• 10-01-2013, 04:56 AM
    Active vs. passive preamps - recent experience
    A couple of years ago I sold my tube preamp and replaced it with a passive. I was satisfied with the experience in combination with my Class D Audio SDS amp, however when I decided to experiament with a different sound in the form of a Forte 5 amp, I questioned the adequacy of the passive. Many people have stated that passives repress dynamics and, to be sure, the Forte really lacked "PRaT".

    So I bought a new, active preamp, an Audio Research LS9. It's a solid state preamp; one might question that decision but let's leave that aspect aside. I wanted a clear, neutral, balanced preamp and that's what the LS9 is.

    So what are are my conclusions to this point?

    First, with the Forte 5 the increase in dynamic contrast is relatively huge. What I took to be an excessively laid-back if not down right boring amp is actually pretty decent thanks to the active LS9.

    Secondly -- and surprisingly -- the SDS' PRaT is also somewhat increased. I'm not sure of the fundamental cause in this case: I'm using the balanced outputs on the LS9 and the SDS is optimized for balanced input, so is it purely the active preamp or is it the amp responding to balanced inputs? Dunno.

    Thirdly the high frequencies seem very slightly boosted for both amps -- mostly a good thing in the case of the Forte 5, entirely a bad thing in the case of the SDS. Is the effect related to the preamp's improved dynamics or is it just that its got boosted (or distorted) highs? Dunno.

    The think that does seem clearly confirmed for me is that an active preamp can significantly improve the dynamic contrast of the music depending on the associated equipment.
  • 10-01-2013, 08:03 AM
    Congrats on the new preamp. Have you tried the preamp and SDS with single ended IC's instead of the XLR? It would be interesting to see if there is a difference.
  • 10-01-2013, 08:26 AM
    2 Attachment(s)

    Originally Posted by blackraven View Post
    Congrats on the new preamp. Have you tried the preamp and SDS with single ended IC's instead of the XLR? It would be interesting to see if there is a difference.

    I haven't done that yet but it would be worthwhile to see the effect.

    I can mention a 4th finding. With the CDA SDS, from the LS9 using the balanced inputs, the bass is tightened a bit. The bass drum beat around 9:20 of the Stranvinsky The Firebird recording on Reference Recordings mentioned in your 'Reference recordings' thread is remarkably more controlled and life-like than I've heard it before.

    (stock photos) ...

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  • 10-01-2013, 01:49 PM
    Congrats on the nice Pre. Now you are listening to the Pre and it will make most amps appear to sound better, but it's all about the Pre and less about the amp.

    My VAC makes all my amps sound good and with a lesser pre, like my Hafler 945...not as good but expected.
  • 10-09-2013, 05:19 PM
    I've had a great experience w/ passive pre between Sony ES cdp (2v output) and AES tube power amp (1v input for max output).
    The issue with passive preamps is they can compensate for change in impedance between gear and at different volume settings. When it doesn't work it's because of an impedance mismatch between gear. As you have discovered its all about synergy.