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Toltec 18th August 2011 11:10 AM

Leach Amp Project
Hi All,

After many years away from hobby electronics I've decided to get my hands dirty again and build the Leach 4.5. My plan is to build it precisely as per Prof Leach's plans. Besides the enjoyment of doing this, I'd like to know that the end result will be better than my current setup, which is:

CD Player: Marantz CD7300
Amp: Marantz PM7200
Speakers: Bowers and Wilkins DM603 S3

I intend to reuse the CD player and speakers, possibly upgrading in the future sometime. In the opinion of the forum, can I expect as good or better performance with the Leach? Any opinions will be appreciated.


AndrewT 18th August 2011 11:25 AM

I don't know your amp nor your speakers.
Are the speakers 4ohm or 8ohm or some other impedance?

I would expect the Leach Lo Tim 4.5 to drive 8ohms very well, but with a two pair output stage and low efficiency, 4ohms speaker, it may not be at it's best. A big PSU will help.

The Leach is pretty good, I think you will be pleased.

ingenieus 18th August 2011 11:36 AM

Will you limit the pre-amp to a volume pot with no input selector, tone controls or (oh my goodness) loudness button?

Would work fine of course. ;)

Just bear in mind that the Leach amp is not really a beginner project, but if you have wielded a soldering iron before you should be OK.

Toltec 18th August 2011 12:07 PM

Thanks for the replies. The speakers are 150W 8 ohms 90dB/2.83V/m floor standers. The amp 95W into 8 ohms.

Yes, since I only use my amp for CDs I only intend using a volume pot. I'm on the brink of ordering the components from Mouser... looking forward to the smell of solder again!

frederic75 18th August 2011 12:26 PM

Leach amp is a very good choice. Why ? Because you will find all documentation on Leach's site, see FAQS for more details.
Regarding speaker impedance : No probleme for 4 ohms. This amp use two pairs of Bipolar (140 V 20 A 250 W !!) But it could be necessary to adjust current limiter. But is it realy necessary ? For normal use, i am not sure.
Please see those links :

Leach Amp Protection Circuit

The Leach Amp - Part 2


osscar 18th August 2011 12:45 PM

For your speakers Leach amp power will be sufficient IMHO. Many do not like the TO-3 transistor assembly - for such there are also versions for Leach with on-board plastic transistors. good luck !

AndrewT 18th August 2011 01:32 PM

expect a lot more than 95W into 8r0 from the Leach.
I don't know where that figure came from.
I built the Leach clone with the 3pair output stage.
From 230:40+40Vac transformer I got 170W into 8r0, one channel driven. My 3pair of 230W plastic (MJL) devices has similar SOA to a 2pair To3 using 250W devices.

I got over 300W into 4r0, one channel driven, but that does not prove it is 4ohms capable.

Look at using the NJL devices with the integrated diodes. These 4 diodes would fit exactly into the Lo Tim 4.5

Toltec 25th August 2011 08:54 PM

Thanks all for your input.

I'm in the process of buying components. I intend making the pcb myself. I'd prefer to use 2 oz copper but it seems that getting it in the UK is all but impossible unless you're willing to pay mad shipment prices from the US or the East. Is 1 oz ok?... perhaps doing as someone else suggested elsewhere and soldering copper wire along the high current traces. Any input would be appreciated!


prairiemystic 26th August 2011 09:37 PM

I would recommend 2oz copper and laminate thicker than 1.6mm (0.062") for power amps. A PCB house starts with 1oz and electroplates to 2oz, for typical double-sided boards. Solder has almost 10X resistance of copper, so adding solder to PCB traces does not help as much as we think.
diy member Jens Rasmussen did some nice Leach amp clone PCB's that you should checkout:
DELTA AUDIO - Leach Amp Clone

a.wayne 26th August 2011 10:48 PM

Here's a great Leech build ....:)

The Double Barreled Amplifier 300watt HOMEMADE - YouTube

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