Thread: Tube Screamer doesn't scream....

Hi all

Flush with my success from building my first tube amp, I pulled out my effects-building bits and set to work on a Tube Screamer clone. I used the circuit board and layout from Tonepad.

Finished it this weekend, but -

All I get out of the thing is a slightly louder version of what I put in. The tone and volume controls work, but the Drive pot does nada. It's like the clipping diodes aren't even there. I pulled the diodes out and tested them ( still good) and tried the pedal with the diodes removed. Sounds the same. Checked my schematic and layout to make sure I'm not putting them in backwards. Nope. Signal in = Signal out. I made a couple of resistor substitutions to use parts I had on hand, but I thought the values would be close enough for rock 'n roll....

If someone wants to look over the info on the Tonepad circuit

tonepad -- FX projects

And tell me if my resistor changes might be the problem?

1) the 2 510K resistors are 560K
2) The 1K going to the base of Q1 is 1.5K
3) The 220 ohm res. coming off the Tone pot ( thru the.22 cap) is 200 ohm
4) The 51K coming from the Drive pot is 56K

That's it folks, everything else is exactly as listed on the layout.

I've tried 2 different Drive pots, so that's not it. Also, it's not wired thru a bypass switch yet, it's still hardwired on my bench, so it's not a bad switch either.

Grrrr......

The 4k7/.047uf pair that connects pin 2 to Vb needs to be there in order for the pedal to have any gain. Those diodes and pot can be absolutely unimpeachably good, but unless there is a path from the inverting (-) pin to Vb you won't get any gain whatsoever, or no matter how you adjust the gain knob.

So, for starters, check to make sure that path is functioning as intended.