Recent Posts

91

Crack / Re: Bottlehead Crack Channel Imbalance Issue

« Last post by Paul Joppa on April 28, 2024, 12:35:51 PM »

Well then, it's likely to be the 6080.

The attenuation of a pot is the ratio of two resistance measurements, wiper-to-ground divided by hot-to-ground. You seem to have measured wiper-to-hot. Assuming 7:30 is all the way off, then it represents hot-to-ground, so subtract your measurement from the 7:30 measurement to get wiper-to-ground, then divide that by the 7:30 value.

Example: left channel 9:00 measured 82.55K; subtract that from 86.2K to get 4.65K wiper-to-ground. Divide that by 86.2K to get 0.0423.

Do the same on the right channel to get 0.041.

Those are the attenuation factors at the 9:00 position. Comparing the two channels, the left is 4% louder at the 9:00 setting. I did the rest and got left 7% louder at 12:00, and 7% quieter at 2:00. That kind of variation is typical for ordinary pots.

92

Crack / Re: Bottlehead Crack Channel Imbalance Issue

« Last post by afrank on April 28, 2024, 10:26:30 AM »

Paul, thank you for the input, it was helpful, here is what I was able to do:

I have a friend who also likes playing around with amps and happened to have two old 12U7 tubes (I think from a guitar amp?), we tried both of them, and the imbalance persisted.  :'(

Next, I tested the pot at several different positions, and here are the resulting resistances (in OHMs):

Vol.  pos.   Left          Right
100%          1.4               1.3
2:00  pos.   54.82K       58.45K
12:00 pos.  73.8K          83.3K
9:00 pos:    82.55K        92.2K
7:30 pos:    86.2K          96.1K


Based on the above, it looks like the issue may actually be with the pot (the right channel has 7-13% higher resistance than the left), I assume this is likely the culprit of the channel imbalance? Is this a reasonable assumption?

93

General Discussion / MY SOLDERING IRON HAS BEEN AT ROOM TEMP FOR TO LONG

« Last post by Thermioniclife on April 28, 2024, 08:13:30 AM »

Hey all, has anyone built a cool kit audio or not lately? my iron has not been used for a while, I need to build something or risk going crazy!

94

Crack / Re: Bottlehead Crack Channel Imbalance Issue

« Last post by Paul Joppa on April 27, 2024, 03:48:28 PM »

Hi Paul, thanks for the quick response.

A note on how I arrived at the 9% level, using the windows left / right channel balance, when the left channel is at 89-91% and the right channel is at 100% the amp sounds balanced.

There is a bit of unbalance that goes in the other direction at very low volume levels (the right channel is much closer to the left) but much past the 7 or 8 o'clock position the imbalance increases to and remains constant as it is turned up. I have noticed low level imbalance issues on many amps, which goes away once the volume level is turned up to a certain amount. This seems to be a different issue.

Is there any way to identify if this is a pot issue or tube issue?

Measuring the effect of pot position, as you have done, is a pretty good test. Looks like it's a tube; most likely the 12AU7.

I did try turning up the volume up all the way (with the amp OFF) and measured the resistance through both channels of the pot, and it was equal. Not sure if this is an accurate way to determine if this could be causing the in balance.

No, you need to measure all three pins of each channel to determine balance.

95

Crack / Re: Bottlehead Crack Channel Imbalance Issue

« Last post by afrank on April 27, 2024, 02:18:52 PM »

Hi Paul, thanks for the quick response.

A note on how I arrived at the 9% level, using the windows left / right channel balance, when the left channel is at 89-91% and the right channel is at 100% the amp sounds balanced.

There is a bit of unbalance that goes in the other direction at very low volume levels (the right channel is much closer to the left) but much past the 7 or 8 o'clock position the imbalance increases to and remains constant as it is turned up. I have noticed low level imbalance issues on many amps, which goes away once the volume level is turned up to a certain amount. This seems to be a different issue.

Is there any way to identify if this is a pot issue or tube issue?

I did try turning up the volume up all the way (with the amp OFF) and measured the resistance through both channels of the pot, and it was equal. Not sure if this is an accurate way to determine if this could be causing the in balance.

96

Crack / Re: Bottlehead Crack Channel Imbalance Issue

« Last post by Paul Joppa on April 27, 2024, 01:57:44 PM »

A 9% difference is less than a decibel. The two likeliest causes of small differences like this are the volume control and the tubes; both are +/- 20% parts.

Volume potentiometers are most unbalanced at lower settings - at what setting did you determine the 9% difference?

Better balanced pots are available. Better balanced tubes are also available from most dealers. At added cost in both cases, of course  :^)

97

Crack / Bottlehead Crack Channel Imbalance Issue

« Last post by afrank on April 27, 2024, 11:07:33 AM »

Hello!

As the title says, I have been having an issue with my right channel audio being about 9% quieter than the left channel.

I have carefully inspected all of my wiring and soldering, and although it would be difficult to rule it out completely, I do not believe the issue is related to a cold solder after multiple careful inspections by myself and several friends.

I am wondering if this issue could be due to a tube related issue?

Here are my resistance checks:

1. *
2. *
3. 0
4. *
5. *
6. 0
7. 2.93K
8. 0
9. 2.95K
10. 0
12. 0
13. *
14. 0
20. 0
22. 0
B3. 2.93K
B6. 2.95K
RCA L: 89.0K
RCA R: 99.8K
Ground: 0

And here are my voltage checks:

1. 80.9V
2. 173.4V
3. 0
4. 173.0V
5. 84.3V
6. 0
7. 107.8V
8. 0
9. 108.6V
10. 0

Any thoughts on what the issue might be would be greatly appreciated. Happy to provide additional measurements / data if this would help.

Best,

Andrew

98

MonAmour / Re: New 2A3 recommendations

« Last post by Larpy on April 27, 2024, 10:21:07 AM »

Do you mean the Mon Amour amps?  I haven't heard them myself but the Electro-Harmonix Gold 2A3s have received good reviews.  The EMLs are viewed as excellent, though they cost quite a bit more than the EHs.

In the U.S., you can still find NOS 2A3s for around $150-$200.

99

Moreplay / Re: Moreplay add ons - were there still any upgrades planned?

« Last post by denti alligator on April 27, 2024, 05:00:21 AM »

Any updates on this project?

100

S.E.X. Kit / Re: Buzzing sound

« Last post by JuhyunKim on April 26, 2024, 09:50:52 PM »

I sent pictures to you

I did measurements again and terminal 16 measured about 1m ohm , t32 is 109 ohm t31 is 109 ohm, t30 is 108 ohm, h3 is 1525 ohm, h4 is 109 ohm, h5 is 109 ohm, h6 is 1526 ohm, and h7 is 109 ohm.