MAB
Major Contributor
Here are the results of measurements of a stack of classic Bryston gear from the mid-1990s. A BP-25 preamp, 10B-Sub electronic crossover, and a 3BST power amplifier.
I bought these three pieces new. The BP-25 preamp has been in various systems over the years, is the basic model without the optional phono preamp or DAC modules, but does include the remote control. The 10B electronic crossover has great performance, but it has no ability to manage in-room response outside of independent control high and low filters. The 3BST amplifier has been in daily use in various systems for most of it's life, except for a few years when I lived overseas. None of the gear has ever been serviced and has worked flawlessly since new. Bryston amps and preamps have a 20 year warranty. They have a reputation for their gear not breaking, and for them fixing it for free when it does.
Let's see if these three also maintained performance over time.
BP-25 Preamp:
Here is the ASR dashboard test for comparison to preamps Amir has reviewed. Using a QuantAsylum QA403, I fed 4 Volts at 1 kHz to the XLR inputs, volume control set to unity gain, and measured the signal at the XLR outputs. The overall performance is great.
SINAD of Left and Right channels is 104 dB and 103 dB respectively.
Also note, the Left and Right channels are exactly level-matched at this volume setting with the balance control centered. I test the L-R balance below.
Bryston specs THD at 3 Volts to be < 0.0015% (see attached brochure in a following post). Here is the same dashboard as above but at 3 Volts:
I measure THD well below what Bryston claimed in their literature back in 1996 (~0.0004% vs. 0.0015%). The reason why I measure 'better' distortion can be seen in Bryston's published specs of their test setup in the 'Final Check' test report they shipped with each piece of electronics:
The QA403 is over an order of magnitude better performance than the 0.001% residual of Bryston's test gear back in 1996.
Sweeping input and measuring the resulting THD and Noise shows the preamp maintains great performance up to 8 Volts:
Bryston claims the device can deliver 30V, here are the measurements to 30V:
I have to attenuate the input signal to my analyzer at this high voltage, but you can see it actually meets Bryston's claim at 30V!
The volume control is excellent above -20dB system attenuation. The Left-Right channel imbalance grows below -20dB, is still acceptable.
The motorized volume control is smoothly adjustable with the remote. Both holding the volume button, and tapping it provide smooth control. I've never had any surprises with the gain getting set to maximum accidentally.
The volume remote control is aluminum, solid, with durable smooth buttons, made of materials that are resistant to finger oils. It controls the volume, mute, and phase. That's it. 
The frequency response of the left and right channels are identical, as shown offset by 0.1dB below. At 20kHz it's down only ~0.1dB, almost perfectly flat to 20Hz. It does start rolling off below 5 Hz, I just didn't capture that in the graph.
The measured frequency response flatness exceeds Bryston's spec.
It has great distortion performance across the audible band, Left and Right channels matched, perhaps the Right channel is slightly worse at high frequencies between 50mV and 500mV output.
These results are all fantastic, transparent across the audible frequencies. It has Distortion and Noise performance slightly worse than some of the top tested preamps at ASR like a few Hypex and Topping. But it has output that can drive almost any conceivable load, and very flexible I/O that is not present on many modern preamps.
My only gripes: I miss tone controls. Especially a rumble filter since most phono preamps inexplicably do not include a rumble filter. I also would have liked a processor loop, but am happy with the tape loop.
These are small gripes, this is already a usefully flexible preamp, with excellent performance that hasn't significantly degraded over time. I often it used with Bryston's electronic crossover, tested next.
10B-Sub Crossover:
I've used this crossover in several active systems with dual subwoofers, also for two active 3-way systems. I haven't used it for years, it was set aside when I got Linkwitz Phoenix active crossover boards which I modified for my DIY speaker and sub purposes. I wanted the additional filters, and two channels of sub control was no longer enough. Later, I replaced the Phoenix with MiniDSP devices. After dusting the old Bryston crossover off, I was eager to see if it had as good performance as originally claimed.
