Zero Feedback Impedance Amplifiers

suiraMB said:
As Sheldon said, the solder interface should work, because you keep it liquid while using a vice to press the device to the sink, so it should let the air out. The pressure on the vice will make the solder layer as thin as possible. I believe the indium solder can properly wet the surfaces. And the cleaning/fluxing should eliminate other impurities that could impede heat transfer.

Of course, the thermal conductivity of indium (81.8W/m/K) is lower than that of the heatsink, but I assume some of the other components of the solder have higher conductivity.

One approach that would be excellent with these devices, is to get a copper block with a water-maze and peltier element (something like this)
to enhance the cooling. And, of course, use solder to attach the device(s).

The theoretical minimum thermal resistance in this way is about 2.0K/W, due to the junction-case thermal resistance. Add a single peltier element, and you can lower the temperature by 20 deg C, which means you can get close to 45W continous dissipation.

Ok, but now we are getting away from a key attribute of the JFET version, which is its simplicity. In fact, I think I'll even try a simple unregulated supply for the first go.

Sheldon
 
Yeah, sorry.

I've occasionally been (rightly) accused of having a tendency to go overboard on a few things, cooling and other details of mechanical construction being a good example.

I agree that the key point of the JFET version is the simplicity, derived from autobias and a more robust device. Though these suggestions do not impact the electrical complexity, they do raise the bar with regards to actually building one.

I'm requesting a quote for a low-voltage EI power trafo and step-up toroid from a local company now, so with some luck, I'll be able to play with it myself.

I'd also like to try it with some 9Ah 1.2V rechargeables, mostly just for fun. I recently measured the RMS voltage over my speaker terminals at normal listening volume, and found the peaks to be less than 2Vrms.
 
jkeny said:
I'm about to start gathering parts for this - any advice on output transformer for use with nominal 16ohm 82dB effecient Rogers LS3/5A?

Thanks
John

Those are pretty inefficient, so you'd want as much as you can get. If your power supply is around 11 volts and you wind your OPT for 1:1, you'd see 22Vpp at the output or a little less than 16Vrms, for about 16watts into 16ohms. That would do for modest listening levels in a smaller room. If you want more than that, you'd have to step up the output.

Sheldon
 
Output Transformer

Hello everyone,

I found this transformer as output for Zeus.
Can you please comment before I buy it (AU$100)?

http://www.altronics.com.au/index.asp?area=item&id=M1124
(picture and diagram)

High power toroidal transformer for audio use. Input and output windings can be reversed or be configured differently i.e. Input windings series connected for 100V and output windings paralleled for 4 Ohm.

Primaries:

For 100V line use, connect in series, ie. join blue & yellow. Use grey & brown.



Connections:

Connected In Series:
Input 100V
Output 8 Ohm
Connected In Parallel:
Input 50V
Output 2 Ohm



Secondaries:

For 8 Ohm use, connect in series, ie. join black & white. Use red & orange. For 2 Ohm use, connect in parallel, ie. join orange & black and use white & red.



Specifications:

Max power: 150 Watt
Frequency response: 20Hz - 20kHz ±3dB
Dimensions: 110mm Ø x 50mm
Weight: 2.1kg
Fly lead length: 200mm



Thank you

Alfonso
 
Wavebourn said:
Hi Suzan;

you've made a nice implemtation of 100% negative feedback by voltage using symmetrical source follower. Now you may take complementary pair of FETs and remove transformers with distortions they add.

You might want to read Susan's site (or perhaps, a bit more of the tread), wherein she explains the reasons for selecting this topology, and for using a transformer. Whether on not you agree with her choices, if you want to propose something completely different, as you have, that's a topic for another thread.

Sheldon
 
Sheldon said:


You might want to read Susan's site (or perhaps, a bit more of the tread), wherein she explains the reasons for selecting this topology, and for using a transformer. Whether on not you agree with her choices, if you want to propose something completely different, as you have, that's a topic for another thread.

Sheldon

I propose further development of the same idea. It is up to her to discuss it, or not to discuss.
 
Wavebourn said:
I propose further development of the same idea. It is up to her to discuss it, or not to discuss.

She did discuss those issues in the first few pages of the thread:

" 1. In the event of a device failure substantial DC could be placed across the speaker - which lets the magic smoke out.

2. With two sectioned secondaries I can match for the loudspaker impedance by series or parrallel switching, whereas this is not possible using the center tapped choke method.

And with the options of the secondary windings I can even reconfigure to drive sub ohm impedance loudspeakers.

Q. Okay, why would I want to do that?

A. Line arrays.

My amplifier can drive line array speakers with ALL the drive units wired in parrallel. A line array with 16 off 2" full range 8 ohm drivers become a 0.5 ohm impedance loudspeaker.

