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Kustom Defender 5H Mods 
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Joined: Tue Jan 22, 2013 9:21 am
Posts: 417
Location: Danbury, CT
I picked up a Kustom Defender 5 watt head to use as a pedal platform for lower volume jamming after my daughter goes to sleep. At five watts, I figured it would do the low volume thing pretty well, but it doesn't really do low volumes as well as I had hoped. If I keep the volume low enough to be "quiet" it sounds completely choked off like there is a blanket over the speaker cabinet, but if you turn up the volume to around 9:00 where the tone starts to open up, it's too loud for my intended use. Also, there is very little headroom, by the time you get close to noon on the volume knob the amp is distorting, and since I am using the amp as a pedal platform, I want it to stay completely clean.

So, I tracked down a copy of the schematic and put my Homer Simpson style monkey brain to work. By removing C4 and C5, I was able to decrease the gain in the circuit enough that it stays clean almost all the way through the volume sweep. In addition, the tone is much clearer at lower volumes and the volume taper from quiet to loud is much more gradual.

Nothing ground breaking, but I wanted to post this on the off chance anyone else had a similar experience with the Defender 5H and wanted a quick and easy fix. You don't even have to take the board out of the chassis, you can snip the capacitors off from the top side of the board, so it literally only takes a few minutes from start to finish.


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Amps: 5150 (w/bias mod), 5150 II, EVH 5150 III 50 watt, FJA PV XXX, Framus Dragon, FJA PV Penta, Marshall 9100, PV Ultra 120, GK 2100 SEL, Ultra Plus 1x12 Combo
Cabs: Mesa Recto 4x12, 3 Marshall 1960B, Marshall 1966B, Avatar 2x15, Mesa Recto 1x12, misc 2x12's.


Wed Nov 16, 2016 4:55 pm
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Joined: Sun Jan 20, 2013 9:22 am
Posts: 1935
Location: Manchestoh, UK
Someone here did a bunch of mods to theirs iirc. You might want to consider removing the cathode bypass cap on V1 too. It doesn't work in the same way that it would for a preamp stage, i.e., influence the frequency range of the gain boost it adds, but some people like how the power amp overdrives without it as the bias will drift sooner. It's easy enough to add it to a dpst/dpdt switch if you like both sounds.

There are a few other options for dropping the power output; The most fiddly is adding in vvr/power scaling but it is great. The other is to add inline attenuation to the speaker outs and that isn't a big problem to do in such a low powered amp. The 1 Watt Marshalls do this to switch between 1W and 0.1W and I intend to add it to an ecc99 build I'm currently hacking out of my junkpile.


Thu Nov 17, 2016 4:06 am
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