New at runoffgroove.com: Thunderbird

[B Tremblay]

Thunderbird is an original overdrive inspired by the sound of a cranked Marshall Super Lead amp. Check it out:
http://runoffgroove.com/thunderbird.html

[Bucksears]

In my head, I'm dancing right now. In reality, I'm at work and remaining calm.

[sajy_ho]

AWWWWWWESOOOOOOOOOME!

[Frank_NH]

Just purchased the PCB from 1776 Effects.  Superb design - can't wait to build it.  Thanks again Runoffgroove!   

[samhay]

Looks like there are some interesting snippets in there that might find themselves in other projects.
Anything special about the particualar Schottky used for the clipping?

[stm]

Looks like there are some interesting snippets in there that might find themselves in other projects.
Anything special about the particualar Schottky used for the clipping?

The Schottky diodes are of the signal type (1N5711) and were chosen because they have a different clipping threshold compared to the signal silicon diodes (1N4148.)

[dschwartz]

Hi sebastian como estas!!!
Very nice design!!! Two questions, what are the first diodes for? The first stage has a very low gain, no enough to reach the forward voltage of a diode..specially with a 3k3 resistor in series...is that there to emulate the first stage clipping if you use an external booster?
Also, why tantalum caps? They are ussually avoided like the plague..

Cheers from santiago!!!

[stm]

Hola Daniel!  It's been a long time!

I'm glad you like this design.  We put a lot of time and effort into this circuit.  First ideas and circuit snippets date from late November 2013; the circuit took its final form by mid December 2014, after which the rest was devoted to prepare the official release (audio samples, writeup, PCB project, final testing, etc.)  As you can see this is not the typical weekend DIY project, as it is more involved in terms of complexity and less forgiving with regards to parts substitution, however we believe it outperforms our previous Thor and Thunderchief pedals.

With regards to your questions:

Very nice design!!! Two questions, what are the first diodes for? The first stage has a very low gain, no enough to reach the forward voltage of a diode..specially with a 3k3 resistor in series...is that there to emulate the first stage clipping if you use an external booster?

The first diodes are there to prevent the second opamp from reaching clipping with very hot input signals.  Believe it or not, my average humbucker pickups can put out +/-3 volts in the oscilloscope when playing barre chords around the fifth fret. I'm sure there are hotter pickups out there, and as you already noticed, we wanted to be prepared if someone boosts the signal.  When the Tone and Gain controls are set to max, the first two diodes will conduct whenever the input signal around 500 mV at 1 kHz, which is not too high for a guitar pickup.  This is intended to hit the next diode stage (after the second opamp) with the maximum possible signal, but without having the opamp hard clipping getting in the way.

Also, why tantalum caps? They are ussually avoided like the plague..

Yes, tantalum capacitors have a bad reputation for audio use because they add some distortion under certain circumstances, especially when they have no DC across.  In our circuit the tantalum capacitors are used where they belong and where they can outperform aluminum electrolytics: to filter the 24Vdc power supply because of their lower internal resistance (ESR).  Only power supply capacitors (1uF and 10uF values) are marked as "tant" for tantalum.  All signal path capacitors are suppossed to be aluminum electrolytic type.  Perhaps this is not crystal clear in the schematic, thanks for noting this.

Also note that all polarized capacitors in the signal path do have a well defined DC voltage across them (respecting the polarity), which is the proper way to keep signal distortion under control.

[guitarkill]

Cool. 

[Bucksears]

Sooooo....
Have any 'end users' built this yet? I've had too much garage remodeling over the last week to etch a board, but want to by this weekend.

[dschwartz]

This is such an interesting design. the shifting dc bias for clipping at the 2nd stage is brilliant and simple...i think im going to try that for my next designs,  its a pretty accurate tube distortion emulation..

I heard the demos and the tones are very right in the spot, crunchy, dynamic and bity, and somewhat spongy, very nice indeed!!

Its a pleasure to see that the Rog team are still active and pushing the envelope of desing after all these years..I've  been away for almost 5 years, and its a nice surprise to find this on my comeback..

My best regards to the team and specially to my coterrain Sebastian..im so proud he is chilean like me..

[Blitz Krieg]

Sooooo....
Have any 'end users' built this yet? I've had too much garage remodeling over the last week to etch a board, but want to by this weekend.

ROG Thunderbird. Ke-rrrang!

[blackcorvo]

This is a really wonderful circuit, and it inspired me to try that type of asymmetrical clipping for myself!
I ended up with this: http://40.media.tumblr.com/08ee2d4ddf30241d3d3bdc523440a6a5/tumblr_nj6cq2gJ681r4gqjso1_1280.jpg

It's a "frankenstein'd" overdrive with the Thinderbird's clipping circuit, a Danelectro HoneyTone tone control, and the "cab sim" from Thor.

And here's a late-night, low volume clip of it. I'll record a better one later today: http://youtu.be/ULFPcXpt8n4
I had it's output going directly to a TDA7240 and the speaker is a Vox Bulldog from a Pathfinder 15R.

I really like it so far!

[Edit]
Here's a louder sound sample: http://youtu.be/QkTm9PD-ePo

[Frank_NH]

Some pictures of my build using the 1776 Effects PCB...(box is still unlabeled... )




A wonderful circuit capable of massive, crunchy overdrive.

(edit: hopefully you can see the images now)

[bluebunny]

We'd love to see your pictures, Frank, but you need to fix up those URLs.   

[stm]

The schematic in the project page has been tidied-up a bit and some build notes have been added.  There are no changes to the parts values or the circuit topology.  Current revision number is 1.2.

http://runoffgroove.com/thunderbird.html

[jishnudg]

Love this!!  Hey so I was wondering.. Could this duty cycle modulation thing using the electrolytic caps be patched into the LM386 or a transistor gain stage as well? 

[Quackzed]

+1 that second stage bias shifting triode sim would make a cool pedal all by itself...

[bluebunny]

(edit: hopefully you can see the images now)

They do!  Nice neat build.

[Giglawyer]

Could this be modded to emulate a Marshall Super Bass, or are the circuits too different?