Monday, January 26, 2009

Amplifier Shootout: Tubes vs. Solid State

This weekend I pulled my UREI 813A cabinets out of storage and connected the Altec 604 and Eminence drivers back up. It has been five months since I've last heard these beasts so I was a little surprised on how good they sounded. I got familiar with their good points again - the dynamics are simply incredible. There is a clarity and rightness to the overall sound that easily surpasses many speakers that I've heard. But of course no speaker is perfect - there is no big wide soundstage and if you don't sit back far enough the drivers will not integrate all that well. The UREIs are a bit forward and dry too. They also require loud playback levels to sound their best which makes them perfect rock n' roll speakers but not all that suited for baroque. This playback level can also makes them less than popular with anyone not actively listening to them.

With all that in mind, I decided to compare the Threshold S/500 to my DIY Single ended EL156 tube amplifiers. In fairness I invited my fellow audiophile friend over. He has many years of experience with the UREIs - owning among many things a pair of 'no letter' 813s himself. He also has a marvelous set of ears and has always had a top notch tube based system to listen to.

First up were the EL156 amplifiers. This was the first time I've had a chance to hear them on the UREIs so I didn't know quite what to expect. These monoblocks only put out 20Ws or so of class A power and the UREIs aren't that efficient compared to Klipsch, Altec, etc horn speakers. So we were taken aback how loud and dynamic the amplifiers sounded. Bass was surprisingly deep for a single ended amplifier - in this setup I actually preferred it over my more powerful 60W Dynaco Mark IIIs. I know it sounds odd, but the Hammond output transformer on the SE amplifier is a beast and the loop feedback must help too. However there was a slight uncontrolled quality to the deepest of bass notes. Midrange and treble were both very natural sounding - quite like the 'real thing'. Dynamics were also good and only on some big drums recordings - like the Audioquest recorded Terry Evans - did the amplifier seem to run out of steam. At this point the amplifiers sounded a little blurry as the music overwhelmed the short peak power available. But the clipping never sounded harsh or terribly unnatural.

The Threshold S/500 was then fired up and allowed to settle in for a bit. We talked a bit about the pros and cons of electrostat speakers before doing any serious listening. The first cut of a Bob Dylan remaster showed an amplifier that is very neutral. As a side note my friend also remarked that the remaster sounds slightly softer than his original LP. Listening to a few cuts I noted that the top end is extended and the midrange has an inner detail that is some of the best I've ever heard. Bass control is tight as the 250Ws and low impedance really controls the large 15" Eminence woofer. On the Terry Evans cut the snap of the drum stick on the snare or tomtom was shocking and bullet fast - drums would literally hit you in the gut like the real thing. The UREIs certainly excel at reproducing the drum kit. Perhaps there was a little less 'body' than the tube amplifiers, but there was also an overall 'rightness' and coherency from the lowest to the highest frequencies. Power was never an issue either.

What amplifier is the best? Well my friend likened the EL156 amplifiers to a good film print. Very natural and beautiful. The Threshold is more like a high definition digital TV with crisp detail and bright colors. And that pretty much sums up my feelings - the tube amplifiers were natural sounding and a little less 'hi-fi' than the S/500. But they also lacked the total information retrieval that the S/500 amplifier had. As for what sounds best would be determined on what you are looking for in an amplifier. Personally in this system I preferred the S/500 for the dynamic contrasts and detail. But again I could easily live with the more 'romantic' tube amplifier. In the end I was proud of how well my DIY creation held up to the powerful competition.

Threshold FET-10/HL linestage
RAKK DAC with Phillips DVD player
UREI 813A speakers
Cardas 300B interconnects (preamp to amp)
Cardas Crosslink interconnects (DAC to preamp)
speaker cable was Weico silver coated stranded wire

Roxy Music - Avalon hybrid SACD
Terry Evans - Puttin' It Down CD
Bob Dylan - Blood on the Tracks hybrid SACD
Richard Thompson - Shoot out the Lights hybrid SACD
Buddy Guy & Junior Wells - Drinkin' TNT 'n' Smokin' Dynamite CD


Tuesday, January 20, 2009

How Vinyl Records are Made

A nice little video on how masters are cut and the pressing machinery. Via YouTube of course.

