Almost every day I read postings on this and other forums, about the relative merits of different commercial microphone amplifiers, together with opinions about why they sound different. Everyone seems to have an opinion, and more often than not it?s a simplistic view of various parts of the circuit; whether a transformer adds ?colour?, or the relative merits of different chips. It seems that almost no-one stands back from the subject and sees the whole picture.
I?m not trying to give answers here, I?m just trying to put things into perspective and stimulate debate and original thinking.
One of our biggest problems is the inability to understand the refinement of our own ears. Yes, we can measure amplitude frequency response and ?distortion? down to what we think are very fine limits, but our understanding of physics does not sit well with the real world of perception; for example, how important is frequency response? As a sales tool it used to be paramount, yet the reality is that it is very much less important to our ears than relative phase response (one reason why the few good EQs can enhance a sound while most destroy it!).
It?s so obvious, yet so overlooked and misunderstood that the most important factors in ?quality? of sound are accuracy of transient response, and phase relationships.
Looking at basic microphone preamp design, and the factors that I have read about recently in the forums?..
Yes, I?m sure that the Jensen transformer is as good as they get. The use of a transformer on the plus side brings galvanic isolation and the ability to ?match? the input impedance to the microphone. (to achieve an optimum bridging load), but the downside is that it will introduce phase distortions at the extremes, although these can be thought of as beneficial.
It?s good to get rid of the input coupling capacitors! While I include comments of ?smearing sound by electrolytics as snake oil, input caps often add limitations to LF performance, and can prove unreliable.
The amplifier itself is probably the biggest source of political opinion.
Modern op-amps, when used correctly are truly transparent. BUT the devil is in the detail! The amp will only operate perfectly if the power supplies are truly zero impedance and the current paths in the components around the amp are exactly as envisaged by the designer. This is never the case, so small performance changes occur between layouts and designs.
I believe that many ?front end? operational amplifiers suffer from stability problems during transients, and that while such ?distortions? are extremely difficult to measure, they can be clearly heard and described as ?brittle? or ?cold? sounds, that is why in my own designs I restrict the gain on ?front end? amplifiers and tend to use balanced circuit forms where there is at least a chance for some of these momentary distortions to cancel themselves.
Another remedy is to adopt low gain discrete circuits; less feedback means less chance of instability in this case.
The use of class A discrete circuitry of course has another major advantage, that is that non linearities in the amplifier show themselves as 2nd order distortion?. Acceptable to our ears; but that?s a favourite hobby horse of mine so leave it at that.
The last subject that has a gross effect on performance, yet is rarely mentioned, is overload margin. I learned the importance of overload margin designing preamps for broadcasting. It used to be a compromise between overload margin and noise, but that hardly applies now. A good mic amp set up with a ?normal? overload margin of say 20dB is going to sound distinctly average?. It will sound clean but uninteresting because of how it is treating transients; they will be hitting the power rails and causing those momentary instabilities. Increase the overload margin to 30dB and suddenly you have air and space in the sound reproduced; note, this is not an attribute of a great mic amp?. It?s what should have been there all along!
So, to sum up, it?s not the inherent quality of the SSM2017 or the new chips from ?Thats? that are important, it?s the way the mic amp deals with the unmeasurable, accidentally or on purpose!
:guinness:
I?m not trying to give answers here, I?m just trying to put things into perspective and stimulate debate and original thinking.
One of our biggest problems is the inability to understand the refinement of our own ears. Yes, we can measure amplitude frequency response and ?distortion? down to what we think are very fine limits, but our understanding of physics does not sit well with the real world of perception; for example, how important is frequency response? As a sales tool it used to be paramount, yet the reality is that it is very much less important to our ears than relative phase response (one reason why the few good EQs can enhance a sound while most destroy it!).
It?s so obvious, yet so overlooked and misunderstood that the most important factors in ?quality? of sound are accuracy of transient response, and phase relationships.
Looking at basic microphone preamp design, and the factors that I have read about recently in the forums?..
Yes, I?m sure that the Jensen transformer is as good as they get. The use of a transformer on the plus side brings galvanic isolation and the ability to ?match? the input impedance to the microphone. (to achieve an optimum bridging load), but the downside is that it will introduce phase distortions at the extremes, although these can be thought of as beneficial.
It?s good to get rid of the input coupling capacitors! While I include comments of ?smearing sound by electrolytics as snake oil, input caps often add limitations to LF performance, and can prove unreliable.
The amplifier itself is probably the biggest source of political opinion.
Modern op-amps, when used correctly are truly transparent. BUT the devil is in the detail! The amp will only operate perfectly if the power supplies are truly zero impedance and the current paths in the components around the amp are exactly as envisaged by the designer. This is never the case, so small performance changes occur between layouts and designs.
I believe that many ?front end? operational amplifiers suffer from stability problems during transients, and that while such ?distortions? are extremely difficult to measure, they can be clearly heard and described as ?brittle? or ?cold? sounds, that is why in my own designs I restrict the gain on ?front end? amplifiers and tend to use balanced circuit forms where there is at least a chance for some of these momentary distortions to cancel themselves.
Another remedy is to adopt low gain discrete circuits; less feedback means less chance of instability in this case.
The use of class A discrete circuitry of course has another major advantage, that is that non linearities in the amplifier show themselves as 2nd order distortion?. Acceptable to our ears; but that?s a favourite hobby horse of mine so leave it at that.
The last subject that has a gross effect on performance, yet is rarely mentioned, is overload margin. I learned the importance of overload margin designing preamps for broadcasting. It used to be a compromise between overload margin and noise, but that hardly applies now. A good mic amp set up with a ?normal? overload margin of say 20dB is going to sound distinctly average?. It will sound clean but uninteresting because of how it is treating transients; they will be hitting the power rails and causing those momentary instabilities. Increase the overload margin to 30dB and suddenly you have air and space in the sound reproduced; note, this is not an attribute of a great mic amp?. It?s what should have been there all along!
So, to sum up, it?s not the inherent quality of the SSM2017 or the new chips from ?Thats? that are important, it?s the way the mic amp deals with the unmeasurable, accidentally or on purpose!
:guinness:
Maybe OK for broadcast, but not good for recording...
