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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old 10th May 2012, 08:24 AM   #2441
MagnumOpus is offline MagnumOpus  Norway
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Quote:
Originally Posted by jacobthellamer View Post
My JLH is all cased up and running well



JLH 10 Watt class A amplifier-imgp8220-jpg

Looks pretty good

Where did you get the casing and what psu are you running?

Kenneth
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Old 10th May 2012, 08:36 AM   #2442
jacobthellamer is offline jacobthellamer  New Zealand
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Quote:
Originally Posted by MagnumOpus View Post
Looks pretty good

Where did you get the casing and what psu are you running?

Kenneth
Cheers Kenneth

2 simple power supplies. Each has a 160VA transformer, bridge rectifier and as much capacitance as could fit in the case/budget.

Case:
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Old 10th May 2012, 09:35 AM   #2443
mikelm is offline mikelm  England
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Very Nice Implementation
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Old 10th May 2012, 09:41 AM   #2444
homemodder is offline homemodder  Portugal
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Some time back I suggested someone try an improvement to the circuit as JLH proposed in one of his books. Anyone try it yet ??

(Use of CFP for phase splitter).
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Old 10th May 2012, 09:32 PM   #2445
philpoole is offline philpoole  England
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Jacobthellamer
Nice case! really nice finish.

I'll post some pics of mine soon. It's been sanded down and painted black, its a bit too big, but after reworking the grounding a bit ( a star of stars, rather than a large bus bar arrangement), and snubberising, it has much lower hum.

Homemodder; I've been reluctant to try the CFP for the phase splitter because it may well oscillate (I used a CFP in a preamp recently, and found oscillation a problem), and I'm quite happy with mine as is for now. I also assume JLH would've used a CFP it he thought it would be suitable.
But a reasonable suggestion - if you can get it right.
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Old 11th May 2012, 07:05 AM   #2446
sonata149 is offline sonata149  Malta
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Hi all, thanks for an interesting and informative thread (long, huh!) even if a chunk of it is beyond a newbie like me. Anyway, a couple of days ago I finished my first Class A transistor amp (!) in the form of JLH's 1969 single-rail circuit. I used one of the kits available on ebay.

After much fiddling of the pots I finally got it working at 27V, 1.2A (approx.) as recommended on the seller's instructions. For PS I'm using an 350W-27V switch-mode ps followed by 3x 22uF/40V caps. The sound I'm getting is good but I'm worried that after some time (particularly when changing records /CDs) the ps fan switches on and runs for about 30 secs. This happens while the heatsinks are warm but not at all hot. Isn't this a sign that something is being stretched beyond its limit? Is this normal for an smps with this Wattage on such an amp like the JLH?

This reminds me that during setting-up the mA-meter used to beep and finally shut off and I have to start the process again. The beeping is a sign of overload, no? Usually, when this happens (but not always) the fan switch on and stop some time later.

My worry is that something could be wrong which might damage/destroy my (costly) speakers. Are there any checks which I can make (with a multimeter pls) to put my mind at rest?

Thanks for your help.
Regards.
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Old 11th May 2012, 08:48 AM   #2447
Jonathan Bright is offline Jonathan Bright  Australia
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If you are using the 1969 single rail supply version there should be no problem for your speakers. The amp will have a coupling capacitor (around 2,500uF or more) and that should protect them from DC faults. I can not comment on the PS. I haven't used that type. Cheers and good luck, Jonathan
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Old 11th May 2012, 10:41 AM   #2448
sonata149 is offline sonata149  Malta
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Thanks Jonathan for your reply. I can live with the fan switching on for a few seconds as long as I know the speakers are protected. Maybe someone who is using an smps (Nico Ras?) will report if he's experiencing the same phenomenon.
Regards to all.
Joe A
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Old 11th May 2012, 11:16 AM   #2449
john65b is offline john65b  United States
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You could turn your bias down a bit if you think your overloading your SMPS.

I have four 65W Laptop "Brick" SMPSs running a 2 channel First Watt F5 and acually stress the power supplies less than a running laptop.
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Old 11th May 2012, 12:06 PM   #2450
mikelm is offline mikelm  England
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your supply appears to be running well within it's stated specification - I suspect the fan is just a normal part of it's operation - so I think you do not have to turn down the current as long as your heatsinks are not too hot - and as long as the noise of the fan is not annoying you.

I just wonder how quiet the o/p of your SMPS is so I would be tempted to try a small choke between two of your caps for a final CLC filtering stage - might improve the sound.
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