Thursday, 29 October 2015

A More Ambitious Upgrade - Part 5

Progress has been made, in improving the quality of the volume control, but there is still clearly audible degradation. As a first major reworking I altered the circuitry around the potentiometer to turn it into a shunt topology, with immediate, obvious, audible benefit - the series resistor in the top arm leg was a fairly large value with the intended result that much more of the pot travel would be used in normal listening. Very much a step upward in the sound, and at first I was very pleased, thinking that maybe enough had been done to offset the inherent flaws in the construction of the potentiometer part; but, being the sort of person I am I immediately started using more testing recordings to highlight details of behaviour, and - you know what's coming - finally tried a track where the losses were very clear: a 'dirty' quality could be heard, which temporarily went away when the volume setting was jiggled, cleaning the contact points momentarily.

So, more has to be done! I'm not keen on simply buying, installing a much more expensive, 'higher quality' pot - I suspect that I won't make the problem go away, based on previous experience, merely slightly lessen the audible degradation - what I want is a complete solution. Without spending silly money, or going through strenuous contortions to get a better mechanism in place ...

That said, the system is in a pretty good space - most recordings come across very well, much better than the typical standard of 'audiophile' rigs: solo piano, harpsichord, is intense, rich and vibrant; massed string section playing has that sweet, satisfying sheen to it ... but, "poorly recorded" tracks catch it out still.

Friday, 23 October 2015

A More Ambitious Upgrade - Part 4

The usual process is taking place, that is, as movement forward is made, the remaining inadequacies that were not readily noticeable earlier become more prominent, become easier to discern and easier to tie directly to some part of the whole. In my previous update I said I felt I was in good shape, but underlying that was the concern that the volume control, a cheap Alps potentiometer implemented in a very conventional way, would start to rear its ugly head - volume controls are a huge concern in audio, and my previous experiences are that all straight analogue methods are too great a degrading factor; hence, and luckily by accident, I have always used digital control or semiconductor circuitry to date - no raw switches or wiper on tracks used. With good results ...

Which brings me with dealing with the NAD amp. Its virtues have shone brightly enough so far, but a day or so ago an album which quite quickly developed a dirty, irksome edge to the sound got my attention. Was this the volume pot becoming too much a problem, finally? Yes, it was - a quick jiggle of the volume setting cleaned up the sound momentarily and then the unsavoury quality to the tone started to fairly quickly build up again. Bummer !!! Now that I can "hear it" I'll always be aware of its effect, unfortunately.

So, I'll have to bite the bullet! I've never done a major exercise of resolving potentiometer quality issues up to now, I've always been able to sidestep them - but this time my focus is different: I really want to get the best out of the gear without major re-engineering of parts of the components - a "simple" solution is to rip out the pot and install a full-blown, very high quality semiconductor or possibly discrete relays and resistors circuit. But this is an involved, relatively expensive approach - I won't go there until all low cost alternatives are explored.

This means that I'm now in full flight in investigating what the experiences of others are, what tweaks and tricks have been used - and will start trying the best ideas that I come across ...

Friday, 16 October 2015

What do I mean, Audio Conjuring ??

Simply put, the intention is to create an illusion that one is hearing the "real thing" when listening to replay of musical recordings - which then brings in one's interpretation of the word "real", in this context. Most would have an intuitive understanding of what I'm getting at, a simple example is a CD recording of some classical, solo piano music: if this is always able to "fool" you and anyone else into thinking that there is a real grand piano, and real, highly competent pianist in your home, say, both on a casual coming across the sound of it happening, and also when closely, carefully listening to the quality of the tone and other elements of how the sound comes across.

This just then naturally extends to any and all recordings being played on the audio system: they never draw attention to the fact that they are a 'fake', they are convincing in their presentation. One should never be aware that you are listening to an electronic, mechanical contrivance doing the work of generating the sound in the space - if this happens, then the conjuring "trick" has failed.

It's as simple as that ...

Thursday, 15 October 2015

A More Ambitious Upgrade - Part 3

Appears that I've cleared the first major hurdle in this process - the system now has 'mojo', the ability to draw one into the sound; it just "works" as a way of experiencing a 'historical' musical event - I don't have to make mental excuses for it "not being quite right" ...

