redesign of leach amp pcb for integrated TO-247 output devices

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BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
#1
Ever since I finished my leach amp, I have been thinking of ways to improve the design. I have decided to redesign the pcb in order to use TO-3P (TO-247) devices that will be integrated into the pcb, and effectively eliminating a lot of external wiring for the amplifier (12 wires to be exact).

I have the pcb layout mostly worked on paper, and have about half done on the computer. Here are a few pictures of my progress:

http://brian.darg.net/leachamppcb

Feel free to add comments to the pictures in the gallery.

The preliminary board specs will be these:
4" x 6" dimensions (dimensions might approach 3" x 6" if possible)
2 layer pcb
0.093" board thickness
2 oz copper on both sides
soldier mask on both sides
silkscreen on top layer

Preliminary parts list with dimensions:
http://brian.prohosting.com/leachamp.xls

I most likely will use the MJL3281A/MJL1302A (more linear) devices instead of the MJL21193/MJL21194 output devices, but since I currently have some MJL21193/MJL21194 devices, I will use them for prototyping.

Any comments/suggestions on this project would be appreciated. I will update the pictures of my layout, as I near completion. I should finish the layout soon, and get some prototype boards made in august, then if everything works good, get a large batch of production quality boards made for myself and some friends, possibly opening up room for others, but this is a couple of months off, so I will discuss this later.

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Brian
 
#2
I have the pcb layout just about done, and have posted the new board layout, also with a component view without the traces, and a parts list.

http://brian.darg.net/leachamppcb

If anyone is interested in building one of these Leach Amps with the new boards, let me know.

If you want to see pictures of my first leach amp, using the 4.5 boards, go here:

http://brian.darg.net/leachamp-2channel

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Brian
 
#4
It is no different from the normal Leach amp, which outputs around 120w per channel.

I am not getting boards made until August, as I am in France studying for the summer (Georgia Tech has a campus here).

As for the price, I am not sure yet. I am just wondering if there is enough interest for me to order a batch of pcbs. They should cost no more then $50 for a pair including shipping inside the US, if I order a high enough quantity. They will be double sided with soldier mask, silk screen, 2 oz copper, and 0.093" thick board.

Does anyone who has built and modified a leach amp have any suggestions for any modifications to the design?

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Brian
 
#9
Yes, but his board was for integrated TO-3 devices. I have a similar goal to his, but I want to use the newer case devices, which are much easier to use with heatsinks.

Comparison of devices:
http://brian.darg.net/leachamppcb/aaj

The metal ones are the old to-3 output devices and the plastic case ones are the TO-247 (also called TO-3P).

By the way, the board design is done:
http://brian.darg.net/leachamppcb/

--
Brian
 
#10
does it have to be two-layer board?

It will be difficult for most diyers to make the board by themselves
if it is not single-layer. I think one of reasons why Leach Amp is
so popular is that the board is quite easy to make. 😀
 
#11
Re: does it have to be two-layer board?

EJ said:
It will be difficult for most diyers to make the board by themselves if it is not single-layer. I think one of reasons why Leach Amp is so popular is that the board is quite easy to make. 😀
Click to expand...

I agree with this, but keeping the design single sided would have limited the design quite a bit. By using double sided, placement can be more controlled, jumper wires eliminated and shorter traces can be used. I have the board currently done, so that I can send the gerber files off to any board manufacturer and have the double sided boards made with a nice silkscreen. If there is enough interest, I will do a large order for other people on this forum to join in. It doesn't cost too much for the boards, if a lot of people join in.

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Brian
 
#14
nice layout! what if ....

Brian:
Your layout really looks good! What's the possibility of adding patterns to use the 2SA1349/2SC3381 monolithic duals in their special wierd package for the dual diff stages in addition to the usual TO-92 package devices currently being used and adding patterns for different voltage gain driver devices (say, the 2SA1210/2SC2912 in the TO-126 package) in addition to the TO-5 package devices currently used? Just to be clear, I'm saying adding patterns (pads, holes, routes, etc.) IN ADDITION to the original Leach selected parts. That way, one could build the original design and experiment/update with more modern parts without tearing up the PCBs.

By the way, I think I'll be looking for six boards 🙂
mlloyd1
 
#15
Re: nice layout! what if ....

ooops! forgot to add the device pics!

mlloyd1 said:
Brian:
Your layout really looks good! What's the possibility of adding patterns to use the 2SA1349/2SC3381 ....and adding patterns for .... the 2SA1210/2SC2912 in the TO-126 package....
mlloyd1
Click to expand...
 

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#16
Sorry, I cannot add extra pads for these devices, but the existing pads are spaced far enough apart for use of these devices, and the holes are big enough for the leads of your devices.

I have posted a new version of the leach amp pcb at:
http://brian.darg.net/leachamppcb

Revisions include:
- room for larger caps (film and electrolytic) in the input stage
- spacing set for use of terminal blocks for input and output
- added information to silkscreen
- greatly fattened the trace where the output device currents sum up
- widened the board by 0.5" to accomidate the wider trace and the larger caps. This also left room to fit the terminal block for the inputs.

I believe that I have finished the pcb layout. If anyone has any suggestions, let me know.

Thanks a lot to those who have e-mailed me suggestions for board improvement!

--
Brian
 
#17
Similar project

Hello there

At the moment I'm making a set of PCB's for the Leach Amp.

The concept is like this:

Small signal board with overything but drivers and output transistors

Output board with driver and output transistors. And an option to put in more output transistors.

This way it's easy to try out different transistors in the output stage without having to assemble severel different sets of PCB's

There is a thread for this.
 
#20
nice job!

Nice looking board! And it seems to be single sided, making it easy for me to reproduce one by myself. 😀 However, why did you put all your components on the copper side? Doesn't this make your soldering difficult for components such as elec.caps?
 
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