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The REAL John Linsley Hood Headphone Amplifier
The REAL John Linsley Hood Headphone Amplifier
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Old 14th May 2018, 03:40 AM   #91
kimbo is offline kimbo  Australia
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Quote:
Originally Posted by EUVL View Post
There is only one way to find out.


Patrick
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Old 14th May 2018, 03:51 AM   #92
EUVL is offline EUVL  Europe
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As you have seen, if 5mm extra length on a transistor leg is the cause and cure of oscillation, then it is also highly layout dependent.
Which is why we Beta test the revised PCB by someone else, just to catch these pitfalls.
Which is also why we are so particular about layout (see the F5-HA for all those uneducated copies).

Of course I encourage you to do your own PCB for a leaded version.
But be prepared that you will have issues and that you have the skills, time and patience to handle them.

Having said that, it probably only applies to the modified version.
I trust Mr. Linsley Hood would have thoroughly tested his.
And maybe the original version is less prone to oscillation.
But it will probably also have a hard time driving low impedance loads.

So back to my previous statement, there is only one way to find out.
It is part of the fun of DIY.




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Old 21st May 2018, 08:51 PM   #93
EUVL is offline EUVL  Europe
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Glad to report that the 2nd channel has been successfully built by the Beta tester without oscillations.
So my results can be repeated.


Patrick

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Old 6th June 2018, 06:03 AM   #94
Morde is online now Morde  Finland
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At last, after the oscillation problems, I got it all together and had some time to listen to the Xen version of the JLH headphone amp. The circuit is really simple to build as you get familiar with smd soldering with only few parts in this Xen version. The DC offset on the output was quite easy to set to a level of +-10 mV and the bias was configured to 150 mA.

So here are my first impressions with a basic power supply (common for both channels). Usually my first impressions don’t change much.

It seems to be a very musical and pleasant to listen to. You easily forget yourself in listening and in no time the song ends and you have no notes about sound quality in mind. I would say that’s a pretty darn good feature for a headamp.

What else can I say... Soundstage is wide, sound signature is clear and crisp, very effortless. Bass is tight, but not quite as deep as with UTHAiM, still very good. Vocals are good but I think some contestants are better on this regard. The highs are really sparkling, but not too much.

Great design once again. There seems to be some magic with this simple circuit!

My test setup was the following:
  • Raspberry Pi with Moode Audio player software => Ian Canada's isolator board => Allo Kali reclocker board => I2S output
  • I2S input to DDDAC DA-converter (a single Tent shunt board version)
  • All music files were FLAC 16bit/44.1kHz ripped from original CDs with dB Power Amp software.
  • The volume levels were matched by feeding a 1 kHz test signal to the DAC and the voltage was measured from the headphone jack while my Audeze LCD-2 phones were connected.
  • Volume control was the same for both headamps: Arduino based LDR volume and source selection controller.
  • My headphones used for the test were Audeze LCD-2.2 Fazor
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Old 6th June 2018, 03:21 PM   #95
EUVL is offline EUVL  Europe
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Many thanks for the Beta test and the listening impressions.
Maybe some photos of your final test setup ?

The updated BoM and Gerber files will be posted in a few days.
The original JLH version using the same PCB will also be beta tested.
But this might take a while longer.


Cheers,
Patrick
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Old 6th June 2018, 07:13 PM   #96
Morde is online now Morde  Finland
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Oops, I forgot to take the photos of my test setup. I will shoot a few the next time on it. I will start acquiring parts for the original JLH version too.
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Old 8th June 2018, 06:09 AM   #97
EUVL is offline EUVL  Europe
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As promised here the Gerber files.

The Bill of Material in Post #35 has the following changes for the XEN modified version :
R13,14 -> 470R
Cf1,2 -> leave open
Rz -> 5.1R

It is important that you only use 5mm standoffs to keep the legs of the output transistors short.

The original JLH version has yet to be tested, as mentioned before.


Happy building,
Patrick

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Old Yesterday, 02:26 PM   #98
passive420 is offline passive420  United Kingdom
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Patrick, forgive me again. Just looking through the BOM for these boards and once again it's one resistor value that is difficult.

3R3 thin film resistors for R11/R12 are very hard to find even in 1206 - can these be thick film types or is there some margin to play with values for these say to 4R7?

As MELF were specified, I take it they are critical?

They are on the transistor emitters so would a certain selection of HFE allow a different resistor value?
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Old Yesterday, 03:48 PM   #99
EUVL is offline EUVL  Europe
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You can use thick film 1206.


Patrick
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