BAJA Orange OTR120 Graphic MkII amplifier pedal 9v 160318

bajaman · Post by **bajaman** » 16 Mar 2018, 06:16

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

cheers
bajaman

bajaman · Post by **bajaman** » 16 Mar 2018, 07:05

: Baja OTR120 vero cuts.png (7.5 KiB) Viewed 4249 times

soulsonic · Post by **soulsonic** » 09 Jan 2020, 20:02

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!

Dr Tony Balls · Post by **Dr Tony Balls** » 09 Jan 2020, 20:45

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.

bajaman · Post by **bajaman** » 10 Jan 2020, 02:51

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.
cheers
bajaman

Dr Tony Balls · Post by **Dr Tony Balls** » 10 Jan 2020, 14:27

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.

vergadehule · Post by **vergadehule** » 04 Oct 2022, 08:04

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!

bajaman · Post by **bajaman** » 04 Oct 2022, 09:48

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

vergadehule · Post by **vergadehule** » 10 Oct 2022, 20:28

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 ?

bajaman · Post by **bajaman** » 11 Oct 2022, 00:19

"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
cheers
bajaman

vergadehule · Post by **vergadehule** » 07 Dec 2022, 10:41

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 !

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