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Pls recommend a good class-A
Pls recommend a good class-A
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Old 27th June 2005, 12:36 PM   #1
goldyrathore is offline goldyrathore  India
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Cool Pls recommend a good class-A


Where can I find a good class-A (solid state) with a clean output of 25-30 Watts.

Thanks in advance,
Audio enthusiast/hobbyist
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Old 27th June 2005, 12:46 PM   #2
Stuart Easson is offline Stuart Easson  United Kingdom
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Default You want to build these?

Assuming you are talking about DIY, solidstate...

Zen v4
Aleph 3 clone
Krell KSA clone

These are all really great amps, they have different strengths, weaknesses etc. You'll want to read peoples comments to find which could be the amp of choice for your needs.

There are probably others, if you perform a forum search for these you'll find many people who have built and are building them here.


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Old 28th June 2005, 04:27 AM   #3
amplifierguru is offline amplifierguru
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Hi goldy,

Here's one that's -

FET cascode input
comp MOSFET output with thermal comp.
DC coupled so no capacitor smearing
low cost low parts count
minimum Class A power consumption
can revert to class AB when you get your power bill!

A bit fiddly to set up
some DC drift.
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File Type: png class a.png (3.3 KB, 1621 views)
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Old 28th June 2005, 04:48 AM   #4
Mark A. Gulbrandsen is offline Mark A. Gulbrandsen
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If thi is your first amplifier constriction project than either the Aleph Mini, Aleph 3, or the he Krell KSA-50 clone are really pretty easy. They are very different sound amps though so investigate before you build. The nice thing about the Krell, the Mini, or the 3 is that they do not really require any super accurate transistor selection to get excellent results as long as you get all your devices from the same lot code.

Investigate, build, listen, enjoy!

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Old 6th July 2005, 09:10 PM   #5
chicco_36 is offline chicco_36  Macedonia
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Default To amplifierguru

Your fet amp schematic is very interesting. Iím planning to build this amp, even did pcb layout in the Eagle wich wasnít hard at all. Can you give me (us) more info for successful results, like what else must be on the heatsinks except output transistors, and resistor values for safe class AB operation?
Also, wich diodes to use and right value of one resistor?
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Old 7th July 2005, 12:53 PM   #6
AKSA is offline AKSA  Australia
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I agree Chicco_36,

This simple design of Ampguru's elegantly solves many of the usual issues in audio amp design.

I think it's very clever, and it's simplicity and originality shows considerable depth of thought about the problem.......

Congratulations, Ampguru!

Now, how does it sound, and what are its strengths and weaknesses in Class AB?


Aspen Amplifiers P/L (Australia)
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Old 7th July 2005, 05:28 PM   #7
jcx is offline jcx  United States
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are we looking at the same schematic?

amplifierguru's "elegant" single ended circuit has an output Cap! -talk about "capacitor smearing" - has to be an electo for 8 Ohms load (typos happen, I expect 100 mF was meant) - electros are much worse in measurable distortion than the polypro or even polystyrene you could use as an input coupling cap with a fet

without input offset or other adjust for bias the amp will be very "fiddly" to avoid offset from fet idss distribution eating into output swing - show pots or tell where Rs need triming
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Old 7th July 2005, 06:43 PM   #8
tschrama is offline tschrama  Netherlands
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here's a dc coupled version... I think the original auteur didn't mean cap-coupled amp.. but to make use of the pinch-off voltage of a JFET.. now dc out is minimal...
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Old 7th July 2005, 07:59 PM   #9
Geoff is offline Geoff  United Kingdom
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Originally posted by jcx
are we looking at the same schematic?

amplifierguru's "elegant" single ended circuit has an output Cap! -

I think you will find that the 8R+100nF is a Zobel network and that the speaker is in fact direct coupled to the top end of the 8R resistor.

An output electrolytic should not be used on a dual supply rail amp due to the lack of a dc polarising voltage (unless of course the output is deliberately set to give a dc voltage, but then you would lose some output voltage swing).
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Old 8th July 2005, 01:10 AM   #10
jcx is offline jcx  United States
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there are a couple of schematic conventions to to avoid such confusion, simply extending gnd and output wires beyond the zobel would be a clue, attaching a R named Rload is definitive

nonpolar electrolytic output caps are preferred acording to Bateman, they have several times lower distortion than polar electros, even if the polars are biased

without output cap I would be suprised the cirucit would be safe without a regulated supply
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