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Old 20th September 2008, 12:26 AM   #601
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Brutepuppy, You have email. Tad
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Old 20th September 2008, 01:32 AM   #602
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Not quite the same page BP. See http://www.delta-audio.com/Leach-Clone.htm This board has 10 output devices.
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Old 22nd September 2008, 03:01 PM   #603
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Default Leach clone PCB

That's the one I'm interested in (as I try to post enough to escape moderation.....)

Best wishes,
Keith
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Old 22nd September 2008, 05:23 PM   #604
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Quote:
Originally posted by BobEllis
Wiki page http://www.diyaudio.com/wiki/index.p...ice+Group+Buy+

Brute Puppy - that's the new layout awaiting prototyping. The Wiki has a link to the current board or you can visit http://www.delta-audio.com/Leach-Clone.htm to find Jens' writeup on his design.
Interest in original Jens version added to WIKI

Bob Ellis, can you please clarify - WIKI notes indicate a 55-65V PS is required. Is that refering to the Front End?
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Old 22nd September 2008, 05:35 PM   #605
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Rob - 55-65V is appropriate for the entire amp. That should net you between 125 and 150W RMS.

You can go down to a little over 45V, but below that you'll need to change the cascode reference zeners. You can go higher than 65, but then a few other things change and you need to watch the load impedance doesn't dip too low.

You can separate the front end an regulate it separately from the output rails if you wish.
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Old 23rd September 2008, 06:29 AM   #606
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Bob,

Is 0-45VAC dual, 600VA good enogh for stereo application?

Fred
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Old 23rd September 2008, 07:02 AM   #607
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OK Bob,
Try the picture below. Now if that is correct, I have a question or three. Can I build an amp with this board using TO-3's and wire them from board to heat sinks? Can I build the board with less than 10 outputs per channel (like 4,6,or 8)? Are there part changes or jumpers required and who, where, will I get direction to build the lesser design?
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Old 23rd September 2008, 01:35 PM   #608
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Fred - 0-45 VAC x 2 is heart of the envelope - you'll get about 62V rails. Professor Leach's recommended transformer is 600 VA, so, yes, I think that will do.

BP, that's the one.

Yes, as mentioned earlier you can use leads from the board to TO-3 sockets - the original Leach amp did. Stay with slower output devices and short as possible leads to minimize the risk of oscillation, though.

Yes, you can reduce the number of output devices used. No jumpers are required, just leave a pair or two unpopulated. Earlier in the thread a rough 3 plastic devices = 2 metal equivalency was mentioned.

The deign trade-offs are something you'll need to crank though yourself, although you'll get plenty of help here. There isn't a "how to scale my leach amp" reference I am aware of.

In general, at a given rail voltage, the fewer output devices, the less tolerant of low impedance loads the amp will be. You can improve this with more heat sink, but you'll need to run through safe operating area calculations that are both temperature and voltage dependent.

As rail voltage is reduces, the number of output devices needed decreases for a given load. If you want to drive a 1 ohm subwoofer array you'll still need multiple devices no matter what the rails.

While I know many are on a tight budget, IMHO, not fully populating the output section tends toward penny wise and pound foolish (false economy). Even at the single piece price, it costs less than $100 more to fully populate a pair of boards compared to using 3 pairs of outputs (the minimum recommended number of plastic outputs). In return you get a more robust amp that is tolerant of impedance dips at higher output levels. You can even use a bit less heat sink and still maintain reliability.

About the only instance I would consider not fully populating the output section would be for a dedicated tweeter amp in an active system.
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Old 23rd September 2008, 05:16 PM   #609
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600VA will support outputs between 300W and 600W economically.
45Vac will allow about 350 to 380W into 4r0.
Stereo will cause quite a bit of voltage sag in the PSU but will still perform adequately.
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Old 23rd September 2008, 05:32 PM   #610
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Phew! When I saw AndrewT had replied, I was afraid I'd messed up something with my answer.

I'll add that except possibly subwoofer duty, you'll only be using a few watts most of the time anyway. 600 VA ought to be plenty. I use a 800VA transformer to feed four channels of each in my biamped system which never seems to get into rail sag. I have another amp for my subwoofers.
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