Bryston 7BST 600 Watt Monoblock Review

[DVinylfan]

A few years ago I had a Bryston 4B-NRB that was well out of warranty when a channel blew. I sent it to Bryston UK and asked for a quotation for the repair.
A few weeks of silence later and I received an email telling me that the repair had been completed, the entire channel had been replaced, the bill was £500, and there was a new fault: the power LEDs were blinking every second or so when in use. The fault could be repaired, I was told, but might be costly because the likely cause was located at the bottom of the reassembled amp.
Feeling I had no alternative, I paid the £500, got the amp back, and stuck some bits of black tape over the blinking LEDs.
I'm not going to name and shame anyone, but the engineer that did the repair shared their name with a very funny and famous English comedian. Based on my experience, maybe they are the same person.
Five years later, the same channel blew, and I sold the amp cheap to an enthusiast who unlike me had the skills to repair it.
I may be the only person ever to have a poor experience with Bryston customer support, but that's what happened.

 

[leonroy]

A few years ago I had a Bryston 4B-NRB that was well out of warranty when a channel blew. I sent it to Bryston UK and asked for a quotation for the repair.
A few weeks of silence later and I received an email telling me that the repair had been completed, the entire channel had been replaced, the bill was £500, and there was a new fault: the power LEDs were blinking every second or so when in use. The fault could be repaired, I was told, but might be costly because the likely cause was located at the bottom of the reassembled amp.
Feeling I had no alternative, I paid the £500, got the amp back, and stuck some bits of black tape over the blinking LEDs.
I'm not going to name and shame anyone, but the engineer that did the repair shared their name with a very funny and famous English comedian. Based on my experience, maybe they are the same person.
Five years later, the same channel blew, and I sold the amp cheap to an enthusiast who unlike me had the skills to repair it.
I may be the only person ever to have a poor experience with Bryston customer support, but that's what happened.

Bryston UK repairs are handled by PMC (the speaker company) and in my limited experience their service and attitude leaves a little to be desired. They are not the same as Bryston Canada - more their local distributor and partner.

From what I’ve heard Bryston HQ in Canada offer very good customer service indeed.

 

[DVinylfan]

Indeed, thanks for clarifying that.
I'd argue that Bryston customers should be able to expect consistent customer support regardless of which territory they find themselves in, and that if Bryston appoint official overseas agents to carry out repairs, as in this case, they have a responsibility of oversight to ensure the same high standards as those enjoyed by customers in Canada are upheld.
Anyway, this story has a happy ending. The guy I sold the 4B to was delighted, will enjoy repairing it, and hopefully listening for many years to come.
And I bought a Topping PA5 II for €170 which, with the caveat that I live in an apartment and rarely listen at high levels, sounds at least as good or better than the Bryston, won't give me a hernia, and will never cost £500 to fix.

 

[EJ3]

Indeed, thanks for clarifying that.
I'd argue that Bryston customers should be able to expect consistent customer support regardless of which territory they find themselves in, and that if Bryston appoint official overseas agents to carry out repairs, as in this case, they have a responsibility of oversight to ensure the same high standards as those enjoyed by customers in Canada are upheld.
Anyway, this story has a happy ending. The guy I sold the 4B to was delighted, will enjoy repairing it, and hopefully listening for many years to come.
And I bought a Topping PA5 II for €170 which, with the caveat that I live in an apartment and rarely listen at high levels, sounds at least as good or better than the Bryston, won't give me a hernia, and will never cost £500 to fix.

You can never go wrong with: all parties are happy with the deal!

 

[Angsty]

I would never buy older than sst series used. There is no comparison in components, design and layout to the sst. Previous version are rehashed 1978 originals.

A 7B-ST (older than SST) can be a good buy if properly serviced.

I have a 4B-ST that I adore. I had it recapped and “resto-modded” in 2021 as preventative maintenance. I plan to keep it another 20 years.

 

[Angsty]

The quad complementary circuit was Chris Russell's design.

The sst series have the mjl type transistors in a to-264 case, far superior to the old to-3 types used in pre sst units.

As far as 4x less distortion, there is no less distortion even in the current amps compared to the 1983 models when an additional compensation network was added to the input pairs to reduce hi frequency thd to mid band levels. The thd was below .005% then and it is virtually the same now.
Every circuit update in the past 40 yrs. addressed noise levels until the cubed Salomie circuit and even that reduced thd by only 6db. An amp that makes the benchmark look like a topping pa5, btw.

Even the split gain configuration was Chris' idea, carried over from his two stage phono amp. Not exactly genius when 100x=40db and 10x + 10x=40db it's just that nobody thought of it before and it took 20 yrs. for the guy who proposed it to implement it somewhere else. Maybe Otola was still taken seriously years after he speculated that doing that would increase TIM.


Even so, speaking to the level of refinement associated with the amps you need to look no further than a photograph of this 7B and a 20 yr. old 4BSST, there is no comparison. That includes longevity, those mjl devices reduced failures from some to none. Finding someone who has had to service his pre sst amp is easy, for sst and newer almost impossible. Still, if you want to buy a pre sst amp you go right ahead.

A 'star' grounding method is a myth carried over from the hardwired, tube days. No amp with a pcb has one or needs one and I have never seen it done.

I did have my ST serviced by Bryston in 2010 (under warranty) after a cross-county move created a persistent noise in the amp. I asked the tech about upgrading the amp to SST power transistors and he discouraged it. The ST transistors were performant and did not get replaced during the later resto-mod, either.

