My contribution...

[yodermr]

Thanks to everyone for giving me enough to read...and get this far on my second question...I almost proved a novice can just read everyone's work and come out with this. hopfully I added something here

Here is my new baby...Up and running but needing a bit of help. All voltages look reasonable, plays great. Actually very quiet. VVR is very cool, to me its seems to change the compression as you dial down. Anyway...

Hoping I can tap into some troubleshooting support... Mid from 0-2 o'clock the volume is attenuated a bit, Mid > 2 I get quite a volume boost, sounds great but the Treble, Mid and Bass controls don't really do anything. Double checked the wiring I can't see anything. I'm decent at troubleshooting, but short of disconnecting the pots and checking if they are good I'm not sure how to figure out what's going wrong in the tone stack.

Thx
Mark

[yodermr]

more pics...

[yodermr]

my pictures suck....

Pin 3 of the treble pot is connected to pin 2 of the bass pot. The wire is just up under the lip

M

[Richie]

resolder the ground on the mid pot.. see if that helps.. if it is loose or cold solder joint, the amp will have alot of gain, and effect the other controls.

[hairyandy]

Yodermr,

This might be too obvious, and Richie hinted at this I think, but make sure you're getting good continuity to ground from the pots. Sometimes that gets forgotten when you use an anodized or powder-coated chassis that won't conduct. You might have to take the pots out and use a dremel to remove the powder coat from around the pot holes.

Andy

[El_Martin]

Hi!

Check value of mid pot. If you use too large (like 1MOhm) pots you get some kind of preampboost and less efficient controls.
Basically the same effect as bad grounding.

I did have some pots where the slider lost contact to the resistive surface...intermittent madness.

Amp looks fine. Youre gonna get it fixed. Patience needed.

Ciao
Martin

[yodermr]

Thanks for the clues. Can't really see it from the pics, each pot has a (crap what do you call it), spade connector (but the ring washer type) between the pot and the the chassis (which is ground to metal around the hole). I have these lugs bent around and connected in the front with a long copper buss wire.

I was measuring the mid pot in place, "thinking" that it should give me a straight forward resistance reading with only pin 2 and 3 connected. So with the meter on the ground lug and pin two, sweeping the pot, right at that 2 o'clock position the resistance goes from a few hundred ohms to just about 1meg. It stays at about 1meg for the rest of the range of the pot. That measure was consistent whether I went from the buss wire or pin 3.

Now I'm pretty damm sure that that pot says 25K on it. My novice brain is telling me the mid pot might be bad, If its really a 25K pot (I will triple check) why would the resistance go to 1 meg? At most it should be 25K.

But I might not understand if this is accurate measuring in place

Maybe a bad solder. I will reflow and recheck

Thx
Mark

[El_Martin]

Hi Mark!

TAKE CARE OF HI VOLTAGE! DISCHARGE CAPACITORS!

Connect your DVM in OHM mode as follows:
1. one clip to ground.
Now check w. the other tip the three tabs of the 25k pot.

One should be grounded: zero ohm or very low readings 0,1 Ohm or so.
Middle tab should be 0-25k depending on position of pot.
If your last pin isn't connected it should read around 25k independent of position of pot.

If you have another 25k pot at hand, measure first and if OK replace it.
I tend to fry pots from time to time or ruin them by tightening them to much. Or the solder flux residues drip into the pot.
The newer lead free solder using higher temperatures is a PITA

Good Luck!

Ciao
Martin
PS: is the buss wire grounded?

[yodermr]

Sounds like a plan, I check that when I get home.

One point of confusion I had, didn't see it in the layout diagrams out there..."PS: is the buss wire grounded?" My buss wire is grounded at the front of each pot through the washer spade connector around the pot shaft(contact point ground clean of paint). You can see it in the two side pics

Is that sufficient? I didn't see any diagram that indicated that I should run a separate wire from the buss line to a star ground. I assumed that it just a happened through the chassis

Thx
M

[yodermr]

Looks to be a bad pot

Ground looks good
Middle tab is 0-30k in the first 20% of the sweep then goes right to 1.4meg for the rest of the range.
Last pin reads 1.4meg ohm

Not sure what I could have done to take out a 2w pot. No sign of solder dripping anywhere


M

[drhulsey]

...Not sure what I could have done to take out a 2w pot.

Maybe it was just bad from birth

[Wayne]

Bad pot happens - even if you grow your own.

Don't ask me how I know

W

[yodermr]

Nudge, nudge, wink wink...say no more aye?

[El_Martin]

Well, does it behave now?

I choose to have a isolated buss wire across the pots and NOT ground them via their housing.
This way I can decide WHERE I ground the buss. I just solder a cable to the buss wire and check the noises of different grounding points.

Btw: Debugging amp problems should be part of the "upper class twit of the year" games...

Ciao
Martin

[Structo]

I wander over here occasionally.
The way I do it is to use a ground buss or wire and then ground it at one point, which is usually to a star ground by the input.
If you have multiple ground points along it you might set up some ground loops that will drive you crazy.
I know you said it is quite but....
Replace the pot and get back to us.