Effect of Regulated DC Filament Supply - 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 18th March 2013, 11:16 AM   #1
diyAudio Member
 
overmind's Avatar
 
Join Date: Feb 2002
Location: Singapore
Default Effect of Regulated DC Filament Supply

Hi,

I am comparing the effects of having a regulated DC filament supply for my DIY preamp, loosely based on C22.

There are 5 tubes in this pre-amp. Three for audio and two for power supply.
As I have 9Vac and 6Vac outputs from my transformer, I used the 9Vac supply for 3 ECC83s for audio and the 6Vac for two tubes in power supply. The schematic is attached.

The 7ohm is to represent a load of 0.9A for three filaments connected in parallel. I am using 6.3V filament supply and each filament current should be 300mA.

I like the effect from converting the filament supply from AC to DC. So thought I could improve by having the supply regulated for the 3 Audio ECC83. The schematic is also attached. I am using a ST LM317 instead of the LT1085.

The results of regulation using the ST LM317, to my surprise, is terrible! No life in the music any all. Very unmusical! Flat and mechanical sound.

Does any one have experience with DC filament supply to share?
If I can change the voltage regulator to LT1085, would it be better?
Or is there any topology of DC filament regulation that would yield good sound?

Please help.
Attached Images
File Type: jpg UnregulatorPS.JPG (69.8 KB, 941 views)
File Type: jpg Regulated PS.JPG (72.9 KB, 890 views)
  Reply With Quote
Old 18th March 2013, 12:14 PM   #2
Tesla88 is offline Tesla88  Italy
diyAudio Member
 
Tesla88's Avatar
 
Join Date: Dec 2011
Location: Italy
Stupid question : Have you measured true DC voltage with the simple CRC circuit and with the LM317 ? Maybe LM317 is not feeding a 6,3V supply to heaters
  Reply With Quote
Old 18th March 2013, 12:14 PM   #3
Loren42 is offline Loren42  United States
diyAudio Member
 
Join Date: Sep 2008
Location: "Space Coast" Florida, USA
Quote:
Originally Posted by overmind View Post
Hi,

I am comparing the effects of having a regulated DC filament supply for my DIY preamp, loosely based on C22.

There are 5 tubes in this pre-amp. Three for audio and two for power supply.
As I have 9Vac and 6Vac outputs from my transformer, I used the 9Vac supply for 3 ECC83s for audio and the 6Vac for two tubes in power supply. The schematic is attached.

The 7ohm is to represent a load of 0.9A for three filaments connected in parallel. I am using 6.3V filament supply and each filament current should be 300mA.

I like the effect from converting the filament supply from AC to DC. So thought I could improve by having the supply regulated for the 3 Audio ECC83. The schematic is also attached. I am using a ST LM317 instead of the LT1085.

The results of regulation using the ST LM317, to my surprise, is terrible! No life in the music any all. Very unmusical! Flat and mechanical sound.

Does any one have experience with DC filament supply to share?
If I can change the voltage regulator to LT1085, would it be better?
Or is there any topology of DC filament regulation that would yield good sound?

Please help.
I think you are hearing things. I just can't see how a heater can impact sound quality based on type of regulation, provided you have the correct voltage applied to the tubes.

Heaters bring the tube up to operational temperature, that is it. Using DC to drive the heaters only serves to cut potential hum.

For that matter, regulation will not buy you much with a constant load, which the heaters represent, except smaller capacitors and better efficiency of the power supply.

If you really feel that the sound quality has changed, I would check the voltage to the heaters to make sure it is with specifications.
  Reply With Quote
Old 18th March 2013, 12:18 PM   #4
diyAudio Member
 
overmind's Avatar
 
Join Date: Feb 2002
Location: Singapore
Quote:
Originally Posted by Tesla88 View Post
Stupid question : Have you measured true DC voltage with the simple CRC circuit and with the LM317 ? Maybe LM317 is not feeding a 6,3V supply to heaters
Yes, I have measured the voltage from the regulator.
I first played with 6.3Vdc
Then 6Vdc for a for a while.
They have the same characteristics. However, with 6Vdc, the sound is a bit dull compared to 6.3Vdc.
  Reply With Quote
Old 18th March 2013, 12:24 PM   #5
diyAudio Member
 
overmind's Avatar
 
Join Date: Feb 2002
Location: Singapore
Quote:
Originally Posted by Loren42 View Post
I think you are hearing things. I just can't see how a heater can impact sound quality based on type of regulation, provided you have the correct voltage applied to the tubes.

Heaters bring the tube up to operational temperature, that is it. Using DC to drive the heaters only serves to cut potential hum.

