BAJA Orange OTR120 Graphic MkII amplifier pedal 9v 160318  [documentation]

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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bajaman
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Post by bajaman »

So many different orange amplifier schematics and so many different topologies - I settled on the 72 graphic mkII to base this pedal on.
Hope you like it - here is the schematic for now - vero layout to follow shortly :wink:
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Baja OTR120 Graphic MkII pedal 9v 160318.GIF
Last edited by bajaman on 16 Mar 2018, 07:17, edited 1 time in total.
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Baja OTR120 vero cuts.png
Baja OTR120 vero cuts.png (7.5 KiB) Viewed 11555 times
Baja OTR120 vero layout.png
Baja OTR120 Graphic MkII pedal 9v parts not fitted on vero160318.GIF
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Post by soulsonic »

I'm loving these new amp-in-pedal designs you've been coming up with these past few years while I was away. I'm definitely going to give them a go!
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Post by Dr Tony Balls »

FWIW that's not how the filter switch on an OR120 works. The caps are actually in series. Not that the schematic isnt completely valid as its own thing, just making a note for clarity.

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Post by bajaman »

FWIW that's not how the filter switch on an OR120 works
Agree - but it achieves the same result. I have seen quite a few differing schematics depending on what year it was built also. The "filter' merely selects different values of coupling capacitance and allows one to roll off the bass response of the preceeding gain stage progressively.
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Post by Dr Tony Balls »

bajaman wrote:
FWIW that's not how the filter switch on an OR120 works
Agree - but it achieves the same result.
In theory but the values you have here are also pretty far off from an Orange to have equivalent capacitance. On an Orange the equivalent at the six settings is roughly 68nF, 4.4nF, 2.3nF, 1.1nF, 500pF, 200pF. Your values equate to 680nF, 280nF, 44nF, 21nF, 9.8nF, 3.3nF. Again this circuit is its own design, so if it sounds good it doesnt matter, just noting the differences.

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Post by vergadehule »

Nice! im going to start soon this project, as a newbie here i dont see, on the Schematic, any 9V conection to the transistors BC547B, but in the Vero Layout i see that the 9V goes one on the Base and another on the Emitter of the BC547B....... not that im saying that something is wrong... ( most likely its me being wrong) but i just wanna clear this out in my head before starting the project.... cheers!

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Post by bajaman »

there is no 9v connection to the transistors - the vero layout is a little confusing because the base leads are shown on top of the transistors instead of underneath them - but it does say to snip the collector leads off - if you study the schematic you will see that both transistors have there emitters connected to the base of each other
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Post by vergadehule »

Thanks a lot Bajaman for the reply and enlightenment, im sure i was a bit confused by the Vero layout... Exited to build this one, as im a little tired of those "amp in a box" using FETs and biasing thing and inconsistency of the circuits somehow... Thanks for this great OpAmp variation.... By any chance is there a video or audio examples of this build ?

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Post by bajaman »

"By any chance is there a video or audio examples of this build ?" - not yet sorry - but if you get it working please feel free to post a demo
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Post by vergadehule »

im sorry for not getting back until now.... i was a bit sick and also had no time to move on with the project... now waiting to the odd resistor values to arrive ( like 2k7,1k2, 3k9, as i dont have them around and also i cant get close to the values combining values from what i have around )that i can continue building it, and hopefully i can verify it soon !

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Post by Caleb »

Built this, and it works, however I feel like there’s not a lot of Gain or Volume available, I have to have both at max in order to push my amps, and even then it basically seems like a boost pedal. I was expecting more epic orange gain? Am I missing something?

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Post by bajaman »

Caleb wrote: 07 Sep 2023, 22:00 Built this, and it works, however I feel like there’s not a lot of Gain or Volume available, I have to have both at max in order to push my amps, and even then it basically seems like a boost pedal. I was expecting more epic orange gain? Am I missing something?
try increasing the 3k3 feedback resistor in the 2nd to last opamp stage - perhaps replace it with a 20k preset pot ;-)
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Post by vergadehule »

bajaman wrote: 08 Sep 2023, 03:41
Caleb wrote: 07 Sep 2023, 22:00 Built this, and it works, however I feel like there’s not a lot of Gain or Volume available, I have to have both at max in order to push my amps, and even then it basically seems like a boost pedal. I was expecting more epic orange gain? Am I missing something?
try increasing the 3k3 feedback resistor in the 2nd to last opamp stage - perhaps replace it with a 20k preset pot ;-)
cheers
bajaman
Hello sir. I must say that i replace the 3k3 resistor with a B 22k ( as i didn't had a 20k)
And it opens a bit more gain to the circuit, but listening videos of the amp, the pedal still seem to miss some more epic orange grit/gainy texture... is there any mod to do in order to achieve that , maybe?

Big respect for all your great circuits.. i did lately the orange AD200B and never leave my bass board.. thanks

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Post by bajaman »

Hello sir. I must say that i replace the 3k3 resistor with a B 22k ( as i didn't had a 20k)
And it opens a bit more gain to the circuit, but listening videos of the amp, the pedal still seem to miss some more epic orange grit/gainy texture... is there any mod to do in order to achieve that , maybe?
it has been so long since i designed this circuit - unfortunately there were many variations of the orange amplifiers back in those days - some had the tone stack and switchable filter sections in completely different places - perhaps i based my circuit on the wrong orange amplifier - i will take another look and se if i can improve on it
In the meantime you could try increasing the value of the 2k2 feedback resistor around IC2a for a bit more gain
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bajaman
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