This came about through eliminating the Balance pot, potentiometer - I knew it was causing some degradation, because moving its position when the sound was irky, and thus momentarily cleaning the contacts, decidedly improved things. So, this part was effectively chopped out of the circuit and fixed resistors which mimicked a centre setting for the control were inserted. But I was still surprised by the degree of improvement - I note that the service manual "proudly" states that these parts are by Alps ... this didn't help much ... :-)

Even CD-R disks which are straining the error correction circuitry, as evidenced by the popping and snapping sounds, and much skipping, are quite possible to listen to .... for a while.

So, I'm a happy chappy - there is still much that can and needs to be done, but the quality is already at a very good standard - plenty of potential to exploit.

A More Ambitious Upgrade - Part 2

Some major movement forward, up to now I've given the gear the benefit of the doubt, and just hooked it up to the mains in a very conventional way - but the tonality issues were now getting too strident ... the prime culprit turns out to be the CDP, by virtue of the highly inadequate isolating of mains noise junk from causing cross-interference - extremely typical of usual audio. I use very simple, zero cost or close to it techniques for troubleshooting - the simple exercise of setting up a dedicated mains spur for the CDP alone with some token mains filtering pinpointed the cause of this quality aspect. This now gives me very good solo piano tone, capable of being run at realistic levels, which sounds pretty good directly in front of the speakers as well as the other end of the house, and outside - vastly better to listen to than the typical ambitious, expensive audiophile rig, :-P .

But interestingly, I seem to have a bit of a noise issue - never experienced this before as being so noticeable. This is classic, resistor thermal noise hiss - not the recording, a digital album still shows the problem. I wonder if this is because all of the NAD circuitry is discrete - yet more investigation needed !

A More Ambitious Upgrade - Part 1

I've been motivated to fix up and optimise another cheap system: some discarded NAD units, almost 20 year old CD player and amplifier driving good, "boombox" speakers. Very promising early signs, tonnes of genuine dynamics in the raw state; has the usual flaws of developing a very 'dirty', unpleasant edge with steady playing - quite a bit of cleaning up and tidying to be done, but excellent potential ...

There's a NAD C 540 CDP (CD only player), 304 integrated amplifier, and Sharp boombox speakers - from a classic, modern 3 identically sized boxes with all the electronics in the middle system; the speakers have a solid bass/mid unit, rated to take 200W, so no prob's there.

As usual, all the issues are with the electronics: to start with, the full setup had a cheap but cheerful sound, at least for a while from startup, until the electronics got really a dirty tone with ongoing use. As expected, the internals are riddled with weaknesses, poor implementation details, which all have to be sorted - the unfortunate thing is that mildly ambitious units like the NAD get lots of things right, but all the leftovers then combine to drag down the potential dramatically, they often sound considerably worse than a very simple, totally unambitious sound unit, in the sense of being less "musical".

Which is a way of saying that I'm in that awkward middle stage of tweaking, where quite a number of flaws have been bypassed, lifting the standard in some aspects, but putting the remaining ones in much sharper focus - the whole now very easily produces downright unpleasant sound, :-P . Many people could give up now, saying they preferred the easier to listen to, somewhat gunked up sound of the raw units - but that would be a failure of effort, big time !!

The CDP has a pretty hopeless reader mechanism engineered, CD-Rs are a huge obstacle, sound much worse than an LP with continual crackling and popping as the error correction struggles, all my other rubbishy computer and audio CD drives handle these disks with zero audible problems. But, NAD is known for this, ;-)   - will explore some avenues here.

My other recent fiddling with cheap stuff was much easier, because so many flaws were eliminated by virtue of close integration of the electronic elements - the designers got that part right! The NADs, like nearly all of this type of electronics, have flaky elements everywhere  - and each and every one has to be tracked down to get the best out of the whole.

A couple of thoughts on current progress: can do big orchestral climaxes with greater SPL than my other recent efforts, but tonality still has some way to go; massed strings, piano and such are often not right, sweetness goes off far too quickly ...