EH Soul Preacher UPDATE!

[markm]

So it was part of the Deluxe and not a unit on it's own.
From the schem it looks like a Hybrid between the Dyna and the O/S type.....weird.
How's it sound on it's own....any clue?

[Bernardduur]

It was also a standalone unit; I asked EH for a schem and they had one of this unit but they had to search for it.............

I am still waiting

How does it sound; I dunno yet; the unit is faulty as it keeps oscillating but underneath I hear this compression that is quite crude. I will replace the 3080 in it quite soon as it is the only thing I haven't tried

[markm]

It was also a standalone unit; I asked EH for a schem and they had one of this unit but they had to search for it.............

I am still waiting

Ummm, could I get a copy of that schematic when you receive it?! 

[Bernardduur]

Why not use mine

Will do!

[analogguru]

Which brings us to the input buffer.  Though I can't imagine that the BC239 is an atrocious choice for input buffer, neither is it known as a low-noise unit either.  It was simply the default NPN medium-hfe transistor at E-H for a little while.

1.)  BC 239C IS a low-noise transistor with F<4dB.

2.) The only less noisy transistors this time (when BC 550C was not available) were the BC 413 with a noise figure < 2,5 dB or the japanese 2 SC 1000 with F<2dB

3.) The gain of a BC 239C is 450 - 900 !!! what is not really bad or "medium".

There may well be other trannies that can yield a quieter input signal.  Note that this applies to the input stage only, and not to trannies in any of the other non-audio positions.

4.) The input stage is only a buffer with a gain of approx 1 (one).  So i can´t imagine, how to achieve a "qieter" input-stage, since the noise of the transistor doesn´t have any influence on the signal - maybe the high-impedance resistors will have more.

5.) the "Threshold"-Amp has a gain up to 111 ("resistor-noisy" with 110k in the feeedback loop - for "noiseless" applications this resistor should not  be higher than 10k, cause the resistor noise will be higher than the opamp noise).  You can try: to lower this gain (and noise) by exchanging the 1k resistor (from inverting-input to 10µ to gnd) and adding an amplifier-stage with a gain of 10 between pin 1 of the opamp and the rectifier-input

6.) the transistor of the input stage can be exchanged to any transistor - if you dont like this input buffer place a standard Ibanez input buffer of the ts-5 series there and exchange.

analogguru

[markm]

Incidently,
This circuit is plenty quiet as it is.....surprisingly!

[Mark Hammer]

Right.  I failed to distinguish between BC239 in general and the C-suffix version which is generally a higher hfe version, regardless of which transistor it happens to be.  I haven't personally run across any 239s that measured hfe more than a few hundred, hence my assumption of "medium' gain.  I also haven't seen it used explicitly in anything *because* of low-noise characteristics.  As you rightly point out, though, just because something doesn't get targetted as a "low noise" unit in the popular literature doesn't mean it ISN'T low noise, relatively speaking.  The BC239C may well be about as good in terms of noise as the design can permit/support.  On the other hand, given that it is followed with a gain of as much as x111, every db of noise can make a difference to some folks in some circumstances, so I encourage exploration of other appropriate semis, even though the 239 seems to be about as good as most folks need (keeping in mind that the compressor may well be followed by distortions and BBD-based effects contributing far more noise than even the worst BC239 might contribute).

[analogguru]

Assuming, that the next effect or amplifier will not need more signal as from the guitar comes and assuming, that with no signal the Fet will be in a high-impedance state, the gain of 111 (~40db) is only needed for the control voltage generation.

The Fet in conjunction with the 220k resistor works like a voltage divider.  Normally you will find a resistor (max. 1M) parallel to the Fet which gives a fixed "ratio" when the Fet moves toward higher impedance.

220k is pretty much, typically you will find max. 100k and 220k parallel to the Fet. In the high-impedance state of the Fet, you willl only "loose" about 3db, so 37 db !!! of gain are not necessary to have equal output signal.

I have never build or listened to this unit, IMHO this unit works more like a limiter which is always limiting at higher gain settings.  so the input signal is always attenuated by the Fet.  Lets assume, that the BC239C produces 1µV noise.  For the reason that the Fet most of the time attenuates the signal this 1µV "noise" will also be attenuated by the Fet, thus will not have any influence on the noise floor.

The noise "generated" by the FB-resistor is always amplified by the op-amp and will exceed the noise of the input stage in a remarkable amount even when the Fet attenuates the input signal and the "BC239-noise".

So the high gain in the signal path is only necessary to generate the control-voltage of the Fet.

Remarkable that there is no signal feedback to the gate of the Fet to reduce distortion.

Also remarkable the 20k resistor which was jumpered.  this resistor influences the attack-time and seems to be a really high value, also the 4M7 for the release-time.  IMHO this is a limiter with long time-constants and for this reason works like an Automatic-Volume-Control used in a tape-deck.

analogguru

[markm]

I have never build or listened to this unit, IMHO this unit works more like a limiter which is always limiting at higher gain settings.  analogguru

I would have to say that you would be correct for the most part.
It's attack and decay are very quick and it will not get overly "squishy" like a Dynacomp but it is very quiet and "transparent" ( I don't like to use that catch phrase but, it is!).

[Xavier]

Whoa MarkM, these are two VERY, VERY nice layouts. When my layouts are half as good as yours, I'll be happy. Soundwise what is the difference between the Ross comp and the saffron squeeze? I may use it in my bi-comp instead of the Ross circuit I currently have

Thanks for another huge piece of work !!!

[markm]

Thanks for another huge piece of work !!!

Ha!!
I get it!

Whoa MarkM, these are two VERY, VERY nice layouts. When my layouts are half as good as yours, I'll be happy. Soundwise what is the difference between the Ross comp and the saffron squeeze? I may use it in my bi-comp instead of the Ross circuit I currently have.

Thanks Xavier!
The jury is still out on this one for now.
I haven't had the chance to A/B it with a Ross Clone but, to me it sounds a "tad" darker on the high Compression side but a bit tighter as well.
I like it...it sounds like....well.... a modded Ross!! 

[rankot]

I know this one is quite old, but I am looking for this updated layout. Anyone can help? 

[rutabaga bob]

There is one in the Layouts Gallery...type in Soul Preacher.

[rankot]

Thanks a lot!