Bryston B135³ Integrated Amplifier

Canada really does seem, if I may employ a cliché, to punch above its weight when it comes to high fidelity equipment. Hailing from Ontario, Bryston is a maker of true, high-end electronics. And it’s not the only one, but it would be rude to name the others here. The Bryston B135³ is the company’s only current integrated amplifier. It leans more towards pre and power amp combos. But if all integrated amps were of this quality, perhaps there would be no need for pre/power systems.

tl;dr

• Stereo integrated amplifier
• Also known as the Bryston B135 Cubed Integrated Amplifier
• 2 x 135 watts per channel into 8 ohms, 2 x 180 watts per channel into 4 ohms
• THD less than 0.005% across audio bandwidth at rated power into 8 ohms
• IMD less than 0.005%
• Noise better than -108dB referenced to rated output
• Slew rate more than 60 volts per microsecond
• Frequency response from less than 1 hertz to more than 100,000 hertz, -3dB
• Damping factor: over 500 at 20 hertz into 8 ohms
• Seven analogue sources via stereo RCA
• Optional moving magnet module which repurposes one input to phono
• Tape loop out
• Pre-out and power amp in
• Optional 192kHz, 24-bit DAC module with 2 x coax and 2 x optical
• Dual mono configuration
• 433mm wide by 116mm high by 353mm deep
• 12kg
• Delivers music with superb authority via loudspeaker. Headphone output performance compromised by audible noise. Remote control extra-cost option.
• 20-year warranty!
• Available here.
• Price: Varies according to configuration. For example, with DAC module: $14,600.

More on the Bryston B135³ integrated amplifier

So, broadening things out a little from the recital of facts and figures above, we have an integrated amplifier – preamp and power amplifier combined into one unit – that has a certain pleasingly retro aspect to its appearance. On the brushed aluminium front panel, the large volume knob has a row of press-buttons to either side. Most are for selecting inputs, two are for adjusting left-right balance and one is to mute the unit. Several have indicator LEDs above them, and an extra LED is provided to indicate if the unit is clipping.

That indicator did not illuminate at any time during my use of this receiver, which seems appropriate. The amplifier is rated at 180 watts per channel into 4 ohms. I was using Dynaudio Contour 20i loudspeakers which are both, nominally, 4 ohms in impedance and 180 watts in rated IEC power handling. Even though their sensitivity is fairly low at 86dB for 2.83 volts input – 3dB below what I’d estimate to be the average high fidelity loudspeaker sensitivity – 180 watts might have been a bit over the top.

(A naïve calculation suggests 2.83 volts into 4 ohms is 2 watts. 180 watts is 19.5dB more than that. So full power would potentially deliver 105.5dB.)

This amplifier is configurable, in that you can add one or two modules to it. I’ll return that that, but in basic trim it is entirely analogue. It has a bunch of RCA sockets on the back for inputs. See above for details. But what the basic recitation of features above doesn’t emphasise is the real, dual-mono design of this receiver. The left and right sockets for any input are mirrored across the back panel, all the left inputs on the left side, all the right on the right side.

Two unusual features both involve outputs. First, there’s a good old-fashioned tape loop output. These were ubiquitous in the olden days when we all had cassette decks. The output level from these is fixed.

The other is the preamp outputs. And the power amplifier inputs. Each pair – matching input and output – is accompanied by a switch which breaks the internal connection between pre and power amps.

All that provides, of course, a great upgrade path should you decide you need a dedicated power amplifier loudspeaker for your speakers, or perhaps an even higher-end preamplifier.

The build is very solid. The RCA connections are well spaced and quite a bit longer than usual. That made it easier than normal to attach the clamping RCA plugs I mostly use.

On the review unit there were also several unusable connections. You can add a moving magnet phono module or a 192kHz/24-bit DAC module. Or, rather, the dealer can. Adding the former costs you one set of line level inputs because that connection is repurposed. The two coaxial digital audio and the two optical digital audio input sockets are already installed in the unit.

Now, returning briefly to performance, a nice touch is that rather than just some “QC” sticker on the side, each Bryston B135³ amplifier comes with a “Final Checkout” test sheet. The review unit tested at less than 0.0016% THD at 135 watts output at 20 hertz, 200 hertz and 2000 hertz. At 20kHz the number was 0.0049% or less. IMD was tested at 0.00295% for one channel and 0.00239% for the other. Output power at clipping (2kHz into 8 ohms) was 160 watts per channel. And noise was at -109dB referenced to rated output power.

Headphone output

The headphone output on this amplifier is a slightly odd beast. In practical terms, it operates in the usual way, muting the speaker (and pre-amp) outputs when a 6.35mm headphone plug is inserted. What’s odd is that the manual says that “[o]nly headphones with impedances of greater than 50 ohms should be used.” When my eyes landed on that, I hastily unplugged the Fostex TH-909 headphones I’d been using. They are rated at 32 ohms.

One thing I’d about the sound with those headphones was a low level, but clearly audible, slightly buzzy noise. I say audible, but that was only between tracks. This noise was at the same level regardless of the volume control settings, so presumably it was picked up or generated at some point in the circuit after the level setting components.

