mosfet treble booster?

[John Blund]

Hi.
First of I'd like to say that this is a really great forum, practically everything I've learned(perhaps not enough!) about audio and electronics comes from here, and sites like geofex,amz etc.

My question is if the following schematic would work like a treble booster? maybe if I would substitute the input capacitor with something like 150pF?
or perhaps I should ask if it will work at all?
the schematic is more or less a composite of the unity gain amp in runoff grooves ruby or little gem amp, the amz mosfet booster and what I've understood from the geofex mosfet booster article.



Thanks

[R.G.]

What you show there will not work as a treble booster, or anything else much unless you meant for there to be connection dots at R1-R2-D1 and the gate of the MOSFET to provide the MOSFET bias, and also at R5-C2 and the drain of the MOSFET. Otherwise, the MOSFET gets no bias and the output can't get out. Put the dots there and audio now gets through.

However, it's not necessarily a treble booster. A 0.1uF cap into the input impedance of the two 10M's in parallel gives a low frequency pass point of 0.318Hz, not exactly a treble booster. If you made the input cap 100pf, then it's more of a treble booster with a rolloff point (i.e., where it starts cutting bass) of about 318Hz. But you can pick any place in between to make it what your ears want to hear.

Clever design you have there.

[MartyMart]

John, where did you get that partial schematic from ?
As it's 80% of a Zvex "SHO" schem, perhaps it "sho uld" be removed ??

MM.

Sorry John, I realize that you're new here and didn't mean to "pull the rug" from under you
it's just that Zvex posts here and it's agreed that his stuff wont get posted .... perhaps it's
an innocent mistake ?

[John Blund]

Yes yes, of course there should be a connection between r1-r1-d1-mosfet and r5-c2, sorry! sloppy drawing on my part. But it would work and give a decent high-pass at the input if I put a say 150pF at C1?
the partial is part of a bigger schematic of a stompbox  I made in expressSCH it has an octave down part, dist and some other stuff, but of course I'll remove it if there is any problem!

the feedback is much appreciated!

[R.G.]

ACK! Oh, my goodness! Is that 80% of the SHO?

John said it was a composite, so I thought he came up with it on his own.   javascript:void(0);
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[zachomega]

I wouldn't have known it...It is a pretty generic looking schematic. 

-Zach Omega

ACK! Oh, my goodness! Is that 80% of the SHO?

John said it was a composite, so I thought he came up with it on his own.   javascript:void(0);
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Shocked

[markm]

ACK! Oh, my goodness! Is that 80% of the SHO?

John said it was a composite, so I thought he came up with it on his own.   javascript:void(0);
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Shocked

Ya know, the SHO is not a super complicated circuit however, this does seem to look like about 80% of it doesn't it?!
This probably is not so.... however, alot of the "core" of the SHO can be found between GEO and AMZ.
One would suspect that Zachary spent some time there however, and like I said, it probably did not happen that way.
The similarity is if nothing else, Interesting.

[tcobretti]

Marty, please don't be pissed off; I am not trying to be a jerk. 

It seems like pointing out that this bears a similarity to the SHO is actually more damaging than post the schem in the first place.  It seems like every week somebody posts a "new" booster, and if the similarity to the SHO had gone unsaid I think no one would have thought twice about this circuit.

Now, if the original poster had said, "here's a circuit based on the SHO" things would be different.

[petemoore]

  Nice high imput impedance, Mosfet...perhaps there is a simpler way to connect a mosfet gain stage?
 Perhaps only one base bias resistor?
 With near equal source and drain resistors, what is the gain of this stage?
 

[John Blund]

I'm sorry have I done something bad!? I mostly looked at the variable bias network 2 in the mosfet article at geofex, the amz and the peppermill overdrive (not the ruby/little gem. sorry it was a few months since I made schematic) at runoff groove and though that preamp section looked alot like the drawing at geofex. so I took the 10M input impedance and variable bias resistance form the amz, replaced the red led with a zener as it said one could on the peppermill and added the end with anti-pop from some other booster schem i found.

[markm]

I can see how this could happen.
Like I said fellas, spend ALOT of time reading at both R.G.'s site and Jack's site and you'll see there is a boatload of MosFet info there that could easily become a SHO-type booster. I know this first hand as I have spent many evenings there.....just ask my wife! 
Most of which does resemble the "core" of the SHO.
It's not exact but perty-darn-close.

[tcobretti]

John, you just stumbled onto a circuit that is similar to a pedal made by a boutique pedal builder.  We try not to discuss the boutique guys' pedals here so we don't hurt their business.  No one is mad at you or anything; unfortunately, this is kind of an ongoing discussion here.

[zachomega]

I still take the position that it is a pretty generic looking circuit...even if it was identical to the boutique circuit.  It's like trying to copyright a word.  They are the basis of language.  In this case, it is a rather fundamental circuit.  No harm...and additionally, I don't think the intention to sell this pedal or design was ever out there.  Just my two cents.  I'll put my soap box away now.

-Zach Omega

[Barcode80]

8 parts. lets not pretend that amounts to anything. its like saying that putting an output volume pot on the end of a circuit and filter protection is an indirect copy of the thousands of circuits that have those things. this snippet, or small variations, is everywhere in a very generic way. how about we redirect the thread to answering his questions?

[burnt fingers]

THis is an interesting thread.  I have that very schem on my harddrive. It's been there since July. I  Don't know where I found it but it was similar to another schematic(similar = identical) that I found three years ago on the web in an old text file drawing.   Seems that this simple little booster has made it's rounds and a few have copied it.

Scott

[Processaurus]

I made a AMZ MOSFET booster a treble booster by making the cap in series with the 5k pot smaller.  Actually it made it a treble knob, with flat freq at one end and a painful level of treble at the other.  Maybe a bigger cap than I used would give it some boost too.

I haven't had the opportunity or interest to take apart a real SHO, but from a bootlegged schematic I saw on the net I would have naturally been inclined to modify the circuit I saw to be like the AMZ.  No crackle, even though it's okay.  Its sacreligious, but after trying the Mosfet boost, for my uses I feel a opamp booster with a low noise FET input opamp and a charge pump for more voltage would be a higher gain, cleaner, quieter alternative to any of these.

I was really suprised with the tiny current draw it had when it was idling, though.  It'd be good built into a guitar.

[rockgardenlove]

As for the SHO issue, I don't think the harmful part is the schematic, just the point that somebody pointed out that it was close.   
If somebody was trying to copy a SHO they'd pass this by had somebody not pointed out the similarity.

ANYWAYS, yeah, the capacitors on there are too big to really cut any bass.  Replace the input with something smaller like R.G. said you'd have one.

[petemoore]

  Well..I started building when RG said mainly hookup the base bias R's to the Q. Looked like an easy way to use these 10m's and I have large batches of 2n7000's, not my favorites, but I figured throw one in a bias scheme that works and see one more time if I can get to like 'em.
  I have a Mosfet boost sounds pretty good with one in it, just a bit hard', I know..I should get BS170 or something..
  So far I've done alot of debugging, maybe I'll find something new on it tomorrow.

[MartyMart]

As for the SHO issue, I don't think the harmful part is the schematic, just the point that somebody pointed out that it was close.   
If somebody was trying to copy a SHO they'd pass this by had somebody not pointed out the similarity.

...... Yup, I realize that ..... now  !!   

Just seems like a "close" accident .... that's all, no one's mad at John, least of all me 

Appologies to John, Aron and "Z" ..... I'll crawl back in my hole now .....


MM.

[d95err]

Small analogy: It has been said that the human genome is something like 98% identical to that of the Chimpansee. It's the last 2% that makes the difference...