Leach Amp transformer

[Wynand]

I have a Leach Amplifier PCB with components that has been lying around for quite sometime. The problem I have is the transformer....

What is the minimum voltage rating that I need?

Any help would be appreciated.

Wynand

[acenovelty]

From Dr. Leach's web site:

The recommended transformers have a secondary rating of 80 V AC rms. With these transformers, the power supply puts out about +58 V and -58 V. With 12,000 uF filter capacitors, the energy stored in the power supply is about 40 joules. This is enough energy to lift a 10 pound dog almost 3 feet off the floor.


http://users.ece.gatech.edu/~mleach/lowtim/

Good idea to read everything there.

Sources:
http://www.plitron.com/
http://avellindberg.com/
http://www.toroid.com/

Regards

[AndrewT]

Hi,
the Leach lo tim can run off a range of transformers.
If you go higher than 2*40Vac you will need to thoroughly check all the device dissipations to ensure reliability. Not recommended for a beginner.
You can certainly run off lower voltage transformers. Either 2*30Vac or 2*35Vac would do.
The Transformer VA rating should be about 1.5 times the maximum power you intend to draw for a monoblock and about 3 times for a stereo amplifier.
The smoothing capacitor bank should have about 2mF per peak Amp of output current.
If you stay with the Leach recommendation then 2*40Vac 450VA +-18mF/channel smoothing caps will give you a good start for a 130W to 150W into 8ohms per channel stereo amplifier.

If you build a stereo amp then try to find a 4*40Vac transformer for slightly improved performance or lower voltage if you decide to go that route.

[Wynand]

Perfect... I happen to have a transformer with 2 x 32V secondaries.

THanks for the replies

[AndrewT]

Hi,
2*32Vac will give about +-48Vdc on your rails when the bias is set low (10mA to 20mA) as you increase the bias to operating level your rail voltage will fall slightly.
When producing full power the rails will fall even further (~=44Vdc) this is significantly above the Zener voltage set at 40V.

You will need to check that your resistor values to the various stages are OK at this low voltage. Leach has optimised his for +-58Vdc. Some resistor values WILL need to be changed.