The reason the noise was audible was that at realistic listening levels – or even somewhat unrealistic ones, with the level set for a 0.5-volt RMS output for a full-scale sine wave – the noise level was at -72.1dBA into an open circuit, or -73.9dBA into a 300-ohm load. And also because of the character of the noise. Here’s the noise spectrum:

Those spikes are at 50 hertz, 150 hertz, 250 hertz and so on. And on. The apparent step up at 7kHz is just a visual artefact due to the logarithmic horizontal scale. What that says to me is 50 hertz mains interference and odd-order harmonics thereof. Here’s what the waveform looks like:

Ignore the random noise – that’s normal. It’s the regular repeated pattern that I could hear. The upwards spikes are exactly one fiftieth of a second apart. Combined with the downwards spikes, they result in the 50 hertz noise and those odd-order harmonics.

Variable impedances

Now, why the 50 ohms or more limitation? Could lower impedances imperil the output stage? In the manual Bryston says that the “headphone output is driven directly from the preamplifier section utilizing separate headphone buffers.” That doesn’t sound as though it would be particularly fragile. Some measurements cast light on the matter.

First, into an open circuit the maximum output voltage (ie. just before clipping) was 15.0 volts at 100 hertz, 15.8 volts at 1002 hertz and 16.3 volts at 10,000 hertz. Into 300 ohms they dropped to 10.69, 10.64 and 10.94 volts respectively, thanks mostly to a greater readiness to clip into an actual load. I didn’t test maximum output into my 16-ohm load, given the warning about 50 ohms minimum.

But I did test the output into a 16-ohm load with the open-circuit voltage set to around 0.5 volts so I could work out the internal impedance of the output. It came out at around 73 ohms, which is quite high.

That’s certainly the case for the Focal Elear headphones, which I used for some of the listening, and which have a nominal impedance of 80 ohms. But it’s uneven. The impedance of these headphones peak at about 300 ohms around 50-60 hertz according to Inner Fidelity’s measurements (PDF), and 70-80 hertz according to mine.

Since the Elear’s meet the 50-ohm lower bar, I donned them and spun up Alice Cooper’s School’s Out. The bass guitar work and larger toms in the drum kit were noticeably louder than usual.

All of which means, if you are planning on using the amp with headphones as well, take your headphones with you to the store to audition. Or if you’re going to buy them later, choose headphones of a higher impedance, and preferably with a flat impedance across the frequency spectrum. This amplifier can certainly drive them. Into the 300-ohm load, it produced more that 350mW, or nearly 26dB above the sensitivity rating of the headphones. That’s impressive.

And, all that said, I did rather like the sound delivered by the right set of headphones driven by the Bryston amp. During tracks the noise was well and truly masked. It was only apparent in what should have been digital black silence. I switched to the Audeze LCD-2C headphones which, being planar magnetic, have an even impedance across the full audio bandwidth, and since that impedance is 70 ohms, it conforms to Bryston’s stated requirements.

I did not measure the loudspeaker power output of this amplifier for two reasons. One is that my method is fairly crude: wire up some 250 watt 8-ohm resistors and the oscilloscope, and advance the volume until clipping appears, then back off slightly. Assuming of course protection circuitry doesn’t cut in. I’d prefer to go by Bryston’s own measurements, shown above.

One interesting point did become clear during the testing. I’d just assumed that the unit uses an analogue volume control, likely a high-quality potentiometer. But as I finely adjusted the volume control, I could see discrete jumps in level on the oscilloscope. A few measurements with the volume control set at 9, 12 and 3 showed that each step was 0.5dB. Note, the volume control is still analogue. There’s no conversion to digital in this unit. It’s just that the volume control seems to key some ladder array of resistors to set the level.

In use

I ran this amplifier for a couple of weeks, first into my old VAF Research Signature I93 floorstanding loudspeakers – they have a nominal impedance of 3 ohms – and then into my new Dynaudio Contour 20i stand mount speakers – they have a nominal impedance of 4 ohms.

The amp did a superb job of controlling the bass end of the VAF speakers – they have a couple of 203mm woofers and a solid output down to 21 hertz, if the amplifier can deliver. The Bryston B135³ did, with speed and remarkable control. My 20-year-old VAFs aren’t really the thing anymore for gorgeous mids and highs –they’re pretty old. It was the Dynaudio Contour 20i speakers which showed what a seductively smooth performer this amp can be, especially with a wide range of classical and jazz. Yet when I threw some of Eminem’s The Slim Shady LP at it, the amp drove the speakers with superb punch and rhythmic intensity.

I wouldn’t hesitate to use any quality loudspeakers with this amplifier.

Conclusion

The Bryston B135³ integrated amplifier is a lovely device which should easily drive any loudspeakers to their best performance. If you’re a frequent headphone user, you may be a little more cautious. Obviously, I can’t speak much to the quality of the phono or DAC modules, not having checked them out. But I will note that Bryston does sell separately some well-regarded phono pre-amplifiers. If you need moving coil rather than moving magnet, it also sells an audiophile step-up transformer – you can choose 20dB or 30dB of step up – which should work well with the MM module.