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Thread: Firebottle Power Amplfier

  1. #1
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 6,089
    I'm Alan.

    Default Firebottle Power Amplfier

    My creative juices have been flowing again and I have made a prototype hybrid power amplifier.

    It will be known as the Firebottle AXOLOTL

    Here are the innards of the prototype:



    It takes the best of hybrid technologies with my 'super linear' triode amplification and MosFET output.

    The circuitry isn't finalised yet but should offer 80W rms per channel, with a zero feedback approach.
    Inspired by Croft but improved by Firebottle and it is NOT a copy.

    Just listening now and it trumps my OuTLaw OTL valve amplifier, just oodles of clarity, air, but with lots of 'heft' that some power on tap can provide.

    Last edited by Firebottle; 02-09-2015 at 16:47.
    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

  2. #2
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

    Default

    That looks interesting Alan. Valve MosFET hybrids have always seemed a good idea to me. Not tried one though, but I enjoy valve amps and have enjoyed MosFET amps, so the potential for the best of both worlds is rather appealing.

    Looking forward to hearing about the finalised design.


    Weren't the old Moscode amps this type of design? Seem to recall they were.
    It is impossible for anything digital to sound analogue, because it isn't analogue!

  3. #3
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 99,005
    I'm Grant.

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    Thats a bosker of a transformer...what does that put out?
    Not convinced of the name tjough..
    Regards,
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  4. #4
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 6,089
    I'm Alan.

    Default

    The transformer came included in the 'parts' deal I did with Macca, it is the correct output voltage but way over specified for the job in hand at 500VA

    Geoff it does seems rather appealing to use the best of both worlds. Been listening for a while now and the attack and clarity makes instruments so realistic, plus the amp runs very cool, definitely not what I could say for my valve OTL amplifiers
    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

  5. #5
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

    Default

    I thought so. Moscode hybrids:

    https://www.youtube.com/watch?v=j5JhcMhfuzo

    Looks rather good.
    It is impossible for anything digital to sound analogue, because it isn't analogue!

  6. #6
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

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    I'm checking for spy cameras in my workshop I'm working on something so similar I'll wager they're virtually the same....

  7. #7
    Join Date: Jan 2013

    Location: Birmingham

    Posts: 6,772
    I'm James.

    Default

    Interesting Beast Alan. You can't stop tinkering
    Main system : VPI Scout 1.1 / JMW 9T / 2M Black / Croft 25R+ / Croft 7 / Heco Celan GT 702

    Second System : Goldring Lenco GL75 / AT95EX / Pioneer SX590 / Spendor SP2

  8. #8
    Join Date: Dec 2008

    Location: East Riding of Yorkshire these days

    Posts: 4,779
    I'm Shaun.

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    Loving the concept behind this as I adore Croft amplifiers but find they do not have enough 'welly'. Also love the idea of zero feedback and what it does for 'air' and 'space'. I shall be watching this one intently.

  9. #9
    Join Date: Jan 2009

    Location: Essex

    Posts: 31,859
    I'm openingabottleofwine.

    Default

    Looks interesting Alan,

    I have always thought the use of a valve driver with a MOSFET output stage to be a good one: high impedance input with good overload properties and a high current, low impedance output to match the speakers. The secret of a good valve power amplifier lays with the design and quality of the output transformer; so avoiding them is, IMO, a very good idea - though Anthony might disagree! Is it single ended?

    Apropos the name: AXOLOTL, it's appropriate as your design is indeed 'output transformerless', but does it have the self-repairing capability of the Axolotl ? https://en.wikipedia.org/wiki/Axolotl
    Barry

  10. #10
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 6,089
    I'm Alan.

    Default

    Quote Originally Posted by Barry View Post
    but does it have the self-repairing capability of the Axolotl ? https://en.wikipedia.org/wiki/Axolotl
    Good one Barry, I'll have to build that in

    That said it is a very cool running amplifier and I have improved the bias stability to the output stage. It really is a fantastic match for the respective input and output tasks, ideal for being driven with whatever passive preamp you may prefer, or active as your prediliction dictates.

    I don't know why I haven't researched this approach before, probably because of a 'tubes only' attitude previously.

    I have been experimenting with the driver stage today and have achieved 100W rms with one channel driven with a stunning square wave response.
    Previously I was tinkering with voltage doubling from the main transformer to power the driver stage but it performs better with a traditional transformer/rectifier.

    Definitely the most transparent sounding power amp I have built to date.

    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

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