BSM Best Treble Booster vs. my RM clone

[Stompin Tom]

Sorry about another rangemaster post, but...

I've been borrowing my friend's BSM RM clone and it sounds fantastic (even through my SS labseries L5).  I've been trying to replicate it and I can't quite get it.  I've tried all sorts of input cap values and different Ge trannies (smallbears oc44 sounds best to me).  I've read the geofex article and biased the trannie, too.  But, the bsm just gets more gain and is creamier and smoother (more mids?).  I've also tried adding resistors to the volume pot per a suggestion (sorry, don't remember who) in the archives.  That did seem to increase the gain a bit, but still not quite the BSM.  I can't figure out what they've done...  any ideas?  Do they just use the most awesome trannies ever?

[Mark Hammer]

I made a RM clone using a 2SB172 a couple years ago, before they started being commercially cloned by everyone and their cousin, and it was wonderful.  Brought it in to a local vintage store to demo and the owner gave me $60 for it on the spot.  Regardless of what he has going through his store (and there is LOTS of nice stuff), it has remained a part of his pedalboard since then.  Unfortunately, no matter how many other GE transistors of the same or other type I've had in my mittens (and thanks to local stores, the very generous Mike Irwin, and others, that has been a LOT of them), I have yet to get anything that sounded quite as good as that one I sold (though I haven't yet tried out the OC70's that Chris Darlington graciously sent me, or those weird "flying saucer" Russian trannies).  So, my vote is gonna be for having a pile of transistors to sort through.

[Stompin Tom]

Thanks.  I was afraid of that.  FYI, BSM swears that they use oc44s. 

Has anyone had any exceptionally good results from the small bear stock?  I've tried an oc44 (sounds best to my ears), oc71, oc77, and the cheap japanese one...  I guess I'll have to start lurking on ebay.

[Mark Hammer]

Note that I have NOT used any OC, NKT, or AC-prefix trannies.  It may well be that the pile you have to sort through to find a good one is dramatically smaller.  But I've gone through a tiny mountain of 2SC and 2SB units, with only one real success so far.  I'm just glad I got them cheap.

[Stompin Tom]

ummm... good to know.  Thanks again.

[stm]

Since it is clear that the transistor characteristics play such an important role in sound, it would be a good idea to take the scientific approach (if possible and if allowed by the owner) so as to measure hfe, leakage current and actual operating voltages of the circuit to see if it is possible to find a correlation between actual parameters and good sound (like the 70-130 hfe's for the fuzz face).

[Stompin Tom]

Well, stm, that is a good idea... except that bsm has sealed the circuit in some sort of black plastic box that has been glued to the aluminum chasis.  I can't get it apart to save my life.  Maybe the glue costs $200, making the $250+ price take for a new bsm booster reasonable...

[stm]

I see... Then it might be that the better sound is not only due to a well selected tranny, but to some circuital differences with respect to the original R.M. as well.

[petemoore]

  I read this post, measured resistors for todays RM clone...
  Two of the Q's tried were OC44 and 2sa49, both very close in hfe [75 and 76 'cool'] the OC44 drifted up to about 91hfe, the 2sa49 up to 111hfe when hand warmed for 15 seconds.
  at 'cool' Hfe's, they sounded different, not too surprizing ? I guess since the Mesa construction method is alot different than Planar technology [I think the OC44 is Planar].
  The OC44 had lots of gain, not as much as the 49, but sounded smoother, just a different voice.
  Also tried were Ge transistros of "SB", NTE158, and other '2sa' Mesa types, Hfe's measured from 22 through 159, nothing in the 50hfe range, which is where I guess unity gain 'starts'.
  Gain / Leakage /...and Tone ?

[Stompin Tom]

Maybe they select for high hfe oc44s... 

has anyone ever done anything weird to this circuit?  I don't know what- like add clipping diodes/leds or something?  Would that even work?

