Maestro FSH-1 : noise generation part

[ricothetroll]

Hi,
I'm currently building this pedal from Tonepad's schematic :
http://www.tonepad.com/project.asp?id=50 (first version)
When I came to the noise transistor selection step, I breadboarded the piece of circuit around Q1 and IC3a, with +9V and -9V from my LM317/337 "lab" PSU. I tried lots of different 3904 and I always get a squarewave at the output of IC3a instead of noise. I a transistor it in the circuit and S&H and VFC do work but as it is driven by a cyclic source it doesn't sound random neither. As I don't have received my MAX1044 yet, I supplied the circuit with the same PSU. The outputs of my "lab" PSU are filtered by 22uF + 100nF (+ 220u on the circuit supply inputs) capacitors, maybe that could play a role.
Would anyone have an explanation for this phenomenon ? What should I do to get that nice noise from that circuit ? One of my last posts was about fighting noise, this one is about getting as much as possible of it
Best regards.
Eric

[hannibal827]

I found that the biggest variable in the noise was the NPN transistor itself, and that 2N3904s didn't achieve "the sound" for me.

I'm using a BC109 in mine, but other builders have found success with 2N5088, MPS222A, BC337, etc.  Read the build reports @ Tonepad or do a search here for more comments on this.

Good luck.

[ricothetroll]

Hi,
Thanx for your answer !
I'll try some other transistors I have in my drawer. Nevertheless, it seems weird to me that I could only get a squarewave out of the noise tran + derivator circuit, trying like 20 different 3904...

[lonewolf]

I tried different transistors for the noise (3904/5088/5089)..the 3904 was too weak..5089 was too intense..I settled on the 5088..gets me that ELP karn evil 9 effect...the trans seem to change the intensity of the s&h not the random sounds..was considering adding a DPDT switch and using the 5088/5089 and switching between them or something else..

[ricothetroll]

Hi,
I tried with a 5088 I had, now I get some kind of triangle with cut top waveform, and it sounds a lil more random, but I still do not understand why I have built an oscillator instead of a noise generator

[frequencycentral]

Ground the base of the noise transistor. Then pretty much any transistor will work. Trust me.