As a novice I have looked at a lot of amplifier designs and decide to go for the Aleph-X. I’am going to build a three way active cross-over and of course three times an amplifier per channel. I’am thinking of : 20 Watts for the tweeter, 30 watts for midrange and 150 watts for the woofer. I noticed that multiple IRFP044N are placed parallel in order to obtain a certain capacity.
- Well why don’t I see the IRFP064N or IRFP1405 applied.
- Why are there in the power stage relatively many resistors used. Would eg the MP930 series from Caddock not do very well. High power and low induction.
- Does it make any sense to separate the power for drivers and power stage? (Regulated power for driver?)
- I noticed a relative low rail voltage. Why not going for a higher supply in combination with eg IRFP1405
Pls any advice is very welcome in order to make the right decisions for the project I have in mind.
Thanks!!
- Well why don’t I see the IRFP064N or IRFP1405 applied.
- Why are there in the power stage relatively many resistors used. Would eg the MP930 series from Caddock not do very well. High power and low induction.
- Does it make any sense to separate the power for drivers and power stage? (Regulated power for driver?)
- I noticed a relative low rail voltage. Why not going for a higher supply in combination with eg IRFP1405
Pls any advice is very welcome in order to make the right decisions for the project I have in mind.
Thanks!!
" Well why don’t I see the IRFP064N or IRFP1405 applied."
I suppose you could if the capacitance, transconductance and other parameters are similar to IRFP240.
" Why are there in the power stage relatively many resistors used. Would eg the MP930 series from Caddock not do very well. High power and low induction."
Many have used the Caddock and other similar type resistors in the Aleph amplifiers. I doubt that you would hear much of a difference between them and high grade 1% wire wounds though. The Caddocks also may need to be heat sink mounted in order for them to be able to operate at max dissipation. That is somewhat of a disadvantage along with would amount to a very marginal gain in sound quality if any at all. They are also very expensive.
"Does it make any sense to separate the power for drivers and power stage? (Regulated power for driver?)"
Actually there is a constant current source for the input stage, and in these Alephs ther is only an input and an output stage anyway. There is not really a driver stage in there per say.
" I noticed a relative low rail voltage. Why not going for a higher supply in combination with eg IRFP1405"
An X amplifiers rail voltage requirement is dependent on a number of things including output stage bias, output power requirements, and power required into low impedances, say 4 ohms. It would be nice to hear from Grey Rollins on this one
Also keep in mind that all the semiconductor devices need to be hyper matched, or even better, matched in place in the operating amplifier circuit you intend to use. This is necessary to achieve the lowest possible DC offset at the output terminals. So be ready and set up for doing that!!
Mark
I suppose you could if the capacitance, transconductance and other parameters are similar to IRFP240.
" Why are there in the power stage relatively many resistors used. Would eg the MP930 series from Caddock not do very well. High power and low induction."
Many have used the Caddock and other similar type resistors in the Aleph amplifiers. I doubt that you would hear much of a difference between them and high grade 1% wire wounds though. The Caddocks also may need to be heat sink mounted in order for them to be able to operate at max dissipation. That is somewhat of a disadvantage along with would amount to a very marginal gain in sound quality if any at all. They are also very expensive.
"Does it make any sense to separate the power for drivers and power stage? (Regulated power for driver?)"
Actually there is a constant current source for the input stage, and in these Alephs ther is only an input and an output stage anyway. There is not really a driver stage in there per say.
" I noticed a relative low rail voltage. Why not going for a higher supply in combination with eg IRFP1405"
An X amplifiers rail voltage requirement is dependent on a number of things including output stage bias, output power requirements, and power required into low impedances, say 4 ohms. It would be nice to hear from Grey Rollins on this one
Also keep in mind that all the semiconductor devices need to be hyper matched, or even better, matched in place in the operating amplifier circuit you intend to use. This is necessary to achieve the lowest possible DC offset at the output terminals. So be ready and set up for doing that!!
Mark
Aleph-X Some Thoughts 2
Hi Mark,
Thanks for your reply.
My comment starts with '-'
" Well why don’t I see the IRFP064N or IRFP1405 applied."
I suppose you could if the capacitance, transconductance and other parameters are similar to IRFP240.
- Yes I think you right however devices parrallel also double the capacity, at least I learned so.
" Why are there in the power stage relatively many resistors used. Would eg the MP930 series from Caddock not do very well. High power and low induction."
