Another Yet Another Fuzz Face question - Testing Question and more problems :(

[mrmrcoleman]

Hello, if you have read my previous posts over the last couple of days you will know that I am (unsuccessfully) trying to build the YAFF circuit from Jack Orman (www.muzique.com/lab/yaff.gif).

I built the whole circuit on a breadboard and it didn't work so I thought I would build it bit by bit and test it as I go along using an audio probe on new bits of the circuit.

I decided to test Q1 (PN2369) first so I put in the following components. (See Schematic)

Q1
R1
R2
R4
R7
C1

Basically everything around Q1, and then connected it all up to the jacks, pots, battery etc.

When I test the audio probe at the base of Q1 I get the usual sound as would be expected. However when I test the audio probe at the emitter of Q1 I get nothing. I thought I would get an amplifed signal?

I tried the probe everywhere and nothing which means nothing is getting through the transistor right?

The voltages on Q1 are:
Collector: 3 volts
Base: 0 volts
Emitter: 0 volts

Does this indicate anything to anybody? Should this even work?

Sorry for the long message but I thought it was better to be thorough.

Thanks in advance for any help,

Mark

[petemoore]

Hello, if you have read my previous posts over the last couple of days you will know that I am (unsuccessfully) trying to build the YAFF circuit from Jack Orman (www.muzique.com/lab/yaff.gif).

I built the whole circuit on a breadboard and it didn't work so I thought I would build it bit by bit and test it as I go along using an audio probe on new bits of the circuit.

I decided to test Q1 (PN2369) first so I put in the following components. (See Schematic)

Q1
R1
R2
R4
R7
C1

Basically everything around Q1, and then connected it all up to the jacks, pots, battery etc.

When I test the audio probe at the base of Q1 I get the usual sound as would be expected. However when I test the audio probe at the emitter of Q1 I get nothing. I thought I would get an amplifed signal? The signal path is through the collector of Q1

I tried the probe everywhere and nothing which means nothing is getting through the transistor right?

The voltages on Q1 are:
Collector: 3 volts
Base: 0 volts
Emitter: 0 volts
  The base must be biased about .6v above the emitter, collector usually ends up a a volt +/- somewhere around there.
Does this indicate anything to anybody? Should this even work?
  Q2 also biases Q1, it looks as though somehow the Q1 base *may somehow be connected to ground.
Sorry for the long message but I thought it was better to be thorough.
 
Thanks in advance for any help,

Mark

[mrmrcoleman]

petemoore, I think you forgot to reply!

Mark

[bioroids]

I dont think you can remove Q2 and expect the circuit to work fine. It provides part of the bias thru the feedback resistor.

It is better if you build the entire circuit and then you can audio probe from the input to the output to see were the sound gets lost.

With 0v on the base, Q1 is fully off and no sound will ever get out of it. Im suprised you dont measur 9v at the collector, so I think you also may have some miswiring over there.

Hope this helps!

Miguel

[mrmrcoleman]

Thanks, thats what I thought, I'll try again in the morning.

Mark

[petemoore]

   I'ts a *single two transistor feedback *amp, both transistors play a role in bias.
  My reply starts *under where I quoted...
  *emitter 0v

[MartyMart]

Mr Coleman, how are you getting on with this ?
I decided to build one, as it looked like a cool fuzz & to give
you some "readings"
Here's the correct voltages with 1k "fuzz" pot at MAX :
Q1 
C 1.97v
B 0.67v
E 0.0v
Q2
C 4.79v ( this is about right and sounds good used a 10k trim pot here from 9v)
B 1.97v ( same as Q1's collector as they are directly connected )
E 1.24v ( this will change depending on where the "fuzz" pot is, this is at MAX fuzz setting )

The only problem I had was a "bad" 1k pot, which kept "jumping" as the track was damaged
a new one solved that.
It's worth persuing, as it's a very "Ge" sounding silicon fuzz 
Hope this helps some ?
Remember that your readings will be "slightly" different, but thse are "ball park" figures
from a working circuit.
My only "change" was to use the trimpot for Q2 ( easy to adjust voltage ) and I used a
22n output cap, have no 10n's at present.
Transistors are a pair of 2n2369a's

Marty.

