Looking at the feedback we get here from our stats most people who visit the site are interested in our subwoofers and hybrid amps. Well I've promising a revamped version of the old 1997 design for some time, starting with A DOWNLOADABLE REPRINT OF THE ORIGINAL ARTICLE. With the passing of time the design has been further developed and an all  new version is being polished up ready for publication.

Back in 1997, in the dying months of John Major’s Britain, Electronics World published the ‘Roaring Subwoofer’ article. This project was the culmination of  years of subwoofer design and building starting in 1978. As far as I know this is the only published motional feedback design. I had several designs to publish  at the time so I decided to use an alias. Russel Breden is definitely Jeff Macaulay. Typically because it didn’t have my name on it the design was a great success!

Motional feedback speaker systems have always been perceived as ultimate speaker systems because the advantages of negative feedback are applied around the driver to linearise the output. Basically one attaches a transducer to the speaker cone and feeds back the resulting signals into the amp’s feedback loop. Sounds simple in principle but, as always, there are problems to overcome.

In this project I used the signal from a second un-driven voice coil on the speaker as a signal pickup. Because this is essentially a magnetic induction pickup the signal produced is proportional to the cone’s velocity. External circuitry is then used to get the required response ( proportional to cone acceleration )from the system.

Considering that the designs over a decade old now there’s little I want to change. About the only  devices that may be trouble to find are the BDT65C’s. These can be substituted with TIP121’s with no change in performance, everything else is still available off the shelf. There’s no harm ,or advantage to replacing the 2N3055 with their plastic equivalents, TIP3055. Although this reduces the number of holes needed in the heat-sink.

Some people experienced difficulty with the power amp. Although on investigation these problems turned out to be wiring errors. Unfortunately although there is a lot to be said for using a PCB the design has been so improved in the interim decade that there is little point in producing a suitable PCB for the original design.

Finally the Volt DVC250/1’s  drivers originally used in this project. Although they work OK we can now supply matched pairs of drivers whose Theille /Small parameters are matched to this project, sound  better and are less expensive.( What more can you ask? ) PRICE LIST

For the past year we have been bringing you the very best of Jeff Macaulay’s new designs, free gratis. Unfortunately the bank manager has strongly suggested  that we should engage in some ‘proper’ work and so, from today,  we are offering our new designs on CD rom for which we will have to charge a nominal fee of £5( approximately equivalent to $10 or €7 ) . But fear not. Anyone who obtains a CD from us will get the full £5 refunded  towards any future product they purchase (excluding other CD roms!) and there’s no postage to pay on the CD’s wherever in the world you are.

Due to the continuing interest in the older  magazine designs we are also making these available on CD rom  complete with any necessary designer approved updates. Starting this month  3 oldies but goldies from the archives.
So, on ROM 1, all the new stuff you’ve been able to download plus this months new project/article. A hybrid Line level Preamp. This top of the range  preamp is based upon the ECC82 valve feeding into a solid state constant current source. THD is <0.03% at standard line level output. Bandwidth extends from 5Hz  - 50kHz and noise is ,-100db ref 775mV standard line level. What the statistics don’t reveal is the real benefits of this design. A finely layered sound stage, silent backdrop and dynamics that will shake you!. Although this is a stand alone project we also had it in mind that it could be used to upgrade our, or anyone else’s, passive preamp. So bearing this in mind we can offer a dual preamp with one active output and a passive output so you can decide for yourself which you prefer!


New products:-
Hybrid Line Amp
Inline Active Xover
Feedbackless hybrid amp
Passive preamp
3W Single-ended class A amp
+PDF reader


Past Masters:-
Versatile Power Amp
Versatile Audio amp
Loudspeaker Damping
Who Said the Valve was Dead
+PDF reader

At last on the net. ORIGINAL AUDIO DESIGNS. You wont find any derivitive 'me too'designs on this site. Life is too short. Instead you will find the best of Jeff Macaulay's  new audio pre and power amplifier, valve, solid state and hybrid designs. Now you can take advantage of my 30 years of inovative and exclusive  design expertise.We will also be offering updated diy kits for these and previous 'HERITAGE' DESIGNS. So getting the best dosn't need to break the bank.We will also be featuring subwoofers and active speakers, including an updated version of 'Electronics and Wireless World's motional, feedback sub. All these and more will be upcoming during the next few months so bookmark us.