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Reviewed by
Jeff Van Dyne


Threshold Audio
S/3700e Multichannel Power Amplifier

Features SnapShot!


Model: S/3700e

Price: $3500 USD
Dimensions: 19"W x 7"H x 21.5"D
Weight: 64 pounds

Warranty: Three years parts and labor


  • Five channels (standard), expandable to six or seven channels
  • All discrete components
  • Direct-coupled, input to output
  • Massive toroidal power transformer

Features (cont'd)
  • Military-spec precision resistors, computer-grade capacitors, military-grade glass-epoxy circuit boards
  • Isolated power reserves for voltage and current gain stages
  • Gold-plated RCA jacks
  • Swiss-made XLR connectors
  • Cardas gold-plated binding posts
  • Intelligent 12V DC trigger for remote startup
  • Soft-start turn-on
  • Modular construction
  • Rack-mountable design
  • Attractive polished silver-anodized aluminum front panel
  • Hand-assembled in the US

Threshold Audio was founded by Nelson Pass in 1974 -- I remember listening to a Threshold amp in the late ’70s, when I was still in high school. Though way out of my price range, it was one of the nicest-sounding amps I’d heard at that time. Almost three decades later, I hadn’t heard anything about the firm for several years and had assumed they’d gone out of business. Actually, Threshold ran into economic trouble in the late '90s, and it was purchased by a Texas-based company ran by Kevin and David Lee, who headed speaker manufacturer Nova Audio at the time. It has since come back strong; the S/3700e multichannel power amplifier is only one of the new products the revived company has introduced in recent years.

A formidable presence

To look at the Threshold S/3700e ($3500), you might assume it’s the typical 200Wpc powerhouse that seems to be all the rage these days in home theater. At 19"W by 7"H and 64 pounds -- a good 20-30 pounds more than many competing designs -- it’s one of the larger home-theater amps I’ve had in the house, and its 21.5" depth meant that it didn’t quite fit the equipment rack in my smaller theater room. But while the S/3700e is built like a powerhouse, it puts out only 120Wpc.

From the front, the S/3700e is simple but attractive, with a slightly sculpted silver aluminum front panel that allows for rack mounting. The rear panel sports heavy gold-plated RCA jacks, Swiss XLR connectors, and Cardas speaker binding posts. Also on the rear are a 12V trigger input and output and a standard IEC connector. Like several other amplifiers I’ve recently auditioned, the S/3700e is a modular design. Five channels are standard, but open sixth and seventh slots will accept additional amplifier modules at $500/each, should the need arise.

The removal of 20 screws let me peel off the black aluminum top plate and view the S/3700e’s innards. I’ve peered inside my share of amps over the years, and few have looked as neat and orderly as this one. Each module is on a self-contained circuit board of military-grade glass epoxy, the only external connections being power taps and a few short wires to the binding posts. Output is provided by two matched pairs of Motorola ON Semiconductor complementary NPN-PNP bipolar power transistors per channel, cooled by large heatsinks. Up front is a large toroidal power transformer with a 1039VA primary tap and a 990VA secondary. Between the transformer and the amp modules are two Nippon 80V, 33,000F filter capacitors. Threshold states that all resistors are metal-film and noninductive metal-oxide. There are no capacitors in the signal path, and those in outlying circuits are high-quality film and silver-mica caps. In short, there’s nothing inside to complain about and plenty to applaud. The S/3700e has what I want to see when I open up an amplifier: a clean layout, quality construction and parts, and short signal paths.

Setup was straightforward, as you’d expect from a modern solid-state amplifier. I first connected the Threshold to an Outlaw 990 preamp-processor and five Snell Series 7 speakers I had in for review. Later, I replaced the Outlaw with my own Anthem AVM 20 and the speakers with my reference Magnepan MC1-CC3 system. Both processors and the Threshold offer balanced connections, but I have very short cable runs and decided to stick with the RCA connections for consistency over the series of tests I was working on at the time. I also used the trigger connection to remotely control power cycling from the processor.

The S/3700e elicited a soft flutter from all speakers during power on and off, but nothing loud or potentially damaging. Though the amp never got anything more than moderately warm during my testing, Threshold recommends connecting the channels in a specific sequence for improved heat dissipation. Other than that, the only thing you have to pay attention to during setup is to select between the balanced and unbalanced inputs for each channel.

Formidable performance

My Magnepan speakers aren’t the most difficult loads to drive, but they aren’t the easiest either, and they’re fairly inefficient. Some amplifiers don’t drive difficult loads to high levels all that well, but this was never an issue with the Threshold S/3700e. During The Bourne Supremacy, the louder I pushed the system, the more it opened up. Only when the volume level was high enough to be painful did the sound become harsh or compressed. The dynamics of the apartment explosion in chapter 9 were the cleanest and loudest I’ve ever heard from this system, including with some 200W amplifiers that I doubt could have done better.

