schematic is here:
BRYSTON 7B SST PWR SCH Service Manual free download, schematics, eeprom, repair info for electronics
images from inside are here:
https://www.helios-online.nl/en/shop/product/28-118/7b-sst2
test report and measurements are here:
Bryston 7B SST<SUP>2</SUP> monoblock power amplifier Measurements | Stereophile.com
Sound is very bad in all respects by a wide range of different speakers with 4 ohms or lower impedances. No clean and tight bass and high frequency reproduction too crispy and harsh. This impression I had get by two different device-sets of this Bryston mono power amps. What could be therefore the main reason?
And a second question:
What benefit should provide the topology from the output stage and what is its naming as colloquial term (see schematic - this topology - where I note a normal darlington and a compound darlington at the same time - I have never seen before)?
Thanks for advices.
BRYSTON 7B SST PWR SCH Service Manual free download, schematics, eeprom, repair info for electronics
images from inside are here:
https://www.helios-online.nl/en/shop/product/28-118/7b-sst2
test report and measurements are here:
Bryston 7B SST<SUP>2</SUP> monoblock power amplifier Measurements | Stereophile.com
Sound is very bad in all respects by a wide range of different speakers with 4 ohms or lower impedances. No clean and tight bass and high frequency reproduction too crispy and harsh. This impression I had get by two different device-sets of this Bryston mono power amps. What could be therefore the main reason?
And a second question:
What benefit should provide the topology from the output stage and what is its naming as colloquial term (see schematic - this topology - where I note a normal darlington and a compound darlington at the same time - I have never seen before)?
Thanks for advices.
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Good Question? Maybe the Amp Experts can determine why Bryston amps have negative sonic issues.. John Curl, mentioned something about amp characteristics, are determined in the first 10 watts, if my memory is correct..
You describe the characteristics, very well.. I've owned/listened to nearly all Bryston models, over the years, starting in the late 70's..
Bryston units are typically a stepping stone toward something better..
Popularity, has zero correlation, to sonic endowment.
You describe the characteristics, very well.. I've owned/listened to nearly all Bryston models, over the years, starting in the late 70's..
Bryston units are typically a stepping stone toward something better..
Popularity, has zero correlation, to sonic endowment.
Some people prefer effects boxes, some people prefer amplifiers that merely make signals bigger. The former will not like the Bryston amps.
-Only make signals bigger - Is this possible, without adding something foreign, or removing something from the original signal?
I think the OP is asking, what, in the Bryston circuit, creates the Bryston sound.
Getting this question answered, I would find very interesting🙂
I think the OP is asking, what, in the Bryston circuit, creates the Bryston sound.
Getting this question answered, I would find very interesting🙂
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The "sound" is flat frequency response, low source impedance, and low distortion, i.e., absence of sound.
If you have a speaker with a wild and low impedance curve, that will sound different with an amp with a high source impedance versus an amp with low source impedance, because of differences in frequency response. That's just a matter of EQ if you want those frequency response changes using a low source impedance amp.
In a cosmic sense, no. In a practical sense (evaluation by ears), yes.
If you have a speaker with a wild and low impedance curve, that will sound different with an amp with a high source impedance versus an amp with low source impedance, because of differences in frequency response. That's just a matter of EQ if you want those frequency response changes using a low source impedance amp.
In a cosmic sense, no. In a practical sense (evaluation by ears), yes.
Not easy to read the circuit - any better quality?
At first sight it seems there are LOTS of problems, but need to see clear diagram. For example: IC input stage (potential to overload/transient distort); a differential input second stage pair (NPN-PNP) both without degen-emitter resistors (more potential to suffer transient distortion) and finally an output stage with gain. Difficult to stabilise easily.
Most DIYers will know the better configurations now: differential input with degen resistors; cascode VAS either single or Darlington with common mode current regulation or current mirror to single ended VAS; double or triple NPN/PNP only output stage (no triplets) for low crossover distortion.
