TubeCube Gone Bad…

I can’t say I was entirely surprised, but the TubeCube started acting up. I normally have it turn on with the rest of my desk–I have a remote switch which turns on the lights, TubeCube and DAC. I noticed the tubes would not light up until maybe 10-15 minutes later.  As the next couple of weeks went on, it would take an hour or two for the tubes to light up.  Finally, it quit turning on altogether.

Crap. The audio circuitry is dead simple, but the power supply? Forget it. It is a switching power supply which utilizes all sorts of SMDs (surface mount devices) that are impossible for me to work on.

I did notice that the capacitors in this unit were all off-brand chinese capacitors. Some were labeled Chong, and I couldn’t help but think of them going “up in smoke.” At any rate, I had read elsewhere that there were two pairs of capacitors in the audio circuit that could stand improvement by changing the values–the cathode capacitor, and the coupling capacitor.

Armed with that idea, and a set of calipers, I went to examining all of the electrolytic caps in this amp. I figured that I wanted to upgrade those two pairs of audio caps, but with the problem I was having, for not much additional money, I could replace all of them with quality Nichicon caps.

Mouser order. Nichicon Muse caps in the upper right, and the eraser-colored caps are the WIMA film caps.

I built up my order at Mouser, had it shipped, and went about replacing the caps. Upon closer inspection as I began removing the old caps, I noticed that I missed one!! A tiny cap tucked behind two large ones, against the side of the case.  And I figured that with my luck, that one might be the capacitor causing the problem.  I tested it in place, and got a reading close enough to its nominal value.  Crisis averted.

Upon removing the original caps, I took to measuring them with the multimeter.  Every one of them was at the very low end of the ±20% tolerance range…just barely within tolerance.  One cap in particular, though, was far out of range, and was (if I recall) about 25%-27% out of range on the low side.  And, that was a cap that was located right next to the IC that is essentially the “brains” of the switching power supply, which is mounted to a heatsink.

So, I soldered in all the new caps.  All Nichicons, except that one pair in the audio circuit were Nichicon Muse caps (their audiophile series), and the other pair was WIMA film caps.  Reassembled the case.  Plugged everything in.

It worked.

Small electrolytic cap just to the left of the heatsink was way out of spec!

My only issue now is that one of my reissue Mullards is getting a little noisy–the left channel occasionally makes a rustling sound, which stops when I tap on the left EL84.  Ah well.  At least it’s working, and if/when that tube gets annoyingly worse, I’ll pick up a new pair.

I also want to pick up a different 12AX7.  This amp ships with a rolled off high end.  The capacitors did open things up on the highs a little (thanks to the increased value of the WIMA film caps, but I did notice the amp had a little more cojones.  It is not a powerful amp, but after increasing the capacity via those Muse caps, it has a bit more heft to it and seems to play cleaner at a slightly louder level than before.  So, the caps did make a difference.

As for that 12AX7, due to the rolloff, I want to find an affordable 12AX7 (new issue, or new old stock) that still has some meat in the bass, but has a more tilted up top end to help compensate for more of that rolloff.

Project completed, though. It’s doing nightly duties for anywhere from 4-6 hours.  And it still looks cool up on the desk…

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An ARTful change to the ART7

I noticed the last few times that the Dynavector XX2 Mk. II was souding a bit strange.  Oddly, I’d say it sounded “cheap” as it has not been tracking very well, reminding me of the muddy sound of some of the cheap phono cartridges I used to own (like the crap Ortofon I had on a Dual turntable).  It not only has been sounding very congested, there was dull sibilance where I don’t remember it being before.  Something’s up, and I need to send it out to be looked at.

I needed a replacement. I had a few on my short list (like the excellent, musical Hana SL), but ultimately ended up with the Audio Technica ART7.  For the uninitiated, this is a low output moving coil with “special line contact” stylus on a boron cantilever.  I got it lined up using the MintLP protractor, and still have yet to finish dialing in the SRA and azimuth.

