Why so many transistors in a mic pre?

[gct]

HI

Just trying to understand what all the transistors in the input of a mic pre are doing. I built a simple pre with 2 transistors. My Voicemaster has many more. The API seems to have a whole army.

Why so many transistors? How are they shaping the sound?

Seems like the more the merrier!

Cheers

GCT

 

[abechap024]

The more transistors you have in parallel the quieter the preamp. Seems like the opposite would be true, but because the transistor noise is basically random hiss, it actually cancels out the more transistors you have. A crazy phenomena of nature.

 

[gct]

OK Thanks. Oh yeah a couple of red leds stuck in the circuit  too.

Noise wasn't a problem in my simple preamp but it sounds quite different from the Voicemaster. I'm looking for something that's softer on the highs (Always loved valves on guitars and tape sounds more musical to my ears.) But without having to buy (much) more gear. Impossible right?

Cheers

GCT

 

[JohnRoberts]

The more transistors you have in parallel the quieter the preamp. Seems like the opposite would be true, but because the transistor noise is basically random hiss, it actually cancels out the more transistors you have. A crazy phenomena of nature.

It's not quite that simple.. paralleling devices can drop the noise voltage but will increase the noise current so the new effect depends on source impedance. i.e. for a low source impedance the total may drop, for a high source impedance it could increase.

It is impossible to answer what the different transistors do, they do different things in general.

JR

 

[abechap024]

The more transistors you have in parallel the quieter the preamp. Seems like the opposite would be true, but because the transistor noise is basically random hiss, it actually cancels out the more transistors you have. A crazy phenomena of nature.

It's not quite that simple.. paralleling devices can drop the noise voltage but will increase the noise current so the new effect depends on source impedance. i.e. for a low source impedance the total may drop, for a high source impedance it could increase.

It is impossible to answer what the different transistors do, they do different things in general.

JR

Thanks John, I knew as I was typing that I was missing something, so it depends on the impedance. That makes sense, Like how FET input opamps are usually used with high impedance because less current noise and bi-polar usually for lower impedence, again I over simplify, but fascinating stuff!

OK Thanks. Oh yeah a couple of red leds stuck in the circuit  too.

Noise wasn't a problem in my simple preamp but it sounds quite different from the Voicemaster. I'm looking for something that's softer on the highs (Always loved valves on guitars and tape sounds more musical to my ears.) But without having to buy (much) more gear. Impossible right?

Cheers

GCT

are you using an ne5534 chip in the focusright?

 

[gct]

It's standard issue - I just looked at the components on the preamp.

 

[gemini86]

Guess what's inside those ic opamps? A bunch of transistors.