For that matter, regulation will not buy you much with a constant load, which the heaters represent, except smaller capacitors and better efficiency of the power supply.

If you really feel that the sound quality has changed, I would check the voltage to the heaters to make sure it is with specifications.

"DC to drive the heaters only serves to cut potential hum"
maybe the hum is always there, but we are unable to pin point it.

I have have much cleaner sound by converting from AC to DC filament supply.
  Reply With Quote
Old 18th March 2013, 01:01 PM   #6
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
'Flat and mechanical sound' could be the result of missing hum/buzz, if the original AC heaters were not wired correctly. Now you may be hearing the music as it is, without artificial aids.

Another possibility, assuming you are running the DC heater supply from the same secondary as you were previously using for AC, is that the extra load on the transformer has changed the shape of the primary current. This, perhaps combined with some HT PSU weakness, could result in a different amount of hum IM via that supply.

Or it could all be imagination.

The one thing which won't happen is that the valves themselves will notice the difference between AC and DC heaters: the heater-cathode system has far too long a thermal time constant for that.
  Reply With Quote
Old 18th March 2013, 02:12 PM   #7
Tesla88 is offline Tesla88  Italy
diyAudio Member
 
Tesla88's Avatar
 
Join Date: Dec 2011
Location: Italy
If I read correctly :
-You tried DC heather supply vs. AC supply for heather with simple CRC network and you liked the result
- Then you tried an LM317 to provide regulated DC but results in a bad sounding mod

I will try , just to be sure is not pure fantasy , a selector to switch between the 2 DC supply , if you still notice difference i will check with a scope the DC output from the 317 .

As stated by DF96 the heater-cathode system has far too long a thermal time to notice difference between the 2 systems , and if TRUE RMS voltages are the same , i will check if LM317 is self-oscillating using a scope ...
  Reply With Quote
Old 18th March 2013, 03:02 PM   #8
diyAudio Member
 
overmind's Avatar
 
Join Date: Feb 2002
Location: Singapore
Quote:
Originally Posted by DF96 View Post
'Flat and mechanical sound' could be the result of missing hum/buzz,
humming sounds like "mmmmmm", and that is not life to me.....

Quote:
Originally Posted by DF96 View Post
'Another possibility, assuming you are running the DC heater supply from the same secondary as you were previously using for AC.
The comparison is between an unregulated DC and Regulated DC via LM317. Not involving AC filament connection.


Quote:
Originally Posted by DF96 View Post
Or it could all be imagination.
My father, 70+ year young, who is not into Audio can actually tell that regulation does not sound as good when listening out of my room.

Quote:
Originally Posted by DF96 View Post
The one thing which won't happen is that the valves themselves will notice the difference between AC and DC heaters: the heater-cathode system has far too long a thermal time constant for that.
I really do not know if the tubes know about the difference.
  Reply With Quote
Old 18th March 2013, 03:03 PM   #9
diyAudio Member
 
overmind's Avatar
 
Join Date: Feb 2002
Location: Singapore
Quote:
Originally Posted by Tesla88 View Post
i will check if LM317 is self-oscillating using a scope ...
Yes. I will check..
  Reply With Quote
Old 18th March 2013, 03:23 PM   #10
diyAudio Member
 
funk1980's Avatar
 
Join Date: Sep 2011
Location: Groningen
It sounds like there is something very wrong with the actual DC output. A flat 6.3 volt DC filament supply to a 12AX7 will always give better results in terms of hum etc. then a AC supply. But even the difference between AC and DC shouldn't be that audible with these kind of indirectly heated tubes.

First thing I notice is the LM317 schematic. For max performance, both the LM317's in- and ouput should be bypassed with a small value foil cap (MKP, MKS, whatever) for shunting high frequency content. Datasheet states 100n@input and 1u@output.
- Have you measured the output voltage loaded or unloaded?
- Did you check the output with an oscilloscoop to check if it's flat?
- Did your new supply maybe cause noise in ground or a groundloop?
- Is the transformer up to the task?

Last edited by funk1980; 18th March 2013 at 03:26 PM.
  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
DC Filament supply boards pmillett Tubes / Valves 20 17th October 2010 11:24 PM
DC filament supply without electrolytic(s)? CarlyBoy Tubes / Valves 12 12th January 2010 02:33 PM
Hot running regulated dc filament supply for aikido preamp 2004ex Tubes / Valves 6 27th September 2006 01:38 PM
When using a DC filament supply on a DHT... Saurav Tubes / Valves 31 18th September 2003 06:03 AM
DC Filament power supply oldstyle Tubes / Valves 26 2nd November 2002 02:26 PM


New To Site? Need Help?

All times are GMT. The time now is 03:20 AM.


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