[mrmrcoleman]

Thanks for the feedback Marty. I am getting highly annoyed with my Anologue Multimeter so I am off to go and buy a Digital Auto Ranging type, hopefully I will be able to get some better results with that.

I rebuilt the pedal into a breadboard and I get the same problem again, one thing I have noticed is that when I am measuring the voltage between ground and the positive rail I get about 18v. Does this mean that my ground is connected to my negative somehow, or is this normal? I thought the voltage between ground and positive should have been just under 9 for a new battery?

Mark

[bioroids]

I rebuilt the pedal into a breadboard and I get the same problem again, one thing I have noticed is that when I am measuring the voltage between ground and the positive rail I get about 18v. Does this mean that my ground is connected to my negative somehow, or is this normal? I thought the voltage between ground and positive should have been just under 9 for a new battery?

Mark

This is a very strange reading, you should measure about 9v between ground and positive (if using a 9v battery).  You can disconnect the battery and measure the voltage between the two terminals, you should get about 9v with a fresh battery. If measuring the battery alone gives you strange readings, then you should get another multimeter.

Luck

Miguel

[mrmrcoleman]

Well I am going to get a new DMM in an hour, so I will try the same thing when I get back and report back.

Mark

[mrmrcoleman]

Ok, I got my DMM and the analogue was broken, the battery reads 9.88 volts, which is good.

I now get 9 volts at the collector on Q1?

Also, when I am measuring 'inside' the circuit should I be measuring AC?

I think I may need to back track a little and make some very simple circuits because I just can't understand what I am doing wrong, here is my track layout incase anybody has time to go through it for me.

Q1
Collector: 1
Base: 2
Emitter: 3

Q2

Collector: 4
Base: 1
Emitter: 5

R1: +ve, 1
R2: +ve, 6
R3: 4, 6
R4: 2, 7
R5: 7, via C2 to gnd, gnd
R6: 8, to footswitch, gnd
R7: 3, gnd
R8: 5, 7

C1: from footswitch, 2
C2: gnd, fuzz pot
C3: 6, 8

Thanks for everyones continuing support with, I really appreciate it.

Mark

[MartyMart]

9v battery is  "DC" direct current,  which may have the sign :  V=  with small dots under it
the "AC" section has V- with a "wavy" line under it  ( on the DMM )
Set it to read up to "20" volts DC
Check my readings, collector of Q1 should be around 2 volts !!

Marty.

[mrmrcoleman]

Ok, well the collector voltage on Q1 is 9 volts, so thats one problem. I have just also found that the audio probe sound that I get just after the input is very weak, which may well explain some problems. I am giving up for today, I am going to start over in the morning with fresh components, pots, switch etc.

Are there any tests that I can do as I go to make sure things are going well?

Mark

[MartyMart]

Not really, as Q1/Q2 effect each others "bias" you need the complete circuit
done to get sensible readings.
Sounds like you have a "short" from 9v somewhere, correctly wired with a 33k to Q1
and a 6k2 ( roughly ) to Q2 you wont have anywhere near 9v at Q1's collector.
If you can use a trimpot to Q2 do so, it will make "tuning it in" so much easier.
Dont forget the 330 ohm between Q1/Q2 on the power line too ....
Check all the resistors with your DMM to make sure you use the right
value... it's VERY easy to mix up a 100k with a 100 ohm  !!! I"VE DONE IT  !

Dont get too angry/down about this ... YOU WILL GET IT WORKING  !!
..... and learn a ton of information in the process too 

Cheers,
Marty.

[mrmrcoleman]

I'm not getting angry.. yet!

In a way the pedal not working first time is good because it is making me going back to the theory and look at everything in more detail, I have definately learnt a lot already. I am going to do a full rebuild today, and see what happens.

Mark