Another Leach Amp - Have we lost our Marbles? - diyAudio
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Old 5th December 2004, 10:11 PM   #1
Byrd is offline Byrd  South Africa
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Default Another Leach Amp - Have we lost our Marbles?

Hi Guys

Out comes another lurker! I have recently finished a set of Leach amps and thought this post a few pics that may provide some inspiration to others as others posts have done for me. Brian GT is one contributer I remember well - but there were many many others. The B/W pics were done by one of my buddies - Moo - Thx Moo

Have we lost our marbles? - well no - we have in fact found them. Have a look at the power switches on the front. I did not like any of the switches that I was able to get here in South Africa so I decided to Macgyver one. I hope this gives a few of you guys some ideas, I have thought of using them for volume knobs as well as selector switches. I have special Audiophile versions of these marbles for sale at only $900 US each - Each expertly machined by dwarves follwed up with a generous sprinkling of the famous "Fairy Dust"

I am absolutely ecstatic with the way this amp sounds - way better than alot of the commercial amps I have heard. I can best describe it as quite smooth & neutral. I have mainly been exposed to "mid-fi" Rotel - Nad - Marantz etc. As a huge generalisation I will say these can "sound loud" at high volume levels - I dont get this from the Leach - even though my neighbours think otherwise .

I have read alot about the reported lack of bass. My opinion is that the Leach amp provides a very natural 'detailed' bass if that makes any sense. It probably wouldn't to me unless I had actaully heard it for myself - NB it is not for everybody.

I found it very interesting that the amount of noise out of this amp with no input source was disturbingly low. I would have to place my ear within +- 5cm or 2.5Inches from the speakers to be able to hear anything, as compared to the NAD integrated that I owned where I could hear hiss from half way across the room.

Thank you Prof Leach for giving this design to the Diy Audio community - your contribution is greatly appreciated.

I will be following up with a website with a couple more pics & details as soon as I get done with the project I have on @ work . I will show you how to get slave labour working for your DIYAudio project

Keep building dudes!!!
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Old 5th December 2004, 10:15 PM   #2
paulb is offline paulb  Canada
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Very nice indeed. How thick is that front panel?
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Old 5th December 2004, 11:49 PM   #3
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Give us a peek at the innards, please.
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Old 6th December 2004, 07:44 AM   #4
Byrd is offline Byrd  South Africa
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Default And some more

Sorry guys - I am under moderation
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Old 6th December 2004, 07:44 AM   #5
Byrd is offline Byrd  South Africa
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Default And another

And Another
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Old 6th December 2004, 07:44 AM   #6
Byrd is offline Byrd  South Africa
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Default And Another

The Front Panel is 12 mm Aluminium Plate - The Router enjoyed enjoyed its lunch that day!
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Old 6th December 2004, 07:44 AM   #7
Byrd is offline Byrd  South Africa
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Default And Another

And finaly - the insides

This is the second build of the amp - the first looked terrible without the Power supply PCB. I also created a PCB for the Clipping indicators (As per Leach's circuit) & power lamp. This PCB also holds the push switch.

The toroid is a 700VA (the largest that coule be manufactured localy) unit yielding 60 Volts DC under load.

Power output on the amp was measured with a scope as 128 into 8 & 242 into 4 with no sign of clipping.
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Old 6th December 2004, 08:17 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
What is that extra block of alloy attached to the heatsink above the transistor? diodes?
Did you have to rotate the transformer to minmimise hum? or did it work in first position?
I am impressed with the doubling of power into 4R. Is this one channel driven? Can you test with both channels driven?
Have you increased any of the time constants to help the bass response? details please.
regards Andrew T.
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Old 6th December 2004, 11:07 AM   #9
Byrd is offline Byrd  South Africa
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You are correct Andrew - that is with one channel driven - at the time I didn't have enough power resistors to measure both channels, and my buddy who owns the scope has now moved to another province so I no longer have access to it. I would imagine that the value will be significantly lower with both channels driven in this way as the transformer is unlikely to provide the necessary current. I will say though that I have driven a pair of 4 ohm floorstanders with good results.

The extra blocks are certainly for the biasing diodes, and I didnt attempt to position the transformer in any special way - It simply didn't introduce any nasties first time off. They are of quite high build quality - and filled with resin to minimise hum. To my ears they are virtually hum free - Some of the other EI transformers I have tried were terrible in this regard

The amp was built stock standard with nearly all parts as per the Leach spec - including the silvered mica caps. IE I did nothing to improve the bass (although I have read that biasing it higher can give more "thump" - I am more of a construction man that an amplifier design expert & prefer to leave those decisions to people that know more than me
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Old 6th December 2004, 06:01 PM   #10
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Im curious what type of router/bits you use for tooling the aluminum. I plan to make my chassis from aluminum. I would appreciate any info you can share.

Thanks, Terry
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