Friedman BE-100 JFET emu

Stompboxes circuits published in magazines, books or on DIY electronics websites.
caspercody
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Post by caspercody »

I took the Friedman BE-100 amp schematic and cleaned it up so it is just the pre-amp stage. You would just need to replace the tubes with a JFET, and adjust the drain voltage with trim pot's. I am sure there will be other things to do, but wanted to get something to start with.

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Rob
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be 100.pdf
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Optical
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Post by Optical »

Any progress on this?
The Pal 800 is a proven circuit and very similar to the BE100, it would be a good place to start teaking http://www.freestompboxes.org/viewtopic.php?f=1&t=28165

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Post by caspercody »

I just posted a schematic, was not planning on building it.

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Post by caspercody »

I finally got around to trying to do a Veroboard, and I started with the Friedman BE-100 Emu.

But, I know this is to wide. The veroboard I have is 34 holes wide. So if someone wants to help and make this not as wide, please let me know and I can send you the DIYL layout.

Thanks
Rob
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BE BOM.pdf
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BE VEROBOARD.pdf
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Post by caspercody »

Here it is to fit a Veroboard, 34 holes wide
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BE VEROBOARD.pdf
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Post by caspercody »

I deleted the 220K resistors, and 10K resistors on the power to the trimmers. I do not think we need them, since the trimmers do the adjustment.

Please let me know if you see any issues, or any suggestions.
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BE VEROBOARD.pdf
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Post by roseblood11 »

caspercody wrote:You would just need to replace the tubes with a JFET, and adjust the drain voltage with trim pot's.
That's how this jfet pedal thing started many years ago, at runoffgroove.com and other sites. But we learned that it isn't that simple...
But you should build that pedal and compare it to the opamp based version and the real amplifier.

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Post by caspercody »

Finally got time to build. The veroboard works. A lot of treble in the sound, and I need to find more time to set the voltages correctly.

I do not have the real amplifier, but did make a BE-OD pedal. Will try to compare.

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Post by J0K3RX »

Might want to consider making the tone stack to scale? Also the source resistor on Q5 should be around 10k or 22k.. use your ear and make sure you get good range from the bass, mid and treble pots.
Attachments
BE100 tone stack HV tube amp scale.
BE100 tone stack HV tube amp scale.
BE100 tone stack to 9V pedal scale.
BE100 tone stack to 9V pedal scale.

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Post by caspercody »

Thanks JoK3RX!!

Roseblood, I would love to make other amp emu's of different tube amps using IC's, but I m not smart enough, or have time to do that. I can however look at a schematic of a tube amp and convert it to JFET, and maybe it is pointless to do it, but I had to try. I have created a vero board layout for the Orange Rockerverb, Bogner Uberschall, ENGL E530, Fender Blue Junior, Vox AC15. I was going to make them, because I have not found any IC versions, but maybe not now.

Is there anyway to convert a tube amp to a IC pedal version?

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Post by HENK »

Yep; see Bajaman in:Ready-to-build... :wink:

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Post by J0K3RX »

HENK wrote:Yep; see Bajaman in:Ready-to-build... :wink:
+ 1 on that! He covered just about every amp that I could think of with the exception of the Framus Cobra/Dragon and the Fortin hulk (evil pumpkin) modded Marshall...

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Post by caspercody »

I did build his Uberschall version, but it did not seem to have much gain?

I added a bax style tone control, maybe need to add a TMB like the real Uberschall uses. Should I reduce it like you showed for the BE100?

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Post by caspercody »

I decreased the tone stack like JOK3RX suggested, and sounds better.

Also, if you place a buffer in front of pedal, you can turn gain to 100% without it squealing at you.

There still seems to be to much treble, or weird noise with the middle strings. I have noticed this noise on other JFET builds. Hard to describe.

I might try to adjust the trim's a little higher, they are all set to half of supply voltage.

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Post by caspercody »

I also eliminated the resistors on the schematic after the tone stack. So Treble pin 2 is going straight to Volume pin 3, and Volume pin 2 is out.

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Post by J0K3RX »

What are you using for Z1 and Z2? Might also stick a buffer after the output volume..

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Post by caspercody »

2N4401

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Post by FuzzMonkey »

caspercody wrote:I decreased the tone stack like JOK3RX suggested, and sounds better.
Casper; I'm interested to learn how much of a difference the scaled-down tone stack made when compared to the amp-scale version you previously had installed. Was it a dramatic difference? I assume 'sounds better' might that there was some form of performance improvement?

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Post by caspercody »

The pedal still has a lot of treble to it, and I am not happy with the tone I am getting out of it. If I turn the mid control to 0, and turn the treble up to about 8 or 9 o'clock, then it sounds good. I really want to figure out a good tone stack to use with this, or any JFET clone. I do feel scaling it down I did loose bass response, meaning the bass control does not seem to have as much variance when you turn the pot.

I did change my guitar strings, and that seemed to get rid of the weird noise in the middle strings, and I changed the pick up from a SD 59 to a Dimarzio Super distortion. I think it was mostly the old strings.

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Post by FuzzMonkey »

Casper; try putting a 1nf cap to ground after the 33k gate resistor i.e. 33k resistor || Gate of the first Jfet || 1nf cap to ground. This will form a high pass filter and should help. 1nf might be overkill so try and few different valves, the high the value the more the treble will be tamed and vice versa. Let me know how you get on.

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