16/05/2026
Weekend Wittering:
I'm sure most of us have wondered why amplifiers exhibit differing sound qualities in varying systems and cabling. To date, I've yet to see any in-depth discussion as to why - the case being left hanging so to speak, vague references being mainly concerned about cables and other external influences on the performance of an amplifier rather than going to the root of the problem. Perhaps the root of the problem is largely misunderstood so dear readers, read on.
Well, many seed thoughts have resulted in much experimentation here and I have to suggest that although amplifier topology and strategic layout of the circuits may have claimed many audible sonic benefits, the root of this phenomenon has yet to be nailed down.
Some years ago, I read an article in a certain magazine outlining something known as 'Nested Differential Feedback Loops' and a design published for the constructor to make. Measured performance figures suggested this strategy, majoring on the lightly addressed area of amplifier feedback, would bring about substantial improvements in the reproduction stakes. I read this article many times over the years leading to my own thoughts on the subject of feedback.
To date, most designs employ a 'Monkey see, Monkey do' system where a proportion of the out put of the amp is channelled back wholesale as far as the frequency spectrum is concerned, to the most sensitive part of the circuit - the input stage. This feedback is not the pure version of the large signal the amplifier is sending out but a melange of unavoidable trash being returned by that giant motor - the loudspeaker voice coil along with associated crossover components. Stopping a voice coil and speaker cone is one thing but reversing its direction instantaneously is a whole different ball game - rather like putting a formula one race car into reverse on the straight and expecting it to instantly respond. Whilst the coil in quiescent mode is simply an inductance which becomes a linear motor, under drive conditions it becomes a generator and who knows just what it gets up to between these states.
The signal presented to the amplifier circuits via the cables - which incidentally may transfer or 'snub' various harmonic content as it may please them to do, is by no means an accurate facsimile of the outgoing force from the amplifier as we like to suppose and truly contains a whole panoply of self generated trash for the feedback to deal with.
At this point, I'd like to return to the original thought and explain why feedback is used: A proportion of the output from the powerful drive signal is returned to the input section to maintain stability and reduce the distortion to acceptable figures. This returned signal in no way represents what was sent out and the input stage of the amplifier, tasked to respond, finds all manner of trash it has to deal with or most likely, ignore completely. As there is no such animal as a 'clairvoyant' electronic circuit, the response is always behind the beat. Traditionally, the frequency spectrum is returned wholesale with little or no regard to 'tailoring' what is sent back or dumped and the front end, in attempting to deal with this unwanted intrusion, injects further trash into the equation.
You'll note that distortion figures are usually calculated using a dummy load or at best, a resistance shunted by a capacitor - never a combination of various components representing real loads in real time.
My thinking along the lines I've outlined above has led to designs that limit certain bands of energy from reaching the input stages of the amp. Allowing only particular frequencies and phase angles (more discussions later) - those necessary to maintain stability, into the feedback loop has resulted is some remarkable outcomes. For starters, the treble region has been released to flow in a marvellous way, the bass performance, unhindered by restrictive feedback, achieves a depth of detail otherwise hidden to the listener.
My thoughts and deliberations are only the beginning as I see immense benefits looming on the horizon. Thinking 'out of the box' has brought about the SE series of amplifiers which, if granted further years, I hope to develop and hopefully, realise the sound I've had in my head for many, many years.
Thanks for reading so far, I look forward to further thoughts as the investigations gather pace.
Further Reading: