How low should PSU ripple voltage be in a 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 6th February 2003, 08:33 AM   #1
diyAudio Member
 
Join Date: Jan 2002
Location: Canberra, Australia
Default How low should PSU ripple voltage be in a preamp?

I'm in the process of building a single stage valve preamp using triode connected EL84's with plate loading chokes and NiMH bias.

Although high voltage electros are awkward to get hold of where I am, 80H 560 ohm dcr chokes that'll handle upwards of 70ma can be obtained with relative ease.

I'm using 2 as my plate loads but I thought, Hey, why not use one in the PSU as well?

Plugged a few values into Ben Duncan's "psu designer 2" and with 200u, 80H series, 200u, 200r series, 200u, 200r series, 200u and a draw of 50mA I'm getting the terrifying total of 470nV (that's right! NANOVOLTS!) of ripple on my 270V line.

The plan was to have the main psu tranny and CLC in an offboard enclosure. The RCRC was to split to both channels as soon as the PSU feed entered the preamp housing. I accept that on a 270v valve preamp rail this is overkill but the choke's easy to get hold of and of known quality. Should I just run with it?

TIA

drew
  Reply With Quote
Old 6th February 2003, 11:47 AM   #2
halojoy is offline halojoy  Sweden
On Hiatus
 
Join Date: Nov 2002
Arrow As low ripple as possible - In Pre Amps

PreAmps should of course have as low PSU ripple as possible.
To give a nuber on how many mV is acceptable,
is impossible.
Different amplifiers are diffeently sensitive for ripple.
They have different PSRR. Power Supply Rejection Ratio.

But I would say it is good if you have only 10-50mV ripple.

/halo - ripples a lot
  Reply With Quote
Old 6th February 2003, 01:36 PM   #3
Joel is offline Joel  United States
diyAudio Member
 
Joel's Avatar
 
Join Date: Oct 2002
Location: Brooklyn, NY
Default Re: How low should PSU ripple voltage be in a preamp?

Quote:
Originally posted by DrewP
...and with 200u, 80H series, 200u, 200r series, 200u, 200r series, 200u and a draw of 50mA...
Drew, 800uF of capacitance in a tube power supply is a waste of money, harmful to the rectifier and power transformer, and will require a lot of horsepower to keep it charged.
To spite the sim results, with any standard preamp sized transfrmr, your hum will probably be worse than a similar supply with only 100uF of capacitance.

15H-->100uF-->500 ohms-->100uF is all the filtering you would need to have.
I used that for a mic preamp - and I get no hum in headphones.
  Reply With Quote
Old 6th February 2003, 02:08 PM   #4
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Default ripple and noise

the CAD models (I use multisim) will show you results without the real world crud which comes about when circuits heat, etc.

You have to distinguish between "ripple" and "noise" while the CAD model puts the ripple at nV, there are probably tens of millivolts of noise modulating the ripple -- this is why a good low noise scope is so helpful.

BTW, the TEK 5XXX scope are dirt cheap and very good for this purpose. They have plug-ins which are capable of differential measurements of 5uV/cm . This series of scopes were used in biomedical applications in the 1970's and they are a bit bulky but you can find them for sale on EBay (with time base and plugins) for less than $50. They have a much bigger screen than the TEK 7XXX series.
  Reply With Quote
Old 6th February 2003, 02:46 PM   #5
diyAudio Member
 
Brett's Avatar
 
Join Date: Jan 2002
<b>80H 560 ohm dcr chokes that'll handle upwards of 70ma can be obtained with relative ease.</b>


Drew,

Do you have a source for those chokes that you'd care to share (by email if you'd like)? I'm in NSW, and might even have some electros available.

I also agree with Joel and Jack, that for a line stage 100uF is enough. I never bother with more, except in poweramps.
  Reply With Quote
Old 6th February 2003, 07:43 PM   #6
diyAudio Member
 
Join Date: Jan 2002
Location: Canberra, Australia
Brett, I was going to source my chokes through Lancroft. They have been very favourably recommended by a freind who does LOTS of valve work in the ACT.

http://www.users.bigpond.com/triode/

I was going to use the CHSFO4 at $110 ea for my plate loads.

On second glance however, the chokes are current limited until I go up to FS05 for my PSU purposes as they'll be taking the draw from both channels.
Hope this helps.

The 100uf 400v caps i can get from Jaycar if necc.

BTW, was planning on diode rectifying not tube.

Drew
  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
Huge AC ripple voltage - Help Please! johnmax Power Supplies 5 2nd February 2008 10:54 AM
How to determine ripple voltage? beerman Power Supplies 4 21st February 2007 07:27 PM
Optimal ripple voltage on b+ supply nhuwar Tubes / Valves 14 1st February 2007 05:01 PM
Aleph ripple voltage Pumuckel Pass Labs 11 10th November 2003 10:06 AM


New To Site? Need Help?

All times are GMT. The time now is 04:50 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