Wednesday, December 17, 2008

Threshold S/500 amplifier review

I've been a tube guy ever since 1989 when I first heard a pair of Quad ESL-63 speakers driven by a heavily customized McIntosh 240 amplifier. The glow of the vintage Genalex KT66s were magical as was the sound coming out of the electrostatic speakers. It was that day that I became an audiophile for life - a man obsessed with wringing the last bit of detail and realism from my favorite recordings.

So far it has been an interesting journey - filled with tubed gear from Dynaco, Harman Kardon, Eico and my own DIY creations. Over the years I've also dabbled with solid-state, owning at various times a SAE preamplifier, a McIntosh 250 amplifier, an Adcom 565 preamplifier and even building a kit or two. But in my heart of hearts I still remained a tube guy. To my ears tubes always came out on top for sheer musicality. But I've always kept an interest in the industrial art solid-state 'super' amps - brands like Threshold, Krell and Mark Levinson still hold some magical awe for me. These were the amplifiers that only the rich and well-heeled reviewers used with their uber-expensive exotic loudspeakers. However I've never actually known anyone who has owned any of these 'super' amps so I never had the opportunity to hear one. Surely they couldn't compare to a good tube amp!

Recently I've started to have an interest in purchasing a pair of Magnepan 1.6QR speakers. The problem was the low efficiency. I didn't trust my refurbished and upgraded Dynaco Mark IIIs to provide enough power, so I started thinking about getting a more powerful McIntosh solid state amplifier. I love the sound of my vintage MC250 and if I could capture that sound in a higher wattage model then I would be rather pleased. Well a chance conversation led me to buying a used Threshold linestage and amplifier instead.

The Nelson Pass designed Threshold S/500 was built from 1983-1988 and boasts 250WPC into 8 ohms. The power doubles into 4 ohms and the amplifier still has the grunt to even drive a 1 ohm load. This kind of power was needed for driving Apogee and other high end speakers of yore. Even today, some manufacturers build speakers with difficult and punishing loads that require arc-welding amplification.

For a sense of history the original Stereophile review of the S/500 can be read here.

The S/500 amplifier is huge and weights in at a portly 92 pounds. Removing the top panel reveals a massive toroidal power transformer, four huge power supply capacitors and ten pairs of output transistors per channel. The input/driver board is gold plated but to my jaded eyes some of the passive parts certainly look a little pedestrian. But you have to realize that this amplifier was made before the days of ultra-tweak parts.

It is rather funny how bias works - and I'm not talking about Class A versus Class B operation here - but human expectations. My mind was biased against this amplifier for several reasons - it doesn't have tubes, it is some 25 years old and it is high powered. I told myself that solid state design has surely improved over the years and low-powered amplifiers always sound better than their big brothers. And take a look at the insides there - it is just a bunch of silicon parts - where is the mystery and romance of the vacuum tube? A nice black-plate Tungsol 6550 or a Western Electric 300B output tube must be the only way to sonic nirvana. At best I was hoping a tube preamplifier could tame some of the solid state nastiness.

With low expectations I hooked the S/500 up to the Threshold linestage and as I switched it on, I was greeted with a small thunk through my KEF C-75 speakers. I turned up the volume, sat back in my sofa and gave it a listen.

The S/500 simply dominates any speaker it drives. The sheer power, low impedance and high damping factor controlled my KEF speakers more so than any of my tube amplifiers. But yet the sound had a refinement that was totally unexpected from such a monster. Treble was light and airy with incredible extension. Not only was it clean, but it was also free of etch. Based on my past experiences with silicon amplification this is the total opposite of what I had predicted. The midrange was glare and grit free, reminding me of some of the best tube amplifiers I have heard. Not exactly like a tube amp mind you, but very similar with warm musicality and excellent body. And the bass - the bass! - I cannot accurately describe the bass except to say it is the best I've ever heard. Not only is it low and controlled, but it is extremely musical. I can hear different bass shades and musical interactions that were just hints when coming through a tube amplifier output transformer. I never knew a KEF C-75 8" woofer could go so low!

This amplifier is really a high definition piece, besting my old McIntosh 250 by leaps and bounds when retrieving detail. I also feel it is an improvement over my Dynaco Mark IIIs, offering more bass, detail and drive. In some way the clarity reminds me of my SE EL156 amplifiers. But my EL156 amplifiers certainly can't drive difficult low impedance loads like the S/500 can.

Is this the best amplifier in the world? I don't know about that, but I'm certainly interested in seeing how it sounds with my UREI 813A and future Magnepan speakers. The S/500 has forever changed my mind about solid-state amplifiers. They can sound very good indeed and money permitting, I'm curious enough to try out some more upscale solid-state pieces in the future.

If you're interested in trying out a Threshold S/500 for yourself (or any vintage amplifier for that matter), you may want to consider a replacement of the aging power supply capacitors done by an experienced technician. That and some passive parts upgrade will not only increase the longevity but it could also improve the sonics. Right now my S/500 is running completely stock but I will be upgrading once I can.

Source: Phillips DVD player with RAKK DAC
Preamplifier: Threshold FET-10HL
Amplifier: refurbished Dynaco Mark IIIs or Jenison Audio Ultra SE-1 monoblocks
Speakers: KEF C-75 or PSB Stratus Bronze
Wire: Cardas 300-B Microtwin interconnects and Canare Starquad speaker cable