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JLH Headphone Amp
JLH Headphone Amp
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Old 21st August 2018, 07:03 PM   #771
philcrack23 is offline philcrack23
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Join Date: Aug 2018
My first contribution here. Am very happy about this thread. I bought only as a fun kit from eBay. This has already chosen me to my favorites because I have tried many. The experience with the offset, I have so far out that must be everything? I am very interested in it then i have some experimental opamps from my Lehmann. Here are a few pictures of me and everywhere construction site


Click the image to open in full size.

Click the image to open in full size.
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Old 28th August 2018, 06:32 AM   #772
hkknudsen is offline hkknudsen
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Join Date: Oct 2009
Hi guys, I've been lazy and ordered a finished board. I can always follow recomendations and tweak it if I like it.. I am a bit keen on this 15V / 2.1A transformer, as a couple have had problems with heat on a 30W and this should be a step up. However for the board they recommend a 12v-0-12v transformer, and this transformer will probably give more than 15V if not too heavily loaded (that is correct, right?). Could this pose a problem, there is quite a difference from maybe 16-18V to 12V?

Thanks
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Old 29th August 2018, 05:20 AM   #773
mercedese63 is offline mercedese63  United States
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Join Date: Apr 2018
Default Op-amps??

Quote:
Originally Posted by philcrack23 View Post
My first contribution here. Am very happy about this thread. I bought only as a fun kit from eBay. This has already chosen me to my favorites because I have tried many. The experience with the offset, I have so far out that must be everything? I am very interested in it then i have some experimental opamps from my Lehmann. Here are a few pictures of me and everywhere construction site


Click the image to open in full size.

Click the image to open in full size.
What's the purpose of the photo showing different op-amps?
Obviously, the JLH HA doesn't use any op-amps like the Lehmann does.
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Old 29th August 2018, 05:42 AM   #774
mercedese63 is offline mercedese63  United States
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Join Date: Apr 2018
Quote:
Originally Posted by hkknudsen View Post
Hi guys, I've been lazy and ordered a finished board. I can always follow recomendations and tweak it if I like it.. I am a bit keen on this 15V / 2.1A transformer, as a couple have had problems with heat on a 30W and this should be a step up. However for the board they recommend a 12v-0-12v transformer, and this transformer will probably give more than 15V if not too heavily loaded (that is correct, right?). Could this pose a problem, there is quite a difference from maybe 16-18V to 12V?

Thanks
Using a 15V-0-15V will only make the regulators run even hotter than they do with a 12V-0-12V transformer.
They already run quite hot with a 12V-0-12V transformer, so I would not personally use a 30V CT transformer.

Also, be sure and measure the DC offset at the outputs of your JLH example BEFORE connecting any headphones to it.
The offset can range from a few millivolts to several volts depending on the temperature of the output devices.
Without a DC servo, your precious/valuable headphones can easily go up in the "magic smoke" from the high offset of your JLH HA.

All of my JLH HAs have a DC servo and that's the only way I would even consider using them.

Be careful and happy listening!
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Old 29th August 2018, 05:47 PM   #775
hkknudsen is offline hkknudsen
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Quote:
Originally Posted by mercedese63 View Post
Using a 15V-0-15V will only make the regulators run even hotter than they do with a 12V-0-12V transformer.
They already run quite hot with a 12V-0-12V transformer, so I would not personally use a 30V CT transformer.

Also, be sure and measure the DC offset at the outputs of your JLH example BEFORE connecting any headphones to it.
The offset can range from a few millivolts to several volts depending on the temperature of the output devices.
Without a DC servo, your precious/valuable headphones can easily go up in the "magic smoke" from the high offset of your JLH HA.

All of my JLH HAs have a DC servo and that's the only way I would even consider using them.

Be careful and happy listening!
Thanks so much for input mercedese63 If you don't mind I have a few follow up questions;
- I can just as well use a 2 x 0-12V, connected at the middle, as a center tapped transformer, right? Would 30VA be enough with 12V?
- I've seen no figure for the output power, is it possible to estimate or measure? I'm specifically wondering how much power it can put into 300 ohms.

I've seen the servo recommended yes, that will be in the next round if the thing wants to make sounds at all ;-) Considering an output cap so not to risk anything until then..
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Old 13th September 2018, 09:12 PM   #776
DIP8 is offline DIP8  Italy
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Join Date: Sep 2010
Location: Italy
Good evening guys; i've received some days ago this amp and with my grado sr125e..i love it.
I burn it for almost 10 minutes ever, before connecting it because the voltage is high.

I would to ask you.. Can it be good for a pair of 250 ohms dt880? or will an A1 clone be better?
thank you
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Old 14th September 2018, 04:28 PM   #777
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by DIP8 View Post
I would to ask you.. Can it be good for a pair of 250 ohms dt880? or will an A1 clone be better?
A good JLH implementation should work perfectly fine for a DT880-250. It's not a major load on the output stage and would in all likelihood be perfectly happy with a fraction of maximum output level. Expect hitting 100 dB SPL at around -80 dB of distortion (and even that mostly 2nd) - for the most part, at least as good or better than the headphones themselves.

A more modern design would post even better distortion performance at substantially reduced idle power draw and would not require having to adjust output DC offset manually, but the JLH is good enough.

Not sure how your JLH in configured, but you can always go with a 100 ohm output resistor to emulate the Beyer amp more closely.

Quote:
Originally Posted by hkknudsen View Post
- I can just as well use a 2 x 0-12V, connected at the middle, as a center tapped transformer, right? Would 30VA be enough with 12V?
(a) Yep.
(b) Plenty. The circuit requires about 6 W and change. Even 15-20VA would do fine.
Quote:
Originally Posted by hkknudsen View Post
- I've seen no figure for the output power, is it possible to estimate or measure? I'm specifically wondering how much power it can put into 300 ohms.
Simulation suggests about 10 Vp or >150 mW, supply voltage limited. That's approaching 120 dB SPL from 97 dB/mW Sennheisers, definitely more than enough. Distortion is above -70 dB at this point, but at deafening volumes like that, who cares.
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Old 14th September 2018, 04:38 PM   #778
DIP8 is offline DIP8  Italy
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Thank you! Mine is a Chinese clone...
100 ohm in series for each channel?
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Old 15th September 2018, 04:35 AM   #779
mercedese63 is offline mercedese63  United States
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Join Date: Apr 2018
Quote:
Originally Posted by DIP8 View Post
Thank you! Mine is a Chinese clone...
100 ohm in series for each channel?
Yes, use 100 ohm for each channel instead of 2.2 ohm.
Personally, I use Vishay RN55 68.1 ohm for each channel in my builds.

My board is a Chinese clone as well, but I'm currently laying out my own board that has provisions for my DC servo board.

Personally...I think the Chinese JLH kits are simply the best value in a HA for under $20 once you add a DC servo to it to control that nasty DC offset!

The sound is PHENOMINAL for the price.

Have fun with your JLH build.
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Old 15th September 2018, 10:30 AM   #780
DIP8 is offline DIP8  Italy
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unfortunately the two led legs of led made contact. it stinks of burning.
I put a new LED but unfortunately a channel is gone
some components of the dead channel are cold...
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