Pearl Two - Page 120 - 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 14th December 2011, 10:36 PM   #1191
diyAudio Member
 
richluvsound's Avatar
 
Join Date: Sep 2010
Location: LONDON
I removed Q7 and still Q3 is low .... the voltage @ Q1 is as it should be . Pulled R9 and it is 500R. Short of stripping the board and starting again ... ?
  Reply With Quote
Old 14th December 2011, 10:51 PM   #1192
diyAudio Member
 
richluvsound's Avatar
 
Join Date: Sep 2010
Location: LONDON
I could try swapping out C6
  Reply With Quote
Old 15th December 2011, 01:00 AM   #1193
diyAudio Member
 
PierreQuiRoule's Avatar
 
Join Date: Feb 2004
Location: Ottawa
Quote:
Originally Posted by richluvsound View Post
I removed Q7 and still Q3 is low .... the voltage @ Q1 is as it should be . Pulled R9 and it is 500R. Short of stripping the board and starting again ... ?
Hello Rich - it is possible that the jfet you did put in the Q7 spot was shorted.

Be mindful that the voltages that Wayne shared are for his particular jfet samples. My samples draw more current, and yours possible more than mine. So our Q3s all land in a different spot. What was 10 V for Wayne is 3 V for me, and you must figure out where Q3 will land for which devices in your case. Note that each jfet added below R9 draws current from R9 and brings Q3 further down. This is normal.

I note that your last measurements are different than those reported in Post 1137. I guess you were using different jfets. I calculate that the jfet of Post 1137 drew 5.2 mA. The last one your tried drew 12.6 mA. These figures are extremes for 2sk170BL which I assume is what you are using. Do you still have the jfet from Post 1137? It is a keeper. Let's try to find some that work and draw less than 12.6 mA.

Although I am no expert, I suspect that if the jfets draw a lot of current (high Idss), it is possible that using four devices in parallel brings the voltage at the bottom of R9 too close to ground. We can't change the value of R9 without changing the whole RIAA network (as Wayne kindly indicated). But no worries. The front end will operate with 3 jfets instead of 4. Or 2 for that matter.

At this point it would be useful if you tried two or three different jfets in the Q6 spot (one at a time) and measured all three voltages around Q3. You will want to label them .

Changing voltages can be due to many things. The voltmeter perhaps? Or cold solders? On Wayne's board, some pads connect to the ground plane, and require more heat to solder properly. Checking for cold solders is easy: I like to push and pull hard on every lead to verify that it does not move.

Pierre

Last edited by PierreQuiRoule; 15th December 2011 at 01:04 AM.
  Reply With Quote
Old 15th December 2011, 01:45 AM   #1194
diyAudio Member
 
richluvsound's Avatar
 
Join Date: Sep 2010
Location: LONDON
Thank you most kindly for your help Pierre ,

I will need to test the fets again .... they were all mid 7's mA for the quad and
mid 8's for the diff pair .... I also have a handful of 370's that need to be measured ... . I'll try and figure out how test them and hopefully post the values tomorrow . I vaguely understand what you are saying ... the fets are drawing too much from Q3 , not leaving enough go around ? Basically , I need
to find lower current fets .

Rich
  Reply With Quote
Old 15th December 2011, 10:27 AM   #1195
diyAudio Member
 
richluvsound's Avatar
 
Join Date: Sep 2010
Location: LONDON
This is my rig for testing fets ..... why am i not getting a reading ? Meter is set to mA , battery is good in Meter and test supply ! I'm doing something wrong ... I managed to it before LOL
Attached Images
File Type: jpg DSCN0236.JPG (937.0 KB, 138 views)
File Type: jpg DSCN0237.JPG (510.2 KB, 129 views)
  Reply With Quote
Old 15th December 2011, 11:17 AM   #1196
diyAudio Member
 
PierreQuiRoule's Avatar
 
Join Date: Feb 2004
Location: Ottawa
Rich - isn't there an expression in English that applies here... when it rains, it pours?

I see no mistake in your set up. What I would do first: Replace the jfet by a 1 kohm resistor. You should read 10 mA. If you don't, check or replace the fuse in the meter.

Pierre
  Reply With Quote
Old 15th December 2011, 12:00 PM   #1197
diyAudio Member
 
richluvsound's Avatar
 
Join Date: Sep 2010
Location: LONDON
going to buy some 1 A fuses .... I'm not reading anything !
  Reply With Quote
Old 15th December 2011, 12:35 PM   #1198
diyAudio Member
 
Join Date: Jul 2011
I had that happen when I strted Idss matching my fets. No reading. Indeed it turned out the fuse from my meter was blown.

Anyway, good luck with your Pearl II, I hope I'm not going to get into the same trouble as you.

By the way, my 2SK170 quads are 9.26-9.27mA and 9,30-9,36 mA. Should I change something in the schematic? (R10?)
  Reply With Quote
Old 15th December 2011, 12:55 PM   #1199
GOR3 is offline GOR3  United States
diyAudio Member
 
Join Date: Jun 2011
Location: Connecticut
In your picture, the negative post of the battery is not connected.
  Reply With Quote
Old 15th December 2011, 02:53 PM   #1200
diyAudio Member
 
richluvsound's Avatar
 
Join Date: Sep 2010
Location: LONDON
the fuse was gone ....

I have the following :

7.09 mA
7.01
7.18
7.08
7.09
7.14
7.06
7.10

Rich
  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
Another diy-pearl... lykkedk Pass Labs 18 15th June 2007 04:44 PM
ono or pearl PCB's mantisory Pass Labs 1 28th September 2006 11:12 PM
Pearl need help dzkh63 Pass Labs 1 26th September 2006 03:16 PM
WTB: Pearl PCB aire Pass Labs 1 26th February 2006 10:51 AM


New To Site? Need Help?

All times are GMT. The time now is 12:15 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