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Project 003 - Fender Supersonic 22 Modification

DISCLAIMER: This modification is experimental, so if you decide to do it yourself then you are on your own, I can't be held responsible for any problems/issues/damage/injury that may occur if you decide to follow this build.


The guys and I have been ressurecting our old band of late and it got me thinking about my own guitars & amplifiers in terms of the sound I now seem to be chasing. Any guitarist will tell you that as the years roll by your idea of the perfect sound changes, maybe not dramatically but it does change.

For me I have always played Fender Strats, but got tempted recently by the warm chicken pickin' sound of a ash bodied Fender Telecaster through a vintage Fender tube amp.

So what attracted me to the Supersonic 22 is the varying sounds it can reproduce from different Fender amps, and for practicing in the home or small gigs I reckon it's a better sound, or better suited than it's bigger brother the Supersonic 60. So, I purchased a used one via Ebay.

One thing about the Supersonic 22 is that it's the little brother in the range and as such is missing a couple of features that it's siblings have, notably the ability to alter the gain on the external effects loop. This control is often used when by-passing the effects loop with a short lead (single ended) and using it as an instant boost control for lead breaks etc. However, without a gain control this method is not possible on the 22.

After studying the schematic diagram it was obvious this could be very easily implemented with a small modification.

U4 - TL072 op-amp drives the FX Send. The original fixed gain on the op-amp is 1.33, and with the addition of a 10k potentiometer in series with R83 (3.3k) the gain can be adjusted from 1.33 to 2.33.

Please note that this mod requires a single ended cable to be used (not a balanced cable), I may look at a tweak to retain proper balanced cable usage later.

Modified schematic:



Other suggested mods to early Supersonic's (haven't tried them myself, not implemented in this article):

C7 - Remove it - this is the bright cap on the vibrolux channel. Stick a switch in series with it so you can have it in or out.

C1 - Try 2.2uf or 2.7uf. This tightens things up quite a bit in the lead channel especially. You do lose a tiny bit of bounce on the clean, but depending on your required tone it's worth it overall.

C15 = 2.2nf (or 1.0nf for slightly more harmonic content)



Available in black or blonde it's a great wee amp.


Barely in the house 2hrs and it was ripped apart and on the workbench. Topside is the main circuit board, underneath out of sight are the transformers and valves.


Centre of photo: R83 and U4 op-amp prior to modification.


The new 10k potentiometer mounted on the rear panel. If the truth be told some screened cable would have been better used to keep any noise down, but after testing with the short run of unscreened 7/0.2mm wire it's not a problem.


The quick and dirty mod on R83 prior to adding a spot of silicone sealant to keep things static.


The labelled up pot on the rear panel. Fully left basically sets the gain as factory set, fully right gives it about double.