Brian May Deacy Amplifier Build Project Part 2 – Circuit Board Assembly

In part two of a series of three videos about making a replica of Brian May’s legendary Deacy amplifier, I unbox the Knight Audio Technologies (KAT) custom kit of electronic components and assemble it, discussing the characteristics of key components such as the transformers as I progress. The video duration is 21 minutes.

Brian May Deacy Amplifier Build Project Part 1 – Introduction

In part one of a series of three videos about making a replica of Brian May’s legendary Deacy amplifier, I briefly discuss the origins of the Deacy amp circuit (salvaged from a vintage transistor radio that John Deacon found in a London dumpster in 1971) and what Queen tracks Brian used it to record on. I then move on to talk about the new Knight Audio Technologies (KAT) amplifier board kit and the other component parts required including suitable vintage and modern woofer and tweeter loudspeakers and the cabinet itself. I finish by introducing the only official Deacy amplifier replica which was made by Knight Audio Technologies between 2011 and 2019.

Vox VBM-1 Brian May Special Amplifier

Launched in 2003 and retailing at US$199/£149, the Vox VBM-1 Brian May Special amplifier remains a popular choice for guitarists seeking to replicate Brian May’s signature tones at low volumes and on a limited budget despite being discontinued in 2005. It was designed to fulfil a specific purpose: to replicate the distinctive sounds of the legendary Deacy amp. Check out my latest musical equipment section article on this unit:

Brian May Deacy Amp Replica

Check out the third article in the musical equipment section of this website which covers the Brian May Deacy Amp replica made by Knight Audio Technologies (KAT):

It contains the original pictures shown below, technical specifications for the amplifier, hyperlinks and four embedded YouTube videos, including Jamie Humphries‘ review for Guitar Interactive magazine and some demonstrations recorded by Martin Pitcher at the 2018 and 2019 Brian May Red Special enthusiast meets.

KAT Studio-D Deacy Style Amplifier

Following up on the recent story of the KAT Studio-One all-valve practice amplifier, Nigel Knight has released details of the other part of his R&D endeavour over the past few years. Nigel recently announced:

Brian was never happy that we had to discontinue the production of the Deacy Amp replica, but the decision to do so was based purely on the fact that we could no longer source transistors with the correct characteristics that matched the original, either locally or globally and certainly not in the numbers we needed to extend production. So from the point that Deacy Amp replica serial number 0150 rolled out the door, I was on a bit of a mission to design its replacement.

This then, is the Studio-D. It is germanium Deacy’s silicon brother if you will. After years of trawling through transistor specifications, we finally found a set that could be configured to provide the same responses as the original AC125, AC126 and AC128 transistors. We are still using the original Deacy circuit, transformers and components albeit with the odd bias-tweak here and there and it still fires into a single 6.5″ twin-cone speaker. The resulting amplifier sounds magnificent and we’re really pleased with it.

The Studio-D is equipped with an adjustable battery simulator (DABS Unit), HF tone trim pot (that mimics the tone dulling effect of putting a tea-towel over the amplifier) and a built-in attenuator that has been optimised to the speaker and Deacy responses and, like the Studio-One, allows you to dial-down the volume.

KAT Studio-One Practice Amplifier

Nigel Knight recently revealed a prototype 1 W (max), all-valve 2 x 6.5″ bedroom/studio combo amplifier. The styling and overall cosmetic appearance pays homage to the legendary Vox AC30 used by Brian May.

The valves (vacuum tubes) are biased such that at each stage, the grid starts to go positive at exactly the same point that a Vox AC30 would at full volume.

The KAT Studio-One guitar amplifier features:
• Two newly developed KAT DSP 6.5 TC speakers which have an on-board filter network that tailors the frequency response to give the full bodied mids of Brian’s Deacy amplifer but without the high frequency fizz audible in many 6.5″ twin-cone drivers.
• A built-in attenuator that has been developed in-line with the speakers to ensure the same tone is produced at all output levels. -24 dB attenuation brings it down to almost whisper level whilst still producing jangly cleans and smooth full-on distortion.
• Plywood cabinet construction.

Nigel has deployed all his electronics design expertise and experience producing and maintaining Brian May’s gear to offer the holy grail that amateur Queen players have been seeking for some years: the full on Wembley ’86 tone in your home, or Project BMIB (Brian May in your Bedroom) as I’m calling it. [Other Vox AC30 + Deacy amplifier emulation BMIB solutions are available, such as the Fryer Guitars Mayday effects pedal.]

Nigel has recorded a short demonstration video in the link below using a KAT STB Stomper and Retro Sonic chorus pedal. The amplifier is still at the prototype stage and is not available for general sale yet. Note that corner protectors have been made but are not fitted to the prototype illustrated in these three images (photo credit Nigel Knight).

Update as of 25 September 2022. I recently bought three units and have released a brief (6m 43s) YouTube video in which I unbox them and show you around the inside and outside as well as a quick demonstration through my KAT Brian May rig. Please also check out my gear page for this amplifier here: