Tube Amp Buzzing Noise Varying with Volume and Changes Channels

[Lavane]

There should be a ground coming from the PCB to the chassis ground that's connected to the earth ground of the power socket. It looks like it is?
A black wire coming from the PCB connected to the green ground wire coming from the earth ground on the power socket. Both should be grounded the chassis.

 

[Classified]

Hopefully someone will chime in with how this was modified to be able to use as a headphone amp. Did you buy it from the person that built it?
If so could you ask them what mods they made?
Have you contacted the seller about the issue your having with it?

Yep I reached out to the seller who built it originally I'll update this thread if I hear back

 

[Lavane]

The 6N1's are the Russian and Chinese version of the 6922 family of tubes.
I'm not sure the 6H6pi is a good sub though. I would expect all four tubes would be 6922 types. I haven't looked, but 6N1's may not be pin campatable with 6922's. I know 6N2's don't have the same pinout as a 12AX7.
It would be good to know if the board is meant to use 6N1's instead of 6922's. Maybe there are jumpers on the board that let you select between the two?

 

[Classified]

The 6N1's are the Russian and Chinese version of the 6922 family of tubes.
I'm not sure the 6H6pi is a good sub though. I would expect all four tubes would be 6922 types. I haven't looked, but 6N1's may not be pin campatable with 6922's. I know 6N2's don't have the same pinout as a 12AX7.
It would be good to know if the board is meant to use 6N1's instead of 6922's. Maybe there are jumpers on the board that let you select between the two?

They originally came with these, replaced with a new set of the exact same ones matched and balanced and didnt notice any difference

 

[Classified]

The 6N1's are the Russian and Chinese version of the 6922 family of tubes.
I'm not sure the 6H6pi is a good sub though. I would expect all four tubes would be 6922 types. I haven't looked, but 6N1's may not be pin campatable with 6922's. I know 6N2's don't have the same pinout as a 12AX7.
It would be good to know if the board is meant to use 6N1's instead of 6922's. Maybe there are jumpers on the board that let you select between the two?

Took some more measurements with the multimeter, the pot does appear to be properly grounded. From PCB ground to the grounds on the pot I'm getting consistently 1-2 ohms. Checked the pot body and as far as I can tell it's grounded too (getting 0 ohms resistance). I'm wondering to your point earlier if there is a ground loop, could the wiper terminal be on a ground loop which causes the buzzing to change as the resistance in the wiper terminal increases? If so how would I go about testing this or look for other ground loops?

 

[Lavane]

I don't think I've ever had a ground loop cause a buzzing. It's always been a hum. I've had 60hz and 120hz hum.
Anyway you can post a short video of that noise?
Also, have you tried using the first set of tubes agsin that you changed out?
I have had bad tubes that hummed, popped, crackled, and made other weird noises. I had one signal tube that tested fine, but when used in the first gain stage hummed. Used as a splitter it was quiet.
Hopefully the builder will get back to you with some info on his build.

 

[Classified]

I don't think I've ever had a ground loop cause a buzzing. It's always been a hum. I've had 60hz and 120hz hum.
Anyway you can post a short video of that noise?
Also, have you tried using the first set of tubes agsin that you changed out?
I have had bad tubes that hummed, popped, crackled, and made other weird noises. I had one signal tube that tested fine, but when used in the first gain stage hummed. Used as a splitter it was quiet.
Hopefully the builder will get back to you with some info on his build.

So weird development, putting the original tubes back in introduced a much louder buzz with an accompanying hum that is not present with the other new set of tubes. Here's the audio of the original tubes, you may have to turn it up a bit. You can hear the buzz that to my ears sounds pretty dead on to the other tubes. The other new tubes buzz was a little too quiet for my mic to pic up but definitely audible

 

[Lavane]

That doesn't sound like a hum to me.
try taking out just the first two left and right tubes closest to where the volume control connects to the board and see if it still does it.

 

[Classified]

That doesn't sound like a hum to me.
try taking out just the first two left and right tubes closest to where the volume control connects to the board and see if it still does it.

It was a quieter hum but the buzz was still there.

Just to clarify, take these two out and try it as is? That wont damage the amp/headphones?

 

[Lavane]

Ya those two. It won't hurt anything.
Put them back and take the other two out now.

 

[Classified]

Ya those two. It won't hurt anything.
Put them back and take the other two out now.

