Yet Another JFET Phono Preamp - Page 11 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, 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 25th October 2010, 05:24 AM   #101
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
See, we did a little back-and-forth on noise, and the concept morphed at bit - didn't take long, either. I'm adding positions for LEDs on a PCB I'm designing for the current-injection concept (an update to the old "All American" board with room for Russian polystyrenes, which are nice, but kinda klunky).
  Reply With Quote
Old 8th November 2010, 02:26 AM   #102
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
Here's response curves for the RIAA circuit that was posted at the beginning of this thread. The actual board is shown in post #33. Gain matching between the two sides is right on par. This preamp and its accompanying lineamp should have made to Burning Amp last Saturady, but events conspired against me. I'm hooking the box back into my living room ststem tonight to see if I've exorcised all the demons (large and small) that have been plagueing me. I may have to replace the source selector switch, but that's just grunt work.
Attached Images
File Type: gif COMP_RIAA_RES.gif (114.8 KB, 231 views)
  Reply With Quote
Old 8th November 2010, 03:32 PM   #103
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Are they a bit ''hot'' at 20k? Cant be sure I read it well. *-19.6dB ref 1k is the textbook level at 20kHz.
  Reply With Quote
Old 8th November 2010, 05:37 PM   #104
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
The networks have the 50 kHz zero for "cutter compensation", so as a consequnce, the 20 kHz may be a bit high. I'll have to check. First on my agenda, though, is replacing a no-good source selector switch.
  Reply With Quote
Old 8th November 2010, 05:47 PM   #105
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
I haven't had good HF whenever I tried the ''cutter'' alignment both in valve and Jfet open loop phonos. Bright. Was playing with a TAG McLaren gimmicky BJT phono once, had a front plate button for that extra constant also, so I could readily A/B it. Bright.
  Reply With Quote
Old 8th November 2010, 06:23 PM   #106
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
If you're running an MC cartridge, maybe the extra HF attenuation makes a difference. I've still got the Grado Gold, which is probably between an MC and the usual MM cartridge in terms of response. It's easy to short across the extra resistor in practice, and I may try it once I get other pressing concerns out of the way. What I want to do at this point is wire in a new selector switch to my preamp box, as the one I'm using flat doesn't work (or is intermittent) for some reason. Once everything is running, I'll want to take some time to get used to the new box, as I've already had some indications that It'll change the sound of my system yet again, probably for the better.
What I've done in the go-round is to pair up the RIAA preamp with a "Liniac-Like" lineamp with gain. Once I get things configured to my liking, I'll be able to mix and match preamp and lineamp modules without a whole lot of fuss.
  Reply With Quote
Old 8th November 2010, 06:29 PM   #107
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
MMs droop. I run a low MC 250uV. Those peak. My best fun with MM is a 100kOhm trimmer and no extra pF for input load. Matches them pretty good for response after hunting high and low. 47k + pF cap is inadequate. Especially for Grado. I would play between 10k-22k for a Grado.
  Reply With Quote
Old 8th November 2010, 07:16 PM   #108
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
I did a simulation with the Land R values of a Grado and came up with 16k, which is what I'm using for a default value. Once things are settled down, it's time to break out the test record...
  Reply With Quote
Old 13th November 2010, 04:13 AM   #109
diyAudio Member
 
wrenchone's Avatar
 
Join Date: Feb 2004
Location: Silicon Valley
The attached schematic shows one side of another module I've just finished based on the "current boosted common source" principle introduced in the "All American" thread, reiterated here. It's a somewhat simpler version of the All-AM, as it uses a PN4391 jfet instead of a ZNN3306A mosfet in the second amplifier stage, making biasing a bit more straightforward. I also omitted a source follower in the output stage, as it is going straight to a 50k pot. You may choose differently. I originally was trying to use the PN4391 in both the input and output stage, but found the J110 fet a little easier to bias in the input stage. I chose a J110 matched pair that required relatively high bias current to keep the distortion down.

I tested the gain-phase of both sides, and they matched to within 0.5dB - not as tight as my last effort, but still ok. I'll post the scan results when I get back to work Monday, as I didn't get the chance to scan the paper results into the computer. I suspect that the difference is one of absolute gain between the two sides rather than tracking differences between the two RIAA filters, as the filter components are matched very well.

The power supply used is different than the one shown in the beginning of this thread, using a current mirror loaded 2SJ74 diff pair and LED voltage reference instead of the zener-based reference shown at the beginning of this thread. This will be a test of the supply as well as the amp circuit when I load it into my preamp box.
Attached Images
File Type: gif ALL_AM2.gif (16.5 KB, 164 views)
  Reply With Quote
Old 13th November 2010, 07:59 PM   #110
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Looks populated enough at first glance when its very utilitarian in essence and well bound electrically. Will you be passing it through AP2? Any early impressions against the older All American?
Attached Images
File Type: gif AM.gif (15.2 KB, 145 views)
  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
new phono stage or old preamp with phono? flohmann Analog Line Level 2 2nd October 2008 09:51 PM
How to house a JFET phono pre jackinnj Solid State 10 10th July 2008 12:59 PM
D.I.Y. "Duplex" 2sk369 jfet mm phono preamp doggy Analogue Source 6 26th September 2006 08:23 AM
Phono pre, valve or jfet lndm Analogue Source 7 4th April 2006 02:11 PM


New To Site? Need Help?

All times are GMT. The time now is 04:00 PM.


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