| Stefanoo |
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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| Nelson Pass |
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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| Stefanoo |
| 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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| Magura |
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.
Magura :) |
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| Stefanoo |
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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| Magura |
What's the efficiency of the speakers you intend to drive with the amp?
Magura :) |
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| 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 |
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| Magura |
| 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.
Magura :) |
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| JPeitzman |
| 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 :devilr: . 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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| Stefanoo |
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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| JPeitzman |
| quote: | | 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. |
I am sure there are other little things that Mr.Pass sneaks in there add that last little bit of magic that are in all his amps. The newer ones (the XA___.5's) as far as I know, and Mr. Pass or anyone else feel free to correct me, use a variation of the UGS. There is info on this on the forum and versions have been built using scraps and crumbs dropped along the way by Mr. Pass. However an official schematic of the UGS has not made it out of the Pass Labs camp. They do use use JFET's at the input and make interesting use of current mirrors. There is no reason though that you couldn't build a Aleph-X with JFET inputs, think Aleph-J or Babblefish X'd.
http://www.6moons.com/audioreviews/...s/open3_big.jpg
^^Close up of the input section on the new XA30.5. The UGS are the two raised piggy-back PCB's in the foreground with the JFET pairs right in the dead center.
| quote: | | obviously with a modulare structure it works great to start from the baby and expand it.... |
Yes and when you build it like this it allows you to get to know the circuit and understand it's workings. Even if you didn't build a little XA and expand it I think it would be a good idea to build one anyways or a regular Aleph. This way you minimize the chances that you will end up with hundreds of $$$ of parts, lots of headaches, 24+ matched MOSFETS, and a warmly buzzing box (amp) that doesn't do much. Knowledge is power.
Of course I fully support the "jump right in head first" way of building, that is the way I started :D .
| quote: | | ...as i am concerned a good power amplifier doesn't have problem if connected to a good speaker no matter if it is... |
Even though some amps are better suited for some speakers I agree with this completely.
| quote: | | hope this post my make a sense and somebody might give me some good advice. |
Makes sense to me perfectly, as for the good advice, I don't know if I can help in that department :) .
Cheers
James |
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| Stefanoo |
thank you very much for your kind answer.
the picture is really helpful.
A good 3d about UGS is this one, but there are many other
http://www.diyaudio.com/forums/show...25&pagenumber=5
with regard to the AX-J 's 3d i am following it with great interest but it's not getting to a specific point yet.....unfortunately.
then...with regard to the AX with UGS at the input...i don't fully understand how to connect them in order to drive the stack of output devices.
where would i find some good ideas on how to do that?
and....weeelll...eheheh....UGS modules use 2k389s and 2sj109s...i obviously don't have then nor a way to get them anywhere since they are definitely out of stock.....so......what would i use in place of them?
thank you very much for your advice |
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| Stefanoo |
ah just one last observation.
on the shot of the 30.5 you have attached i can't see any coupling cap ( i don't know if that orange think is cap or something else)...but in the X2,3 service manual...the preamplifier uses the UGS modules and the pre needs the coupling caps at the input and outptut and since it uses two stages....ehehe....there are too many coupling capssss.......anywayss....why does the amplifier look ike iut has none and the preamplifier lots...and they still use same module??
and...why do you guys think there is the need to have this module on a separate board? |
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| Nelson Pass |
Whether you see it or not, you can be assured that the cap is
there. Can you make an amp or preamp without it? Of course
you can.
We put the core of the circuit on modules for QA and service
purposes. It's a lot easier to pull a defective circuit than to tear the
whole amp apart. |
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| GRollins |
Nearly everything I do is modular. The amp I've been fiddling with has separate boards for rectification & first cap bank, front end rail boost and regulation, output rail regulation, etc. Naturally, the audio gets its own board. That way I can revamp portions of the circuit without having to redo one massive circuit board.
Grey |
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| macka |
I agree with the module idea based on recent experience.
Stefanoo,
My recommend is to build the F5 and see how you go.
iMac |
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| Stefanoo |
| quote: | Originally posted by Nelson Pass
Whether you see it or not, you can be assured that the cap is
there. Can you make an amp or preamp without it? Of course
you can.
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ehehehe....can't you?.....of course you can........look at the F5 NO CAPPPSS!!!
:cool: |
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| JPeitzman |
| quote: | | hen...with regard to the AX with UGS at the input...i don't fully understand how to connect them in order to drive the stack of output devices. |
.
http://www.diyaudio.com/forums/show...3&highlight=UGS
May give you some ideas, take a look at the attachment in the first post. BTW the UGS blocks used in the project are described more here:
http://www.diyaudio.com/forums/show...0&highlight=UGS
| quote: | | and....weeelll...eheheh....UGS modules use 2k389s and 2sj109s...i obviously don't have then nor a way to get them anywhere since they are definitely out of stock.....so......what would i use in place of them? |
Matched 2SK170/2SJ74, J310/J271(?), others may be able to weigh in more on this. That is what I would recommend.
Sorry to be OT but I was reading the linked thread that Stefanoo posted on UGS and came to this :
| quote: | | /pass/: doesn't like surface mount because he can no longer see the parts. |
-Mr. Pass
Maybe it is because it is 2:15 in the morning here and I am not thinking clear, maybe it is because this reminded me of my dad's dislike of SMD, but for some unknown and probably stupid reason this tickled me in a very funny way :clown:
Cheers
James |
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| Stefanoo |
i don't know if this is a stupid idea or not....i'll just throw it.....hope you guys won't laugh at it.....ehehe.....
i was thinking....would it be a bad idea of using the F5 output stage drive it with the UGS module with the super symmetry configuration at the front end?
Do you guys think it would be a nice idea? |
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| Stefanoo |
wow!
it's a great schematic.
I was trying to do something like just few minutes ago as i was playing around with spice.
That looks like the F5 output stage with the UGS.
feedback through R85/84. (there's no value...what value for the two resistors would be more approipriate?)
Is that a current feedback, right?
What voltage value for the output stage?
the higher it can be handled the better?
is this a Class A design?
has anybody ever tried to build such a nice elegant design?if so, with what results?
thanks a lot jacco for the link. |
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