Grey,
I am taking a guess here that your second idea is to somehow incorporate Nelson's X-supersymmetry topology into the SOZ as a back-end design. I could be wrong totally.
However, since you have a Baby SOZ as well as the Alephs, could you please spell out which is sonically preferred. I understand that damping is low in the SOZ. That apart, what about the other aspects.
By the way, I just put together Andrea Ciuffoli's Power Follower 99, a single ended Class A design similar to the Zen amp but without any voltage gain. I heard it yesterday driving at a lower power level that it is capable of. It simply sounded excellent. To put it simply, it has no sound of its own. The electronics almost disappear totally. I am interested to know about the sonics of your possessions since I want to finally decide between Andrea's design, SOZ and Aleph for my personal listening.
Thanks very much.
I am taking a guess here that your second idea is to somehow incorporate Nelson's X-supersymmetry topology into the SOZ as a back-end design. I could be wrong totally.
However, since you have a Baby SOZ as well as the Alephs, could you please spell out which is sonically preferred. I understand that damping is low in the SOZ. That apart, what about the other aspects.
By the way, I just put together Andrea Ciuffoli's Power Follower 99, a single ended Class A design similar to the Zen amp but without any voltage gain. I heard it yesterday driving at a lower power level that it is capable of. It simply sounded excellent. To put it simply, it has no sound of its own. The electronics almost disappear totally. I am interested to know about the sonics of your possessions since I want to finally decide between Andrea's design, SOZ and Aleph for my personal listening.
Thanks very much.
Samuel Jayaraj,
I have also built Andrea Ciuffoli's Power Follower 99, and I think it sounds OK. But I don't like to have a big capacitor at the output ot the circuit. Otherwise I think it's a nice circuit. I've been using the Power Follower for about 20 months or so. And during that time I have replaced a couple of MosFets, and now a small electrolytic cap seems to be damaged. I run the power follower with a 38V 500VA transformer/channel at a bias current of 2A or 4A (I have a switch to switch between the two values) and a 0,34K heatsink per channel. So I recommend you to use a lower supply voltage than I did, otherwise you will probably have to replace a couple of Mosfets.
The so called "Virtual battery" PSU works OK too. But I wonder if it would sound better with a normal PSU with some large caps after the diode bridge instead.
Right now, I'm about to start building the Aleph 30. But with some small modifications. I'm thinking of running it at a higher bias current to give 60W output at 4ohms. And I will also use a bigger PSU (2*18V 600VA, 24 * 10000uF), separate PSU for each channel. And I will not use a preamp infront of the Aleph, I will simply use a DACT CT2 10k stepped attenuator. And use my own switch (one push button) to change between different sources, It's controlled by a 'ring counter IC' which controlls the relays and also lights a nice blue LED to indicate what source I'm using.
However I'm a little unsure how to change the bias of the Aleph 30. Should I simply reduce the values of (R34-39). Should I increase the voltage over these resistors (R34-39). Or should I simply use more output devices.
What's the best solution?
I think the best should be to just double the output stage from 6 devices/channel to 12.
What do you think?
/Freddie
[Edited by Freddie on 09-10-2001 at 10:53 AM]
I have also built Andrea Ciuffoli's Power Follower 99, and I think it sounds OK. But I don't like to have a big capacitor at the output ot the circuit. Otherwise I think it's a nice circuit. I've been using the Power Follower for about 20 months or so. And during that time I have replaced a couple of MosFets, and now a small electrolytic cap seems to be damaged. I run the power follower with a 38V 500VA transformer/channel at a bias current of 2A or 4A (I have a switch to switch between the two values) and a 0,34K heatsink per channel. So I recommend you to use a lower supply voltage than I did, otherwise you will probably have to replace a couple of Mosfets.
The so called "Virtual battery" PSU works OK too. But I wonder if it would sound better with a normal PSU with some large caps after the diode bridge instead.
Right now, I'm about to start building the Aleph 30. But with some small modifications. I'm thinking of running it at a higher bias current to give 60W output at 4ohms. And I will also use a bigger PSU (2*18V 600VA, 24 * 10000uF), separate PSU for each channel. And I will not use a preamp infront of the Aleph, I will simply use a DACT CT2 10k stepped attenuator. And use my own switch (one push button) to change between different sources, It's controlled by a 'ring counter IC' which controlls the relays and also lights a nice blue LED to indicate what source I'm using.
However I'm a little unsure how to change the bias of the Aleph 30. Should I simply reduce the values of (R34-39). Should I increase the voltage over these resistors (R34-39). Or should I simply use more output devices.
What's the best solution?
I think the best should be to just double the output stage from 6 devices/channel to 12.
What do you think?
/Freddie
[Edited by Freddie on 09-10-2001 at 10:53 AM]
Vince,
You betcha. You'll be first to know.