JOhn
At first sight it seems there are LOTS of problems, but need to see clear diagram. For example: IC input stage (potential to overload/transient distort); a differential input second stage pair (NPN-PNP) both without degen-emitter resistors (more potential to suffer transient distortion) and finally an output stage with gain. Difficult to stabilise easily.
Most DIYers will know the better configurations now: differential input with degen resistors; cascode VAS either single or Darlington with common mode current regulation or current mirror to single ended VAS; double or triple NPN/PNP only output stage (no triplets) for low crossover distortion.
JOhn
Except that the measurements (including PowerCube, done at Audio Critic) show that the stability is excellent. Taylor is a superb designer.
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Joined 2009
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I have a Bryston amp and for sometime I found it too harsh in the treble. It seems to be a combination of components as the problem is noticeable mostly when I use a particular speaker cable (a long one, heavy, expensive and bi-wired) and with particular speakers (PMC floorstanders) in a large room dominated by hard surfaces. When used in a smaller room with different (short lamp wire) cables and my DIY Martello-2 speakers there is no issue at all. I have used the Bryston as my reference amp, all my DIY amps have been compared against it as I believe the Bryston to be very honest and neutral.
Used a Bryston 4B-ST for quite some years in the past. It drove Dynaudio Crafft, quite a difficult load. I was very pleased with the impression of effortless and natural reproduction. There was, however, a problem with the treble. It only sounded really right after continuous operation of around two weeks. As soon as I turned it off for some days, e.g. during holidays, I had to wait for two weeks until the "magic" returned.
Looking at the schematics, I of course only can speculate. One thing that really springs into the eye is that Bryston does not use any emitter degeneration in input stages of input buffers or power section. This might lead to a high susceptibility against EMC problems. Unfortunataley, I could not listen until now to a SST or SST2 version; Bryston has changed the distribution in Germany, and dealers do have problems with that.
With the introduction of the SST and SST2 versions, Bryston said that they have worked on their grounding topology, and comparing the schematics, I find, among others, a change in input filtering. This might support the above assumption.
All together, I think that Bryston does a good job in using reasonable engineering to deliver high sound quality. If you simulate their circuits, then you sometimes are astonished about the simplicity and cleverness of their solutions (e.g., input resistor at non-inverting input of the power section).
Reading the reviews on the SST and SST2 generations of their amplifiers, I really would be interested in hearing their current 4B version.
Kind regards,
Matthias
Looking at the schematics, I of course only can speculate. One thing that really springs into the eye is that Bryston does not use any emitter degeneration in input stages of input buffers or power section. This might lead to a high susceptibility against EMC problems. Unfortunataley, I could not listen until now to a SST or SST2 version; Bryston has changed the distribution in Germany, and dealers do have problems with that.
With the introduction of the SST and SST2 versions, Bryston said that they have worked on their grounding topology, and comparing the schematics, I find, among others, a change in input filtering. This might support the above assumption.
All together, I think that Bryston does a good job in using reasonable engineering to deliver high sound quality. If you simulate their circuits, then you sometimes are astonished about the simplicity and cleverness of their solutions (e.g., input resistor at non-inverting input of the power section).
Reading the reviews on the SST and SST2 generations of their amplifiers, I really would be interested in hearing their current 4B version.
Kind regards,
Matthias
Just one comment concerning the output stage.
The topology of output transistors is *really* clever. First, if you simulate it, you will find a rather wide transisition region between positive and negative half-wave. This means, that output transistors do not have to be turned off that fast, which is always a problem (at least at high output levels).
Secondly, they use the same current from drivers twice: once for a pnp, and once for an npn output transistor. Thus, they can gain a higher gain-bandwidht product with their rather slow output devices (MJL21193/4, nowadays). These devices are really good (look at their output diagram: much less early effect than others).
