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Series feed SE OPT with no air gap and low flux??

61.18.170.85

Tube747

A

My friend has sent me a link last night that is about a French winder
offers SE output transformer with no air gap and low flux. However,
this is absolutely a series/direct feed type SE transformer.

This is the link for the documentations about this particular SE
output transformer called SC-OPT:

http://www.polisois-audio.com/informazioni_eng.html

Looks like this is not a conventional type SE output transformer, but
how can it get any inductance???

ABB Transformer (Open in New Window)

Follow Ups:

RE: Series feed SE OPT with no air gap and low flux?? - danlaudionut 23:37:58 03/16/12 (17)
Tube747

It is a variation on an old idea called a current mirror.
DC current flowing equal to the regular current in the
opposite direction that cancels the needs for an air gap.
The cancelling currents prevent saturation of the core.
The bypass cap shorts the signal across one winding so
that the iron retains half the inductance of the PP OPT.
Which is still much more than any SE OPT has.

DanL
- RE: Series feed SE OPT with no air gap and low flux?? - Tre' 08:51:22 03/17/12 (16)
  Dan, using that circuit, can we do the same thing with any PP output transformer?
  
  Tre'
  Have Fun and Enjoy the Music
  "Still Working the Problem"
  - RE: Series feed SE OPT with no air gap and low flux?? - danlaudionut 09:10:54 03/17/12 (15)
    Tre'
    
    No, you need one that has seperate windings
    instead of just a center tap because
    the tertiary winding is wired backwards.
    Remember if you want a 5K OPT for your circuit
    then you need a 10K because you are using
    only half of the windings for the signal.
    
    DanL
    - Cool - Tre' 13:38:27 03/17/12 (14)
      My pair of Stancor A-8072 should work. If I remember right, they have two separate primary windings.
      
      I also have a pair of Freed output transformers with 4 separate primary windings.
      
      What value should the shunt cap be?
      
      Tre'
      
      Have Fun and Enjoy the Music
      "Still Working the Problem"
      - Why not a parafeed instead of gone thru so much trouble? (NT) - pushpulltriode 02:04:40 03/21/12 (0)
        
        In Reply to: RE: Cool posted by Tre' on March 17, 2012 at 13:38:27
        
        nt
      - RE: Cool - dave slagle 07:32:19 03/18/12 (11)
        
        In Reply to: RE: Cool posted by Tre' on March 17, 2012 at 13:38:27
        
        The cap will effectively short out a winding. This will reflect a very low impedance to the other windings through the core severely loading down one of the tubes.
        
        I don't see the concept working very well in practice.
        
        dave
        
        RE: Cool - Tre' 08:28:57 03/18/12 (10)
        
        In Reply to: RE: Cool posted by dave slagle on March 18, 2012 at 07:32:19
        
        "The cap will effectively short out a winding. This will reflect a very low impedance to the other windings through the core severely loading down [the output tube]."
        
        I'm sure glad you have my back. Sometimes I leave my brain in the other room.
        
        Thanks
        
        So how about a CCS at one end, set to the idle current of the output tube on the other end of the primary winding of a PP transformer?
        
        That should work, no?
        
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        RE: Cool - dave slagle 08:46:15 03/18/12 (9)
        
        In Reply to: RE: Cool posted by Tre' on March 18, 2012 at 08:28:57
        
        Yes, that will work. The currents need to be reasonably matched and make sure you have a load connected since the CCS will fight with the inductance and possibly oscillate.
        
        dave
        
        RE: Cool - Dave Davenport 18:13:49 03/20/12 (3)
        
        In Reply to: RE: Cool posted by dave slagle on March 18, 2012 at 08:46:15
        
        Hi Dave,
        
        "... since the CCS will fight with the inductance and possibly oscillate."
        
        Would you please elaborate on this?
        
        Thanks
        Dave
        
        RE: Cool - dave slagle 18:24:07 03/20/12 (2)
        
        In Reply to: RE: Cool posted by Dave Davenport on March 20, 2012 at 18:13:49
        
        I have used a simple LM350 as a CCS on a tertiary winding of an output for a GM70. The goal was to run 2A of current through a low turn winding to offset 100ma of primary current.
        
        In testing I found out the hard way that there was about 700V at 60Khz appearing across the primary with the CCS operating. This was without the Rp of the tube or a speaker load both of which damped out the oscillation. The OT also had an amorphous core which may have played a role.
        
        In any event the basic idea of not putting two current sources in series is the basis for my warning so they will both fight to be in control which can lead to oscillation.
        
        dave
        
        RE: Cool - Dave Davenport 21:16:15 03/21/12 (1)
        
        In Reply to: RE: Cool posted by dave slagle on March 20, 2012 at 18:24:07
        
        Thanks for reporting this incident. I find it very curious - do you have a thought of what the oscillation mechanism is? And what is important about an amorphous core?
        
        Dave
        
        RE: Cool - dave slagle 15:40:04 03/22/12 (0)
        
        In Reply to: RE: Cool posted by Dave Davenport on March 21, 2012 at 21:16:15
        
        This was a dozen years ago for the GM70 amp I took to NY Noize. A choke approximates a current source and when you put two current sources in series they fight each other. I suspect the CCS was winning but the choke has that "inductive kick" that the regulator then corrected for.
        
        I think the amorphous core was key because it has lower losses at high frequency and since this was happening at 70Khz the core may still be in the picture.
        
        dave
        
        RE: Cool - dave slagle 19:36:27 03/18/12 (4)
        
        In Reply to: RE: Cool posted by dave slagle on March 18, 2012 at 08:46:15
        
        I should also point out that this is a very different design concept to using "loosely" coupled windings to offset the effect of a shorting cap.
        
        dave
        
        RE: Cool - Tre' 11:32:04 03/19/12 (3)
        
        In Reply to: RE: Cool posted by dave slagle on March 18, 2012 at 19:36:27
        
        "...using "loosely" coupled windings to offset the effect of a shorting cap."
        
        Is that what ABB is doing?
        
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        RE: Cool - dave slagle 12:12:00 03/19/12 (2)
        
        In Reply to: RE: Cool posted by Tre' on March 19, 2012 at 11:32:04
        
        ABB???
        
        dave
        
        RE: Cool - Tre' 14:30:32 03/19/12 (1)
        
        In Reply to: RE: Cool posted by dave slagle on March 19, 2012 at 12:12:00
        
        The company that the OP referred to who are making these non-airgapped SE transformers.
        "...Audio Output Transformers for Single Ended Amplifiers
        without gap using an Ari Polisois license of Self-offsetting allowing a very low flux (near 0) also for high d.c. idle currents....."
        Tre'
        
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        http://www.audiodesignguide.com/abb/abb.html (Open in New Window)
        
        Edits: 03/19/12
        
        RE: Cool - dave slagle 15:51:56 03/19/12 (0)
        
        In Reply to: RE: Cool posted by Tre' on March 19, 2012 at 14:30:32
        
        Yes. they seem to be using a design that uses a loosely coupled winding is series with a cap across is.
        
        I tried in spice to get this to work but was unable to get anything near flat results. I still do not see how this idea would work.
        
        dave
      - RE: Cool - danlaudionut 17:18:43 03/17/12 (0)
        
        In Reply to: RE: Cool posted by Tre' on March 17, 2012 at 13:38:27
        
        Tre'
        
        Depends on the inductance of the transformer.
        The Lundahl LL9202/PP worked out to 22uFd.
        
        DanL

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