Guest MJ.

Inca Tech owners thread - Dead but not forgotten

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Col is semi retired now, but is planning to release an easy to build kit of his Single Ended Class A (SECA) amps. The cost ought to be very low (compared to his recent SECA design for TQ, which retailed at approx. £6k), but we'll have wait for the PCBs until he can tell us for sure. They will be a more developed version of the original TOCA amps but with potential for very exciting upgrades.

There is a mailing list of sorts, it can be found at AudioChews.

Likewise, I'd appreciate a heads-up on those, when they are available. I'll check out the mailing list.

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Col is the man, I like the path he treads when it comes to amp designs.

Hoping there should be some news on the kits some time reasonably soon! :roll::)

BTW, Col really rates Steen Doessing's designs, so his gear ought to match very nicely with those SD1. :^

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Very impressed with the Oberon. Just played Crash Test Dummies then the new Morrissey effort, both on CD. It devours them with ease, presenting the music in front of me. LPs next.

One question is I don't seem to get any sound when using the CD Direct jacks. Is there anything stupid I could have done?

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Yeah, it was me being stupid! Button on front!!

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Mr Inca Tech (Colin Wonfor) now has his DIY kits available. There is some kind of mailing list accessible from Audiochews and some early builds.

This is just Colin himself making his expertise available to end users. He is currently a one man band, hence my enthusiastic support.

The first kit available is for a SECA (Single Ended Class A) power amplifier. It is a more advanced version of older Inca Tech designs, which progressed to TOCA amplifiers. This kit is several levels of development on. It consists of circuit boards and a freely available Bill of Materials. It was designed to be easy for a novice to tackle.

The PCBs are very cheap indeed.

There is talk of an uprated SECA amp being available soon, and a SECA pre amplifier has been prototyped.

All these designs are streets ahead of the Inca Tech and TOCA amplifiers that were once produced by Colin.

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Oh that's exciting! Novice, I very much am, but would love to give something like that a try.

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Single Ended Class A (SECA) amplifier kits available from Inca Tech designer (Colin Wonfor) - they sound incredible with the dynamic PS. I mean incredible, better than original TOCA SECA.

(He is contactable on AudioChews.)

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Inca Tech Claymore - update kit which allows replacement FETs or upgrades to current ones - Colin has just made these available.





Set of four £15 (Sept 2015).

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Hi Guys,

Here is few photos of the kit amp built by you guy and great work.

My ugly Thunderbird 5 look a like prototype case supplied by Quickie thanks Paul.


Paul,s stereo version he has also done a mono set.


Here is Sam first ever project in electronics it got published on Hi-Fi Answers, it is a Old PC case (cheap)


Here is the PCB done by Chris and his first time.


Here is Alan IGBT SECA and again worked first time.


Here is the large versions based on TOCA published in Wireless World.



Here is Sam the History Student from St Andrews Uni building his first venture in electronics.


The ID25 review.


So it can be done and with care and a few e-mails you can do it also.

Circuits and info are plastered ever which way. I put them here later so you can build it your way and enjoy the pleasure it will give you to say "I made that" well done all and thanks for your support.

  • Upvote 2

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Here is the latest KISS designed SECA amp circuit, PCB are available but it can be build on vero board with extreme care on STAR earthing please.


Dave Green Goddess on AudioChews is made on Vero Board and has been working for a few year now.


Ignore the old design of cable in the back ground the new stuff is much better.

Here is the BOM


Here is a block diagram to show you haw to connect it all up.


A guide to heatsinks and current settings.


Basic iss1 PCB layout.


The Two PCB on the left are the Amps and the other two on the right are the PSU boards.


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Since when will an amplifier sound better the louder it plays? Sure, louder can be more exciting, more enjoyable perhaps, but usually one reaches a point where things get a little ‘ragged’. This can manifest as harshness, sibilance, collapse of soundstage or loudness. Yes, I said loudness, which seems to me to be an artefact of distortion. (A really clean amplifier will be playing much, much louder than you think because it doesn’t sound loud. You will feel the bodily impact of music but your ears will not be suffering, tiring or bleeding.)

All amps have their limit. My main (Single Ended Class A) amps clip at theirs (I hear a ‘crackle’ on peaks) and this means they are physically running out of power. They don’t distort in any way until this point, which seems to be unusual. The designer, a Mr Montgomery Scott, explained to me that these particular Class A amps don’t relinquish their extraordinary damping factor even as they clip, which gives two things to be pleased with: 1/ the loudspeakers are not in any danger when the amp clips, and 2/ I have the purest most undistorted clipping possible. As a serious audiophile this is important to me.

