Does anyone have sound clips yet?

[Hal]

This looks like a cool design :-D

[aron]

Well, it's a drop in replacement for one of the two op amps in a dual op amp or a replacement for a single op amp.

To me it has more "feel" than the "real" op amp, and at higher drive settings there's a distinct compression (or sag). It's a very, very rewarding circuit.

You can use it in a lot of the op amp circuits; especially in my Shaka circuits.

VERY NICE!

[BramcoteLorne]

oooh!

this looks pretty

[Hal]

ooh, I get it, I didnt really read anything about it, just looked at some pictures  :twisted:

mm something to play around with...I need to buy some 5087's.  Did anyone try with 3904/3906 ?

[Peter Snowberg]

Let's see..... So many pairs to choose from!

5088 / 5087
3904 / 3906
2222 / 2907
4401 / 4403
TIP29 / TIP30
3055 / 2955 :shock:

[the_badcliff]

Could this be dropped in a Tube Reamer or Dist+ with minimal or no component changes then?

[aron]

Yes, any single side of an op amp. Yep!

[Jehle]

Getting back to the subject of the post then, do you have a comparison between a garden variety op amp and this diode replacement?  Where would you want to use this?  Would it work just as a buffer for the input? Is it better suited for higher gains?

Thinking ahead, it would be cool to use this project in combination with the minimal screamer to get a totally discrete 808 clone.  Nothing against IC "bugs", I think it was just have some extra cool factor to have a transistor only version of the TS 808.  

[Peter Snowberg]

This is untested.....



R1 was selected for future Q1 swapping.

[brad]

I whipped up this PCB/Perf layout for a dual version to see if it'd fit inside a Boss pedal.  The diodes would go on the solder side.  I'm just throwin' around ideas here, but I reckon it'd be cool to open up a SD-1 and see a daughter board with an 8 strand ribbon cable going into the opamp socket.  ...make that an 8 strand RAINBOW ribbon cable!  

[aron]

Nice work Brad!!!!!

[Joe Davisson]

Peter, I think you have the + and - inputs swapped! The opamp part is right, just not the way it's hooked up. Looks good otherwise. :mrgreen:

Running wires to a DIP adapter is a good idea, and the rainbow cable would actually make it easier to keep track of the wires. A hard drive (or floppy drive) cable also comes to mind, since you can rip off the number of wires you need.

As far as where to use it, it's intended for making smoother distortion than an IC opamp, but I would stick with IC opamps for things like tone controls/oscillators/etc. I haven't studied the effects of the diode on other circuit applications, only as a non-inverting amplifier, and inverting amplifier with the required cap mod mentioned on the page.

[Peter Snowberg]

:oops: WHoops. Thanks Joe. Corrected.

I WAS going to swap the transistor positions initally and forgot 1/2 way through the drawing. Hehe.

[brad]

As far as where to use it, it's intended for making smoother distortion than an IC opamp, but I would stick with IC opamps for things like tone controls/oscillators/etc. I haven't studied the effects of the diode on other circuit applications, only as a non-inverting amplifier, and inverting amplifier with the required cap mod mentioned on the page.

That's a good point...I didn't think about that.  Perhaps the solution for something like an SD-1 would be to build a daughter board with a single discrete opamp for the clipping stage, and then have a single IC opamp next to it for use in the tone control.

For example:

[Joe Davisson]

It should work now, I tested something nearly identical besides some resistor/cap choices. What is the schematic drawn with? It looks kinda like plotter output...

I think one good mod would be an extra footswitch that chooses between 2 gain controls and switches between feedback diodes and diodes-to-ground. An easy, but good sounding 2 channel box. I'll try to hammer that out sometime.

[Peter Snowberg]

The schematic was drawn with ExpressSCH from http://www.expresspcb.com/ , it was then screen captured (alt-print_screen), pasted into Photoshop, cropped, resized to 50% of original, and saved as a GIF. It does have that plotter aesthetic to it.

I'm going to play with JFET inputs this evening.

I like the idea of two gain controls, one for each diode configuration..... but which diode configuration sounds 'best'? Optimum may be both diode pairs on but each with a series resistor. These are the instances where I get lost in the "too many options" syndrome.

[vdm]

this seems like a great idea for a pedal.
i was curious as to whether there is any noticeable difference in noise level? i'd guess it would have a little more noise due to the nature of discrete transistors, but please tell me if i'm wrong.

this looks like it might be going in my second build of the bluesbreaker.

also is power consumption lower than a standard opamp?

trent

[Joe Davisson]

The noise shouldn't be bad from the transistors. The diode could cause some radio/noise issues, but I've not had problems using metal enclosures. I think it uses less power, or at least it has limited output drive vs a real opamp.