EL84 Push-Pull ccs bias - 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 28th April 2007, 06:21 AM   #1
Tobruk is offline Tobruk  Italy
diyAudio Member
 
Join Date: Oct 2005
Default EL84 Push-Pull ccs bias

Hi,
about diyparadise.com El84 amplifier schematic ,what sound difference between resistor chatode bias and LM317 ccs.Have you an idea about LED CCS ? Thanks..
regards
  Reply With Quote
Old 28th April 2007, 07:52 AM   #2
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
He says that the CCS gives a lot cleaner stronger sound, with more bass . This would be my experience of CCS bias as well.

Shoog
  Reply With Quote
Old 1st May 2007, 10:24 PM   #3
diyAudio Member
 
Join Date: May 2005
Location: Pretoria, South Africa
Me again, Tobruk,

I don't want to lead you astray, but there was comment about the frequency response of the LM317 elsewhere. You must remember that such a device would have to be a CCS over at least the whole audio band. It is not clear that all power chips could do that. But I regret not recalling where I read that. Perhaps others could help.

Then to repeat, I would suggest as I did on another one of your threads that you ask a moderator to group the lot (if I am correct that it is about the same project) for your benefit.

Regards.
  Reply With Quote
Old 2nd May 2007, 08:07 AM   #4
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Quote:
I don't want to lead you astray, but there was comment about the frequency response of the LM317 elsewhere. You must remember that such a device would have to be a CCS over at least the whole audio band. It is not clear that all power chips could do that. But I regret not recalling where I read that. Perhaps others could help.
If adequately bypassed this is a none issue.
I think in the case of the diyparadise amp he uses no bypassing - the frequency response then becomes a real issue. I think possibly that he has the LM317 set up as a differential pair - which makes the quality of the CCS less of an issue.

Shoog
  Reply With Quote
Old 2nd May 2007, 09:49 AM   #5
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
Quote:
Originally posted by Johan Potgieter
Me again, Tobruk,
. . .
Then to repeat, I would suggest as I did on another one of your threads that you ask a moderator to group the lot (if I am correct that it is about the same project) for your benefit.

Regards.
Let me add that the best way to DO NOT SUCCEED is to "cut and paste" parts of schemos from -may be valuable- different sources but will lamentably fail to match together.

Look at your project as a whole.

Yves.
  Reply With Quote
Old 2nd May 2007, 01:39 PM   #6
diyAudio Member
 
Brian Beck's Avatar
 
Join Date: Dec 2004
Location: South Florida, USA
The DIYparadise EL84 amp drives the output push-pull pair from one side only. So the output stage MUST behave as a differential amplifier to work properly. To cause diff-amp behavior, there has to be a large tail resistor at the EL84 cathodes. The DIYparadise schematic shows just a 135 ohm resistor, which in my view, is inadequate. He later suggests using a CCS. And, in this case, you would not want to bypass the CCS with a cap, because one EL84 cathode must be able to "talk" to the other cathode for push-pull behavior to occur, when only one side is driven.

As Johan notes, an LM317 used as a CCS will fall down at higher frequencies. AudioXpress magazine recently published a very interesting two-part article by Walt Jung (April and May 2007) about CCS circuits and measurements. In effect, the raw LM317 has a roughly 400K resistance in shunt with a 350pF capacitance, and both components will be non-linear to a degree. A CCS in the cathode side of a tube circuit can be less critical than in the plate side because the impedances are much lower, but I would prefer to see the LM317 cascoded with a BJT or FET to reduce the effective capacitance (the resistance will go higher too in cascode, but 400K at low frequencies was already plenty good enough for this situation). Jung shows a circuit with an LM317 cascoded by a DN2540, giving outstanding performance, close to measurement floor across the entire frequency band.
__________________
Brian
  Reply With Quote
Old 2nd May 2007, 01:46 PM   #7
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
IMHO, the DIYparadise EL84 is just a single ended one.
The second EL84 can hardly do more than cancelling DC current in the OPT, wich is already not so bad.

I've not the schemo at hand, but I hope that the EL84 are not triode strapped.

Yves.
  Reply With Quote
Old 2nd May 2007, 01:49 PM   #8
diyAudio Member
 
Brian Beck's Avatar
 
Join Date: Dec 2004
Location: South Florida, USA
Quote:
Originally posted by Yvesm
IMHO, the DIYparadise EL84 is just a single ended one.
The second EL84 can hardly do more than cancelling DC current in the OPT, wich is already not so bad.
Without a CCS tail, it is indeed a partial SE amp. With a CCS, the other side comes alive and you have true push-pull.
__________________
Brian
  Reply With Quote
Old 2nd May 2007, 07:42 PM   #9
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Brian,
Your suggestion about caps between the cathodes, and then the earth reference lifted with a 1meg resistor seems appropriate here. Worked for me with the LM317 and avoids the need for bias adjustment.

With this circuit I always wondered what was the mechanism by which the second valve was driven - now I know. I wouldn't dismiss it as a design as a differential output stage has outstanding performance.

Shoog
  Reply With Quote
Old 2nd May 2007, 09:12 PM   #10
diyAudio Member
 
Brian Beck's Avatar
 
Join Date: Dec 2004
Location: South Florida, USA
Shoog,

I guess you're referring to the the two-CCS circuit we discussed in another thread. Yes, it should work here too, keeping each tube separately DC biased, while at the same time connecting the cathodes with caps for diff-amp behavior.

For a very simple design, I agree that this one-sided-drive diff-amp output stage amp should not be dismissed. But the CCS(s) has to be stout.
__________________
Brian
  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
EL84 push pull slideman82 Tubes / Valves 4 19th June 2009 03:40 PM
Will this work for an EL84 push pull? zobsky Tubes / Valves 5 10th October 2006 07:42 PM
modify parallel push-pull EL84 to single push-pull chungtat Tubes / Valves 12 3rd November 2005 11:25 PM
EL84 push pull idea mark_titano Tubes / Valves 20 13th June 2005 02:51 PM
EL84 Push Pull amp. hacknet Tubes / Valves 8 23rd September 2004 05:53 AM


New To Site? Need Help?

All times are GMT. The time now is 04:09 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