Debugging Boss Slow Gear Help

[Malius]

is your 3pdt switch wired as the diagram shows?

i had it wired up how i thought was correct and it never worked.  i switched everything except the 3pdt switch and it still didn't work.  then i switched the 3pdt and within 5 minutes i had it working great!

http://www.generalguitargadgets.com/pdf/ggg_sgo_lo_wiring.pdf

No, my switch is wired up differently. Could it really make that much difference? I will change it anyway as you say it probably will haha.

FYI it's currently wired like this:

Input to board -                      +9V to LED -                        - Output from board
Tip of i/p jack -                       +9V from board -                 - Tip of o/p jack
                     - jumper            nothing -                             - Other end of jumper

> Are you sure removing the T2 JFet is a good idea?

Either two experienced circuit benders are yanking your chain, or it IS a useful step in debugging. You do have to be careful about free advice, but if you've skimmed some of Gurner's posts you see he's no chain-yanker.

You got low-no signal. It could be mis-wiring anywhere around T1 T3, _or_ it could be something about T2. With T2 out, signal should flow like a simple buffer (what it then is). If not, bebug the buffer. If it buffers fine, now we stare at T2.

Sure, I was just double checking things before I went and de-soldered the board. Plus I like to understand everything that I'm doing.

I do however have a fine signal now, just no effect, so I'm assuming we need to debug the effects circuit.

However:

> T4  BC549   E = 1.29  B = 1.90 C = 1.37

R20 and R21 have the same value, and flow the same DC current. (The only side-paths are through the huge 390K and caps that block DC.) How-come R21 has 1.29V and R20 has 9.15V-1.37V= 7.78V? Wrong part? Wrong connection?

How come B of T5 and C of T4 have the "same" voltage? Is C13 shorted?

I checked the voltages on R20 & R21 and they both appear to have 1.3V.

The B of T5 has 1.36V and T4 has 1.9V. I have checked for shorts and cut the copper strips bigger to make sure.

Now the B of T4 has: 3.6V
T5 has 0.2V

Are you sure removing the T2 JFet is a good idea? Everything I read suggests it si a very important part of the circuit and is used to slowly open up and let the signal through, i.e. the volume swell.

It is, for troubleshooting purposes, a good idea, but you say you do have *some* sound with the effect engaged now.  So...

What are all the voltages now?

CHAD

The voltages now are as follows:

Voltage at the circuit board end of the red battery lead = 8.96v
Voltage at the circuit board end of the black battery lead = 0v

Component          Name (description)       V

T1           BC550 (yes I checked the pinouts)   E = 3.60  B = 4.03  C = 8.95
T2           2SK30A                         D = 5.35  G = 3.9 - 4.5  S = 5.35
T3           BC549                           E = 6.38  B = 6.53  C = 8.94
T4           BC549                           E = 3.06  B = 3.62 C = 5.82
T5           BC549                           E = 0.3  B = 0.3  C = 5.32
T6           BC549                           E = 0.3  B = 0.3  C = 5.32

IC1         496-741                         1 = 0.00              5 = 0
             CA3140E2                       2 = 4.48             6 = 4.57
                                                   3 = 4.42             7 = 6.97
                                                   4 = 0                  8 = 5.96

D1       5.6V Zener               Anode = 0  Cathode = 5.34

I haven't done an aural test since removing what must have been a short on C13 or thereabouts. I will post my findings after breakfast!

[seedlings]

In a search I found this thread: http://www.diystompboxes.com/smfforum/index.php?topic=71352

Along with some voltages for reference, there is this quote:

I just came across this old thread by accident and I might have a suggestion...

On my build I wasn't getting any swell at all just gateing and then I stuck an extra electrolytic in parallel with C6 on the schematic (that goes to the attack pot) IIRC it was 22uF as that gave the best swell but anyway, that basically got the unit going for me and seemed to be very important to the swell so perhaps you could poke a parallel electrolytic in there if you haven't scrapped the effect for parts by now.

Looking at the datasheet of that CA3140 again, pin 8 is 'strobe' and shouldn't be connected to anything at all.  I know you already checked this, but it's worth making sure some solder didn't flow over to that pin.  If yours is socketed, just bend pin 8 up so it doesn't seat in the socket.  Other than that your voltages are similar to those referenced in above thread.  Granted, he reported having trouble, but had some functionality.

CHAD

[Seven64]

fwiw i had the stomp wired the same was as above and it didn't work until i switched it to that diagram.  i have absolutely no idea why tho.

[seedlings]

If pin 7 has 7V, and that's after a 1K R18... then your opamp is drawing 2mA of current?  I don't know, but that sounds like a lot.  Maybe that IC is bad?

CHAD

[PRR]

> your opamp is drawing 2mA of current?  ...sounds like a lot.

I did not check his specific opamp, but generally 0.5mA to 5mA covers it. LM741 at 30V is 1.7mA; TL071 1.4mA; SE5534 4mA; and this spec is not tightly controlled.

[Malius]

Hey guys, I'm getting some volume swell now. but it sounds very 'glitchy' on the decay. I'm pretty sure that's not correct. Also the attack needs to be all the way up for any signal.

I'll have a read of the links in the morning as I'm pretty tired right now.

But I thought I'd post that so you guys can think on that and know where I'm up to.

Cheers!

[Malius]

So, the op amp is okay? Or should I try another? I've bent pint 8 up and out of the way so that it doesn't conduct.

I think I will try changing the switch layout next. I'm reluctant to add an extra capacitor in there, especially as that guy said he had no swell at all.

[seedlings]

So, the op amp is okay? Or should I try another? I've bent pint 8 up and out of the way so that it doesn't conduct.

I think I will try changing the switch layout next. I'm reluctant to add an extra capacitor in there, especially as that guy said he had no swell at all.

The original poster had no swell, the comment I quoted was from a guy who did make it work.  It's worth a try to just touch another cap in parallel with your existing cap.  I can't say about the opamp, but if you have another one, slap it in to see.  Also, on the original article you linked the fella said something about messing with the fet under 'Critical Part Substitutions'.
http://topopiccione.atspace.com/PJ03BossSG1.html

CHAD