GG Overdrive Schem, opinions welcome :)

[hammerheadmusicman]

So, this is my first go of delving in to this for myself, so, the first half is the madbean open source tubescreamer, but with some more diode spaces in the to give me flexibility with the testing of diodes etc..  the op amp is a burr brown, we did A LOT of testing, and i preferred the sound of that the most. The second half is based on the black 65 tone stack, as i wanted a TMB tone stack, i think more pedals should be a bit more 'dialable'.

so my idea with the comp switch, is to have the symmetrical position as 'Vintage mode' with 2x 1n914's in for the classic TS kinda sound. The Asymmetric position i want something a bit more crazy, i have some germanium diodes which i tried in my green bean test board at the start, and it sounded kinda like a fuzz! so i want something really dirty and a bit different, to make this pedal really versatile.

EDIT: I have built this up, but we had to tinker with some stuff, and things were attached ont he end of wire etc.. I am going to etch my new layout tonight, but it sounded good, and the tone stack worked really well.

open to any suggestion about the diodes (and circuit in general)




Also, just wanted to say a MASSIVE THANK YOU to Brian, for putting in the crazy amount of work you do around here! Also, the guys who have helped me alot this last year or so, Jon (midwayfair) and Jacob etc..

[madbean]

I think this is a good idea that can be simplified a whole lot without compromising it tone-wise.

If you are open to suggestions this is what I would do if I were designing this.

Drop the entire input buffer and replace it with the output section.
Move the tone section to right after the drive section.
Move IC1A to directly after the tone section. Make R11 and R15 a small value--anything between 3k3-10k (they should be the same value or R11 a little higher to increase output). Tie R15 directly to Vb, NOT the non-inverted input.
Use a high value decoupling cap at the output of that stage and then a Volume control directly after it.

So, the overall order would be:
JFET input  - gain stage - TMB controls - recovery stage - output.

The reason I'm suggesting this is that IC1A is superfluous as you have it drawn. You do not need any kind of gain or tone shaping stage between IC1B and the TMB controls. But, you do need a recovery stage after the TMB and since you already have a free amp, it makes more sense to put it there than the JFET stage. However, the JFET input is another thing to set it apart from other designs. Plus, it will "cook" the input a little. You might want to increase the value of R5 a bit if you do this, but I'm not sure.

One alternative idea: drop the input and go straight into IC1B, leave the JFET at the output and make IC1A a buffer for Vb instead.

Anyway, take these suggestions with a grain of salt. Your ears are the best decision makers, of course Keep it up!!

[hammerheadmusicman]

Thanks Brian! Really appreciate your sage advice what I will do, is build the new layout I already have in it's current configuration, and do the alterations you suggested, build that, and then compare the two.

Also,

1) What are your opinions on diodes for the 'dirty' section?

2) the thing I've never got on with about the TS's is it doesn't play to well with humbuckers? I was thinking of a way to have a switch for marrying the pedal up with single coils/humbuckers? Do you think the fat comp switch would accomplish this? E.g. Fat mode for single coils? If not is there another way to accomplish this?

Thanks again

George

[culturejam]

I agree with Brian on moving the tonestack before IC1A and about the buffers.

The asymmetric side of your diode switch is VERY asymmetric. And I don't think zeners are a good choice.

[hammerheadmusicman]

I did say in the post, there are so many sockets, just for experimentation. I'm not using Zeners either, just realised they all say Z1 Z2 etc..

I have some germaniums which sounded pretty good in there, almost fuzzy.

The reason I put so many sockets for diodes. Is this - I have a 91' TS9 which I did the standard mods to, and was never too happy with it, when I found the 'tubescreamer on steroids' mod, which is. A switch with a one of 1n914's with the end lifted and 3 (I think) 1n60's
In series, and it sounds really good. So I put a loa of extra spaces, so I can do some experimenting..

[hammerheadmusicman]

Is this close to what you were thinking?




thanks

George

[midwayfair]

Is this close to what you were thinking?




thanks

George

Quibbling with some choices:

1) Although I agree with the placement of the mid and treble controls, I highly disagree with the placement of the bass control. Too much bass into IC1B may cause more distortion than is desirable, and if you cut it enough to ensure that the classic TS sound is still in there, then it's GONE. You can't get it back in just by adding a tone stack. Remember, controlling the bass between gain stages is one of the most important considerations in getting a good sounding drive.
2) If you have a BMT tone stack -- isn't the FAT switch redundant?
3) I know I'm in the minority of designers here, but there is almost nothing to lose by using a series Schottky for polarity protection instead of the reversed diode to ground. The 1N4001 in that configuration basically does nothing except provide visual evidence after it blows for a builder that the guy he built the circuit for plugged it into the wrong kind of power supply.
4) An source follower (like the emitter follower in your first schem), rather than a drain follower, on the J201 would bypass any and all biasing issues you may run into with FETs. Worth considering since the gain isn't that high.

[hammerheadmusicman]

Definitely food for trout John! Ill build this latest incarnation, do some tests and if I'm not happy build one to your suggestions, or maybe just do it anyway, and A-B-C them. If the fat switch Is redundant, I will get rid of it.

Also, have done that zen drive etch layout too, do you want a copy of it once its verified?

Thanks

George

[hammerheadmusicman]

Usually I would go back and change any bizarre autocorrect words. But 'food for trout' not 'food for thought' made me laugh!

[midwayfair]

Also, have done that zen drive etch layout too, do you want a copy of it once its verified?

It's yours, you did the work converting it. You can post it publically, just send it to me -- whatever you like.