Right out of the gate, it is an excellent tracker, the best I’ve had since retiring the old V15 Type V.  It still has a few dozen hours to fully break in, but it has a lot of clarity going for it with the improved tracking ability.

The only achilles heel right now is the phono stage–I am really not liking how noisy the Phonomena II+ is.  I’ve even replaced the $1.50 chinese switching mode power supply with a linear regulated power supply, but the noise remains. This is basically “amplifier rush,” that white noise that comes from high-gain amplification.  I have records so quiet that the noise from this phono stage is audible over the vinyl’s background noise.

I am only afraid that if I replace it, the replacement will also have similar noise. Step-up transformer? Perhaps, but I got this phono stage to eliminate having yet another device in the system, and to have many loading options available.

On my short list is the Pro-Ject Tube Box DS2, largely due to its two selectable outputs, one of which I can sum to mono using a Y adapter at the output and use in a spare input on the preamp.  I can also roll tubes to shape the sound as needed.

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No longer an Amazon Prime subscriber

OK, I admit it–I was an Amazon Prime subscriber for a few years.  I took advantage of an attractive student discount where I paid half the normal Prime rate.  When my last renewal came up, it would have been for the full $99/year subscription rate.  Looking at it for more than a few minutes, I realized what a poor offer it really is for me.

Amazon Prime offers both free two-day shipping and now, access to certain video programming.  It offers other benefits I’m sure, but I really only wanted to have access to the fast, free shipping.

The problem is, I never watch video on Amazon, nor do I use any other Prime services, so I am paying for something I never use.  Two day shipping?  Only in rare cases have I ever needed something in two days.  The way Amazon has been opening up distribution centers lately, most of my orders from their warehouses have been arriving in two days anyway.  As for the free shipping, it takes me almost nothing at all to come up with a $25 order to meet their minimum.

If I am in a situation where time is of the essence, I could pony up for a single month’s Prime subscription.  So it is not like it is totally inaccessible.  But otherwise, Amazon has improved enough in other areas that I really don’t need to pay for a full-blown yearly membership.

What I would really like to see is a service called Prime Shipping.  Offer it for $39 or $49/year and I may just resubscribe. And it might bring others on board who feel the $99 price is too steep and, like me, have no use for the other Prime benefits.


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TubeCube|7 — A nice little desktop power amp

I picked up the TubeCube|7 a few years ago.  I’d never owned a true tube power amp before.  I knew that this amp would never find a place in my main system, as it only puts out a tiny 3.5 watts per channel.  Yet I had a perfect use case–I was retiring my Altec Lansing computer speakers (which sounded OK, but had an annoying background hiss whenever the system was on), and wanted to up my game a bit.

Late night listening by the glow of vacuum tubes…

Since getting the Oppo BDP-105, I had a spare DAC–a Cambridge Audio DACMagic.  With a newly-built computer, I used the optical Toslink connector from the computer to the DAC, in order to isolate it completely from the computer.  (No, I’m not one of those who feels Toslink is worse than Coaxial–there is a reason our Internet backbone runs on fiber vs. copper!)

I also needed speakers for the new computer desk–I located a used pair of Boston Acoustics CR65 bookshelf speakers that fit the side shelves perfectly.  I knew bass would be no great shakes with these speakers, so I picked up a Dayton 6.5″ powered subwoofer which tucks neatly under the desk.  The CR65s have one flaw in that there is a resonance hump at 125Hz.  I had to notch that out in JRiver.  Much as I hate using digital EQ, this helped clean up the speaker’s response, at least until I can get in there and brace the cabinet, and perhaps deaden the cabinet walls and/or add some fiberfill to help out with that resonance.  Beyond that, the speakers have a nice midrange and the highs are easygoing.

