Kurt, any chance you could make it on 6th?
Out of all participants, does anyone already has set up for matching? I could supply all the tools and several good multimeters. I also have some Hafler MOSFET matcher that I never figured out how to use. Maybe we could modify that for our purpose? It is complete with power supply, measuring instrument and plugs for inserting MOSFETS both TO3 and TO247, as far as I remember. I have to find it first. Or if someone send me the schematic of their desired gig I could modify it before the event - even better!
Out of all participants, does anyone already has set up for matching? I could supply all the tools and several good multimeters. I also have some Hafler MOSFET matcher that I never figured out how to use. Maybe we could modify that for our purpose? It is complete with power supply, measuring instrument and plugs for inserting MOSFETS both TO3 and TO247, as far as I remember. I have to find it first. Or if someone send me the schematic of their desired gig I could modify it before the event - even better!
" ... Single ended class A is unbelievably hot running ..."
Transistors turned on all the time, continuously = no crossover / switching distortion ... I get it.
Yet another reason for using some other design = IMOP. My engineering background precludes my desire to build inefficient devices ... even if they may sound a tiny bit better.
Transistors turned on all the time, continuously = no crossover / switching distortion ... I get it.
Yet another reason for using some other design = IMOP. My engineering background precludes my desire to build inefficient devices ... even if they may sound a tiny bit better.
I started thinking about the math on single-ended and I have come to the same conclusion. I tend to leave my systems on all the time, so having an extra 200W space heater is probably not something I want to do.FastEddy said:" ... Single ended class A is unbelievably hot running ..."
Transistors turned on all the time, continuously = no crossover / switching distortion ... I get it.
Yet another reason for using some other design = IMOP. My engineering background precludes my desire to build inefficient devices ... even if they may sound a tiny bit better.
So I guess I'll be going for a push/pull design. Anyone have a source of P-channel mosfets in a TO-3 package to go with these IRF250s?
" ... So I guess I'll be going for a push/pull desige ... "
Ditto that!
Also MOSFET makers usually measure "efficiencies" while under full loads, continuous, which music is not. Duty cycles for music, even when played loud seldom exceed 50%. Thus (as an example) when making calculations for heat sink requirements, overkill is the rule, rather than the exception. IMOP the Pass Labs prototype chassis we all are trying to rebuild and upgrade or repair ... have huge amounts of sink capabilities for push / pull designs. I like that, and I expect my setup (~ 250 to 300 watts) to run only a few degrees above ambient temp. = effectively cool to the touch. ... We shall see ...
Ditto that!
Also MOSFET makers usually measure "efficiencies" while under full loads, continuous, which music is not. Duty cycles for music, even when played loud seldom exceed 50%. Thus (as an example) when making calculations for heat sink requirements, overkill is the rule, rather than the exception. IMOP the Pass Labs prototype chassis we all are trying to rebuild and upgrade or repair ... have huge amounts of sink capabilities for push / pull designs. I like that, and I expect my setup (~ 250 to 300 watts) to run only a few degrees above ambient temp. = effectively cool to the touch. ... We shall see ...
Preiter,
I forget what kind of output transtors you have?
Most chassis have 240's and 9240's - Push pull configuration, NOT single-ended
If you have this now, then you don't need the 250's - you are set already, with no work required for the output devices, no matching either! If you have the bipolar devices then Fast Eddy offered to trade side panels with someone, because he isn't going to use the devices now on the chassis. If THAT doesn't work, the guys making single ended devices will have 9240's galore to give you, and quite likely the 240's also.
The F4's are push pull, just they are run in Class A so still are somewhat hot, but not like single ended. These amps might run hot, but they DO sound VERY good.
I forget what kind of output transtors you have?
Most chassis have 240's and 9240's - Push pull configuration, NOT single-ended
If you have this now, then you don't need the 250's - you are set already, with no work required for the output devices, no matching either! If you have the bipolar devices then Fast Eddy offered to trade side panels with someone, because he isn't going to use the devices now on the chassis. If THAT doesn't work, the guys making single ended devices will have 9240's galore to give you, and quite likely the 240's also.
The F4's are push pull, just they are run in Class A so still are somewhat hot, but not like single ended. These amps might run hot, but they DO sound VERY good.
I have the bipolar output stage with 4 sets of output devices per channel.
