Guitar Boost pedal - transistor help

Alec_t

Joined Sep 17, 2013
14,280
why does it self-bias?
If the FET tries to draw more current the drain resistor will drop more voltage, hence the gate voltage supplied via the 10meg resistor will fall and so try to turn the FET off, reducing the current. This is called negative feedback and stabilises the working point of the FET.
 

Thread Starter

Justincharlesmoses

Joined Mar 15, 2014
16
I don't mean to necro but I honestly do not know what is happening. I keep taking long breaks to keep from getting frustrated so, I am still on this same project. Here are some photos of the diagram and the protoboard layout
http://[URL=http://s30.photobucket.com/user/mosesthecoot/media/6d72f871-f0a7-45fa-8ac5-510971daf179.jpg.html][/URL]
http://[URL=http://s30.photobucket.com/user/mosesthecoot/media/photo1.jpg.html][/URL]
The orange and red wires go to the outer variable resistor lugs and the center lug goes to the guitar amplifier. The green wire on the left is connected directly to the guitar. I have to be missing something. Please help as I'm getting frustrated with myself. Thank you for all of your help thus far!
 
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Alec_t

Joined Sep 17, 2013
14,280
Looks to me as though the drain of the FET is wrongly connected. It should connect to the other side of the electrolytic cap, i.e. to the junction of the 2k7 and 10meg resistors.
Why the paper wrap over the 10meg?
 

Thread Starter

Justincharlesmoses

Joined Mar 15, 2014
16
I just tried switching the drain but no luck. The circuit is supposed to be boosting the volume but it's acting more as a master volume knob. When it's fully on, the signal is actually quieter than the original signal and when the knob is entirely counter clockwise, there is no sound at all. Not to mention tons of ground noise (which may just be a grounding issue. One problem at a time haha :).

the tape was there just as a reminder for me that it was 10k.

thanks for responding, alec
 

Alec_t

Joined Sep 17, 2013
14,280
the tape was there just as a reminder for me that it was 10k.
It should be 10 meg :).
The third block of your breadboard has 2 columns with contacts grouped in fives. Is there electrical continuity from one group to the next? If not, you are missing a ground (-ve) connection to the 100 Ohm resistor and the 5k pot.
 
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Thread Starter

Justincharlesmoses

Joined Mar 15, 2014
16
Sorry for the delay, I was away for the weekend. It's 10meg, that was a typo. I am fairly new to circuit building so, I'm not entirely sure how to test the DC voltage at the Drain. I have an analog multimeter that can be set to 10, 50, 250, and 500v. I've got to assume the answer is obviously 10v but I'm not sure where to place the probes.
 

Alec_t

Joined Sep 17, 2013
14,280
If that picture shows your actual measurement, the meter was being used on the 10V DC range and the probes were as you stated (which was correct) then the drain voltage is about 2.6V, which is ok.
I don't see a ground connection for your signal input?
 
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Thread Starter

Justincharlesmoses

Joined Mar 15, 2014
16
What I've done is taken the input to the circuit and wired it to a 1/4" jack. The ground connection is grounded to the other jack but not to the battery which, I thought was correct?
 

Thread Starter

Justincharlesmoses

Joined Mar 15, 2014
16
Ta-daaaaa! Well, I'm learning for sure. Thank you very much for ALL of your time I really appreciate it! Any parting words of wisdom on what I would change to make the sound distort less? It's supposedly a clean boost but it seems to be distorting/overdriving the signal.
Thanks again!
 
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