Before permanently installing the TubeCube|7 in my desktop system, I gave it a try on the big rig.  My speakers at the time were not terribly inefficient (they were around 89-90dB/w efficient), but this amp struggled to get a usable volume out of them.  This amp may work well with horn-loaded speakers with high efficiency, but don’t expect it to drive most typical speakers today without running out of gas quite quickly.  The bass in this case was rather ill-defined, since there simply was not enough current to drive the woofers.  What also didn’t help was that there was a rolloff in the highs–everything sounded dulled through the amp.  After purchasing it, I found another review online which echoed my comments, and backed it up with measurements for exactly what we were hearing.

I don’t know, then, if it was the amp’s circuitry that was rolling off the highs, or the unidentified Chinese tubes that shipped with it.  But, not all was lost.  In a desktop environment, with speakers in a nearfield arrangement, it is actually nice to have a softer treble.  More on that shortly.

I did replace the tubes about 18 months after buying the amp–I went with new production Mullards–a pair of EL84s, and a 12AX7.  I noticed the sound is slightly cleaner and less gritty.  Did the highs improve?  I don’t know–I think there is a bit more life to the sound now.  These tubes definitely helped.  If I went with a brighter 12AX7, I’m sure I could bring up the highs even more.  Switching to silver interconnects may also help.  Given the inefficient speakers I am using now in my main system, there is no way for me to easily check how the amp sounds after being retubed.

Anyway…the amp lives in nicely in my desktop system at the moment.  I know I used the word “easygoing” a few times above–that is exactly my impression of this system.  Given its somewhat soft demeanor and the nearfield speaker array, I can listen to this system literally for hours and not get tired of it.  For me to say that with a digital source is even more telling. As expected, the midrange is sumptuous, and the system throws a nice soundstage considering the far from ideal speaker placement.

One tweak I have yet to make is to use a crossover for the amp. The speakers are currently running full range.  Blocking the frequencies below 100Hz would go a long way towards improving headroom a bit, since the amp would not be struggling with the bass.  Parts Express sells a pair of crossover RCA plug adapters in various frequencies, so those may work out perfectly for this installation.




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No, I am not imagining it!

I have had my vinyl system for a couple of years now, and have gone through a couple of different cartridges to arrive where I am at right now.  While I do like the sound I am getting for the most part, I still wondered if I was really hearing a difference, or falling to the placebo effect.  On records I have owned for decades, and even more so on some recent audiophile reissues, I have never heard the records sound this good.  On many, the system is revealing details I hadn’t heard before.

While going through CDs this past week, I found a CD-R someone had sent me many years ago, a needle drop of an album that is nearly impossible to find today.  I can’t even remember who sent it, and even then it was another party who had sent this person the needle drop.  I had considered cleaning up the numerous pops and ticks in an audio editor, since this record was pressed on lousy vinyl and any copy that I have known anyone to own (even a sealed copy) has had these flaws in the vinyl.

Having ripped the CD, I played it back on my computer-based system (tube amp, DacMagic DAC, etc.).  What surprised me after about 30 seconds is that the quality of the needle drop sounded, for lack of a better word, “cheap.”  While the cartridge wasn’t blatantly mistracking, you could hear it was less than capable, with a rather odd balance to the highs and a somewhat thumpy quality to the bass.  The background noise, that “vinyl noise” or “turntable noise” that lurks as an undercurrent to the music, was plainly audible.  While it is not of such a poor quality, it reminded me of going from my rather modest high school mid-fi system to one of the many Panasonic “Thrusters” systems that friends owned.

I have not yet really “converted” anyone from digital to vinyl, nor do I really want to, but this whole exercise makes me want to demonstrate to others how a well-made, properly set up turntable system can extract so much more of the music out of the grooves than typical mid-fi setups.  Or even just show the non-believers how good it can sound.  The real haters will still nitpick everything to death (“See? I heard a tick! Right there!!“)  But anyone with an open mind can certainly grasp the concept.

I could do the same for high-res vs. CD, but that is a harder sell than vinyl vs. CD.  Still, I do hear differences between CD and high-res, and am slowly getting a few sample tracks together to demonstrate it clearly.

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