Leach amp questions

[AndrewT]

Any hints or tips, please?

Leach input stage

Figure 6. Amplifier input stage.

Q5 and Q6 form cascode common-base stages which conduct the diff amp error currents to the load resistors R11 and R12. Q5 and Q6 also function to reduce the voltage across Q1 - Q4 by about 18 V to prevent voltage breakdown in these transistors. Diodes D13 through D16 are 20 V Zener diodes which regulate the voltages that set the bias currents in the diff amps. Each zener diode is biased at a current of about 3.3 mA. Although a single zener diode could be used in place of two series diodes, I have found that the error tolerance in the voltage is less with the series connection of 2 diodes. C2 through C5 are ac decoupling capacitors which ensure the bases of Q5 and Q6 are at ac signal ground. R15 and R16 set the tail bias current in each diff amp to about 3.25 mA.

para 2 details the LTP current and the zener diode selection.
Download Leach's lo tim paper and read it.

 

[Sergelisses]

Leach Amp Plans - Part 1

 

[weinstro]

hi

Is the Schematic on the first post ,the same than the actual Leach Amp PCB group buy ?

Unlikely, Serge.

The schematic I posted is directly from Dr. Leach's website. Boards based on that design can be purchased through Dr. Leach. He has an email address listed on his website, and he can be slow to respond, but he does respond.

There are several Leach PCB group buy threads. Most of these have several modifications from the original Low-Tim design, such as plastic output devices instead of TO-3's, more output devices, etc.

 

[djk]

"Thanks - should the diodes be Schottky, switching, or rectifier types? "

I would use 1N4734 type.

 

[wahab]

mr leach designed many variations of this topology..
all are not equal, but in brief, the complementary differential
is one if not the best topology to date...
even basically, it has great performances, and with
some minor additions, it s simply almost impossible to beat...
just use modern devices , like toshiba bjts, and you ll end
with a high end audio amp, even if it s the basic design...

regards,
wahab