Jose Arredondo Guitar Amp Mods

[CJ]

I found one schemo for a Marshall.

Just looking for more to store here for easy access.

 

[12afael]

Any idea what diodes are in the master volume

 

[bjosephs]

Any idea what diodes are in the master volume

Zeners. Some people use low values like 4.7v but I think something closer to 20 is more reasonable.

 

[dai h.]

haven't checked this out personally, but I think this (supposedly the Fortin Cali mod schematic) is some modern offshoot of the many "Jose (Arredondo) (Marshall) mods" :

https://elektrotanya.com/fortin_cali_mod_amplifier_sch.pdf/download.html#dl
This Youtube channel by an Aussie guy might be interesting. He goes through (analysis, tutorial) all sorts of mods and amps (his latest is the Marshall Bernie Marsden signature amp).

https://www.youtube.com/@HeadfirstAmplification/videos

 

[CJ]

wiring diagram for Jose master

 

[bjosephs]

wiring diagram for Jose master

Doesn’t seem right. Tons of production amps have copied the Jose master volume and they all use some sort of symmetrical clipping scheme (zeners, high VBE bjts, fet clippers, etc. What would be the use of putting a regular diode in series with a zener when all it would do is raise the threshold of the negative going signal by .6v?

The Jose mods seem to have been an attempt to simulate power tube clipping, which would have been symmetrical, before the main loudness knob so that the effect of cascading preamp saturation into the power stage could be approximated at lower volumes. I think those diodes should be back to back zeners of equal Vz.

 

[Gus]

Has anyone tried the limiter circuit that VOX used in some solid state amps?

 

[musipol]

I have to agree with bjosephs, the stuff I have seen back in the day was 2 zeners. I used to do the same using 15V or 20V zeners. IMO you get most of the asymmetrical clipping effects from the preamp so I went for symmetrical clipping after the follower(pre tone stack). Just my opinion.

 

[MadJack]

I have this! Hope it help!

 

[musipol]

Strange that the zeners in this cameron schem are labeled 2n5400 (PNP transistor), maybe diode connected transistors?

 

[bjosephs]

Strange that the zeners in this cameron schem are labeled 2n5400 (PNP transistor), maybe diode connected transistors?

Yup. 2N5400 have an emitter-base breakdown of 5V. I believe the way you see them wired in dai h.’s link above shows that they are trying to leverage that attribute. I couldn’t tell you if it’s actually more appealing than Zeners or why it would be.

 

[CJ]

there's jose and i threw in rivera at no extra charge

 

[dai h.]

This? (sounds interesting)

https://www.premierguitar.com/adjustable-clipping-in-vox-amps
https://music-electronics-forum.com/forum/amplification/guitar-amps/theory-design/49250-#post751412
http://www.voxshowroom.com/us/amp/v1133_preamp_hood.html

Has anyone tried the limiter circuit that VOX used in some solid state amps?

The Headfirst Amps guy has a video on the diode clipping "saturation switch":