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What's Wrong With My Cartridge/Setup?

Please help this newbie sort out a problem with my cartridge, tonearm or installation.

Here's my system: Shure V15VxMR Cartridge mounted on an older Rega Planar 2 Turntable with glass platter into either an Audio Experience Concerto Tube Phono Preamp or a Conrad Johnson SC-22P SS FET Phono Preamp (in a homebrew box) into a CJ Preamp and Anthem Amp-1 tube amp. This system is new to me (most parts are used with the exception of the cartridge which was bought with 'only a few hours use' and the phono preamp (which I ran for 30 hours burn-in).

So here's the problem: My LPs sound like crap. The highs are badly attenuated, the lows are a weak and the entire sound lacks punch. The sound field is totally flat. I've compared a number of vinyl LPs to CD releases of the same material played on my Music Hall CD-25 and the CDs sound considerably better than the vinyl.

I've played with some of the mechanical parameters of the cartridge (tracking alignment, VTA, weight, anti-skating) using a test LP and a scope (as well as my ears). The changes generally have a audible effect but are small compared to the magnitude of the problem. The loading the cartridge is 'seeing' was measured to be very close to the spec of 47K ohms and 250 pF. The two phono preamps I've tried sound pretty similar, so the problem would appear to be with the cartridge/turntable/tonearm setup.

Any ideas? Could cartridge break-in account for such a major sonic impact? Is it fair to compare an LP to a CD of the same material? Help!!!

.... Brian
odourboy
odourboy OP
4 posts
 
Marakantz - To answer your question, with the AE Concerto turned off, the input measures 47K with a DVM. With the unit powered on, this drops to about 9K resistance. I don't have a schematic (so I'm not sure what I'm measuring) nor do I know if the DVM can provide a valid measure with the preamp turned on (tubes are funny things), but there may certainly be a loading issue here. Can you comment?

The CJ on the other hand is nailed at 47K regardless of whether the unit is off or on - but this is no surprise given the very high input impedence of a FET, so I'm basically measuring the input resistor.
marakanetz's avatar
marakanetz
5,473 posts
 
Brian,
Stepping through your comments and experiments made so far, it seems that AE isn't functioning well and the load resistance should NOT change when you turn it on.

My first scientific guess is that the output of your phono is getting short somewhere and feeding back to an input. It may be due to a bad tube(s).

Check thoroughly an output and feedback circuit(if such exists in phono pre).
herman
2,238 posts
 
I would suspect, as you seem to, that the difference in resistance that you measure when on versus off has to do with some voltage being fed back through the input to the meter rather than the input impedance dropping. Switch your meter to volts and see if you get a reading with the amp on. Whether this is normal or not is impossible to tell without a schematic.

As you are probably aware, a better test is feed a signal to the preamp and then insert resistance in series until the signal at the input drops to 1/2 the original. The inserted resistance is then equal to the input impedance. The problem with conducting this test is that the signal levels are so low it is difficult to get accurate measurements.
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