Pentode buffer. - 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 12th July 2012, 10:35 AM   #1
diyAudio Member
 
Join Date: Feb 2005
Location: S.England
Default Pentode buffer.

Can someone please point me to a good pentode based buffer amplifier to sit in-line with my Marantz CD player and Arcam amplifier? I'd like to try one out & build it myself.

Thanks in advance,

Andy
  Reply With Quote
Old 12th July 2012, 10:46 AM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
What are you trying to achieve? Why do you feel a pentode is the right choice?
  Reply With Quote
Old 12th July 2012, 10:57 AM   #3
diyAudio Member
 
Join Date: Feb 2005
Location: S.England
I have been asked to 'include' a tube in a setup. Why? Hmmm, probably purely conjective, but there you have it!

Why Pentode based? After having looked around at a lot of tube designs, starting off with Triode based designs (one of which I built based on an Aikido CCDS but gave way too much gain for what I was after) I 'think' that a Pentode based design is perhaps better for a buffer?

Hell, I could be wrong: Tube design is not my forte by a looong chalk and TBH I have been thrashing around trying to settle on a design for this.

Hence any input on this would be GREATLY appreciated before I sell my soul to the devil and buy a cr@ppy Chinese kit from fleabay.

Andy
  Reply With Quote
Old 12th July 2012, 11:56 AM   #4
diyAudio Member
 
the_manta's Avatar
 
Join Date: Nov 2006
Location: Munich, Bavaria
Problem is:
Buffer is a cathode follower (gain~1)
Cathode follower usually means load resistance at the cathode.
Hence the cathode is floating with the output voltage.
unfortunately the pentode needs a G2 supply between cathode and G2. Wouldn't be a problem for a grounded cathode amplifier.
In your case, you need a separate, galvanic isolated G2 supply which is floating on the cathode voltage.
You have the same problem with Pentode based tube power supplies or pentode based OTL-Futterman amplifiers.
A lot of effort for a simple buffer if you ask me....
You could the standard configuration for the G2 as well and use a very large bypass cap if the screen current is low, but i don't know abou the performance.
BTW: Depletion MOSFET curves are the same as Pentode curves and I bet everything, that you wont hear a difference between source follower and a pentode cathode follower. (As long as you still habe impedance bridging)
__________________
Терпенье и труд все перетрут

Last edited by the_manta; 12th July 2012 at 12:00 PM.
  Reply With Quote
Old 12th July 2012, 12:20 PM   #5
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by underwurlde
my Marantz CD player and Arcam amplifier? I'd like to try one out & build it myself.
Quote:
Originally Posted by underwurlde
I have been asked to 'include' a tube in a setup. Why? Hmmm, probably purely conjective, but there you have it!
I'm still not sure why. Did you just decide to try it, or has someone else requested it?

Conjective? Not a word I am familiar with. Wordnik says it means "In projective geometry, said of two projective primal figures of the same kind of elements when both are on the same bearer." Possibly not what you meant to say?

Do you actually need a buffer to cope with long interconnects or non-linear port impedances, or are you really after a mild FX box to give 'tube sound'? Pentodes have very high output impedance when used in grounded cathode, so no good for a buffer. When used as a cathode follower (OK for a buffer) they are either used in triode connection or involve extra complication to ensure g2 tracks the cathode signal; might be simpler to use a triode.
  Reply With Quote
Old 12th July 2012, 01:53 PM   #6
diyAudio Member
 
Join Date: Feb 2005
Location: S.England
Hell, I thought conjective meant something else entirely. I need to swallow a thesaurus. My bad...

The guy wants a tube in-line with his music. Why? Heavens knows, but he wants to see it there hence so be it, I shall try my best to give my friend what he wants. I'm sure a MOSFET will do the same thing, but unfortunately not the purpose of this strange exercise.

Quote:
or are you really after a mild FX box to give 'tube sound'?
Well put! After speaking with him, he was glad this was mentioned, so yes he does indeed require the tube sound of old.

I think therefore that a Pentode connected as a Triode is what we're after. From what I see, this makes it easier than just simply using a Triode to get the lower gain required for a buffer style circuit? Could be miles out of course, very steep learning curve for me this, but VERY interesting!

Thanks again for your input / interest

Andy
  Reply With Quote
Old 12th July 2012, 02:26 PM   #7
Fenris is offline Fenris  United States
diyAudio Member
 
Join Date: Jun 2004
Location: The last frontier
A vacuum tube isn't magic. Properly implemented, it will have no discernible sound. I think that the psycho-acoustic effect would probably be fulfilled if you just wired up a black box with a tube poking out of it (with the heater connected for the glow) and the line-in connected to the line out.
__________________
Listen to the music through the stereo, not the stereo through the music.
  Reply With Quote
Old 12th July 2012, 04:11 PM   #8
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
A triode is simpler than a pentode connected as a triode. Either can give you the just-below-unity gain of a genuine buffer.

If your friend wants genuine 'tube sound' then he may need a valve amplifier. If he just wants some low order distortion, and a little hum and noise, then a cheap chinese 'tube buffer' may satisfy him. Check that the valve is actually used in the circuit, as some have been known to cheat.

Used properly valves don't produce 'tube sound', except in guitar amplifiers but they are a completely different way of using valves.
  Reply With Quote
Old 12th July 2012, 04:23 PM   #9
diyAudio Member
 
Join Date: Feb 2005
Location: S.England
Understood. He does not want a valve amp though - I think he has something else in mind too (he is a music producer)... this is going somewhere I'm sure. I will try and pin him down tonight if he's around.

In the meantime can you point me to a good design for each implementation you mention please? I have searched and searched many designs both here and on the internet and am getting overwhelmed with all the options - but nothing which does what I want it to (as far as I can tell).

For now I shall avoid those ebay kits and will knock something up myself. I have knocked up a power supply already which I can tailor to suit and more valves to hand than I care to mention! I have the technology, just lacking the knowledge (of valve / tube design).

Thanks again,

Andy
  Reply With Quote
Old 12th July 2012, 04:38 PM   #10
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
You probably don't want a good design, as a good design won't change the sound hardly at all. You need to look for a poor design, or take a good design and damage it (e.g. wrong bias, too low supply voltage).

You may have gathered by now that I am not a fan of tube buffers, so I am not the right person to advise you. However, perhaps I have helped you clarify what you are looking for.
  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
Diamond Buffer - Super Buffer peranders Solid State 34 16th May 2010 01:46 PM
pentode buffer Sheldon Tubes / Valves 19 20th April 2010 07:34 PM
a better pentode for less! smoking-amp Tubes / Valves 16 12th August 2008 01:58 AM
A small no-fuss pentode/pentode SE amp Tubes4e4 Tubes / Valves 13 1st January 2006 05:16 AM
Opamp + buffer, how to bypass buffer at HF for unity gain? Christer Solid State 10 29th October 2003 06:50 AM


New To Site? Need Help?

All times are GMT. The time now is 01:35 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