SOLVED Pharmacist overdrive - Too clean

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salin4

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I have a problem with the pharmacist overdrive.
Everything works fine except that the pedal is clean even with gain at max value.
Someone would have a clue ? Here are some photos and voltage for the transistors and the charge pump.

Thanks !
 

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salin4 said:
I have a problem with the pharmacist overdrive.
Everything works fine except that the pedal is clean even with gain at max value.
Someone would have a clue ? Here are some photos and voltage for the transistors and the charge pump.

Thanks !
Click to expand...
This is important to make sure your pinout is correct as you have not use the 2N2222A TO-18 version!

2N2222A Pinout.jpg

Check the part number on the Transistors you have used???
As PER your PCB
VVVVVVVVVVVVVVV------- Opposite Pinout
220px-2N2222%2C_PN2222%2C_and_P2N2222_BJT_Pinout.jpg
 
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music6000 said:
This is important to make sure your pinout is correct as you have not use the 2N2222A TO-18 version!

View attachment 22617

Check the part number on the Transistors you have used???
As PER your PCB
VVVVVVVVVVVVVVV------- Opposite Pinout
220px-2N2222%2C_PN2222%2C_and_P2N2222_BJT_Pinout.jpg
Click to expand...
Thanks for the reply , I first tried to solder them the other way that the one you can see on my photo, but I had no sound at all. So I reversed it and now it works but I only have a clean tone If I don't engage the boost . I think it's an EBC version as it is written" 2n2222a 58 C" on it.
I bought it there :

www.musikding.de

2N2222A, 0,21

2N2222A npn universal Transistor Hfe 50-300
www.musikding.de www.musikding.de
 
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Have you listened to this?
Have you read this?
Unless you have high-output pickups, the Normal channel will run clean. The first 2 stages have plenty of headroom; any dirt is made in the last stage. Don't bother measuring the voltages on the charge pump, the best indication of how it's performing is the voltage on Vcc and that's good. The BOOST pot should be C1K if you're going to mount it on the front panel. The voltages on Q1-Q3 look good. I can't read the standing up resistors. R5 is obscured, confirm it's 22K. Note to builders: Do not obsess over the value of R3. 330K or 360K are plenty close. I can't read the GAIN pot, confirm it's A250K and not A25K. The only cap I can read is C9, it's correct. Do the BASS, MIDS & TREBLE controls work?

My best guess at this point is the JFETs are too cold. Where was the BOOST pot set when you measured Q6-S? Not all JFETs are created equally and if their Vp and Idss are low, the gain will be low as well. I don't suppose you measured Vp on the JFETs before installing them.

R36 looks like it might be 6.8K, should be 68K. Verify.
 
Last edited:
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Thanks for the reply !
Have you listened to this?
Click to expand...
Yes but the fact is that the amp is already overdriven so ....
Have you read this?
Click to expand...
Now I have, thank you !
Unless you have high-output pickups, the Normal channel will run clean
Click to expand...
With my strat It's Clean and with my Les Paul and gain at max settings I have a very slightly overdriven sound more like a boost.
I have checked every resistors value and it's ok. The same for the capacitors... Gain pot is 250k so it's ok and every other pots works.

Where was the BOOST pot set when you measured Q6-S?
Click to expand...
It was at max settings.
I don't suppose you measured Vp on the JFETs before installing them
Click to expand...
No, I don't know how to do that.
I've found this :


I should try this , unless somone knows an easier way to do it.
 
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That's how it's done. I recommend putting a 470Ω resistor in series with the battery+. It prevents the FET being damaged if it's plugged into the test circuit wrong.

Try setting the BOOST pot to 500Ω (noon if it's B-taper) and measure Q6-S. I get around 500mV on mine.

So you're sure R36 is 68K? If it's too low, it reduces the gain of the last stage.

I suspect your Dr. Robert is doing what it's supposed to do. If you want a dirty fuzz pedal, this ain't it. If you want a boost that can overdrive a tube amp, then you have the right pedal.

BTW, that BOOST pot is very touchy at the top end, which is why I recommend C1K if you're gonna make it external. Dan has the BOOST trim set at noon in the demo, which I think is a good spot.
 
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Chuck D. Bones said:
That's how it's done. I recommend putting a 470Ω resistor in series with the battery+. It prevents the FET being damaged if it's plugged into the test circuit wrong.

Try setting the BOOST pot to 500Ω (noon if it's B-taper) and measure Q6-S. I get around 500mV on mine.

So you're sure R36 is 68K? If it's too low, it reduces the gain of the last stage.

I suspect your Dr. Robert is doing what it's supposed to do. If you want a dirty fuzz pedal, this ain't it. If you want a boost that can overdrive a tube amp, then you have the right pedal.

BTW, that BOOST pot is very touchy at the top end, which is why I recommend C1K if you're gonna make it external. Dan has the BOOST trim set at noon in the demo, which I think is a good spot.
Click to expand...
Can he raise R36 - 68K to a higher value ie 100K to see if he prefers that?
 
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Try setting the BOOST pot to 500Ω (noon if it's B-taper) and measure Q6-S. I get around 500mV on mine
Click to expand...
Impossible : when I'm at max settings I get only 1,5 Ohms . Is it normal ? I changed the pot ( to put a C1k as you recommended) and it's the same.
It's strange as the boost pot seems to work fine when I play.
Anyway I tried to put it at noon ( roughly) and I have 250/300mv on Q6-S.

So you're sure R36 is 68K? If it's too low, it reduces the gain of the last stage.
Click to expand...

Absolutly sure I checked it three times :).
 
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Not impossible. When you had a linear taper pot in there, noon is 500Ω. Now that you have a reverse-audio taper pot in there, noon is 150Ω. Turning the pot clockwise should reduce the resistance and vice-versa. Your voltage measurement is in the ballpark.

You can increase the gain of the 1st stage a few dB by changing R2 to 1M. You can increase the 1st stage gain further by decreasing R7. Try 1.5K.
Try these one at a time, in the order given. It won't exactly be a Dr. Robert anymore, but it might be more to your liking.
 
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