Zero Feedback Impedance Amplifiers

[Susan-Parker]

Hi Apelizzo,

Originally Posted by apelizzo

Hi Susan!

Thank you so much for helping me out with this integration. I like your brilliant idea of using XLR and I will do so. I completed the 75 transformers following your instructions. I got 1.1/2 M6 laminations under the bed for long time initially for a 6c33c SET project which I reconsidered and now used for Zeus

I've got 98dB efficiency speakers I built connected to my 2A3 SET and I thought to boost the power output with Zeus to improve dynamic response keeping the "2A3 as driver" footprint.

I like the idea of using Depletion mode mosfet but I'm not sure about the sound compared to enhanced mosfet like the STW34NB20 you recommend (Ciss is 2300pF).
With regards to the IXTH20N50D I'm not too sure... I'm worried about the high Ciss 6300pF specified.
It's funny because I've got 2 datasheets of the same part number:
2006 release Ciss Typ 2300pF
2009 release Ciss Typ 6300pF

Regards

Thanks for the info.

Whilst Ciss is specified a bit higher, I have not found it a problem.

The much greater simplicity plus having EVERYTHING ground referenced is a big plus.

The diferences sonically are very small, and I beleive would not cause unhappines.

It is relativly easy to try out both versions, would be interested to have your impressions if you do

My own system uses three IXTH20N50D per channel (pre amp is SE) and has been in almost daily use for something like four years.

Best wishes,
Susan.

P.S. slightly hasty lunchtime at work reply...

[apelizzo]

Originally Posted by Susan-Parker

Hi Apelizzo,



Thanks for the info.

Whilst Ciss is specified a bit higher, I have not found it a problem.

The much greater simplicity plus having EVERYTHING ground referenced is a big plus.

The diferences sonically are very small, and I beleive would not cause unhappines.

It is relativly easy to try out both versions, would be interested to have your impressions if you do

My own system uses three IXTH20N50D per channel (pre amp is SE) and has been in almost daily use for something like four years.

Best wishes,
Susan.

P.S. slightly hasty lunchtime at work reply...

I would like to try IXTH20N50Ds but it's hard to get them
I just missed a Buy group on forum. Also I already bought the STs from RS. I think I will try the STs first then when I get the chance to buy the IXTH20N50D I will be able to compare them.

[Susan-Parker]

Hi Apelizzo,

Originally Posted by apelizzo

I would like to try IXTH20N50Ds but it's hard to get them
I just missed a Buy group on forum. Also I already bought the STs from RS. I think I will try the STs first then when I get the chance to buy the IXTH20N50D I will be able to compare them.

Future Electronics is showing them as available from one piece, although you would need more that four to get the two matched pairs.

IXYS | IXTH20N50D | IXTH Series Single N-Channel 500 V 330 mOhm 400 W Power Mosfet - TO-247 AD - Future Electronics

Although they aren't showing any stock...

... IXYS website however shows it as an active part.

Anyway, the ST parts will work well too. I do recommend using a third mosfet per pair for the tracking bias scheme.

Best wishes,
Susan.

[Susan-Parker]

Hi Mike,

Hope you are keeping well.

Originally Posted by mikelm

Hi Susan, nice to see you here.

Your idea, as usual, is simple, practical & sensible

( the XLR plug one )

Thanks.

I do like the idea of the knife switch though, it would be very steam punk

Best wishes,
Susan.

[EUVL]

> Hope you are keeping well.

Same to you.

BR,
Patrick

[Susan-Parker]

Hi Patrick,

Originally Posted by EUVL

> Hope you are keeping well.

Same to you.

BR,
Patrick

Okay, thanks.

I don't seem to have had a lot of time for audio recently (have a day job), but still trying to wedge in the odd moment to keep things moving.

I will be going along to the 128th AES convention this weekend, since it is in London this time (just down the road for me).

How are you?

Best wishes,
Susan.

[EUVL]

A bit more time for audio than you I guess, and suffered a bit from the eco crisis (hence time available for audio). Otherwise fine.

Good to hear from you again.


Patrick

[imfree707]

Originally Posted by Susan-Parker

As requested a seperate thread on transformer based solid state amplifers.

The schematic:



... and what it looks like in practise ...



Everything to the right is power supply, and everything from the middle is amplifier.

See: Zero Feedback Transformer Audio Power Amplifier for more details.

This amplifier is based on Impedance Amplification and has similar distortion characteristics to valve triode designs.

It is relativly easy to build and only has one twiddle pot to set the bias level. The pic shows a monoblock which I built nearly ten years ago and it has not needed adjustment since.

Best wishes,
Susan.

P.S. Yes, it does work.

Aaaah! That's awesome! With good transformers, such an amp performs delightfully well and is exquisitely simple! Here's one I built in 1983 using bi-polar transistors in Darlington, with power transformer iron, multi-filar wound. It sounds amazing good, considering how crude it is! Have to get it out of that dead, rustbucket Caddy and fire it up one more time!

*Aprox. 120 W X 2, Idles under 500ma, Draws 26 A, peak, heavily driven.

[Tyimo]

Hi!
How many cm2 is the cross sectional area, (Afe) of the original 35W Zeus
OPT?

Greets.
Tyimo

[wrenchone]

This was a bit of awake-up call. I've had a partially assembled Zueus sitting in my basement for some time now. I planned to use toroidal power transformers for both stages. Maybe it's time to take the design all the way to completion. BTW, to my knowledge, no one has dragged a Zeus-type amplifier to the Burning Amp festival in San Francisco as of yet. Perhaps it's time to change that, too.