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Old 8th July 2014, 11:16 PM   #151
AndrewT is offline AndrewT  Scotland
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PMD16K100 Lambda
Sure enough they are Darlington

I read the A40 in a Pass website from a few incarnations ago (maybe 15years ago).
I recall the schematic roughly as showing ordinary transistors in the output stage.
Never occurred to me that they are actually Darlington.

Sorry for the confusion.
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Old 9th July 2014, 01:38 AM   #152
Bigun is offline Bigun  Canada
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I suspect that best performance for multiple output pairs when operated in optimal (as per D. Self) Class AB bias it's necessary to match the turn-on characteristics of the power Darlingtons and unfortunately I suspect there's quite a bit of variation when you have two Vbe junctions cascaded in one package - whereas for Nelson operating in Class A this is likely not so much a problem but rather he cares more about current sharing which is achieved with relatively high emitter resistors. The need for matching may eliminate any cost benefit of using common power Darlingtons ???
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Old 9th July 2014, 03:28 AM   #153
6L6 is online now 6L6  United States
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The Darlingtons are about $1.60 in lots of 10, that's not too bad if you need to winnow out a few in the matching process. But I have no idea how variable they are in modern production...

The largish emitter resistors probably loosen the matching requirements, and more power is available with smaller resistors, and tighter matches, as NP mentions on the first page.
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Old 8th September 2014, 05:56 PM   #154
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G'Day

Finally finished building this amp had some spare time. Used 2sa970/2sc2240, bd139/140 & Tip142/147, rails at 24v,bias 0.1amp, dc offset 25mV ish, very stable. Coolest running amp of Nelsons I've built yet doesn't seem right lol.

On soak at the mo, then give it a play. Cheers Nelson again.

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Bruce
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Old 8th September 2014, 05:59 PM   #155
osscar is offline osscar  Latvia
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nice to see a "live" AB 100 !
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Old 9th September 2014, 05:16 AM   #156
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Great to see one AB100 finished !!

I have some transformers and heatsinks spare. Guess I'd
like to build a pair as well if there would be PCBs available.
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Old 10th September 2014, 05:38 PM   #157
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Ok running at 40v rails now all good, want to dump the pot and use a pre what changes would you recommend, amp will only look after the bottom end.

Drop the gain, altering the feedback would this upset the loading of the front end.

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Bruce
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Old 10th September 2014, 08:03 PM   #158
Bigun is offline Bigun  Canada
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Before you mess around with it, what can you say about it's sound qualities (compared with?) ?
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Old 11th September 2014, 12:20 AM   #159
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Sounds great, bottom end is impressive, however it won't be replacing my Aleph J clone any time soon.
Also would have to build 2nd channel and correct the errors on the board tidy it up etc.

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Old 11th September 2014, 08:39 AM   #160
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do you have a scope ? did you measure anything ?
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