Brian May AC30 modifications: Peter Michalowski version

Over the past year Greg has worked with both Mike Ryde and Peter Michalowski on modifications to their Vox AC30 Brian May amps. Both Mike and Peter are very experienced with the Brian May guitars pedals and amplifiers, and feel that their AC30 BM amps have been much improved soundwise by these mods.

Please click here for Mike Ryde’s website where you can download a pdf file about modification of the AC30 BM to the Dave Petersen BM spec. Mike’s site is extremely informative about his experience with the Brian May equipment in general.

In late 2008 Peter Michalowski from Sweden had his amp tech Ola Lehnert do the mods that Greg Fryer suggested, and together through 3 versions of the mod they experimented to tweak the amp to what Peter thought sounded best.

Ola Lehnert is a well respected amp builder and repairer in Sweden.

For Ola’s website see

Click here to read Peter Michalowski’s comments about the BM AC30 mod and to hear his soundclips of the Greg Fryer and Dave Petersen modified BM AC30s.

Below are Greg Fryer’s schematics of the Peter Michalowski version of the AC30 BM amp mod.

Warning: please bear in mind that this sort of modification voids the warranty of your Vox AC30 BM amp, and that amplifier repairs and modifications should only be carried out by experienced qualified technicians.

Double warning: guitar amp modding can be a fun home hobby if you become experienced in valve electronics, take it VERY seriously and read up bigtime about it, but because of the high voltages involved it can also kill or seriously injure you and its not much fun playing your super hot amp with your super hot guitar when you’re dead! So if you’re interested please ask your amp tech to do this work for you.

BM AC30 schematics: please excuse the rough hand drawings

BM AC30 preamp schematic

BM AC30 preamp schematic

BM AC30 EL84 Output stage schematic

BM AC30 EL84 Output stage schematic

Note: screen grid resistors can also be 270 ohm/3 watt metal oxide or 330 ohm/3 watt metal oxide

BM AC30 power rectification schematic

BM AC30 power rectification schematic

More details soon for the BM AC30 regarding which component numbers and turret post numbers etc are involved. Mike Ryde’s website pdf document gives a very clear view of all this too.

Coming soon: improved Vox AC30 standby switch system for both GZ34 and silicone diode rectifier amps.

But for a GZ34 rectifier AC30 you really don’t need a standby switch at all. Just leave your standby switch in the ON position permanently, and turn the amp off and on by using the Mains On/Off switch. Your GZ34 will last a LOT longer this way.

Click here to read Lyle Caldwell’s excellent in-depth article about why you don’t need a standby switch on a GZ34 rectifier AC30 at

AC30 suggestion: if you need to mute the AC30 for guitar or pedal changes or whatever, simply pull the guitar lead halfway up out of the black plastic input socket. This will earth the signal going into the first valve thereby muting the amp. And you don’t have to scramble around looking for that guitar lead on a dark stage…

More soon.

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Guitar and electronics designer/manufacturer
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