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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
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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syntax's avatar
syntax
2,193 posts
 
Koetsus are very sensitive for proper alignment.
Most think, they have done it correctly, but from my experience, most fail. And this piece of wood - which may be called tonearm from some - is hardly something done right.
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