|
Maestro FSH1 a.k.a. Madbean Sharkfin on the bench A look at the LFO and sample&hold section and a fix for the noise generator last update: Oct 11, 2014 Copyright
2014-2022
by H.
Gragger. All Rights Reserved. All information provided herein is
destined for educational and D.I.Y. purposes only. Commercial re-sale,
distribution or usage of artwork without explicit written permission of
the author is strictly prohibited. The original units with
their
associated trade-names are subject to the copyright
of the individual copyright owner. The Author is by no means affiliated
with any of those companies. References to trade names are made for
educational purposes only. By reading the information provided here you
agree to the Terms
of Use.
|
||
| MAIN PAGE>MUSIC
STUFF>FSH-1 random CV Index  AbstractFixing The Noise GeneratorReferenceAbstract This is an closer look at the FSH-1īs[1],[2] CV (control voltage) generator in lieu of driving the Colorsound Dipthonizer clone with the random values this produces. The envelope generator and VCF section are disregarded. The FSH-1īs CV part consists of a of a LFO section that triggers a sample and hold circuit, which samples a noise generator plus some more filtering and level shifting circuitry. The sonic result of using this in the Dipthonizer 13x00 was inferior, so it was abandoned. However a sure fix for the noise generator has been found and tested. Back To Index Fixing The Noise Generator According to plenty of internetīs stomp box builderīs experiences the noise generator part is seemingly notoriously vulnerable. It is not known, what their problem was, presumably too little noise from the noise generation transistor Q4, which leads to a lot of mojo regarding transistor choice. The original circuit uses a reverse biased transistor with the base open, which is very strange. It is not easily explainable, how this is supposed to work, no reference could be found that supports that wiring, however it is easily comprehensible that this does not work in many cases. In contrast, a better known circuit is to use the base-emitter junction of a transistor in reverse, which exhibits an excellent zener diode breakthrough at about 6 Volts. Zener junctions are known to be noisy. Naturally, a 6V (or thereabouts) zener diode will work too. The subsequent OPA (operational amplifier) is there to boost the noise signal to a useful level. The first transistor that was tried worked like a charm - why should it not. The unused collector pin can be tied to the base or being left open - this makes no difference. Unstable existing designs can thus be fixed by just soldering those two pins together. Any old NPN transistor should work. For j-fets BF245A type work well, type B or C may not work due to the increased voltages needed to turn them off. Since it was originally planned to install this subcircuit into the same housing as the Dipthonizer 13x00, the power supply section of the FSH-1 had to be adapted for the single-ended circuit the latter uses. What has been termed "GND" on the FSH-1 now is termed "VRef" on the "Random CV" subcircuit. A ultra-bright LED was used with a comparably large current limiting resistor. Not that increased brightness was being asked for, but low current demand. The increased brightness however helps the LED to be appreciated since the pulse with of the sample pulse is very small. Although the random CV subcircuit works great per se, it did not sound too great together with the vowel sounds and thus did not make its way into the Dipthonizer 13x00 housing.
Back To Index [1] Madbean Pedals, Sharkfin, http://www.madbeanpedals.com/projects/Sharkfin/Sharkfin.pdf [2] Tonepad, Maestro Filter Sample Hold, http://www.tonepad.com/getFile.asp?id=138 Back To Index Update History
MAIN PAGE>MUSIC STUFF>FSH-1 random CV |
||
MAIN PAGE
| MUSIC STUFF | IMPRESSUM  (c) 2014-2022 AQUATAUR Musik & Elektronik |
