Jfet BOZ - Page 53 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 28th January 2008, 04:19 PM   #521
diyAudio Member
 
Join Date: Jan 2007
Location: Iowa
Sorry to interrupt but I have been very closely following this thread and the JFET BOZ Mods thread very closely. I have all my parts ready to become a JFET BOZ owner except for the the JFET...lol. My question is can I use something like a J212 or a different JFET in place of the 2SK170 or should I just suck it up and go through Newark (MCM) and get some 2SK170's? I know the 2SK is a great part but I love that I can get 100 J212 through Mouser and for the price of about 10 2SK's. Also is it OK to order 2SK's through MCM, I thought at one point they had problems with Toshiba's that where fakes, 2SC5200's I think, but maybe a bad memory.

Lastly has anyone used the LSK170 from linear systems? I know there was some talk a little while back I saw about the LSK389, has anyone tried that since SK389's seem to be commanding the same price point as my Tung-Sol 6SN7's....and my car!
  Reply With Quote
Old 28th January 2008, 04:42 PM   #522
diyAudio Member
 
Join Date: Sep 2005
I got mine here: Selling JFETs - 2SK170-BL, 2SJ74-V
  Reply With Quote
Old 29th January 2008, 01:32 AM   #523
diyAudio Member
 
Join Date: Nov 2006
The J212's should work just fine. I've used J105's -- which sound great. Also, J310's work, but I haven't heard them yet -- that preamp is on my test bench. (all the above are available from mouser),

JJ
  Reply With Quote
Old 29th January 2008, 02:06 AM   #524
diyAudio Member
 
Join Date: Jan 2007
Location: Iowa
Thanks so much to both of you! I guess I will go ahead and order from Mouser. Thanks yggdrasil, one of the cheapest places I have seen them (either of the JFETS). I might have to order up some SK170's also for the JBOZ and for future projects. Sorry for the late reply, I actually saw your response earlier, but I had homework to do, then I had to watch Underworld Evolution! One of my favorite genre's (crazy action / vampire / zombie / B-grade)...I know large genre. Well that and I am a huge Kate Beckinsale fan, especially when she is in tight leather and putting the hurt on some werewolves .

Plus it sounds pretty good not in 5.1 through my JLH Original and zombied ESP P88 line-stage (jerryed from the junk I could find in my parts bin b/c I needed a pre). I can't wait to hear in with the JBOZ and eventually with some A5's or AX's...by that time though I might have a UGS Line-Stage...or a Pumpkin .Thanks again and sorry for the needlessly winded post .
  Reply With Quote
Old 8th April 2008, 09:40 PM   #525
diyAudio Member
 
Join Date: Sep 2005
I have been putting together a new variation of the Jfet BOZ.

This variation have a constant current source at Jfet source pin and a feedback loop. The feedback can be disconnected with a switch at the back panel of the amp.

I have attached the schematics. In the build R5 is 2K7, in order to get ~8V at the drain of the Jfet.

I matched the Jfets roughly with regards to Vgs, and quite close at 7.4mA Idss.

I have installed a switch to control feedback on/off, and I have switched a few times back and forth with the power on. When doing this I found one thing that puzzles me: When the feedback is off, and I hold my hand over the amplifier (~10cm from the amp) I get a quite audible hum. When the feedback is on there is no audible hum. My guess is that the hum is louder than the ~10dB feedback, but cannot be sure.
Attached Images
File Type: jpg v9_1.jpg (48.6 KB, 2365 views)
  Reply With Quote
Old 8th April 2008, 11:54 PM   #526
flg is offline flg  United States
diyAudio Member
 
flg's Avatar
 
Join Date: Jul 2005
Location: North East
I would guess, due to your wiring to switch in/out F.B., you now have a little antena. Little antenna's don't do much because they generally arent long enough to pick up much signal. And when using low impeadance, it wouldn't stand a chance. But, in a high gain, high impeadance input You have something floating that needs to be terminated
  Reply With Quote
Old 9th April 2008, 12:19 AM   #527
diyAudio Member
 
Join Date: Feb 2005
Hi Yggdrasil,
I see the drawing date is late Feb, have you built it and how does it sound?
Perhaps try using Leds in place of D3,4 and perhaps buffer the 16volt supply to R11 (ie R7a,C2a) - maybe no improvement.
__________________
... jh
  Reply With Quote
Old 9th April 2008, 09:53 AM   #528
diyAudio Member
 
Join Date: Sep 2005
Thanks flg for the explanation.

