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Old 29th November 2005, 01:59 AM   #1
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Default Leach SuperAmp

Leach SuperAmp
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Old 29th November 2005, 02:00 AM   #2
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Look Ma, no wires
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Old 29th November 2005, 02:01 AM   #3
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Hangin' on the heatsinks
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Old 29th November 2005, 06:35 AM   #4
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Ingenious way of connecting the boards, front looks great.
Welcome back, Ace.
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Old 29th November 2005, 09:11 PM   #5
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Thank you, Mr. V.
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Old 30th November 2005, 01:27 AM   #6
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AT LAST!

Looks great! How's she sound?

Can't wait to hear your review.

Blessings, Terry
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Old 30th November 2005, 02:16 AM   #7
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Howdy Terry,
Thanks for the kind words and your past help.
She's a bit stronger than any of my past SuperAmps. With the bias set to the recommended 125, it's a little on the bright side. 200mA seems a better choice for more mids and low end. If your recording is flawed in any way, you'll hear the defect most clearly. On the other hand, hearing the singer take a breath is quite astounding. Leo Kottke on 12 string guitar is a real treat if you don't mind hearing his fingers pluck the strings. And Nana Mouskouri singing Amazing Grace will give you goose bumps.
As you know, I tried to calibrate the meters with several clipping indicators. Since none of them would light up the led indicating clipping, I had to finally give up on that idea. Just drove them up to +3 at full blast thru a 250 watt 8 ohm resistor. The resistor got real hot and began making a ringing noise after a couple minutes. Either I built all the indicators wrong or this baby does not clip at all. I'll try Rod Elliott's project 23 soon and see if it will work. I really don't believe the amp does not clip at all, but I have not put it on a scope yet. This is a proven circuit and didn't seem necessary. I have only played it at about half volume tho. My room is too small to turn it up all the way without hurting us.

Trust you and yours are keeping well.
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Old 30th November 2005, 09:30 AM   #8
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I really like the look of those meters! Excellent job Ace.
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Old 1st December 2005, 08:24 AM   #9
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Hi Acenovelty,
is that two output quads (cascoded pairs) you are using?
Is that 125mA per quad or total per output stage?

200mA total is still only 100mA per quad and well below the maximum allowed (recommended). This equates to about 5W per device so heat should not be a problem.
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Old 1st December 2005, 04:00 PM   #10
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Howdy Pinkmouse,
The meters are from your neck of the woods,
http://www.sifam.com/ tho I managed to find the only US distributor in Los Angeles area. Very high quality product with corresponding price tag. They are back lit thru the scale face by an incandescant lamp. Kinda maintains the retro look I was after.

AndrewT,
The board layout provides a way to wire the drivers without all the rats nest normally associated with this amp. In all other respects it is a standard Leach SuperAmp. Tho I did increase some cap voltage values purely because this is what I had at hand and changing from 100V to 250V on a poly cap is not a big deal IMHO.
Prof. Leach recommends 125mA bias setting for this version which is supposed to relate to 100mA in the Low TIM. My personal preference is to set the bias near 200mA which seems to improve the low end and satisfy the wife's opinion that it is a bit "bright" sounding on our system. Always a good idea to keep a high WAF. The heatsinks are 8.25"x16" with 1" fins on a .25"base. Thus far the sinks feel "warm" to the touch even when driven as loud as my room will allow without eardrum damage.
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