Many have used the Caddock and other similar type resistors in the Aleph amplifiers. I doubt that you would hear much of a difference between them and high grade 1% wire wounds though. The Caddocks also may need to be heat sink mounted in order for them to be able to operate at max dissipation. That is somewhat of a disadvantage along with would amount to a very marginal gain in sound quality if any at all. They are also very expensive.
- Oke but we are working on these projects because we want it all. Some folks think that parallel resistors (or evices) create e 'foggy sound'. The prices from mouser.com are acceptable.
"Does it make any sense to separate the power for drivers and power stage? (Regulated power for driver?)"
Actually there is a constant current source for the input stage, and in these Alephs ther is only an input and an output stage anyway. There is not really a driver stage in there per say.
- Almost every amplifier has a current source. People like http://www.borbelyaudio.com/ and http://www.lcaudio.com/ go for this theory.
" I noticed a relative low rail voltage. Why not going for a higher supply in combination with eg IRFP1405"
An X amplifiers rail voltage requirement is dependent on a number of things including output stage bias, output power requirements, and power required into low impedances, say 4 ohms. It would be nice to hear from Grey Rollins on this one
Also keep in mind that all the semiconductor devices need to be hyper matched, or even better, matched in place in the operating amplifier circuit you intend to use. This is necessary to achieve the lowest possible DC offset at the output terminals. So be ready and set up for doing that!!
- Yes as I noticed from the excel configuration sheets. It is difficult to order all info from this site and filter only this information that is important.
However I get the strange feeling that this amplifier is a potential dangour for my valuable speakers isn't it.
Regards,
Jan
Hi Mark,
Thanks for your reply.
My comment starts with '-'
" Well why don’t I see the IRFP064N or IRFP1405 applied."
I suppose you could if the capacitance, transconductance and other parameters are similar to IRFP240.
- Yes I think you right however devices parrallel also double the capacity, at least I learned so.
" Why are there in the power stage relatively many resistors used. Would eg the MP930 series from Caddock not do very well. High power and low induction."
Many have used the Caddock and other similar type resistors in the Aleph amplifiers. I doubt that you would hear much of a difference between them and high grade 1% wire wounds though. The Caddocks also may need to be heat sink mounted in order for them to be able to operate at max dissipation. That is somewhat of a disadvantage along with would amount to a very marginal gain in sound quality if any at all. They are also very expensive.
- Oke but we are working on these projects because we want it all. Some folks think that parallel resistors (or evices) create e 'foggy sound'. The prices from mouser.com are acceptable.
"Does it make any sense to separate the power for drivers and power stage? (Regulated power for driver?)"
Actually there is a constant current source for the input stage, and in these Alephs ther is only an input and an output stage anyway. There is not really a driver stage in there per say.
- Almost every amplifier has a current source. People like http://www.borbelyaudio.com/ and http://www.lcaudio.com/ go for this theory.
" I noticed a relative low rail voltage. Why not going for a higher supply in combination with eg IRFP1405"
An X amplifiers rail voltage requirement is dependent on a number of things including output stage bias, output power requirements, and power required into low impedances, say 4 ohms. It would be nice to hear from Grey Rollins on this one
Also keep in mind that all the semiconductor devices need to be hyper matched, or even better, matched in place in the operating amplifier circuit you intend to use. This is necessary to achieve the lowest possible DC offset at the output terminals. So be ready and set up for doing that!!
- Yes as I noticed from the excel configuration sheets. It is difficult to order all info from this site and filter only this information that is important.
However I get the strange feeling that this amplifier is a potential dangour for my valuable speakers isn't it.
Regards,
Jan
As stated in some other threads around here: if possible, avoid using TO220 devices as output transistors. Though the IRF1405 looks impressive from the datasheet, you will run into problems if you have to get rid of serious amounts of heat. I have cooked lots of them in high power dc motor driving applications at only 10 watts of power losses.
And, those extremely high power FETs indeed have an enourmous amount of input capacitance, you will need serious driving current to feed them.
And, those extremely high power FETs indeed have an enourmous amount of input capacitance, you will need serious driving current to feed them.
The IRFP044, 140, 240, etc. series of TO-247 transistors really are the best. They can dissipate quite large heat loads without much trouble.
I think you'll find that if you are using parallel FETs in the output stage, you probably don't need to use huge power resistors. In my Aleph-X I was able to use BC 1W metal film resistors for every place in the power stage. They are far less bulky than 3W types and non-inductive.
