Zero Feedback Impedance Amplifiers

Hi,

Sorry for the delay in replying, only just seen your posts.

I was at the AES UK conference all weekend (Friday to Monday) as well, so still catching up with my correspondence.



If you are using EI lamination transformers then b and c should be okay to get going with.

There is even a line of thought that says a small imbalance is preferable as it keeps the domains "primed" however I would want to do a bit of specific testing to look at this. A lot of the tube based rule of thumb stuff is not really applicable here as the source impedance and number of turns are so much lower.

If you are using toroids then perhaps not so good, as there is no intrinsic gap unlike where the E and I laminations butt together.

When mine come I can mix and match something better for you.

As to your list, the spread is about 2:1 which is what I would expect from my own experience with a sample group.

Best wishes,
Susan.

Thanks Susan for your comment. I've done the 75W EI transformer following your guidelines so a little mismatch in the mosfets would not saturate the core. In the meantime to be safe I ordered and received another set of 12 as I was afraid to be stuck half way in the project. So now I've got 2 sets of 12. I will test the second set tomorrow. I will try to find another close match and the rest I will send to you when you get yours. As I don't intend to keep all of them for myself, I will be happy to leave a few pairs for sale in the future.
 
Zeus Bi - For Digital, Linear Solid state, and Vacum System

I've had this in my mind for quite a while and I try to explain by points:

1- I like high efficiency 2-way speakers with compression driver connected to waveguide. I love the live sound stage that can produce - BUT if not setup properly they can go wild.
2- The design of passive crossover for point 1- may result costly, expensive and difficult to design.

3- DSP cross-over boards (like miniDSP) can be cheaper than passive crossover and can be one off cost as it can be configured and calibrated via software.

4- For point 3- Bi amp is required. The two amplifiers don't need to be wide band, so the output transformer doesn't have to produce wide range of audio frequencies, doesn't have to use special laminations and it can be winded up to be hi-pass and low-pass.

5- Hi pass transformer can protect the compression driver for accidental low freq signal, eg disconnection of input patch lead or switch on-off-off noise. It would not require to introduce capacitor to protect the horn. If not carefully used, a wide range amplifier connected directly to the compression driver is capable of destroying it.

6- Design of Zeus Bi - two identical units with the exception of the output transformer. I leave open the input stage as I would like to use vacum for driver.

7- No time for rest
 
The two amplifiers don't need to be wide band, so the output transformer doesn't have to produce wide range of audio frequencies, doesn't have to use special laminations and it can be winded up to be hi-pass and low-pass.

You can make the mid/high transformer smaller, as you don't need the inductance for LF output. But with the multifilar windings, you won't make the "low pass" version a low pass transformer. No advantage I can see to trying to purposely limit the HF response.

Hi pass transformer can protect the compression driver for accidental low freq signal, eg disconnection of input patch lead or switch on-off-off noise. It would not require to introduce capacitor to protect the horn. If not carefully used, a wide range amplifier connected directly to the compression driver is capable of destroying it.

I don't think that a "low pass" transformer really protects the driver in the same way that a capacitor does. You could still get large transient spikes from a relatively small transformer. That said, if you are using an input transformer, the amp had good immunity to spikes from input connections. It's also pretty much immune to turn on/off transients.

Design of Zeus Bi - two identical units with the exception of the output transformer. I leave open the input stage as I would like to use vacum for driver.

Susan's design uses the input transformer as a voltage amplifier and phase splitter. However, a low impedance source is required to reproduce low frequencies. Her line driver is a buffer. Do you intend to use the tube stage as a voltage amp into a transformer phase splitter?

Sheldon
 
the italian version

of Zeus:p
(CFP)
 

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Hi Susan,

I copied the specifications of the 75W transformer from your website:

==================
Electrical

Inductance of each winding = 99 mH @ 1 kHz, 468 mH @ 120 Hz.

Impedance of each winding = 3.9 KΩ @ 1 kHz, 1.25 KΩ @ 120 Hz.

Inductance between input and output windings (wired for use) = 2.68 H @ 1 kHz, 181 H @ 120 Hz.

Inter-winding capacitance between input and output windings (wired for use) = 9.34 nF

Windings to laminations/frame capacitance (wired for use) = 176 pF

Output impedance in PP NMOS circuit when powered = 0.94 Ω @ 1 kHz, 0.90 Ω @ 120 Hz.
=======================

Can you confirm the inductance 181H at 120Hz? I thought the inductance was less at lower frequency.
 
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not yet

but today or tomorrow I will
because I have all the parts

Steve CFP in essence, a high gain super transistor, somewhat similar to a Darlington. But there are major differences. Unlike Darlingtons, there is some voltage gain with Sziklais. Another unique feature is local feedback.
 

