need debug help - ROG Double D/Bounce

[Matt505]

Hello,
I perfed up a 2nd Bounce-only version of the Double D, plugged er in, and got nothing cept a high squeal with the gain knob maxed. The squeal stayed there even with the switch off/TB. TB works fine otherwise. I've tried swapping a new 4049 and a new J201 in both input & output buffer.
I'm getting ~5V at the drain of the input buffer, VCC where is should be (I think).
Hearing the squeal even while bypassed HAS to mean something, right?? Any help?
I'll get to some more voltages later...anyone know what other DC voltages I should be seeing on the 4049??
Thanks in advance!!
Matt

[Ripthorn]

You know, something strange with my double d: I get the same squeal when gain maxed (much quieter in TB but still there) with one guitar but with another guitar the problem vanishes.  No idea why, I just know that such is the case.  Sorry I have no idea what causes it, I will be interested to see, though.

[Matt505]

Huh, but you get the effect, even with squeal? man, I'd take that at this point! 
Here are some DC voltages
VCC 12.7V (from a wall wart clearly marked 9V output! but it's worked on other effects just fine...)
V+ 9.3V
Input J201
VDS 4.7V
VGS -0.2V

Output J201
VDS 8.2V
VGS -1.0V

I noticed that when I click the switch on, the output J201 voltages move 0.3-0.4V up/down, but not the input J201??

only so much I can do with DC voltages, no scope...

but what do you think?
Thanks!
Matt

[Ripthorn]

Have you tried backing off of the gain to see if the squeal goes away?

[Matt505]

yes, the squeal was only noticeable when the gain knob was just about maxed and the volume was turned up a bit...but again, I'm NOT getting the effect, just the squeal!

I figure the fact that I can hear the squeal even in bypass means I've got a wiring mistake somewhere, but I can't "see" it! I've checked pinouts several times, gone over the layout again...

I looked at voltages on the 4049 -- on the unused side, I get ~0V at the inverter inputs, and V+ at the outputs, I think that makes sense...on the side I'm using for the Bounce channel, on 2 of the 3 inverter stages, I get about 0.7V *higher* voltage on the output as the input (about 3.5V on the input, 4.2V on the output). The middle stage voltages are about the same - 3.5V on both input and output. I don't know enough about how the 4049 is working here to tell if that's "normal"...

Anybody make sense of these voltages?

Thanks!
Matt

[Matt505]

bump

I'm at a loss...

is there more info I can provide??

thanks
Matt

[Matt505]

Some more info -

I wired this up for DC jack only, no battery...so I used another mono jack for the input.
I used GGG's switch_lo_3pdt_tb_dcjack diagram from their tech pages, and just omitted the battery & it's connections - is that ok?

Again, since I'm getting the squeal (with gain knob ~maxed) even while bypassed, I suspect some odd grounding issue or somesuch...maybe I'm focusing too much on this "clue"!  Again, I get No effect...getting close to starting all over, ugh...

[Matt505]

ok, swapped in a 3rd 4049 and plugged in, got the same thing - no effect, squeals at max gain - so I started wiggling things...when I wiggled the input J201, the LED went out and squealing stopped (still no effect).

I'm staring at all these pretty trees in a...what's it called?...oh yeah, a forest! 

why would the LED go out? I somehow broke it's ground connection? That's provided thru the switch and a connection ~3/4 of the way across the board from the J201...I did a quick continuity check of my ground bus while wiggling, seems ok...how else might that happen??

the problem is right in front of me, laughing...any suggestions?!?

your dogged debugger awaits sage advice...
Matt