BAJA ENG overdrive pedal 080218

bajaman · Post by **bajaman** » 08 Feb 2018, 10:41

Here is my take on the Engl 530 preamp including tone stack (can be left out if desired).
Because the Engl does not use a cathode follower before the tone stack the final gain stage clips only on one half cycle of the waveform - for this reason I have used only one clipping transistor base/emitter junction

enjoy

bajaman

bajaman · Post by **bajaman** » 09 Feb 2018, 10:00

Here are the frequency and phase response graph comparisons - red is the Engl schematic and green is the pedal
cheers
bajaman

FeVeR2112 · Post by **FeVeR2112** » 09 Feb 2018, 16:19

bajaman wrote:Here are the frequency and phase response graph comparisons - red is the Engl schematic and green is the pedal

VERY close match!

deltafred · Post by **deltafred** » 09 Feb 2018, 19:57

Is an AC30 a suitable candidate for similar modelling?

bajaman · Post by **bajaman** » 09 Feb 2018, 21:40

Is an AC30 a suitable candidate for similar modelling?

So far I have concentrated on high gain preamp distortion pedals that do not really rely on the phase splitter power amplifier section distortion to achieve their response.
The Vox AC30 does rely on the power amplifier section - in particular the high voltage gain EL84 output tubes to achieve it's sparkle crunch sound (although the cathode follower before the tone stack does introduce significant asymmetrical distortion which is a key part of it's sound

).
I will take a look and see what I can come up with

cheers
bajaman

Cub · Post by **Cub** » 10 Feb 2018, 10:13

Ooh, that would open up so many possibilities for so many more great projects!

Jmpj48 · Post by **Jmpj48** » 12 Feb 2018, 21:46

what about the ada mp1 would it be worth it to try to model the overdrive channels. I know on the ada mp1 it has a opamp driving the first tube.

zilla · Post by **zilla** » 13 Mar 2018, 19:33

any feedback on how this sounds compared to jok3rx's screaming eagle circuit?

temol · Post by **temol** » 15 Jan 2019, 09:55

bump...

My version of the ENG overdrive. PCB is designed for 1590BB (vertical). For me, there is definitely not enough gain with default schematic values (check frequency response plots to see a difference). So I changed IC1A 8k2 resistor to 15k, IC1B 2k7 to 6k8 and 3n3 to 1n5. This gave me around +10dB (see the graph below).
I also find a tone stack adjustment range quite limited, especially for mids, but I left it as is.

For a comparison I attach freqency response plots from my ltspice e530 models. From top to bottom - tube engl, jfet engl, my ENG, original ENG.

T.

elkulon · Post by **elkulon** » 15 Mar 2019, 16:00

I've been searching info to make a decent preamp, to load with a SS PA, and avoid the need of a heavy and "non-confortable-to-carry" head amp.
I have to say I'm very impressed with all these Baja preamp designs, but Engl has always been a must-have.
Now, The PA I have is feeded with 24V; I have enough amper to feed the preamp too, so my question is: would this sound cleaner with more voltage because of higher headroom??

thetragichero · Post by **thetragichero** » 18 Mar 2019, 02:17

does the tone stack bypass provide a volume boost?

I have a number of tda power amp boards so I'm looking to box up a couple of solid state 'backup' amps in 1590bb enclosures, and if I can avoid components that's cool

Jrg770 · Post by **Jrg770** » 20 Jul 2019, 06:35

Thank you for the schematic and effort.

Jrg770 · Post by **Jrg770** » 08 Aug 2021, 08:16

The Finished pedal.