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    Impedance mis-match

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    rustybutt

    Posts : 40
    Join date : 2015-01-12
    Location : Alameda, California

    Impedance mis-match

    Post by rustybutt on Tue Aug 25, 2015 7:23 pm

    Earlier this year I took delivery of an SP13 preamp with a PH12 phono board, built by Troy.  I loved it, but my wife didn't.  The old preamp was a Bryston solid-state unit which was a fine piece.   But introducing the SP13 my sound went from a very, very good stereo to something wonderful.

    My wife is a front-line professional violinist who works with the San Francisco Ballet Orchestra.   I mostly listen to jazz and cabaret music, which she likes.  But when I put on something classical she hated it.  She said that strings sounded harsh and screachy.  Uh-oh...   I had dropped $1500 on a piece of gear unheard and here she was giving me grief.   Mind you, we spent $12,000 on her violin bow a few years ago, so I had some slack here.  You don't want to know what players at her level pay for a violin...

    I tried swapping out the provide RCA clear tops with Brimer Mazda 6CG7 tubes, which seemed to help.  I also put in plenty of burn-in hours, which also helped a bit, but still it wasn't right.   Discussion with Troy suggested there might be an impedance issue with the load the SP13 was facing.  

    My loudspeaker is the Linkwitz Orion system, which is tri-amplified and comes with an active crossover, which is what the SP13 feeds into.  An e-mail to Siegfried Linkwitz revealed that the input impedance of the Orion crossover was 10 kohms, which is much lower than the SP13 was intended to work with.  Once we realized this, Troy sent out some 1.5 uf metalized poly caps which I installed.  

    Wow...  What a difference!  It sounded good before, but now it's frightening.  I was listening to Taj Mahal last night and it sounded like we were sitting in the studio.  The acapella tracks were amazing.  And my wife approves the sound of strings now Thank Goodness.  

    The point behind this tale is to be aware of potential impedance issues if your tube preamp if feeding into something solid state.  If it's some Mystery Gizmo, make a point of finding out what its input impedance is.  This took my preamp from something wonderful to something startlingly amazing.

    Thanks for the help Troy!

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Impedance mis-match

    Post by zx on Tue Aug 25, 2015 7:57 pm

    Thanks for the info....an time....
    1.5uf were added to stock output caps ?...or old caps were removed an the 1.5uf were added.....what were the uf of stock caps...........





    thanks for the site Bob...............

    rustybutt

    Posts : 40
    Join date : 2015-01-12
    Location : Alameda, California

    Re: Impedance mis-match

    Post by rustybutt on Tue Aug 25, 2015 10:14 pm

    Originally Troy had installed .33 uf Russian PIO caps. He sent me 1.5 uf Audyn metallized poly caps as a replacement. I just wired 'em in parallel instead of pulling the old caps. It sounds awesome and more.

    wgallupe

    Posts : 84
    Join date : 2014-05-18
    Age : 62
    Location : Central Mass.

    Re: Impedance mis-match

    Post by wgallupe on Thu Aug 27, 2015 9:33 am

    Interesting story Rusty! What would also be interesting is to know how those Mazda tubes compare to the RCAs now that you have the impedance issue resolved. Any chance of you doing a comparison for us? The opinions of two professional musicians can only be taken with respect!!!

    Wayne

    rustybutt

    Posts : 40
    Join date : 2015-01-12
    Location : Alameda, California

    Re: Impedance mis-match

    Post by rustybutt on Thu Aug 27, 2015 10:05 am

    The Mazda tubes seemed to help sweeten things up before I installed the new caps. I'll have to go back and move some things around. Maybe this weekend. I'll report back here.

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