BAJA REACTOR 010119  [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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sixthfloor
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Post by sixthfloor »

mecmast wrote:Maybe very stupid question but i couldnt stop myself from asking :)

I am gonna use 9v power supply. What's the purpose of "Vbias" labels on the vero board?

Really sorry for my question. And thank you for your replies. :)
The labels are used as a reminder of which parts of the vero are connected to the biasing voltage I think. Just ignore those :wink:

EDIT : just got beaten to it by plush :D

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rpc66
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Post by rpc66 »

I'm glad to see you taking the power amp into account. I see amp sims and cab sims galore, but no one seems to address the effect that the power tube has. I've been searching for specs/frequency analysis for a Vox AC30 2 x 12 cab (with Alnico Blues). I'm hoping to tweak an existing cab sim design to these specs. Would you be able to point me in the right direction?

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rpcanfield
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Post by rpcanfield »

bajaman wrote:UPDATE alert:
I had a closer look at some Marshall, Mesa, Orange quad box impulse response curves and produced the following small update to the gyrator (sallen key filter) section.
cheers
bajaman
Baja Reactor 010119 rev1.png
I'm glad to see you taking the power amp into account. I see amp sims and cab sims galore, but no one seems to address the effect that the power tube has. I've been searching for specs/frequency analysis for a Vox AC30 2 x 12 cab (with Alnico Blues). I'm hoping to tweak an existing cab sim design to these specs. Would you be able to point me in the right direction?

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rpc66
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Posts: 8
Joined: 27 Feb 2019, 06:13
Completed builds: Adding LED to Original Rat.
Built Purple Persuader Tube pedal by MOD DIY
English Gent kit, Klon Klone kit
RAH from Veroboard layout.
Location: Ocean City Maryland, USA
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Post by rpc66 »

I was wondering, this seems to be a project that expands the scope of the Presence and Resonance Effect - https://www.freestompboxes.org/viewtopic ... 67#p272867. I'm all for it, I just want to know if I'm looking at it correctly.

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rpc66
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Joined: 27 Feb 2019, 06:13
Completed builds: Adding LED to Original Rat.
Built Purple Persuader Tube pedal by MOD DIY
English Gent kit, Klon Klone kit
RAH from Veroboard layout.
Location: Ocean City Maryland, USA
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Post by rpc66 »

bajaman wrote:
After simulating the response characteristics of a Soldano SLO output stage driving an approximate electrical equivalent of a Celestion quad box, I have come up with this functionally similar 9v dc pedal which can be placed anywhere in your effects pedal chain, but preferably as the last pedal before a solid state amplifier or mixer, daw recording device etc.

The signal is fed via an input level (DRIVE) control (ideally set to 18% to maintain unity gain), to one input of a differential instrumentation amplifier. The voltage gain of this amplifier is the same as the 12AX7 differential input stage of the typical tube amplifier (12dB). After this stage, the signal is fed to an op-amp gain stage designed to simulate the speaker rising frequency response at high frequencies and a gyrator designed to introduce the "hump" at 100Hz typical of the speaker cabinet resonance.....

No attempt has been made to model the frequency response characteristic of the speaker in this design, just the electrically equivalent interaction with the tube power amplifier output stage.
If the 4x12 closed cab resonance has a 100Hz hump, what would a 2x12 open back look like? And how can we take this a step further to model speaker characteristics? I'm looking specifically at the Alnico Blues - https://celestion.com/product/13/celestion_blue/ . The specs are on that page, but how do they translate when installed in an open back cab being driven by EL84's?

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Optical
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Post by Optical »

Ive just built this using one of Bajamans pcbs.
Have to say, it works really well. I was trying a tube preamp into a solid state power amp, and it had no mojo. But with this reactor circuit, mojo restored and the result is similar to using a tube power amp.
Impressed/10

I tried some various diodes but also didnt like the results. It did sound like power tube clipping to my ears but maybe there are some improvements that could be made in that area.

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bajaman
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Post by bajaman »

Hey Optical
Glad you like it :D
cheers
bajaman
be kind to all animals - especially human beings

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boukman
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Post by boukman »

Hi!
Thanks @Bajaman for this unique project!I`ve ordered some parts that are missing and i`ll built it soon!I was wondering if we could use a transformer in there for a more "realistic" power amp feel as they have used in the Supro pedals??What do you think?Would it work and how??
Thanks again!!!

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