JLH 10 Watt class A amplifier

minek123, Thanks!
but in the shown circuit there is no correction capacitor of 100 pF, without it the circuit is inoperable. And with a capacitor, the signal propagation delay time is 1.2 μs, which is 150 times longer than required by the Hafler criterion (SWDT). Therefore, it is not surprising that such an amplifier is idle in the garage.
This is a typical Douglas Self amplifier. Transfer to class A eliminated only switching distortions, while other types of distortions responsible for sound quality remained unchanged. Therefore, this is a useless stove (heater)
 
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gerbers and pdfs
Hi Prasi,
I want to have this pcb produced in jlcpcp. But I have to pay an extra fee because of the ear flaps on the side. Can you edit the gerber file?
 

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Rallen

Member
2010-06-09 4:48 pm
I get a quite loud pop/thump when turning off my JLH69 connected to a pair of high sensitivity speakers.

Was about to order a speaker protection circuit, but then I realized that it probably wouldn't work, since all it does is add a delay before turning the speakers on.

Is there anything else I can do to avoid the loud sound at power off?
 
I get a quite loud pop/thump when turning off my JLH69 connected to a pair of high sensitivity speakers.

Was about to order a speaker protection circuit, but then I realized that it probably wouldn't work, since all it does is add a delay before turning the speakers on.

Is there anything else I can do to avoid the loud sound at power off?

The loud thump in your speakers could be caused by DC from the amp, which is normally blocked by the output capacitor. There is a possibility of a leaky output capacitor, especially with old or worn electrolytics.

My guess is there is a slight DC leak from the cap, and the thump is caused by the DC collapsing when power is disconnected. Probably only picked up by sensitive speakers.

Measure the output of your amp and you should not get any DC if your capacitor is working. Change is cap if you detect DC. Or check polarity, I've got that wrong on occasions.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Is there anything else I can do to avoid the loud sound at power off?

Yes, you need a 'proper' relay delay circuit that not only gives a delay but that also drops out instantly. These are usually done by detecting removal of AC and so they disconnect the speakers in just a few milliseconds.

This is one I use by Doug Self from the mid 90's. Easily modifiable and tweakable to suit different supply and relays.

Screenshot 2022-07-12 060321.jpg
 

Rallen

Member
2010-06-09 4:48 pm
Thanks for all the suggestions! Much appreciated.
Will probably start by swapping the output capacitors, since I mean to try that anyway..

The loud thump in your speakers could be caused by DC from the amp, which is normally blocked by the output capacitor. There is a possibility of a leaky output capacitor, especially with old or worn electrolytics.

My guess is there is a slight DC leak from the cap, and the thump is caused by the DC collapsing when power is disconnected. Probably only picked up by sensitive speakers.

Measure the output of your amp and you should not get any DC if your capacitor is working. Change is cap if you detect DC. Or check polarity, I've got that wrong on occasions.

I have a pair of these lying around. I suppose they would be ok for a start?

Mundorf Mlytic AG 2200uF

https://www.audiohobby.eu/en/mundor...lytic-ag-glue-on-2200-uf-63vdc-125c-2pin.html
 
I'm listening to this amp(JLH 69) for more than a week and i must say this amp is divine! This is my first class-a & i'm really impressed. The only problem is it produces a lot of heat :irked:
That's the charm of the A class. Once you get used to it, it's hard to replace it with something that heats less;)
 

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If energy efficiency is the top criteria, then it has to be class d driving in-ear monitors.
A crime to listen to speakers with any amp, in comparison.

Or just use your smartphone directly ? :)


Cheers,
Patrick
not a bad idea (necessarily) to listen from my phone, but I can't connect my cd-player nor my turntable or my cassete deck.
Cheers