Hi There
I have built a couple of discrete and chip amps so far with success, but felt it time to delve into some Class-A.
The decision is which one. I have read through some of the forum posts and as a beginner I though I would go for the Aleph X, but that may not be the best starting point hence my choice of two candidates.
The F-5 or the Aleph-J due to their simplicity and move on to something more exotic later.
Now for the questions:
-Which one sounds better
-Which is the easiest to build
-Which is the cheapest to build
-Can they be bridged for higher output
-Can they be cascaded with additional output drivers
I know these are newbie questions, but you gotta start somewhere.
My partslist so far if it makes any difference
2x 300VA 18-0-18 Toroidals
2x 475VA 21-0-21 (DC) SMPS
670000uF of capacitors
Enough watercooling kit for around 600W at ambient plus 10 degrees
One last question - Is it possible to drive Hexfets with an opamp (the likes of an TL072). It was a concept Ii was toying with about 15 years back. I will post a design later if I can find the stone tablet I carved it out on.
All help and advice appreciated
Wizard
I have built a couple of discrete and chip amps so far with success, but felt it time to delve into some Class-A.
The decision is which one. I have read through some of the forum posts and as a beginner I though I would go for the Aleph X, but that may not be the best starting point hence my choice of two candidates.
The F-5 or the Aleph-J due to their simplicity and move on to something more exotic later.
Now for the questions:
-Which one sounds better
-Which is the easiest to build
-Which is the cheapest to build
-Can they be bridged for higher output
-Can they be cascaded with additional output drivers
I know these are newbie questions, but you gotta start somewhere.
My partslist so far if it makes any difference
2x 300VA 18-0-18 Toroidals
2x 475VA 21-0-21 (DC) SMPS
670000uF of capacitors
Enough watercooling kit for around 600W at ambient plus 10 degrees
One last question - Is it possible to drive Hexfets with an opamp (the likes of an TL072). It was a concept Ii was toying with about 15 years back. I will post a design later if I can find the stone tablet I carved it out on.
All help and advice appreciated
Wizard
It's a subjective toss-up, having built F5 and variations of Aleph (I've yet to fire up my built AlephJ version..currently listening to SOZ...don't want to dismantle it just yet), I personally have an affinity for Aleph. You already have the expensive parts taken care of, 18V 300VA transformers per channel are the correct voltage/size to run either. The AlephJ uses either 1x 2SJ109 or 2x 2SJ74 for inputs, both discontinued, but still available. F5; 2SK170 (discontinued) and 2SJ74 for inputs, again both are still attainable. F5 can be bridged for more current delivery, which you may or may not need. A bridged AlephJ is essentially an AlephJ-X. And I do believe both versions can have their inputs cascaded if you have higher voltage requirements. AlephJ has minimally higher parts count, you've got the hard parts taken care of, I'd say build them both. You definitely won't be disappointed with either. As for your last question, from what I've learned, yes you can, but I haven't a clue, if you post a schematic or a pic of that stone tablet, I'm sure someone will help.
-john
-john
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Thank for the reply Mega
Are there equivalent replacements for the 2SJ109 2SJ74 2SK170 & 2SJ74 that are suitable or do they have to be used.
Also when I meant cascaded I was referring to the concept below with more fet's in parallel for higher current...or am I being a numpty.
The concept I was playing on goes something like this. I know it is incorrect in many aspects, but it was all I could CAD up since my post. Criticism and/or ideas welcome. I know it is an AB amp, but I was thinking with enough bias and a decoupling cap it could operate as a class a. Either that or have a single rail suplly and run it in bridge mode. Again I am a class a newbie....sorry.
![URL]](/community/proxy.php?image=http%3A%2F%2F%5BURL%3Dhttp%3A%2F%2Fimg193.imageshack.us%2Fi%2F123zw.png%2F%5D%5BIMGDEAD%5Dhttp%3A%2F%2Fimg193.imageshack.us%2Fimg193%2F6837%2F123zw.png%5B%2FIMGDEAD%5D%5B%2FURL%5D&hash=752d3f70d453c7ec8a5067da8de03118)
If the pic doesn't show please someone tell me how.
Direct link to schematic
Imageshack - 123zw
Are there equivalent replacements for the 2SJ109 2SJ74 2SK170 & 2SJ74 that are suitable or do they have to be used.
Also when I meant cascaded I was referring to the concept below with more fet's in parallel for higher current...or am I being a numpty.
The concept I was playing on goes something like this. I know it is incorrect in many aspects, but it was all I could CAD up since my post. Criticism and/or ideas welcome. I know it is an AB amp, but I was thinking with enough bias and a decoupling cap it could operate as a class a. Either that or have a single rail suplly and run it in bridge mode. Again I am a class a newbie....sorry.
If the pic doesn't show please someone tell me how.
Direct link to schematic
Imageshack - 123zw
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Hi thanh1973
I can understand the want to avoid opamps, but on paper they have great thd performance and are easy to use...in my opinion anyway.