Thirdly, they cleverly pre-load the output with a quite large output capacitor. Together with the usual output inductor it forms a circuit whichs resonance frequency is well below the unity loop gain frequency (ULGF) of the whole circuit. Thus, additional capacitive loading may never compromise the stability. Given the pre-loading, they can optimally control the stability margins in the circuit.
Number four: if you look more closely into the embedded loop formed in the output stage, you find this parallel circuit of 150R and some 100 pF in the base of the driver. Simulating it, you find an imrovement of the phase margin in the embedded loop. But by which means: it is that simple.
You see, I'm really impressed by their engineering. One thing remains: these un-degenerated input stages ...
Matthias
The topology of output transistors is *really* clever. First, if you simulate it, you will find a rather wide transisition region between positive and negative half-wave. This means, that output transistors do not have to be turned off that fast, which is always a problem (at least at high output levels).
Secondly, they use the same current from drivers twice: once for a pnp, and once for an npn output transistor. Thus, they can gain a higher gain-bandwidht product with their rather slow output devices (MJL21193/4, nowadays). These devices are really good (look at their output diagram: much less early effect than others).
Thirdly, they cleverly pre-load the output with a quite large output capacitor. Together with the usual output inductor it forms a circuit whichs resonance frequency is well below the unity loop gain frequency (ULGF) of the whole circuit. Thus, additional capacitive loading may never compromise the stability. Given the pre-loading, they can optimally control the stability margins in the circuit.
Number four: if you look more closely into the embedded loop formed in the output stage, you find this parallel circuit of 150R and some 100 pF in the base of the driver. Simulating it, you find an imrovement of the phase margin in the embedded loop. But by which means: it is that simple.
You see, I'm really impressed by their engineering. One thing remains: these un-degenerated input stages ...
Matthias
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This is certainly true, and looking into other threads you will find that I'm on the "engineering side". But there has to be some more to it.
As I already indicated: my first candidate is EMC. This meets with the impression of some audiophiles that the system only sounds right with power conditioning or snubbing circuits at the mains sockets (sold for incredible amounts of money!).
I admit that I cannot bring this together with my impression from the 4B-ST, that they only sounded right after long continuous operation. Do main rail capacitors improve their HF properties with formation? Is it something else? Do not know. But you really can hear it.
Matthias
The Brystons are honest. From following the reviews of the last years, I think they have largely resolved the issue with harsh treble (see above posts).
1. Did you "burn in" for some time?
2. Which pre-amp do you use? According to the schematic, they load the input with 100R + 470p. This normally reasonably terminates the cable (see Bob Cordell's book), but does the pre-amp like it?
3. Are your speakers on the "bright side"? Do they have metallic HF units?
4. Bad bass? This is certainly not a Bryston issue.
Bass is, however, really well controlled; at the beginning, this sounds like "not enough bass".
Matthias
PS. After all this Bryston defense, I hope that you still believe me that I'm independent.
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But you will admit that the 2 weeks continuous you talk about is suspiciously close to the time it takes the brain to adapt to something.
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Joined 2009
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I don't know about their latest units, but the one I have appears to have a very good limiting circuit - using an RC filter to keep the limiter out of the way except at very low frequencies. It looked so clever to me that I copied it into my TGM5 amplifier design.
Yes, I will admit that. On the other hand, as an example: in every day live, you hear how a plosive or an 's' in normal speech does sound. You can compare it to the sound of the radio speaker coming out of the boxes. What if the similarity between both improves over time?
Of course: it might be that I have invested a lot of money (Bryston is not really cheap), and somehow I'm forced to perceive an improvement over something I was initially not contend with. The only thing I can respond: this impression of improving sound did repeat again and again over the years. Sometimes, one just has to turn off the beast.
Matthias
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Joined 2009
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I have a colleague whom I built a pair of speakers for, Mark Audio 10.3 Pencils. He swears that it takes 2 weeks after a break for them to sound 'right'. After two weeks they sound wonderful. He drives them from an SV-811 SET.
