Debugging Tonebender MKII pro vero layout

[cuthbertg]

Hi all - this is my first build related post, so please be gentle! 

I have built 5 successful pedals now and have a few which fell by the wayside which I would like to get up and running and learn a bit more in the process!

After having success with Ulysses SRV special vero layout, I thought I'd try the tonebender one posted here: http://www.aronnelson.com/gallery/main.php/v/ulysses/ulysses_layouts/ulysses_tb_pro_mkII/ulysses_ss_tone_bender_vero_1_2.gif.html.

I figured that the +9v wiring point on the board is the ground (I'm using OC75s from smallbear) and I have used a DPDT switch with true bypass/input switched to ground,  and have replaced R3 with an 18k resistor as suggested by smallbear

The problem I'm getting is a gated/blatted sound so I have been trying to work through R.G. Keens troubleshooting page - the voltages i  have are:

Q1 E 0.00
     B -0.07
     C -8.19

Q2 E 0.00
     B -0.11
     C -0.68

Q2 E -0.68
     B -0.68
     C -9.26

To me, the values in bold look highly suspect and potentially indicate a short? Though to be honest, I do feel as if i am stabbing in the dark here, so any help or suggestions would be greatly appreciated.

Many Thanks,


CG

[cuthbertg]

Ok, still troubleshooting and thinking out loud here,

The base of Q3 is connected to the collector of Q2, so I suppose it makes sense that those values would be the same....

So I'm wondering if my problem is between the base and collector of Q2?

I have checked for shorts with a jewellers thingy - and cannot see any + I always clear anything using a very thin fret saw after soldering....

I have built a PNP negative ground tonebender before, and that kind of worked but I wasn't completely satisfied with it - However the wiring for the switch was the basic TB type, so I'm thinking that maybe positive ground circuits might not like the input to ground switching??

[cuthbertg]

Been doing some more work on this...

I have been working through the blatty or gated sound debugging page and looking at the schematc for the TB MII Pro and noticed that R3 goes to the collector of Q2 and the base of Q3...

R3, originally 47K on the schematic, has been changed to 18k according to the instructions receieved from smallbear.

the hfe according to the packaging from smallbear are Q1 - 77, Q2 - 90 and Q3  - 108

I tested them on my multimeter and got Q1 - 125, Q2 - 144, and Q3 170 - so at least I still have them in the right order!! I also tried putting some AC128s in, and had the same problem...

So I'm starting to think that R3 may be the problem?? But would I need a lower value, or higher/closer to the original schematic?

Any help would be appreciated - many thanks!

Battery voltage was 9.66 BTW

[cuthbertg]

OK, got it working!

It appears to be the switch wiring that was the culprit - for some reason it didn't like the input switched to ground, so once I changed it to the jacks to middle lugs type it started working

Maybe it's that because its a positve ground circuit it caused problems - I dunno.