Passive pre amps

Discussion in 'General Audio Discussion' started by vintage 5.0, Jul 8, 2018.

  1. vintage 5.0

    vintage 5.0 vintage 5.0 Subscriber

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    I really like using passive pre amps. I do think for them to be effective one of the most important things is amp matching. I have used a passive with monarchy SM 70 amps and the results were amazing. I also use them with McCormack amps with the same results. I see folks say they are not as dynamic and to me I get the opposite effect. I hear the music only and it seems to be more alive. This is with the right amps. I was curious what others have found using passive pre amps.
     
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  2. Poinzy

    Poinzy Super Member

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    I use passive attenuators from time to time. I don't use them for sound-quality purposes, just for extra control of the signal level.
     
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  3. mprince

    mprince AK Subscriber Subscriber

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    I use a Luminous Audio Axiom II with a modified/restored Adcom GFA-545 amp, sounds absolutely great to these ears, better than the previous Adcom preamp/tuner I had in the rotation. Inputs to it are a Rothwell phono pre and a very inexpensive Fiio DAC. Technically it has 3 inputs, but I only use 2 as the third input is a "direct" input and I have not had sources that play nice with it in the past. When I've had more sources, I've used an inexpensive RCA switcher and that works well.

    My system is very simple/basic, but the Axiom II works perfectly in it for me.
     
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  4. sqlsavior

    sqlsavior AK Subscriber Subscriber

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    I use a magnetic passive preamp, which uses a multi-tap transformer to attenuate the signal, rather than a potentiometer or resistor arrangement. As far as I can tell, this reduces or eliminates the need for amp matching due to impedance concerns. And it is very quiet. I haven't experienced any reduction in dynamics, just an increase in clarity, transparency, and resolution. I feel that my Promitheus TVC really lets me hear what's what.

    Oddly, I've never used a resistance-based passive, so I can't compare, but as a minimalist, I believe in them, too. Sometimes less is more.
     
  5. Danddd

    Danddd AK Subscriber Subscriber

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    I really like my TLC with the Sonic Frontiers tube amp, it's a good match. I do find my VTL 2.5 pre was a better match to my DNA 0.5 though. More dynamics and a lush sound. Lush may not be preferred to people, but the difference was significant to the TLC. Still all very nice units.
     
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  6. E-Stat

    E-Stat Addicted Member

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    Attenuators can provide a very cost effective way to improve resolution. One does have to have enough gain and a good impedance ratio. I used one for about ten years that I built using DACT attenuators, JPS Labs wire, Cardas connectors in a Par-Metals cabinet. With a GamuT CD-1 source and low cap JPS Labs interconnects, it outperformed an Audio Research SP-9 MKIII in terms of resolution and stage width. I didn't think it reduced dynamics until... I heard better.

    My current SP20 definitely does better at the low end of the dynamic scale using wide range content.
     
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  7. vintage 5.0

    vintage 5.0 vintage 5.0 Subscriber

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    That is interesting info about the VTL 2.5 pre amp. Sounds like it really worked well with the DNA .05.
     
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  8. mjw21a

    mjw21a Super Member

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    I tried a 50k Khozmo Akustyk passive preamp with both Red Wine Audio Signature 30.2 mono blocks and a Quad 405 copy and found it to be boring and lacking dynamics.

    On the other hand my Schiit Saga (passive resistor based ladder with a tube buffer) to give the best sound I've heard in my life paired to either a Quad 405 copy or darTZeel NHB-108B copy. That's both with and without the tube buffer engaged. Extremely dynamic and transparent to a fault.
     
  9. dcmfan

    dcmfan AK Subscriber Subscriber

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    Lately I've been using an Antique Sound Labs Passive preamp. (Passive TX-1DT).

    Transformer Volume Control means no resistors in the attenuator. Very clean and detailed sound.
     
  10. Mark B

    Mark B Yamaha Fan Subscriber

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    I really like the passive line stages and the "no gain" buffer line stage that I'm using. All are different designs.

