Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 20th January 2012, 09:18 PM   #1
kianbach is offline kianbach  United Kingdom
diyAudio Member
Join Date: Apr 2005
Location: anglesey
Default Strange.................

Just rewired my Aikido linestage e88cc/6sn7.....Sounds nice and really quiet..Problem is when i switch it off and touch either the 6sn7 bases or the output caps i get a loud buzzing from power amp.Any ideas????????
  Reply With Quote
Old 20th January 2012, 09:47 PM   #2
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
It's called mains hum. Your body is acting as one plate of a capacitor. The other plate is your mains live wire. Quite small capacitance, but the input impedance of most power amps is quite high. When the linestage is turned on it has a low output impedance so that greatly reduces the effect.
  Reply With Quote
Old 21st January 2012, 07:59 PM   #3
Sch3mat1c is offline Sch3mat1c  United States
diyAudio Member
Sch3mat1c's Avatar
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Could also be parasitic oscillation; the additional capacitance from your finger could be tipping the system just out of stability. Now, fingers usually dampen rather than excite systems, since there's a lot of resistance in the body, but if it's oscillating at a relatively low frequency (~MHz rather than 100MHz+), the impedance is probably quite high, in which case your finger will look like a good capacitor.

In either case, however it's picking up the noise, if through some radio-frequency voodoo, or just plain old finger-buzz, it might be worth double checking your layout, make sure inputs and outputs are far apart, that sort of thing.

Seven Transistor Labs, LLC
Projects and Resources / Electronic Design and Consultation
  Reply With Quote
Old 21st January 2012, 11:57 PM   #4
kevinkr is offline kevinkr  United States
diyAudio Moderator
kevinkr's Avatar
Join Date: Sep 2004
Location: Boston, Massachusetts
Nothing strange, once off the pre-amp has a high source impedance and as DF96 explained you are capacitively injecting signal into your amps.

Now the biggest question arises as to why you aren't really following good power sequencing practice which is to turn off the power amps first, then the line stage and finally everything else. Power up should be reverse sequence.
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
  Reply With Quote


Strange.................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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
This is strange… DJ Exprice The Lounge 4 26th July 2007 07:08 PM
Strange old BJT Pozar Parts 0 9th May 2005 07:29 AM
Strange... vpharris Forum Problems 1 16th February 2005 11:10 PM
Brazil, and some strange laws, not too much strange! destroyer X Everything Else 0 11th September 2004 01:38 PM
Strange or what? Circlotron The Lounge 11 18th March 2004 02:28 AM

New To Site? Need Help?

All times are GMT. The time now is 03:57 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio