Class A low power (5-10w) amp suggestion needed - diyAudio
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Old 21st February 2010, 08:22 AM   #1
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Default Class A low power (5-10w) amp suggestion needed

Hi all,

I'm building 3-way active xover speaker systems and stuck on selecting simple and quality amplifiers for duty of amplifying tweeters and midranges.
Not much power is neede in such duties, but quality is required.

Currently i'm using lm3886 chimp amps for all ways, but i think 50w is way too much, and although the chipamps are nice quality, i'd like to try going real solid state class A, without feedback if possible.

The power supply i have is giving 34v per rail (25v unrectified), 400va.

I'd like to stick to already made boards, because i can't make the boards on my own.


Thanks!
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Old 21st February 2010, 09:46 AM   #2
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The two that come to mind are the John Linsley Hood 10 watt Class and the Nelson Pass ZEN series. The JLH is just about to celebrate its 41st birthday but is still going strong. These two are originally single supply amps but with multi amping a small protective cap feeding the speaker can be made part of the cross over and the output cap dispensed with etc. (The later 1996 JLH came in split rail form.) The nice thing about both these is that the bugs have been ironed out of them. An exhaustively thorough website for the JLH can be found by entering "Class A amp" in Google and you'll find that it comes up pretty soon. Geoff Moss runs that. There is a thread here dedictaed to it with something over 10,000 posts. The Pass section of this forum is similarly detailed about the ZEN series.

I am not personally familar with the Pass design but both are highly regarded.

Edit: I think boards for both are available but both are v.simple and the JLH can certainly be made without a board by using point to point or "rat's nesting" to use the more formal expression....!

Good luck, Jonathan
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Last edited by Jonathan Bright; 21st February 2010 at 09:50 AM.
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Old 21st February 2010, 10:37 AM   #3
Hurtig is offline Hurtig  Denmark
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I would also go for the old JLH design. I have build this design again and again... Very simple and always seems to surprice me. It really does something special. Only problem is the lack of control in the low frequency area. But if you are going to use it for tweeters only, this is no problem. Then you can also replace the large electrolytic capacitor in the output, by a small film capacitor.
This amp will give you "bang for the buck" like nothing else!
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Old 22nd February 2010, 06:22 AM   #4
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Default ...now that you mentioned JLH

Good day,

my JLH have been running (and heating my room in this tropical country) for the past six years. it's the 1969 design with dual rails, no output capacitor, I will not forget Rudy Van Stratum for this.

It has given me big pleasure in music 'till now. I did'nt know if anyone has tried but i recently discovered that by using tube buffers these amp sounded marvelously warm & "tubey"!!!

Great for those with inefficient drivers, as the JLH has 10W, compared to a SET that has 3-5W output, plus you'll be needing costly horn loaded, highly efficient drivers, unless you have a very healthy bank account

Best Regards

efren
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Old 22nd February 2010, 06:41 AM   #5
h_a is offline h_a  Europe
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Hi s3tup,

I'm doing exactly the same ;-)

For tweeters I'm going to build in the next days a low power ClassA Krell-clone with about 15W ClassA and low feedback.

If everything works well, I will offer boards.

Have fun, Hannes

PS: your toroid is not well suited for low ClassA-power amps as the rails are too high. Maybe you want to continue to use a chipamp for midbass?
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Old 22nd February 2010, 08:50 AM   #6
wahab is offline wahab  Algeria
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a simple or symetrical differential amp with bias in class A is IMO
the best solution.
It will wipe out the JLH or almost any Nelson pass s "wonderful things"...
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Old 22nd February 2010, 08:53 AM   #7
danzup is offline danzup  Romania
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DIY Class-A 2SK1058 MOSFET Amplifier Project
best for you !
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Old 22nd February 2010, 10:37 AM   #8
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s3tup, you might look at De-Light it,s the new zen type amp from Nelson, so simple it doesn't need a circuite board. You can easly use your transformer for the required 60V dc.
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Old 22nd February 2010, 10:53 AM   #9
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Might as well add Glen's K10A Hybrid amp :
The Kleinschmidt 10A

Rotten shame that Glen Kleinschmidt recently decided to skippy these premises, but there are plenty of people left who have Glen's email adress in case you'd like to contact him for the K10A files.
Afaik, Glen sold all K10A boards of his 50 PCB run, but the single-sided board is easy to etch/drill yourself.
Other alternative is asking/posting for K10A boards, usually only a small fraction of distributed boards are put to use, most end up in a drawer to wander off in oblivion.
Your 25Vac transformer would fit right in.
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Last edited by jacco vermeulen; 22nd February 2010 at 10:56 AM.
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Old 22nd February 2010, 11:00 AM   #10
Telstar is offline Telstar  Italy
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If you are going for the JLH for the tweeters, use the '69 version, not the "updated" ones, since they ruin the excelleng HF performance of the original circuit.
The NOS output mosfets are possible to find with a little research.

It is not zero NFB, but the sound comes close to that.
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