    - Yamaha YPC-1 - passive line stage using an Alps RK501 potentiometer (10k ohm output impedance) for volume control.
    Impedance matching between this line stage and amplifier is critical. An ideal match is an amplifier with an input impedance of 100k ohm or greater (10 x the
    output impedance of the YPC-1. I've found that the YPC-1 works well with some amps with input impedance as low as 25k ohm such as the Yamaha M-2.

    - Townshend Allegri - passive line stage using an autotransformer volume control. This design is easy to match to amplifiers.

    - Horn Shoppe The Truth - active buffer no gain line stage using a photo cell for volume control. This design is easy to match to amplifiers.
     
    Last edited: Jul 10, 2018
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  11. vintage 5.0

    vintage 5.0 vintage 5.0 Subscriber

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    That makes sense why the passive sounds good on my McCormack amp. I checked and it has a 100 K ohm input impedance.
     

     

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  12. vintage 5.0

    vintage 5.0 vintage 5.0 Subscriber

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    Thanks for all the good info. It is good to hear others like the passive pre amp.
     
    Last edited: Jul 9, 2018
  13. DeeCee

    DeeCee Super Member

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    Well, this is what I thought...

    https://www.audioasylum.com/reviews/Preamplifier-SS/Sonic-Euphoria/PLC/amp/97587.html
     
  14. Pio1980

    Pio1980 AK Member Subscriber

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    Of course these "passive" controllers aren't really "preamps" in that no active stage gain occurs.
    I've used a passive control center for decades, off and on as my standard, recently displaced by a Pass Labs B-1 active unity gain buffer controller. The jury is still out on the differences, but it's still in use at present.
     
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  15. rothwellaudio

    rothwellaudio Forums Sponsor Sponsor

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    The term "preamp" when applied to a passive controller does make sense when viewed with some historical perspective. What we now usually refer to as power amplifiers were simply called amplifiers back in the 50's. Anything that came before the amplifier in the signal chain was known as a pre-amplifier. It's therefore perfectly logical to use a simple passive device before the power amp if nothing else is needed and refer to it as a preamp.

    Actually, the modern terminology that does annoy me is the "passive plus buffer" preamp such as the Nelson Pass B1. People routinely refer to it as a passive preamp and never put it into the "active" category. If it isn't active, how come it won't work without any power?
    Nelson Pass himself doesn't claim his design is not an active preamp - it's just the people who talk about them on forums.
     
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  16. Dr Tinear

    Dr Tinear AK Subscriber Subscriber

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    I tried passive volume control when I was testing a pair of EPI 180 speakers that I had just re-foamed. I hooked them up to a Dynaco Stereo 400 amp and fed the amp directly from a Magnavox CDB-460 CD player, using the amp's left and right volume controls to regulate volume and balance. The sound quality was superb. I've tried other source and electronics combinations with the EPIs since then, but I keep coming back to the big Dynaco with a CD player driving it directly because it just sounds right.
     
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  17. DeeCee

    DeeCee Super Member

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    Actually, in your context, "pre-amplifier" makes a lot of sense. I never thought of it that way. But in my case (a TVC passive controller) it does add gain without power, so both descriptions work (in a sense)!

    What a deal! ;)
     
  18. Pio1980

    Pio1980 AK Member Subscriber

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    Yes, and no. Signal energy is not enhanced as with an "active" stage, tho' the voltage/ current ratio can be "transformed".

    The downside is that cable capacitance and output loading has a greater effect on the output end when voltage increases and current reduces in that end with passive transformation. An active stage adds current (and voltage if gain occurs) from a power source to the signal to overcome to an extent both capacitance and resistance/ impedance loading.
    No "free lunch" here with a transformer alone.
     
    Last edited: Jul 10, 2018
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  19. DeeCee

    DeeCee Super Member

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    Which is why careful matching of source and cable is a must to get maximum performance from a passive (for resistive and transformer types.)
     
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  20. Pio1980

    Pio1980 AK Member Subscriber

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    And of course, very dependent on the drive energy potential of a given signal source. The active buffer approach is a minimalist-plus solution. The downside there is that a couple of blocking capacitors get added in the chain with the active element, and choice options ensue. My choice would be for the more theoretically "perfect" capacitors practicable, but left in the Sonicaps that came in the B-1 for the time being. I'll likely go with Wima FKP if I change them out.
     

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