When this same designer, a long confirmed miracle worker, loaned me his latest amplifier to try I was only too pleased. So here is my jumble of thoughts on the Elsdon-Wonfor (EWA) M-50 power amplifier. It is powered by a small warp coil following a failed experiment with Trans-warp drive. The following is copied from the EWA website:

•    Bandwidth 5Hz - 40KHz ±0dB
•    Bandwidth 2Hz - 100KHz -3dB
•    Output Power 50W/ch @ 8Ω
•    Output Power 98W/ch @ 4Ω
•    DC offset ≤ 10mV typically 2mV
•    Damping Factor ≥ 100 typically + 100

Each pre-drive section is set to run in SECA mode with all of them driven by a single SECA stage this being the only voltage gain stage. This allows us to use minimum feedback and thus reduce the sometimes drastic effect feedback can have on the music. The main reason for having any feedback is to keep the DC offset very low, which in turn reduces the forced positioning of the voice coils in the speaker leading to less distortion.

The drive stage is biased as a SECA with a constant current load in the same way as the SECA designs in the EW Audio range. However this stage is running only at 1W thus the heat dissipation is minimal, this works so well the amplifier runs cool or just warm under normal use.

The damping factor is unusual in that it increases as the load is increased. This is due to the unique bias technology where the output impedance decreases as the current demand is increased.


The version I have is a late pre-production prototype so the finish is a little rough; the amp resides in a DIY case and there are other little things that are less than perfect (The sliding doors stick - they don’t make build them like they used to) but the final version looks exemplary.

If you know Mr Scott’s work, then you’ll immediately feel at home with the M-50.  It has a familiar presence, power, speed and a certain warmth. It is variation on circuitry seen over the years in various SECA (Single Ended Class A) amps and even the old Magnum amps, and of course the Inca Tech Claymore. The basic idea has been refined and improved over many decades as he hasn’t been able to come up with a new one.

Loudness: This amplifier genuinely sounds better, the louder it gets. The loudspeakers feel more under control, the response faster. The M-50 requires next to zero warm up time and its power feels like it may be limitless. The character stays consistent, it doesn’t shout, there is no ‘coolness’ to it. The soundstage advances across the room towards me instead of collapsing as the volume increases, instruments feeling farther apart as I wander about the front of the stage (Derek Trucks is playing in my lounge today); the settee is vibrating like a massage chair, my cupboard door vibrates (I hear this on quiet spells). My neighbour’s kitchen units are in danger of falling of her wall, she tells me, and she is not happy (and she is hard of hearing). She leaves in a huff after banging the window, and Derek Trucks leaves with his band too. I’m sad to see them go but I’m not sorry. I feel like a naughty teenager.
We got the volume up to about the 1oclock position that time.

Soundstage and image really impresses with the M-50. I experiment with my loudspeaker positioning (They are modified Triangle Antal ESW). I move them much farther apart along the long axis of my room (they are now nearly five meters apart, I am sitting just over two and a half meters back) and the soundstage is just solid. No hole, no weakness at all. Such positioning can cause a certain ‘dry’ quality to the bass but not so with the M-50. We have staging, imaging and texture with warmth. The bass itself is actually staging with pinpoint accuracy which is an impressive trick all the big Wonfor amps carry off.

The M-50 is fast, oh so fast. It starts and stops with real impact (inertial dampers?). The leading edge of percussive strikes and bass notes is really felt viscerally. Not with a dry staccato edge (I’m looking at you, otherwise gorgeous ESL57) but with an easy reality that would be recognised by anyone who has played ensemble music. Percussive dynamics are really, really fun via the M-50 and it’s possible to enjoy Steve Gadd’s playing on whole a new level.

Human voice really feels eerily real, both male and female. In fact, eerily real could describe how the M-50 presents just about every instrument out there. Not just realism though, but the interplay between the instruments. Yes, on a timing level and many good amplifiers do this, it is especially important with Jazz, but I mean more tonally and texturally. The way each sound overlaps and can create a new aural ‘flavour’ (harmonic) for a moment in time, and its setting with an acoustic space. The M-50 gets this so right.

A slight change, to some electronic music. Engineered sounds can be a very pure way to get to hear an amplifier’s voice. Today I am loving Massive Attack, Younger Brother and Zoe Keating. The M-50 can manage the whole nightclub feel with ease, so much power on tap with loads of headroom. The room is energised, the layers of production on these carefully crafted records becomes apparent, the games the composers and producers are playing with our ears. The M-50 is like a diagnostic instrument in its ability to present a wide clean representation of music which can be taken as whole, or allow you to peer into the minutiae of a piece with forensic analysis. Banging.

This may just be the best amplifier I could conceive of. Fifty watts class; this M-50 eats just one pathetic little Watt at rest but is capable of driving very hard when required. It doesn’t even get warm unless your loudspeakers are a difficult load being pushed at volume. My Pre-amp idles at seven Watts! This is a genuine class A amplifier that you can leave switched on, there is no real electricity consumption or heat dissipation. Does that make the M-50 a holy grail of domestic HiFi? I believe it does.

There are just a few areas where one might prefer a really special (really hot!) single ended class A amp, but this is well into the realm of personal preference, nit-picking and frankly crazy audiophoolery. The M-50 is easily capable of being the last amplifier anyone would want, it is a keeper for sure. A lovely thing indeed, you’ve done it again Mr Scott!


I posted this elsewhere. The only thing worse than a hifi review is one you write yourself, so enjoy if this is your sort of thing...

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