Leach amp troubleshooting

[nattawa]

.....So, can I shift the voltage at the bases of the transistors T1 and T6 until I get the output voltage is close to zero (when I use 5 pairs of output transistors MJL4281 & MJL4302)?

By doing that you would be hiding the problems rather than solving them. And the price you're paying would seem to be high. By altering the voltages at base of T1 and T6 you would have offset the tail currents that defines the degeneration of the PNP and NPN input pairs, further breaking the symmetry where the beauty of a complimentary IPS-TIS front end lies.

If matching the transistors in hand is not possible, I had tried matched pairs of 2SA970/2SC2240 offered on ebay a few years ago. I had these on my "pimped citation 16" amp which is my own Leach amp variation, and I have 2mV DC at output on one channel and 3mV on the other.

 

[gmphadte]

I matched my own and the dc offset is 0 mV.
However I took care to match the corresponding resistors.

Gajanan Phadte

 

[spookydd]

i use thermal cut-outs that AndrewT talked about, it protects your amp from overheating...

Hi,
Who would know of a source for those types of switches at a good price?

 

[AndrewT]

They are available in two types.
Normally open when cold.
Normally closed when cold.

Find out which type your protection circuit needs for over temperature sensing.

Most retailers stock them.
RS
Rapid
Farnell
etc