I measured the high-pass output with the crossover set to 40Hz with 6dB/octave slope. The unit's gain is 5.9 dB, I fed it 2 Volts at 1 kHz. The results don't disappoint, SINAD of 101 dB and 99 dB for the left and right channels respectively is a great result.
The crossover filters are 6, 12, and 18 dB/octave Butterworth.
The filters are accurate and precise. For example, both the high- and low-pass for 80 Hz have 3dB-down at 77 Hz. So while the exact crossover point is about 4% low, each filter is aligned and will sum as Butterworth should.
I plotted distortion vs. frequency, despite the fact the filters can't be defeated and do interfere a bit with the measurement, more so with the low-pass output. I set the high-pass at 40 Hz, and the low-pass at 500 Hz to get them as far out of way. That being said, the unit has less than 0.001% THD from 20Hz-20kHz on either output, more like 0.0005% across most of the range.
These results are excellent, just slightly worse than the preamp. It's a 100 dB SINAD device with flexible low- and high-pass filters, there is a lot to like about this performance.
3BST Amplifier:
This is possibly my most used component, it's powered lots of speakers, active and passive. I have the more powerful 4BST and 7BST variants, they test the same as this unit, I don't have a dummy load that can handle the power of these, perhaps later.
Here are the 5 Watt dashboard results for the amp:
This is another great result. 97.5 dB SINAD puts it in the vicinity of the NAD M28 and the Neurochrome Modulus-286.
Here is the THD and Noise vs. Power:
Left and right channels are matched, each just exceed 150 Watts. Distortion stays below 0.001% from 1 to 150 Watts.
The amp maintains good performance across frequency, here is the left channel at a few frequencies:
Here is the right channel at 4 Ohms. The 4 Ohm performance sees the amp start to distort at 200 Watts. The clipping indicators start to gently flash at 245 Watts, just a bit below 1% distortion. The left channel tests the same.
The amp's frequency response is flat. -0.1 dB at 2.5 Hz and 21 kHz.
I am happy with these results. After almost 30 years, the amp and the rest of the electronics perform nearly as new. Quite frankly, better than I expected.
I'll post some additional documents I scanned with specs in a bit. Thanks for your attention.
I bought these three pieces new. The BP-25 preamp has been in various systems over the years, is the basic model without the optional phono preamp or DAC modules, but does include the remote control. The 10B electronic crossover has great performance, but it has no ability to manage in-room response outside of independent control high and low filters. The 3BST amplifier has been in daily use in various systems for most of it's life, except for a few years when I lived overseas. None of the gear has ever been serviced and has worked flawlessly since new. Bryston amps and preamps have a 20 year warranty. They have a reputation for their gear not breaking, and for them fixing it for free when it does.
Let's see if these three also maintained performance over time.
BP-25 Preamp:
Here is the ASR dashboard test for comparison to preamps Amir has reviewed. Using a QuantAsylum QA403, I fed 4 Volts at 1 kHz to the XLR inputs, volume control set to unity gain, and measured the signal at the XLR outputs. The overall performance is great.
SINAD of Left and Right channels is 104 dB and 103 dB respectively.
Also note, the Left and Right channels are exactly level-matched at this volume setting with the balance control centered. I test the L-R balance below.
Bryston specs THD at 3 Volts to be < 0.0015% (see attached brochure in a following post). Here is the same dashboard as above but at 3 Volts:
I measure THD well below what Bryston claimed in their literature back in 1996 (~0.0004% vs. 0.0015%). The reason why I measure 'better' distortion can be seen in Bryston's published specs of their test setup in the 'Final Check' test report they shipped with each piece of electronics:
The QA403 is over an order of magnitude better performance than the 0.001% residual of Bryston's test gear back in 1996.
Sweeping input and measuring the resulting THD and Noise shows the preamp maintains great performance up to 8 Volts:
Bryston claims the device can deliver 30V, here are the measurements to 30V:
I have to attenuate the input signal to my analyzer at this high voltage, but you can see it actually meets Bryston's claim at 30V!
The volume control is excellent above -20dB system attenuation. The Left-Right channel imbalance grows below -20dB, is still acceptable.