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but today or tomorrow I will
because I have all the parts
no news? have you built it?

Another unique feature is local feedback.
unique feature? I wouldn't say so. Any follower configuration (such as the one used by Susan) does have plenty of it.

As for the next version, it does depart quite a bit from Susan's original idea, which is to get all the voltage gain only from transformers and use active devices (as followers) only for current (power) gain. Yet it may be worth trying. Let us know if you do.

BTW: I don't see it fair to call your variations ideas "Zeus n". The name "Zeus" referred to an audio amplifier is sort of a de-facto "trademark" of Susan. I think only she has the right to call "Zeus n" a variation/evolution of her own design.

Using the name "Zeus" as a form of "citation", together with something which makes it clear that it is a different, derived work may be acceptable (e.g. something like "Son of Zeus" or "CFP Zeus-like", etc). But "Zeus n" isn't. IMHO.
 
eBay transformer core kit3

For winding your own output transformer, has anyone tried one of these?
..and if so, can you comment on sound quality?

Can someone knowledgable on transformers comment please on suitability of this double C core material for a Zeus?

I've read this entire thread and I know that Susan had intended to try and report on C cores. However, I don't recall ever seeing a report.

Thanks
 
time travel

Thank you all for this thread. It`s like a time-travel for me. This topology (with Ge BJT`s of course) was my first solid-state amplifier. Later I used Si transistors (2N3055, what else?), added sliding bias (I reinvented Malcolm Hill`s heat generator) and learned a lot about transformers.
 
Thank you all for this thread. It`s like a time-travel for me. This topology (with Ge BJT`s of course) was my first solid-state amplifier. Later I used Si transistors (2N3055, what else?), added sliding bias (I reinvented Malcolm Hill`s heat generator) and learned a lot about transformers.
If you want to make a second time-travel, check out this threads:
http://www.diyaudio.com/forums/soli...id-state-audio-amplifier-components-want.html
and
http://www.diyaudio.com/forums/parts/167680-vintage-transistors.html
 
For winding your own output transformer, has anyone tried one of these?
..and if so, can you comment on sound quality?

Can someone knowledgable on transformers comment please on suitability of this double C core material for a Zeus?

I've read this entire thread and I know that Susan had intended to try and report on C cores. However, I don't recall ever seeing a report.

Thanks


I think she has been pretty busy lately and hasn't finished testing yet, you might see her website bout building your own if you are especially ambitious.
 
toroidal output as VAS stage

I found a way to equalize the response of the speaker
using the power consumption (shunt resistor)
and eliminating the need for cross-over:)
so speaker (16-18cm max) is not filtered

also uses a toroidal power
as a voltage amplifier
because transistors have hFE flexing
with increasing voltage
so are suitable to amplify only the current:rolleyes:

Note that the sum of the balanced input signals
is done with a transformer signal
and constitutes an important contribution to the realism of the scene:p
 

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Double C core output transformer for Zeus

Hi Charlie,

For winding your own output transformer, has anyone tried one of these?
..and if so, can you comment on sound quality?

Can someone knowledgeable on transformers comment please on suitability of this double C core material for a Zeus?

I've read this entire thread and I know that Susan had intended to try and report on C cores. However, I don't recall ever seeing a report.

Thanks

[I hope to be able to get something made and start testing some C-cores over the next month or two. Note however that I will be using amorphous c-cores so it will not be quite identical.]

For a full bandwidth Zeus one would use the Kit 4:

Tube Audio output transformer Double Cut Core kit 4 | eBay

The seller says "It’s a special order of this Japanese silicon steel core material that design not for 60Hz but 400Hz (Equal or better then M6) together with the stunning ultra thin 0.23mm lamination thickness. It’s the best in class silicon steel core type material you can get for audio transformer building.".

Note that the material is silicon steel and compared to M6 material. This is still good as the thinner lamination thickness should reduce Eddie current flux.

Whether this is audible, I can't say as so much depends on other factors.

If your music source is only CD then I suspect the improvement would be minimal. If you have a full analogue system with vinyl then I think there is a good chance for that to be audible.

BUT it depends on so many factors that it is difficult to be definitive without full end to end control (which is why I designed my own phono cartridge and build my own speakers as well as the bits in the middle).

However compared to the price of buying ready made transformers then with a bit of patience one has the possibility of making something that is cost competitive and should be at least as good as a M6 EI core part. Don't forget that the magnet wire is also a fair cost these days.

Hope this helps.

Best wishes,
Susan.
 
Power Transformer Cores?

Decades ago, I have used power transformer cores for audio, not super hi-fi, in PA amps, car stereo power amps, and other general purpose audio power amps, with fairly good results. I'd be interested in some discussion regarding performance limitations expected by use of power transformer iron in audio use. Thanks.