Zero Feedback Impedance Amplifiers

zinsula said:
Doesn't this depend frome the driver too? Note that Susan seems to use line array speakers, each driver being 2".

Well, my post was too late...and not quite correct...VERY nice looking speakers. Did you get those from a sculptor? ;)


I have a separate bass speaker for that - which amongst other reasons is to minimize the Doppler effects
And those bass speakers fired with another of your amps? Or a passive crossover?

Tino
 
Hi Tino,


zinsula said:


Well, my post was too late...and not quite correct...VERY nice looking speakers. Did you get those from a sculptor? ;)

And those bass speakers fired with another of your amps? Or a passive crossover?

Tino

Thank you.

Not exactly, they were made at a marble place outside Lisbon in Portugal. I have another two white shells and a couple of pairs of the previous version with smaller 50mm drivers.

That's all that exist on this planet - the marble place closed some years ago.

I did get quoted from sculptors here in the UK, and they were wanting about a thousand pounds each shell! Not commercially viable.

I am working on a torroid version (they don't work for a full range amp) amp for the bass speaker (which is 4 ohms). I know that torroids have been used for valve amps, but that is different. These saturate at about 10 kHz and start turning sine waves into square ones.

However at the moment we live in a small apartment and low bass isn't a strong requirment as we don't want to be anti-social!

IMHO crossovers should be in the pre-amp part, not in the speakers.

I use wide range drivers, first order crossovers and non-ported enclosures.

===

Hi PMA,

how about all of that electronics before your impedance amplifier. Does not it destroy the sound?

Not really. Like any electroncs design there are better and less good ways of doing things.

Most good systems are okay until one:

A. Uses phono cables to interconnect pieces of equipment.
B. Uses negative feedback amplifiers to drive loudspeakers.
C. Pays $10,000 for a pair of cables.

I am still refining the drive circuit for my amplifiers, but what I have at the moment works okay for the time being.

==========

Best wishes,
Susan.
 
Kit

Susan,

Good lord, 9 pages in 2 days. I think you're doing 10 times better than Nelson Pass at the moment.

And I still think that you could offer interested parties a kit. Why not make the output transformers yourself and offer the pair at a fair price. And don't start work until you have say 20 units sold. John Clancy is starting a group buy in another thread for S&B input transformers, and says price drops significantly after 20 units. So if Sowter does not want the business, I am sure someone else in the UK might be.

You complain of having no success promoting your equipment commercially. Now this may be a start -- even if it may not make total sense financially. At least you're a lot more well known than 3 days ago. : )

Keep it going. Time to start a DAC thread under the digital forum, and a speaker thread at the speaker forum. Full invasion of diyaudio from 3 directions. : )


Patrick
 
Hi Everyone,

This is the bass speaker that goes with the spheres.

It was designed to be driven by a high power version of my amplifier.

susan-bass-speaker-1s.jpg


http://www.susan-parker.co.uk/susan-speaker-bass.htm

As before I have pulled off the text I was using in the hope of commercial sucess - but everyone seemed to have been sold on the idea of ported designs. "Never mind the quality, feel the hammer blows to the tummy". Shrug.

Best wishes,
Susan.
 
Re: Kit

Hi Patrick,

EUVL said:
Susan,

Good lord, 9 pages in 2 days. I think you're doing 10 times better than Nelson Pass at the moment.

And I still think that you could offer interested parties a kit. Why not make the output transformers yourself and offer the pair at a fair price. And don't start work until you have say 20 units sold. John Clancy is starting a group buy in another thread for S&B input transformers, and says price drops significantly after 20 units. So if Sowter does not want the business, I am sure someone else in the UK might be.

You complain of having no success promoting your equipment commercially. Now this may be a start -- even if it may not make total sense financially. At least you're a lot more well known than 3 days ago. : )

Keep it going. Time to start a DAC thread under the digital forum, and a speaker thread at the speaker forum. Full invasion of diyaudio from 3 directions. : )

Patrick

I didn't realize I was doing well at this - being the first time on the forum an' all.

If there really are people interested in having a go then I would be happy to do something.

However I will have to put in something for my time, and regretfully charge VAT (where appropriate).

I am reluctant to take money from people just because I think I have the best thing since sliced bread. I know how easy it is to get enthralled in ones own creations and forget that the rest of the world isn't necessary of the same opinion or reasoning.

I would propose that I could put together some bits for a stereo pair and send them to some third party (perhaps Graham Maynard if he has the time and is willing) who could give an independent and informed opinion.

It may be disappointing to me if it is not liked, but at least I won't have my name in the mud and people after my blood.

If it gets the thumbs up then I would be more than happy to supply kits to others interested in the amplifier - I could also match up mosfet pairs (I reckon that I need at least twenty from a batch to find close matches).

Whilst I would love to get involved in speakers and DACs for the time being I will have to content myself with this one thread about amplifiers as I regretfully don't have the time to deal with more than this (boring things like earning a living and homemaking).

Plus I have a commitment to finish off the design for a model steam locomotive boiler (totally different from anyone elses of course) which I want to have built for display at the Sandown Park model engineering exhibition (end of December).

Many thanks once again for your interest, enthusiasm and positive comments.

Best wishes,
Susan.
 
I am reluctant to take money from people just because I think I have the best thing since sliced bread. I know how easy it is to get enthralled in ones own creations and forget that the rest of the world isn't necessary of the same opinion or reasoning.

hey, people on this board build amplifiers for interest. We had amps made from power regulators, digital logic chips, lighbulbs, and high output impedance amps (see www.firstwatt.com). Who thinks he is in need of Krell or Mark Levinson gear should go an buy some. Who thinks he needs an easy to build sucess guarantied amp will build a gainclone. Who will be interested in your amp will be aware of it is only suitable for special taste and special speakers.
 
Hi Till

till said:


hey, people on this board build amplifiers for interest. We had amps made from power regulators, digital logic chips, lighbulbs, and high output impedance amps (see www.firstwatt.com). Who thinks he is in need of Krell or Mark Levinson gear should go an buy some. Who thinks he needs an easy to build sucess guarantied amp will build a gainclone. Who will be interested in your amp will be aware of it is only suitable for special taste and special speakers.

Thank you for your post and the reference to the First Watt amplifier, which I had not seen before.

----

I will look into the costs of supplying a basic amp kit if that is what people would like.

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

I have asked a US based lamination manufacturer if they will supply direct to individuals in the US as the cost of shipping gets prohibitive over 2 kgs (4.4 lbs). Europe isn't as bad.

What would you consider to be the essential components required in a kit?

Many thanks.

Best wishes,
Susan.
 
Susan-Parker said:

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 :)
 
Hi Everyone,

Many thanks for your enthuisam.

Netlist said:


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 :)

---------------

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

---------------------

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.

---

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

---

This should help a lot with the shipping costs.

Best wishes,
Susan.
 
Hi Stuart,

405man said:
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.
 
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.
 
Hey Susan!!!

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!!!