Dynamics are great, but I’ve always contended that the best surround systems are those that handle subtle sonic cues with the greatest finesse. In Gladiator, the creaking of the carriage, the rattling of gear, and the sound of hooves outside as Commodus and Lucilla near the battlefield, were all around. For me, it’s the subtle placement and level of detail of such sounds that separate merely good systems from the truly spectacular. With the Threshold, my Anthem-Magnepan system entered the latter realm.

The performance with movies was fine, but it wasn’t until I began listening to music that I began to fully appreciate the S/3700e’s potential. One of the first discs I spun was Monty Alexander’s My America [Telarc SACD-63552]. It’s a nicely mastered SACD, though I sometimes think the surround channels are used too heavily for this material. A point in case is "Summer Wind": I find the bongo in the right rear channel horribly distracting. Still, My America gets a thumbs-up from me for its otherwise excellent sound and ambience. On "Honky Tonk," the Threshold S/3700e allowed the Magnepans to really open up and sing at higher volume levels, with no hint of compression, distortion, or harshness.

For something a little different and just for fun, I dropped disc 1 of The Bill Wyman Compendium [Koch 8056] in the player. If you can listen to this CD without tapping your feet or bobbing your head and smiling, seek help. Early in "What a Blow," Wyman’s vocals sort of swim around the front soundstage a bit, but I’d never heard quite the eerie, ethereal quality I heard with the Threshold in the system. The soundstage and imaging were more reminiscent of what I hear from my reference analog system, which is high praise indeed.

The S/3700e’s noise floor was nearly nonexistent. Threshold doesn’t publish signal/noise ratios, so, in an admittedly unscientific test, I turned my preamp-processor’s volume all the way up while the source was in Pause. With my ear only 3" from a front speaker, I heard only a barely audible hiss. Because this hiss would also have included any noise from my preamp and/or source, I think it’s safe to say that the S/3700e is as close to electronically silent as is possible.

A surprising discovery

At 140Wpc, the Chiro C-300 ($1500) is rated to be marginally more powerful than the Threshold, though it never sounded like it. Driving my Magnepan MC1-CC3 theater system to high volumes, the Chiro began to show signs of strain. In comparison, the Threshold S/3700e produced clear, open sound all the way up to the limits of any kind of marginally comfortable sound level. In fact, the Threshold smoked the Chiro in every important performance category.

What was more telling was that I began to favorably compare the Threshold S/3700e to the modified Cayin TA-30 tube amp ($899) in my reference analog system. This rare event was quite unexpected. Both amps have a basic purity of sound that can’t adequately be described in words, but that I suspect has to do with the minimal number of components placed directly in each amp’s signal path. The Threshold even managed to retain much of the expansive, swirling soundstage that’s appealing in so many tube amps -- without the owner ever having to bias a set of tubes.

A not-so-surprising conclusion

If you’ve read this entire review instead of just skipping to the end, it should come as no surprise that I’ve grown very fond of the Threshold S/3700e in the last few months. If I hadn’t completely blown my equipment budget building a new dedicated theater and reviewing space, the Threshold S/3700e would easily qualify as a keeper. Boxing it up to ship it back to Threshold will be difficult.

The Threshold S/3700e is a solid value for those looking for a high-end multichannel power amplifier. It’s built to last and handles difficult loads with ease. While it’s not the most powerful amplifier in its class, it seemed impossible to fluster or strain under extreme conditions during my testing. More important, the S/3700e has a purity of sound when playing music that was unlike any other solid-state amplifier I’ve heard in recent memory. For all those reasons, I highly recommend it.

Review System
Speakers - Magnepan MC1 (mains, surrounds), CC3 (center); Snell M7 (mains), K7 (surrounds), LCR7 (center), Basis 300 (subwoofer)
Preamplifier-Processors - Anthem AVM 20, Outlaw Model 990
Amplifiers - Rotel RB-976, Chiro C-300, Cayin TA-30
Sources - Pioneer DV-563A DVD player, Sony SAT-HD200 DirecTV receiver, Hughes DirecTV HR10-250 HD TiVo
Cables - Analysis Plus, Audio Magic, Monster Cable, Straight Wire
Monitor - Hitachi 46F500 rear-projection HDTV

Manufacturer contact information:

Threshold Audio, Inc.
P.O. Box 41736
Houston, TX 77241
Phone: (713) 466-1411
Fax: (713) 856-0278

E-mail: sales@threshold-audio.com
Website: www.threshold-audio.com

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