Harshness, Clicks and Pops

So far, I've talked about phono stages and the different approaches.

1. The "afterthought" in a cheap amp (it'll be active!)

2. The "bandwagon" interstage passive (faults as described)

3. The fast-active (very rare)

The "afterthought" is just about guaranteed to obliterate the music in favor of record surface noise.

The "bandwagon" is something that I've built on multiple occasions and has its own built-in partial "scratch filter."

The fast-active passes the lot without modifying the scratches, clicks, pops, or music. If the rest of the system was equally-well designed, then it's doubtful you will hear the scratches, clicks, and pops because the music dominates.

But what happens if the rest of the system was NOT equally-well designed? And how can that happen?

Early on in the 1970s, Matti Otala was tasked with investigating why amplifiers could sound bad. Philips recruited him from university. He later wrote a paper on it for the AES (1972).

I don't remember anything about it in Britain at the time, and I'd only heard of the basic gist, but it was sufficient for me to understand the prerequisites of fast-active design.

The batten was also taken-up by Walt Jung and associates in the American "Audio" recreational magazine. In several editions, Jung went straight over the reader's heads in explaining what made amplifiers corrupt the signal.

Again, such things never featured in any of the British technical press, and so it was a matter of piecing together the imaginations in my head and hoping I'd got it right.

It has only been the last 22 years since the Internet has made it possible to visit "other worlds," and with thanks to those who archived such works, the British designer (me?) has been able to connect-up the missing pieces.

It was with great relief that I learned I'd been on the right road and had now found a wealth of techniques to further my interest in better audio. Most British designers were of fine reputation and had done their best in "blindfolded" Britain. Those with access to American information were making better amps.

Douglas Self had been our only connection with the professional design world, and John Linsley Hood had also done his best.

By the early 80s, Paul Miller had started testing high-frequency amplifier performance. With his listening panel, he could mate-up the listener's reports with the technical test data. He found that amplifiers having poor high-frequency control sounded spitty and noisy.

With all the above information, I was able to rate my chances of making fast-active phono stages. I knew the ones I sold to owners of "sensible" amplifiers would be the winners. I became highly suspicious of hi-fi bullsh*t. I knew the market would never be massive but also realised that I would never compete big-time as a one-man-band.

The above knowledge served me well in developing a headphone amplifier. The Solo has changed little in its 20-year history. Auditioning using vinyl records, if hearing harshness, clicks, and pops, I knew the design was wrong, and I must try harder.

Again, the Proprius, the lack of harshness clicks, and pops told me the product would be acceptable. It has significantly helped in the development of the proposed DAK kit amplifier. It always highlights stability problems and enables me to troubleshoot a circuit. Even though I do a lot of auditioning using digital files (for convenience), I could not imagine developing highly musical line-level and power amplifiers without the transparency of the fast-active vinyl source.

I started writing this topic because it would seem new people are joining us, hoping to solve their vinyl issues, but without much, if any, understanding of the systems they've chosen.

Some of the vast mid-market amplifiers' choices are being equipped with whistles and bells, often featuring microprocessors and logic chips to select sources. To me, this is a backward step that can only result in some form of uneducated revolt against the electronics art my career holds so dear.

The loaner program might now be a bad idea. I liken it to the misfortune of Eddie Hall, always being challenged to a fight each time he walks out of his front door.

With the flood or dumping of - dare I say it - highly technological looking amplifiers from China - subsidised by the Chinese Communist Party (HMRC is watching), which are little more than convenience electronics made to look hi-fi, it is only a matter of time before the conjurers trick (the one I mentioned earlier in this topic) stops working.

This conjurer's trick of fast-active circuitry is one I stand up for because, in effect, it isn't a trick - that's my sense of humour: the no-cheating method of preserving the vinyl signal such that it may be passed on by equally fast, carefully considered circuitry to obtain almost faultless vinyl reproduction.

Next time I hope to discuss the difficulties and solutions required for the smallest of signals

What's worrying in a world full of misinformation is that the truth can be easily trashed, especially if not supported by the crowd.

You must accept that audio signals have nothing at all in common with high-frequency signals, or that is what is expected of you. It serves a purpose, but a very dishonest one.

Musical hearing is in the musician's dominion, as if by special decree. The audio design engineer can only have a musical hearing if also a musician. I cannot read or play music, and the less said about my singing voice, the better.

However, if I wire the ground connections of op-amps to a "ground mecca" on a printed circuit board where the path is already catered for by a solid ground-plane and say I can hear the difference it makes, I am lumped with the lunatic fringe.

I insist the grounds are wired in such a way on every Accession MC, but I don't on an Accession MM. It isn't that the two use a different kind of electricity; it is because my senses cannot detect any difference once past an order of magnitude.

Measurement techniques coupled with the prescribed notion of how things work have limited the test engineer to measuring the stuff of Harold Black's day. They are mostly 100 years out of date! Opinions - many imaginary - have multiplied, while measurement technology has stagnated. It is not that some of these phenomena are fanciful - world governments dictate that EMC must be proven, don't they?

