EWA amplifiers and a custom build

edited January 28 in Amplifiers
In the interests of disclosure, I work with Colin and help him sell EWA products.

The last six months or more have been interesting for me on the amplifier front; Colin's newest design, the EWA Oberon has been here several times and I've been helping Colin out as a beta tester of sorts. The Oberon is a really lovely class A integrated amplifier that manages to sound just like the mighty EWA M-100 amplifiers, at normal listening levels. Really, just like them - a remarkable feat: stupendous bass impact and speed, rich texture and all the detail you can imagine. Colin has done something very, very special (along the lines of power factor correction) with the power supply and squeezed most of an M-50 power amp into the case, alongside a full M-50-P pre amplifier. it's basically a 2u sized integrated amplifier (with heat sinks).

You might be able to tell - I really love it, and thought I would end up owning one. I actually preferred it to a full M-50 pre and power set.

However, I also made a change to larger loudspeakers about the same time. The Oberon isn't as happy in this context, driving 88dB/1W@1M / 4ohm as it was driving my Triangles (93dB/1W@1M / 8ohm). The sound tends to harden up at higher levels. So although the Oberon is probably the finest Wonfor designed amp I have heard - at all - it's not going to work for me as a final destination amplifier, with such loudspeakers. 

So I've asked Colin to build me a custom M-50 pre and a special power amplifier, based on a lower power version of the M-100 turbo. I'm really excited about this, so I plan to share thoughts and pictures here. It isn't a standard EWA product but it won't be too far off, just with a few extra features.

The cases are already ordered and on their way to Colin from Italy (we ordered two), and I'm hoping Col will send lots of pictures from the build to be that I can post on Chews.


  • edited January 28

    This is the first step. I have rebuilt my LS-50 speaker cables - which needed doing anyway (as I had the first build, ratty production prototype set). This set now features an additional set of cable within the webbing. This isn't for bi-wiring, rather it's part of a device Colin will use that allows his amplifier to correct for electrical losses or errors in the cable. The effect being akin to directly connecting the amplifier to the loudspeaker.

    The loudspeaker ends will connect conventionally (red & Black) using the existing terminals, but the amplifier itself will sport an additional set of 4mm sockets. I hope Col will explain some of this, as I cannot! (I think that it may be an attempt to take negative feedback from loudspeaker terminals and apply it (phase reversed) to the amplifier input.)

    Edit: I've been reading a little on google to try and find where I remember this stuff from. Two places - Deltec amps and also Urei 813 monitors. They all utilised 4 wires to each loudspeaker - conventional +&- and also ground from speaker and a 'sense' wire. Is that what you're doing Col? Kelvin sensing?

    For now the additional wires are taped off to avoid shorts.
  • edited January 28
    Kelvin what a chap he was but my hero is Tesla so to answer question.
    The same technique is used on large PSU.s as remote sensing allowing the voltage to stay constant to the reference voltage at all loads. Now a audio power amp reference voltage under idle is zero volts but in dynamic mode( playing Ugly Music) the feedback signal follows the audio and compensates for the loading dynamic and phase load/frequency change and loses due cable delay times and load. So faster cable helps but more can be got out of the system even playing ABBA.
    We are also helped as this amps are balanced out/bridge so no nasty zero volt current loops and it makes the feed back better as both feedback signals are not relative to zero volts.
    The other nice thing for me is the lower voltage to power rails can be so I can have more current in class A and this helps to keep the heatsink smaller.
    The PSU as Alan describe in the Oberon is a 50Hz resonant type nasty evil beasts lots of current.But some evil high voltages but hidden from fingers safe and secure.
    Does this help ?
  • Pffft!

    It helps me know how much of nothing I understand!

    Thank you Col, I appreciate your taking the time. That Oberon is really impressive, so I imagine the new amplifier will be even moarer spectacular. 👍

    The sense thing looks very interesting indeed, but looks like more than Kelvin sensing from what you say. 

    At least tell me I built the cables right? 🤔
  • The amp sounds as if it'll be a great thing!
  • uglymusic said:
    The amp sounds as if it'll be a great thing!
    I believe so! Col's last two designs have been terrific advances (Oberon & M-100 series).

    This is the same thing but not so large, also some features that Colin has mentioned before: 

    • Kelvin sense/compensation system at speaker output.
    • Bias switch: pure Class A 'hooligan mode' for music and class A/B for everything else - the amplifiers will be powered up for hours and used every day as part of the AV system.
    • Balanced mains power built in.
    • Fully bridged and balanced pre and power (because there is a variation of the compensation (Kelvin) circuit that corrects this part of the system also - so Colin can control everything about the signal from the input on the pre to the loudspeaker terminal.
    • Precisely matched Riaa/Reversed Riaa input on a RCA input on pre amp. I have this on another Wonfor pre, and it's a winner.
    I've heard some really heavenly sounds from Colin's recent amps, I'm hoping that this will be the most wonderful yet.

  • Good luck!

    I love my custom SECAs (OK there's a lot of TQ in them).
  • uglymusic said:
    Good luck!

    I love my custom SECAs (OK there's a lot of TQ in them).
    Oh Rats

  • But a TQ with 100% 14.
  • Tell the press that, GM claimed he designed it all
  • edited February 1
    If I wanted truly esoteric amplifiers I might ask someone like GM; however I can only afford a Colin Wonfor! 😂

    So 100% C14 will do for me. 👍
  • Esoteric! LOL!
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