I tried swapping tubes. I first changed the phase inverter 12AX7 tube to a known good tube. Since I didn’t have a set of 6550 tubes on hand, I briefly tried a set of known good 6L6GC tubes to rule out tubes as the cause of the hum.
Tried in a different outlet with a different power cable.
Tried a modeler into the line input. I can hear the volume and noise fluctuate a bit in this scenario, but the PS-100 still gets loud and other than the noise works fine.
Adjusting presence, depth or the loadbox switches has no effect on hum.
Changing channels has no effect on hum.
Adjusting volume DOES have an effect on hum.
What the hum sounds like:
At the end of the clip I turn the channel volume up and down.
I can’t see any physical damage to any part, except for a gray resistor right below the blue R307 resistor in the output PCB where the jacks are mounted. It looks slightly charred in the middle. I can’t see the label of this part.
Can this part be the cause of the hum? What value part should I replace this with? I can’t clearly read the value lines on it.
Understood. It helps to have the serial, if you do have a chance please send me that. I’m discussing this with our design team. I have been informed that theissue your experiencing wouldn’t have anything to do with that particular resistor. I’ll get back to you with a solution to help you out. Please send the serial when you get a chance. Thank you!
The fact that the noise can be turned down indicates that the source is not the preamp or power tubes.
The burned resistor would likely not contribute such a noise, but to be sure, what happens when you try using it with an amplifier?
Just FYI, that is a 680 ohm, 2W resistor. There was an update about a year or so ago to change that resistor to 6800 ohms. In order to do this change, there is another resistor on that board that would also need to change from 68 ohms to 680 ohms. That will prevent the one in the photo from getting hot when you run your amp cranked for a significant amount of time.
Back to the noise, which I do not characterize as “hum” because that’s a bit misleading. I would say it is possible that the input stage buffer on the front panel control board may be causing the noise. That buffer is between the resistor in your photo and the volume control, so there is a chance that it could have been overloaded, and since the volume control is after it, that would explain why the noise is affected by the volume.
I used my BluGuitar Amp 1 Iridium Edition hybrid for safety because not having a load won’t harm it.
You can think of the Vintage channel I used as like a modded JCM800 tonewise, and with the master at 7 it’s ungodly loud like a 100W tube amp.
LP style guitar → BluGuitar 8 ohm out → Fryette PS-100 8 ohm in and out → 8 ohm 4x10 cab
Fryette was set like this:
Loadbox switches both in up position.
Level switch set to “Lo” (push button out).
Volume at 9:30 - 10:00 o’clock.
Presence/depth all the way down to the left.
Through the PS-100, higher volume can bury the noise, but the volume fluctuates where randomly it would jump to a much higher volume for a few seconds. I played for maybe 10-15 minutes and warming up didn’t change this behavior.
Issues occur with both channels and adjusting volume does not seem to help. It’s more noticeable at louder volume as the jump seems bigger.
What’s the other resistor that would need to be changed to the higher value?
Earlier you said “Adjusting volume DOES have an effect on hum.”
Later you say “Issues occur with both channels and adjusting volume does not seem to help.”
In your clip you describe turning the volume down at the 10 second mark.
What I would advise now is to connect the Amp 1 FX Send to the PS-100 Line in or FX Return. And also clarify the volume control comment.
This is probably mostly academic as I think it needs to be looked at. My current opinion is still the possibility of a problem with the buffer stage. We have a service center in Germany that I can refer you to.
Tested effects loop and line-in. No difference to the Amp in behavior. Noise is more noticeable the lower the input signal is.
The PS-100 was initially behaving nicer today, with less loud noise but it was still there. No random volume fluctuation either.
But as I used it further, it suddenly lost a bunch of volume and the noise was highly amplified.
As luck would have it, I managed to capture both scenarios with different amps dialed for roughly similar sounds. Amps were connected to the Amp In on the PS-100.
The first part is when it’s behaving nicer. Noise can be mainly heard when I am not playing and even that seems to change as it’s first a bit louder, then I play a bit and mute my strings. At that point the noise is a bit less.
Then I swapped amps, and I played probably 30 minutes with the above scenario, where the noise wasn’t too bad to bother. All of a sudden the noise just went to almost as loud as the amp, while the overall volume level dropped a good bit. This can be heard in the second part of the clip after the very short gap.
Just a smartphone mic again, which probably compressed the second clip a good bit.
