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Old 7th May 2008, 07:22 PM   #1
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Default Advice for a new amp

Hi,

i would like to start a new interesting project.
I was first interested on building an high current version of the Aleph AX but then i came across with the F4/5'threads.

The preamplifier i have recently built is -output attenuator configuration/AC Gain- set for a maximum gain of 1.6 (+4dB).
I could rise it to a maximum of 12db (8Vpk-pk) by lowering the AC resistor down to the lower limit of 200ohm, but i don't know if it would be a proper thing to do.
I have read that in order to take fully advantages of the F4's potential, at least, a +14dB gain preamp would be required.

I have also read F5's thread but i am not so convinced about it.
It seems that the subject is not mature enough yet.
More, the amp is not a pure Class A but runs in Class B as well (i know this is not harmful but i would like to build a pure Class A).

I don't know but F5 looks like a very good but little Amp compared to the AX.

I am sure that an high current version of the aleph AX will be more expensive due to the big transformers and big heat-sinks...but at the same time..I don't know if you guys think that Aleph AX is getting a little passed by this F4/5 or what and that would be smarted to build these other designs.

I hope you guys can give me some suggestions or share with me some experience gained building one of these projects.

Thanks a lot for the attention.
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Old 7th May 2008, 11:50 PM   #2
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The F4 has about the same bias as the F5, and both operate
Class A to 25 watts or so into 8. Beyond those figures, both
are considered Class AB.
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Old 8th May 2008, 01:15 PM   #3
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would it be possible to make it run in class A for a wider range lets say 50W or so, by paralleling more output devices and increasing bias as it's been done for the aleph X without compromising the sonic signature?
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Old 8th May 2008, 04:33 PM   #4
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How about just building an F4 or 5 and see if you still feel there is a problem.
You need to gain some experience with amps. Once you have some experience, those questions may either not arise, or you will know the answer yourself.

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Old 8th May 2008, 10:15 PM   #5
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thank you for your reply.
I don't feel there is any problem with F4/5, don't get me wrong.
It's just that I like to build something more consistent (i don't like the idea of having just 2 mosfets per ch. and a small 300VA trafo and that's it).
I know, F5 is an excellent amplifier and i know there are advantages on only having two output devices and i am clearly amazed by the square wave response of that little baby.

F5 as far as it goes is a $3K product but the AXs are a much more expensive piece of equipment.
Therefore i am wondering if, by starting to build the Aleph XA version that better fits my requirements, at the end of the experience, i would gain more experience and a better power amp,well it would be great.

Obviously if the expense required to build an high current version of the AX (i am just thinking about the cost of a good 1KW plitron transofmer, big heatsinks and big reservoir capacitors.....) wouldn't be worth the final sound if compared to the performance of the F5...OBVIOUSLY i would go for the newer First Watt

I don't know if this makes sense to you.

If anybody has the possibility to share with me his opinion/ideas it would be great.
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Old 8th May 2008, 11:37 PM   #6
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What's the efficiency of the speakers you intend to drive with the amp?

Magura
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Old 9th May 2008, 01:07 AM   #7
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"What's the efficiency of the speakers you intend to drive with the amp?"

^Second

You could take the money and time to build a Aleph-X and instead build a F5 and a Aleph-3 or Aleph-J. You could even save a little more money and build a Aleph-M and top it all off with a Zen. Really though if you build a F5 on-the-cheap (though I do not condone this behavior) and a Aleph-M/J/3 you can get a good taste of the sound of both since the Aleph-X is after all related to the other Aleph's. This would also allow you to understand the workings of the Aleph circuit before you decided to attempt a Aleph-X. Besides, it is hard to lose with a Aleph and a F5 sitting side-by-side!

Cheers

James
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Old 9th May 2008, 01:21 AM   #8
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Quote:
Originally posted by JPeitzman
"What's the efficiency of the speakers you intend to drive with the amp?"

^Second

You could take the money and time to build a Aleph-X and instead build a F5 and a Aleph-3 or Aleph-J. You could even save a little more money and build a Aleph-M and top it all off with a Zen. Really though if you build a F5 on-the-cheap (though I do not condone this behavior) and a Aleph-M/J/3 you can get a good taste of the sound of both since the Aleph-X is after all related to the other Aleph's. This would also allow you to understand the workings of the Aleph circuit before you decided to attempt a Aleph-X. Besides, it is hard to lose with a Aleph and a F5 sitting side-by-side!

Cheers

James
Not to mention the fact that just about all the amps James just mentioned, works straight out of the box, not so for the AX in most cases I have seen.
So far I guess less than 20 of the 400+ AX boards from the group buy, have ended up as working amps....loads of people have some very expensive and not working projects laying around.

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Old 9th May 2008, 04:49 AM   #9
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Quote:
Not to mention the fact that just about all the amps James just mentioned, works straight out of the box, not so for the AX in most cases I have seen.
So far I guess less than 20 of the 400+ AX boards from the group buy, have ended up as working amps....loads of people have some very expensive and not working projects laying around.
A good point. The Aleph-X can be an amazing amplifier, life changing, once you get all the kinks worked out. Personally I would build a F5, Aleph-(something), and a Zen and compare them all. Three projects for the price of one. If it where me I would save the Aleph-X for the long-term, "collect parts as you go" projects list. For instance, buy a bunch of MOSFET's, match them for the A-X, then use unmatched strays for a Zen or Aleph-M...or SEWA. Just a thought but trust me, if you decide to go "all out" and build a high power Aleph-X you will have lots of support. One more thing, I would build the small "baby" Aleph-X first and then scale it from there, much less frustration down the road.

Quote:
i don't like the idea of having just 2 mosfets per ch. and a small 300VA trafo and that's it
When properly heatsinked the IFRP240 and IRFP9240 have a fairly large SOA. Sides FET's don't mind as much being warm, not like those picky BJT's. I guess the tube guy in me likes my amps warm though, my house soon to be complete with central DHT heating, keep me toasty on those cold winter nights . If you wanted you could beef up the supply, 500VA or bigger, but really no need for a 1kva or anything like this here. This is a bit different of an animal than a 100watt+ Aleph-X.

Cheers

James
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Old 9th May 2008, 01:02 PM   #10
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thanks to all of you guys for your replies.
I have B&W 805 so efficient is on the average i think something like 87dB but they sink a lot of current as many amplifier i have tried so far weren't able to properly drive it.

anyways...i would like to build a power amp that is close to the load change inviariant condition.
I know this is very difficolt if not impossible....but as far as i am concerned a good power amplifier doesn't have problem if connected to a good speaker no matter if it is a B&W or a Avalon or a Thiel or a Klipsh....or whatever

that's my point.

Somebody told me that XA that Nelson makes...the commercial product i mean...is another thing compared to the DIY version as he uses jfets and other features.
So i guess that the original XA is obviously an expensive product but i don't feel it could be the same for the AX though.....this is my two cents.

F5 is a commercial and very well studied project by NP and i am sure that it sounds nice.
I just would like to have the possibility to expand it....build a monoblock balance X version of the F5.

somebodyelse told me to look at the F5 3d for balance version...but i see some attempts....i would not consider tims's attemps as well..and there is somebody else that asks to nelson if a bridge version would be better than X'd ..but i haven't seen an actual schematic with a balanced x version of the F5.

Putting aside the idea of buying parts for a 40W and then recycle them for a 60-80 or 100W....well....which is not possible i personaly like to find a good train of thoughts and a good project to work on and continue with that till it doesn't properly work.

obviously with a modulare structure it works great to start from the baby and expand it....

hope this post my make a sense and sombody might give me some good advice.

thanks a lot.
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