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Old 11th February 2002, 04:34 AM   #1
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Default Modified version of Leach amplifier

Hi!
Here is a picture of my leach amplifier. It is quite different from Mr Leach design since I wanted to build a more 'up-to-date' amplifier -- that agrees more with todays design. First I used Klass Malman's design ( you can find the link on Mr Leach website) since the transistors were on the board. I added capacitors on the board (smaller ones in parallel). The amp schematics is exactly the same as Mr Leach's 4.5 version. I only changed the layouts. I believe it's a lot easier to build my amp since you don't have much wire to solder...everything is on the board.
Here is the pictures, let me know what you think...
Don't pay attention to the wirering, this is just to test...


Click the image to open in full size.
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Old 11th February 2002, 05:02 AM   #2
BrianGT is offline BrianGT  United States
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Wow! that is a great update to the prof. leach's design. Why did you use so many big caps? What is the advantage of using series and parallel combinations instead of one big one, besides the ability to fit the design in a low profile case? How low profile case can you fit this amplifier in? It looks great. Where did you have your boards made? Where did you get the heatsinks?

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Brian
gte619j@prism.gatech.edu

EDIT: It sure was a bitch wiring the power transistors to the board, with the original design. that is a much better design!
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Old 11th February 2002, 05:30 AM   #3
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The caps are not that big (about 2 inch high 5600uF). I had places in my case to put 8 caps per rail...I know that this is a lot but when you look in hi-fi magazines, the most expensive amps usually have around 70 000 + uF...I really don't know if it makes a difference but it was not more complicated to do it. I also read that smaller caps discharge faster, so it gives more precision than a big one...Honestly, I'm not an audiophile so I can't really tell you if it is true. I'm a hardware guy so I thought : 'just do what they say...'

I etched the board myself and they look pretty good I think. It's a lot cheaper and you get the same result.

I made the heatsink myself...Actually this was a very big heatsink used in a truck or something...I cut it to fit the amp.

As for the case, I'm currently working on it. It should be not more than 2 high.
I'll set up a webpage in the near future with all the layouts, part lists and more pictures...
Thanks
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Old 11th February 2002, 05:43 AM   #4
BrianGT is offline BrianGT  United States
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Sounds good. So, you have all of the caps in parallel, giving you 44800uF per rail? The boards look great. Can you take a picture of the bottom of the boards? This looks like a great design.

So, etching wasn't that bad? What did it entail? Do you have any links to pages describing the process?

Thanks,

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Old 11th February 2002, 01:40 PM   #5
BrianGT is offline BrianGT  United States
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It would be great to modify this design for the Leach SuperAmp, it would not be too bad, except for the placement of the output transistors, since there is 8 instead of 4. Does anyone think this is possible? Could you get away with having a double row of output transistors on the end of the board and just having a larger heatsink?

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Old 11th February 2002, 09:16 PM   #6
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Etching is quite easy. I use MG chemicals products. It takes no more than 30 min overall for both boards. Drilling is a bit more tedious, and you need something like a Dremel to do a good job...takes about 2hours overall.
Here is a link to mgchemicals webpage that explains the process.

http://www.mgchemicals.com/techsupport/demo.html

As I said, I'll make a website when the amp is finished with more pictures. If anyone really needs the layout now, just email me. I use Orcad Layout.

I was not planning to modifie the Leach super amp. I don't know what it would involve... If anyone tell me that it makes a very good subwoofer amp, I'll do it guaranteed. I still have a lot of spare parts so I could reuse them.
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Old 11th February 2002, 09:39 PM   #7
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Leach's Superamp should make a GREAT subwoofer amp.

Really, it should. Though I think by pushing the rail voltages
to 75 volts and using three or four output pairs, Leach's lower
power amplifier design should work just as well. You could use
MJL21193/4 devices (plastic case) and simplify heat sink design
by not having to drill so many holes for TO-3 devices.

The Superamp is configured to safely use lower voltage output
devices by placing them in series/parallel so that current is
shared and voltage halved across each device. This makes for
a slightly more complex design, including additional driver
transistors, but that was the safest way to get that much power
out of existing transistors at that time.

At any rate, eliminating the extra wiring and socket contacts
as you've done, is always A Good Thing. Should help stability
and get rid of some problematic ohmic contacts.

I run with 30,000 uF/rail on my dual-mono chassis because I like
LOTS of capacitance to lower ripple and ESR. I should add that
I found it advisable to include a surge resistor in the AC line; may
have saved me a bridge rectifier or two over the years. I also
added 500 ohm/rail bleeder resistors for safety, and to ensure
symmetrical discharge, which seemed to help with a stability
problem I had with the older driver boards after the amplifier
was turned off. The ver. 4.5 boards don't seem to have that
problem.
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Old 13th February 2002, 01:40 PM   #8
bawang is offline bawang  Malaysia
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Default Nice!!!!

gretzteam,

Nice set of amps! Having built a 3 channel version, I can say this sure beats the chore of connecting 14 cables per board! Please set up your pages with the layouts etc ASAP! Is it possible for you to change the layout for the output devices so that Toshiba 2SA1943/2SC5200 devices can be used? Thanks in advance!
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Old 14th February 2002, 11:22 PM   #9
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Hi Damon Hill!
Are you saying that i'd get a better subwoofer amp by simply add ouput transistors to my design than to go through the chore of redoing the entire layout for the superleach amp?

Bawang :

It might take a while before I set up the web page...I'm doing hard classes this semester so it might not be before the end of april...Can you tell me what is the advantage of using Toshiba transistors?

Thanks a lot
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Old 15th February 2002, 12:18 AM   #10
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the toshiba devices listed above are most probably the most linear BJT devices available.... they just aren't particularly hardy.
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