Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Variation on the JC-2 preamplifier
Variation on the JC-2 preamplifier
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 25th March 2020, 07:18 AM   #371
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Variation on the JC-2 preamplifier
Like this:

Variation on the JC-2 preamplifier-test-image2-jpg

Upload the image in the normal way and then right click the link and copy it. Paste the link into the post making sure it has image tabs wrapped around it. The link needs to be within the tags like this[IMG]insertlinkhere[/IMG]

Variation on the JC-2 preamplifier-untitled-png

Make sure the images aren't to large. You might need to experiment.
Attached Images
File Type: jpg Test Image2.jpg (80.0 KB, 337 views)
File Type: png Untitled.png (375.0 KB, 314 views)
  Reply With Quote
Old 30th March 2020, 06:42 PM   #372
Zung is offline Zung  Switzerland
diyAudio Member
 
Join Date: Apr 2005
Location: Geneva
Quote:
Originally Posted by keilau View Post
...
John made it crystal clear that this circuit needs well matched JFET for the IPS, which I doubt the e/bay version (either one) had.
For what it's worth, I've just got this headphone amp kit from Aliexpress, basically a JC-2 with different input JFets and MOS output buffers. I wasn't expecting much, but the matching of the input Fets is a BIG surprise: inside of a ziplock bag, there were 4 n-ch and 4 p-ch with a hand written label : 10.22

And so I tested them, at 9V and 25C:
  • 2SK246: 9.48, 9.42, 9.42, 9.50 mA
  • 2SJ103: 9.28, 9.38, 9.32, 9.29 mA
To me, it looks like a 1% matching! I have no idea where the original "10.22" comes from; maybe they have their testing facilities in Siberia

The seller is no longer in business, but I found another one and ordered a spare.
  Reply With Quote
Old 30th March 2020, 10:11 PM   #373
keilau is offline keilau  United States
diyAudio Member
 
Join Date: Mar 2013
Location: Windy City, US
Quote:
Originally Posted by keilau View Post
John made it crystal clear that this circuit needs well matched JFET for the IPS, which I doubt the e/bay version (either one) had.
Quote:
Originally Posted by Zung View Post
For what it's worth, I've just got this headphone amp kit from Aliexpress, basically a JC-2 with different input JFets and MOS output buffers. I wasn't expecting much, but the matching of the input Fets is a BIG surprise: inside of a ziplock bag, there were 4 n-ch and 4 p-ch with a hand written label : 10.22

And so I tested them, at 9V and 25C:
  • 2SK246: 9.48, 9.42, 9.42, 9.50 mA
  • 2SJ103: 9.28, 9.38, 9.32, 9.29 mA
To me, it looks like a 1% matching! I have no idea where the original "10.22" comes from; maybe they have their testing facilities in Siberia

The seller is no longer in business, but I found another one and ordered a spare.
My earlier quote may not apply to your new found gem. I have learned from several forum members that Chinese clone small signal JFET can work very well. They can give excellent result when well matched. Please, check the matching of the small jFET before you solder them in place. Yours seem to match very, very well. I will not be surprised if you get an excellent sounding headamp. The output MOSFET K2381/J407 may not be optimal and have high non-linearity. But they still sound fine with high feedback in the circuit.

I used an E19 board with almost identical circuit. The K2381/J407 are switching MOSFET. I am waiting for a few pairs of Toshiba 2SK2013/2SJ313 from parkit to replace them. I can't say if the improvement is audible or not because the E19 with K2381/J407 sound excellent too. I set my E19 board to 60 mA bias current which is the same as your kit. It keeps my Sennheiser HD600 and HD598 well inside class A operation. The K2381/J407 case surface go to about 40F above ambient temperature when the case is open. It should be ok in any air conditioned room. In class A, it does not get warmer even when you run the headphone in high volume. My headphone amplifier case stays 13-15 degree above ambient when closed.

Good luck and let us know how the project turns out. Do you see their headamp in a completed box? It uses 2 10000uf/60V capacitor for the PS.

Last edited by keilau; 30th March 2020 at 10:28 PM.
  Reply With Quote
Old 30th March 2020, 11:25 PM   #374
Zung is offline Zung  Switzerland
diyAudio Member
 
Join Date: Apr 2005
Location: Geneva
Quote:
Originally Posted by keilau View Post
... The output MOSFET K2381/J407 may not be optimal and have high non-linearity...
I think you're right: EUVL tested them and found pronounced thermal hysteresis. As replacements, I ordered some IRF710/9610 from Digi-key; they just came in today after some comical mishaps, compliments of UPS. I'll test them tomorrow.