Hi Guys
The lack of emitter degeneration is not an indication of poor design, just as the use of emitter degeneration is not a guarantee of good performance. How many input stages are operated open-loop? if you had a need to do that then Re comes into its own as local feedback, linearising the stage and providing a wider signal handling capability.
However, that is NOT how most input stages are used, and in most cases the input stage is protected from the outside world through passive or active filtering. In the 7B-sst there is a diff amp at the input - actually cross-coupled diff amps to generate the balanced signals to drive the two power amps. The actual input of the power amp circuit is well protected from the outside world and any EMI threat. Even back at the diff amp stage, the input filtering and gain rolloffs keep the signal across the BJT bases within their linear range.
Emitter Rs add noise, so if you want to get rid of noise you get rid of Re. In the overall design approach of Bryston's circuits, matched input devices has always been the rule, and this imparts very special attributes to the amp and greatly reduces the need for bandaids like Re. The quietness and linearity of the product is proof that their methods work. I believe some of Bryston's "magic" comes from the symmetric circuitry with compensation that is not the usual Cdom found in the ubiquitous Linn-Thompson circuits.
To the poster who thought he saw an IC input stage: go to Bryston's site and look at the PDFs there. Bryston's audio circuitry is all discrete. There is an IC circuit to monitor the error voltage across the PA input that triggers the clip LED. It is well-buffered, so has no impact on audio performance.
We assess equipment subjectively. We tend to be nostalgic about the first sound we heard since that was exciting. We can be excited by accurate sound if that is how our ears and brain work - for me accuracy is exciting. Accurate sound will feel weak in the bass to those unaccustomed to accuracy. Bryston is built to be as accurate and neutral as possible. For some, this is not what they want and that is perfectly okay.
Then there is the issue that when you insert something truly accurate into a very coloured system, the character of those other pieces will scream at you. The net system is different, and maybe the power amp that was int there before had its own character that complemented the other pieces better?
Have fun
The lack of emitter degeneration is not an indication of poor design, just as the use of emitter degeneration is not a guarantee of good performance. How many input stages are operated open-loop? if you had a need to do that then Re comes into its own as local feedback, linearising the stage and providing a wider signal handling capability.
However, that is NOT how most input stages are used, and in most cases the input stage is protected from the outside world through passive or active filtering. In the 7B-sst there is a diff amp at the input - actually cross-coupled diff amps to generate the balanced signals to drive the two power amps. The actual input of the power amp circuit is well protected from the outside world and any EMI threat. Even back at the diff amp stage, the input filtering and gain rolloffs keep the signal across the BJT bases within their linear range.
Emitter Rs add noise, so if you want to get rid of noise you get rid of Re. In the overall design approach of Bryston's circuits, matched input devices has always been the rule, and this imparts very special attributes to the amp and greatly reduces the need for bandaids like Re. The quietness and linearity of the product is proof that their methods work. I believe some of Bryston's "magic" comes from the symmetric circuitry with compensation that is not the usual Cdom found in the ubiquitous Linn-Thompson circuits.
To the poster who thought he saw an IC input stage: go to Bryston's site and look at the PDFs there. Bryston's audio circuitry is all discrete. There is an IC circuit to monitor the error voltage across the PA input that triggers the clip LED. It is well-buffered, so has no impact on audio performance.
We assess equipment subjectively. We tend to be nostalgic about the first sound we heard since that was exciting. We can be excited by accurate sound if that is how our ears and brain work - for me accuracy is exciting. Accurate sound will feel weak in the bass to those unaccustomed to accuracy. Bryston is built to be as accurate and neutral as possible. For some, this is not what they want and that is perfectly okay.
Then there is the issue that when you insert something truly accurate into a very coloured system, the character of those other pieces will scream at you. The net system is different, and maybe the power amp that was int there before had its own character that complemented the other pieces better?
Have fun
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