How to reduce background noises on a smd-built distorsion clone ?

[eh la bas ma]

Hello,

This is my first effect pedal, bought used for 20 euros, several years ago.
I'm sure it's a clone but I don't know what is the original unit. Maybe Boss sd1 (from the similar names) with an EQ with two knobs instead of the boss's tone control ?

Anyway, I like very much how it sounds. The only issue is the great amount of background noises when the "High", or Sustain, or Dist controls are set above 12' (just when it is getting interesting).

This noise sounds like the wind is blowing, like several high gain circuits are stacked, set on max levels : I built several distorsion circuits and this one is really noisy next to them.

I tried several power supplies without any change, and it is not working at all when i try powering it with a 9V battery, like it is supposed to.

If I leave the guitar input unplugged, there is a very high pitched whistling coming from it, when engaged.

I hope someone might have an idea about the original circuit, and an other to help reduce the background noises, even if it is smd soldering.








The biggest IC reads "dbx 1252 Singapore 9245ME090"

[D_Ex_Patria]

Well that IC actually appears to be for DBX noise reduction, which is not an SD1 part at all.  There's also two op amps in there, an Lm358 and a JCR 4560. If I had to guess, the LM358 is being used for some utility task, like voltage reference, and the JCR is doing the amplification

Without any tracing, I gotta say it's a bit of mystery to me. My gut says the JCR could be replaced with a lower noise JFET to reduce noise, but that's just a guess.

What does it actually sound like when you play it?

[eh la bas ma]

Here is the only demo I could find :

https://www.youtube.com/watch?v=0Fh2l1zeBaU

I will upload a sample on souncloud now.

[iainpunk]

the LM358 is really noisy, i hope it isnt used for gain stages, that would be really bad. in another scenario, it could be injecting noise in the bias voltage, which would be really bad.

if it were a through hole board, i'd recommend a ''dirty gate'' in-between gain stages, although it alters the sound, it removes a lot of noise. i guess it would be harder to achieve on an SMD board.

looking at the JRC4560 data sheet, i am impressed by the low noise and slow-ish slewrate, generally traits of a chip with nice sounding distortion when it clips to rails.

cheers, Iain

[eh la bas ma]

Here is a sound sample : https://soundcloud.com/ehlabas-ma-chaussure/sd100samplewav

[PRR]

> that IC actually appears to be for DBX noise reduction

Better to say it is a general-purpose VCA. Which could be the core of a DBX (why they worked on stuff like this), but other things too.

[eh la bas ma]

Thank you for your answers.

First time I see "dbx" designations. Are they unusual in effect pedals ?

I guess I won't be able to reduce the background noises...

I would like to build a variant of this circuit, which would allow me to add some mods. I didn't find any reference on internet. Can someone tell me the name of the original effect, please ? Something from Boss surely ?

[eh la bas ma]

It looks like this circuit has been sold under various brand names : Xpression SD-100, Boston SD-100, Odak SD-100, WSL SD-100...

No mention of an original version, either it's a well kept secret, or it's an original distorsion made inside some mysterious factory (Elder Audio Manufacture is written on the back of the enclosure).

[anotherjim]

If the DBX chip is only a VCA, then the LM358 is probably only providing the sidechain control for the VCA which it is well suited for.
If the FX is as a compressor/sustainer then increased noise at some setting is an occupational hazard as the low-level sound gets the most gain and the noise is low-level sound although it should appear to duck down under a strong signal.
OTOH, the VCA could be a noise gate and it has failed somehow.
There's a lot of small signal diodes on the board (some will be in the VCA circuit) so distortion might be added with clipping diodes afterwards.

[eh la bas ma]

Here is some pictures from different angles, in case someone can  recognize some similarities with an other circuit :








it seems like there is a lot of components in there :  3 ICs, 14 transistors , 9 diodes, around 60 resistors and 30 capacitors ...

Sound sample in reply #4

Thank you for your help !

[eh la bas ma]

Could it be a Boss MD2 clone ?