The stagnating measurement gurus, on whose equipment we produce product specifications, is so outdated that the ultimate proof of a product's compliance can only occur in a government-approved compliance lab! Come on, guys, surely you can do better than that?

References are usually included at the end of every scholarly article. I would dearly love to substantiate my recent posts with a revealing research article from an old Wireless World issue, but Big-Tech, in the form of Mozilla Firefox, deleted it. It is comprehensive at removing all you wanted to keep, including its browsing history! If I were a budding researcher, I would seriously avoid Firefox! So why do I use it? I use it for its web developer tools.

There is substantiated proof that

A capacitor has resistance and inductance.
A resistor has capacitance and inductance.
An inductor has resistance and capacitance.
A wire has inductance.
A PCB trace has inductance.

The scholarly article I wanted to feature here plainly shows that most wire and PCB trace sizes used have an inductance of 20nH per inch.

Although audio frequencies may be classed as DC, in that such small values change absolutely nothing, what they do is act on radio frequencies.

Radiofrequency interference is insidious, and the active components used to make an audio circuit are very capable of working at radio frequencies. Now, if you're unsure of that, you need to look at plenty of op-amp bode plots and plenty of power amplifier bode plots. The transition frequencies are also quoted in the tabulated sections of datasheets.

Capacitors are placed across circuits to attenuate radio frequencies, but lead length places inductance in series near to transition frequencies. The sum between capacitance and inductance often cancels the effect of the capacitance.

A capacitor used to stabilise a circuit can therefore be rendered useless. The answer has been to use leadless capacitors as used in surface mount construction. Unfortunately, the printed circuit traces then take the place of the missing leads.

Chips in digital logic are often pinned to reduce the need for long printed circuit traces, and in some cases, op-amps have featured optimised pinning to reduce inductive trace lengths.

If an op-amp "takes off" (becomes unstable) due to radio frequency interference (which is at an all-time maximum right now), then it will not perform a proper function at audio frequencies. There will be very high-frequency modulation on the audio signal waveform. Still, we have detractors who will say the audio is still audio, often pointing at multiplexing as their proof.

Even if the oscillations do not change the audio signal, they affect the power supply because they all use electrolytic capacitors to some degree for energy storage. The capacitance alone is not the problem. The inductance is the problem.

The foils are bifilar-like wound, and it is therefore claimed that the only inductance an electrolytic capacitor contains is due to its lead length. In that case, a radial 1000uF electrolytic should be purely capacitive well-up into the MHz. Unfortunately, it isn't, and somebody is a bit economical with the truth.

To prove otherwise, you'd need a signal generator, 'scope, and a suitably sized resistor. Electrolytic capacitors cannot do high frequencies!

Electrolytic power supply capacitors get hot when the circuit they supply oscillates - where the output swings to each supply polarity. That indicates resistance, and the resistance can only come from inductance.

The above explains why localised decoupling is used and becomes the power supply at high frequencies.

What usually causes an audio amplifier to oscillate, which would otherwise be stable, is its power supply. Therefore, a power supply is not just a black-box you wire to a circuit - it is present inside the circuit too - or needs to be.

The takeaway from this post is not that audio circuits go high-enough in frequency to be influenced by inductance, but that stimulus due to RF encroachment, or an unstable active device, can, and will, make the power supply under-perform. When storage devices get hot (or warmer than they should), they do not work correctly and ultimately fail.

A stroke of genius?

Like I said earlier, we didn't get American magazines. It was news to me that Mr. Vereker's power amplifier was 'intentionally narrow-band,' as its component values tell the opposite story!

The design does the utmost to prevent output stage oscillation, and the base stoppers are as discussed in the 70s amplifier topic. Some power amplifiers need them, while other designs might not.

I can't say the same for all amplifiers, though. If an output stage is prone to spurious oscillation, or the margin for stability isn't as good as it should be, then a fast transient can result in small repetitive moments of chaos.

If our source is vinyl, and even the best records have surface/groove imperfections, moments of chaos resulted in exaggeration - we hear a louder click or pop than the real amplitude of that click or pop.

In the sixties, the 'silicon rush' was seen as a cow for milking, and non-technical entrepreneurs soon discovered they too could make amplifiers.

All it needed was an 'early chip type module,' and Japanese industry was quick to oblige. Whether the modules were inherently unstable or the entrepreneurs were ignorant about how to implement them is moot. The fact that they 'smoked' if the user accidentally unplugged a speaker betrays instability. I speak from personal experience - these amplifiers reproduced clicks and pops far better than the music!

It must have been very annoying to proper amplifier manufacturers, having to compete with such upstarts. If they'd known, they might have been able to use my argument here, trounced them, and made vinyl so listenable that CD would have had a hard time competing. It wasn't to be.