One golden transistor to create noise in a drum machine

[JohnRoberts]

That is very strange. It looks like part of the exponential converter, which uses an emitter-connected pair in the LM3046. I can't  figure out what it does or what it's for.

It hurts my head to look at that but the 3046 is a simple small signal transistor array. They are only using two of the internal transistors, the ones connected internally to make a LTP (differential "long tail pair").

From a quick look it appears to be making a current source to feed a sawtooth generator. C2 sucks a small constant current from C3, Q3 resets the sawtooth with positive pulse.

Q1 and Q2 may be some form of temperature compensation but not obvious to me.

JR

 

[living sounds]

Would it be possible to use a PNP transistor "backwards" instead of the 2SC828 (NPN) here? I've got a very noisy Germanium transistor I'd like to try.  8)

 

[JohnRoberts]

The last time I messed around on the bench making noise on purpose was more than 4 decades ago, and as I recall it was disappointing. 

The reversed b-e junction zener is pretty universal phenomenon AFAIK, but some transistors are engineered to not zener that low (I think). For example transistors used as output mutes (I've seen them in tape recorders), are often used backwards for lower DC saturation voltage and must pass audio without zenering (but many of those were modest signal level too).

For one off DIY, just try what you have laying around, for production I don't trust using this mechanism, especially now with cheap digital.

JR

 

[PRR]

Well-engineered Silicon devices are engineered to B-E Zener right around 7V for good gain.

Older Ge devices did not all do this. Some are high breakdown both ways.

But WHY are you asking?? It is two wires! Try it.

 

[DerEber]

It is two wires! Try it.

Yea, now everyone is curious!

 

[living sounds]

Well-engineered Silicon devices are engineered to B-E Zener right around 7V for good gain.

Older Ge devices did not all do this. Some are high breakdown both ways.

But WHY are you asking?? It is two wires! Try it.

I did - it didn't work.  :

 

[marcn]

I put a pot for the noise level on my diy'ed 808 sound modules. The level of the noise affects the sounds which use it quite a lot, the higher the 'grainier' it becomes, could be the sizzling effect you describe on the snare f.ex.
I wouldn't be surprised if the trim pot in original 808s has drifted a bit over the years and small changes can mean a drastic change in sound behaviour here if i remember correctly.
I don't buy into the obscure component myth.

 

[saint gillis]

  Who want to buy a Behringer RD-808 and see what's inside?

 

[Jarno]

I did - it didn't work.  :

You did what and what didn't work? A transistor noise circuit is decidedly simple, and not fussy about components.
As mentioned, I have a board which has a transistor noise circuit, so you can audition different transistors.