DEMO Symbolic Overdrive (Mad Professor Simble Overdrive)

This post contains an audio or video demo

MichaelW

Well-known member
Build Rating
5.00 star(s)
Continuing on my quest to build all the Bjorn Juhls circuits I can find, I found out after I ordered the board that the Mad Professor Simble Overdrive was not a Juhl's design but rather was designed by another Finnish designer named Lassi Ukkonen for Mad Professor. Apparently there was some trademark issues as Juhl's is known as the "Mad Professor" and they were marketing a design that he had nothing to do with. It was discontinued by MP and the name "Simble" has been re-purposed for a boost pedal (presumably designed by Bjorn).

Anyway, looking at the schematic of this pedal it's evident that it's pretty much a Zen drive with some interesting twists, like how the clipping circuit is arranged.
It's almost like a backwards Zen drive. Some of the components are slightly different, like the opamp and no Ge diode, it uses all BAT41's.

I have to admit I wasn't too excited about building another Zen variant if it wasn't deigned by Bjorn but since I already had the board and ordered the parts for it I decided to go ahead and build it out this weekend for a looky look.

I socketed some of the key components and did some experimenting with swapping some of the BAT41's for various Ge's of different Vf values. I also tried a couple of different opamps.

Ironically, I wound up back with the stock values as it sounded the best. I'm actually very pleasantly surprised at how much I like this drive.
Yes, it's a Zen, and ergo has its roots in a TS808. It definitely has the Zen thing going on but, using the stock BOM (BAT41's and TLC2272 opamp) it's also a bit different as well. It has more gain, I would say it goes into distortion territory and the gain structure is a little bit different as well.
To my ears, it sounds a bit more aggressive and also a bit more "open" sounding than the stock Zen drive especially at lower gain settings. All while being somewhat "chewy" like the other Mad Professor circuits I've built. It may not have been designed by Juhl but I think it certainly was designed "in the spirit" of a BJFE circuit.

I'm not exactly sure what part of the circuit contributes the most to the difference in how it sounds. My understanding is that the TLC2272 is like an "uber-TL072" with increased dynamic range. I'm not sure if it's adding to the additional gain but it sounds different from the LF353 I tried first.

The differences are nuanced but to my ears definitely present. I recorded a demo clip comparing it to my stock Zen drive. (The only thing non-BOM on my Zen is the opamp, I used a NE5532 instead of an AD712).

Anyway, if you're a fan of the Zen drive, the Symbolic Drive is definitely worth checking out as a pretty neat sounding variant.

IMG_4247.JPG

The TLC2272 I used was the SMD version, I couldn't find a DIP-8 version, it's riding on an adapter board from PedalPCB. (It just barely clears the back cover by 1/2 a hair using pin headers plugged into an 8-pin socket)

IMG_4248.JPG

Here's the schematic for the Symbolic. It's not in the build docs but it was posted by Mr. BuggFX himself in a thread on FSB.
Schematic-Symbolic.jpg


Demo was recording using my PRS SE 245 Standard with a pair of Wolftone Legends. Quite possibly the best vintage output PAF's I've ever played. Fantastic pickups.

 
Last edited:
I've got one that I built last year. I suspect I fried the IC because it was one of my first builds and I didn't socket it. My multimeter is in another country so troubleshooting it will have to wait. I actually had an original and quite liked it.
 
Another great build-report-demo combo.


An aside:
Diggin' the Zen's reflection of the fan (looks centred around the top left knob), and the way the camera is smearing the LED when it's on.

And thanks for posting Robert's schematic.
 
Continuing on my quest to build all the Bjorn Juhls circuits I can find, I found out after I ordered the board that the Mad Professor Simble Overdrive was not a Juhl's design but rather was designed by another Finnish designer named Lassi Ukkonen for Mad Professor. Apparently there was some trademark issues as Juhl's is known as the "Mad Professor" and they were marketing a design that he had nothing to do with. It was discontinued by MP and the name "Simble" has been re-purposed for a boost pedal (presumably designed by Bjorn).

Anyway, looking at the schematic of this pedal it's evident that it's pretty much a Zen drive with some interesting twists, like how the clipping circuit is arranged.
It's almost like a backwards Zen drive. Some of the components are slightly different, like the opamp and no Ge diode, it uses all BAT41's.

I have to admit I wasn't too excited about building another Zen variant if it wasn't deigned by Bjorn but since I already had the board and ordered the parts for it I decided to go ahead and build it out this weekend for a looky look.

I socketed some of the key components and did some experimenting with swapping some of the BAT41's for various Ge's of different Vf values. I also tried a couple of different opamps.

Ironically, I wound up back with the stock values as it sounded the best. I'm actually very pleasantly surprised at how much I like this drive.
Yes, it's a Zen, and ergo has its roots in a TS808. It definitely has the Zen thing going on but, using the stock BOM (BAT41's and TLC2272 opamp) it's also a bit different as well. It has more gain, I would say it goes into distortion territory and the gain structure is a little bit different as well.
To my ears, it sounds a bit more aggressive and also a bit more "open" sounding than the stock Zen drive especially at lower gain settings. All while being somewhat "chewy" like the other Mad Professor circuits I've built. It may not have been designed by Juhl but I think it certainly was designed "in the spirit" of a BJFE circuit.

I'm not exactly sure what part of the circuit contributes the most to the difference in how it sounds. My understanding is that the TLC2272 is like an "uber-TL072" with increased dynamic range. I'm not sure if it's adding to the additional gain but it sounds different from the LF353 I tried first.

The differences are nuanced but to my ears definitely present. I recorded a demo clip comparing it to my stock Zen drive. (The only thing non-BOM on my Zen is the opamp, I used a NE5532 instead of an AD712).

Anyway, if you're a fan of the Zen drive, the Symbolic Drive is definitely worth checking out as a pretty neat sounding variant.

View attachment 41571

The TLC2272 I used was the SMD version, I couldn't find a DIP-8 version, it's riding on an adapter board from PedalPCB. (It just barely clears the back cover by 1/2 a hair using pin headers plugged into an 8-pin socket)

View attachment 41572

Here's the schematic for the Symbolic. It's not in the build docs but it was posted by Mr. BuggFX himself in a thread on FSB.
View attachment 41573


Demo was recording using my PRS SE 245 Standard with a pair of Wolftone Legends. Quite possibly the best vintage output PAF's I've ever played. Fantastic pickups.

They both sound amazing. What delay and or reverb are you using?
 
Delay on this demo I think is my Deep Blue Delay with modulation + MBP Tourbus (Deluxe Memory Man) and the touch of reverb is my Gravitation reverb. (EQD Levitation.
 
Back
Top