Try driving that with any solid state amplifier!"

And:

"Also I have put in a lot of design effort into this amplifier and then been constantly pooh pooed by "those that know" so I must admit to have been a bit anxious about airing it publicaly on the forum.

Most people tell me to ditch the transformers - totally missing the point - and use conventional circuits. What is the point of that sort of comment? It then just becomes another "me too" design and I wouldn't have started on this path in the first place if what was available worked properly."

There's plenty more in the tread available for minimal effort.


Sheldon
 
Re: Toroid Audio transformer

apelizzo said:
Sheldon,

I believe is 2:1

0-50 0-50, 0-24.5 0-24.5


with the primary in series, centre to GND and secondary in series for 8 Ohm load should do the job.


Alfonso

Should work ok for 1:1 (parallel primaries) or 2:1. Susan recommended that the OPT use exact same number of turns on each of the secondaries. I would think that most good toroids are wound this way, but might be worth checking. If they are, the voltages on each secondary should be identical. Also check the resistance and add a bit of series resistance to equalize, if needed.

Sheldon
 
Hi Sheldon,

Thank you for covering the points raised.

I have been very busy getting a consumer product (DVB DTT STB) that I have been working on since Easter through EMC compliance testing - pleased to say it has passed on first submission and the client received a nice shiny new test house certificate on Friday afternoon.

Still got to finish off all the production information etc. but at least I am now able to sleep at nights.

Best wishes,
Susan.
 
Susan-Parker said:
Thank you for covering the points raised.

Just trying to save you the trouble, and hoping that I quoted your words in an appropriate fashion. Though I have to admit to some self serving intent here. I've been participating in the forum for a couple of years now, and have seen too many examples of knowledgeable contributors drop out in frustration at having to contend with argumentative intrusions that contribute nothing to the discussion at hand. I'm enjoying this thread and value your participation. I don't want to see things start down that road.

Susan-Parker said:
have been very busy getting a consumer product (DVB DTT STB) that I have been working on since Easter through EMC compliance testing - pleased to say it has passed on first submission and the client received a nice shiny new test house certificate on Friday afternoon.

Still got to finish off all the production information etc. but at least I am now able to sleep at nights.

Best wishes,
Susan.

Always nice to finish up a big project. Trust you have a chance to listen to some music before hitting the pillow.

I should get the Jfet's soon. My pre amp (DEQX) has 75 ohm output impedence and can be set at several levels from about 0.8 to 4Vrms. So with a 10V DC supply and and 1:2 input transformer, I can drive it directly from the pre. I'll give that a shot first, then try driving it with the tube amp. Have to wind a transformer first, so I'll keep that simple too. Just four parallel windings on a single bobbin.

Sheldon
 
EUVL said:
Susan,

Good to hear you are doing well.

Cheers,
Patrick

Hi Patrick, thanks. Yourself?


Sheldon said:


Just trying to save you the trouble, and hoping that I quoted your words in an appropriate fashion...

(snip)

Sheldon

Much appreciated.

Hope all goes well for you.

Look forward to hearing how things progress with the JFETs.

Best wishes,
Susan.
 
Hi Susan,

I put together Zeus on my bench last Saturday and on Sunday I spent all afternoon listening music. I could not leave my room. It's FANTASTIC!!!
I first start experimenting with unmatched pair of IRF540 with a 12V 2A battery as power source. Adjusting quiescent current slowly up to 50mA after that my meter showed ~2000mA. I found out that they were very unmatched :)
The problem went away after I got a matched pair of IRF540.
Then I start beeing more confident about switching to higher DC and I installed a pair of IXFH58N20. WOW!!
I would like to post some pictures and spectrum shots.
I'm impressed how the 100V 100W PA output toroidal transformer works for the entire spectrum as the EI is not ready yet.
Input transformer:Claritronic toroidal 30VA 2x115-0, 2x12-0
Output Transformer:powertran (Altronics) toroidal 2x50-0, 2x24.5-0 8Ohm
Mosfet: 2 x IXFH58N20
Bias: 7805
Power supply: 25VAC 80VA toroidal, bridge, Aerovox 10.000uF 100V

Best regards,

Alfonso
 
Hi Alfonso,

Thank you for your post

Great to hear of your progress.

apelizzo said:
Hi Susan,

I put together Zeus on my bench last Saturday and on Sunday I spent all afternoon listening music. I could not leave my room. It's FANTASTIC!!!

(snip)

I would like to post some pictures and spectrum shots.

(snip)

Alfonso

Look forward to the pics and info.

Very pleasing.

Thanks.

Best wishes,
Susan.