• Re: Enter the 'Mour-- Thanks Paul & VS! - Endeavour 12:02:40 01/13/04 (0)
  In Reply to: Enter the 'Mour-- posted by Endeavour on January 12, 2004 at 15:22:32:

  If anyone asks for me, tell 'em I am lost deep in the archives :)
  
  

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• Re: Enter the 'Mour-- - Paul Joppa 16:56:19 01/12/04 (9)
  In Reply to: Enter the 'Mour-- posted by Endeavour on January 12, 2004 at 15:22:32:

  OK, so I'm an idiot to say this (since I get a few bucks every time Doc sells a Paramour!). But with 104dB speakers, you will be hard pressed to completely eliminate hum with **any** DHT amp that has AC filament power.

  The fully original stock Paramour, with the SRPP driver stage, has (if I recall the numbers right) 4 or 5mVrms hum, which comes from the power supply at the driver stage output. The C4S upgrade, included in the kit, pretty much eliminates that source of hum. That leaves two sources at the output stage, power supply ripple and the AC heated filament. Again, I am unclear on the numbers but I think it is around 1 or 2mVrms. Both sources are approximately equal, so any significant improvement must address them both.

  With the new power transformer, the 2.5v winding is shielded to minimize common-mode noise, which is capacitively coupled and therefor emphasizes higher frequency components (buzz). That's a modest improvement. A RRSF or high-voltage Schottky diodes would also probably help with buzz. You can raise the power supply caps to 100uF, or replace the 270 ohm resistor with a filter choke, or both, to get the power supply ripple down. (The latter is part of the iron upgrade package.)

  Even with all these tweaks, there is still some hum from the filament heating which can only be killed by using DC filament power. The transformer is not designed to support this; I'll have to study the problem to see if something creative can be done using the 6.3vCT winding. You would have to switch to a Type 56 or other 2.5v driver, which will give you low gain but with a Foreplay it could work out.
  
  

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  • I've got 103 dB speakers - VoltSecond 19:30:41 01/12/04 (5)
    In Reply to: Re: Enter the 'Mour-- posted by Paul Joppa on January 12, 2004 at 16:56:19:

    My fully tricked out amp isn't bad for hum. The problem with hum is that it often comes with very annoying buzz. The buzz can be killed dead. Then what is left is a pure low frequency note. DC heaters can easily bring back some of the buzz even thought the hum goes away. Make DC heaters absolute last on the mod list.

    I have only one tube I hear hum from and that is my AVVT mesh plate.
    
    Play safe and play longer! Don't be an "OUCH!" casualty.
    Unplug it, discharge it and measure it (twice) before you touch it.
    
    

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    • Re: I've got 103 dB speakers - fshmstr 07:42:10 01/13/04 (3)
      In Reply to: I've got 103 dB speakers posted by VoltSecond on January 12, 2004 at 19:30:41:

      Volt Second, What are the stratagies for killing this buzz dead. I've got a little of this on my 'mours (simple snubber on diodes) and the same type of buzz on a homebrew pp 6bq5(DC heaters floated off a voltage divider that also serves as a bleeder for the HV rail, also with a small cap across the silicon rectifiers). It's very annoying and any help to fix it is greatly appreciated.
      
      

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      • Re: I've got 103 dB speakers - VoltSecond 19:09:15 01/13/04 (2)
        In Reply to: Re: I've got 103 dB speakers posted by fshmstr on January 13, 2004 at 07:42:10:

        1. Filament snubber capacitors on driver tube. Very critical in the Paramour.
        2. HV snubber
        3. .01 uF ceramic cap signal ground (terminal 12) to chassis (13)
        4. Filament snubber on 2A3
        5. Balance pot trim mod.

        All my notes are on my Paramour page.

        In the other amp, add a UF4007 inseries with the normal diode bridge.
        
        Play safe and play longer! Don't be an "OUCH!" casualty.
        Unplug it, discharge it and measure it (twice) before you touch it.
        
