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Pastyface Low output

Started by Loztboy, April 30, 2013, 09:03:34 PM

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Loztboy

I'm building a Pastyface with Vox Tonebender MKIII specs.
The output with everything om max is below unity.
I have subbed C3 6.4uF with 4.7uf and i use a 500k trimpot.
I hear no difference when turning the trimpot, but when i test the trimpot with a multimeter it changes value from 0 to about 500k
I use OC75 transistors Q1 and Q2 is 70hfe Q3 is 100hfe
I measured every component before soldering it.
Here is a pic of the component side of the PCB.

Bret608

I think the first place to check might be the orientation of the transistors. Anytime I've had low output or gain on a build, it's always been a transistor facing the wrong way.

Loztboy

#2
I'm pretty sure they are oriented the right way. If I flip them around i get less gain.
I'm getting about 4.5 volt on q1 and q2 but 72mV on q3.
Hmm, is R7 connected to the right hole? R7 is next to R12

Edit. It seems like I have connected r7 to ground instead of connecting it to the trim pot :(
What is that ground hole for anyway? Is it a trap ;)

Loztboy

Now R7 is connected to the trim pot, not to ground  :-[
The trim pot is now working and I get about unity gain when everything is on MAX.
Is it supposed to be like this or, do I have to use a lager Volume pot to get more output?

What change does the cap sub I did make? (I have subbed C3 6.4uF with 4.7uf )

KCTigerChief

#4
I actually had this same problem...It was frustrating.  What did it for me, is the resistor that is on the volume pot (I want to say lug 2, but I could be wrong...I pulled that and just used a wire to bridge the connection.  Now unity gain is at about 2-3 o clock, and quite a bit of boost if I turn it all the way up.

EDIT: Checked the schematic and it's R10 I believe...pull the resistor and just use a wire...let me know if that helps, because I'm pretty sure that's what I did.  I can check for sure when I get home.

Loztboy