Well done - I recall playing with a similar architecture back in my student days (I only had a 2N3055 and a Hitachi MOSFET ex ETI-5000 to play with and no money to speak of) but never went any further than a quick jury rig. Sounded nice when it wasn't oscillating.
I only stumbled on this thread today (I need a search on "more than N of these people posting in the same thread"
)The unusual output combination like in the NAD 310 is sometimes the result of economies of scale. For instance, a company has a huge leftover of trannies suitable for CFP N side, and a hard to refuse offer to buy a huge quantity of P FETs! And sometimes that's how good sounding amps are created. Pure chance.
Ranchu,
If you want to eliminate the influence of NFB circuit elkos, that are over one year old, on the sound of amp you can reform it in the following ways:
a. Make a regulated PSU using old small transformer and 7815 3-pin IC (like a member dvv) for elco reforming
b. Use 9V battery with 9V battery connector and a pair of alligator clips.
Panasonic app. note suggests 30 minutes reforming.
If you want to eliminate the influence of NFB circuit elkos, that are over one year old, on the sound of amp you can reform it in the following ways:
a. Make a regulated PSU using old small transformer and 7815 3-pin IC (like a member dvv) for elco reforming
b. Use 9V battery with 9V battery connector and a pair of alligator clips.
Panasonic app. note suggests 30 minutes reforming.
Interesting ideas AndrewT and ivanlukic, I will rig something up and give it a go.
On an unrelated matter, I've done some more testing and the bias is not as stable as I first thought. With the trimpot adjusted to, say, 50mV at quiescent, after I stop the music after a long, hard session, the bias drifts to about -200mV or so. I'm going to experiment by placing another diode in series and see if that helps. Failing that I'll try increasing the value of Rbe on the Vbe multiplier.
On an unrelated matter, I've done some more testing and the bias is not as stable as I first thought. With the trimpot adjusted to, say, 50mV at quiescent, after I stop the music after a long, hard session, the bias drifts to about -200mV or so. I'm going to experiment by placing another diode in series and see if that helps. Failing that I'll try increasing the value of Rbe on the Vbe multiplier.
I'm going to say something heretical: use an output capacitor.
If you're using large electros at the end of your power supply be, you're already running your signal currents through them.
My Quasimodo design which uses same mosfet / quasi transistor output stage does use a large output cap and, is indeed, a single rail supply- nothing "heretical" about that at all!
It uses a sum total of just four transistors, one mosfet and a simple diode bias chain per channel, idles at around 20mA current and rarely climbs above 60mA even after a good loud session.
The bias diodes aren't even touching the heat sink!
There is something inherently "right" about a well designed single voltage rail amp that I find really appealing.
But of course, what would someone without an electronics engineering background as myself know about such matters?!
That big speaker decoupling output cap is one of the most affective speaker protection devices there is, and, of course, absolutely no mucking about trying to stabilize any d.c. offset as there is none!
Edward Rotgans of Adelaide Speakers commented on his most recent Quasimodo as having "The best bass definition he had ever heard so far"
Single supply amps rule as far as I'm concerned!
It uses a sum total of just four transistors, one mosfet and a simple diode bias chain per channel, idles at around 20mA current and rarely climbs above 60mA even after a good loud session.
The bias diodes aren't even touching the heat sink!
There is something inherently "right" about a well designed single voltage rail amp that I find really appealing.
But of course, what would someone without an electronics engineering background as myself know about such matters?!
That big speaker decoupling output cap is one of the most affective speaker protection devices there is, and, of course, absolutely no mucking about trying to stabilize any d.c. offset as there is none!
Edward Rotgans of Adelaide Speakers commented on his most recent Quasimodo as having "The best bass definition he had ever heard so far"
Single supply amps rule as far as I'm concerned!
Update and listening report
Hi guys...
Output stage bias:
I had a little time last night to play with the output bias generator. I removed the diode and this has improved matters: the bias does not jump nearly as much after the music stops. Bias stability is heading in the right direction now, so I'll play around with the Rbc resistor to see if further improvements are possible.
Listening report:
The DC offset and bias under control I felt confident bringing it up to the living room and hooking it up to a pair of speakers worthy of a proper test. The speakers in question are a pair of large 3 way transmission line loudspeakers by noted speaker builder Edward from Adelaide Speakers. These displaced a pair of (considerably more expensive) Whatmough Monitors.
I listened to an eclectic mix of high resolution recordings, including piano concertos performed by Ingrid Fliter, a violin concerto by Jennifer Pike, West Side Story by the San Franciso Symphony, before moving on to some old favourites from Bob Dylan, John Lennon, The Eagles, Michael Jackson, Bee Gees, INXS, to name a few. For a final test I ran the "Best of Chesky" sampler disc.
