JCM800 recording preamp

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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mozwell
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my favorite amplifier: home made SVT2
Completed builds: baja tube driver, several TS variants, Sansamp GT2, Ross Comp
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Post by mozwell »

a preamp i built to directly record guitar into my Digital Audio Workstation
I dont like the free vst plugins, so this was an alternative to micing up a guitar amp
You could also use it straight into a power amp
I modified our guitarist's little Marshall MG30FX and added a line in 1/4" jack. The amp had a 1/8" line in for a MP3 player, but i added the extra input so he could still use the effects on his amp when using this preamp.
One other mod i did to this little amp was to add an extra 4700uF 35V capacitor to each side of his power amp power supply. This made the amp sound more strident.
Our guitarist comment using this preamp into his little transistor marshall was "this is as close to a JCM as im going to get without dragging a half stack around. The way this little amp sounds now blows me away. This preamp has great cleans & an awesome crunch, but for searing over the top distortion, i just hit my outboard OD pedal"
This preamp takes pedals well, as its basically just the preamp from a JCM800, with a speaker cabinet emulator (Run Off Groove Condor cab sim)

The file for the amp is too big to post here, but if you want to know how i did it, PM me and include your email & i will email you the details

In the build doc there is a link so you can listen to how this sounds.

A quick word of warning, there are high DC voltages on the tubes and mains wiring, so if you are not sure of what you are doing, do not attempt this project. These voltages can KILL you if you don't know what you are doing.

Enjoy :)
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Building a JCM800 preamp for recording.pdf
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m_pre.zip
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mozwell
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Posts: 112
Joined: 11 Mar 2009, 23:01
my favorite amplifier: home made SVT2
Completed builds: baja tube driver, several TS variants, Sansamp GT2, Ross Comp
Location: Melbourne, Australia
Has thanked: 22 times
Been thanked: 68 times

Post by mozwell »

apologies, i had D9 and D10 the wrong way around on the pcb overlay
This is corrected in the attached file
Please ignore the zip file in the first email
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vangelismetheny
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Post by vangelismetheny »

Great work Mozwell! Thank you for share dude.
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jarrodthebobo
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Post by jarrodthebobo »

For a bit more fun, I'd try adding a push pull power amp into this pre using a small triode stage such as a 12au7 or a 6sn7. You can purchase 1 watt output transformers for those little blackstar amps that are perfect for this sort of project; and they're cheap too. This way you can get some additional 'power amp' distortion as well as the possibility to run the pre directly into a speaker for some quiet shits and giggles. It also allows for some legitimate and fully functional NFB and presence circuit. Throw some fat-ish resistors for an attenuation circuit on the output and you've got yourself an awesome recording amp/pre.

Example!


Also for some direct stuff:
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