I think you'll find that if you are using parallel FETs in the output stage, you probably don't need to use huge power resistors. In my Aleph-X I was able to use BC 1W metal film resistors for every place in the power stage. They are far less bulky than 3W types and non-inductive.
Please note that both the Aleph and Aleph X amplifiers
require that the negative rail of the front end requires
the same voltage connection as the output stage.
The only thing you can gain with a separate + supply for the
front end is perhaps a bit less noise, but even then you can
achieve this with some decoupling to the supply rail which
powers the current source for the input diff pair.
require that the negative rail of the front end requires
the same voltage connection as the output stage.
The only thing you can gain with a separate + supply for the
front end is perhaps a bit less noise, but even then you can
achieve this with some decoupling to the supply rail which
powers the current source for the input diff pair.
There's nothing sacred about the '044. If you've got some other device you'd like to try, feel free to do so. Just keep an eye on the SOA for whatever you decide to put in.
I use Caddock resistors in mine. I've got/had several versions of the Aleph-X drawn up (found some schematics that seem to have survived the recent hard disk adventure--thank goodness for floppies). As I said in the Aleph-X thread, the circuit I run isn't quite the same as the one I published. Given the high cost of Caddock and other boutique resistors, I felt that the circuit would reach a wider audience if it didn't call for comparatively rare, mega-buck parts. It's the values that are important. If you want to use Vishay, Caddock, Mills, etc. and your wallet is thick enough, then go for it. Consider heat sinks for the Caddocks, as they're only good for a couple of watts without them. The internal solder connections come unstuck if you overdo it.
Regulate the entire rail if you really want to max the thing out. I'll eventually go that route, but am not doing so yet. The regulator circuit is ready and tested and I've even got the parts, what I lack is the time to do a circuit board.
I'm not sure why people are so startled by the low rails; it's a bridged amp, and low rails/high current go with the territory. If you want to use higher rails, you'll end up with a higher powered amp. No problem. But...you'll have to increase the bias in order to keep from current limiting into lower impedances, and that implies lots and lots of heat. You'll need big heat sinks. Or you could consider going water cooled. Broadly speaking, the rails determine the output wattage, and the bias current determines how low an impedance you can deliver that wattage to. If you're not careful, you'll end up with an amp that can deliver 500W...into a 100 ohm load. Clearly not a practical amp for general use.
Grey
I use Caddock resistors in mine. I've got/had several versions of the Aleph-X drawn up (found some schematics that seem to have survived the recent hard disk adventure--thank goodness for floppies). As I said in the Aleph-X thread, the circuit I run isn't quite the same as the one I published. Given the high cost of Caddock and other boutique resistors, I felt that the circuit would reach a wider audience if it didn't call for comparatively rare, mega-buck parts. It's the values that are important. If you want to use Vishay, Caddock, Mills, etc. and your wallet is thick enough, then go for it. Consider heat sinks for the Caddocks, as they're only good for a couple of watts without them. The internal solder connections come unstuck if you overdo it.
Regulate the entire rail if you really want to max the thing out. I'll eventually go that route, but am not doing so yet. The regulator circuit is ready and tested and I've even got the parts, what I lack is the time to do a circuit board.
I'm not sure why people are so startled by the low rails; it's a bridged amp, and low rails/high current go with the territory. If you want to use higher rails, you'll end up with a higher powered amp. No problem. But...you'll have to increase the bias in order to keep from current limiting into lower impedances, and that implies lots and lots of heat. You'll need big heat sinks. Or you could consider going water cooled. Broadly speaking, the rails determine the output wattage, and the bias current determines how low an impedance you can deliver that wattage to. If you're not careful, you'll end up with an amp that can deliver 500W...into a 100 ohm load. Clearly not a practical amp for general use.
Grey
Grey & Nelson,
At the moment I am looking to scale several X Alephs to bi amp and eventually quad amp
I have done a search but not found anything specific regards low supply rail limitations.
I recall Nelson at one point saying idealy the X Aleph is best with 25 volts. Is that per rail or rail to rail.
Just curious.
Ian
At the moment I am looking to scale several X Alephs to bi amp and eventually quad amp
I have done a search but not found anything specific regards low supply rail limitations.
I recall Nelson at one point saying idealy the X Aleph is best with 25 volts. Is that per rail or rail to rail.
Just curious.
Ian
Ian,
At the moment, I've got an Aleph-X running at roughly 20V rails (a little over 60W output) and a bodacious amount of bias current. No real game plan there, it's just that I had a pair of power transformers on hand that seemed lonely.
