Replaced all pots, now amp volume seems quite a bit lower

[professormudd]

Greetings,

I am trying to get my D-Lite Blue Monkey 44 in dancing shape, and I am so close....

I replaced all of the pots with CTS brand potentiometers from Amplified Parts, as the ones that came with the kit had been pretty hammered and would stick while rotating. There was also no shielded cable on the drive or level pots, so I corrected that. The shielded cable I went with was what I had on hand, Bill Lawrence Low Capacitance Cable.

The amp sounds beautiful, but it really does sound like it is about half the volume I would expect. Prior to changing the pots, it felt louder as well but I did not measure with a decibel reader or anything.

I compared it to a 5e3 with a NFB engaged, both at 12 o'clock on all controls, and the 5e3 was way louder.

I am looking for any advice as to how to locate and kill whatever is leeching volume. For reference I am attaching the layout.

[pompeiisneaks]

We'd need to see photos of the amp. The layout, I believe is one that's known to basically be good, so showing a layout of a known good amp won't help us understand why yours isn't working. I'd wager it's more likely a wiring or soldering error is related to this, but that's just a first guess. I don't have enough information to know for sure.

For reference here's one thread on people discussing these amps. https://ampgarage.com/forum/viewtopic.php?t=7830

They're basically based off the bluesmaster from the quick read I got on the above thread, but I didn't read the whole 3 page thread. Not sure if yours is exactly the same amp, but I believe it's by the same vendor.

~Phil

[professormudd]

We'd need to see photos of the amp. The layout, I believe is one that's known to basically be good, so showing a layout of a known good amp won't help us understand why yours isn't working. I'd wager it's more likely a wiring or soldering error is related to this, but that's just a first guess. I don't have enough information to know for sure.

For reference here's one thread on people discussing these amps. https://ampgarage.com/forum/viewtopic.php?t=7830

They're basically based off the bluesmaster from the quick read I got on the above thread, but I didn't read the whole 3 page thread. Not sure if yours is exactly the same amp, but I believe it's by the same vendor.

~Phil

Okay. Here are some photos. I can take better photos of specific locations. If you need me to.

[professormudd]

I suppose I just assumed there might be typical causes and someone might say, "check where x connects to y".

My apologies for irrelevant information.

[brewdude]

Shot in the dark...
Do the pots you used have the same taper?
If you turn the amp volume knobs up, does it sound “correct”?

[professormudd]

Shot in the dark...
Do the pots you used have the same taper?
If you turn the amp volume knobs up, does it sound “correct”?

The sweeps feel/sound right. I followed the tapers from the layout. I have linear on some, audio/log on others.

[professormudd]

I was concerned that I might have buggered up the tube sockets from pushing them in and pulling them out, so I tried different combinations of sockets (keeping in mind to keep at least 1 tube per side of the OT) with no change.

I pulled out an old fender Champ25 I had lying around to yank the tubes out in case one of the JJ 6L6 I have is buggered up. SCORE! Set of USSR Sovtek 6L6GC. I placed them in the blue monkey. It didn't fix the volume issue, but I think the tubes are a little neater, so I am keeping them in.

So, no progress other than ruling out tubes/sockets.

I suppose I expect a 44 watt tube amp to be rather alarming when all the volume is at 12 o'clock and I am sitting 3 feet from a 4x12 cab full of Vintage 30s. I could still hear people talking, though. It definitely wouldn't keep up with a band.

I can try swapping out all the 12ax7s next and see if it helps, unless there is an easier way to determine if a 12ax7 is not doing its job. I do know the filaments are all working, the tubes are all warm.

[drew]

Do you have another amp with a preamp out that you could plug into the effects loop return?

[pompeiisneaks]

I'd think that if they were working before the swap out of pots they're still working. I'd check that there's no shorts to ground anywhere on the signal path or fairly low resistance to ground on any of the pots other than the ground connection. I didn't see any specifically obvious problems in the pictures. make sure all pots have good earth connections as well.

~Phil

[ChopSauce]

Yes, it's easier to short to ground when using shielded cable - since if I understand well you did not only replace the pots but also rewire them.

[professormudd]

Do you have another amp with a preamp out that you could plug into the effects loop return?

I will try that today and report back.

I'd think that if they were working before the swap out of pots they're still working. I'd check that there's no shorts to ground anywhere on the signal path or fairly low resistance to ground on any of the pots other than the ground connection. I didn't see any specifically obvious problems in the pictures. make sure all pots have good earth connections as well.

~Phil

Yes, it's easier to short to ground when using shielded cable - since if I understand well you did not only replace the pots but also rewire them.

Yes, I replaced hookup wire with shielded wire on the drive and level pots. I will keep checking around all of the connections. I think I am getting it narrowed down to the OD channel, since the volume seems to drop with OD engaged and it sounds kinda muddy.

Man, what I wouldn't give to have one of you be my neighbor and COVID to be over. You would be swimming in all the beer I would be buying you.

[brewdude]

Is there an OD trim pot?

[professormudd]

Is there an OD trim pot?

Yes. I can hear differences when I change it. And I just used a multimeter to verify that the resistance is approximately what it should be based on the position.

[professormudd]

New finding/sign/symptom.

When OD and PAB are both engaged, and only when BOTH are engaged, if I turn the input volume to 12 is suddenly cuts to squealing. I will double check to make sure I didn't mess up that pot.

[pompeiisneaks]

I ended up with some oscillations in OD due to the leads being to close between the first stage and the second, I ended up swapping the triode sides on V1 so that V1's first input was farther away from the V2 OD tube, This could be similar behavior you weren't getting when it wasn't working as optimally? Try at a minimum carefully putting some kind of grounded shield between V1/V2 and see if that does anything. Just don't touch the anodes or you can create a disaster.

~Phil