Sure, the SST and SST2 are improved models and might be worth an extra splurge if you get the opportunity. But, the ST models can be a great value.

 

[Marc Bungener]

I recently reviewed a stack of classic Bryston gear, including a 3BST amplifier. I was pleasantly surprised at the good results. I have the big brothers of that 3BST amp, the 7BST monoblocks. I also recently built a resistive load with enough capacity to test such a powerful amp. Here is a test of this classic amp.
View attachment 480210

I got the amps used years ago. They have powered a range of speakers. They have been reliable. Mine were manufactured in 1999 according to the date code. I have never opened them. I have no idea what the previous owner did with them, except they appeared well-cared for when I bought them 12 years ago.

It has balanced inputs using TRS or XLR, and unbalanced RCA. It also has 'parallel' and 'series' modes. The amp is actually two modules, which can be operated bridged, or in parallel. It can drive very difficult loads in the parallel mode.
View attachment 480203

5 Watt 1 kHz Performance Dashboard
Following usual ASR practices, using the amps' balanced inputs with a QA403.
4 Ohm Parallel Mode
View attachment 480191
96dB SINAD lands it at the bottom of the excellent category. This is a pretty good result despite the mains noise. I wonder if that is age-related.

4 Ohm Series Mode
View attachment 480192
SINAD degrades to ~90dB in series mode. Much of it is increased noise. Which makes sense since the amp is bridged in this mode.

8 Ohm Parallel
View attachment 480193
8 Ohm Series
View attachment 480194
Again, excellent performance with degradation in series mode compared to parallel. We will later see how much power is available in each configuration.

Lastly,
2 Ohm Parallel
View attachment 480195
2 Ohm Series
View attachment 480196
Excellent performance at this moderate power level into 2 Ohms.

Power Output
Here is the THD+N vs. Power for 8, 4, and 2 Ohm loads. Parallel and series modes were measured except for 2 Ohm load which I only measured in parallel. I also didn't quite make it to 1% distortion on each run, call me a chicken!
View attachment 480156
In any case the amp exceeds the following power figures at 1% distortion:
2Ω Parallel: 775 Watts
4Ω Parallel: 475 Watts
8Ω Parallel: 250 Watts
4Ω Series: 850 Watts
8Ω Series: 610 Watts

I didn't want to redo the runs to 1%, suffice to say they have a ton of power.

The amp has clipping meters incorporated into the faceplate's LED:
View attachment 480201
Onset is about 2% THD, the LED start turning amber. By 3% distortion the meters are lit up solid red. I tested a second amp and it has the same clipping threshold for the LED. They provide very useful feedback. They look tasteful, yet appropriately urgent when they turn red.

Here is the THD alone across power for the various loads and mode:
View attachment 480157
The amp did get warm doing these high power sweeps, but didn't complain, protect, or blow a fuse.

Distortion and Nose across frequency
Looking at THD+N at 4Ω in serial mode across a range of power from 130mW to 200W, the amp shows little dependence of distortion and noise across frequency.
View attachment 480166
4 Ohms in parallel mode, even better performance.
View attachment 480170

Here is THD alone into 4 Ohms in parallel mode, the amp is well controlled across frequency:
View attachment 480172

IMD / Multitone distortion
Here is the intermodulation distortion at 5 Watts, 19 + 20kHz
First into 4 Ohms in parallel mode:
View attachment 480173

And into 4 Ohms in series mode:
View attachment 480174
Both are great results. I can see some noise at 35kHz that goes away in series mode. Looking at Bryston's description from the owner's manual:
View attachment 480175

View attachment 480178
Is this out of band noise at 35kHz getting nulled in bridge mode? Or did something get turned off in my house? Not sure, I can't hear it, but interesting.

Here is multitone into 8 Ohms, parallel mode:
View attachment 480179
19 bits of distortion margin, 16 bits including the noise.

And serial mode into 8 Ohms:
View attachment 480180
18 bits of of distortion margin, and 14 bits of noise margin. The amp is noise limited, still excellent performance.

Frequency Response
Here is the frequency response into the three loads, in parallel and series modes:
View attachment 480182
-3dB down at 60kHz or higher depending on load and mode. The parallel mode has the most extended response at a given load resistance, which isn't surprising.

Matching
Here is the performance of the second 7BST compared to the one I just tested.
View attachment 480189
Except for some slightly questionable noise the second amp (right channel, red trace) is matched to the first, after 35 years of use.

I'm glad I measured these, and didn't blow anything up. I now have a better understanding of the parallel and series mode. I also wondered if the amp was as clean as I thought it was into low impedance loads, which it is. I've driven Infinity Kappa speakers years ago, and even more difficult speakers with the previous version of the 7B, and it worked well never overheating or shutting down, sounding great. This confirms my impressions of it's performance.

I hope this is interesting, and encourage questions and suggestions.

Glad to see a review of these as I own the successor 7B SST which I believe doesn’t have this choice of parallel / serie. They were made in 2006 and I purchased them in 2021 after testing them 10 days with my Wilson Audio Sophia Serie 1 from 2001. Clearly a 4B would have been sufficient for my speakers but this is was I found back then when I needed. What I appreciate the most is that they are not fatiguing at all even at high SPL.
One transformer emits a small vibration but it is inaudible from my listening position with zero music and zero noise (like middle of the night) one has to put the hand on the case to feel it. Prior to these I have tested D class monoblocs from Bel Canto which had a fantastic sound but everytime I spent an evening with them I felt exhausted - so they did not SOUND fatiguing but it was worst than that. Something was wrong with the Bel Canto. Everything right with the Bryston for me.