As far as speakers go, nothing to talk about. Incarnations I have put together myself over the years. Lets say freq response of 100hz to 10000hz at an spl of 60db per w...if you know what I mean.
The beauty of the idea is scalability if the opamp can handle the extra fets. The original had a much smaller component count and at the time seemed a good idea.
What is the reason for aversion to opamps in general. I always had them in high regards due to paper specs.
I can understand the want to avoid opamps, but on paper they have great thd performance and are easy to use...in my opinion anyway.
As far as speakers go, nothing to talk about. Incarnations I have put together myself over the years. Lets say freq response of 100hz to 10000hz at an spl of 60db per w...if you know what I mean.
The beauty of the idea is scalability if the opamp can handle the extra fets. The original had a much smaller component count and at the time seemed a good idea.
What is the reason for aversion to opamps in general. I always had them in high regards due to paper specs.
It's not that op-amps are bad...
My personal reason for avoiding op amps is their lack of ZEN. They may make the designer's life easier, but they are anything but simple on the inside. Most of the amps in the Pass forum are of a simple nature, much like your cascade--minus op-amp, and, philosophically (some would argue audibly), desirable.
I will build the simplest class a possible with op amp and thanks for the insight into the simplistic concept carpenter (makes perfect sense), but thought one component to do most of the leg work was the way forward.
Now back to the Zen approach and my initial post.
Any other feedback on the questions asked as I will be starting the parts order very soon.
Also what power supply capacitance would suffice...as I have posted I have access to virtually unlimited uF and can somebody let me know what is the best way to 'charge' them up especially if it is very high capacitance. I once designed a slow charge circuit that kicked in a relay to bypass a limiting resistor in series, but is there a better way?
Thanks again
Wizard
Now back to the Zen approach and my initial post.
Any other feedback on the questions asked as I will be starting the parts order very soon.
Also what power supply capacitance would suffice...as I have posted I have access to virtually unlimited uF and can somebody let me know what is the best way to 'charge' them up especially if it is very high capacitance. I once designed a slow charge circuit that kicked in a relay to bypass a limiting resistor in series, but is there a better way?
Thanks again
Wizard
Op Amps make me shudder. I can't get past the 741, which was "perfect"in the day. Op Amps have 60 or more db of open loop gain and 3 or more gain stages. The 741 started to roll off at 10 Hz.
There are much better op amps (or so I have been told). To me, an op amp front end would be easy to do, but very hard to do right. I think a low parts count discrete front end is the way forward.As far as capacitance, it depends on the size of the amp. For 25 Watt class A, look at the F5 and make the caps on the same order of magnitude and use the thermistors.
Hit the nail on the head
I have a few LM3875's collecting dust, they do get pulled out from time to time, but mostly to be dusted. I also have an LM4562 based line amp, it is a fairly highly regarded op amp, I sampled them from National back when they first came out and where near imposable to get. Let's just say that it was added to the dust collecting pile after about 5min of listening to a JFET Bride of Zen. The op amps may be salvaged for a cheap phono that I can through in my pocket, or they may be forever banished to my "glad I tried that" dust pile.
James
will you be water cooling the F5? If you live fearlessly then by all means....I built it this way, it worked great until I biased up to 3A @ 35V. You can parallel the outputs...which in hindsight is what I should have done from the outset. There's a schematic floating around in the F5 thread somewhere about it.
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I have to chuckle a bit. Op-amps are the standard when it comes to electronic crossovers. Many high end set-ups use electronic crossovers. I get zero complaints from my audio friends regarding my set-up.
Unless you build a discrete op-amp (and it won't come close to the specs of a commercial unit from what I've read) you're going to be listening to an op-amp somewhere in the audio chain... come to think of it, there's that CD player over yonder... and it's cousin, the DVD player... oh, let's not forget the Comcast box... my, but they sound pretty good to me.
Well to be technically correct it's not watercooling....it's a non-conductive liquid called Feser One so we shall dub it F1cooling. Use it in my PC and works a treat. At full load (around 250w) runs at ambient plus 7 degrees.
that is almost three times the designers recommended bias current.
A dissipation of 105W/Q cf 33W/Q is rank stupidity.
Did you look at the SOA of the devices you overloaded?
Did you calculate the reserve power to drive a load at that bias current?
Did you think
Maybe water cooling is a miracle worker!
skimmed over it, made a paper airplane out of it.
No calcs. Had 480,000uF, 1500VA transformer, then variac.
Totally over-rated. In the grand scheme of things, I did keep a fire extinguisher handy, so there was a least some thinking happening.
I knew full well it was on borrowed time, about 30 mins actually, and it sounded wonderful! Its DIY dude, if you're not blowing something up, you're not having fun. I did find some industrial cooling plates, so that definitely looks like the way to go.
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I love that one.
It is all about having fun, just don't set your house on fire.
Have you started building another one yet?
Go with 3 pairs this time, and then you can crank it to 9A
Well maybe not 9A. 3A to 4A is a good number.
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