Zero Feedback Impedance Amplifiers

[Sheldon]

Originally posted by suiraMB
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

[suiraMB]

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]

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

[Sheldon]

Originally posted by jkeny
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

[jkeny]

Thanks Sheldon,

Yea I know they are innefficient but funnily enough the SI t-amp gives enough power to listen comfortably in a largish room without the volume being all the way up - about half way - go figure?

John

[apelizzo]

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.as...=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

[Sheldon]

What is the turns ratio?

Sheldon

[Wavebourn]

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.

[Sheldon]

Originally posted by Wavebourn
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

[Wavebourn]

Originally posted by Sheldon


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.