There're a few things I don't like in the original kit, so I'm thinking of doing these:
  • MOSfet will be IRF's
  • Standing currents to be set at 2, 5 and 100mA: these seem to be OK on simulation
  • Add a standard +/- 18V pre-regulator to feed the board, and a mix of Silmic's and KT's (Nichicon) for smoothing
  • Add local FB to the VAS (I'm a tube guy, and the standard SS practice of applying 60dB+ of FB scares me to death)
  • Maybe change the poles & zeros as a result of the above
  • Remove the FB caps and use DC servo's instead
  • Use the matching AL box as a heatsink, with all the TO-220's bolted to it
LTspice thinks I'll get -120dB of H2 and H3; we'll see. I'm waiting for the nylon washers for the TO-220 that I forgot to order, so it'll be another month before real testing time.
  Reply With Quote
Old 31st March 2020, 12:10 AM   #375
keilau is offline keilau  United States
diyAudio Member
 
Join Date: Mar 2013
Location: Windy City, US
Quote:
Originally Posted by Zung View Post
I think you're right: EUVL tested them and found pronounced thermal hysteresis. As replacements, I ordered some IRF710/9610 from Digi-key; they just came in today after some comical mishaps, compliments of UPS. I'll test them tomorrow.

There're a few things I don't like in the original kit, so I'm thinking of doing these:
  • MOSfet will be IRF's
  • Standing currents to be set at 2, 5 and 100mA: these seem to be OK on simulation
  • Add a standard +/- 18V pre-regulator to feed the board, and a mix of Silmic's and KT's (Nichicon) for smoothing
  • Add local FB to the VAS (I'm a tube guy, and the standard SS practice of applying 60dB+ of FB scares me to death)
  • Maybe change the poles & zeros as a result of the above
  • Remove the FB caps and use DC servo's instead
  • Use the matching AL box as a heatsink, with all the TO-220's bolted to it
LTspice thinks I'll get -120dB of H2 and H3; we'll see. I'm waiting for the nylon washers for the TO-220 that I forgot to order, so it'll be another month before real testing time.
I am a lateral MOSFET person and never feel comfortable with the IRF vertical.

For the E19 I have, I use a twin LT1083 board and set it at +/-21 volts. Your amp has onboard Zener regulated PS which can be easily bypassed.
s-l640c.jpg LT1083CP_2channel.jpg
I considered DC servo at one point too. But the matched input keeps the output DC in less than 1-3 mV all the time and is stable. I gave it up.

Last edited by keilau; 31st March 2020 at 12:15 AM.
  Reply With Quote
Old 31st March 2020, 08:33 AM   #376
Zung is offline Zung  Switzerland
diyAudio Member
 
Join Date: Apr 2005
Location: Geneva
Quote:
Originally Posted by keilau View Post
.... Your amp has onboard Zener regulated PS which can be easily bypassed...
... Or converted to a cap multiplier to provide some measures of insolation against the nasties from the regulator. JC's been doing that since forever.

Quote:
... I considered DC servo at one point too. But the matched input keeps the output DC in less than 1-3 mV all the time and is stable. I gave it up.
Thanks for the data. There has been others who confirmed this. It's not the offset I'm concerned, it can be nulled out; it's the offset drift over time/temperature. I'll look into it.
  Reply With Quote
Old 31st March 2020, 10:18 AM   #377
adason is offline adason  United States
diyAudio Member
 
adason's Avatar
 
Join Date: Nov 2004
Location: Maryland
Quote:
Originally Posted by Zung View Post
For what it's worth, I've just got this headphone amp kit from Aliexpress, basically a JC-2 with different input JFets and MOS output buffers. I wasn't expecting much, but the matching of the input Fets is a BIG surprise: inside of a ziplock bag, there were 4 n-ch and 4 p-ch with a hand written label : 10.22

And so I tested them, at 9V and 25C:
  • 2SK246: 9.48, 9.42, 9.42, 9.50 mA
  • 2SJ103: 9.28, 9.38, 9.32, 9.29 mA
To me, it looks like a 1% matching! I have no idea where the original "10.22" comes from; maybe they have their testing facilities in Siberia

The seller is no longer in business, but I found another one and ordered a spare.
Thanks for the link you provided. I wonder why chinese use word 'tube' to describe transistors. Is it some stupid google translate slang? Or on purpose?
  Reply With Quote
Old 31st March 2020, 10:50 AM   #378
Zung is offline Zung  Switzerland
diyAudio Member
 
Join Date: Apr 2005
Location: Geneva
Not really "stupid", but the Chinese language has lots of homonyms/synonyms, therefore the confusion.
Try Google translate, look for "transistor": it's "晶体管", the short form is "管". Now translate it back to English, and you've got "tube", QED.
The funniest version is "bile", which actually is the short for bulb (as in lamp): 胆.

Last edited by Zung; 31st March 2020 at 10:53 AM.
  Reply With Quote
Old 31st March 2020, 10:57 AM   #379
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
晶体管 means tube made from crystals.
Which is a good description, not ?




Patrick
__________________
xen-audio.com
  Reply With Quote
Old 31st March 2020, 11:29 AM   #380
Zung is offline Zung  Switzerland
diyAudio Member
 
Join Date: Apr 2005
Location: Geneva
Quote:
Originally Posted by EUVL View Post
晶体管 means tube made from crystals.
Which is a good description, not ?




Patrick


But wait until you look into the Chinese grammar: orange is 橙, oranges is also 橙. Context sensitivity is everything, which loops back to the initial Q.
 

Reply


Variation on the JC-2 preamplifierHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
ONO variation for AX Tyimo Pass Labs 8 3rd March 2007 10:10 AM
zen variation 2 Antonello Pass Labs 1 23rd July 2002 10:07 PM


New To Site? Need Help?

All times are GMT. The time now is 08:55 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki