Whisker bisquit help, please.

DaveBasser · March 14, 2012, 07:48:23 PM

So, I'm putting together a Whisker Biscuit.
http://www.runoffgroove.com/whisker.html

And I'm changing the following...
1- 1uf caps all the way through
2- 6 position rotary switch with diodes
3- AMZ presence tone control, body and tone pot version
http://www.muzique.com/lab/tone3.htm

Ok, it sounded great on the breadboard but when I got it all boxed up something is not right.
It sounds like its struggling, a little gatey and if I play an open string and let it go, the sound is like on the edge of a threshold, going up and down in volume, almost like a switch going on and off.

I've read through most of the debugging page. I don't have much experience in these matters so I'm asking for help.

I measured voltages and will post a pic below. Obviously something is wrong with Q2, I looked for cold solder joint and reflowed one but with no change.

I'm using this for bass, btw, if you're wondering about the 1uf caps.

Thanks in advance for the help!

joegagan · March 14, 2012, 11:09:44 PM

i don't recall specific voltages for the bazzfuss, but i have a few ideas.

you might have complicated things with the add-ons. if possible disconnect the diode switch ( go back to the schematic specs ) totally bypass the tone control to see how it work/sounds. then add them back in slowly and one at a time to see what happens.

joegagan · March 14, 2012, 11:13:19 PM

also, even for experienced chefs, a homemade darlington can sometimes get a little weird. double, triple check your darlington.

DaveBasser · March 15, 2012, 07:23:10 AM

Thanks. Yeah, there's something happening around, near, before that Darlington. The body knob, which is after the Darlington, definitely doesn't work as before. Probably not getting enough juice.

Ben N · March 15, 2012, 08:36:58 AM

Do you have an MPS13 you can sub in for Darlington as a test?

DaveBasser · March 15, 2012, 08:59:20 AM

Quote from: Ben N on March 15, 2012, 08:36:58 AM
Do you have an MPS13 you can sub in for Darlington as a test?

I don't, thus the homemade version. I'm thinking about swapping those for one 5088 but that would really be tough. Might be worth it...

joegagan · March 15, 2012, 12:00:36 PM

ben, you read my mind.

PRR · March 15, 2012, 03:51:01 PM

> will post a pic below

A picture of text??

0.61V at "Darlington" base says it is not working as a Darlington. Single transistor, even hi-gain, is not the same. We need the Base to sit up near 1.1V.

Check your leads.

> it sounded great on the breadboard but when I got it all boxed up something is not right.

That's something else. Something pinched shorted broken when put into the box.

DaveBasser · March 15, 2012, 06:02:25 PM

Yes, a picture, because I was not at home and this way I can take the picture/measurements with me.

Check my leads? I think I'm going to try and swap out the Darlington and put in another. That might prove a little too messy, but...

Quote from: PRR on March 15, 2012, 03:51:01 PM
> will post a pic below

A picture of text??

0.61V at "Darlington" base says it is not working as a Darlington. Single transistor, even hi-gain, is not the same. We need the Base to sit up near 1.1V.

Check your leads.

> it sounded great on the breadboard but when I got it all boxed up something is not right.

That's something else. Something pinched shorted broken when put into the box.

DaveBasser · March 15, 2012, 06:44:42 PM

I put in new transistors for the Darlington and no go. I think I'll just make a new board, I have spare parts anyway...
Thanks for the help, fellas!

DaveBasser · March 20, 2012, 09:44:53 AM

Ok, I made a new board after I ordered some mpsa13's. I'm am now getting absolutely no signal, dead. I have a fresh battery, power to the board, and my grounds are good.
I made an audio probe and I get signal to the base and emitter of the first transistor but nothing at the collector. The 100r and 100k resistors have signal at the end connected to E & B, but no signal on the ground side of the resistor.
So, signal is not making it to the collector of the first transistor, and I changed it out with no difference. No signal through the feedback loop of first transistor.
Oh, and I socketed the transistors this time.
Any thoughts or advice?
Thank you!

PRR · March 20, 2012, 10:35:14 PM

Same voltages exactly?

Ben N · March 21, 2012, 04:40:33 AM

You sure about the transistor pinouts?

DaveBasser · March 21, 2012, 08:09:25 AM

Ok, here's what I just measured, and it doesn't look good.
Q1-5088
E1.07
B1.56
C8.87

Q2-mpsa13
E0.0
B0.0
C0.0

Q3-5088
E0.08
B0.69
C0.69

Thanks for your help.

DaveBasser · March 21, 2012, 08:40:16 AM

Quote from: Ben N on March 21, 2012, 04:40:33 AM
You sure about the transistor pinouts?

Yes, I looked up the darlington to to be sure.

joegagan · March 21, 2012, 10:20:01 AM

something misrwired or shorted around Q2. once this is sorted, Q3 may bias correctly as well.

PRR · March 21, 2012, 11:45:29 PM

> read through most of the debugging

There's a place for "battery voltage". It helps to know if "C=8.87V" is full battery voltage or something less. Without that, I've had to guesstimate some "correct" (or more-likely) voltages below.

Q1-5088
E 1.07 (0.05V)
B 1.56 (0.55V
C 8.87 (5V) (suspect "10K" is wrong-value or short)

Q2-MPSA13
E 0.0 (OK)
B 0.0 (1.1V)
C 0.0 (1.6V) (10K not hooked to +9V _or_ short from collector to ground)

Q3-5088
E 0.08 (0.05V) (maybe OK)
B 0.69 (0.55V) (maybe OK)
C 0.69 (5V) (looks like short base-collector)

I can't know your skill level. Please don't take offense. Are you sure of your soldering?

DaveBasser · March 22, 2012, 12:08:31 AM

PRR, no offense taken. It actually helps that you give me things to look for. I feel like I've read up about debugging and the FAQ, not so sure I know how to fix things once I've diagnosed them, mostly.

I've built a hog's foot/mole clone and Bazz Fuss successfully, so given my sound preferences and skill level, the Whisker Biscuit seemed the next logical step up.

Thanks for the help, I'll check those things in the morning.

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Whisker bisquit help, please.