BMP clone no worky

Started by Danny G, June 08, 2004, 09:56:30 AM

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Danny G

I'm building a Big Muff Pi clone from GeneralGuitarGadgets.com, and it isn't working so far...  http://www.generalguitargadgets.com/v2/diagrams/bmplo2.gif

I used perfboard and hand wired the circuitry, and have noticed some mistakes but fixed them.  So far, there is only the faintest signal (I mean FAINT) coming through when the effect is on, but mainly the tone control works as a radio antenna...  No guitar singal seems to come through, on or off.  I haven't had time to completely re-check the board yet, just noticed some things wrong and took care of them.

Input jacks--how do i know which is the tip, sleeve, ring?  
The lugs on the pots are numbered 1,2,3 on the parts layout--is that looking from the bottom of the pot or the top?

petemoore

DMM on beep mode, and 20V range.
 Beep mode I use to sort out jack wirings, with a bare jack, and a cable plugged in...well in this case a stereo cable, you can map the connections.
 the sleeve should connect to the jacks threads, the tip will connect to the tip prong and one lug, the other' lug is the ring.
 Most pots just work backwards [turning it 'up' turns it 'down'] as long as the middle/wiper is connected 'right. invert to two outer lug connections to have it turn 'up' when you go clockwise.
 You can take voltage measurements with the DMM at all transistor leads B<C and E for each one, from ground, post them here for analysis, or look at GEO for transistor biasing info, and everything else.
 The debugging page has the audio probe, which I made with two wires, 4 alligator clips, and a DC blocking cap..  1uf .1uf 2.2uf...or your choice. This simple debugging device is indespesibe for finding where the signal is lost, boosted, attenuated, gating etc. I like to work from the input >ways to find what happens to signal at points beyond input/toward output.
 The signal injector is another one I use more than anything. Any signal source will do, strumming the guitar and probing before the signal fades is no fun, get an old keyboard and tape one of the keys down, so it plays a constant note, connect an output cable's from the signal source ground to circuit ground, and a cap on a wire to the cable tip [signal path of source] use this to inject signal into the circuit at various points to find where it's getting 'messed up' or lost. I prefer my thumb as signal source, and it requires no ground connection, starting from the output, and working my way in<, testing various [all?] points in the signal path till I find a loss section, then I probably will be looking transistor pin voltages [and other 'stuff' near the non amp B/C in signal path] to find why the base is not louder than the collector in the signal path.
 For BMP bugs anyway, any transistor that isn't an emitter follower, the base should sound louder than the collector when source signal is injected into the circuuit signal path.
 Source signal comes from a source, signal path is a 'map the signal uses to find it's way through a circuit' lol , and is almost always sprinkled with active inputs and outputs, coupling caps and sometimes resistors.
 Be sure to set the knobs in the middle, if you don't know which way is 'up' on them.
 First thing I do is check for continuity between battery + and -, that indicates a short in the circuit...then stop everything and find that short...could be anywhere, might take some looking.
Convention creates following, following creates convention.