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Headphone Systems Everything to do with Headphones

E19 headphone amplifier board K2381 J407 MOSFET Yuanjing Audio
E19 headphone amplifier board K2381 J407 MOSFET Yuanjing Audio
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Old 25th September 2017, 06:06 PM   #51
nattawa is offline nattawa  Canada
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Then could there be a possibility that the perceived "hysteresis" behavior in threshold was a result of the threshold Vgs being modulated by the die temperature dynamic, which is nothing out of ordinary?
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Old 26th September 2017, 02:56 AM   #52
EUVL is offline EUVL  Europe
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Same measurement for a NOS Sanyo "Switching" NMOS.
Not all FETs are created equal.


Patrick

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File Type: png Sanyo Switching NMOS.png (9.7 KB, 195 views)
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Old 26th September 2017, 03:48 AM   #53
keilau is offline keilau  United States
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Quote:
Originally Posted by EUVL View Post
A few comments, just stumbled into this by accident :

uPC1237 is meant for loudspeaker protection, and has a trigger point at +0.7/-0,2V.
One can decide whether it is high or not, but I guess most over-ear phones should survive 0.7V DC.
In any case some protection is better than none.

On 2SK2381 / 2SJ407, we got curious, bought some, and curve traced them.
They are one of the most horrible curves we have seen.
They were traced with a triangular wave form (linear current ram) at 100Hz.
So it is just normal operating condition.

You can see that the positive and negative swings followed completely different curves, with a huge hysteresis.
So that was end of story for us. The 5 pairs we bought went to the bin straight after.

You always get what you pay for.


Patrick

.
Were you able to compare 2SK2381/2SJ407 pair from US distributor? Were you able to verify that the units you got were NOT line rejects?

The 2SK2381/2SJ407 are good devices and standard units should not behave the way you measured. I am not sure what the source of the problem is, but suspect defective line rejects sold by Ebayer.
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Old 26th September 2017, 04:25 AM   #54
EUVL is offline EUVL  Europe
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> The 2SK2381/2SJ407 are good devices ...

If you say so.


Cheers,
Patrick
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Old 26th September 2017, 01:14 PM   #55
keilau is offline keilau  United States
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Quote:
Originally Posted by EUVL View Post
> The 2SK2381/2SJ407 are good devices ...

If you say so.

Cheers,
Patrick
It doesn't matter what I said. Toshiba has been making MOSFET for a long time. Yes, the 2SK2381/2SJ407 are not the proper pair and they may not be the best choice for audio output devices. But your test result looks very unusual for Toshiba device that I used.

Get some 2SK2381/2SJ407 from Digikey for your test. It is not fair to treat fake products from Ebay as the genius part.

Quote:
Originally Posted by EUVL View Post
You always get what you pay for.
I can't agree more with you on this.

Last edited by keilau; 26th September 2017 at 01:24 PM.
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Old 29th November 2017, 02:47 AM   #56
phase is offline phase  United States
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It looks like the original version of this amp is available once again;
http://diyhifishop.com/new-assembled...diy-p-216.html

The site was pretty dim a year or two ago, with nothing showing available, however it looks like that has changed...
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Old 29th November 2017, 02:20 PM   #57
keilau is offline keilau  United States
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Quote:
Originally Posted by phase View Post
It looks like the original version of this amp is available once again;
http://diyhifishop.com/new-assembled...diy-p-216.html

The site was pretty dim a year or two ago, with nothing showing available, however it looks like that has changed...
How do you know that they are active again?
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Old 29th November 2017, 09:27 PM   #58
phase is offline phase  United States
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A while back there wasnít much showing available, looks better now...

Havenít ordered from them however.
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Old 25th June 2018, 01:15 AM   #59
keilau is offline keilau  United States
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Quote:
Originally Posted by keilau View Post
Yes, I am disappointed, but NOT exactly surprised. It is the nature of getting China-designed-made electronics on Ebay. There were very high quality gems mixed among junks. I tried to identify reliable sellers and come to forum like this to get information. A few years ago, it will not be possible to assemble this professional looking headphone amp at the cost I paid. Most importantly, the amp does sound very good driving the HD598.

I could have purchased the E-5 head amp board and pre-drilled enclosure at the same total cost. I felt like being more adventurous when I bought the E19. With more effort and additional parts, I believe I can get a hum free, high quality head amp box. Wish me luck in my adventure.

The hum is barely noticeable with Sennheiser HD598, but I am very sensible to hum. With the Sennheiser PXC250 or the very old HD-420, the hum is hardly audible. As is, the E19 head amp with the filter cap for the protection circuit may be acceptable to 90% of the users. It is a fun project to add the regulated supply.
The upgrade with a regulated PS is finished. I used a simple pair of L7815/L7915. The picture show the stock form PCB vs. the modified PCB for the regulated PS. There are 4 jumpers in red for the positive PS side and one in white for the negative side.
IMG_2149.jpg IMG_4728.jpg
The good news is it works and the hum is greatly reduced to almost inaudible level. The bad news is the hum is still barely noticeable. But it is so low that I can ignore it. It took me only 2 years to finish this project. In between, I retired from my day job and moved from St. Louis to Chicago.

The sound driving a Sennheiser HD-600 is wonderful with a good depth of the sound stage. It is particularly good when listening to symphonic music where the orchestra is projected in front of me, not in the head. The regulated PS also give a more authoritative bass. The overall sound is very open and similar to the unmodified board.

The quality of the E19 PCB turned out to be very good with dual surface trace and plated through holes. It was a real struggle to removed the 4 6800uF main filter capacitors. The headphone amp did not work when I put it back together the first time. I eventually found that one of the plated through hole was damaged and cut off the 12V supply to the protection relay. I added an extra jumper and everything are fine.

One side note on the L7815/L7915 regulators. I purchased 10 of each with the intention of selecting the best matched pair. Alas, the L7815/L7915 are 0.4 volt apart on the average. The lowest 7815 output is 0.2 volt higher than the highest 7915. Fortunately, the E19 seems to have very good CMRR. Despite the unbalanced PS, the output DC offset is only 1 mV on one channel and 9 mV on the other without trimming.

The schematic of the PS that I used. It is a kit PS that I have idle on my work bench for many years.
kit83-PS_schematic.png

The E19 board has very well designed amplifier topology. The circuit board construction is very good. But the ground loop in the PCB layout is terrible as nattawa pointed out earlier.

Last edited by keilau; 25th June 2018 at 01:27 AM.
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Old 1st July 2018, 01:47 AM   #60
phase is offline phase  United States
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What are you using for main filter capacitors?
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