Low noise Rangemaster transistor!

[coxy46]

I have been experimenting with the RM circuit for quite a while now, and today I tried in it an AC128. Wow it is so quiet, when the volumes rolled off on you guitar the background noise is so quiet you hardly know it's on. In the past I have always tried silicon transistors as I thought with silicon being modern they would have less noise, and I did study all the datasheets regarding the Noise db figure and went out and got the lowest ones which were available. they were npn ones -BC184, BC109, BC550B. But all these are so much more nosier than the AC128. Yes the AC128 has less gain around 100 compared to 300 for the rest. But even a BC550A that i tried (gain measured at 150) was a lot noisier than the AC128.

The AC128 is germanium as you will all know, is there a low noise Silicon one that anyone knows of that will be as quiet (if not quieter - if thats possible) than the AC128? As i do prefer the harsher sound that the Silicon ones produce. Or is there an even quieter transistor around that will slot nicely into a npn or pnp RM?

[RDV]

There are quite a few low noise NPNs out there like 2N5089 or MPSA18. I gotta think that the reason for the noise is the higher gain of the Si NPNs Vs. the AC128. I've never made an NPN Si RM.

OK?

RDV

[Steben]

Where in your setup is this RM situated? Right after the guitar?
-If not, it is normal you have less noise with the AC128, since it has less gain, less amplifying the noise of the thing in front.
-If it is, it's remarkeable, since germaniums normally have more inherent noise.

[petemoore]

There are quite a few low noise NPNs out there like 2N5089 or MPSA18. I gotta think that the reason for the noise is the higher gain of the Si NPNs Vs. the AC128. I've never made an NPN Si
  After 'correcting' the biasing to convert an RM to an Si Booster ... I think it's called "LPB". An Si'll 'work' as in gain, but the bias isn't 'optimal' with an Si in an RM circuit...or is it, you decide..!

[nelson]

There are quite a few low noise NPNs out there like 2N5089 or MPSA18. I gotta think that the reason for the noise is the higher gain of the Si NPNs Vs. the AC128. I've never made an NPN Si
  After 'correcting' the biasing to convert an RM to an Si Booster ... I think it's called "LPB". An Si'll 'work' as in gain, but the bias isn't 'optimal' with an Si in an RM circuit...or is it, you decide..!

Screaming tree 

[mac]

For a Si version of the RM you will need to change the 470k. Use a 330k if hfe is around 100 - 300 to get 6.7v - 7.0v at the collector. MPSA42 has a gain of about 100.

mac

[smallbearelec]

You are fortunate that this particular AC128 turned out to be quiet. Gross variations in gain, leakage and noise level are the norm for germanium, even among devices of the same type. Enjoy your new pedal!

SD

[mac]

I've tried a lot of NOS Ge for my RM and they all are quiet:

pnp matsushiita --> 2sa101, 2sa102, 2sb172, 2sb175, 2sb176
npn      "     "      --> 2sd352
npn sanyo --> 2sd72k
pnp toshiba --> 2sa49, 2sa52, 2sa53, 2sb56
pnp siemens --> af106
npn --> ac187k, ac176

I guess that being all from well-known companies makes a big difference when it comes to noise and tone.
I decided to use a 2sa102 hfe 77 leak<150uA because of the tonal response. Leakage current forced me to use a 560k instead of the 470k to get 6.7v at the collector.

mac