Hot House Model Six Hundred Amplifier PRM 165 Reference Monitor

Hot House amps have been around since 1987, and the Six Hundred, priced at $2,499 ($2,698 with optional mirror finish polished panel), is one of the new improved models the company has recently introduced. Previously based on evolutions in MOSFET design, Hot House amps have always had an openness about them that some other FET amps lacked.
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Hot House amps have been around since 1987, and the Six Hundred, priced at $2,499 ($2,698 with optional mirror finish polished panel), is one of the new improved models the company has recently introduced. Previously based on evolutions in MOSFET design, Hot House amps have always had an openness about them that some other FET amps lacked.

The new design, however, takes full advantage of recent developments in bipolar intelligent output device technology, with constant bias, thermal protection and other functions handled right on the chip.

Hot House sent over to PAR its latest iteration of the Six Hundred amplifier and its new passive PRM 165 closefield monitor for a quick test drive.

Reduced circuit clutter

The new line of Hot House amps are said to be the best versions yet. According to the company, the Class A/AB circuit employs "trick new" bipolar output devices that offer the sonic benefits of Class A without excess heat and without global feedback. The output devices themselves are self-biasing. Heat protection is done at the output device, eliminating the need for corrective feedback networks and complex, sonic-robbing heat-protection circuits. According to the company, the end result is an amp that is more transparent sounding and bullet-proof at high power with low impedance loads. In fact, Hot House claims you can dead short the output posts with a screwdriver with the speakers still connected - and no damage will occur.

The Model Six Hundred is a rather modest looking, black rackmountable amp that outputs 200 watts per channel into 8 ohms, 275 watts into 4 ohms and 325 watts into 2 ohms. Distortion is rated at less than 0.005 percent at full power. The damping factor is listed at greater than 300 at 1 kHz, and the signal-to-noise is rated at 105 dB.

The three-rack space Model Six Hundred weighs in at a lightweight 36 pounds. Connections are simple with combo XLR/1/4-inch TRS inputs and five-way Cliff speaker-binding posts.

Although the amp runs, at least partially, in Class A, I found it surprising the amp had no top vents for extra heat dissipation. The substantial external heat sinks seemed to do the job; the amp got warm, but not hot.

A resolute amplifier

I sampled the Hot House Model Six Hundred using a Legacy High Current Preamp with SACD, DVD-Audio and CD tracks: both prerecorded and stuff from my studio. Interconnects included stranded cable from Kimber Kable and solid conductor wire from Alpha-Core. For the 16-bit PCM and DVD Audio playback, I used Bel Canto's excellent DAC-2 192 kHz upsampling stereo DAC fed by a Panasonic RP-91 DVD-A player. The SACD playback was via a Sony SCD-777ES.

Speakers included the Hot House PRM 165s (8 ohms), my reference Legacy Classic IIs (4 ohms) and a pair of Westlake Lc6.75s (4 ohms). Though both are more expensive, I threw in my reference Bryston 14B SST amp (bipolar, Class A/AB output) and a Pass Labs X-150 Class A FET amp.

The Hot House exhibited a nice, present top end openness, akin to the Pass Labs Class A FET amp. Bass was very good with a nice tightness that also compared favorably to the Pass. Stereo imaging was excellent with the ability to aurally pinpoint the individual instruments.

I thought the amp sounded best with my tower Legacy Classic IIs because of the lower extension of the bass. However, the sound was no slouch on the smaller Westlakes and the Hot House PRMs (more on that later). SACD and DVD-A sounded particularly good, especially recordings of acoustic guitar and piano.

Although not an apples-to-apples comparison, a side-by-side listen with my reference Bryston 14B SST ($6,000 vs. less than $3,000), the little Hot House was close in the imaging and detail departments with all the speakers. It did not, however, have the speed of the Bryston in the bass department. The Hot House has very good bass, but the Bryston 14B is nearly in a class by itself.

Speaking of speakers

The Hot House PRM 165 speakers are a no-hype, small monitor system that are very flat in the treble region. In fact, you might think they are dark compared to other speakers that get a lift in the 8 kHz to 12 kHz region, but they are actually quite smooth and fatigue-less.

The speakers, which use a 1-inch dome tweeter with a 6.5-inch woofer and a rear-ported cabinet, sounded good at 5 - 6 feet from the listener. Dispersion off-axis was excellent. Bass was very ample for such a small enclosure - without exaggerated puffiness from the mid-bass, which is often a problem with small, ported speakers.

The Verdict

For the brief trial period I used the Hot House Model Six Hundred amp I had no problems and found it to be quite a useful, analytical and accurate tool in the studio, and it seemed to have plenty of power. Bigger and smaller versions are said to sound the same.

The PRM 165 speakers are a nice set of small monitors that are not hyped in the treble, which makes for cleaner vocals and less harsh percussion transients. Imaging is quite good as well.

For more information about the Hot House Model 600 and the PRM 165, contact Hot House at 845-691-6077, www.hothousepro.com