Zero Feedback Impedance Amplifiers

[planet10]

Originally posted by enochRoot
i agree...transformers only, but maybe make matched fets an add-on option for those of us that don't want to bother (or can't) match fets

That would be it...

dave

[Netlist]

Originally posted by Susan-Parker

mosfet matching helps to reduce the nonliniarity, but is not essential to get the amplifier working.

You could drive the outputs in that manner for an integrated amp.

At what matching accuracy are we looking? 100mV, 10mV?
If you say you need 20 or so mosfets to get a pair, they should be matched pretty decently.

/Hugo

[till]

I am assuming thta I needn't worry about normal parts like DC power supply componets, heatsinks etc.?

Only obscure parts to me are the input and output transformer. Everything else i have in stock.

[jam]

Hugo,

I liked your old avatar better.....................

[Susan-Parker]

Hi Everyone,

Many thanks for your enthuisam.

Originally posted by Netlist


At what matching accuracy are we looking? 100mV, 10mV?
If you say you need 20 or so mosfets to get a pair, they should be matched pretty decently.

/Hugo

I would hope to match to better then 10 mV, however I can't tell until I have a representative number to set up.

For calibrating my RF power mosfets I use a constant current source at 5 mA to avoid heating effects.

I need to check that this tracks to the 250 mV bais voltage as my RF amp version is full power FM so has a 100% amplitude sine wave the full time.


Good news for those in the US, the lamination manufacturer will sell small quantatied direct

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http://www.thomas-skinner.com/single_phase.htm

We will be happy to sell small quantities to individuals here in the US.

To facilitate small orders such as these, we accept credit cards for payment.

Please have interested parties call us at 317-923-2501.

Our customer service staff is ready to help them.

Ed Richardson
Sales and Marketing Manager

Thomas & Skinner, Inc.
1120 East 23rd Street
PO Box 150
Indianapolis
IN 46206

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I will advise exact details as appropriate.

They offer SuPer Orthosil "a superior line of grain oriented electrical transformer steels available in .007"(M-2), .009"(M-3), and .011"(M-4)".

My current transformers are in M6 Orthosil, a grain oriented electrical transformer steel.

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I will be able to supply a wound bobbin plus the other bits to assemble the transformer.

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This should help a lot with the shipping costs.

Best wishes,
Susan.

[405man]

Susan

Congratulations on a very original and exciting design. Have you had any thought to using this amplifier with an output transformer designed to directly drive electrostatic speakers possibly Quad ESL63s

Stuart

[Susan-Parker]

Hi Stuart,

Originally posted by 405man
Susan

Congratulations on a very original and exciting design. Have you had any thought to using this amplifier with an output transformer designed to directly drive electrostatic speakers possibly Quad ESL63s

Stuart

Thank you.

Yes, I have.

Should work but would require careful transformer design to maintain the coupling.

The bandwidth might be a bit lower, perhaps no more than 50 kHz.

I like electrostatics but don't have the space to use them in a small living room.

I even have a pair of ESL63s, but they are on loan to someone because of this (and unfortunantly not accessible for experimentation).

I have the schematic somewhere and as far as I can recall the transformers secondaries are multi tapped for that phase delay thingy. But it was a long time ago and I am very hazy on the exact details.

But in principle, yes.

Best wishes,
Susan.

[Circlomanen]

Could you make a much more powerful version without sacrificing
the wonderful simplicity???
400 watts????

[john curl]

No, it would be impractical, BECAUSE the distortion will rise directly as the power out, (presuming 3rd harmonic is dominant). How much distortion can you tolerate? 1%, 10%? High power amps require a re-think of the approach. Sorry, Susan, didn't mean to break-in like this, but I stated this principle on another thread, recently.

[darkmoebius]

Talk about a grand entrance - sheesh!! 5,600+ views in 2 days.

Congratulations on an exciting debut post. In case you don't know, for just about every response there have been 50 other people reading this thread.

I can't wait to hear the reports from others trying out your design.

BTW, thanks for finding a US manufacturer to wind the trannis, there are plenty of us across the pond who will be interested in this project.

A couple of trannis, 3 resistors, 2 zeners, and a pair of Mosfets - brilliant!!!