BAJA EVH overdrive pedal project 090218 [documentation]
- bajaman
- Old Solderhand
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Here it is at long last - the Peavey EVH 5150 preamp section in a nice friendly 9v overdrive pedal format.
You can build it with or without the tone stack and recovery stage or make it switchable - the choice is all yours
This circuit is my attempt to mimic the frequency and phase response characteristics of the original Peavey EVH 5150 head preamp section.
I also paid close attention to the clipping behaviour which occurs asymmetrically in the 5th gain stage first and then in the 4th gain stage.
There are six gain stages in this amplifier with a lot of attenuation and select filtering between each stage to get the desired overall frequency response.
I found it easier to get the desired double asymmetric clipping by using a red led and a pnp transistor in this pedal and considerable gain juggling was required to get the same response to clip as the actual amplifier does
Anyway, without further ado - here it is - enjoy and have fun
bajaman
You can build it with or without the tone stack and recovery stage or make it switchable - the choice is all yours
This circuit is my attempt to mimic the frequency and phase response characteristics of the original Peavey EVH 5150 head preamp section.
I also paid close attention to the clipping behaviour which occurs asymmetrically in the 5th gain stage first and then in the 4th gain stage.
There are six gain stages in this amplifier with a lot of attenuation and select filtering between each stage to get the desired overall frequency response.
I found it easier to get the desired double asymmetric clipping by using a red led and a pnp transistor in this pedal and considerable gain juggling was required to get the same response to clip as the actual amplifier does
Anyway, without further ado - here it is - enjoy and have fun
bajaman
be kind to all animals - especially human beings
- bajaman
- Old Solderhand
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Here are the plots for the frequency and phase measured at the output just before the tone stack - the red line is the peavey 5150 schematic simulation and the green line is the baja pedal simulation.
As you can see they are very closely matched between 100Hz and 100kHz.
cheers
bajaman
As you can see they are very closely matched between 100Hz and 100kHz.
cheers
bajaman
be kind to all animals - especially human beings
- sixthfloor
- Breadboard Brother
As far as I understand this resistor is a pull-down resistor. You can remove it, but you might experience popping sounds when turning the pedal on.
- bajaman
- Old Solderhand
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as sixthfloor states - it lessens any popping when tone stack is switched on / off.
If you are using an unswitchable tone stack you could leave it out
If you are using an unswitchable tone stack you could leave it out
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- bmxguitarsbmx
- Cap Cooler
Theoretically, the two clipping sections will dump current into the high impedance bias supply and cause bias shifts with long integration times. Could be a problem, could sound awesome!
These high-impedance Cap filtered Resistive divider bias supplies will drift when expected to absorb asymmetrical wave forms. The large value Capacitor doesn't lower the impedance, it only lengthens the time constant to return to equilibrium. Not to mention that DC shifts will cascade through each stage to the next, even if they are not DC coupled.
A 10uF or so cap on the output of the op would let you ground the rectifier/clipping transistor.
These high-impedance Cap filtered Resistive divider bias supplies will drift when expected to absorb asymmetrical wave forms. The large value Capacitor doesn't lower the impedance, it only lengthens the time constant to return to equilibrium. Not to mention that DC shifts will cascade through each stage to the next, even if they are not DC coupled.
A 10uF or so cap on the output of the op would let you ground the rectifier/clipping transistor.
- 287m
- Breadboard Brother
yeah, i think that too.sixthfloor wrote:As far as I understand this resistor is a pull-down resistor. You can remove it, but you might experience popping sounds when turning the pedal on.
my small brain always think the pulldown is the first or the last to ground. hahaha
i wonder, you are shaman too. How you know i want remove that dpdt switch?bajaman wrote:as sixthfloor states - it lessens any popping when tone stack is switched on / off.
If you are using an unswitchable tone stack you could leave it out
ah, this circuit is hard too make onboard pots
- 287m
- Breadboard Brother
Oh No. I did!
Have s some 1/8W resistor or 1/4W standing isn't crime, right?
And still can build in perf
Have s some 1/8W resistor or 1/4W standing isn't crime, right?
And still can build in perf
- Attachments
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- BAJA-EVH.zip
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I would suggest an AC coupling cap after IC2b and tying the red clipping LED to ground instead of Vbias. I haven't tried this specific design, but I tried something similar recently and the LED to Vref made the bias network unstable, resulting in a sort of fuzz like effect to the note decay.
Impressive work by the way. Interesting how all the opamps tie together and the clipping is done by just two components at the end. Diferent approach from most pedals.
Impressive work by the way. Interesting how all the opamps tie together and the clipping is done by just two components at the end. Diferent approach from most pedals.
Hey 287m, did you test this layout?287m wrote:Oh No. I did!
Have s some 1/8W resistor or 1/4W standing isn't crime, right?
And still can build in perf
- 287m
- Breadboard Brother
Not yet Sir, out of some componen and good mood to bending leg komponen in perfNefi_fatobene wrote:Hey 287m, did you test this layout?287m wrote:Oh No. I did!
Have s some 1/8W resistor or 1/4W standing isn't crime, right?
And still can build in perf
Information
I've Just built this beast and I really like the tone I can get out of it!
However I'm having a couple of issues with the Tone stack and the gain Knob, seems like they are working only on the first quarter of turn...
Any idea of how can i fix this thing? Thanks!
However I'm having a couple of issues with the Tone stack and the gain Knob, seems like they are working only on the first quarter of turn...
Any idea of how can i fix this thing? Thanks!
- jhergonz
- Breadboard Brother
how about other type of taper for the gain knob?sego91 wrote:I've Just built this beast and I really like the tone I can get out of it!
However I'm having a couple of issues with the Tone stack and the gain Knob, seems like they are working only on the first quarter of turn...
Any idea of how can i fix this thing? Thanks!
This is interesting because I made a MB throttle box clone recently and got "a sort of fuzz like effect to the note decay", and found the boost/eq section was the culprit. Do you think a similar fix could be done (before IC2a in the schematic)?rockhorst wrote:I would suggest an AC coupling cap after IC2b and tying the red clipping LED to ground instead of Vbias. I haven't tried this specific design, but I tried something similar recently and the LED to Vref made the bias network unstable, resulting in a sort of fuzz like effect to the note decay.
- FeVeR2112
- Breadboard Brother
The BC557 is being used as a diode (emitter not used). In 287m 's layout, he used a 3mm LED as the diode. What would be another (or better) diode to use in this build?
Also, wouldn't a transistor be better instead of the single-OpAmp (IC4)
Also, wouldn't a transistor be better instead of the single-OpAmp (IC4)
- bajaman
- Old Solderhand
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Actually it is the collector that is not usedFeVeR2112 wrote:The BC557 is being used as a diode (emitter not used). In 287m 's layout, he used a 3mm LED as the diode. What would be another (or better) diode to use in this build?
Also, wouldn't a transistor be better instead of the single-OpAmp (IC4)
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Hey Bajaman !
It's a great job you did and I have a little question about it (ok, maybe a dumb one)
I was thinking if it is possible to "daisy-chain" this OD/Preamp pedal with your presence and resonance schematic
(viewtopic.php?f=13&t=29369)
Something tell me it's not that simple but maybe it is !
It's a great job you did and I have a little question about it (ok, maybe a dumb one)
I was thinking if it is possible to "daisy-chain" this OD/Preamp pedal with your presence and resonance schematic
(viewtopic.php?f=13&t=29369)
Something tell me it's not that simple but maybe it is !