Weird Sound Coming From Amp/Cab

[Brandon]

I just got a chance to crank my new metro (with pillows muffling the cab) and I hear this strange sound in the undertones, and I cant figure out if it's coming from the amp or cab.

The amp is a 69' spec metropoulos and the cab is a 1960TV cab with Anniversary G12H 30s

The sound happen more in the treble, and only happens when the overdrive of the amp comes on, not really when clean even at loud volumes.

When I hit the high E and B strings hard (think spanish castle magic) you can really hear this piercing sound happens with a lot of undertone, it sounds almost as if the treble is too high for the speaker to take and is making that staticy threshold sound, like when an amp is too loud for a mic... like when you try to record your 100w marshall with a computer mic

Can anyone tell me what's going on? Is this normal?

[rockstah]

parasitic oscillation. can you post a clip of the amp making this sound?

lead dress and grounding as well as filtering can contribute as well as will resolve this if it is what i think it is.

can you post pictures of the chassis as well?

Mark

[Brandon]

EDIT: bigger photo

[Brandon]

I'll try to get some audio up today too

EDIT: Also it happens when whether the MV is up or down, I feel like its MV related, but I'm a novice

[rockstah]

checked the bias on it?

i would swap out the 1.5k grid resistors on the two outer two power tubes for 5.6k's on all of them.

[rockstah]

someone can correct me if i'm wrong but that PPIMV is not wired correctly.
i believe the pot should be grounded and not to the bias supply.

[Scumback Speakers]

If it's not the PPIMV or the parts Mark has noted, the only other answer I can come up with is cone cry.

Does it sound like this? I found this file online, and saved it just for occasions like this. I can't remember what brand the speaker was, but this is one form of cone cry. Another type is on the low strings (A/E) from the 3rd fret to the 12th, and it sounds like an almost perfect (but not quite) sub-octave howl, nasty double note tone.

http://www.scumbackspeakers.com/pita/conecry.mp3" onclick="window.open(this.href);return false;

[Brandon]

Here's an audio clip, It's the clip titled "PO"

The noise is not that noticeable at first, but it because more clear in the middle and especially at the end.

http://www.soundclick.com/bands/default ... ID=1155029" onclick="window.open(this.href);return false;

It seems to be very influenced by the mid and treble knobs, the higher the knobs the more noticeable the noise.

[Brandon]

If it's not the PPIMV or the parts Mark has noted, the only other answer I can come up with is cone cry.

Does it sound like this? I found this file online, and saved it just for occasions like this. I can't remember what brand the speaker was, but this is one form of cone cry. Another type is on the low strings (A/E) from the 3rd fret to the 12th, and it sounds like an almost perfect (but not quite) sub-octave howl, nasty double note tone.

http://www.scumbackspeakers.com/pita/conecry.mp3" onclick="window.open(this.href);return false;

It doesn't quite sound like that audio clip, which makes me see more that it's probably something in the amp, but it does seem to have an under note that is very strong and slightly off harmony, no good!

[toner]

Your clip does sound like PO to me. That extra "sizzle" on top of the notes. Just to confirm, is it doing this with the amp mounted in the head cab?

It doesn't sound like the speakers are the cause. You could try another speaker cab to make sure but I think it's the amp. Is this the amp George built?

Like Mark said, you can try 5.6k resistors on pin 5 of all four power tubes. Also try lifting the green wires on the preamp tubes up away from the chassis.

...but it does seem to have an under note that is very strong and slightly off harmony, no good!

I don't hear ghosting in your clip but your quote above is a good description of it. If you turn up the master and play notes on the G and B strings around the 12th fret on a neck pickup and you hear an out of tune pitch below your note, that's ghosting. It's pretty common.

[rockstah]

i believe the master is wired in correctly. with thats style of master,keeping the existing bias feed resistors(220k's), the pot needs to go to ground and not the bias supply.

[Brandon]

Your clip does sound like PO to me. That extra "sizzle" on top of the notes. Just to confirm, is it doing this with the amp mounted in the head cab?

It doesn't sound like the speakers are the cause. You could try another speaker cab to make sure but I think it's the amp. Is this the amp George built?

Like Mark said, you can try 5.6k resistors on pin 5 of all four power tubes. Also try lifting the green wires on the preamp tubes up away from the chassis.

...but it does seem to have an under note that is very strong and slightly off harmony, no good!

I don't hear ghosting in your clip but your quote above is a good description of it. If you turn up the master and play notes on the G and B strings around the 12th fret on a neck pickup and you hear an out of tune pitch below your note, that's ghosting. It's pretty common.

You said to hit the 12th fret on G string with the neck pickup and hear's what I got, the file is "PO2". Is that ghosting?

http://www.soundclick.com/bands/default ... ID=1155029" onclick="window.open(this.href);return false;

Yes it is the amp george built me. He said it could be because the amp still needs to be broken in, or it could a tube issue. He sent me out some new tested tubes, so hopeful that goes well.

[toner]

Yeah, there's a little bit of ghosting in that second clip. The amount you're getting is normal; nothing to worry about. It will happen mainly with the MV on 10 and the volume around 7 or higher (overdriven) using a neck pickup. You'll notice it more with humbuckers. If you move notes up and down (like 9th fret through the 14th fret) you'll hear an out of tune harmony note that follows below the note you're playing.

I still mainly hear a high frequency "fizz" or "sizzle". It may go away after the capacitors, OT and tubes break in a little. The amp will gradually start to sound warmer and the treble will get smoother as it breaks in. I'd just play it for a while and try the tubes George is sending. Make sure to set the bias on the new tubes. The bias will probably drift a little over the first 10 hours of use so check it a few times.

If it still sounds like your first "PO" clip after 20 or 30 hours of use and new tubes, then you can do some easy fixes.