Q-Drive - Treble Boost + AC-30 Amp Sim

[Frank_NH]

Hello Brian May Fans!

Here's a design I cooked up over at freestompboxes.org, consisting of a treble booster (in this case, the Runoffgroove Omega) driving Bajaman's amp simulation of the Vox AC-30 Normal channel.  The idea is to replicate Brian May's favorite boost+amp arrangement in a 9V stompbox.  The result, in my opinion, is a versatile distortion pedal that really does cop the Brian May tone.

The controls are:

(1) Range - controls the treble content of the treble boost
(2) Boost - adjusts the treble boost output
(3) Gain - adjusts the amp sim gain
(4) Tone - provides a treble cut control just like the AC-30
(5) Level - overall output level control

I've built this circuit already (so you can consider this verified) and I'm having a great time playing the solos in Bohemian Rhapsody

Have fun and let me know if there are questions.

[nostradoomus]

Awesome. Want to put this up against my Fuzzdog Figaro which supposedly is after the same sound. I like it but it's not quite Rory Gallagher enough for me haha

[Frank_NH]

Here's the FSB thread for reference:

http://www.freestompboxes.org/viewtopic.php?f=13&t=28872&start=20

Check out all of the amp sims Bajaman has created with simple op amp stages.  It's really amazing.  I've breadboard a few of the designs and they all sound great (at least as good as some of the FET style amp sims we're familar with).

And I think Bajaman will be moving on to a Hiwatt amp sim soon.  If so, I see a Pete Townsend pedal with a super fuzz + Hiwatt in a single box...

[MAO]

Thanks for posting this Frank NH!

Thinking of giving it a go.

My Britannia has to much hiss for my liking, same issue with the Azabache.

How's the hiss level on this one?

Any changes or suggestions now that you've had it for a few weeks?

[Frank_NH]

Hey MAO.  I just finished boxing mine.  It's reasonably quiet as long as you don't turn the boost up too much, and the Omega booster really does a great job cleaning up the wooly low end.  You might also try Bajaman's vero for the AC-30TB at FSB, which would be a better one-to-one comparison with the Britannia.  I plan to build that one too at some stage.

[MAO]

Cool, will probably knock this one out tomorrow night :0) I think I already have everything I need.
 
Did you stick with the 47nf feeding the 100k Gain pot?

[Frank_NH]

Yeah, the 47n should be fine.  I experimented with this on the breadboard and the difference was minor, especially after putting the Omega booster in front.

[MAO]

I built it using my own layout, so I must have goofed something as it sounds very shrill.

The tone control doesn't seem to be doing much, if anything, and with the boost turned down low, I'm not getting any real gain with just the gain control. That can't be right.

Unfortunately I won't have a chance to troubleshoot it till the weekend.

[Frank_NH]

Yes, there is something amiss.  I get lots of gain, and the tone cut works fine.  I'll see if I can make a video of my build and post it on vimeo.

[MAO]

That would be awesome!

It was killing me I ran out of time last night.

A selfish ask, would you mind demo-ing the tone control range and the gain with lower boost seetings?

Much appreciated.

[MAO]

No luck tonight, but I'm sure it's something with my board.

I bypassed the Omega, making a temporary input where the connection to Boost 2 was, and there is less than unity gain through the rest of the circuit. And it sounds poor.

I'm thinking there is a bad component, or maybe even incorrect values somewhere.  

Need to get out my audio probe tomorrow as I couldn't find any solder bridges or misplaced parts.  

I'm fairly certain the layout I used is ok, the only change I made was some added DC filtering. And the different pinouts for the transistors I'm using.

Here it is in case someone wouldn't mind looking it over for errors.

 

[Frank_NH]

Hi MAO,

Sorry you're having trouble with your build.  I would use an audio probe to see where the circuit may be going bad.  It's probably something simple.  

Here's a link to a quick camera phone demo of my pedal.  The controls are: top row (L to R):  Gain, Treble Cut (Tone), Master Volume, bottom row: (L, R) Boost, Range.

The Master was only half way, and actually you should run it with it near full up, and adjust the amp for overall volume.  Anyhow, I think it rocks!  

Q-Drive Demo

[MAO]

Thanks for the video Frank!

Found the lack of gain issue, a bad "J1".  Now it has plenty of gain on tap.

Appreciate your time, thanks again.

 

[Frank_NH]

Glad you got that sorted out, MAO.  Lately, I've been soldering in my transistors (sockets just don't hold them well) so I should be testing mine before doing that, JFETs in particular.