BMP : BC239, 2N5088, 2N5133... ?

[billou_35]

Hello,

I made this project :
http://www.generalguitargadgets.com/diagrams/bmpsc.gif

I put 2N5088 with hfe around 500 and was deceived with the sound. I was not really breathing, and as filtered : not so much bass, ... I should have made a mistake ?

So I bought a Sovtek Green with I think 2N5088 in there (same package), hfe near 500. This version has real bottom end, much more breathing..., much more bandwidth.

I saw a schematic with triangle BMP and seems different from mine ? Is it enough to explain the difference ?

I wanted to know which transistors is sounding best according to you ? I know that everyone is looking for something different but is there a consensus about it ? Which Hfe range ?

I saw this :
http://home.exetel.com.au/mosrite/Electro_Harmonix_Big_Muff_Pi_Triangle_Model.php

Do you agree ?

Thank you ! 

[Bernardduur]

I can highly recommend the thundertomate schematic for the 1981 BMP; it sounds soooo good!

[billou_35]

Thank you Bernardduur !!! 

[Mark Hammer]

At this point, I've built a couple of BMPs, all with the same schematic, and pretty much entirely with 2N5088s (once with MPSA18, maybe).  And you know, they all sound different.  I realize there are different schematics for different issues, and different transistors associated with different issues (and strongly held opinions about them).  But you know, I'm gradually coming to the conclusion that no one has ever done the sorts of comparisons across issues to be able to say conclusively that the sonic properties of THIS specific issue are consistently XYZ and are conistently a product of use of transistor Q.  My creeping sense is that variations within each type of transistor, not to mention variations introduced by other component tolerances (and especially the way components would change, seemingly week by week, in the early days of E-H) introduces enough inconsistentcy in circuit behaviour that all we're really left with is the generic effect of a double clipper (which will always produce a nice wooly sound, as long as you give it enough bandwidth and lotsa gain) and a particular type of tone control.  After that, it is all happenstance.  It's like a recipe that says to us 3 eggs and set the oven hot, with no further detail beyond that.  Hard to expect the product to be the same all the time when you don't know how big the eggs are supposed to be, and what he oven temperature is.

Now, I'm not pooh-poohing the mods that people have done which improved the tone to their liking in their particular case.  What I am a little skeptical of, though, is the assumption that ALL the 2N5133s or BC239s or2N5088s that buyers at E-H ever got their hands on were identical and consistent within type, and that any unit built with BC239s will sound exactly like all other units built with BC239s, and that all units built with 2N5088s would always sound different than all those built with BC239s in identifiable and consistently-occurring ways.

The thing to keep in mind is that BMPs are built according to a schematic.  What you will not find on them are trimpots that permit them to be built according to a spec.  That's an important distinction.

[gaussmarkov]

mark, you make a point that i have been wondering about for a while.  you are talking about the bmp, but this variation is going to occur in other circuits too.  for example, i built two red llamas.  i liked one much better than the other.  i don't think there was any significant difference in the builds, but i couldn't say for sure.

so everyone, if this is true for a bunch of the things we all build here, it would be nice to know (esp. for newbies) which ones have the most variation.  from what i have read, and my limited experience, fuzzes have pretty high variability.  tube screamers are fairly consistent, yes?  how about cd4049 circuits?  compressors?  phasers?  tremolos?

i guess part count adds a lot to variation in builds, too.  or are there some circuits for which (taking away the higher chances of making mistakes) this is not true?

just ruminating from the road, gm 

[petemoore]

  First note all by builds may not be good 'lab specimens', but after building 3 [at least if you count socketting Q's as 'another one'...]...all were built to the schematic values, all biased properly, all passed boosted signal & knobs work right etc...all sounded different.
  Two triangles and a Green...
  The one Triangle is the BMP I'm actually having in the line up these days, it is using Mesa and other Ge transistors...one fine box...
  One lacked the gain of the other, the basic tone of course was different' also.
  Considering the number of and amount of gain the BMP stages produce, small differences in gain near the input [first/second stage?] being multiplied by successive stages...small differences become larger ones, this may explain why there's a BMP camp of those who know the BMP to be different one to the next...besides the fact that factorty units used 10k or 12k collector resistors depending on which was closest to the board at the time...
  I prefer Triangle Muff circuit...they're all a little different...so I can't say 'clinically' that my preference is based on anything tangible, it could be that's just how it worked out...the Green one just didn't perform as well for me, in my limited comparisons...

[billou_35]

I'd like to thank you all Guys !
Thank you to share your experience with me... I think I just have a thing to do... continue again & again to make experimentations !