pics of my leach amp - just finished

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Yeah, it really came out professional looking. Smart Devices was very nice to help me with a case for this design. I am going down there next week to see if I can find anything to build a Leach SuperAmp with... should be interesting.

Does anyone know a source to get Leach SuperAmp boards? There were posts a month ago, with a few people offering them, but not now. I have most of the parts ready to build it, and am just awaiting the boards. I have not ordered the transformer, but I will be getting it from Victoria Magnetics, the company who makes the transformers for Smart Devices, and the supplier of my Leach Amp transformer.

Last night after listening to my Leach Amp for a while, I looked back at the design and realized that I had left off the capacitor and resistor off of the output speaker terminals. Does anyone know the effect of these two on the output. (C25 and R50). It sounds fine without them, but I will add them tonight, and see if I notice any difference.

Also, for dc offset at the output source for each channel, I am getting around 10mV for each channel, with no signal attached at full gain. Prof. Leach said that was pretty good for an amplifier. I matched my zener diodes with a bench meter and transistors with an expensive curve tracer at gatech.

I'd recommend installing the Zobel network as it helps keep the
amplifier stable into reactive loads. Some speaker/wire combinations will make many amplifiers unstable, and the
near-RF oscillation may not be obviously audible. If the heat
sinks get really hot for no obvious reason, that may be a clue.

You may not be having problems right now, but with a different load that may not be the case. Keep that in mind if you change
your setup.

I also matched the Zeners, used 1% metal film resistors and tried
to match the diff amp transistors with a curve tracer.

In addition, I used Black Gate electrolytics for the diff amps and
the 220 uF feedback cap (non-polarized N series). As per Self and Sloan, I installed a 1 uF film cap across R36 (emitter to emitter of the driver transistors), which helps improve output transistor turnoff and slightly lowers high frequency distortion.

The final touch was MJ21193/4 output transistors in place of the
recommended MJ15003/4. They're a bit more linear, twice as fast,
and more rugged.

Junky as my project looks, it does sound quite good.
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Joined 2002
When you say:
: "The final touch was MJ21193/4 output transistors in place
: of the recommended MJ15003/4. They're a bit more linear,
: twice as fast, and more rugged.

Do you think that this improves the overall sound quality? In bulding a Leach SuperAmp, which is basically the same circuit with double the transistors, is this a better choice? I managed to purchase the mj15003 and mj15004 for $1.63 and $1.73 each at the int atlanta, since they were going out of business and the parts were 50% off. I also picked up 100 each of the two transistors used in the diff amp for around $10.

As for the heatsinks getting hot... I ran the amp at full volume for a little over an hour, just to see how hot the amplifier got, and it barely got warm, with the oversized heatsinks. As stated below ". The total surface of each heat sink is 364 square inches" I am just running 8 ohm speakers and 16ga monster cable.

I am taking my amp into Leach's audio lab to test the distortion levels on next thursday or friday, and I will see how the distortion is.
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Can I build a power supply to use a leach amp in my car?


Does anyone know how I would build a dc-to-dc power supply that would allow me use a leach amp in my car? I am considering building one for use as a car amp, if I find plans for a working power supply.

The Leachamp board requires +58 and -58. Is this possible to do in a car? I will not run the amp very loud, so I would think that current would not be a problem.

I can't hear a difference between the devices, so I think you're
just fine using the MJ15003/4s. Good deal on the other transistors, too!

A dc to dc converter is a little tricky to design, but it should work
quite well, aside from the RF noise. I think a resonant mode
converter has lower noise. This is very commonly done for
high performance car audio, to derive a higher split voltage from
the auto's 12 volt supply.
Very nice work.

I have built a number of WML amplifiers and had 1 of the previous version (#3) as my main amp for many years (built in the mid 70s !!). Still works and is as good as many commercial amps costing a lot more money.

Doesn't quite have the transparency of SE class A, but will serve you well and for those considering building one I would certainly recommend it. Especially for those averse to the heat/hardware of class A.

Happy listening, Mark :)
BTW ..... there was a time I intended building the "Superamp", to which end I have had sitting idle in my workshop 2 toroids, 2 BCBs, and a complete set of output transistors for some time now (over 10 years actually) ......

Your problem is I'm in Adelaide, Australia .... the asking price is simply a kind smile and some pictures of the finished article, but you've gotta organise getting them ..... :)

From the Smart Device web site:
Fabulous "Retro look" with art deco styling. The unique, attractive appearance of this product is something you want to display to your guests. The striking two-tone finish goes well with your other system components. You may recognize this amplifier as one of the dominant premium performers of the 1970's and 80's. We understand the original manufacturer abandoned the design because it became too costly to produce and sell at a popular price.

Art deco?
(Retro, maybe, but if the 70s/80s qualify as "art deco" then I guess disco must be "real" dancing...)
Actually, the case takes after the original Hafler DH-200 (of which I have one with a dead channel that I acquired a while back--keep meaning to do something with the corpse), but the product didn't die in quite the manner they imply. It was superceded by the DH-220 which had a rather odd (to my eyes) olive-drab paint job and tapered heatsinks, and went on to sell another zillion units. They were certainly good for the money, but " of the dominant premium performers..." is a bit of marketing hyperbole.
Anyone know what their patent is? The hoo-rah seems to imply that they use the same circuit Hafler did, or at least one very similar.

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Joined 2002
Their circuit it a combination of mosfets and a tube. That is the model that they are currently in production. I went into their production facility, and it definately is not an old design. Smart Devices has been around for a while in the professional market, and is just recently entering the home theater market. Their professonial movie theater equipment is in used in the majority of cinemas around the country, and the new amplifier that my case is from is an adaptation from a popular older design of theirs that used to be used in a lot of movie theaters before all of the new equipment. If you go to the pro section of their website, you will see what I am talking about. I have spent a few hours down there in there facility, and looked at many of their designs, in looking for a case for my leach amp. They are a great company. I don't work for them, I just really appreciate what they did to put together a leach amp case for me.

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Joined 2002
If you go to:

The new pictures are 123-2317 on, and the pictures of the top are in there.

Does anyone want any other pictures before I close this thing up?


EDIT: by the way.. it is made out of brushed stainless steel. It looks really good when you get rid of the finger prints that it likes to collect.

EDIT AGAIN: the stainless steel top pictures are 2322-2334
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