Taking the front two out caused a very loud buzz (slightly deeper tone) in both channels louder in the right that increased in volume until I had to unplug the headphones because it got too loud

 

[gadget73]

I'm wondering what the heater setup is here. Maybe it lacks a ground reference or something and thats causing issues. May (probably) also need some heater elevation. Akido circuits have an "upper" tube where the cathode is considerably above ground potential. There is a limit to heater-cathode voltage difference in tubes, and pushing it can cause leakage and hum.

the usual way to provide that is a simple voltage divider off B+ and the heater circuit is tied to that.

 

[Classified]

Ya those two. It won't hurt anything.
Put them back and take the other two out now.

Sorry got stuck in a meeting only got to test the front two, just tested both sets.

Taking out the front two(just using back tall 6n6P): super loud buzzing that increased in volume and I had to quick kill the amp before it felt like it was going to blow up my headphones
Taking out the back two (just using front short 6nIP-EB): absolutely silent.

Do you think this narrows the issue down to the tall preamp tubes? Or something on that circuit?

 

[Lavane]

Something at that end maybe. Can it use just the 6N1's in all four sockets,
or does it have to have the 6H6pi's in the last two sockets, do you know?

 

[Classified]

Something at that end maybe. Can it use just the 6N1's in all four sockets,
or does it have to have the 6H6pi's in the last two sockets, do you know?

Unfortunately I don't know what the requirement is, I can ask the seller but I haven't heard back yet

 

[Lavane]

It would be nice to know more about that board. 6N1's can be used as a sub for the 6922/ECC88/6DJ8, etc., but the 6N1 pulls more heater current than the 6922. So the power supply needs to be able to handle that extra current. The 6H6 looks like it can replace 6N1's and 6922's in some circuit designs. So you should be able to use four 6N1's if the 6.3v heater supply can produce enough current. If the board was designed to use 6922's, 6JD8's and ECC88's, the 6N1 and 6H6's may not be the best match.

 

[Classified]

It would be nice to know more about that board. 6N1's can be used as a sub for the 6922/ECC88/6DJ8, etc., but the 6N1 pulls more heater current than the 6922. So the power supply needs to be able to handle that extra current. The 6H6 looks like it can replace 6N1's and 6922's in some circuit designs. So you should be able to use four 6N1's if the 6.3v heater supply can produce enough current. If the board was designed to use 6922's, 6JD8's and ECC88's, the 6N1 and 6H6's may not be the best match.

Shoot, so just to confirm it's not safe to swap the back two 6922 with the extra 6N1s I have without knowing more about the board? Or is it safe to plug them in and test it and the results will tell us if it works?

 

[Lavane]

It should be ok to use 6N1's in all four positions. It'll draw less heater current too. Both the 6N1 and 6H6 are pin compatible. Just doing some searches at DIY audio and a few other sites, there were posts stating the 6H6 especially may not be a good match for the 6N1or 6922 in some circuits.
No responce from the builder?

 

[Classified]

It should be ok to use 6N1's in all four positions. It'll draw less heater current too. Both the 6N1 and 6H6 are pin compatible. Just doing some searches at DIY audio and a few other sites, there were posts stating the 6H6 especially may not be a good match for the 6N1or 6922 in some circuits.
No responce from the builder?

Thanks! I tried that and unfortunately it's the same buzzing issue, so it's narrowed down as something in that chain/circuitry using the back two tubes instead of the tubes themselves. I will say 4 6N1s sound much "punchier" than 2 6N1s and 2 6922s, very fun. I may break it open again and reflow all the solder going immediately to and from those back tubes, if that doesn't work I may be SOL without the board schematics

 

[Lavane]

Thanks! I tried that and unfortunately it's the same buzzing issue, so it's narrowed down as something in that chain/circuitry using the back two tubes instead of the tubes themselves. I will say 4 6N1s sound much "punchier" than 2 6N1s and 2 6922s, very fun. I may break it open again and reflow all the solder going immediately to and from those back tubes, if that doesn't work I may be SOL without the board schematics

I couldn't find a match for that board from Glass Audio. Maybe an older version?, or its made by someone else. The voltage regulator circuit using that tube regulator looks like its from Glass Audio though. There may be some printing on the other side of that 4 tube PCB that may identify it.
Like a brand and version number.