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Old 28th August 2006, 10:51 PM   #1
bernhix is offline bernhix  Philippines
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Default Leach Amp Component substitution

Hello There,

I want to build the "Leach Amp" but my problem is that the the components particularly the transistors are not available in my country(Philippines), can I substitute this part? If it is, what factor do I need to watch out? Is there any bias component need to be changed?

Best Regards,
nhix
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Old 29th August 2006, 01:51 PM   #2
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I used:

Q1,2,5,7,9,10 MPSA42
Q3,4,6,8,11 MPSA92
Q12,15 MJE350
Q13,14 MJE340
Q16 MJE15032
Q 17 MJE15033
Outputs MJ21193 and MJ21194 (or MJL...)

as recommended by Jens. Sounds good.

Note that most of the pinouts will be different, be careful! Also the MJE*** are TO126 or TO220 which makes heatsinking easier but might be tricky with the existing boards.

My boards were done specifically for these transistors (and for TO3 outputs); you're welcome to the design if you want to get someone to make you a pair. No shortage of PCB manufacturers in Philippines!

As for setup and bias, I followed Prof, Leach's instructions and both channels worked first time.
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Old 29th August 2006, 01:54 PM   #3
djQUAN is offline djQUAN  Philippines
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Quote:
No shortage of PCB manufacturers in Philippines!
I'm actually looking for one and haven't found one yet. must not have been looking hard enough.
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Old 29th August 2006, 02:12 PM   #4
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http://www.futurlec.com/

not quite sure where these guys are, but the boards they did for me were excellent, and shipping is a few dollars anywhere in the world.
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Old 29th August 2006, 02:29 PM   #5
djQUAN is offline djQUAN  Philippines
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checked out their prices and for 100pcs of 0.5" x 6" boards will set me back $180 incl shipping.

still much cheaper if I did it by DIY photoetching. saves me a lot of time and messy chemicals though if I let them do it.

although you can't beat the quality of boards made by PCB manufacturers..
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Old 29th August 2006, 02:49 PM   #6
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Quote:
Originally posted by djQUAN
checked out their prices and for 100pcs of 0.5" x 6" boards will set me back $180 incl shipping.

still much cheaper if I did it by DIY photoetching. saves me a lot of time and messy chemicals though if I let them do it.

although you can't beat the quality of boards made by PCB manufacturers..
Plus double-sided allows much better layouts, and through-plated holes make for tougher pads.

Try www.olimex.com in Bulgaria.
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Old 29th August 2006, 02:54 PM   #7
djQUAN is offline djQUAN  Philippines
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well, I need the boards for an LED lighting array that each board will hold 24 SMD led's and 8 current limiting resistors so double sided and hole plating is not necessary though FR4 is needed for reliability.

checked out olimex and they're cheaper than futurlec for small quantities though for mass production, seems like futurlec is cheaper. but diy is still much cheaper.

seems like I have no choice.
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Old 29th August 2006, 08:36 PM   #8
bernhix is offline bernhix  Philippines
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Guys,

I will try to source out this suggested component here in my locality. I will post an update soon i can get this components.

any available suggestion is still welcome. Thanks guys.
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Old 30th August 2006, 09:08 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
BC550/560 or BC546/556 can be substituted for the MPSA42/92.
They have the same pin order but the BC transistors must be turned around 180degrees for the correct legs to fit the correct holes. Use c grade if you can obtain them.

MJL plastic packaged devices must be run cooler than the MJ To3 types. Most To247 and To264 have less power dissipation compared to the 250W To3 packaged MJ21193/4 or the MJ15003/4, both of which have Tj max @ 200degC. However running three paralleled To247 rather than two paralleled To3 solves this dissipation problem but may still require a slightly larger heatsink to keep the Tc to an acceptably low level.

The MJE1503x (To220) series are very robust drivers that suit all output stages driving any load down to 2ohm.
I prefer 2sb649/d669 (To126) as a driver pair but they are less robust and I believe should never be used on a load of less than 4ohm. Again the pin order is the same as the MJE but reversed.

I have used 2sa1360/c3423 as the VAS stage transistors and for the Pre-Driver as well. There are many 2sa/c alternatives that can be substituted into these locations. The original To5/39 cased transistors specified by Leach have a lower power limit.
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Old 7th September 2006, 02:52 PM   #10
bernhix is offline bernhix  Philippines
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Thanks AndrewT for a nice input. Iwill also source out this part...
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