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Koetsu RSP Sound Problem

I recently bought a Koetsu RSP from a very reputable dealer. The cartridge is about 10 years old (based on serial number) and sat unused, after about 150 hours of initial use, for almost a decade.I now have about 100 hours on it myself.
It is mounted in a Reed 2A 12" Cocobolo arm on an SP-10 and runs through a Coincident phono stage (retubed with NOS Mullards) and Coincident Frankenstein monoblocks with Takatsuki 300b’s.

The RSP sounds very good with excellent bass and surprisingly extended treble but has leanness in the lower midrange and somewhat accentuated upper midrange (sibilant). I am fairly confident of the alignment and have tried VTA’s from slightly above to slightly below level, adjusted azimuth visually, electronically and sonically and have run VTF from 1.92g to 2.00g. I have also been adjusting loading and have tried 100 ohms with both TX2575 resistors and Shinkohs. The Shinkoh provides a slightly fuller midrange but the 2575 has a transparency that is hard to ignore.

No matter what I try and I can’t remove the midrange imbalance which is very contrary to the Koetsu RSP reputation.I also get some mistracking on high energy vocals. I am considering sending it for a rebuild but thought I would post here before shelling out the $$$ to see if anyone else has experienced this issue.




jarrett
lewm
13,228 posts
 
(1) ~2g seems perhaps a bit high for VTF, at least it is for my Urushi.  Have you tried 1.5 to 1.6g? (For all I know without looking it up, the VTF you are using may be the recommended one.) In any case, I would put a few more hours on the cartridge before doing anything drastic, if you think the history is accurate.  On that score, have you examined the stylus under magnification to verify its "like new" condition?  Test LPs with "break-in" cuts on them can be very helpful to wake up cartridges that have been long in storage.  The Cardas test LP is one that does have that feature; I use the 2a, 2b, 2c sections for that purpose.
(2) Have you got a fix on the inherent sound of the rest of the system, using some other cartridge?  Can you be confident that the tonal balance you ascribe to the Koetsu is in fact due to the Koetsu?


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rauliruegas
13,103 posts
 
Dear jarret: """"  I also get some mistracking on high energy vocals.  """

The RSP is not exactly with the same Koetsu sounds signature that all previews models, as you noted has extended high frequency range but even that is different and I can't be sure if that " imbalance " in the mid range is a real imbalance or part of the cartridge it self or part of your own preferences on kind of sound.

What is an " imbalance " is that mistracking because the RSP is way better tracker that what you are experienced. Could be a non proper match with your tonearm, a faulty tonearm at the bearing or a RSP problem in its suspension and if this is the problem only Koetsu can fix that suspension and maybe they do it by free of charge.

Regards and enjoy the music,
R.


daveyf's avatar
daveyf
2,894 posts
 
I think a lot of us forget that there are other issues relating to cartridge wear, besides just the stylus wear. A common problem is the drying out of the suspension components that are internal to most cartridges. After sitting in storage for many years, this would be one of the most likely issues. It would/could also explain a lot of the issues that the OP is concerned about.
Sounds like a re-build would be a good idea.
bobsdevices
100 posts
 
I have personally owned a Rosewood Signature Platinum (RSP) along with several other Koetsu Cartridges.  I loved the sound of the RSP.  After considerable use, I needed to retip it and sent it to Soundsmith for repair.   I was extremely pleased with the results.  I have also send other cartridges to Soundsmith and each time was pleased.  Twice, I got one back with not charge, except for return shipping, when they said that nothing was wrong.  I suggest you go on line and send it in for evaluation.  They say there is a nominal charge for doing that, but you don't have to make a decision up front to rebuild it, you can get their opinion of the condition before making a decision.
inna
7,296 posts
 
Good points above, from people far more experienced than I am.
I would give it another 100 hours of real play, with not valuable records just in case, and only then send it out for evaluation. After ten years it might need time to wake up. 
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