Quote:
Originally posted by jameshillj
Hi Yggdrasil,
I see the drawing date is late Feb, have you built it and how does it sound?
Perhaps try using Leds in place of D3,4 and perhaps buffer the 16volt supply to R11 (ie R7a,C2a) - maybe no improvement.
I just built it last week. I like the sound very much.... But that's expected, wouldn't you say? I'm definitely no writer, but I can point at a few of it's qualities. It is very dynamic and powerful. I'm surprised at how powerful the low end is. The soundstage is convincing. Most of all it is enjoyable and I want to play more.

During the weekend I hope to compare it to the original JBoz, which is on loan to a friend of mine.

I have bag of 1N4148, which is why they are used. I'll look into separate buffers on a later variation.
  Reply With Quote
Old 9th April 2008, 11:55 AM   #529
flg is offline flg  United States
diyAudio Member
 
flg's Avatar
 
Join Date: Jul 2005
Location: North East
1N4148 is one of the best components for low noise biasing You might have to up the R3 to use LEDs, they're higher voltage but also good for low noise.
  Reply With Quote
Old 22nd April 2008, 02:09 AM   #530
diyAudio Member
 
Join Date: Jan 2007
Location: Iowa
Sorry to bring up an old thread, I guess only a few weeks but you know. I just wanted to pop over and say that I finished bread boarding the first half of my long over due JFET BOZ. I was a the Radio Shanty buying some cheap proto PCB's and decided that I have nothing to do tonight so I bought a less than ideal MPF102, the last one they had. I came home and went through my parts bin and saw that I had no 10-Ohm resistors so I had to parallel a pair of 24-Ohm 5% that turned out to give me about 11-Ohms. Also didn't have much for 10uF caps until I found a big ol' oil filled job laying in a bin that said 10uF on the side. Something salvaged for a tube project that hasn't gotten of the ground yet. Took me all of about 5min to rig this thing together on a bread board, and it worked right out of the box. I am interested to see how this thing sounds though once my J310's get here...maybe I will just order up some K170's .

I must say though that it seems to maybe "color" the sound a little bit. I am not sure if it is the amp, the MPF102, the oil-filled can, or something else but the bass is very deep but somewhat loose. Maybe I am not used to the Pass sound since this is my first Pass project. All the lower frequencies seem to be a little heavy-handed, but the mids and highs are still there. It just doesn't seem to be as "not there" as my LM4562 pre. I don't think it is a speed thing, I don't know, maybe some of the other JFET BOZ builders can enlighten me. I am still a young pad-won, in audio, Mr. Passes Zen ways, and life in general, but I can say that it sounds very very good for a few resistors, a FET, and a cap... I can't really even say a handful of parts, maybe both channels would count as a handful. Mates very sexy like with my JLH Original Class-A pumping out approximately 10watts of beautiful vivid music. My soul mates "golden ears" are about an hour and a half away at college until this weekend so I will employ them then.

Thank you Mr. Pass for all the years and support...and for this ugly circuit that is just begging to be tweaked

Cheers!

James
  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
JFet BOZ Tyimo Pass Labs 14 30th April 2006 03:18 PM
Can I replace BF245C JFET with J201 JFET? bigmike216 Parts 2 7th December 2005 06:50 AM
How to use Jfet? lumanauw Pass Labs 5 7th April 2005 03:12 AM


New To Site? Need Help?

All times are GMT. The time now is 12:57 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