rickcr42
Are YOU talkin' to me?
- Joined
- Jun 21, 2001
- Posts
- 13,874
- Likes
- 15
Quote:
the Bongiorno and Leach designs are bipolar output and to my knowledge neither has ever done anything in mosfets.erno borbely on the other hand does nothing but for an output stage and for the ultimate examples of Mosfets look to nelson Pass but with the twist of always in class-A,and for good reasons.
There is a thing known as "the mosfet haze" which is a slight softening of the upper registers when used in a class A/B stage andwhile pleasant is not exactly accurate so you are losing resolution in the treble.Where mosfets have an advantage in an output stage and why you see so many in the pro arena is they do not exibit thermal runaway as does a bipolar resistor so the output is easier to design and protection circuitry is not needed (and with it the questionable sonics introduced
)
So for this reason the best of the high power amps use a bipolar transistor output and have multiple parallel devices to get the required VA output and SAO (Safe Area of Operation).
Also,bipolars rule at current gain,fets/mosfets at voltage gain so a class-a jfet front end to a class-a bipolar driver section to a high bias class A/B bipolar output section is a pretty good path (see Bryston schematics).
Then there is the path taken by Nelson Pass.He has discovered (?) that the mosfet output section limitations are eliminated entirely if the devices are kept in the class-A region for the entire operation.
Being the least efficient method of biasing (though best sonics !) known to humans it is expensive and a mini heat generator as much as it is amplifier so even a 10W amplifier in full class-a will be as big as,and use heat sinks as large as a typical 200W A/B amp.imagine trying for 200W pure class-a and the expenses involved !
So that is my "mini lesson" on amp topology as I understand it
Quote:
.
Quote:
you guys may have noticed,maybe not,that I never reference a design that is not only well documented but has an extensive build history over time to any new to DIY.
While "new" may in fact be fine it is my opinion the cicuits that have not only been built by many,not only have extensive personal build pages,but that have stood the test of time are the only way to go out of the gate until you know enough about amps to look at a design and know if it is for you or not.I have seen many "fad" amps come and go yet also notice a few are built over and over and over and that for decades.
This says a lot about the amp and why I consider the 1976 Leach "Low T.I.M." amp to be a keeper.It is fully balanced from the input to the output,has a serious online document library,is a topology still used in the high end of audio,does not use exotic parts to get it to sound good,is a straight forward build on a standard chassis using standard heat sinks and finally,has a long history of building without a single "I wish I never built this,it sucks" anywhere.Pretty good recommendations
of course I personally have shifted to the dark side and no longer do transistor amps for speakers but the power,I do miss the power
| Will all these high power amps use MOSFETS, that is to say are discreet power transistors out of the question? I still need to educate myself in this area. (so much to do!) |
the Bongiorno and Leach designs are bipolar output and to my knowledge neither has ever done anything in mosfets.erno borbely on the other hand does nothing but for an output stage and for the ultimate examples of Mosfets look to nelson Pass but with the twist of always in class-A,and for good reasons.
There is a thing known as "the mosfet haze" which is a slight softening of the upper registers when used in a class A/B stage andwhile pleasant is not exactly accurate so you are losing resolution in the treble.Where mosfets have an advantage in an output stage and why you see so many in the pro arena is they do not exibit thermal runaway as does a bipolar resistor so the output is easier to design and protection circuitry is not needed (and with it the questionable sonics introduced
So for this reason the best of the high power amps use a bipolar transistor output and have multiple parallel devices to get the required VA output and SAO (Safe Area of Operation).
Also,bipolars rule at current gain,fets/mosfets at voltage gain so a class-a jfet front end to a class-a bipolar driver section to a high bias class A/B bipolar output section is a pretty good path (see Bryston schematics).
Then there is the path taken by Nelson Pass.He has discovered (?) that the mosfet output section limitations are eliminated entirely if the devices are kept in the class-A region for the entire operation.
Being the least efficient method of biasing (though best sonics !) known to humans it is expensive and a mini heat generator as much as it is amplifier so even a 10W amplifier in full class-a will be as big as,and use heat sinks as large as a typical 200W A/B amp.imagine trying for 200W pure class-a and the expenses involved !
So that is my "mini lesson" on amp topology as I understand it
Quote:
| There's this "simple" thing too : http://sound.westhost.com/project101.htm . The good thing with it is in the PCB and support. Lots of details on diyaudio |
.
Quote:
| The recent buzz in Diyaudio is in the Solid State forum. A new kit amp call Simple Killer Amp by Greg (or amplifierguru) of Australia. He offer fully populate pcb or unbuild kit for 150W and 300W power amp at resonable price. You will find endless discussion over Diyaudio and some over audiocircle. |
you guys may have noticed,maybe not,that I never reference a design that is not only well documented but has an extensive build history over time to any new to DIY.
While "new" may in fact be fine it is my opinion the cicuits that have not only been built by many,not only have extensive personal build pages,but that have stood the test of time are the only way to go out of the gate until you know enough about amps to look at a design and know if it is for you or not.I have seen many "fad" amps come and go yet also notice a few are built over and over and over and that for decades.
This says a lot about the amp and why I consider the 1976 Leach "Low T.I.M." amp to be a keeper.It is fully balanced from the input to the output,has a serious online document library,is a topology still used in the high end of audio,does not use exotic parts to get it to sound good,is a straight forward build on a standard chassis using standard heat sinks and finally,has a long history of building without a single "I wish I never built this,it sucks" anywhere.Pretty good recommendations
of course I personally have shifted to the dark side and no longer do transistor amps for speakers but the power,I do miss the power
