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Joined 2009
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I only made one A40 only for testing and learning from
Even though what i made was a crappy job and kitchen table style with almost poor choice of parts the A40 was a solid rock and free from many of known problems existing in consumer amps that feature one pair of Darlingtons that tent to blow very easily .
To advance this a bit farther i will have to include the A40 in the world wide unique output stages since A40 is the only amp ( that i know ) that has multiple Darlingtons in the output .
In the same family ( and world wide unique )you have the Alchemist Forseti which is a CFP with double the CFP thing on the output with in total 4 outputs with 4 drivers per CH .It is known that APD 15 run into stability probs and band aids of 680 pf had to be placed in the output to prevent blowing .
In the same family you Have Nakamichi PA 7 Stasis from NP which also is unique since features CFP output but with many external transistors (10 i think ) also solid rock extremely reliable ( except some soldering issues but this will happen after 30 years !!! ) that also playes very well and has no band aids in the outputs .
Now Do the math why consumer amplifiers with darlingtons fail all the time??? Anythings that is based on TIP 142-147 or BDV 66-67 will eventually fail ..Denon Philps red circuits Kapibara The Notorious John Fisher sorry excuse of an amplifier with catchy title and many more fail like mosquitoes.... Not to forget latest techniques with SAP 15 working just a bit better but still with a huge history of failure .
Why APD 15 run in to stability problems ???
What is common between the A40 stability and the NAk PA7 stability ?
One and only thing called Bias !!! Run them HOT and they are going to be stable !!
...This is what i think .. I would like to have NP's opinion on that
Kind regards
Sakis
Even though what i made was a crappy job and kitchen table style with almost poor choice of parts the A40 was a solid rock and free from many of known problems existing in consumer amps that feature one pair of Darlingtons that tent to blow very easily .
To advance this a bit farther i will have to include the A40 in the world wide unique output stages since A40 is the only amp ( that i know ) that has multiple Darlingtons in the output .
In the same family ( and world wide unique )you have the Alchemist Forseti which is a CFP with double the CFP thing on the output with in total 4 outputs with 4 drivers per CH .It is known that APD 15 run into stability probs and band aids of 680 pf had to be placed in the output to prevent blowing .
In the same family you Have Nakamichi PA 7 Stasis from NP which also is unique since features CFP output but with many external transistors (10 i think ) also solid rock extremely reliable ( except some soldering issues but this will happen after 30 years !!! ) that also playes very well and has no band aids in the outputs .
Now Do the math why consumer amplifiers with darlingtons fail all the time??? Anythings that is based on TIP 142-147 or BDV 66-67 will eventually fail ..Denon Philps red circuits Kapibara The Notorious John Fisher sorry excuse of an amplifier with catchy title and many more fail like mosquitoes.... Not to forget latest techniques with SAP 15 working just a bit better but still with a huge history of failure .
Why APD 15 run in to stability problems ???
What is common between the A40 stability and the NAk PA7 stability ?
One and only thing called Bias !!! Run them HOT and they are going to be stable !!
...This is what i think .. I would like to have NP's opinion on that
Kind regards
Sakis
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Joined 2009
Paid Member
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.
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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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 ???
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.
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.
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.
Regards
Bruce
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.
Regards
Bruce
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