Leach Amp My design

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An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
Hi,
is the output from the regulators running at about 42Vdc?
This will cripple the voltage coming from the early stages of the amplifier (particularly the VAS and pre-driver).
You should aim for the voltage amplifier running at about the same volatge as the drivers+outputs.
Can you feed 60Vdc into the regulators?
Then set them to that same 55Vdc so that both ends of the amp are on similar voltages.
 
AndrewT said:
Hi,
is the output from the regulators running at about 42Vdc?
This will cripple the voltage coming from the early stages of the amplifier (particularly the VAS and pre-driver).
You should aim for the voltage amplifier running at about the same volatge as the drivers+outputs.
Can you feed 60Vdc into the regulators?
Then set them to that same 55Vdc so that both ends of the amp are on similar voltages.


single voltage for low cost

vas stage 42-45 volts

sory bad speak englis
 
Hi,
buy some enamelled copper wire (about 0.5 or 0.6mm diameter) and add about 15turns twice to your toroid transformer.
Couple up the extra windings to give the higher voltage and then run a small bridge rectifier and smoothing caps across the high voltage low current windings. Reset your regulator to 55Vdc (1k0 & 43k) and go with that.
This will only cost a few $.
 
AndrewT said:
Hi,
is the output from the regulators running at about 42Vdc?
This will cripple the voltage coming from the early stages of the amplifier (particularly the VAS and pre-driver).
You should aim for the voltage amplifier running at about the same volatge as the drivers+outputs.
Can you feed 60Vdc into the regulators?
Then set them to that same 55Vdc so that both ends of the amp are on similar voltages.


zerohead_ak47 said:
single voltage for low cost,vas stage 42-45 volts

sorry bad speak english

This should only affect the voltage swing to the output stage and limit the max output. It should still sound good at real world listening levels into reasonable speaker loads.

Good work! I'd try to limit the length of the wiring from the PCB's to the output transistors (also power supply wiring). This could cause stability problems.

Regards, Mike.
 
Hi,
your 2k7 feeding the cascode Zeners is allowing about 1mA to flow. [43V-40V]/2k7=1.1mA
The cascode and zeners and tail require about 8mA to operate correctly. 1.5mA into each half of the LTP + 3mA into the tail + 2mA into the zeners. Change the resistor from 2k7 to 360r would suit your low rail voltage, or change the zeners to 12V.

I would also suggest adding the extra resistor that Leach missed out to convert the limiting to IV, but that necessitates recalculating all the other protection resistor values.
 
AndrewT said:
Hi,
your 2k7 feeding the cascode Zeners is allowing about 1mA to flow. [43V-40V]/2k7=1.1mA
The cascode and zeners and tail require about 8mA to operate correctly. 1.5mA into each half of the LTP + 3mA into the tail + 2mA into the zeners. Change the resistor from 2k7 to 360r would suit your low rail voltage, or change the zeners to 12V.

I would also suggest adding the extra resistor that Leach missed out to convert the limiting to IV, but that necessitates recalculating all the other protection resistor values.
hi
you can redraw schema ?

using express pcb open sch file

thanks
 

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The DC off-set control would work much better attached to the reference voltage for the cascodes, and eliminate some parts too.

Doesn't make much sense to run the front end from ±40V, and use ±55V on the outputs.

The first version of the Leach used a 68R resistor for the driver, I prefer this to the current 220R value (R36).
 
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