Tube Screamer Circuit

[PB2]

Nice analysis done here, looks like more complexity in the bypass circuit than the rest:
ElectroSmash - Tube Screamer Circuit Analysis

I don't see why they didn't use a true bypass switch and make much simpler.

A lot of stories about how Robben Ford used one into a Fender Bassman to get his tone:
"Dumble sound is just a bassman with a tubescreamer" | The Gear Page

 

[Printer2]

Three pole stomp styled switches were not the rage when the pedal was designed I would think.

 

[turk 182]

i think that the transfer curve of the j-fet's used is what's behind why they are liked whether they are in bypass or run full rip but that's like trying to engage in a conversation about distortion in a world where it's perception is still at question...

 

[shanx]

Getting that Robben Ford sound, without the $$$ Dumble..I played through a clone of an Overdrive Special and in the voicing switched to Rock position it definitely sounded more mid pushed and trebly than I would like. Not so much of a Bassman sound IMO.

The overdrive pedal of choice that Robben uses is the Hermida Zendrive. I repaired a similarly built circuit for a friend and had a chance to try it out. It was very much that warm smooth overdrive that rounds out the guitar tone and pushes a tube amp very well, not too compressed and very open sounding. Plug one of those into a Deluxe Reverb and you will pretty much be there.

 

[JMFahey]

I don't see why they didn't use a true bypass switch and make much simpler

I can suggest a 1000 page book explaining it, but the first one reads:

* Mechanical footswitch: $12

* it usually clicks/pops

* When OFF, weak high impedance pickup signal must drive all that cable to guitar amp, but much worse, must drive any other Lo Tech pedal in the chain, think an LPB1 Booster, a Wah, Fuzz, most MXR pedals, etc. , which have lowish impedance, too much capacitance, etc.

* simpler

* Electronic footswitch: about $2

* noiseless

* buffered input and output all the time means it can drive *anything*, also constant 500k impedance is easy to drive and predictable.
Did I say low capacitance?

* more complex, but who cares? ... it´s machine assembled so no big deal.

No need for the other 999 pages

 

[PB2]

Getting that Robben Ford sound, without the $$$ Dumble..I played through a clone of an Overdrive Special and in the voicing switched to Rock position it definitely sounded more mid pushed and trebly than I would like. Not so much of a Bassman sound IMO.

The overdrive pedal of choice that Robben uses is the Hermida Zendrive. I repaired a similarly built circuit for a friend and had a chance to try it out. It was very much that warm smooth overdrive that rounds out the guitar tone and pushes a tube amp very well, not too compressed and very open sounding. Plug one of those into a Deluxe Reverb and you will pretty much be there.

Dumble has that switch for the tone stack so you didn't like the rock position but how
did it compare to the other (is the other one Jazz?)?

 

[shanx]

Dumble has that switch for the tone stack so you didn't like the rock position but how did it compare to the other (is the other one Jazz?)?

Yeah I think the jazz setting was a bit smoother on the high frequencies, though how close to a real Dumble circuit this was I don't know.

 

[Kartapus]

Thank you for information. Very interesting to have a deep analysis. Circuit is well except the switch circuit which could be very more simple: same JFET as switches but with a more simple control circuit. Using IC D flip-flop instead of discrete circuit? less components to mount

 

[PB2]

Never heard of the Hermida Zendrive, here's a DIY version that is nearly a copy:
Hermida - Zendrive Project at FSB.org | La Revolution Deux

 

[shanx]

From what I remember, when Hermida developed the Zendrive, the intent was to use the mosfets wired up as diodes (Gate to Drain wired). But as it turned out the internal body diodes of the mosfets were actually doing the signal clipping. It was suggested to add those series diodes (BAT41, 1N34A) in order to get the mosfets switching and avoid the body diode conduction..it was on an online forum and I can't remember who suggested it. But as it's shown on that schem at FSB.org it looks like the body diodes are still in the conduction path and any mosfet switching would still get blocked by the series diodes. Still it's a good sound and a pretty straightforward circuit to breadboard. Cheers