4 stage, higher gain JCM 800 mod

StratMatt7376

TDPRI Member
Joined
Jan 1, 2022
Posts
52
Age
36
Location
South Carolina
For those of you who like high gain stuff, I did an experiment last night with my 18 watt JCM 800 build. It was kind of like Rob Rob's Cascade and Voicing a Lead Channel mods. I achieved this by adding a (.68 uF) bypassed gain stage before the original first stage of the JCM 800, adding a new filter between the added first stage and the original one, raising the cold clipper value, and centerish biasing and bypassing the grid clipping stage. I was kind of going for a more dual rectifier/soldanoish sound, but without copying the Soldano interstage filters verbatim. So, by using combining a high pass filter with a band pass filter and playing with the component values a little in LTSpice, I was able to pretty closely mimic the Soldano SLO's frequency response at the second stage. The filter I came up with also had the added benefit of providing some of the needed interstage attenuation.

It sounds good. At 3/4 gain, it's kind of like Black Album Metallica, except maybe with a little less bass. If anybody is curious, I can post some pics, a schematic, and some LTSpice analysis.

Has anyone else here done anything similar?
 

dunner84

Tele-Meister
Joined
Jul 15, 2014
Posts
359
Location
Victoria, bc
Great Project! I did something similar a few years ago as a preamp. Kind of an SLO lead channel JCM 800 mash up. I don't remember all the details, but its more SLO than JCM 800.
I tried it through all kinds of power sections, and by far the best was my 50watt JCM 800 with slightly stiffer power supply, and 150ma PT. It played nice with many, but something about running it into that power section was fantastic!

Love to see some pics/clips if available
 

owlexifry

Tele-Meister
Joined
Feb 10, 2021
Posts
383
Location
Adelaide, Australia
For those of you who like high gain stuff, I did an experiment last night with my 18 watt JCM 800 build. It was kind of like Rob Rob's Cascade and Voicing a Lead Channel mods. I achieved this by adding a (.68 uF) bypassed gain stage before the original first stage of the JCM 800, adding a new filter between the added first stage and the original one, raising the cold clipper value, and centerish biasing and bypassing the grid clipping stage. I was kind of going for a more dual rectifier/soldanoish sound, but without copying the Soldano interstage filters verbatim. So, by using combining a high pass filter with a band pass filter and playing with the component values a little in LTSpice, I was able to pretty closely mimic the Soldano SLO's frequency response at the second stage. The filter I came up with also had the added benefit of providing some of the needed interstage attenuation.

It sounds good. At 3/4 gain, it's kind of like Black Album Metallica, except maybe with a little less bass. If anybody is curious, I can post some pics, a schematic, and some LTSpice analysis.

Has anyone else here done anything similar?
hell yes, show us
 

StratMatt7376

TDPRI Member
Joined
Jan 1, 2022
Posts
52
Age
36
Location
South Carolina
Ok, here are some pictures. I'm still deciding whether to return it to stock or to tidy up the point to point and make a home for the extra 12ax7.
 

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StratMatt7376

TDPRI Member
Joined
Jan 1, 2022
Posts
52
Age
36
Location
South Carolina
Here is the LTSpice frequency response plot comparing the Soldano filter (green) to the newly concocted filter (blue). Also the new filter's schematic is on the right. Unfortunately, my recording setup is not working right now, otherwise I would also post some audio.
 

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