        

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        • Re: I've got 103 dB speakers - fshmstr 08:19:32 01/14/04 (1)
          In Reply to: Re: I've got 103 dB speakers posted by VoltSecond on January 13, 2004 at 19:09:15:

          Thanks Volt Second, I will begin working on the above. For the push pull amp, I assume you mean the diode bridge for the filaments. Does it matter where I put the UF4007? before the filter, or in the ground leg of the bridge? Also I forgot to mention that the DC is on the voltage amp and the splitter/driver (6SN7) only, the power stage is AC heated. (My scrounged power transformer has two 6.3v windings) Thanks again.
          
          

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          • Re: I've got 103 dB speakers - VoltSecond 18:35:35 01/14/04 (0)
            In Reply to: Re: I've got 103 dB speakers posted by fshmstr on January 14, 2004 at 08:19:32:

            The UF4006 goes between the rectifier bridge "+" and first capacitor.
            
            Play safe and play longer! Don't be an "OUCH!" casualty.
            Unplug it, discharge it and measure it (twice) before you touch it.
            
            

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    • Good point! - Paul Joppa 23:59:40 01/12/04 (0)
      In Reply to: I've got 103 dB speakers posted by VoltSecond on January 12, 2004 at 19:30:41:

      > > I have only one tube I hear hum from and that is ...

      I should have mentioned that. Some individual tubes just have less residual hum (after hum pot adjustment etc.) than others. There are tricky things that tube designers did using the magnetic field hum of the filament to cancel the electric field hum, for instance. I don't think these tricks are even known today, I've certainly never seen any written description of exactly how it was done. And even then, the tube has to be manufactured to the precise geometry as designed. And has to maintain that geometry through the heating/cooling cycles.
      
      

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  • Paul - filament CLC with CMC ala Buddhafied Afterglow? - John Bennitt 18:44:42 01/12/04 (2)
    In Reply to: Re: Enter the 'Mour-- posted by Paul Joppa on January 12, 2004 at 16:56:19:

    Has anyone tried the CLC shown in the Buddhafied Afterglow article?
    I believe it's a 4.7mH CMC between 5.8uF 50V film caps on the 2A3 filaments - would the stock Paramour power transformer handle the current?

    I'm curious - I have some Panasonic CMC's ... ;)

    John
    
    

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    • Re: Paul - filament CLC with CMC ala Buddhafied Afterglow? - Paul Joppa 15:06:47 01/13/04 (1)
      In Reply to: Paul - filament CLC with CMC ala Buddhafied Afterglow? posted by John Bennitt on January 12, 2004 at 18:44:42:

      The current in the cap would be small, and also 90 degrees out of phase with the heater current - should be no problem. The CMC filter would remove common mode noise, and the cap would damp ringing in the power transformer.

      I would install an RRSF before treating the filament power, if you have the new power transformer - I expect it would do more good. But I have not actually done the experiment yet, so that's just guessing.
      
      

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      • CMCing a filament - VoltSecond 21:02:03 01/20/04 (0)
        In Reply to: Re: Paul - filament CLC with CMC ala Buddhafied Afterglow? posted by Paul Joppa on January 13, 2004 at 15:06:47:

        When a filament is common mode choked, there is a real risk of the CMC resonating with the power transformer capacitance in an audible region. This would be a series resonance where the impedance at resonance will drop to the DCR of the CMC added to the DCR of the transformer windings.

        A way to fix this is to add a series RC on the transformer side of the CMC to star ground. The cap value should be one to two times the transformer's effective capacitance. The resistor's value tuned to the LC tank impedance. When this is done, the series resonance will be of a low Q and a much higher minimum impedance. (2K ohm instead of 50 or so ohms.)

        Tweaker's note: If adding a part hurts the sound, that point in the circuit is sensitive. Before you yank the part back out and smash it to bits, ask why it sounded worse. Occasionally, adding one or two more parts may leap frog you past the sound of the original circuit. Sort of a "take one step back and then take a giant leap forward" type of deal.

        
        
        
        Play safe and play longer! Don't be an "OUCH!" casualty.
        Unplug it, discharge it and measure it (twice) before you touch it.
        

        • LC tank Q Notes.   (Open in New Window)

        
        

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