home brew possibly bound for the trash can

[iknowjohnny]

Unless by some miracle one of you has an idea that works, i think thats basically going to be my only option. I really nailed the tone i was after recently so Idecided to clean up the connections and remove all the solder blobs and all from an amp thats been thru probably close to two years of experimentation and was just a total slop fest and finally be done with it. After the massive clean up it sounded great, but I decided to make a couple further changes back from two last things i had changed during the cleanup just to be sure which value i wanted. One was the slope resistor the other was a resistor in a voltage divider. After i did that it started sounding like a nightmare. I took those two parts out and put the ones that i had removed back but still no joy. The sound is a horrible nasty high end that sounds like the highs are much more distorted than the lows and have a staticy horrid buzz like what you'd hear if you recorded some single notes on the high e string to tape and shoved the record level up twice as high as maximum. That pegging the needle on the level meter kind of distortion. And it gets worse the harder you hit it and the degree to which the issue exists seems to change at times. Sometimes it's so bad it sounds like you turned the bass knob to zero and pegged the treble and presence knobs. heres what i've done so far.By the way, i swapped out a LOT of parts, but once it was determined thet weren't the problem the parts i removed went back in....many of them at least

1-inspected every single solder joint in the amp even turning the turret board board over to look underneath and made sure all grounds are good.Even used a 7x eye loupe to inspect each joint and most have been reflowed
2-swapped every tube
3-replaced V1A's socket, tho all are belton and very tight and new(had reason to suspect it)
4-replaced choke with resistor....choke is fine.
5-every voltage in the amp is fine and bias is right on
6-replaced every cap in the amp including PSU caps (one at a time)
7-replaced most resistors and what i didn't replace i checked
8-replaced every pot
9-disconnected NFB and prob still existed
10-removed OT secondary from switch and soldered straight to jack
11-bypassed 2nd stage and tone was fine. But it's because the gain was super low. W/O the gain it doesn't do it. But grid blockers don't fix it. I also replaced every part in the second stage to be sure it wasn't something there, which is why i mentioned replacing the V1 socket above.

I'm sure theres more but i can't think of it. I know with all i've done it's unlikely anyone can help me. But at this point i'm so out of ideas i don't know what else to do beside trashing it. Any ideas at all would be greatly appriciated, thanks.

[mlp-mx6]

Pictures? What circuit?

[markr14850]

Are you using solid core wire? Maybe you have a hidden internal break?

[iknowjohnny]

Oops, sorry....i meant to post the schematic. And no, it's stranded and 16 gauge !Got a killer deal on it...100 feet for $6, so i had to. That stuff will NEVER break ! Oh, and the 220k in the voltage divider before the 3rd stage is NOT a 220k, it's 470k. Just forgot to update that.

http://s24.photobucket.com/albums/c39/d ... 34amp2.jpg

[mlp-mx6]

A quick look at the schematic tells me that this will undoubtedly be a bright amp. Make that a BRIGHT amp.

.68uF cathode bypass cap on the first triode. 470pF bypassing what I assume is 470K (mislabeled) after the first triode. Hard wired bright cap at .001 (!). Yet another .68uF cathode bypass cap on the second triode. Yet another bypassed 470K after the second triode (no label on the bypass cap). 1uF bypass on the 3rd triode (feeding the cathode follower).

EACH of these will make the amp brighter. All of them together, wow, I cannot imagine how bright this will be.

What type of assembly? Is there any chance that a solder blob is hanging below your circuit board and shorting to the chassis?

Again, a picture would be most helpful.

[markr14850]

Taking mlp-mx6's comments a bit further... I hate to suggest it, but there might be a chance that you previously had some unknown problem which was shunting highs to ground, and when you went through cleaning things up, you "fixed the problem", leaving you with way way too much high end.

[Andy Le Blanc]

pull off all the bypass caps in the pre, including the cathode's and the brite.
Just one side so you can re-attach a couple at a time to see where your
developing the tone. I seen that .001 brite in a traynor, ouchy....

Hi gain is tricky, sounds like you've fixed what was making the great tone.
A bad solder join could act as a resistor in series in the signal path.
You might have to go and brain storm the events that you went through
in your process of cleaning up the amp. One thing to keep in mind....
you can only mod a circuit so much before all the little errors add up and
come back to bite you.