[petemoore]

  I'm sure th'ey have...
  Take a look at the amp sims of ROG, many have LP Filters at/near the end of the circuit [look for a couple 10k or so resistors series in SP, with small ~2n2 or so caps from their junctions to ground, this would give a sharper frequency rolloff compared to just a cap to ground...you said the BSM had 'more mids'...
  There was a 1Q, GE Booster schematic, had like 10 resistors and a few more caps than a Rangemaster...
  WHo knows what's in a BSM, no-one I know...but if I had one here...I bet I could get something built that could get at least comparitively close...might take a few or more years, kind of like how long it's been taking me to 'perfect' one of the two RM's I 'race' against one another.
  Maybe it's boostrapped [if that's possible with a Ge], could have some trickery under the emitter/base...lots of things one could try with small chunx of perf, some trimmers 'n sockets, or a breadboard.

[Stompin Tom]

Point taken... I will continue to experiment.  Thanks Pete for pointing me to the ROG LP filters (I can't wait to try it).  I'm not sure how to bootstrap...  Don't you need two trannies for that?  I'll look into it...

[JHS]

If you check out three BSM RM, they will all sound slightly different, due to the part tolerances.
If you power a BSM RM with a carbon battery, the sound ist more compressed and have more midrange compared to a Duracell batt.

BSM build two RM, the RM1 (built like the original) and the RM2, a creamier version with more mid and bass.

Acc. to BSM-info, they use a 25k pot for gain in the RM1 like some of the Dallas originals that they analysed.

I 've built several RM-clones with 10k and 25k pots and there is a small difference in sound. Slight differences in the bias voltage will alter the sound further (more mellow or sharper). I use AC-136 and AF-126 transistors, 1-2W CC-resistors and WIMA MKT for the small caps and high end audio electrolytic and they sound similar to a BSM.

You can alter the 470/68k resistors to 270/33k this will give a smoother tone with slightly more mids.
An added OA90 diode for temperature stabilisation smoothes the sound furthermore and you can play with the current flow of the tranny and the supply voltage.


JHS

[Khas Evets]

has anyone ever done anything weird to this circuit?  I don't know what- like add clipping diodes/leds or something?  Would that even work?

I have. You can add diodes to ground after the output cap or diodes in a feedback loop (like a BMP). Both add some grit, but I can live without it. Don't forget that it reduces the output, which is the point of a booster. Of the two methods, I preferred the BMP approach.

You can alter the 470/68k resistors to 270/33k this will give a smoother tone with slightly more mids.

I'm guessing that the reduction is the high end is due to the lowered input impedance.

[formerMember1]

when i built my rangemaster, i found out that the oc44 is my favorite,...

I like it with greenie caps,...stock values,..

but added7.2k series resistance to the 10k pot, and this made it great!!!  Way better than stock 10k, 16k was too little and 18k was too high,..

[Doug_H]

I don't know anything about the BSM product. As mentioned, transistor types will make big differences in this circuit. I built one with an AC188 I got from Jack a few months ago and it sounds very good (his AC128's were a close second to that IMO). Then last night I breadboarded an npn RM with the OC140 that Aron sells in his store and I like it even better. It is deeper and richer sounding with smoother highs and a little more gain. (This particular one had an hfe of ~100.) This is an awesome sounding transistor and I would recommend anyone building a rangemaster to give it a try.

My point is that Jack's AC's are a big step up from the garden-variety Ge's I used to play with, but the OC140 is another step up to the next level IMO. 

Doug

[Stompin Tom]

Oh, doug... I think you've talked me into buying one of aron's oc140s.  I'll add a diode per the rangeblaster at fuzz central (and JHS's suggestion), and fiddle with the values of everything.  yeah, this may take forever to get right. 

by the way, has anyone had good results with any of those russian trannies?  I've read in the archives that the 308v is supposed to be pretty good, but I don't think anyone compared one to the oc series.  They're so cheap.  It'd be nice if they worked well.

Thanks everyone for your input...

[Eirik]

I've read in the archives that the 308v is supposed to be pretty good, but I don't think anyone compared one to the oc series.  They're so cheap.  It'd be nice if they worked well.

I just bought a lot of those 308v's of eBay. I suppose I'll get them within a week or so, and I will of course test them in a rangemaster asap.
I'll let you know what I think of them.


Eirik