The complete 6SN7 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 18th November 2002, 06:02 PM   #1
Joel is offline Joel  United States
diyAudio Member
 
Joel's Avatar
 
Join Date: Oct 2002
Location: Brooklyn, NY
Default The complete 6SN7 preamp

I've been asked to show the power supply I'm using with my preamp design posted in the "tube preamp" discussion - so here is the circuit first:
Attached Images
File Type: jpg 6sn7preamp.jpg (23.6 KB, 7107 views)
  Reply With Quote
Old 18th November 2002, 06:06 PM   #2
Joel is offline Joel  United States
diyAudio Member
 
Joel's Avatar
 
Join Date: Oct 2002
Location: Brooklyn, NY
and the power supply...
Attached Images
File Type: jpg 6sn7preamppsu.jpg (15.2 KB, 6545 views)
  Reply With Quote
Old 18th November 2002, 11:40 PM   #3
diyAudio Member
 
Join Date: Nov 2002
Thanks Joel


Your power supply circuit is quite interesting. I was wondering ...
a choke is not needed? Would there be an advantage of having a choke and a RC network?

Its another newbee question..

Thanks
Joe
  Reply With Quote
Old 19th November 2002, 12:03 AM   #4
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
burnedfingers said:
Quote:
I was wondering ...a choke is not needed?
The power supply, as it stands, is perfectly adequate as long as it doesn't run into distortion.
This is because the average current of a class A stage is constant.
However, as soon as you start getting any asymetry, the current varies.
As a matter of fact you can check exactly how much 2nd harmonic distortion a class A stage has, by measuring the change in consumed current.

So, the answer to the question is: It depende how loud you want to play it.
If you want to get the max out; go for a lower impedance choke smoothed circuit.
If you want to economise, and don't want it loud. Use resistors.

Cheers,
  Reply With Quote
Old 19th November 2002, 02:12 AM   #5
Joel is offline Joel  United States
diyAudio Member
 
Joel's Avatar
 
Join Date: Oct 2002
Location: Brooklyn, NY
Exactly what John said.

But you'll find that, whether used as a linestage, or to drive headphones - you will never need to push the tubes in this. There is plenty of gain, and a low enough output impedance to handle either task. A choke will only add cost... to this project. (I really do love chokes people! I swear. But you just don't need one all the time)
  Reply With Quote
Old 19th November 2002, 02:44 AM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
No, you probably don't need a choke there. But you might want to bypass that last filter cap with a film cap of a uF or so. A scope or some headphones and a cap will tell you if that's effective.

I didn't read the other discussion- why use a 6SN7 in the first place for this application? It's a great high voltage driver that can source some current, but for a CF intended to pass a couple of volts at most, a higher gm tube with higher mu might be a better choice from the standpoints of source impedance and distortion. Don't misunderstand me, a 6SN7 will work OK, it's just not optimal.
  Reply With Quote
Old 19th November 2002, 03:04 AM   #7
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default MU

Hi,

I agree higher gm is what makes a CF sing.

Even wouldn't mind a penthode there.

Quote:
But you might want to bypass that last filter cap with a film cap of a uF or so. A scope or some headphones and a cap will tell you if that's effective.
Personally IMO,it's tricky to implement.
You often get the effect"Who stole the bass?" when bypassing.

Cheers,
__________________
Frank
  Reply With Quote
Old 19th November 2002, 03:31 AM   #8
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Well, if there's low frequencies moving around on the rail, you'll be able to spot it with the scope/phones. Though I don't see any reason why this should be greater with a bypass in place; the main effect of a bypass cap is seen at frequencies where the elytic is starting to get inductive.

I agree that a pentode would work well as the CF. For triode purists, a high gm triode (or a pair paralleled as Joel is doing with the 6SN7) will do nearly as well, but one generally has to accept 7 or 9 pin envelopes.
  Reply With Quote
Old 19th November 2002, 09:18 AM   #9
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Quote:
the main effect of a bypass cap is seen at frequencies where the elytic is starting to get inductive.
Agreed. Though electrolytics can introduce distortion. They are a long way away from an ideal capacitor - BTW no voodoo here.
IMO it is essential to have a large enough resovoir; that probably means it's going to be a bit inductive - so bypass it. But in doing do remember; youve made a parallel tuned circuit at "some" frequency. Best to avoid 'lytics if you're a puritan.
Best buy some shares in a PIO company.

Cheers,
  Reply With Quote
Old 19th November 2002, 01:41 PM   #10
Joel is offline Joel  United States
diyAudio Member
 
Joel's Avatar
 
Join Date: Oct 2002
Location: Brooklyn, NY
Quote:
Originally posted by SY
I didn't read the other discussion- why use a 6SN7 in the first place for this application?
Because I have a shoebox full of them.
  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
Which 6SN7 preamp should I build? chrisvw Tubes / Valves 48 12th August 2010 12:08 AM
6sn7 Preamp power supply ambience exists Tubes / Valves 27 26th August 2008 12:12 AM
Help with 6SN7 preamp tubedude63 Tubes / Valves 7 9th October 2006 12:31 AM
Joel's 6SN7 preamp (photo) Original Burnedfingers Tubes / Valves 48 2nd March 2003 12:00 PM
Preamp with 6sn7 & 6sl7 SRPP ??? Gregouille Tubes / Valves 4 18th June 2002 10:41 PM


New To Site? Need Help?

All times are GMT. The time now is 06:41 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