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JLH Class A headphone amplifier
JLH Class A headphone amplifier
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Old 23rd October 2010, 02:47 PM   #21
heliguy is offline heliguy
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Join Date: Oct 2010
Hi
I have just ordered one of these JHL amps from the same ebay source.
After reading this I'm a bit concerned. do I need to make this servo before using with my nice headphones and if so could it be explained in simpler terms. I'm pretty good with a soldering iron but have little or know knowledge of electronics.
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Old 25th October 2010, 12:42 AM   #22
oohms is offline oohms  Australia
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You could use a bipolar capacitor at the output, if you don't want to build the servo.

I wouldn't recommend using the amp without one, especially with expensive headphones
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Old 25th October 2010, 07:16 PM   #23
AndrewT is offline AndrewT  Scotland
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Hi,
the output cap blocks the DC bias that is on the output of a single polarity supplied amplifier.
It does not need to be bi-polar, a polarised electrolytic will do and with the bias voltage will operate better than an unbiased electrolytic at passing the audio signal.

If you increase the output offset from 0.1V to let's guess, 0.5V the electro will perform reasonably well.

Use this as a temporary/experimental measure and listen to it.

If you decide to try the DC servo, you can listen and research at the same time ready for the small modification that is required to add the servo to the circuit.
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Old 25th October 2010, 07:41 PM   #24
heliguy is offline heliguy
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thanks guys
thats the plan, to start with this and experiment while I learn.
So I need a polarised electrolytic Capacitor, can you suggest any values or maybe a part number? and how would I integrate it into the circuit?
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Old 25th October 2010, 07:56 PM   #25
AndrewT is offline AndrewT  Scotland
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Hi,
the cap value determines the LF response of the amp/speaker combination.

Use C=1/[2 * Pi * Rload * Freq]
Aim for freq lower than 10Hz and Rload = headphone impedance in ohms.
C will come out in Farads. Multiply your Farads answer by 1million (10^6) to get a microFarad (uF) value. 16V or 25V should do for headphone use.
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Old 25th October 2010, 08:55 PM   #26
heliguy is offline heliguy
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so that comes out at approx 420uF for 38ohm and 10Hz
and 840uF at 5Hz,
So I should go for something around 500uF that would bring me in just under 10Hz
did I do that right?

Thanks again I really appreciate you guys taking the time to help.

If someone would like to explain how this works I'd love to know.
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Old 26th October 2010, 11:48 AM   #27
AndrewT is offline AndrewT  Scotland
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Hi,
the caps usually come in E6 values: 1, 1.5, 2.2, 3.3, 4.7, 6.8 and decade thereafter.
You could use a 470uF or 680uf or 1000uF. I would be tempted to try both 470uF and 2200uF to hear if there is any difference. They will both be very cheap.

Once you know that you like or dislike listening through the capacitor you can decide whether you want to try a high quality Audio Electrolytic that could be anywhere from twice as expensive to ten times as expensive or go the servo route.

The capacitor is wired in series between the amplifier output and the output socket for the headphone. One cap to each channel.
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Old 26th October 2010, 05:52 PM   #28
ashok is offline ashok
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JLH Class A headphone amplifier
Default Read what's on thi sthread to get additional info on JLH headphone amps

Check out this thread.
http://www.diyaudio.com/forums/headp...phone-amp.html

I tried both single supply with output capacitor ( potentially fail safe ) and the split supply without output capacitor. Both sound very good and I didn't find the offset anything to complain about. It was very low.

Cheers.
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Old 27th October 2010, 05:14 PM   #29
krelac is offline krelac  Norway
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Question capacitors

Hi guys, my knowledge of electronics is very poor L
Iím surprised me with this problem. I recently bought a JHL amp from the same source on E-bay in order to use it with my Grado SR60i (32ohm).
I see that the use of JHL amplifier is not recommended without building servo. I'm not so skillful to make a servo but I could try with two ELNA SILMIC II 25V 1000UF Capacitors or something like this.

Im just not shure if I understood right? I should use capacitors like:

- 470uF or 1000uF or 680uf or 2200UF. ?????
- 16V or 25V ?????
-
integrate capacitors between the outputs on the amplifier and headphone jack (one for L and one for R)?(from amp thru cap to headphone?)

Has anyone tried this already? How does that sound?
Thanks

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Old 27th October 2010, 05:16 PM   #30
krelac is offline krelac  Norway
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Join Date: Aug 2010
Location: Sandefjord
Hi guys, my knowledge of electronics is very poor L
I’m surprised me with this problem. I recently bought a JHL amp from the same source on E-bay in order to use it with my Grado SR60i (32ohm).
I see that the use of JHL amplifier is not recommended without building servo. I'm not so skillful to make a servo but I could try with two ELNA SILMIC II 25V 1000UF Capacitors or something like this.

Im just not shure if I understood right? I should use capacitors like:

- 470uF or 1000uF or 680uf or 2200UF. ?????
- 16V or 25V ?????
-
integrate capacitors between the outputs on the amplifier and headphone jack (one for L and one for R)?
(from amp thru cap to headphone?)

Has anyone tried this already?
Thanks


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