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Old 18th December 2012, 04:24 PM   #11
Krisfr is offline Krisfr  United States
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Has anyone updated the circuit with new topologies lately? Like unstacking the outputs.
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Old 18th December 2012, 04:36 PM   #12
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One can parallel additional output devices and raise the rail voltage on the lower power version to drive lower impedance loads and swing more voltage into higher impedances. Overall a simpler approach than the totem-pole drivers and output devices. May not be quite as rugged as the Super with modern drivers and MJ21195 and -96 outputs in TO-3 cans.

This has been done on several board layouts by DA members.

Apart from that, there have been few if any design changes. I'd like to move on to a new design, but am far from making up my mind what to try next.
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Old 18th December 2012, 08:46 PM   #13
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Quote:
Originally Posted by Damon Hill View Post
I'd retighten the star ground, but you say you're going to rewire it anyway. Also change the diff amp emitter resistors and feedback resistors at the least with metal film, 25ppm .1% or better, and any other resistors you can afford. Maybe a cermet pot for bias; better quality.

Good job on the cooling fans; that'll let it crank out all the watts your ears can stand.
i sold this amp to a friend, but i had bought it back after my 6 six year stint in the Sahkalin island....

this amp was used in a mobile disco and repaired once.....i will consider your recommendations....the super leach sound very good to my ears and is heavily cloned in my side of the pond....

this time, i will be using the amp in my home system, so the fans will be replaced with quieter ones and controlled using thermal cut-outs so that they come on only when needed......
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Old 18th December 2012, 09:18 PM   #14
Krisfr is offline Krisfr  United States
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I went to a disco in Davao many, many years ago, and yes watts, many of them are needed to play music LOUD. It was near the Mt. Apo hotel...
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Old 14th June 2013, 07:33 AM   #15
AJT is offline AJT  Philippines
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in order to rebuild this amp, first i have to dismantle it...

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start with the handles...
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handles and panel removed...
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the two big caps are removed next, the bypass and bleeders will be replaced with something better...
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this is the central ground point bolted unto the chassis at a single point..
the grounded side of the main filter caps are connected by #8 auto cables, the speaker cables are made of #14 auto cables...
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these are the relay boards for soft starting and speaker protector, the sensor and control circuits are on a pcb at the other side of the mounting bracket...
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traffo, power amp modules stored away for later disposition...
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the chassis, front panel and handle are sent to Golden Diamond Powder coaters in Santolan, Pasig...
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the small parts are to be cleaned and reused as much as possible,
the two big NTK 56,000/80 volt filter caps will be retired and replaced with two Nichicon 105*C
68,000/100 volt caps...
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lucky for me, i did not use he whole of the winding window to build this traffo 20 years ago,
it was originally a 55-0-55 volt traffo, and i was able to drive stereo channels into 250 watts per channel back then...
with the available slack in the window, i was able to squeeze in 16 more turns of #14 teflon covered wires for an additional voltage, so that now i have a 65-0-65 volt power traffo..
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Old 14th June 2013, 08:41 PM   #16
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Thinking about it some more, I'd redo the star ground with all soldered connections. Mechanical connections can oxidize/loosen, and this amplifier will crank a lot of current so all connections need to be as 'micro-ohmic' as possible. I'm using a copper pipe cap in one chassis to which all ground returns are soldered, with a big soldering iron.

The SuperAmp's use of a cascoded VAS stage intrigues me; the original design output stage isn't really a cascode as much as a 'totem pole' voltage divider of sorts; the later version (current) is a little more like a cascode. I'm thinking of the same cascode VAS for the existing 'low' power Leach amplifier.

Might consider MJ21193/94 outputs; a bit better Ft and current linearity.
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Old 14th June 2013, 10:01 PM   #17
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the star grounding while using terminal lugs had the wires soldered into it instead of just crimping...
i'll be using gold plated bolts and lugs in my rebuild...
a 4mm bolt was use and extra heavy wires were utilized to minimise losses...
this amp was dead quiet in use, you can turn the volume control fully clockwise..
i will use better trannies this time like the MJ21193/94...
silver micas in place of the ceramic caps
and 100volt caps on the boards, when i assembled it about 20 years ago, such caps were not avaialable so i had to make do with 160v caps back then...
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Old 14th June 2013, 10:16 PM   #18
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I've found in practice with large power supplies that any mechanical connection may loosen/oxidize over time and it's very difficult to tighten to equal the extremely low resistance of a soldered connection. Which in turn has to be done correctly to avoid cold connections.

Everything else sounds good, just what I'd do.
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Old 14th June 2013, 10:29 PM   #19
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i have as a day job worked as QC engineer in an Oil and Gas plant construction and worked around low voltage/high voltage switchgears, and i know the implications of a cold joint...
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Old 25th June 2013, 10:32 PM   #20
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i added 8 bifilar turns to up the voltage from 2 x 55v to 2 x 65 volts....

i used teflon coated #14 wire for the added turns,
good thing that 20 years ago, i did not use the full winding window,
so today i was able to squeeze in more turns
Click the image to open in full size.

since endbells are not available for 2inch cores,
i decided to use "FulaTite" automotive putty to form one.

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Click the image to open in full size.

angle grinders used to shape the "masilya", then fine grit sandpaper prior to painting...
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gray hamertone painting...
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left out to dry for several days...
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