
JPK

December 20, 2023, 09:09:38 PM
Reply #14

Dolbah

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Does the behaviour of channel 1 tell you anything about what this can be?
Sorry, no.

Threshold mutes the audio in a very steep fashion, instad of compressing it.
The signal on TP12 is the side chain signal which  directly controls the VCA's. So we need to know what is going on TP11 and TP12.
TP11 and TP12 works as they should as described in 1.5
Sorry if i was not clear enough on this. After measuring in VDC instead of wrongly setting my DDM to VAC, they checked out.

So as i said, the unit passes all tests on the "In case your CP4500 doesn't work as expected" list :)

1.5
Input 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
• TP5 goes from +0.35VDC to a negative value
• TP11 goes from 0VDC to -3.5VDC
• TP12 goes from 0VDC to +3.5VDC

December 21, 2023, 05:01:03 PM
Reply #15

JPK

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I have added a value on 2 of the tests:
Can you check them:
Step 1.5
When Threshold goes from +15 to -15, TP5 goes from +0.35VDC to -1.2VDC

Step 2.4
DC voltage (VDC) on TP10=-1.2VDC
JPK

December 21, 2023, 07:38:46 PM
Reply #16

Dolbah

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I have added a value on 2 of the tests:
Can you check them:
Step 1.5
When Threshold goes from +15 to -15, TP5 goes from +0.35VDC to -1.2VDC

Step 2.4
DC voltage (VDC) on TP10=-1.2VDC

1.5 = 0.35 -> -1.178
2.4= 0.36 -> -1.14

But, suddenly board 1 is working now, It has been laying still since last time i measured. Weird.  The only thing "out of the ordinary" that happened, was that i touched one of the other testpins on board 2 while testing 2.4. This made the needle go all the way down to the right. After this it is ok!

Sadly no real explenation on the issue, but as with all lucky accidents i've now managed to wreck the T2 trimmer. It does simply not work anymore. I must have overturned it to maye times. New one is allready ordered :)

December 23, 2023, 11:08:22 AM
Reply #17

JPK

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Usual causes for this kind of issues:
- Bad solder joint,
- Forgotten solder joint,
- Components leads cut not short enough and touching something they shouldn't,
- Conductive solder flux creating unwanted connections on the PCB.
JPK

December 27, 2023, 05:04:06 PM
Reply #18

Dolbah

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Usual causes for this kind of issues:
- Bad solder joint,
- Forgotten solder joint,
- Components leads cut not short enough and touching something they shouldn't,
- Conductive solder flux creating unwanted connections on the PCB.
So i have gotten a new T2 now, but still one issue remains.

Firstly:

- Bad solder joint, = reflowed all now
- Forgotten solder joint = No
- Components leads cut not short enough and touching something they shouldn't = Not an issue
- Conductive solder flux creating unwanted connections on the PCB. = both boards Cleaned with isopropanol



Board 1 is now ok, but i am left with one issue i also had at the start of this thread, which i think is the cause of the unbalance.
With 3 VAC measured when bypassed, i can only get around 2.7 VAC max with IN button activated and T2 is turned all the way up to 1K

Tests come out ok, except this:

2.3
input signal = 3VAC
Threshold on +15
Makeup on 0
Signal level (VAC) on

• TP6=1.5VAC,
TP7=1.3VAC
• TP8=1.5VAC,
• TP9=0.06VAC

This leaves me with the original unbalance i had.  Any idea about this?
« Last Edit: December 28, 2023, 01:34:44 AM by Dolbah »

December 29, 2023, 01:39:26 PM
Reply #19

Dolbah

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I realized that the issue with not being able to trim the channel to correct volt has moved from  board 1 to board 2 since we started. I have also moved all VCAs form 1  to 2, so i took a new test switching out all VCAs from 1 to 2 again, and i found out that it is one of the That 2180A VCAs that are malfunctioning.

I'll send you an email to get this sorted.

« Last Edit: December 29, 2023, 01:45:16 PM by Dolbah »

January 19, 2024, 10:06:01 PM
Reply #20

Dolbah

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The new VCA chips fixed the issue. Thanks JPK 🙏🏻

January 20, 2024, 08:44:19 AM
Reply #21

JPK

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