brass master diode question

9 volts · January 19, 2009, 06:23:26 AM

Hey there, I'm trying to throw this together with odds and ends, I have have 1n4004 diodes rather than 1n4001's. Will using these work/ (alter the sound?) Thanks

gigimarga · January 19, 2009, 09:10:23 AM

First i used 1N4148 instead of 1N4001 and it sounded good.
After that i replaced 1N4148 with Schottky 1N5817 and now it sounds better (for my taste).

Good luck!

oldrocker · January 19, 2009, 02:03:19 PM

My guess would be that the 1n4004's would work fine in place of the 4001's.

9 volts · January 19, 2009, 05:35:44 PM

Thanks, I seem to recall reading in an anderton book that increasing the size shouldn't matter (can't find where I read that), I know in a distortion eg mxr distortion or tube screamer it has major changes in tone, I understand that this is a rectified bridge and is doing a different job to diodes in a distortion. Need a bit of theory on this one. Thanks

Meanderthal · January 20, 2009, 07:22:13 AM

Yep, you got it, that's what the diodes are doing, they're not clippers. Shouldn't make any difference to sub 1n4004...

R.G. · January 20, 2009, 09:39:12 AM

Actually, if you look at the schematic closely, the diodes are a true diode ring, not a full wave rectifier bridge. They are all wired cathode-to-anode, no two cathodes or two anodes together.

If the diodes are well matched (!) then it does a pretty good frequency doubler on a sine wave. Yeah, diodes should probably be matched, although you can get along without it. Match for forward voltage at low current.

9 volts · January 21, 2009, 01:58:26 AM

Thanks all. I may check the diode readings once this is up and running. At this stage all is working (even filter bit) except the brass side gets a little blatty as it fades out. (I'm using an mpsa13 for trans 6 and a 2n3392 for trans seven). The rest are 2n3904's with the legs twisted and work fine. I've audio traced it and the problem arises on the c leg of trans 6 (mpsa13) Wondering if maybe it needs to be biased differently from the 2n5308? It would be great to get this up and and running before my board falls apart, ha. Thanks

9 volts · January 21, 2009, 05:57:52 AM

Just read the other posts and gathered that the gating is part of the circuit. It would be great to try to enhance this pedal a little.

Meanderthal · January 21, 2009, 01:28:10 PM

The gating is a very practical and helpful thing when used in a live situation... no need to dance on your bypass switch to get it to shut up! When I play, it passes signal, when I don't, it shuts up. Compared to any other bass fuzz I've tried of this face-ripping intensity, it's far more usable for that reason alone.

9 volts · January 21, 2009, 06:48:27 PM

Got it, the problem I'm having is that when I audio proble the diode section there is a distinct dip in the dynamics of the signal which then rises before the end of the tone. This causes a cut in/cutout cut in for every note....I've got some diodes measured so I'll pop them in today and see if it changes it.
PS RG So the diode ring is a voltage quadrupler?

R.G. · January 22, 2009, 10:57:05 AM

A set of four diodes in a ring is the original of the name "ring modulator". It's used in RF modulation and demodulation.

A diode ring for modulation works best if the diodes are matched. Best is four monolithic diodes in an array. The now-obsolete CD3039 is perfect. But obsolete.

There are quad monolithic arrays of Schottky diodes available. You can also use a CD3046/3086/3096 transistor array, and either use the C-B junctions, or better yet, connect base to collector and use the C/B and E terminals as Anode and cathode respectively.

You can also hand match diodes for forward voltage at some chosen current. 100uA would be about right. This is a 1 point match and is better than unmatched, but monolithic is better.

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brass master diode question