The situation with switching amps is by no means cut and dried.
The noise sitting on the signal, or the effects of this folding back into the audio band can be measured and demonstrated, but the audibility is the key. In the same way that Leak did testing not only to identify distortion but to then assess the effect on listeners.
There is little research into this at present and more certainly needs to be done in order to quantify the subjective effects on the listener.
I can certainly think of one user runing high power switching amps into Impulse Taus horns of all things, and is delighted with the results.
Tony, do you carry such amps and if so what are your thoughts compared to more standard SS and valve designs?
Rob,
I would agree with this whole heartily, it is the implementation of ANY such technology that is the key to its success of dismissal in the audio arena.
Again, main power supply rails, switching frequency for the amplification section, dedicated fully super regulated style supplies for the control module, fully isolated digital and analogue ground planes, at least 4 layer high quality circuit boards, specific RFI/EMI shielding, high quality ouput stage filtering, FET selection and again isolation all play a key role in the finished articles performance.
They are a few designs around that are capable of serious results, The early B & O and Hypex modules have too limited a band width to provide serious performance, they can be made to sound good without question, they just lack musical engagement and emotion for me, however they do have a following and are well regarded in dark and solder fume filled cupboards and garages!
They key words here are 'audible' and how this is perceived by the individual, I have had some pleasing results by moving the switching frequencies of the amplifier into the higher pass bands, a lot of the well know switchers tend to use a switching frequency around the 500Khz mark, for me this is too low and (again for me) does not extend higher enough to 'hide' enough of the switching noise.
We like to use between 1.2 Mhz and 1.65Mkhz for optimum results in our designs, again the FET noise is also a key issue in this particular area.
Having experimented with multiple low pass values, I like to keep it between 90-120Khz depending on FET performance (gate noise, speed rfi emissions and vibration) and switching frequencies, they are various other issues which are factored into the equations too!
Contrary to most switcher designs these days, I prefer torriodial power, ultra quiet and fast rectification coupled with a two stage smoothing and storage bank, consisting of multiple capacitor banks each of around 240K, quality bypassing etc. We also incorporate a large DC blocking circuit into the psu as well.
As with all equipment Rob personal taste is paramount for a possible amplifier purchase, one form of technology can sound 'wrong' or not desirable to a potential buyer.
We stock all the amplification styles you mention Rob, we have very high quality solid state, with no op amps used at all just fully discrete, both class a/b and fully class 'a' designs and valve solid state hybrids.
Valves amps from Puresound to airtight and Waveac, single ended to push pull, each of these designs brings their own flavour to the party, though unless you are running 845's or 211's you are fairly limited to speaker choice, needing at least a 92dB sensitive unit to fully bring out the most of the amplifier.
This may surprise you guys I have admiration for a good 2A3 design and a quality 211, these are my personal favourites.
With regard to the switching amplifiers, I feel if correctly implemented they can sound superb, its not just the bass control or the dynamics, its the ability to portray the interplay between the musicians with consummate ease, render the macro dynamic layering in a way that neither the others can, yet also produce the delicacy and imagery of say a 300B and drive virtually any speaker without fuss.
They also have a speed and liquidity if allowed to shown that will rival a quality valve amp design, I also find an intimacy they give I seldom hear elsewhere.
Are they valve sounding No, will they make you cry tears of joy listening to bespoke harpsichord music at low volumes with merest brush stroke of tonal thermionic colour, most likely not.
However they are no less capable of producing scintillating, engaging and fluid musical sounds that have a high realism factor.
We all take different aspects of music and make them our 'own' what is heaven for one chap is pure hell for another and vice versa.
In the same way they are quite shocking valve and solid state designs, there are very good ones too, the same applies to switching amps.
I personally use a self designed digital amplifier in my own system, I make refinements now and again, but to date I have heard nothing that would make wish to change.
