Volume problem

[crgolfer]

I am having difficulty solving a volume balance problem.  I am getting very little volume out of one channel.  The resistance and voltage tests were fine except I was getting 202 out of the transformers instead of 213 and 174 where the manual says 186.  As it is the same for both channels this is probably not a problem.

All the diodes light up on the C4s boards and I have resoldered all the connections on the bad side and redid all the balance and volume connections but the problem remains.  Also I have moved the tubes around so they seem fine.

Anyone have any suggestions?

 

[Paul Joppa]

The voltages you quoted as different are upstream of the regulators, so it makes no difference to the audio part of the circuit. They will vary with your power line voltage - that's why there are regulators, to remove that variability.

Since all the other voltages are correct, we can conclude the tubes and the amplifier circuits are working correctly. Therefor the problem is most likely in the input or output connections.

Methodical is the way to go IMHO. Start at the beginning - it the problem apparent on all three inputs? If so then the selector switch is not the problem.

Are the inputs ultimately connected to the 300B grid? Measure resistance from the center pin of the RCA input jack to the 300B pin 3 (the grid). With the volume at maximum and the balance centered, it should be about 20K (20,000) ohms.

Then we can check operation of the controls. Leaving the measurement connected (RCA jack center pin to tube pin 3; using clip leads to the meter will make this easier!) rotate the balance control. You should see a smooth variation from around 200 ohm at one end to about 25K at the other end.

Then re-center the balance control and vary the level control. The resistance should increase from 20K to 120K as the volume control is turned down.

 

[Doc B]

Didn't someone else have this problem recently? Maybe they can relate how they worked it out.

 

[crgolfer]

I just used my signal generator to track down the problem.  The readings that I got were, C D selector switch 5v, Balance pot black red 5v and on the volume pot for the black red output 5V ( this is the good channel).  On the other channel A B 5v, balance pot white black 5V, volume pot for white black 0V ( maybe a few millivolts but my multimeter is not that accurate).

The problem appears to be that there is no output coming out of the volume pot on the black white wires. 

The problem appears on all 3 inputs and I switched the output connections off the 475 Kohm resistors and the problem switched channels.
So I have concluded that the problem lies is the right output wiring which gets the white wire from the volume pot.

 

[Paul Birkeland]

Feel free to toss up a picture of the volume/balance pot wiring, I would suspect a miswire is shorting signal to ground.

 

[crgolfer]

The voltages you quoted as different are upstream of the regulators, so it makes no difference to the audio part of the circuit. They will vary with your power line voltage - that's why there are regulators, to remove that variability.

Since all the other voltages are correct, we can conclude the tubes and the amplifier circuits are working correctly. Therefor the problem is most likely in the input or output connections.

Methodical is the way to go IMHO. Start at the beginning - it the problem apparent on all three inputs? If so then the selector switch is not the problem.

Are the inputs ultimately connected to the 300B grid? Measure resistance from the center pin of the RCA input jack to the 300B pin 3 (the grid). With the volume at maximum and the balance centered, it should be about 20K (20,000) ohms.


I Get 19k on the good channel and 90K on the bad

Then we can check operation of the controls. Leaving the measurement connected (RCA jack center pin to tube pin 3; using clip leads to the meter will make this easier!) rotate the balance control. You should see a smooth variation from around 200 ohm at one end to about 25K at the other end.

Good channel 0-23K, bad channel 18-100K

Then re-center the balance control and vary the level control. The resistance should increase from 20K to 120K as the volume control is turned down.

Good channel 20-50K, bad channel 14-100K

 

[Paul Birkeland]

Are you 100% sure that the balance and volume pots are in the correct holes?

 

[crgolfer]

I just checked and they are in the correct holes.

 

[crgolfer]

Since I have the Beequiet kit, I am thinking of installing it now rather than trouble shoot a problem with the balance/volume controls that were going to be replaced anyway.  Does this sound reasonable or would it be best to solve the volume problem first?

 

[Paul Birkeland]

I would solve the volume problem first.  Based on your information, there is certainly a miswire in the volume/balance control area.

 

[crgolfer]

I have done some further tests (balance middle/volume max) and found that measuring from one input RCAs I get 17K and 90K measured to A2 and nothing to B2.  It looks like all of the input is going into the A tube and nothing to the B tube.  I have checked the selector switch connections and they look right

 

[Grainger49]

If you go directly to the Bee Quiet you will probably carry over the wire that is misplaced on the stock balance pot.

 

[Paul Joppa]

I am pretty sure there's a wiring error on the pots. It's confusing - the balance pot is wired symmetrically (the two elements are grounded at opposite terminals) and the volume pot connections are identical (the same end is grounded). There may be a bad solder connection as well - I have not come up yet with a single-error theory that explains all the measurements, but I suspect that at least the volume pot is wired backwards (left for right terminals).

 

[crgolfer]

I just got it working.  I disconnected everything from the volume pot and confirmed that both pots were working properly and connected everything as before.  I then confirmed that I was getting consistent readings with the balance and volume controls.  When I first turned the Beepre the controls were acting funny as the volume seemed affect the balance and vs versa.  After a couple of minutes they were acting properly, I guess that there was some issue with capacitors charging up. 

My problem must have been caused by a poor solder connection (even though this was the first fix that I tried by reheating all connections) as I haven't changed any of the wiring.