Print Page - Low voltage reading on Q1b on mayer fuzzface

Title: Low voltage reading on Q1b on mayer fuzzface
Post by: Mikey707 on October 22, 2015, 02:35:22 AM

Hi all,

This is my first post and my first build and would appreciate some help.

The FF is on a bread board and is producing very low fuzz levels but at a good volume.

The voltage readings i have measured are:

Q1c- 2.32
Q1b - 0.04
Q1e - 0

Q2c - 5.04
Q2b - 2.32
Q2e - 2.29

I am using a trim pot at Q2c to bias.

I have switched the ac128 around and get the same readings.

They are matched with leakage of around .5ma and have hfe of 105.

I believe my issue is the low voltage at Q1b but no matter what i change the reading only varies by .01 v

I would appreciate any help that can be offered.

Cheers

Title: Re: Low voltage reading on Q1b on mayer fuzzface
Post by: Electric Warrior on October 22, 2015, 08:33:09 AM

It's not only that. Q1C is really high (usually between -0.3 and -0.6V in a germanium Fuzz Face) and so is Q2e (should be under -0.5V)

Title: Re: Low voltage reading on Q1b on mayer fuzzface
Post by: Gus on October 22, 2015, 08:41:50 AM

have you seen this? http://www.diystompboxes.com/analogalchemy/emh/emh.html (http://www.diystompboxes.com/analogalchemy/emh/emh.html) or this? http://www.muzique.com/lab/fuzz_face.php (http://www.muzique.com/lab/fuzz_face.php)

Title: Re: Low voltage reading on Q1b on mayer fuzzface
Post by: Mikey707 on October 23, 2015, 02:24:50 PM

Thanks for the replies.

I have had a chance to fiddle a bit and i now get these readings

Q1c- .52
Q1b - 0.02
Q1e - 0

Q2c - 5.7
Q2b - .54
Q2e - .46

The sound I am getting is a boosted signal with more bass coming through with just a bit of fuzz in the background.

Does anyone know why I could be getting such a low reading on Q1b when I am quite close to the voltage readings I should be getting.

Thanks again

Title: Re: Low voltage reading on Q1b on mayer fuzzface
Post by: Electric Warrior on October 23, 2015, 02:49:40 PM

Looks good now. Except for Q1b of course. Not sure what's wrong with it, maybe the leads of Q1b and Q1e are touching?

Title: Re: Low voltage reading on Q1b on mayer fuzzface
Post by: PRR on October 23, 2015, 10:37:19 PM

I would suspect the resistor from Q2 E to Q1 B; or the input cap.

Title: Re: Low voltage reading on Q1b on mayer fuzzface
Post by: Mikey707 on October 24, 2015, 05:16:19 AM

Thank you again for your time.

I thought a little more info might help.

I have started from scratch on a different breadboard and new caps. Below are the new voltage readings

Q1c- .55
Q1b - 0.02
Q1e - 0

Q2c - 4.5
Q2b - .55
Q2e - .48

The resistors i am using are

95k at Q1b usually a 100k
65k at Q1c and Q2b usually 33k
470 as usual from neg power supply to a 3.8k resistor which is a 10k trim pot to Q2c

B1k pot for fuzz A500k pot for volume

2.2uf polarised cap at input and 2 10uf in series at the output of the 1k pot.

Im starting to think I have knackered my Ge.

Title: Re: Low voltage reading on Q1b on mayer fuzzface
Post by: Electric Warrior on October 24, 2015, 09:41:05 AM

Try swapping Q1 and Q2. If Q1 is broken, the voltages will tell you :)

Title: Re: Low voltage reading on Q1b on mayer fuzzface
Post by: Mikey707 on October 24, 2015, 01:04:16 PM

Hi,

I swopped them around and the readings were pretty much the same and when i rechecked them 20 secs later the voltages on Q2e and Q2b had jumped 1.2v.

Any ideas on what is going on.

DIYstompboxes.com

DIY Stompboxes => Building your own stompbox => Topic started by: Mikey707 on October 22, 2015, 02:35:22 AM