help needed with noise in phono preamp - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 May 2007, 06:45 AM   #1
diyAudio Member
 
Join Date: Mar 2004
Location: Albury NSW Australia
Default help needed with noise in phono preamp

Hi guys
Well we are getting there re the sound of this. The 6sn7 srpp line stage is fine but the phono stage is making a fair mount of noise.. some hum and induction noise? Would it be worth putting some form of feedback/noise cancellatiom circuitry in?
If so where.. i have been on tubecad site but would like some advice
Thanks in advance
nick
__________________
"Better to say nothing and keep them guessing than to speak and remove all doubt."
  Reply With Quote
Old 25th May 2007, 07:08 AM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
I've removed the attachment- it's a copyrighted schematic.

If the noise you get is hum, you've got layout and/or grounding issues, not a design one.
__________________
The more you pay for it, the less inclined you are to doubt it.- George Smiley
  Reply With Quote
Old 25th May 2007, 07:25 AM   #3
diyAudio Member
 
Join Date: Mar 2004
Location: Albury NSW Australia
Default oops

Sorry re that.
i got the schematic from these forums and i apologise to the rightful owner.
Nick
__________________
"Better to say nothing and keep them guessing than to speak and remove all doubt."
  Reply With Quote
Old 25th May 2007, 08:13 AM   #4
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Well, let's see what we can do to help. Describe the symptoms in some detail and if it's possible to get some photos of the layout and wiring, post them and something might be deduced.
__________________
The more you pay for it, the less inclined you are to doubt it.- George Smiley
  Reply With Quote
Old 25th May 2007, 01:26 PM   #5
diyAudio Member
 
Join Date: Mar 2004
Location: Albury NSW Australia
Default Thankyou

Thanks for your help.
the noise I think has 2 components
1. Mains hum.... i am running a regulated psu based on a 6as7,12at7 and 5651..
2. a louder lower component (not motorboating i dont think) if i place my hand over the tube it exacerbates or increases it..
If i could email you photos as they will be around 100k
I may even be able to do an mp3 of the noise
Once again thanks for your help, I really appreciate it
Nick
__________________
"Better to say nothing and keep them guessing than to speak and remove all doubt."
  Reply With Quote
Old 25th May 2007, 11:31 PM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
I think that the posting limit for photos is 105k, so if theyre under that, go for it. Otherwise, you can either shrink them a bit or zip them up and attach the zip file. The more eyes on this, the better (and Jim Hagerman, who designed it, is a participating member here).

What you're describing is screaming "grounding and layout." That's much easier to fix than design.
__________________
The more you pay for it, the less inclined you are to doubt it.- George Smiley
  Reply With Quote
Old 26th May 2007, 02:35 AM   #7
diyAudio Member
 
Join Date: Mar 2004
Location: Albury NSW Australia
Default will get some photos up

Thanks for that.
I know it isnt design.. I can hear just how beautiful this phono stage sounds and I am very grateful to Jim for this design.. so i will get some photos up and we will take it from there.
Thanks Again
Nick
__________________
"Better to say nothing and keep them guessing than to speak and remove all doubt."
  Reply With Quote
Old 26th May 2007, 11:19 PM   #8
Jeb-D. is offline Jeb-D.  United States
diyAudio Member
 
Jeb-D.'s Avatar
 
Join Date: Nov 2005
Location: SoCal
Phono pre-amps use a lot of gain and are followed by more gain in the amplifier before it gets to the speaker. So basically as mentioned the layout and grounding are critical and you have to extensively filter the power supply. I'd also consider using rectifiers with minimal "hash" such as Hexfred's or tube rectifiers. Usually for pre amps I ground the chassis to earth for safety, but leave the power/audio ground floating or connected to chassis through a resistor, so that when you attach it to an amp, it gounds to the amplifiers ground through the RCA shielding. This prevents system-level ground loops.
  Reply With Quote
Old 27th May 2007, 03:49 AM   #9
dvisves is offline dvisves  United States
diyAudio Member
 
Join Date: May 2007
Preamplifiers being the first links in the amplification chain are suspect to noise pick up .i would do the follwing things 1)use good shileded cable for the input 2)Ground the input jack ground to the power supply ground with thick copper wire 3) Use a three terminal regulator having a smoothing capacitor of roughly 47 microfarad for powering the preamp.This has helped a lot in my audio projects.Hope this helps
__________________
deevee
  Reply With Quote
Old 27th May 2007, 09:06 AM   #10
diyAudio Member
 
Join Date: Mar 2004
Location: Albury NSW Australia
Default Many Thanks

Hi
I am posting a few photos for comments.
i will go through each suggestion to see if I cn reduce the hum.
Might I addd that the line stage does not have any hum at all. I know the phono amplifies many times more than the line stage but it just so everyone knows
thanks again to all for the help
Regards
Nick
Attached Images
File Type: jpg 2.jpg (80.7 KB, 260 views)
__________________
"Better to say nothing and keep them guessing than to speak and remove all doubt."
  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
Noise on the RIAA phono preAmp diarav Chip Amps 3 23rd March 2007 05:27 AM
Phono Preamp Design Needed AudioFox Tubes / Valves 9 15th June 2006 08:11 PM
Super fast, low noise phono preamp dioklecijan Analogue Source 30 19th July 2004 09:52 PM
Capacitors for phono preamp needed maestro00 Parts 2 25th June 2004 01:49 AM


New To Site? Need Help?

All times are GMT. The time now is 11:09 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