Threshold SL-10 rushing noise on right channel mm phono - 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 19th January 2015, 01:49 AM   #1
diyAudio Member
 
Join Date: May 2014
Default Threshold SL-10 rushing noise on right channel mm phono

Hi. I recently aquired a Threshold SL-10 and noticed a slight rushing noise on the right mm phono channel that gets louder as I turn up the volume. Left side is free of noise/rushing sound.

I decided to recap the entire unit with Elna Silmic II and Nichicon Muse KZ. I also put new big 10000uf Mallory caps in the power supply. It is now sounding very good but the rushing sound hasn't changed. Any idea what to check or replace?

Click the image to open in full size.
  Reply With Quote
Old 19th January 2015, 02:06 AM   #2
diyAudio Member
 
Join Date: Jun 2001
Location: USA, Grand Prairie, Tx
If the power supply rails measure good, maybe a failing transistor. Whats the DC offset on the bad channel?
__________________
KC
  Reply With Quote
Old 19th January 2015, 02:21 AM   #3
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
some info here : Treshold Treasure ?? while Papa was there : SL10 Preamplifier | Zen Mod Blog

rushing noise - without MC stage engaged ?
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 19th January 2015, 02:32 AM   #4
diyAudio Member
 
Join Date: May 2014
I measured DC offset at the recording output and it's pretty near zero. Voltage coming from the power supply is 23v. I am getting 14.25v on the ~15v regulated output.
  Reply With Quote
Old 19th January 2015, 02:58 AM   #5
diyAudio Member
 
Join Date: May 2014
Quote:
Originally Posted by Zen Mod View Post
rushing noise - without MC stage engaged ?
I only used the mm input so far. I will try the mc input later and see if I hear the same noise. Line section is noiseless so I think the problem must be in the phono section.
  Reply With Quote
Old 19th January 2015, 06:44 AM   #6
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
no need to try MC , if it's already excluded - culprit is in that channel's MM stage

first check for cold solder joints ;

proceed with replacing servo OP ; if not , put back old one

then start replacing transistors

it would be nice to have Hfe matched ones for input LTP
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
  Reply With Quote
Old 19th January 2015, 07:54 AM   #7
diyAudio Member
 
Join Date: May 2014
I am reflowing some solder joints and will try again. The OP looks like an RC4136N and there are five MPS6571 and one FPN4250 transistor in the phono. I will try replacing some parts and report back on my findings...
  Reply With Quote
Old 19th January 2015, 07:56 PM   #8
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
ZM is right. 90% bad connection.

  Reply With Quote
Old 22nd January 2015, 01:58 AM   #9
diyAudio Member
 
Join Date: May 2014
Just an update. I examined the board with a magnifying glass and resoldered any joints that looked suspicious but didn't find much improvement. I removed, rearranged and resoldered some of the 100k resistors near the opamp chip and things got noisier on both the phono and line stage. Gain seems much higher for some reason as I can only go about a quarter turn on the volume now whereas I had it around half way before. At least the noise is about equal on both channels now. I am suspecting noisy resistors or opamp but still not sure.

I ordered some parts: new 100k resistors, RC4136N opamp chip, both 7815C regulators, MPS6571 transistors and 4250A transistors plus a few other things.

I will start with the opamp chip and resistors on that end and see if any improvement.
  Reply With Quote
Old 22nd January 2015, 03:08 AM   #10
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
The opamp is just a DC servo, and it would have to be actually broken for
the noise to get through its 100K output resistor.

  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
Threshold NS-10 vs SL-10 preamp gaetan8888 Pass Labs 0 21st February 2013 08:04 AM
threshold sl-10 opa627 Pass Labs 3 29th September 2009 07:01 PM
Threshold sl-10? jonk Pass Labs 14 23rd November 2008 09:21 AM
Threshold SL 10 yeoldestereo Solid State 2 5th February 2008 08:29 PM


New To Site? Need Help?

All times are GMT. The time now is 05:00 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright ©1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2