Prescription Experience help

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Prescription Experience help

John R
http://tagboardeffects.blogspot.com/2016/01/prescription-electronics-experience.html

With some of the switches pressed I get a loud buzz, with other combos it's a dull buzz. There's a very faint very crackly hint of guitar coming through.




Voltages:
Wall wart: 10.75V

Q1
E .18
B .80
C 2.4

Q2
E 1.76
B 2.4
C 8.96

Q3
E .38
B .95
C 7.02

Q4
E .31
B .93
C 8.74

Q5
E .26
B .6
C 10/75

Q6
E .05
B -1.45 (yeah, negative. that's strange)
C .6

I'm using all 3904s. The BC546 pinout is reversed, so I tried Q5 & Q6 flipped around, but it still doesn't work.

In place of C1, i wired up a DPDT with 220n and 22n caps to see what the difference is. The answer is none. None more buzzy.

Other slight differences, based on parts at hand:

78k resistor > 75k
50n cap > 47n
3n cap > 3.3n

I sliced all the gaps and even ran the voltmeter across each gap in diode test mode so I'm certain there's no bridges.

thanks in advance for the help,

John


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Re: Prescription Experience help

Marbles
As a second pair of eyes all parts seem to be in place. Cuts too.

The spot where the double link comes together does look like it can use some more solder? It seems like a hole. The cut on that same row more to the right looks a bit fishy too, but if you have checked that I'm sure it's fine.
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Re: Prescription Experience help

John R
Thank you for looking it over!

The connection on the double-link was OK, but I reflowed it anyways. That cut was OK, and I double-checked all the cuts.  Still just noisy hum. :(

If anyone has built one successfully, could you check/post your voltages, and let me know whether or not to  flip Q5/6? Alex? Strassercaster?

thanks,

John

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Re: Prescription Experience help

Marbles
I haven't built it, so I can't comment on that. Your transistors are placed correctly though.

If you use all the same transistors, what important is that the CBE matches. In your case they do. Could there be a problem in the switches? Like a missing link or something or a missing pot to pot connection?
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Re: Prescription Experience help

John R
here's a pic that shows the pot and switch wiring. I checked and double-checked it, but it is a confusing one with the two switches (i'm still not sure how the circuit flow works there, exactly).



Thanks for taking such a close look.

John
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