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Vintage threads from the first ten years

Re: FZ5 is a REAL BMP??

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6/12/2000 8:26 PM
Gus	Re: FZ5 is a REAL BMP?? yes uses 2sc1815's with transistor buffers and fet switching

6/13/2000 1:18 PM

Okay, this cinches it. I made a BMP that sounds magnificent, with a great rising overtone that blossoms as you sustain a note. Viewing it with the sound card scope software that Jack Orman posted shows a change in one of the lower order harmonics but not the higher ones. Lotsa bottom, too. I was told by someone at a local vintage place that it sounded much like one of the better early ones. Quite frankly, it was a happy accident, rather than an intentional design strategy. I suspect that it results from a combination of transistor hfe, and diode clipping thresholds, and the impact of different characteristics in each clipping stage. If I can stay awake, I'll try my damndest to measure the relevant components. Conceivably, you may be able to swap a few components on a FZ5 or reissue, and get the same bliss.

6/13/2000 1:58 PM

I agree with everyone else: go out and buy a green Sovtek reissue. I've got one and they're decent quality for as cheap as you can find them. Being reissue and having that cheap green paint should make it $40 max used. Here's a list of things to consider about the BMP:

1) Most important thing I guarantee you is to change out the tone section (4 parts) with the original BMP values and use high quality caps like poly film or some other poly-whatever. The Sovteks used some cheap ass caps in their tone control and it makes the thing WAYYY too muddy.

2) Those cheap ass caps are also used everywhere else in the pedal. They are what gives the reissue more of a crunch instead of a fuzz. I personally like the crunch, so I left them in there. I've built a BMP with all poly film caps and that will get you fuzz as well as sustain into next week.

3) The BMP is such a high gain circuit you should not use high gain transistors in it. My homemade uses 2N5088's. Two things happen if you do, the voice of experience says. First, your distortion saturates at about halfway up the drive knob. Second, the unit gets noisy when you do crank it up.

I don't know anything about the FZ5 but I do know that the Sovtek comes in a sturdier box. I'm electrically inclined but not so mechanically inclined, so this matters to me.

quote:
"I made a BMP that sounds magnificent, with a great rising overtone that blossoms as you sustain a note. Viewing it with the sound card scope software that Jack Orman posted shows a change in one of the lower order harmonics but not the higher ones."

As for this, I'd guess that you didn't use all ceramic caps in yours. The ceramics don't seem to sustain as well. Well, they sustain like a high-gain Marshall but with decent caps mine will sustain the note, then get an octave-up sound as you hold it longer. This would be backed up by you seeing the rise in lower order harmonics, in particular the second.

I've got a writeup about my Sovtek BMP conversion and a Sovtek Small Stone conversion that made both pedals sound amazing at
http://pauley2000.tripod.com/

6/13/2000 2:26 PM
Mark Hammer	Well, I would almost agree with you, since I think I used plastic caps all round (though its at home right now and I couldn't vouch for it). HOWEVER, I used the same caps for another one I made and it behaves very differently. Also a great pedal, but very different personality, and not capable of the full-on splat of the first one. Again, I need to look at the two and tell you what's different.

6/13/2000 3:37 PM

Mark measure the power supply voltage and measure the collector voltage on the one that sounds good. I have been building alot of my effects with bias controls and the bias seems to be one of the most important parts of the sound with overdrives (rangemaster) fuzz (FF).

Here is a fun rangemaster in Si .1uf in cap, 100k b to gnd, 220k in series with a 1meg lin pot b to +9,2n3904, 4.7k in|| with 47uf e to gnd, 10k pot c to +9.,.1uf output cap 100k pulldown.

One can realy hear the clipping and harmonic changes with the bias pot. I tend to like the Si Rangemaster at about 7.2v to 7.5v collector voltage

6/13/2000 3:41 PM
Gus	FWIW in the BMP I would also make the 470k collector to base feedback resistors 220k and a 500k to 1meg pot in series this sets the gain a bias point (this will change the harmonics).

6/13/2000 5:49 PM

I don't remember the detailed technical explanation of it, but stages 2 and 3 in a BMP are limited to ~1.3 voltage swing total because of the clipping diodes so there are no biasing issues with it as long as its in the middle of the supply somewhere. Not too hard with 9v.

Given this, any nuances caused by biasing stage 1 differently are going to be torn to shreds by stages 2 and 3. Maybe rebiasing stage 4 could lead to some assymetrical clipping, but that's not really what people use this pedal for anyways. You could probably get better results by switching one side of the diodes in stage 3 with Ge.

Nevertheless, biasing does have a very huge impact on the sound of the FF family of circuits.

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