I must say I was an extremely satisfying experience and I'm very pleased with the result. The bass definition, is deep, well controlled and satisfying. The midrange neutral and clear; treble smooth, with lovely texture and body.
I will say that this does not have the absolute resolution of some others I've sampled; the tradeoff is a lovely unfatiging presentation that can stand up to hours of easy listening
Hi guys...
Output stage bias:
I had a little time last night to play with the output bias generator. I removed the diode and this has improved matters: the bias does not jump nearly as much after the music stops. Bias stability is heading in the right direction now, so I'll play around with the Rbc resistor to see if further improvements are possible.
Listening report:
The DC offset and bias under control I felt confident bringing it up to the living room and hooking it up to a pair of speakers worthy of a proper test. The speakers in question are a pair of large 3 way transmission line loudspeakers by noted speaker builder Edward from Adelaide Speakers. These displaced a pair of (considerably more expensive) Whatmough Monitors.
I listened to an eclectic mix of high resolution recordings, including piano concertos performed by Ingrid Fliter, a violin concerto by Jennifer Pike, West Side Story by the San Franciso Symphony, before moving on to some old favourites from Bob Dylan, John Lennon, The Eagles, Michael Jackson, Bee Gees, INXS, to name a few. For a final test I ran the "Best of Chesky" sampler disc.
I must say I was an extremely satisfying experience and I'm very pleased with the result. The bass definition, is deep, well controlled and satisfying. The midrange neutral and clear; treble smooth, with lovely texture and body.
I will say that this does not have the absolute resolution of some others I've sampled; the tradeoff is a lovely unfatiging presentation that can stand up to hours of easy listening
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Hi guys...
Output stage bias:
I had a little time last night to play with the output bias generator. I removed the diode and this has improved matters: the bias does not jump nearly as much after the music stops. Bias stability is heading in the right direction now, so I'll play around with the Rbc resistor to see if further improvements are possible.
Listening report: ...
Can you kindly post the final schematic, if different from post 95?
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Updated schematic
Hi guys
Prior to Christmas, Hugh and I refined the design at post #140 a little. Whilst I don't want to divulge Hugh's secrets, I do want to provide you an updated schematic that addresses a few shortcomings, namely:
I do encourage anyone that is mildly curious to build and test this design for yourself. In my humble opinion the sound is absolutely sublime; I take no credit here and attribute this entirely to the expert input from Hugh, Richard and Gareth, without whom this project wouldn't have been possible.
I have built a number of complex, "state of the art" designs, and while I find when executed properly these can sound very good, they also tend to all sound much the same.
Designs like Gareth's TGM8 and Rod's P3A each have own unique signature that is difficult to put into words. This one is smooth yet crisp and has a wonderfully deep and rich sound stage. Treble is delicate and the bass performance prodigious for an amplifier of this size.
Some of Hugh's other suggestions promise even better performance, and its not hard to see why he has developed a following of loyal customers...
Hi guys
Prior to Christmas, Hugh and I refined the design at post #140 a little. Whilst I don't want to divulge Hugh's secrets, I do want to provide you an updated schematic that addresses a few shortcomings, namely:
- Gate-drain zobel added to prevent a potential source of instability here. I've used similar in my other MOSFET projects and it really does work wonders to quench any tendency towards oscillation.
- Cdom has been increased slightly to 47p and C8 added to prevent another nasty source of instability that results in HF ringing.
- The input transistor biasing has been simplified, and now uses a simple voltage divider to set its operating point at the base.
I do encourage anyone that is mildly curious to build and test this design for yourself. In my humble opinion the sound is absolutely sublime; I take no credit here and attribute this entirely to the expert input from Hugh, Richard and Gareth, without whom this project wouldn't have been possible.
I have built a number of complex, "state of the art" designs, and while I find when executed properly these can sound very good, they also tend to all sound much the same.
Designs like Gareth's TGM8 and Rod's P3A each have own unique signature that is difficult to put into words. This one is smooth yet crisp and has a wonderfully deep and rich sound stage. Treble is delicate and the bass performance prodigious for an amplifier of this size.
Some of Hugh's other suggestions promise even better performance, and its not hard to see why he has developed a following of loyal customers...
Attachments
Unfortunately not thimios. I did a layout based on the original schematic, and have subsequently "hacked" them to incorporate several changes.
It is probable that I will revisit this at some point in the future, but it isn't a high priority at the moment. I'll update this thread with any further developments.
It is probable that I will revisit this at some point in the future, but it isn't a high priority at the moment. I'll update this thread with any further developments.