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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
dan_ed
2,451 posts
 
Hi Brian,

Good to hear you're making progress. Now that you have narrowed the issue, I would suggest keeping as many things constant in your system as you continue to trouble shoot. So stay with the CJ for the time being and concentrate on the table. If you are getting good bass now I think it would be well worth spending some more time adjusting VTA. You may be able to raise the bearing end and open the highs more. This may tell you if there is hope for the cartridge.

If it does turn out to be the cartridge you may be able to correct the issue with just a stylus change. Though, at ~$200 for a new V15VxMR it might be just as well to buy the whole thing.

I don't have any direct experience with the Audio Experience but there are a good many folks happy with theirs. I have heard that the guy building them is pretty responsive.
odourboy OP
4 posts
 
I've spent a fair bit of time trying to align the cartridge and I can't seem to get it in the sweet spot - so I think it's screwed. Ouch! Time for a new stylus or cartridge. :-(

As an aside, I contacted Chui at Audio Experience and he insists I need to let it fully break-in (100-150 hours) before passing any judgement. I am dubious, but I'll give him the benefit of the doubt.

Curiousity got the better of me so this morning I dragged out some gear and did some tests. I graphed the response curve of the CJ FET phono and found it was within 0.8 dB of the standard RIAA curve and just slightly on the 'hot side' at both ends. (Easily within my error of measurement). The AE tube phono was at worst 4 dB below the line on the bass side of the curve and surprisingly, slightly over 1 dB (at worst) below on the treble side - suggesting slightly accentuated upper mids. So this would seem contradict my own listening tests - but more likely, I messed myself up by changing back to the original noname chinese tubes before running this test. I am an EE and fairly well equipped when it comes to test gear.

Dopogue - I am curious where you saw the less that stellar reviews on the AE Phono Preamp. If you can, please point me at them. Everything I read on Audiogon, Audio Asylum and Ebay feedback was positive so I'm really curious.

Cheers, Brian
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
2,253 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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