Another thing might be an inductive coupling that develops in the layout.
I've had what I thought were very nice projects go tits up too.
Mind any long runs that might cause this between the pre and the plate
leads of the power side.

I would suggest putting it aside for a bit too, go have a beer, relax.
Its no fun getting wound, a bigger hammer isn't always the best fix.

[iknowjohnny]

I know it looks to be bright. trust me, i never thought i should need that much brightening. But believe it or not this is the second one i've built and the first i gave to a friend and i update it whenever i find tweaks for mine that work. So at the moment his is exactly like mine except that the voltage divider at the 3rd stage is not there. instead a 220k grid leak. And his has no problem like mine. It's like mine was till this happened. I would subscribe to the idea i fixed some issue when i cleaned it up, but that wouldn't explain why his sounds great and why mine did too AFTER the cleanup and just went wacky after i replaced two resistors and stayed wacked when i put them back. It would also not explain why the issue is semi intermittent in that one minute it will be worse than the next. Oh, and it still does it with or w/o that .001. It just does it less. I think the brightening caps all contribute to accentuate some nastiness thats happening in the distortion, not causing it. Thats the impression i get. I've run into problems like this before that make no sense at all, but i think this one may never be rectified. I hope i'm wrong....

[mlp-mx6]

Have you tried other tubes?

Failing that, how many people need to suggest you un-bright the amp as a next step before you're willing to try it?

[iknowjohnny]

2-swapped every tube

look, i don't want to get in a flame war here, but you're just going to have to assume i have a reasonably normal IQ instead of asking questions like that. I already tried removing brightening caps but after two years of endless tweaking on this thing, the reason it's the way it is is because it has always needed that much brightening or the bass is cr@p.

I could just as well say how many times do I have to say it sounded great like this and my friends does too with the same circuit minus the voltage divider and that ONE cap. Which like all the other caps in my amp improves the situation when removed but doesn't rid it. So why does his amp not have a trace of this issue? I realize that now i will likely get little to no help, but the fact is i'm only saying what you first said to me. I'm just trying to get help here, not be insulted.

[Blindog]

Don't know if it'll help what you are describing, but you could try a 47-100p cap across the plates of the PI. I upped mine from 47 to 100 and it tamed some fizzies I was getting in my Plexi build. Hope you get it fixed. Do like Andy said and walk away from it a bit and clear your head. I've found that to be big help when you hit the brick wall

Good luck,

Mark

[Deric]

Which like all the other caps in my amp improves the situation when removed but doesn't rid it.

Sounds like a reason to try removing all of them to me....

Just sayin'.

[iknowjohnny]

Don't know if it'll help what you are describing, but you could try a 47-100p cap across the plates of the PI.

No, i've done that in the past but i always found fizz caps never did what i wanted or did too much.
Anyways, i think i found the problem. I'm not sure what it is, but if i pull on some wires in the tone stack the tone all of a sudden goes from harsh and tinny to full and rich like it was before. However, it's connected to the board and a few controls and when i pull it the board moves as do several wires. So it could be any number of things that is shorting or make bad contact. never the less, this is promising and i probably found the problem. Unfortunately right now i have to get to work and this will have to wait, arrrrrg ! (like waiting for the doctor to call to tell you your diagnosis !!!)

[mlp-mx6]

Sorry, missed the part about swapped every tube.

I'm not trying to flame at all, and I have made no negative assumptions about your IQ.

What I *did* was to interpret your responses as meaning that you were not willing to even _try_ what 3 different people had suggested as a path - like you had dismissed it as a valid approach before trying it. What I have learned *the hard way* is that it is often the obvious thing, that I either don't think of or I dismiss out of hand, which ends up solving the problem. Beyond that, I did not recall you mentioning you had tried removing the brightness caps.

No offense intended in any way. I had no insult in mind for you either. You read malice into my question that was not there.

That stuff will NEVER break !

...if i pull on some wires in the tone stack...

Hmm. Maybe not, eh? (like I said, the obvious thing that I dismiss out of hand...)

[iknowjohnny]

I'm sure it's not a wire thats broken. i mean, you couldn't break this stuff if you sat there and bent it back and fourth a few hundred times let alone just sitting in the amp since i built it. I'm more inclined to think it's a contact being moved when the board bends.