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Old 14th March 2012, 09:51 AM   #201
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Location: sheffield , uk
Thanks for the advice Stephan, very useful explanations.

Can anyone comment on any (subjective) differences they have noticed in the sound after making any changes ?
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Old 15th March 2012, 08:08 PM   #202
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Quote:
Originally Posted by sgrossklass View Post
Dropping resistors for the regs. Try ~10 ohms, >=1 W.
..............................
C15/16 (220p) should already be NP0 so no improvement is expected here.
What do the red words mean?
Sorry.
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Old 15th March 2012, 11:17 PM   #203
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Location: sheffield , uk
Dropper resistors are used to drop some voltage if it is too high. They are usually connected in series. I wanted to reduce the voltage my regulators so Stephan suggested i use a dropper resistor.
UK Vintage Radio Repair and Restoration - Dropper Calculations

NP0 (zero, not letter o) refers to the type of material used as the insulator or dielectric in some capacitors. I had not realised but it seems to be considered good for audio.
EIA Class 1 dielectric - Wikipedia, the free encyclopedia
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Old 19th March 2012, 12:31 PM   #204
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Location: sheffield , uk
What is the advantage of replacing the zener with a string of 1N4148 ?
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Old 20th March 2012, 01:24 AM   #205
lung is offline lung  Germany
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Thumbs up My first post in this forum.

Hello to all.

Ordert the kit weeks ago.

Build with changes testet by MilesCampbell.
Great thanks to him.

All el-capacitors Panasonic FC other wima MKT.
Input 1UF wima MKT bypassed with 0,022UF on the solderside.

The pot will be changed to an alps.
Now i'am looking for a nice case.

Sounds great from the beginning.
Tested first with cheap earphone.
Later with DT911 250 Ohm.

This is my first diskret headamp after
some cmoy.

Now some pic.

More will follow if the amp is boxed.

Thank you all for your very helpful comments.

IMG_3765.jpg

IMG_3769.jpg

IMG_3770.jpg

IMG_3779.JPG
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Old 21st March 2012, 12:35 PM   #206
mkusan is offline mkusan  Croatia
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Location: Zagreb
Hello lung,
congratulations for your build. I was just wondering without some of the caps and variable resistors what is your DC-offset now?

Thanks
Marko
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Old 21st March 2012, 10:08 PM   #207
lung is offline lung  Germany
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MilesCampbell explains on post 152 JLH Headphone Amp

I prefer not using variable resistors. I hate them :-) .
It just works.
The caps are not necessary like in the original build.
DC offset not measured now. But will do it.

Last edited by lung; 21st March 2012 at 10:26 PM. Reason: typo
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Old 26th March 2012, 10:25 PM   #208
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Location: sheffield , uk
So I:

Bypassed the rectifier diodes with 47nF
replaced power supply caps after regs with Nichicon FG
Replaced the zeners with 3 1n4148
changed 220pF to 47pF
Bypassed the input cap with another .47uF to make 1uF
Changed 470R to 2k2
Changed the 100uF caps to cerafines
Removed the 100nF caps Miles recommended
removed the 330pF cap
added 10R dropper resistors
changed 4k7 to carbon film

Some made a bigger difference than others. Now the sound is smoother, crisper, tone is better. (all subjective of course)

I also found i could change the flavour of the sound by using different caps on the output. Silmic had more bass and layed back, Nichicon ES more detail and lively. Could even swap between depending on the recording, music, mood.

Not sure how it compares with other headphone amps as i've never had a decent one before.
Keep meaning to bypass the pot to see what influence it has on the sound but not tried it yet.
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Old 6th April 2012, 08:23 PM   #209
krasnal is offline krasnal  United Kingdom
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Join Date: Dec 2011
Hello,

I got JHL kit for ebay on my table right now. I mainly buy this for quite good pcb. Some of you written about offset issues, which rise when apm is powered up and getting low after warm-up. I was thinking instead adding dc serwo maybe it would be better add something like this:eBay - The UK's Online Marketplace What do you think?

Regards,

Michał
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Old 7th April 2012, 12:00 PM   #210
Telstar is offline Telstar  Italy
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Join Date: Dec 2007
Location: Italy
Is Miles still around?
I was waiting his findings and ideas on how to put the optocouplers for volume and how to implement an effective dc servo (out of the signal path)...

And about output transistors. The regular JLH power amp sounded BETTER with the original ones and replacements were difficult. Here we have much bigger choice and I would look into toshibas (cant help since i like the sound of them) -small power parts are reasonably cheap.

BTW it seems to me that making a pcb run of the original JLH headamp first circuit would be a good idea, maybe integrating psu and dc servo.

Lastly, how these PCB
★★Free JLH Hifi Headphone Amp PCB, 0.008% THD★★
look like to use as starting point rather than the ones on ebay?
For starters, the channels are SEPARATED and so is the psu.
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"The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
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