noise analysis - 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 21st March 2005, 01:03 AM   #1
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default noise analysis

I am tetsting the layout included. I have just the powersupply constructed on a wooden chassis. I monitor the secoundary of the OPT
using a oscope for hum. This configuration produces the least amount of hum on the each OPT (5 mv pxp ). My question is when I drag the OPT to where the 2a3 output tube will be I get 25 mv noise. Would this effect the output tube and drivers in any way ?
Attached Images
File Type: jpg layouta.jpg (14.5 KB, 231 views)
  Reply With Quote
Old 21st March 2005, 11:07 PM   #2
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Hi there.......a wooden chassis to poke about with the power supply idea is a reasonable and safeish start....
-> however if you are later going to shift over to a metal plinth you might be disappointed. With any metal chassis there will be minute circulating currents setup from transformers/chokes and with steel sheet it becomes markedly worse..so your layout predictions on wood might become different in reality with metal.
-> Ally is the best bet and is pretty predictable.
A SE design with no nfb....
-> Remember when using a design with nfb, the mutual magnetic coupling between power cores isn't half so bad as the loop reduces the o/p stage working impedances. With SE the in-circuit DC primary current will reduce the stray hum pick up to nearly nil.

-> The o/p tube is rel immune to hum pick up.
-> The golden rule that input tubes should be furthest away from power transformers and even more so with smoothing chokes.......remember chokes have an airgap (which spews out a massive leakage flux) and are prolific 100Hz/120Hz field producers.....Don't be surprised if the mains tranny has a stray magnetic field leakage less than the smoothing choke.

-> It might be best to shift the choke next to the mains trannyand relayout the input end furthest away from any power magnetics. Same applies to driver tranny. Traditionally, this sits between the input and output tube stages. I'm a bit inclined to keep spare space for rotating the driver transformer...
-> A driver stage transformer then this becomes another critical component for hum pick up. This is more sensitive than the o/p transformer. Why ? because circuit placement is usually at somewhat sensitive pre stage impedances with lower AC flux..
Technically, (if you are) using the secondary of an SE o/p trans for monitoring the hum is not ideal as the gap of an SE o/p tranny is fooling the common mode and behaving like that of the smoothing choke...(wild open for pick up).
You are right to have a crack of trying the predicted layout........but you can also try introducing some small sections of steel sheet to see how the hum pattern changes.

Hope this helps... but the old RF agage that inductors make excellent aerials. Brouse at some traditional designs....

I've rambled on.......time for the nest.

richj
  Reply With Quote
Old 22nd March 2005, 12:19 AM   #3
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default noise

richwalters , I would like to thank you for youre detailed help. I do have a more traditional layout I was considering. One Opt has more hum than other but I dont believe the output or input tubes would be a concern> the thing I dont like is THE SIZE ,with hammond 1627se
the thing looks like a UN conference table.


Drowning in analysis
Attached Images
File Type: jpg layoutb.jpg (14.8 KB, 169 views)
  Reply With Quote
Old 22nd March 2005, 04:18 PM   #4
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Default Re: noise

Quote:
the thing looks like a UN conference table.


Drowning in analysis [/B]

Hi there -> don't we all bang our fists on the table..?

this layout is certAINLY better than the previous....I'm tempted to put the choke as close as poss to the mains tranny and a touch inboard (not by much) The rectif pos would still be fine.....the power supply is then fairly compact to keep modulation hum away from input components.
If the choke is on the outside chassis edge........stray cables around the chassis corner can also pick up modulation hum from choke....and create wonderful earth hum loops.

If you can follow all this holler....build it.

richj
  Reply With Quote
Old 23rd March 2005, 01:25 AM   #5
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default layout

Hello ,



Quote:
don't we all bang our fists on the table..?
witty



more like this ?
Attached Images
File Type: jpg layoutb1.jpg (15.4 KB, 129 views)
  Reply With Quote
Old 30th March 2005, 12:22 AM   #6
diyAudio Member
 
tenderland's Avatar
 
Join Date: Jul 2004
Location: us
Default noise measurements

when the tube is located in middle and the choke is on one end and mains xfoemer on other the OPT infront of main xformer has 5 mv noise and the OPT infront of choke has 15 mv noise. When the tube is moved to the outside and the choke next to the mains xformer the measurements are the same- no change , one note as observed earlier the chassis is wood and the measurements are taken with the
OPT unloaded ( z of oscope only).

Jeff
  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
cap analysis yldouright Parts 3 7th January 2005 02:45 AM
Need help in circuit analysis Fossil Tubes / Valves 6 23rd November 2004 08:13 AM
Spectral analysis - use pink or white noise? Circlotron Everything Else 5 20th November 2003 01:13 PM
FFT Analysis RobPhill33 Everything Else 22 19th March 2003 08:01 PM


New To Site? Need Help?

All times are GMT. The time now is 05:06 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