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GB for Leach Low-TIM with 8 + 8 BJT outputs (bare PCB)

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Barrettn

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Joined 2013
Differences between original Leach and Jens design?

Years ago I started a 5.1 channel Leach amp, intending to use it for home theater. Now years later I still have all the parts, but the PCBs were etched by my brother using a process he had access to at work -basically you fed it photo-negative artwork and PCBs came out the other end. Problem is, it looks like the plating wasn't very thick, even just being stored they have some pitting in the traces.

So I'm thinking it'd be REALLY smart of my to jump into this group buy for the PCBs, but I'm worried I don't have time to figure out all the differences between the original Leach design and the redesign Jens has done.

Can someone summarize the differences, or if it's documented somewhere, point me to where? (there's 100+ pages of threads to wade through looking for it!)

I'd planned on using a 84VCT 1kVa torroid to power it all - ~59VDC.

Thanks in advance for any replies!

Barrett
 
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linuxguru

Member
Joined 2007
Barrettn said:
Can someone summarize the differences, or if it's documented somewhere, point me to where? (there's 100+ pages of threads to wade through looking for it!)

I'd planned on using a 84VCT 1kVa torroid to power it all - ~59VDC.
Click to expand...

The schematic I'm following for this layout is Version 1.05.12 by Jens - posted for reference here:

http://www.diyaudio.com/forums/grou...en-leach-clone-group-buy-154.html#post3827845

Briefly, the main changes that Jens made were in the number of O/P devices (6 + 6) updated for modern flatpack devices; changed output current-limiting circuit (senses currents from all output pairs and sums them, and some other changes); on-board large filter/bypass caps in addition to the main off-board PSU filter reservoir.

I added 2 additional pairs and beefier drivers to Jens' last schematic, but kept everything else more or less the same. I moved the clamp diodes and the Zobel network in-board of the output inductor. I also separated the small signal section (LTP + VAS) from the rest of the circuit and added ground shields and optimized placement of the signal ground and power ground traces. Some passives are changed to allow physically larger components. Some other minor changes - I'll get everything into a fresh schematic or a release note later and post it here.
 
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Barrettn

Member
Joined 2013
linuxguru said:
The schematic I'm following for this layout is Version 1.05.12 by Jens - posted for reference here:

http://www.diyaudio.com/forums/grou...en-leach-clone-group-buy-154.html#post3827845

Briefly, the main changes that Jens made were in the number of O/P devices (6 + 6) updated for modern flatpack devices; changed output current-limiting circuit (senses currents from all output pairs and sums them, and some other changes); on-board large filter/bypass caps in addition to the main off-board PSU filter reservoir.

I added 2 additional pairs and beefier drivers to Jens' last schematic, but kept everything else more or less the same. I moved the clamp diodes and the Zobel network in-board of the output inductor. I also separated the small signal section (LTP + VAS) from the rest of the circuit and added ground shields and optimized placement of the signal ground and power ground traces. Some passives are changed to allow physically larger components. Some other minor changes - I'll get everything into a fresh schematic or a release note later and post it here.
Click to expand...


Thanks, exactly what I needed to know. Given the smaller size of the original design and the fact that I already have all the parts and heatsinks for it, I'm hurriedly trying to see if I can track down any of the original boards, but if I don't find any in the next two days I will have to put my name on your list and get the newer parts.
 
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linuxguru

Member
Joined 2007
OK, here's the list or requests (for the 2nd batch);

Tarasque - 8
Earthquake - 8
John Luckins - 4

(The count has reached 20 with a day to go, with several more expressions of interest and some unfilled requests from the 1st batch. I'll probably go with an order of 30..32 boards for the 2nd batch tomorrow or Monday - it's just possible that it will reach 40, let's see how it goes).
 
L

linuxguru

Member
Joined 2007
@Johno: Thanks for the update. One unlabeled jumper in the feedback net is required, from the junction between the output zobel resistors to the 12k feedback resistor. The pads are already there, but the labeling on the silkscreen was inadvertently omitted. This applies to both the 1st and 2nd batch boards (due later this week).

@Earthquake: I'll give an update once the 2nd batch is in my hands and looks OK. The batch size wasn't large enough to get a price break, so these will be the same price as the 1st batch. Everything is the same as the 1st batch, except that some drill sizes were adjusted to avoid some manual drilling which I did on the 1st batch.
 
L

linuxguru

Member
Joined 2007
Update: The 2nd batch has been delivered to me, and I should be ready to begin dispatching them (as well as pending orders from the 1st batch) by the weekend.

If there are any additional requests or earlier requests which did not specify a quantity, please post to this thread or PM me with the quantity required. The price is the same as before, USD 18/board + USD 8 (s&h for qty.4). The shipping charge for additional boards beyond 4 units in the same package will be USD 1/board (i.e. 8 boards will be shipped for USD 8 + 4 = USD 12) to almost any location in the Americas, EU and Australasia.
 
L

linuxguru

Member
Joined 2007
Update: All orders (except one) that were paid in Feb and March have been shipped. This includes everything pending from the 1st batch and everything (except for one pair) from the 2nd batch that have been paid so far.

Any previous requests or expressions of interest will still be met from the remainder of the 2nd batch. There are about 14 uncommitted boards left which I'll provide on a first-come, first-served basis. After that, if there's still interest and if there are reserved boards that haven't been paid for, I'll offer those also. Please PM me or email me at siva dot chander at gmail dot com for details.
 
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