Regarding distortion:
Some preach the Gospel of Bias Current as though it's the only thing going. Ain't so. Rail voltage is important, too. Somewhere in the original Aleph-X thread, I posted some numbers relating rail voltage to distortion. No, I don't remember where, but it's near the back of the thread, so start at the end and work forwards. The upshot is that increasing rail voltage decreases distortion up (or down, depending on your point of view) to a certain point. Obviously, you'll never get to zero. Where's optimal? Well, that's a complex question. You've got to balance rail voltage (higher is better), against bias current (higher is better), and heat dissipation (less is better), the capability of your chosen power transformer, heatsinks, the thickness of your wallet, etc. etc. etc.
It's enough to drive a man to drink.
Hmmm...interesting idea, that one.
There's no one right answer, just as there's not really a wrong one. The 15V rails I showed in the original schematic are there because I developed the Mini-A first, and it ended up having 15V rails because my target power was 10W. The Aleph-X is essentially two Mini-As back to back. There's nothing sacred about 15V rails. I ran up the Aleph-X in its posted version just as a demonstration of concept, not something to be slavishly adhered to. Feel free to adapt the critter to whatever rail voltages/currents you have available. As long as you attend to a few part values, it'll take pretty much whatever you throw at it.
Note that I don't take credit for the thing. Nelson just left a few building blocks on the table and I got to playing with them, seeing whether thay would fit together. They did. But they're his building blocks. He was gracious enough to let me play with them.
Grey
At the moment, I've got an Aleph-X running at roughly 20V rails (a little over 60W output) and a bodacious amount of bias current. No real game plan there, it's just that I had a pair of power transformers on hand that seemed lonely.
Regarding distortion:
Some preach the Gospel of Bias Current as though it's the only thing going. Ain't so. Rail voltage is important, too. Somewhere in the original Aleph-X thread, I posted some numbers relating rail voltage to distortion. No, I don't remember where, but it's near the back of the thread, so start at the end and work forwards. The upshot is that increasing rail voltage decreases distortion up (or down, depending on your point of view) to a certain point. Obviously, you'll never get to zero. Where's optimal? Well, that's a complex question. You've got to balance rail voltage (higher is better), against bias current (higher is better), and heat dissipation (less is better), the capability of your chosen power transformer, heatsinks, the thickness of your wallet, etc. etc. etc.
It's enough to drive a man to drink.
Hmmm...interesting idea, that one.
There's no one right answer, just as there's not really a wrong one. The 15V rails I showed in the original schematic are there because I developed the Mini-A first, and it ended up having 15V rails because my target power was 10W. The Aleph-X is essentially two Mini-As back to back. There's nothing sacred about 15V rails. I ran up the Aleph-X in its posted version just as a demonstration of concept, not something to be slavishly adhered to. Feel free to adapt the critter to whatever rail voltages/currents you have available. As long as you attend to a few part values, it'll take pretty much whatever you throw at it.
Note that I don't take credit for the thing. Nelson just left a few building blocks on the table and I got to playing with them, seeing whether thay would fit together. They did. But they're his building blocks. He was gracious enough to let me play with them.
Grey
The reason that I don't like to go much below 25 volts (+ and -
each) is that Mosfets really like to see a few volts across them,
even at peaks. The issue is the capacitance of the Mosfet which
increases non-linearly as the voltage decreases across the
device, and is a priimary form of distortion at high frequencies.
Just take a look at the capacitance curves.
So I like to keep 5 volts or so left for may gain devices at full
peak output, which means I can get +-20 volts clean off any
output stage, or twice that in the case of an X circuit.
each) is that Mosfets really like to see a few volts across them,
even at peaks. The issue is the capacitance of the Mosfet which
increases non-linearly as the voltage decreases across the
device, and is a priimary form of distortion at high frequencies.
Just take a look at the capacitance curves.
So I like to keep 5 volts or so left for may gain devices at full
peak output, which means I can get +-20 volts clean off any
output stage, or twice that in the case of an X circuit.
Quote:
The reason that I don't like to go much below 25 volts (+ and -
each) is that Mosfets really like to see a few volts across them,
even at peaks. The issue is the capacitance of the Mosfet which
increases non-linearly as the voltage decreases across the
device, and is a priimary form of distortion at high frequencies.
Can you explain the non linear capacitance with voltage and its effect on the circuit in this situation?