The largest problem facing record production today is plastic quality, mastering quality and the mechanics of an aging technology. Much like steam locomotives, replacement parts to maintain the pressing machinery will have to be found or built by hand. Demand is high for vinyl right now, so maybe we will see some advances or new pressing plant machinery.




Friday, January 16, 2009

A visit with the RAKK DAC

(Image from K&K)

The RAKK DAC is a kit (you can also buy a completed version) available from K&K Audio. This unit uses the TI/Burr-Brown PCM1794 DAC coupled with the CS4816 input receiver . I'm currently running the first 'MK 1' iteration that does not have upsampling.

What drew me to this DAC was the novel I/V converter - it does not use an op-amp, tubes, resistor or a mess of transistors - but instead a Lundahl LL1674 1:4 step-up amorphous core transformer. This should provide 'galvanic isolation' from higher frequency digital crud and buffer the PCM1794 from seeing any outside world nasties. This 'transformer' only output is known as the 'Passive Output Stage' and it does suffer from a high output impedance of ~3000 ohms. K&K also offers a lower impedance active output stage using 6N6Ps and Lundahl iron.

A power supply board is also needed - along with RCA jacks, PCB standoffs, wire and of course a bit of solder to hold everything together. I ended up using Vampire RCA jacks and some 21awg solid-core silver wire I bought from Michael Percy.

I stuck the boards and transformers inside of an old Video Generator chassis that already had an IEC plug, fuse and holes for mounting RCA jacks. It sure doesn't look pretty but my DAC budget was already blown by the time I was done buying all the parts from K&K.

How does it sound? It took awhile for the transformers to break in since the treble was initially very edgy and forward sounding. After a few hours, the sound began to settle down. This certainly is some of the best digital I have heard - smooth treble with a fast but surprisingly musical quality. Definition and detail is excellent for Redbook playback, with plenty of appropriate reverb and hall sound coming through. Dynamics are big and lesser DACs sound compressed in comparison. I'm reminded of a good turntable setup - the overall sound certainly doesn't drive me out of the room like some budget CD or DVD players do.

Compared to the Monica 2 DAC, the RAKK is more neutral and has more detail. The Monica is certainly warm and forgiving, but has a thicker sound with a rolled off treble. However the Monica excels at removing the digital nasties from poorer recordings. The RAKK can be more ruthless in comparison.

Compared to the budget Sony SCD-CE595 SACD player, the RAKK has a smoother treble and is more musical sounding overall. That probably has much to do with the 595's op-amp output stage. I'm afraid to say that even SACD discs on the Sony suffer in comparison. The 595 does however slightly outpace the RAKK on information retrieval - but such is the nature of hi-rez digital versus the older redbook technology.

The RAKK has been the only mainstay of my system for the past two years. Someday I'll upgrade or replace it, but for now it continues to satisfy my digital playback needs.


Thursday, January 8, 2009

Dynaco Mark III Resurrection

In an audio trade I received a pair of vintage Dynaco Mark III monoblocks. The only problem is they were missing just about everything except the output and power transformers. I read a lot and did some talking with a few friends before finally deciding to take the steps to rebuild these old amps from scratch.

Here is how they looked underneath before the operation:
I went with the SDS Power Supply boards available from Triode Electronics. In my case, I didn't use the 50uF in the first section in fear of shortening the life of a NOS 5AR4. Line voltages are higher than the old days so I used a smaller value 20uF/630V Solen in the first section and after the 1.5H choke I paralleled the first two sections together on the SDS board.

For the input boards, I decided on the Poseidon driver boards. I used 5751s instead of the 12AX7 and 12BH7s instead of the 12AU7. The neat part about the long-tail phase splitter is the current sink using a LM334Z - in this case when the tied cathodes sees a large impedance it reduces phase imbalance. There is also a trick method they use to balance unmatched power tubes using the original 10k bias pot and a trimming pot.

To finish the job I had to buy all new sockets, new chokes, new bias pots, bias resistors, RCA jacks and capacitors. I did a flurry of wiring and everything worked on the first try without any troubleshooting required. Excellent products and careful wiring paid off!

