Bookmark this guy.
http://user.eduhi.at/aquataur/aquataur/musicstuff/musicstuff.html
It took me FOREVER to find him again.
His "Queen of Tone" article is gold on its own, and the new Umble improvements are certainly worth a really close look (considering he managed to get something far better out of one of ROG's least successful designs).
Helmut is a good guy and his work is always top notch. He has done good work with fuzzes and is never boring.
Thanks for the link Jon!
Yeah somebody once told me about this site but I forgot about it in the meantime. Thank you John!
I couldn't find his Umble modified schematic.
Quote from: ChrisM on July 19, 2013, 06:33:32 PM
I couldn't find his Umble modified schematic.
I don't think he posted a modified schematic for the whole pedal, but here's the umble article.
http://user.eduhi.at/aquataur/aquataur/musicstuff/umble.html
His mods include a compressor/sag circuit that involves like three parts, so of course I had to ask him about it:
QuoteI'm intrigued by your little compression setup, and I had a couple
questions. First, it looks like it's half-wave rectification, so would a
second diode on the hold cap/resistor side provide full peak-to-peak
rectification? Second, could you take a guess as to the /attack/ time (it looks nearly instantaneous?) and the ratio?
QuoteYes it is half wave, but allegedly some state-of-the-art circuits use nothing more. According to the author of the series of books I am citing (Kevin O´Connor, whom I have mixed experience with personally...) it does not make much difference.
Using a second diode would kill the circuit stone dead because it would introduce a positive voltage rather than a negative. A much more elaborate circuit (with a precision rectifier) would be in order, which would probably gain nothing. This is, if I understand right what you suggest. On a scope you can clearly see the compressor kicking in.
The attack time is determined by the series 100k and the 1uF, resulting in 100ms attack/decay time. Although there is no exact number to be determined for the r/c time constants that produce sag when the tube power stage draws current (they all seem different...) 100ms seems a good starting value. If you make the envelope flatter (bigger attack time) you start to lose treble and change the tonality. But fiddle with the cap - by all means.
This primitive circuit seems to work well, I like it much for slide because it takes away some of the "ping" of a brass slide while retaining the raunch. Sounds much better than without. Unfortunately, those things are hard to convey on seconds-long demo files replayed on pc loudspeakers.
Let me know about your findings,
sincerely,
-helmut
Thanks Jon, I'm going to give that little circuit a try.