Need some help for a puzzling issue on a newly built 5e9-a circuit

[mort]

I finished the build, played it hard for a couple of weeks and it performed solidly. I shipped it off, well packed, and the owner received it today and has an issue. He says, and provided a clip, that when he turns the volume knob on the gutar there is alot of loud ass crackle. He tried another guitar and same thing happened. I would think that the problem would lie with the guitar in a situation like this but I believe him that he tried another guitar and that it's a problem with the amp but it doesn't make any sense to me. He swapped out preamp tubes and the issue is consistent. Thoughts?

Second half of the clip has the intensity knob for the vibrato turned all the way up and it starts to cut off a little but that's not a huge issue. Any insight would be appreciated if there's a way to remedy that.

Here's the clip. Language warning. https://soundcloud.com/shea_boy/tremoluxcrackle

[Enzo]

So more than one guitar does this. Did he try more than one cord? It may not be the guitars themselves, but it could be a cord, or it could be something in th electrical environment there. An electrically noisy furnace blower or sump pump might get picked up by the guitar pickups. A cellphone in the pocket might as well.

A good experiment might be to plug a keyboard or tape deck into the amp input instead of a guitar. See if the noise remains.

trem all the way sounds a little too intense, so turn it down from all th way up.

[mort]

I just got off the phone with him. He tried both guitars into a different amp and didn't have the issue. Also says it's intensified by the tone knob. He loves loves loves the sound of the amp. We just need to figure out this crackle thingy. I'll advise him on your suggestions and see what happens.

[Leo_Gnardo]

when he turns the volume knob on the gutar there is alot of loud ass crackle.

Sometimes a pre tube goes wonky and puts a little DC onto the grid. Which finds its way to the guitar volume control, makes it crackle as DC does on a pot. Try a different pre tube.

Language warning? Does he expound in some obscure dialect? Pig Latin? Joisey yiddischa? Lower slobbovian? They're all doing it now, it's called "world music."

[mort]

Nah he's just kind of intense, but a decent fellow

[Chuck H]

Nah he's just kind of intense, but a decent fellow

I know the type. All good.

What Leo said, way. If a new preamp tube doesn't fix it there may be a ground issue or (hopefully not, knock on wood) voltage on the chassis.

I think the trem is probably wonky for a couple of reasons. With the power tubes clipping the trem may get lost anyway being on the PI. Just guessing. This is the case with bias vary trems and the PI is pretty late in the circuit. That's something users don't always get. What I hear is the force of the signal negating the trem and driving the PI tube into cutoff when the trem is up. Maybe try a 1k resistor for the PI bias (and if that makes it worse try cooler, like 2.2k just in case) I think if you reduced both the pot (to 100k) and parallel resistor value (to maybe 68k) it might smooth the control taper and reduce the 'off to too far on' effect. But this is just something to try. No guarantees.

[mort]

Here's another twist, he says when he runs through his pedal board that the crackle disappears completely. I only plugged straight into it and never once had that issue. And had several other people play it at a blues jam with several different guitars all plugged straight in and it was fine as well. He did say he swapped all preamp tubes to no help and against my advice he even bought another set of power tubes which of course didn't help. I'll post more details as I get them. This is a weird one.

Oh and he's tried brand new 12ay7 and 12ax7 in v1 and it didn't touch the issue.

[Leo_Gnardo]

Here's another twist, he says when he runs through his pedal board that the crackle disappears completely.

If it's DC-leaky at the input, then the DC-blocking cap at the output of his last effect pedal keeps the DC level from changing, signal passes from pedal to amp, no scratchy noises. Well, that's one way of "fixing" it but just addresses the symptom. If he had a volume pedal as the last item, I bet that noise would return as he moves the treadle.

Best guess is something got jarred in shipping. (Shipping, grrrr... ) IF the cathode of your first pre stage somehow got grounded, that would force the grid off its typical zero-volt bias and bring on these symptoms. A change of pre tube wouldn't help in that case.

Where's your customer? If he's nearby any of them, one of our MEF correspondents could put the amp back on track in a jiffy.

[mort]

He's in Austin Texas.

Something else that came to mind is that during the whole time I had it, right up until shipping, I had the speaker plug sleeve loose from the plug body and just sitting on the speaker wires. Just before shipping it i threaded the sleeve onto the plug body and off she went. Never thought anything of it. I do know for a fact that the plastic isolator was indeed inside the sleeve as it should be, but is it conceivable that some small trace amount of signal could be shorting to cause such a symptom?

[MarkusBass]

It sounds like DC voltage on the pot. Is it input GAIN pot, or master VOLUME pot? The first thing I would do is to measure if there is DC voltage on the input jack when he plugs in his guitar. Is it possible that he has active preamp, there is DC voltage on the output and you don't have coupling capacitor on the input of the amp? The second test would be to check if there is DC voltage on the pot that causes scratches.

Mark

[Leo_Gnardo]

He's in Austin Texas.

Something else that came to mind is that during the whole time I had it, right up until shipping, I had the speaker plug sleeve loose from the plug body and just sitting on the speaker wires. Just before shipping it i threaded the sleeve onto the plug body and off she went. Never thought anything of it. I do know for a fact that the plastic isolator was indeed inside the sleeve as it should be, but is it conceivable that some small trace amount of signal could be shorting to cause such a symptom?

I doubt there's a speaker hot-to-ground short, that would be another set of symptoms.

Not to worry, things happen. I just had to do a minor fixup on a 5E3 I built last July. Touch-up soldering, she's-a-feex 5 minute.

From our friendly neighbor forum TAG, Cliff Schecht is in Austin. He lists his website paia.com. If that doesn't work let me know & I'll send him a PM.

- - - - - - - -

MarkusBass, the noise is on the guitar volume pot, when plugged into the amp.

[mort]

Sweet. Will do. I'd rather pay him than fedex.

[MarkusBass]

MarkusBass, the noise is on the guitar volume pot, when plugged into the amp.

So there is DC on the amp input. Is there a resistor from the input to the ground?

Mark

[mort]

So there is DC on the amp input. Is there a resistor from the input to the ground?

Mark

It's this circuit, with teh only changes being a 3 prong cord, virtual heater CT, and a 1M speed pot with a series 500K resistor rather than a 2M pot, which is unavailable with a switch on it.

http://www.thevintagesound.com/ffg/s...e9-a_schem.gif

[MarkusBass]

It's this circuit, with teh only changes being a 3 prong cord, virtual heater CT, and a 1M speed pot with a series 500K resistor rather than a 2M pot, which is unavailable with a switch on it.

http://www.thevintagesound.com/ffg/s...e9-a_schem.gif

The schematic looks OK but is the 1M resistor soldered as on the schematic? What would happen when it is not soldered to the ground, or broken, or missing? If you have another amp, you can remove it and check whether you get the same problem.

Mark