Help debugging ROG Big Daddy (first timer)

[petemoore]

to get cleaner solders while I'm at it
  Less solder while the copper heats, just enough to start off the heat transferring through all metals connected, easy on the solder.
  Actually most of the blobs look shiny and 'contained.
  Voltages and debugging thread read recommended for building up circuit debugging chops, is generally preferrable to attempting to duplicating the board, locating the problem and finding a solution helps prevent repeat mistakes, and is the quickest way to finished effects, even in the short run, especially for one-off's.

[ConanB]

Well I fixed up the audio pot, hooked everything up to the breadboard, but things still don't seem right. There's a buzz, and the pots again don't seem to be doing much.

I disconnected the guitar and amp and started poking with the DMM. With the volume and drive turned down to 0 here are some voltages I got:

Battery: 9.07

Where battery connects to FX: 9.07
Where battery black wire connects: 0.00

IC1
P1: 1.10
P2: 0.00
P3: 0.01
P4: 0.00
P5: 0.98
P6: 9.07
P7: 4.47
P8: 1.15

Q1
D: 7.28
S: 0.25
G: 0.00

Also the electro cap:
+ side = 0.25
- side = 0.00

I also check the ohm on the pots, not exactly sure if it would help as I haven't done any electronics before looking into stompboxes...

Drive
0 = 392
half = 322
full = 004

Volume
0 = couldn't get a reading
half = couldn't get a reading
full = 007

To me those pot readings don't look right.

If I had a spare guitar lead I'd probably try and put together an audio probe like RG's example.

[ConanB]

This is what I've been testing with. Inspired by Paul M's board.



I still want to add a DC jack, onboard voltage divider, and the audio probe jack.
Not sure if I'll have permanent pots on it or not.

EDIT: Ok I've just been messing with the wires a little and it seems if I switch the Drive wires so that IC8 goes to Drive lug 3 then it seems to work. Still the buzz to kill, but I'm happy it's at least working

[petemoore]

IC1
*P1: 1.10 *these are the gain set pins
P2: 0.00  {this ones a N/C IIRC on the 386
P3: 0.01   {Input should be on this side, I forget...pin 3 or 4, should bias about 1/2v...
P4: 0.00  Gnd. = 0.0v, ok
P5: 0.98   I forget
P6: 9.07  {IIRC this is the output pin, should be about 1/2v, looks like it's connected to V+
P7: 4.47  {V+ pin and looks like it's not connected to V+
*P8: 1.15*
  Schematic might better jog my memories, the battery voltage is '100%'...so these voltages are 'whatever %' of what the supply voltage *Actually is, iow without V+ reading the pin voltages are a partial equation, but I'm figureing V+ as at, or a little over 9.07v.
Q1
D: 7.28
S: 0.25
G: 0.00
  I remember this as Jfet gain stage? in which case the drain should be about 1/2v, and the source above gate, both having low voltages..gate looks like it might be a little high compared to V+, what is V+?
  DMM Set to small R Range and measure between Source and Gnd. should give a small resistance reading = to the S resistor value.
  Same for gate, but higher range I guess, this one has two bias resistors? measure across any gate resistors, compare value to schematic, testing from 'distant' point...also tests everything between the points...iow, you should see a resistance from V+ at battery to drain, and that'd verify that the battery is getting V+ through the resistor.

[ConanB]

IC1
*P1: 1.10 *these are the gain set pins
P2: 0.00  {this ones a N/C IIRC on the 386
P3: 0.01   {Input should be on this side, I forget...pin 3 or 4, should bias about 1/2v...
P4: 0.00  Gnd. = 0.0v, ok
P5: 0.98   I forget
P6: 9.07  {IIRC this is the output pin, should be about 1/2v, looks like it's connected to V+
P7: 4.47  {V+ pin and looks like it's not connected to V+
*P8: 1.15*

But going by the schematic P5 is the output, not P6, and P6 is connected to the +V.
P1 and P8 are the gain, P2 and P4 are connected to ground. P7 is left open, and P3 is connect to a cap that runs to Q1's D and +V (after the 0.0068 cap and 15k resistor).

Is the schematic wrong considering the IC pins? Anyone else here have experience building the Big Daddy?

[ConanB]

Well I went and grabbed the tech sheets for the 386 and made sure it was correct, which it is.
I also threw together an audio probe based on RG's design and started prodding around. Both gain pins on the 386 had alot of static noise even when no note was being played, which makes me think I have problems with my solder (most likely).

I went back and breadboarded the whole thing just to make sure my vero layout was right and just to get a better understanding of it all. Worked fine, only thing slightly different to the vero layout was the Input hits the 4M7 resistor before it touches the JFET. In my vero layout the Input touches the JFET before 4M7. Would that make a difference at all?

If the order that the Input touches components doesn't matter then the only explanation for the buzz that I can think of is bad solders.