Friday, May 9, 2014

Kenwood KT-6040: incredible resolution and liveliness

Last weekend (first Saturday in May) I modified my Kenwood KT-6040 FM tuner by replacing the 50uS deemphasis capacitors (since it was a European model…KT-6040 in US version so rare it may not even exist) with the 75uS deemphasis caps needed to bring it to the 75uS deemphasis required in the USA.  On Thursday night, I hooked up the newly modified turntable to my Sonos audio network.  The sound has remarkable transparency, resolution, and liveliness, listening to the KRTU college radio jazz station.  It sounds like it has more resolution, depth, and spaciousness than you might get from typical CD's.  It is very fun to listen to, and by the morning I was playing the station in all 3 Sonos equipped rooms in my house as background music.  Bopping away.

Previously used tuner on same antenna was Yamaha TX-1000 (US model).  It also sounded very good, and possibly less noisy, but not quite as transparent as typical CD sound.  Nice, but not as compelling.

The noise on KRTU is something like a background tone in both channels but out-of-phase.  It's not the pure 10kHz tone I've determined to be a station fault on KPAC, but it could be a similar kind of thing (intermodulation of the 19kHz pilot with subcarriers).  It's sounds a bit like (but clearly isn't) the groove noise you might get from a worn out record being hit with metal stylus and 20g stylus force.  It becomes obvious in quite parts, such as between words of the DJ, but then gets hidden in louder portions of the music.  I now believe this noise might be ameliorated with a better antenna (unlike the noise on KPAC, which doesn't go away even with antenna near the transmitter).  Given that it sounds louder than with the Yamaha, I'll have to check if I was using "high blend" or the like with the Yamaha.  Or it could be that it's more obvious on the Kenwood simply because of greater transparency.

Despite the noise, and occasional sense of harshness (probably resulting from the noise) I still like the Kenwood sound much better because it sounds so much more alive.  This is not merely a tipped up frequency balance in the highs (though the frequency balance might be tipped up a tiny bit too).  I'm considering this to be a big improvement, with only minor qualifications.  And I think I can hear the "teflon" sound in the super high resolution and spaciousness.

This project had been delayed for something like 4 years.  For quite awhile, I used the tuner with a Behringer DEQ 2496 to correct the deemphasis externally.  (I figured out exactly the required shelving filter needed to change the deemphasis…and this worked, though hardly elegant or optimal.)  Also, I used other tuners a lot, including the Pioneer F-26 (which now is assigned full time duty for the classical radio station…since it sounds so good on that tuner, better than the KT-6040 with digitally corrected deemphasis for sure).  Then, for over a year, I enjoyed the stellar Kenwood L-1000T which beat all my other tuners on every station, and it has two antenna inputs so I could use both antennas.  I took the Kenwood offline when it seemed to exhibit some power supply instability.  Most recently (well, just the past 2 weeks) I was using a Yamaha TX-1000 for the small college radio stations (keeping the F-26 on classical music station).  On the antenna that works best for the college radio stations, the TX-1000 is remarkably good sounding.  (It sounded horrible on those stations using every antenna position I tried in the master bedroom.)

But the plan had been to get the KT-6040 online for college radio duty asap.  I first hoped the job could be done without new parts and gave it to Luther for modification.  Luther however informed me that parts would be required, and that led to the most recent phase before Saturday…getting the needed parts.  Friend Tim determined which capacitors I needed to change and to what value (the schematic was very hard to interpret because of multiple country options).  What I needed to do was change 1500pF capacitors to 2200pF, right at the output of the MPX chip.  (This was not even suggested by the schematic.)

I first came across some Russian FT-1 PTFE (aka Teflon) 2200pF capacitors.  They were cheap enough that I straight away ordered 5, but with the fear that likely I would not be able to use them.  If they had steel leads, which Russian teflons (created for use in military equipment) were often known as having, I would be better off using something else, even if not quite as good as Teflon.  Then I also ordered some Phillips polystyrene capacitors, which I felt sure would not be using any ferromagnetic parts.

It took over 6 weeks to receive the Phillips caps from the seller in UK.  I got the Russian caps somewhat faster from Romania.  Actually, when I first saw that I was getting a shipment from Romania, I figured it was the custom turntable base I had ordered from Moldova, which at the time I was far more concerned about.  I missed the delivery attempt on Friday and went down to the Post Office on Monday.  They couldn't find the package.  At first they suggested it might have been shipped back.  They would find out and call me.  They never called, so I went down again the next day.  This time I spoke to the Postmaster, and he said he would call his associate at the central post office and be sure it was held and returned to the local post office.  But I was too anxious to wait, so I went to the central post office right then.  The central post office said they did not do any kind of customer pick up. However, they checked again, and said my package had just been delivered!  (Before going to the post office on the second day, I had signed a delivery release form and attached it to the door.)  So I hurried home, and couldn't see the turntable base anywhere.  I checked my mailbox, and there were the Russian caps from Romania, which by that time I had believed were likely useless.

It wasn't until waiting several more weeks waiting for the polystyrene caps that I got around to actually testing the Russian caps with a refrigerator magnet.  Nothing on the test cap showed any sign of ferromagnetism.  The next day I obtained a stronger magnet from Radio Shack and tried again.  Still no sign of ferromagnetism.  Some online discussion at DIYAudio suggested the grey colored leads (which are grey all the way through) are a silver/copper alloy.  That's about as cool as it gets in audio, Teflon caps with silver alloy leads.

Still, I figured the polystyrenes might be safer, so I continued waiting.  Finally I got the polystyrene caps, just before my eBay buyer protection was about to run out.  And to my shock I found the polystyrene caps were definitely ferromagnetic, they showed strong attraction even to the weak refrigerator magnet.

I've been surprised at the many audiophiles and DIYAudio's not aware of the fundamental ranking of capacitor dielectrics with regard to dielectric absorption, and the importance of dielectric absorption with regards to audio.  I've known about this since reading Marsh in 1980.  Here's a more recent article which notes the decline in availability of some dielectrics, especially polystyrene.  The rankings are PTFE (aka Teflon, the best), Polystyrene, Polypropylene, Polyester (aka Mylar), and way below these polymer films are the electrolytic dielectrics aluminum oxide and tantalum oxide.

1 comment:

  1. Hello,

    Can you tell me what capacitors I have to replace to use KT6040 in US?

    Thank you.