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more on Hk W-5m restoration, passive preamp?

174.51.102.111

PeterI

A

The work is progressing. But I am finding lower volume - I think I should leave out one of the 15kohm resistor on the input. Max volume is just ok, would like to raise it. Man, these voltages are high. Will be increasing PS resistors value to try to bring them down. Also, 1st cap after rectifier will be a lower uf.

Because my music source is my laptop (or CD P) and I digital stream into a DAC, there's no volume control. I'd like to make a separate passive preamp to control input to these vintage amplifiers. What would be a good pot value? 100Kohm? more? I've always wanted to make one.

100 degrees here in Denver, but it won't keep me from soldering (soldiering) on.

thanks for any help,
Peter

Follow Ups:

RE: more on Hk W-5m restoration, passive preamp? - Tre' 13:32:22 06/20/12 (5)
If you use a 100k pot it's output impedance will be 25k when adjusted to -6db.

If you have 200pf of cable + Miller capacitance the -3db point will be 32kHz. The phase will be off all the way down to 3.2kHz.

Get a autoformer volume control from Dave.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
- http://www.intactaudio.com/atten.html (Open in New Window)
- That is a pretty good price . . . - John PA 15:05:09 06/20/12 (4)
  for an autoformer. Have you used these?
  
  The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
  iRiver H140/MB Balanced dac/amp/Ultrasone Ed. 9/JH13 Pro IEM's
  
  see images at: www.pbase.com/jamato8
  - RE: That is a pretty good price . . . - Tre' 08:23:22 06/21/12 (3)
    No I haven't but Dave knows his stuff on magnetics. I bet they sound great.
    
    Tre'
    Have Fun and Enjoy the Music
    "Still Working the Problem"
    - I looked at it again and . . . - John PA 17:07:51 06/21/12 (2)
      it is an interesting implementation.
      
      The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
      iRiver H140/MB Balanced dac/amp/Ultrasone Ed. 9/JH13 Pro IEM's
      
      see images at: www.pbase.com/jamato8
      - implementation - Tre' 18:10:26 06/21/12 (1)
        
        In Reply to: RE: I looked at it again and . . . posted by John PA on June 21, 2012 at 17:07:51
        
        Mine has 24, 2db steps. Feeds straight to the SET 5687/6b4g power amp.
        
        An AVC is great in that it's output impedance is the same as the source when turned all the way up and the output impedance goes down as you turn it down.
        
        At -6db you're at 1/2 the winding so the impedance ratio is 4:1
        
        If your source is 1k ohm, the output impedance of the AVC is 250 ohms.
        
        If the input impedance of the power amp is 100k ohms, the source "sees" 400k ohms.
        
        It's a win, win.
        
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        It is nice to see your CL string in . . - John PA 21:47:22 06/21/12 (0)
        
        In Reply to: RE: implementation posted by Tre' on June 21, 2012 at 18:10:26
        
        the supplies.
        
        The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
        iRiver H140/MB Balanced dac/amp/Ultrasone Ed. 9/JH13 Pro IEM's
        
        see images at: www.pbase.com/jamato8

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