BAJA AFD OVERDRIVE PEDAL 2018  [documentation]

Original effect designs complete with schematics, layouts and instructions. Freely contributed by members or found in printed or online publications. Cannot be used for commercial purposes without consent of the respective owners of the copyright.
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bajaman
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Post by bajaman »

Here is another little project for you folks to build and enjoy - based on the response characteristics of the Marshall AFD 100 amplifier high gain channel, in a 9v friendly two control circuit - fits easily inside a hammond style 1590B enclosure too :wink: This pedal will take any clean sounding amplifier into Slash style sounds - cleans up nicely as a boost with the drive set very low - very happy with it :D
I knocked this one up on veroboard - (sorry I do not have the layout as i made it up as i built it).
I recycled an older pedal enclosure I built many years ago but no longer use.
Here is the schematic and a couple of pics of the finished working pedal - maybe someone can do a veroboard layout for it :thumbsup
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bajaman
Baja AFD OVERDRIVE buffered bypass version with BC547B clippers 180118.GIF
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287m
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Post by 287m »

Baja, you rock! nice work

so for true bypass, remove 1K, 100K and 1u?
and how to make switchable buffered and true?

aha! thanks to clipper idea with that trannies
must try in some circ. hehe. sorry for noob excitemen

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roseblood11
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Post by roseblood11 »

If someone is drawing a vero layout: It would be interesting to have two dual opamps, one for IC a and d, the other for b and c!

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Ice-9
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Post by Ice-9 »

roseblood11 wrote:If someone is drawing a vero layout: It would be interesting to have two dual opamps, one for IC a and d, the other for b and c!
I have to ask, why ? with 4 op amp sections it is quite a lot easier to draw it up with a quad rather than 2 duals, is there a particular reason you prefer to use 2 x duals instead ? I'm just interested in your reason.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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bajaman
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Post by bajaman »

True bypass version :wink:
Baja AFD OVERDRIVE True bypass version with BC547B clippers 180118.GIF
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Post by bajaman »

It is not critical which sections of the quad opamp are used for each stage but it is critical that the two gain stages should be TL06x types and not TL07x or OPAx134 type :secret:
(x is 1,2,or 4 :wink: )
All the 1uF capacitors used in this project are multilayer ceramic types :wink:
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bajaman
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EddieTavares
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Post by EddieTavares »

roseblood11 wrote:If someone is drawing a vero layout: It would be interesting to have two dual opamps, one for IC a and d, the other for b and c!
What about remove the input buffer and use a transistor as output buffer. Maybe It makes the guitar volume knob more gain responsible.

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Post by okgb »

The amps are said to be [ or thought ] a bit on the bright side, so I'm surprised you didn't include a High cut kind of tone control,
but I haven't heard your circuit yet , it's on my waay too long list of things to try , Thanks!

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Post by bajaman »

What about remove the input buffer and use a transistor as output buffer. Maybe It makes the guitar volume knob more gain responsible.
NO :!:
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Post by bajaman »

The amps are said to be [ or thought ] a bit on the bright side
I agree :wink:
Most of the extreme treble boost occurs at low gain control settings in the actual amplifier because of the treble bleed capacitor across the gain control - i tried using one in the pedal version but found that it clipped the proceeding gain stage in a very nasty sounding way before the clippers had any effect. i could have used germanium or schottky clippers but then would have to increase the output level - I left the treble bleed capacitor out and the sound improved 100% even at low gain control settings. The amplifier has 24dB of boost at 2kHz compared to it's response at 100Hz with the gain control set to 50%. At 5% it is even higher at 33dB at 3kHz :wink:
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Post by ppluis0 »

bajaman wrote:...but it is critical that the two gain stages should be TL06x types and not TL07x or OPAx134 type...
What's wrong with the TL07X compared to their cousins TL06x ??

