VFE Pedals Dragon Hound

[whomeno]

Building a dragon hound. I need a substitute for the 2N5484.
Any suggestions?

[ferdinandstrat]

I'm like 99% ceratain any other n channel jfet will do, specifically 2n5457

[Fancy Lime]

I'm not so sure. It is used as a constant current sink at the output of IC1.1, the purpose of which eludes me. From where I sit it looks like it may be meant to pull the IC asymmetrical but it doesn't because the OPA2134 can easily compensate for the 1-5mA that the 2N5484 can pull. Could be a trap street: https://en.m.wikipedia.org/wiki/Trap_street

I am almost certain you can just leave it out.

Cheers,
Andy

[Vivek]

I love analysing VFE schematics.

There is always some interesting twist to things, somewhat reminiscent of a good O. Henry short story.

Lots to learn from his schems.

I also respect his decision to release some schems to the public

It would be nice to understand that odd FET there.

[Vivek]

VFE's comments on the MOSFETS :

This soft clipping configuration doesn't saturate until the signal reaches the combined voltage drop of the mosfet body diode and the mosfet Vgs threshold point.

On average, this is around 2.7V, much higher than typical silicon diode clipping (0.7V). The result is greater dynamic range, tighter bottom end, and significantly more volume output. Using the body diode & Vgs threshold is possible on a single mosfet, but would result in an asymmetrical distortion (~2V for Vgs threshold, 0.7V for body diode).

Many overdrive pedals I've seen advertised as "mosfet distortion" are only using the body diodes for clipping...which really isn't much different than if you use silicon diodes. But somehow calling it "mosfet distortion" makes the tone better.

[Vivek]

The Dragon Hound is made up of 2 pedals with a blend Knob between them.

In the original Pale Horse pedal, the 2N5484 FET is used in a different way, and might do something different.

[Fancy Lime]

I love analysing VFE schematics.

There is always some interesting twist to things, somewhat reminiscent of a good O. Henry short story.

Lots to learn from his schems.

I also respect his decision to release some schems to the public

It would be nice to understand that odd FET there.

I used to have the same feeling toward DOD circuits. I found them very intriguing because they made some very hard to understand design choices. I did not understand them, thinking I was the problem. No, turns out the old DOD factory schematics are just teeming withe errors. Hardly any of it would even work at all if you built it as the shematic says. And even the actual circuits contain lots of pointless components or make things that could be done easily unnecessarily convoluted. Sometimes there are reasons for this that have to do with factors other than engineering ("look, we have a million 39n caps in storage but no 100n caps, let's use three parallel 39n instead of one 100n") but sometimes the people who design stuff are just being fallible humans like the rest of us. So if something seems to make no sense never discount the possibility, that it actually makes no sense and someone somewhere just made a mistake. But I personally usually assume that I just don't understand the reasons behind certain design decisions, as the default answer. Drives me nuts sometimes.

Andy

[marcelomd]

A few years ago Peter Rutter was going to close VFE and he sold all his schematics in Eagle format.

There are a few versions of this circuit there. In some of them he uses a BS170 in that position.

They are the ugliest schematics I've ever seen. I am 80% sure he obfuscated things on purpose.

That said, Peter is a great guy and is active on Facebook. We can ask him directly. He also has a series of videos explaining his pedals.