If anyone wants to trade panels for one already configured with complementary MOSFETs, that would be great. Or I will happily take the devices being removed from other boards.
Either way it doesn't look like I will need the bag of IRF250s I have, I'll bring them to the matching event.
If anyone wants to trade panels for one already configured with complementary MOSFETs, that would be great. Or I will happily take the devices being removed from other boards.
Either way it doesn't look like I will need the bag of IRF250s I have, I'll bring them to the matching event.
" ... If anyone wants to trade panels for one already configured with complementary MOSFETs, that would be great. ..."
There should be nothing wrong with your regular bi-polar transistor amps. They are a well thought out design and quite efficient and very good sounding ... IF it is a Class AB or other half off / half on type design with the crossover / switching issues resolved.
Changing over to MOSFET from bi-polar may be simply an exercise in hair splitting. If you are building from scratch, well then, knock yourself out ... get the latest and greatest ... IMOP (In My Opinion) there is nothing inherently wrong with most "old fashioned" push / pull bi-polar design that can't be tweaked for superior results.
There should be nothing wrong with your regular bi-polar transistor amps. They are a well thought out design and quite efficient and very good sounding ... IF it is a Class AB or other half off / half on type design with the crossover / switching issues resolved.
Changing over to MOSFET from bi-polar may be simply an exercise in hair splitting. If you are building from scratch, well then, knock yourself out ... get the latest and greatest ... IMOP (In My Opinion) there is nothing inherently wrong with most "old fashioned" push / pull bi-polar design that can't be tweaked for superior results.
Class A can be theoretically up to 50% efficient. You can see from the specs on Nelson's amps that they're usually about20- 25% efficient. The current sources probably waste as energy as the output devices. The A5 is at the higher end of the range with 60w out for 150w total consumption, or 40% efficient.Tosh said:
I don't think either 240 or 250 matters in so far as being the limiting factor. The A5 uses 240s and the 250 can pass even more current. Rather, the limiting factors are how much power you can get out of the power supply and will the heatsinks be adequate. If your transformer can make 550VA available for the output stage, you could get 200w of output with an A5 design at 40% efficiency with more transistors. I've been assuming that Nelson designed the heatsinks to dissipate all the power that the power supply could deliver, ie, 500w. So determine the power rating of the transformer and work back given the efficiency of the designs you're considering.
- Eric
I'm fine with that, but I'm new at this. I have little confidence in my ability to find a design and adapt it to the hardware that's already mounted on the chassis. Part of the appeal of the F4 (besides the fact that I'm sure it sounds great) is that there are lots of people working on it right here, there are PCBs available (if the current group buy is successful), and there is plenty of support.
All of that increases my chance of successfully building my first discrete transistor amplifier. Saving money on parts and time spent removing and adding parts to the chassis is a secondary concern.
Yes, There are Pass designs, boards, and support for the MOSFET outputs, (the F4 is one) and not one for the bipolar outputs. That's why, as you said, (and Nelson said I believe ) the F4 design is a good bet.How well your preamp works depends on the efficiency of your speakers. My speakers are 95dB efficient and I can listen pretty well with the output from a CD player which one would assume is 2 volts.
Still, a little more gain would be nice and for my speakers a conventional preamp would be PLENTY.
I'm sure you will be able to easily convert to the MOSFETS, as there will be some around, probably free.
Fast Eddy, did you already do that sidepanel swap you had been discussing? If not, here is your opportunity..
I already have some F4's or I would go that way, and I might still..
Still, a little more gain would be nice and for my speakers a conventional preamp would be PLENTY.
I'm sure you will be able to easily convert to the MOSFETS, as there will be some around, probably free.
Fast Eddy, did you already do that sidepanel swap you had been discussing? If not, here is your opportunity..
I already have some F4's or I would go that way, and I might still..
Hi Mark,
Wouldn't want to tip plans over, but it seems we might have more people in the South Bay for matching than in the City. What if we go "green" and have the party down here?
I could possibly host. In fact, I have a membership to TechShop www.techshop.ws in Menlo Park. They have professional benches, scopes, and DVM's for use.
-David
Wouldn't want to tip plans over, but it seems we might have more people in the South Bay for matching than in the City. What if we go "green" and have the party down here?
I could possibly host. In fact, I have a membership to TechShop www.techshop.ws in Menlo Park. They have professional benches, scopes, and DVM's for use.
-David
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