High power from a low power SET amplifier, really!

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avahifi

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High power from a low power SET amplifier, really!
« on: 19 Feb 2018, 09:09 pm »
A friend of mine brought over an interesting device he has developed, a high power booster for low power SET amplifiers.

The device is a simple no feedback unity gain power mosfet current amplifier with a 100 ohm input impedance, a very low output impedance and a 60 watt per channel power rating. It even has regulated power supplies.  Its kind of a power amplifier with no gain stage and no small signal transistors at all, just a pair of mosfet output transistors.

You simply plug in the audio outputs from your low power SET amp into the device, and then plug your speakers into the output of the device.  Now you have a 60 watt output with no load interaction.  Your SET is not working at all driving the new current booster so its linearity is improved and you are no longer limited to super efficient speakers and load interaction.  Dan suggests that tube life should be improved too as they are not putting out any power at all, just their normal voltage gain.

In my reference system the sound was very impressive.  His SET amp could not of worked with my 83 dB efficient speakers at all, but now it could, and really really well.

Could there be a market for this device?  It would cost less than $1000. It would not be an AVA product as it is not needed with our amplifiers (unless you wanted a high power Ultravalve), but Dan is willing to build them for others himself.

Frank Van Alstine

roscoe65

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Re: High power from a low power SET amplifier, really!
« Reply #1 on: 19 Feb 2018, 11:23 pm »
This is very similar to the Firstwatt F4.  Pass sold out of these at $4,000, but you can still build your own from boards at Diyaudio.com.  It is a unity gain current amp that takes the voltage input from a preamp or SET and produces a current output with little of its own signature.  SET booster use requires a loading resistor for the amp.  Power is 25wpc/8ohms, 40wpc/4ohms.

DIY versions of this would cost about $1,000 using recommended hardware and components.  So yeah, if you can make a booster amp for $1,000 that sounds as good as Nelson’s you’ll sell a few.  I would include a conventional gain stage though.  It would broaden your market and still allow booster use with the gain stage bypassed.

RDavidson

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Re: High power from a low power SET amplifier, really!
« Reply #2 on: 20 Feb 2018, 12:36 am »
Other than the F4, the only other "booster" amp I've seen is the Musical Fidelity Supercharger 550K monoblock(s). Agree with the post above. What might be kind of neat would be an add-on gain stage or a switchable gain stage. I know I make this sound simple. I'm sure it's not. Just an idea that could sell more amps...if that's the goal.

planet10

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Re: High power from a low power SET amplifier, really!
« Reply #3 on: 20 Feb 2018, 01:33 am »
There are a number of “booster” amps, aka unity gain follower amps, on diyAudio, th elastest to gain attention the MoFo.

Worth noting that there is also a DIY super F4 (can’t recall the proper name) with more power.

dave

roscoe65

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Re: High power from a low power SET amplifier, really!
« Reply #4 on: 20 Feb 2018, 02:39 am »
The DIY Super F4 is likely  the Burning Amp in one of three different configurations.  The amp is split into gain and output stages.  Column A is choose your gain stage (if any), column B is your output stage:  single ended or complimentary (a la F4).