High Efficiency Speaker Asylum

• Re: Emulating tube amp source Z w. solid-state - is series RL network enuff? - Tom Dawson 13:32:05 11/12/01 (3)
  In Reply to: Re: Emulating tube amp source Z w. solid-state - is series RL network enuff? posted by freddyi on November 12, 2001 at 12:40:46:

  Hi, Freddy -

  Besides signal path capacitor upgrades and a beefed up capacitor value at the output stage supply, it's stock - no changes to resistor values. The damping factor is somewhere between 8-16 across most of the audio band. What I found interesting here that is if I beefed the supply capacitor any more than that, the Stereo 70 particular dynamic character started diminishing, implying that supply droop plays a part in this amp's characteristic sound.

  Your Eico 6BX7 amp sounds like a gem. I have read that the 6BL7/6BX7 share many characteristics of the 6SL7 type such as great linearity and low microphonics, only with much increased power capability.

  As a matter of fact, I am using the 6BL7GTA as a fully DC coupled long tailed differential driver tube for my OTL design which uses 8 6AS7G's per channel as totem pole outputs. One half of the 6BL7 drives the upper 6AS7's as followers and the other half drives the lower 6AS7's as inverters with local feedback from the output to the 6BL7 plate resistor to bring the gain into equilibrium with the upper half of the pp output. Even running open loop, the gain matching is so good with this output arrangement that no assymetrical distortion is visible on an oscilloscope under load or open circuit, which implies very good linearity on the part of the 6BL7 since the plate to cathode voltage of the section driving the lower half of the output stage is biased to 170VDC lower plate voltage than the upper half.
  
  

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  • Re: Emulating tube amp source Z w. solid-state - is series RL network enuff? - freddyi 14:41:27 11/12/01 (1)
    In Reply to: Re: Emulating tube amp source Z w. solid-state - is series RL network enuff? posted by Tom Dawson on November 12, 2001 at 13:32:05:

    Tom -

    wish I had the knowledge/brains to engineer an OTL - pretty cool - don't remember NYAL/Futterman being rully stable.

    I'm looking at cheap solid-state power - might be wrong path widerange(?) but ok for woofers - QSC RMX 2450 is class H (-is that a multi-tiered power supply like old Carver Cube?) - think DJK said QSC were "loud" (implying not much punch - 2450's 1200 w/channel rating @ 2ohms ought to do something... I have no way to audition anything)

    Freddy
    
    

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    • Re: Emulating tube amp source Z w. solid-state - is series RL network enuff? - Tom Dawson 15:29:48 11/12/01 (0)
      In Reply to: Re: Emulating tube amp source Z w. solid-state - is series RL network enuff? posted by freddyi on November 12, 2001 at 14:41:27:

      Hi, Freddy -

      I quickly read a review of the QSC amp - looks like a dual voltage supply. It might be ok SQ-wise for a bass only amp, but I would check out ahead of time in showroom whether the fan noise might be too high for a listening environment.

      I once rented a Crown 2400 from a pro shop for a few days to evaluate it as a possible bass driver - sound was good for SS, but the fan noise was just too much for use in the same room w/the speakers, so I dropped that idea.

      Since then, I got a 'green' Crown K2 for HT SW use - I wouldn't recommend it for a full range amp or for a high end system because it goes into 'sleep' mode under 'no signal' conditions & apparently has an audible delay when 'waking up', but for HT SW power, I figured, what the hey, it gets the most out of a 15A circuit & is well-behaved otherwise.

      However, the Hafler 500 sounds like it has potential to me for more high quality applications requiring power. When I tested one channel into a 3-4 ohm load, I was hitting about 60V RMS at clipping, plus it has a pretty good reputation SQ wise for a SS amp. OTOH, DJK has criticized the 500 for 'mushy' bass in pro sound applications.
      
      

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  • Re: Emulating tube amp source Z w. solid-state - is series RL network enuff? - Tom Dawson 13:40:55 11/12/01 (0)
    In Reply to: Re: Emulating tube amp source Z w. solid-state - is series RL network enuff? posted by Tom Dawson on November 12, 2001 at 13:32:05:

    I forgot to mention that I wound up doubling the overall capacitance at the output stage of the ST70.

    Also, a typo - it's 'asymmetrical'.
    
    

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