View Full Version : EWA amplifiers: What is SECA?

21-09-2020, 09:20
SECA technology - an overview:

Single Ended Class A

EWA amplifiers will provide you with the ultimate experience in musicality and loudspeaker control. State of the art class A performance is guaranteed by Colin J Wonfor’s peerless experience in power supplies and audio engineering.

Colin Wonfor designed and built the largest ever Single Ended Class A audio amplifiers in the world (link (https://www.abcaudio.biz/ewa3)): Class A all the way through from the input to the output terminals. The current generation of SECA derived circuits, available only in EWA amplifiers, is based on this heritage. The Wonfor engineered SECA circuit found in EWA designs brings exquisite class A amplification into our homes in a very efficient manner.

The driver stage of all EWA amplifiers operate in high speed SECA, pure class A between 3 and 5 Watts. Smaller amplifiers in the range then output class A/B to the loudspeaker. The larger amplifiers output class A Push/Pull.

This can be described as a quasi hybrid approach, as the grip, power, control and efficiency of an A class P/P amplifier is in full evidence, but the full character of the sound is very much pure SECA. All EWA amplifiers feature vanishingly low THD due to Colin's expertise. The Claymore measures worst, at 0.01%.

Designed and calibrated with low levels of negative feedback, EWA amplifiers are quite conservatively rated for more than adequate RMS power. You will be shocked at what even the baby Q-20 can do!

EWA amplifiers have very wide bandwidth, stunningly fast rise time and massive damping factor, meaning these amplifiers are in complete control of your loudspeaker. There is virtually zero non-linear phase shift within ten times the audio bandwidth, and every EWA amplifier is uniquely devoid of crossover distortion on the output. DC offset is impressively absent, under 10mV in all cases.

EWA pre-amplifiers are Single Ended, and electrically very quiet. They are superbly fast and detailed, digging deep into every musical nuance. They are also equipped with excellent, high performance headphone amplifiers as standard.

Here is the stunning M-50 - our middle of the range power amplifier that will show up an amplifier costing four times more:

https://i.ibb.co/GP8s52b/M-50-Amp.png (https://ibb.co/BsQ4CZS)

Below showes the first of the 'Sense' amplifiers being build - a true dual differential class A power amplifier of ridiculous measured performance, featuring feed-forward error correction:

https://i.ibb.co/VvMY4B3/20200226-202600.jpg (https://ibb.co/JzrjJkC)

The largest class A amplifier ever built for audio:

https://i.ibb.co/Vj8w3VD/6.jpg (https://ibb.co/BzRnwLj)

21-09-2020, 18:23
I can remember seeing and hearing the TOCA at an Audio Fair at Heathrow, somewhen in the early '90s. I initially thought they were speakers (since they were lconsiderably larger than the speakers being used). It was only on closer inspection that I realised they were amplifiers! :eek:

I believe the origin of the project was to see just how much audio power could be wrought from a 13A mains plug (potentially 3kW).

Colin Wonfor
23-09-2020, 06:49
Hi Barry,

It was to show the USA and Nelson Pass his 50W A Class, reputable a SECA design was not the biggest in the world at the time.
So I made a true SECA 20W, then the 50W,100W,200W and finally the 300W mono's.
The 300W took 1800KW to run each, had 1.5Farrad caps on each of the 3 PSU's inside and at 180Kg each were crazy.
On switch on at the Penta Hotel it took the mains trip out even with slow start, so a day before the show I had to change that on the floor of the theatre.

Colin Wonfor
10-11-2020, 07:48
Watch the video, it will help to explain Class A and A/B. Based on the old Mullard notes it seems.