The motorized volume control is smoothly adjustable with the remote. Both holding the volume button, and tapping it provide smooth control. I've never had any surprises with the gain getting set to maximum accidentally.
The volume remote control is aluminum, solid, with durable smooth buttons, made of materials that are resistant to finger oils. It controls the volume, mute, and phase. That's it. The frequency response of the left and right channels are identical, as shown offset by 0.1dB below. At 20kHz it's down only ~0.1dB, almost perfectly flat to 20Hz. It does start rolling off below 5 Hz, I just didn't capture that in the graph.
The measured frequency response flatness exceeds Bryston's spec.
It has great distortion performance across the audible band, Left and Right channels matched, perhaps the Right channel is slightly worse at high frequencies between 50mV and 500mV output.
These results are all fantastic, transparent across the audible frequencies. It has Distortion and Noise performance slightly worse than some of the top tested preamps at ASR like a few Hypex and Topping. But it has output that can drive almost any conceivable load, and very flexible I/O that is not present on many modern preamps.
My only gripes: I miss tone controls. Especially a rumble filter since most phono preamps inexplicably do not include a rumble filter. I also would have liked a processor loop, but am happy with the tape loop.
These are small gripes, this is already a usefully flexible preamp, with excellent performance that hasn't significantly degraded over time. I often it used with Bryston's electronic crossover, tested next.
10B-Sub Crossover:
I've used this crossover in several active systems with dual subwoofers, also for two active 3-way systems. I haven't used it for years, it was set aside when I got Linkwitz Phoenix active crossover boards which I modified for my DIY speaker and sub purposes. I wanted the additional filters, and two channels of sub control was no longer enough. Later, I replaced the Phoenix with MiniDSP devices. After dusting the old Bryston crossover off, I was eager to see if it had as good performance as originally claimed.
I measured the high-pass output with the crossover set to 40Hz with 6dB/octave slope. The unit's gain is 5.9 dB, I fed it 2 Volts at 1 kHz. The results don't disappoint, SINAD of 101 dB and 99 dB for the left and right channels respectively is a great result.
The crossover filters are 6, 12, and 18 dB/octave Butterworth.
The filters are accurate and precise. For example, both the high- and low-pass for 80 Hz have 3dB-down at 77 Hz. So while the exact crossover point is about 4% low, each filter is aligned and will sum as Butterworth should.
I plotted distortion vs. frequency, despite the fact the filters can't be defeated and do interfere a bit with the measurement, more so with the low-pass output. I set the high-pass at 40 Hz, and the low-pass at 500 Hz to get them as far out of way. That being said, the unit has less than 0.001% THD from 20Hz-20kHz on either output, more like 0.0005% across most of the range.
These results are excellent, just slightly worse than the preamp. It's a 100 dB SINAD device with flexible low- and high-pass filters, there is a lot to like about this performance.
3BST Amplifier:
This is possibly my most used component, it's powered lots of speakers, active and passive. I have the more powerful 4BST and 7BST variants, they test the same as this unit, I don't have a dummy load that can handle the power of these, perhaps later.
Here are the 5 Watt dashboard results for the amp:
This is another great result. 97.5 dB SINAD puts it in the vicinity of the NAD M28 and the Neurochrome Modulus-286.
Here is the THD and Noise vs. Power:
Left and right channels are matched, each just exceed 150 Watts. Distortion stays below 0.001% from 1 to 150 Watts.
The amp maintains good performance across frequency, here is the left channel at a few frequencies:
Here is the right channel at 4 Ohms. The 4 Ohm performance sees the amp start to distort at 200 Watts. The clipping indicators start to gently flash at 245 Watts, just a bit below 1% distortion. The left channel tests the same.
The amp's frequency response is flat. -0.1 dB at 2.5 Hz and 21 kHz.
I am happy with these results. After almost 30 years, the amp and the rest of the electronics perform nearly as new. Quite frankly, better than I expected.
I'll post some additional documents I scanned with specs in a bit. Thanks for your attention.
I have the B60 on my desk. I'm never selling this thing, yet I would like a balanced amp one of these days just to hear a Class D and rid of the noise.
