Very low volume and low buzzing sound on left channel. [Resolved]

[elgringo81]

I just installed 2x Auricap OX 12uF 200v capacitors in my Mainline.
The installation went fine and both channels had the same volume and no issues.

After further reading on this forum, I discovered that the Auricap on the C side was turning the wrong way,
so I turned it around so the inner-foil (Red) is now soldered to 25U and outer-foil (Black) to 30U.

After I did this, my problems started.

Here are some of my observations
All 8 LEDs turn on.
I did the basic voltage diagnostics and the readings seem within range. I will do it again and post it here if needed.
I have re-flowed the joints on the C site but that has not solved the problem.


Here are few things I have tried so far.

I tried swapping the Auricap with the stock Dayton 10uF but that gives me the same results so I think/hope the Auricap on C site is fine.
The volume on Left channel is very low and there is a faint buzzing sound coming through.
This happens on both 4-Pin XLR and TRS are affected.
Both Source 1 and 2 are affected
I can swap the RCA around but always have problems with left channel
I have swapped 6C45s but problem remains in left channel
Tried swapping out the 12AU7 for another one I have in my Crack kit but that did not resolve the problem.
There is no problem with Biasing the 6C45s. Both are steady at 145v.

I hope I am overseeing something simple
There has not been any smoke or pops.


Thanks in advance.

[Paul Birkeland]

It could help to post some photos.  Otherwise another strategy for debugging involves playing a 60Hz tone into the amp at full volume, then taking some AC voltage measurements at various places to compare between channels.  Eventually you'll end up with mismatched AC voltages and that will let you know where to focus.

If you are triple sure your DC voltages are within range, the first thing to check is the AC voltage coming out of the attenuator (the lower lugs on the coarse switch) with the coarse and fine switches up all the way and a 60Hz tone playing into the Mainline (you can use your phone for this, just crank it all the way up).  It doesn't have to be powered on for this step. 

-PB

[elgringo81]

I have now re-flowed the lower lugs on both course and fine and also the lugs on TRS and XLR.
The the volume control has issues. the volume jumps to max volume when I rotate either course or fine.

- Regarding the AC measurements, I was not able to get any reading on the lower lugs on the coarse switch. I played a 60Hz tone and turned off the amp V~ was always 0. I must be doing something wrong there.

I have made new DC measurements. Please let me know if I should need more.
+275vDC = 266v
+6.3vDC = 6,27v
IA on the A = 267v
IA on the B = 265v
IB on the A = 219v
IB on the B = 217v
OB on the A = 145v
OB on the B = 145v
Breg Regulator Board A = 219v
Breg Regulator Board B = 218v
-reg Regulator Board A = 0v
-reg Regulator Board B = 0v
Kreg Regulator Board A = 11,30v
Kreg Regulator Board B = 10,55v

[elgringo81]

Here are some photos. Let me know if you want more specific ones.

[elgringo81]

2/3

[elgringo81]

I am sorry for the picture quality. I will be able to take better ones tomorrow if needed.

[Paul Birkeland]

The the volume control has issues. the volume jumps to max volume when I rotate either course or fine.

Is this on both channels, or just the working channel?  This would tend to suggest an open ground on the coarse attenuator.

- Regarding the AC measurements, I was not able to get any reading on the lower lugs on the coarse switch. I played a 60Hz tone and turned off the amp V~ was always 0. I must be doing something wrong there.

What is the lowest range for AC voltage on your meter?  Your phone will probably put out 200-300mV, so if your meter only has a 200V and 500V setting for AC voltage, these tests won't be possible.

I have made new DC measurements. Please let me know if I should need more.
+275vDC = 266v
+6.3vDC = 6,27v
IA on the A = 267v
IA on the B = 265v
IB on the A = 219v
IB on the B = 217v
OB on the A = 145v
OB on the B = 145v
Breg Regulator Board A = 219v
Breg Regulator Board B = 218v
-reg Regulator Board A = 0v
-reg Regulator Board B = 0v
Kreg Regulator Board A = 11,30v
Kreg Regulator Board B = 10,55v

I think you have an issue with the attenuator that was exacerbated during the installation of your Auricaps.

[elgringo81]

That makes sense.

I will look into it tomorrow and report back.

Thank you for your time.

[elgringo81]

I have re-flowed the course and fine switches and I am back to the original problem.

Volume works fine on the right channel.
Left channel is almost silent, with a faint buzz that does not go up with volume.

It seems not impossible for be to get a resistance read on T1 and T5. it just shows *
I will keep on working on it and report back if there are any changes.

any suggestions are very appreciated

[Paul Birkeland]

I gave you a path to take by measuring AC voltages.  Perhaps it would help if you let us know what multimeter you have?

I generally do not recommend resoldering the connections on the switches themselves, as those switch lugs don't take much heat to solder properly.

[elgringo81]

When I play the 60Hz tone on my iPhone 7 at full volume,
The mainline is connected to power and turned off.
Both Course and Fine switches are set to 0dB

The lower lugs on the course switch give me (White)>97mVac and (Red)>98mVac
The meter is on Auto V~ shows 0,097 and 0,098

I also measured the RCA socket where the source it connected.
L= 154mVac and  Right = 155mVac
The meter is on Auto V~ shows 0,154 and 0,155


I have 2x budget multi meters.
Branford MS8321D
Neoteck Digital Multimeter Pocket Multi Tester 2000.

In case this is relevant.

Resistance Check
15 = 210ohm
25 = * ( Think this one should be between 210-220ohm)
The capacitor I was working on when the problem started is connected to 25 and 30
I did put the Dayton back in between 25 and 30, but that did not resolve the problem.

[elgringo81]

I have solved the problem.

The Black wire from OT-3 on C side towards 26U was broken.
It was hard to see it because it still hangs together on the sleeve but the wire was broken apart.

I hope that its OK that the cable I used for replacement is a little bit thicker.

Thanks for you help.