Final results on one of the monoblocks:

For final tweaks I went with some MIT RTX and Dynamicap capacitors from Michael Percy. RTX capacitors used to seem very high priced, but these days they are a bargain and well worth the money. Rectifiers are the under the radar Hitachi GZ34s. I've also found some Raytheon 'Windmill getter' 5751s and some NOS RCA blackplate 12BH7s. For output tubes I went with the rugged SED 6550c.

Mark IIIs with the Poseidon and SDS boards, good coupling caps, and the right tubes make for an excellent budget tube amplifier. They have rock steady imaging, deep soundstaging, tight bass for a tube amplifier, and a sparkling treble. With these amplifiers I can really hear 'into' the recording. Many vintage tube amplifiers I have heard simply sound compressed in comparison.


Tuesday, January 6, 2009

A visit with the Wharfedale W60s

The Wharfedale W60 was made from 1962 to 1966. It is a 2 way system featuring a 12" Alnico woofer and a paper cone tweeter. Mine are the original W60 which has the '5' tweeter. Crossover is simple - utilizing a single 12uF paper capacitor and an L-Pad to control the high frequency output. Construction quality is high - heavily built with even a separate enclosure for the tweeter.

The later W60D uses the 'Super 3' tweeter. Be warned that Wharfedale was an early user of foam surrounds and problems with foam rot have been reported on these later models.

Two years ago I bought my pair of W60s off of Ebay to be used in my second system. I wanted something that was efficient and durable. My wife really liked the almost Ikea-like looks where I appreciated the overall solidity. Well so it goes. The heavy grille cloth certainly kept out some prying toddler fingers or curious cats.

The Wharfedales are not great performers compared to some of the better speakers that I have owned. But they do really excel in the midrange with very natural smooth sounding voices. This works well when listening to radio announcers or vocal heavy music. Lower bass is lumpy and not quite as deep as you would expect with 12" woofer. Definitely more of the polite 'British' sound than say JBL. The tweeter is also very rolled off on top - lacking high end extension. I ended up cranking the L-pad as far as it would go and then eventually just bypassed it when I went in to replace the old coupling capacitor. Inner detail is also lacking and so are many other audiophile tricks like soundstaging and big dynamics.

Can I recommend these? As an audiophile - no. As a music lover - yes. They are warm, forgiving and work wonders with bad recordings. This is not a moot point in these days of hot overly compressed digital recordings. The W60s return a sense of naturalness back to the music. However in the long run my KEF Q30s won out and the W60s have been shuttled on to a friend who was in need of a new pair of speakers.


Friday, January 2, 2009

A visit with the KEF Q30s

The KEF Q30 is a small 29" tall floorstander that utilizes a single 6.5" Uni-Q (coaxial) driver. Expect to pay approximately $150 for a pair. Built in the early 90s, the Q30 used the second generation Uni-Q driver. Rated for 50Hz-20kHz and 88dB efficiency, the Q30 is best used for a small room. The 6.5" driver can only move so much air and of course there is only a hint of deep bass.

I use a pair of Q30s in my second system utilizing a McIntosh MC-250 amplifier and a refurbished Dynaco PAS preamplifier. The Uni-Q driver is very coherent, providing a nice (albeit small) window into the performance. Pulling them away from the wall decreases the bass response but the imaging as expected from a coaxial driver is fantastic. Treble is very smooth if not a tad rolled off, but with the amp/preamp combination I get a very musical presentation. We listen to hours of music a day through these little floorstanders. Only once in awhile do I wish for a bigger loudspeaker. But hey - that's what my main system is for.

This was my introduction to the KEF 'sound' and it made me curious enough to buy the older and larger KEF C-75. The Q30 is probably best used for small room - condos, dorms, apartments - where you don't want to intrude on your neighbor's ears. They offer a hint of some of the old audiophile tricks - imaging and detail. Pull them away for better imaging or if you need a little more bass they also work well close to the wall. Don't expect big bass or explosive dynamics from these little guys, but do expect a musical and involving presentation. They also would work well as surround speakers that can be tucked into a corner. The wife loves them since they look good and do not intrude into the living room like some of my other speakers.