Blackstone Appliances - MOSFET OD (2SV3.12) [ goop-alarm ]

[RnFR]

thanks for clarifying that rat's nest, bajaman. methinks it 'twas a bit confusing.

[ShortScaleMike]

thanks for clarifying that rat's nest, bajaman. methinks it 'twas a bit confusing.

+1.

Science! Much appreciated. I'm keen to build one of the channels and have a play.

[Silent Fly]

Thanks Bajaman for your comments and clarifications.

Madbean, is there any chance you could convert Bajaman comments in a new schematics?

[MoonWatcher]

this is not a dual channel overdrive - it is a single channel with two preset gain controls and two preset style output level controls - one set is the so called Brown channel and the other is called the red channel.

That's what I thought when viewing the schematic. A fairly straightforward circuit, if you drop all of the "augmentation switching" for the sake of clarity.

[madbean]

this is not a dual channel overdrive - it is a single channel with two preset gain controls and two preset style output level controls - one set is the so called Brown channel and the other is called the red channel.

That's what I thought when viewing the schematic. A fairly straightforward circuit, if you drop all of the "augmentation switching" for the sake of clarity.

Exactly. I think the two, uhh, "modes' approach is clever, but having peeked under the hood it seems a bit overdone (kitchen sink, and all).

Anyway, Baja, as far the the stock setting on the trims, I bought this unit used, so there's no reason to assume that the settings are the way it originally shipped. I'll take a reading and post them along with the single ended version a bit later, in any case.

I'll also add the switching back into the full schem. I had it there at first, but deleted it when I posted it because I thought it would be less confusing that way. Obviously not!

[Caferacernoc]

I'd like to ask a general CMOS question. I've read many times that these chips clip softer than just about anything out there. And that they clip simmetrically. I understand that they have Mosfets inside. Any particularly reason that they would clip softer and more simmetrically than a jfet or mosfet set up in the usual class A "Fetzer Valve" way?

[madbean]

Okay, single-end version is done. Couple of things:

The C10 mystery gets a little deeper. I decided to socket this thing so I could understand what it does. Turns out, not only does it provide some frequency dependent filtering as Baja mentioned, but it actually stabilizes the circuit when it's in buffer mode. Without out a cap there it is warble city. Massive chop, esp. when you have the gain up high and roll the volume down on the guitar. With it in there, it seems to minimize the problem. Whatever engineering principle is behind this (which I'm still guessing is impedance related?), I can't say. Whether or not he arrived at this design on purpose or by accident is also a mystery. I can say that different values work. A 1n provides the stabilization, but I didn't care for it. A 4n7 is what I ended up with...I really like the mid-range you get with it.

Second, the tone control is definitely a bit odd. It seems to have a more pronounced effect in buffer mode, when you can really hear that massive 1kHz roll-off when the knob is all the way down. You can get a fairly decent range of mid cut in buffer mode. In "reactive" mode, the tone control didn't seem quite as flexible. Not useless, just different.

I found a 500kC works best for the main gain control. A 500kA works better for gain2.

About the trims: what I ended up doing was wiring the Gain2 control externally, and I left the trim off for the treble control. My thought here was that it would be interesting to try out different values for C4 to obtain a nice frequency boost with the Gain2 control. I don't like the 1n5 stock, but a 10n sounded really good to my ears. When I box it up, I will probably use a center off SPDT and have the two ends tie to different values caps with the middle position being just a full range second gain control.

With the second gain control wired externally, you will get some pretty useful variations of the OD. With gain1 turned down, and gain2 up, you can actually get a different feel. With both maxed, the effect is pretty noisy and quite unstable, but it also gets very fuzzy and interesting. You can even get into metal territory. There is a massive amount of gain on tap in the circuit, but you can get some decent low gain sounds as well.

All in all, I think it is a good design. I think this version suits my needs and tastes better, but obviously there was some thought put into the design. It is, at least, more unique than anything else I have recently built.

Have fun!

Mysterioso_JR.pdf

[fuzzlab]

Thank you, Madbean.

[bajaman]

Perhaps the combination of C10 and R3 acts like a zobel high frequency stability network and provides an AC reference to ground for the proceeding mosfet inverter stage.
Also R17 is shown as 3MM.3 on the V1.1 and V1.2 schematics instead of the correct 750k value on the later mysterioso jr schematic.
bajaman

[ShortScaleMike]

Thanks indeed Madbean!

[KindaFuzzy]

I love the comic book font in the layout. Thanks for putting this together dude.

[ShortScaleMike]

My first pass at a veroboard layout for the single channel. Any errors pointed out or build reports are most welcome.

[Mich P]

Hi Madbean thank you for your great job on this.
Can we expect a two channel pcb ?
Mich P.

[madbean]

Hi Madbean thank you for your great job on this.
Can we expect a two channel pcb ?
Mich P.

Thanks, Mich. You bet. I am working on the documentation and switch wiring for the "senior" version. The board for this one is slightly larger, and the layout is a little different to accommodate all the pads used for wiring this monstrosity. But, I will have it up soon.

[Mich P]

"Thanks, Mich. You bet. I am working on the documentation and switch wiring for the "senior" version. The board for this one is slightly larger, and the layout is a little different to accommodate all the pads used for wiring this monstrosity. But, I will have it up soon."

Super Cool Madbean !!
Thank you,
Mich P.

[Silent Fly]

[...]I am working on the documentation and switch wiring for the "senior" version.[...]

Excellent! Thanks madbean.

[madbean]

Okay, here's the full version. I think the wiring is correct, but I have not wired this thing up yet. Notes and mods included in the docs.

Mysterioso_SR.pdf

[nikos_sophos]

Thank you so much Madbean

[audioguy]

masterful work!

[borislavgajic]