CB1 / LPB-1 clone problems

[mirosol]

Hello all. This is my first post here. I've started to build stompboxes a few months ago. My first build was GGG's GRO / Green Ringer clone, which was successful at the first try, so i continued with this LPB-1 clone. There were a few threads about LPB-1 clones, but none with similar problems than mine.

First off i made the common mistake and soldered transistor backwards. Burned it during the removal process, and got 2N4401 with sockets as replacement. According to GGG's documentation, it is suitable replacement. Now the voltages on transistor pins are near to those documentation provided. Everything is wired exactly as in documentation: http://www.generalguitargadgets.com/pdf/ggg_cb1_lo.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

Now my problem is this; I get only boosted output. When the device is switched on and the 100K log pot is turned down, there's no signal at all. If i turn the pot all the way open, i get some boost to the sound, but it sounds like something's missing. I think this should be wired in the manner that clean signal is always present..

Or could there be something else wrong?

[PRR]

> 100K log pot is turned down, there's no signal at all.

This is how it was designed.

> If i turn the pot all the way open, i get some boost

Should be more than "some".

> but it sounds like something's missing.

What is missing?

[mirosol]

So 100K pot is just too much resistance? I should probably try 25K or 50K instead.

And about the "missing" element.. I don't know if i quite understand the design, but  should the switch be connected the way that you'll get mixed clean/boosted signal instead of just the one that comes out from the circuit?

Seems that there is a good chance that my LPB-1 clone works just the way it was intended...

[PRR]

> 100K pot is just too much resistance?

It is not the resistance.

> 100K log pot is turned down, there's no signal at all.

Look how the pot is wired. On "10" the output jack gets the full boost-amp output. On "0" the out jack gets *ground*, zero signal.

You seem to be expecting "0' to be unity-gain buffered signal. That may be reasonable, but not how Meyer and Matthews designed/marketed it (44 years ago!!). It boosts about 15X then attenuates from 100% to 0%, originally as an adjustment to the Muff Pi prototype.

If you have an audio-taper pot, "unity gain" should be ~roughly~ "4" on a 0-10 dial.

[mirosol]

>You seem to be expecting "0' to be unity-gain buffered signal.

And you'd be right.

About the pot.. So now that i've read about these too, i understand that on this design almost any pot will do. Here the pot is to simply mix between 0-signal and signal from the board.

So the biggest problem i have, is that i had wrong expectations about the final product. I never had the original and had only used youtube videos and reviews as reference.

But it seems that i have successfully build two working pedals with sheer luck (and ability to rtfm). Actually these projects have taught me a lot. I have dug up information on many things and learned a lot about transistors and now pots.

I think i'll keep this like it is and build another one with two mods.. First off - add switch for Screaming bird cap change, like in this thread: http://www.diystompboxes.com/smfforum/index.php?topic=91835.msg784755#msg784755 - and second.. I'd really like to do opamp output to mix clean signal with the boost. So far i haven't find easy instructions for this. I haven't really looked yet either . But. Then again. This is going to be some future project. I have one Red Llama to hard booster project unfinished and silicon fuzz project on the way...

Thank you PRR for pointing me to right direction!

Building these is fun!

[mirosol]

PRR: Could this work for mixing dry/wet signal in this case?
http://www.groupdiy.com/index.php?PHPSESSID=4g0c9ll14p1fet6khlomgrmrp6&topic=35060.msg429901#msg429901
Or would need something like this:
http://www.wiparat.com/2-input-audio-mixer-using-2n3904/