Sam,
At present, I've only built one channel as a test bed for my ideas. Once I get a little further along, I'll build a pair and report on sound quality. My intention/hope at this time is to come up with something that will work well for my tweeters (quad-amped system--tweeters run from 5kHz up), but as they are about 3 ohms, purely resistive, I'll need a fair amount of current. My tube amps, currently running the tweeters, will move back to the midrange. The Aleph 2s, currently running the mids, will drop to the woofer panels, and that will allow me to put both Thresholds on the subs...until I get the dedicated amps built.
In Petter's thread about the X topology, I mentioned the possibility of mating the Aleph and X topologies. I still intend to try that, but it will be a separate project.
Freddie,
Changing the bias in the Aleph circuit isn't difficult--higher values of R19 increase the bias. If you add more devices to the output, you'll have other things to fiddle with, such as the resistor array at the output. You shouldn't need to add devices anyway, as they're running pretty conservatively and you'll only need to up the bias about 25% to get where you want to go; still notably less than the bias level the Aleph amps were using. Just be sure you've got adequate heat sinking and you'll be fine.
Grey
You betcha. You'll be first to know.
Sam,
At present, I've only built one channel as a test bed for my ideas. Once I get a little further along, I'll build a pair and report on sound quality. My intention/hope at this time is to come up with something that will work well for my tweeters (quad-amped system--tweeters run from 5kHz up), but as they are about 3 ohms, purely resistive, I'll need a fair amount of current. My tube amps, currently running the tweeters, will move back to the midrange. The Aleph 2s, currently running the mids, will drop to the woofer panels, and that will allow me to put both Thresholds on the subs...until I get the dedicated amps built.
In Petter's thread about the X topology, I mentioned the possibility of mating the Aleph and X topologies. I still intend to try that, but it will be a separate project.
Freddie,
Changing the bias in the Aleph circuit isn't difficult--higher values of R19 increase the bias. If you add more devices to the output, you'll have other things to fiddle with, such as the resistor array at the output. You shouldn't need to add devices anyway, as they're running pretty conservatively and you'll only need to up the bias about 25% to get where you want to go; still notably less than the bias level the Aleph amps were using. Just be sure you've got adequate heat sinking and you'll be fine.
Grey
Grey,
Thanks. I'll wait patiently till you're through with the second channel.
Freddie,
Thanks for your input. I have only done some preliminary testing with a lower voltage, bias and heatsink - all under rated. I am surprised that inspite of the adequate heatsink provided by you, the MOSFETS needed replacement. By the way, did you use IRF150s. I used IRFP250s since their Pd rating is somewhere about 180watts. If this amp sounds good enough as compared to the Alephs, then we could try to use IRFP260s (check the RS catalogue) which have Pd ratings of 230watts or so. Can't remember off-hand. However, I think that the Power Follower 99 is a cheaper Class A amp to build than many others. I too don't like the idea of a cap. at the output, but I'm not too sure if it is playing havoc with the sound quality in this particular design. Atleast the designer says that they do not affect the sound quality. Thanks for the tip about the supply voltage. I may stick to about a 30volt transformer.
Thanks. I'll wait patiently till you're through with the second channel.
Freddie,
Thanks for your input. I have only done some preliminary testing with a lower voltage, bias and heatsink - all under rated. I am surprised that inspite of the adequate heatsink provided by you, the MOSFETS needed replacement. By the way, did you use IRF150s. I used IRFP250s since their Pd rating is somewhere about 180watts. If this amp sounds good enough as compared to the Alephs, then we could try to use IRFP260s (check the RS catalogue) which have Pd ratings of 230watts or so. Can't remember off-hand. However, I think that the Power Follower 99 is a cheaper Class A amp to build than many others. I too don't like the idea of a cap. at the output, but I'm not too sure if it is playing havoc with the sound quality in this particular design. Atleast the designer says that they do not affect the sound quality. Thanks for the tip about the supply voltage. I may stick to about a 30volt transformer.
Sam,
The MosFets that blew up was actually IRFP250 (Harris). Right now I'm using MosFets rated at 250W but they have a little to high input capacitance for my liking.
Yes, the Power Follower is bit cheaper to build than other Class A amps. I think it's cheaper cause it uses the 'Virtual battery' PSU (no need to buy large caps). But It's nothing more than a Source Follower with a current source. So a voltage gain stage is needed, and when you add the cost of this it becomes pretty expensive too. With other Class A amps the extra gain stage is probably not needed. But I really do think that it's a good amp, but as I said before you should use a low supply voltage if you want a reliable amp!
/Freddie
The MosFets that blew up was actually IRFP250 (Harris). Right now I'm using MosFets rated at 250W but they have a little to high input capacitance for my liking.
Yes, the Power Follower is bit cheaper to build than other Class A amps. I think it's cheaper cause it uses the 'Virtual battery' PSU (no need to buy large caps). But It's nothing more than a Source Follower with a current source. So a voltage gain stage is needed, and when you add the cost of this it becomes pretty expensive too. With other Class A amps the extra gain stage is probably not needed. But I really do think that it's a good amp, but as I said before you should use a low supply voltage if you want a reliable amp!
/Freddie
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