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panson_hk 5th July 2007 01:12 PM

My Leach Amp Clone (LEACH 150)
2 Attachment(s)
I am finishing my LEACH 150 amp. It is a kit available from DIYZONE in Taiwan. The schematic in pdf can be download from The amp is constructured in mono-block fashion. Each channel has a big toroidal transformer capable of delivering 150 WRMS output.

The figure shows you the assembled PCB and transformers. I will measure the amp using AP System One. I will follow the measurement procedures used in Stereophile equipment review.

Will this clone perform as good as the original LEACH. Some measured data are available from Prof. Leach web site.

panson_hk 5th July 2007 02:08 PM

2 Attachment(s)
After 30 min 1/3 output power (50 W, 8 Ohm) warm up, THD vs output power is measured. The result is shown in the attached figure. At the moment, the heat sink temp is about 62 C. The amp meets the designed output power level, 150 W, before clip.

panson_hk 6th July 2007 12:55 AM

2 Attachment(s)
Here you can see the FFT of 50 W, 8 Ohm load. There are so many harmonics and the level is rather high!

Something wrong!? Circuit or assembly? Need to investigate ....

taj 6th July 2007 03:34 AM

If you normalize the graph it wouldn't look so bad. Approx. -80dB 2nd and 3rd harmonic. I have no idea what is normal or typical for any amp.


taj 6th July 2007 03:38 AM

The schematic link you posted doesn't seem to work. Does it differ from the *real* Leach schematic?


timbarnes 6th July 2007 04:02 AM

There's an extra dot at the end of the schematic URL
I found it works if I try to load it, then delete the last character so the URL ends in [.pdf] rather than [.pdf.]

taj 6th July 2007 05:00 AM

Correct you are. Good eye, Tim!

The schematic is 90% Leach, but its Q7/Q8 are configured much differently than the corresponding transistors in Leach's circuit. I don't think it's just because it's drawn differently. And the servo points are not Leach.


panson_hk 6th July 2007 07:10 AM

In this clone, active current source is used in the differential stage. Its VAS is not cascode where Leach v4.5 does. No output stage protection is employed.

panson_hk 6th July 2007 07:33 AM

2 Attachment(s)
Hi Todd,

I want to see whether it can reach something like NAD M3. Sterephile reviewed it earlier. The results can be found at
, in particular THD performance.

I don't like those higher harmonics, > 3 rd.

THD residual at 50 W, 8 ohm is shown here.

jaycee 6th July 2007 07:41 AM

The VAS is not cascoded in the original Leach. The extra transistor is configured as a protection device to avoid VAS saturation when the output protection activates.

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