What I mean is as we increase the supply rails what tends to happen that improves this aspect of performance and the result of adding devices to share the power dissipation?
At the moment my Drain / Source voltage is about 17 volts.
Aside from the lower capacitance, the curve for the 240 appears to flatten at a lower Vds.
Ian
The reason that I don't like to go much below 25 volts (+ and -
each) is that Mosfets really like to see a few volts across them,
even at peaks. The issue is the capacitance of the Mosfet which
increases non-linearly as the voltage decreases across the
device, and is a priimary form of distortion at high frequencies.
Can you explain the non linear capacitance with voltage and its effect on the circuit in this situation?
What I mean is as we increase the supply rails what tends to happen that improves this aspect of performance and the result of adding devices to share the power dissipation?
At the moment my Drain / Source voltage is about 17 volts.
Aside from the lower capacitance, the curve for the 240 appears to flatten at a lower Vds.
Ian
Nelson Pass said:
I think I heard the effect of this in my zv4 when i played with the R4 pot. 20-22V across Q1 took the life out of piano notes...less weight and the timbre was not right. The sound is livelier and sweeter (IMO) at about 25V...went as far as 30V but after several hours smoked Q1 which in turn took down Q2 and Q5. At 25V the positive cycle will clip/distort earlier than the negative cycle (about 20V)...but at my normal listening level the measured AC voltage at the spkr terminals was about 3.25Vrms (~4.6Vpk)...the first watt is what really matters!
Yeah well those curves are for a reason.
I think this is what makes building up these designs so interesting...you come across a problem, investigate whats happening and learn something.
I'm sure these a lot more to scaling these amps than keying numbers in to a speadsheet.(although its a very useful tool)
Exactly what impact raising the voltage 10 volts apart from pumping up the watts will be interesting with the IRFP044's. I have a tube of 25 of these suckers so I hope it works.
I will try this tonight and post the results.
Ian
I think this is what makes building up these designs so interesting...you come across a problem, investigate whats happening and learn something.
I'm sure these a lot more to scaling these amps than keying numbers in to a speadsheet.(although its a very useful tool)
Exactly what impact raising the voltage 10 volts apart from pumping up the watts will be interesting with the IRFP044's. I have a tube of 25 of these suckers so I hope it works.
I will try this tonight and post the results.
Ian
Hmm,
Those IRP044's a tough, but I might use 2 pair per side and be damned. That will be 4800 pf Gate capacitance in theory (or the equivalent of say 4 IRFP240's) so it will either work or it won't.
As an amusing side note, I have found the Olympic broadcasts a good test signal at least for the Aussie viewers, the applause is much like averaged white noise and its easy to differential spectral balance.
Ian
Those IRP044's a tough, but I might use 2 pair per side and be damned. That will be 4800 pf Gate capacitance in theory (or the equivalent of say 4 IRFP240's) so it will either work or it won't.
As an amusing side note, I have found the Olympic broadcasts a good test signal at least for the Aussie viewers, the applause is much like averaged white noise and its easy to differential spectral balance.
Ian
I have not done the test yet due to other priorities but I note from Nelson's excellent how to article on bias/voltage comparions the problems of Gate Capacitance and selection of mosfets are well illustrated.
For my purposes at least the 044 is less than suitable as I have no intention of biasing the device at say 2 amps and 25 volts for credible performance, particularly for high frequencies where I need it.
I hope I am missing something here but looking at 150-200 watts dissipation for a tweeter amp in a quad amped system with tweeter 105 db seems a little bit silly and perhaps the X Aleph or even is less appropriate for this application.
Maybe a batch of IFR610 would be the way to go?? I think the Rushmore uses scaled down Alephs, the total power dissipation being around 300 watts total per box.
I will probably re install the JLH which uses 80 watts and is to my ear as good or better in some respects in low power applications.
macka
For my purposes at least the 044 is less than suitable as I have no intention of biasing the device at say 2 amps and 25 volts for credible performance, particularly for high frequencies where I need it.
I hope I am missing something here but looking at 150-200 watts dissipation for a tweeter amp in a quad amped system with tweeter 105 db seems a little bit silly and perhaps the X Aleph or even is less appropriate for this application.
Maybe a batch of IFR610 would be the way to go?? I think the Rushmore uses scaled down Alephs, the total power dissipation being around 300 watts total per box.
I will probably re install the JLH which uses 80 watts and is to my ear as good or better in some respects in low power applications.
macka
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