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Amp/Preamp Asylum: REVIEW: Bent Audio NOH Passive Components by GliderGuider

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REVIEW: Bent Audio NOH Passive Components

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Model: NOH
Category: Passive Components
Suggested Retail Price: $1400 (approx)
Description: Transformer volume control preamp
Manufacturer URL: Bent Audio
Manufacturer URL: Bent Audio

Review by GliderGuider on November 14, 2003 at 08:42:00
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for the NOH

I was recently in the market to upgrade my system. When I examined the various options available for the preamp stage, I was increasingly drawn to passive controllers. I was aware of the pitfalls of standard resistor-based units, primarily issues that place limitations on source and amp impedances and cable lengths. In my reading I discovered that TVCs claim to avoid most of these problems while providing an equivalent level of transparency and musical detail. In fact, they are said to operate even better at low volumes due to their inherent I/V conversion - as the voltage drops the current increases, giving better current drive at low volumes.

More investigation turned up Bent Audio in Surrey BC as an active supplier of kits and pre-built units based on the S&B TX102 transformers. Comments on the net were uniformly positive, so I contacted the owner, John Chapman. He told me they were about to introduce a new unit, the NOH, with the same internals but a nicer case. I decided to try one.

The transformers come in both silver and copper versions. After a discussion with John, I selected copper transformers. He feels that silver transformers don't automatically give a sonic benefit commensurate with their price. As you will see, I have had no reason to second-guess this decision.

The NOH is available both as a kit and pre-assembled. I bought the unit pre-assembled. The reason for that is that my only previous experience with soldering was with my only other “passive” preamp – a Corey Greenberg BUF-03 unit that I built over ten years ago. Though the thing worked on the first try, I realized that I have no business even holding a soldering iron.

The design of the new stainless steel and acrylic case is just gorgeous. It exudes a sense of quiet understated elegance that is supported both by the solid feel of the case and the BMW precision of the knobs and switches. All in all it’s a fully realized package.

One of the essential features I was looking for wass remote control of the volume. The NOH offers this as an option, so I had it added in. The remote works just as it should, though some may wish that you could switch inputs as well as just control the volume. Given the mechanical nature of the unit, I suspect it would be difficult to add this capability. Anyhow, I haven't missed it - getting out of the listening chair to select a new source isn't that much of a hardship :-) My only quibble is that there wasn’t an instruction sheet included to tell you how to set it up so the LED in the volume knob goes out when the remote has been idle for a while. No problem, a quick email to John cleared up the mystery. The Zapper that John uses is a very slick little unit that my GF calls “The Star Trek remote”.

Set-up and installation was trivial, though you do need to pay attention to your gazintas and gazoutas because of the asymmetrical layout of the back panel. The quality of the connectors is, of course, beyond reproach (WBTs for the main ones and Vampire for the lesser-used ports). Being able to hard-connect or float the grounds via two switches on the back panel is very handy. It made a big difference in my system, especially with the volume cranked right up.

After all that physical description, the description of the sound is almost anticlimactic. Anyone who has been reading about the TX-102 for a while knows what’s coming next. Holy Whackdoodle, I’m gob-smacked! The clarity! The neutrality! The dynamics! The coherence! The richness! No matter what sonic attribute I listened for, it was better than anything I’d previously heard. This was evident whether I was running it into my KR 18 BSI integrated or into my new Wavelength Triton Blues. Eventually I simply stopped listening for “sonic attributes” and started just listening to music. That transition was easier and more complete than I’d ever experienced before as well.

After I’d let the NOH run in for a couple of weeks I compared it head to head against my previous preamp, a SimAudio P-5. You guessed it - yet another active preamp fails to clear the bar… In comparison to the NOH, the P-5 sounded tonally bleached, a bit slow, a touch hazy, a bit rougher and less dimensional.

The only thing that might have been a problem in this whole exercise is the amp’s input sensitivity. The Wavelengths have a sensitivity of about 1.75Vac RMS, so I’m running the transformers fairly close to the top of the range. Luckily my DAC puts out a nominal 3V in single-ended mode, and 6V balanced, so I’ve got enough headroom in either case. BTW, the number of volume control steps on the transformers (24, I believe)is simply a non-issue. I am always able to get the level I want, though others with different needs or tastes may demur.

The NOH is one of the nicest surprises I’ve had recently. Talk about your giant-killers – in my system this thing makes more music for less money than I ever dreamed possible.

Ye’ll NOH be takin’ this one away from me, laddie!

Product Weakness: No additional gain, so the source output voltage should exceed (or at least equal) the amp sensitivity if full volume is to be achieved. No balance control, since the two volume channels are ganged on a single switch. The volume steps may be too coarse for some applications.
Product Strengths: Very well-built. Intensely musical and transparent. Preserves dynamics and detail at all settings. No evidence of bass or treble roll-off. No grain, roughness or sibilance. Neither lean nor lush - very neutral.

Associated Equipment for this Review:
Amplifier: Wavelength Audio Triton Blue (300B monoblocks)
Preamplifier (or None if Integrated): Bent Audio NOH
Sources (CDP/Turntable): Audio Note DAC 3.1x Balanced / CDT-2 Transport
Speakers: Coincident Total Victory
Cables/Interconnects: Argent Audio Pursang interconnects and speaker cable
Music Used (Genre/Selections): Classical, jazz, folk, blues, soft rock
Room Size (LxWxH): 19 x 12 x 8
Room Comments/Treatments: EchoBusters and RoomLenses
Time Period/Length of Audition: 3 weeks so far
Other (Power Conditioner etc.): Nirvana power cords and digital cable
Type of Audition/Review: Product Owner

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Topic - REVIEW: Bent Audio NOH Passive Components - GliderGuider 08:42:00 11/14/03 ( 5)