JA Pre and MyRef - FE Integration - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

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

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 12th June 2012, 10:03 PM   #1
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Default JA Pre and MyRef - FE Integration

While participating in the beta process for the new LM3886 based MyRef Fremen Edition power amp, I have tested several approaches to volume control. The Parasound JC-2 has been described as a “Straight Wire with Gain” solution. There are already a couple of threads dealing with this design; however the goal here is to focus on a specific offering by an established eBay supplier.

Symmetric Complementary J-FET preamplifier JC-2 kit ! | eBay

A similar product is available but I have not had any experience with the supplier.

JC-2 Preamplifier Class A Dual differential FET input PER-AMP Kit DIY | eBay

For some background on developments here at diyAudio:

Need to build JC 2 preamp

Variation on the JC-2 preamplifier

The primary reason to focus on a kit is simply the availability of a common starting point. Some forum members may prefer a more open approach. A close integration between this preamp and the Fremen Edition power amps could produce a world class combination.


Some other interesting material:
Audio Advisor Insight - Parasound JC-1 and JC-2 Back Story - YouTube
Parasound Halo JC-2 Preamp Review - YouTube

NOTE: These two links are included as general public information only. I contacted Parasound in California and received notice that the kits above are not authorized JC-2 versions, nor do they in any way represent the products and/or designs of that company. Their representative has stated there is no desire to encumber the DIY community on their part, but appreciate a clear distinction between their circuits and those being developed without official sanction. The title of this thread was to be “JA JC-2 Optimization”, but has been changed to “JA Pre and MyRef Integration” accordingly.

In any event, I think it is a killer preamp package and hope it will attract much interest.

The Floor Is Open.
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 13th June 2012, 12:13 AM   #2
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Here are some photos of my current build process. Still needs pot shaft extension, clean-up and painting.
Attached Images
File Type: jpg JCN1.jpg (54.2 KB, 957 views)
File Type: jpg JCN2.jpg (73.8 KB, 928 views)
File Type: jpg JCN3.jpg (77.6 KB, 915 views)
File Type: jpg JCN4.jpg (67.7 KB, 903 views)
File Type: jpg JCN5.jpg (85.1 KB, 888 views)
File Type: jpg JCN6.jpg (36.8 KB, 237 views)
File Type: jpg JCN7.jpg (52.9 KB, 196 views)
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 13th June 2012, 01:01 PM   #3
erin is offline erin  Australia
diyAudio Member
 
Join Date: Nov 2006
Location: http://www.makeitpossible.com/
Is there any dc offset on the output when you turn it on?
  Reply With Quote
Old 13th June 2012, 01:04 PM   #4
erin is offline erin  Australia
diyAudio Member
 
Join Date: Nov 2006
Location: http://www.makeitpossible.com/
How would you describe the sound?
  Reply With Quote
Old 13th June 2012, 01:11 PM   #5
SoIL4x4 is offline SoIL4x4  United States
diyAudio Member
 
Join Date: Nov 2011
Location: Carterville, IL
Great work so far Bob. I am very interested in this project, it may be a good alternate for me if the LN does not work out. Mating it to the MyRef FE project is a great idea too. I think having more FE RC users with a similar setup will help the group agree on the improvements of various component swaps. The price is hard to beat too. A savvy builder could probably build a finished stock unit for around $100.

Thanks Bob
  Reply With Quote
Old 13th June 2012, 01:12 PM   #6
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
One channel is showing 9.1 mV and the other is 5.4 mV. That indicates I need to adjust the on-board trimmers again. The process is clearly explained in the documentation.
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 13th June 2012, 01:28 PM   #7
erin is offline erin  Australia
diyAudio Member
 
Join Date: Nov 2006
Location: http://www.makeitpossible.com/
Sounds worrying to me. Does it drift with heat, or time?
I would not want any DC going to my amp.
  Reply With Quote
Old 13th June 2012, 01:41 PM   #8
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
erin,

From my experience using two types of LDR attenuation, a Dynaco PAT-4A, dbx 234, Carver C-1, the pre on a Lexicon usb module - this unit and the bare pot have been the cleanest and least intrusive. If I had to describe "the sound" I could only suggest a bit of "sweetening" across the entire spectrum.

EDIT: The LDRs don't introduce artifacts to my ears, but there is a bit of horizontal stage drift at the extremes of the controlling volume pot. Both the LS and LN have a balance pot to address this.

Because my eBay pot is now on the pre, I ordered these to pieces to try/compare as both a bare pot and a component of this build. Never had the highly rated Alps (also used by Parasound) so it will be interesting - assuming they are not knock-offs

ALPS 100KA LOG Stereo Audio RK27 Potentiometer Pot 1pc | eBay

1pc PCB for ALPS RK27 RK16 Potentiometer Tin-Spraying | eBay
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."

Last edited by bcmbob; 13th June 2012 at 01:56 PM.
  Reply With Quote
Old 13th June 2012, 01:46 PM   #9
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Your DC concerns are certainly valid. I can only tell you that with several sessions of continued play ranging from four to six hours, the pre has been stable and caused no problems with several MyRefs and the Fremen Eddition betas.
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 13th June 2012, 02:20 PM   #10
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Typo: The value of the alps pot ordered in post #8 is 10K not 100K
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fostex FE-206E OR FE-208 Sigma jvsb Full Range 8 10th April 2014 06:11 PM
FE 126E and FE 126EN bipole? weikertball Full Range 7 10th December 2010 09:20 PM
Clock integration, how to do it? lumanauw Digital Source 6 5th November 2009 02:10 PM
Sub integration JRKO Subwoofers 28 13th September 2006 09:29 AM
sub integration with fostex regal Full Range 4 19th July 2005 04:08 PM


New To Site? Need Help?

All times are GMT. The time now is 08:24 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2