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Post by 287m »

bajaman wrote:
The amps are said to be [ or thought ] a bit on the bright side
I agree :wink:
Most of the extreme treble boost occurs at low gain control settings in the actual amplifier because of the treble bleed capacitor across the gain control - i tried using one in the pedal version but found that it clipped the proceeding gain stage in a very nasty sounding way before the clippers had any effect. i could have used germanium or schottky clippers but then would have to increase the output level - I left the treble bleed capacitor out and the sound improved 100% even at low gain control settings. The amplifier has 24dB of boost at 2kHz compared to it's response at 100Hz with the gain control set to 50%. At 5% it is even higher at 33dB at 3kHz :wink:
cheers
bajaman
Baja, IC 1D.
schemo 3n9 but your build 3n3. Its right? or my eyes play trick on me?
ppluis0 wrote:
bajaman wrote:...but it is critical that the two gain stages should be TL06x types and not TL07x or OPAx134 type...
What's wrong with the TL07X compared to their cousins TL06x ??
https://www.freestompboxes.org/viewtopic.php?f=17&t=328 or duckduckgo-ing The Bi-FET Design Manual

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Post by bajaman »

What's wrong with the TL07X compared to their cousins TL06x ??
Nothing wrong, just brighter and hard edged in comparison - TL06x series is low current and slower device = smoother top end :wink:
Baja, IC 1D.
schemo 3n9 but your build 3n3. Its right? or my eyes play trick on me?
well spotted - I was out of 3n9 so used 3n3 instead :)
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Post by Frank_NH »

I had a go with this circuit on the breadboard, and even though I made some substitutions it sounds great! :D

Here's what I changed:

* TL074 because that's what I had on hand.
* I wanted a little more treble in the crunch, so I changed the 3.9n cap to 1n and the 6.8n cap to 4.7n. Brightens up the tone quite well without causing any oscillation.
* I used red LEDs for the clippers, and they sound just fine in this application. Will experiment with the original transistors and other options.

With more treble in the signal, I can see having a simple treble roll-off tone control before the output buffer stage and will experiment with that on the breadboard.

Thanks again for this circuit, Bajaman!

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287m
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Post by 287m »

Frank_NH wrote:I had a go with this circuit on the breadboard, and even though I made some substitutions it sounds great! :D

Here's what I changed:

* TL074 because that's what I had on hand.
* I wanted a little more treble in the crunch, so I changed the 3.9n cap to 1n and the 6.8n cap to 4.7n. Brightens up the tone quite well without causing any oscillation.
* I used red LEDs for the clippers, and they sound just fine in this application. Will experiment with the original transistors and other options.

With more treble in the signal, I can see having a simple treble roll-off tone control before the output buffer stage and will experiment with that on the breadboard.

Thanks again for this circuit, Bajaman!
yeah! me too, im not alone.
red led good. But, i can't knew bajaman circuit until trannies arrived
time to order trannies, mini elco and 1590A :mrgreen:

thanks Bajaman :thumbsup
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287m
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Post by 287m »

what you think perf? :twisted:
perf guide
perf guide
AFD-etch.pdf
etch version
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Post by Frank_NH »

I did some tests over the weekend. Tried the BC547B transistors and they sounded good but I think I prefer the LEDs (more output and little crisper). Also ended up with the op amp feedback caps at 2.2n for IC1d and 4.7n for IC1c, so no radical change but it does improve the treble a bit. I thought about tone controls, but being a minimalist I think having no tone control is the way to go! :) The only other mod I'm contemplating is to integrate the volume control into the last op amp (rather than just a simple buffer).

The circuit really does sound good and is quite tweakable. I'm working on a vero layout for personal use but will post it when I have it verified. Thanks again Bajaman!

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Post by marcao_cfh »

287m, that's a nice 1590A layout! You can adapt it to use Baja's SLO OD too, I did it here (hope you don't mind I use your layout). I'll try to etch the boards this week, but it'll take some time to build both versions (I have a few projects to finish before I start any other ones).

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287m
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Post by 287m »

Whoah, thanks marcao, my pleasure if 1590A builder like you use that.

ah, for SLO-OD 1590A, i have different layout, about same size, you want?

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Post by marcao_cfh »

I just saw your SLO-OD layout. It'll take some time to build them, I'm still struggling to get dry film transfers to work, but I'll surely use them and post the results here.

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