How can an enclosure modify the "sound" of an amplifier? - diyAudio
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Old 1st February 2007, 06:56 PM   #1
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Default How can an enclosure modify the "sound" of an amplifier?

The question of the subject arise when, some months ago, i get struck with some old amplifers and some old CD players manufactured by Grundig in the eighty's and claimed to sound better not in force of the internal circuits (rather conventional and, for the CDP players, just restyled Philips CDP of the first two series, CD 303 and CD 304, remarked as CD 7500 and CD 7550). but in force of their housing in a cabinet.

Amplifiers appear, at first sight, very careful designed in their grounding system, which avoid any potential (also at high frequencies) ground loop and let the cabinet play just a passive function of screening, with no loops to the circuit, neither on the input sockets (of DIN pentapolar type). CDP appears just with a cabling more cleanly routed as usual. Screws which fix PCB's on the cabinet are mounted insulated: no galvanic continuity is set between the circuits and any kind of fixing gear to the cabinets, neither remotely couplable (by capacitive way) as may be dedicated copper screw pads.

However the overall sound of these appliances appear more "liquid" and "open" toward high frequencies with an overall playing more quiet and less "transistor like" as usual. This may be due to extensive use of loudness circuitry (very sophisticated) but the playing still remain "warm" also when loudness is set off.

The question is: may be the good sound effectively dependent on tipology of enclosures (and mechanical fixing) or clean grounds with dedicated care to defeat any loop (clean or hidden and self-manifesting only at higher frequencies by means of parasitic capacitive couplings) are enough to provide a good explanation of this kind of "pleasantry" on sound reproduction? (especially ad frequencies roughly above 4-5 kHz).

I'm inclined to believe that clean ground system is enough for explain this kind of good sound but I want hear the advices of someone else, especially those of "elder" designers which surely have meet and accomodated in their professional life any kind of subleties may arise from an audio equipment. Some "elders" in the forum were yet engineers when I was just a child!

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Piercarlo
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Old 1st February 2007, 11:36 PM   #2
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I'm short on time, but offer one item for you to chew over:
Magnetic fields from power transformer, inductors (if any), or traces carrying high current will induce currents in nearby metal.
This can influence the sound in at least two different ways. One is that the induced fields are now in your ground circuit, since the chassis is nearly always connected directly to signal ground. Not good--anything in your ground will affect the sound. The other is that the currents induced in the metal have their own magnetic fields, which in turn can induce small currents in the circuit board traces or wires.

Grey
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Old 2nd February 2007, 09:32 AM   #3
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Quote:
Originally posted by GRollins
I'm short on time, but offer one item for you to chew over:
Magnetic fields from power transformer, inductors (if any), or traces carrying high current will induce currents in nearby metal.
This can influence the sound in at least two different ways. One is that the induced fields are now in your ground circuit, since the chassis is nearly always connected directly to signal ground. Not good--anything in your ground will affect the sound. The other is that the currents induced in the metal have their own magnetic fields, which in turn can induce small currents in the circuit board traces or wires.

Grey

Thanks, this is a very nice topic to chew! . An order of magnitude of these influnces? May them "colouring" the mean noise floor of an audio equipment? Well builded of course.

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Old 3rd February 2007, 01:57 AM   #4
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Issues of ground currents affecting the sound of an amp are addressed by properly grounding the amp circuits. Plastic and wood boxes offer no shielding from EM fields.

If the amp isn't grounded properly (and it's hard to do it well in a non-metallic box) then the box can affect the sound quality by not preventing external influences from having their way with the amp.

The conclusion is simply to use a metal box and ground the amp properly and there will be no "box sound" issues.

If you are wondering about which brand of violin lacquer will sound best on your bubinga and zebra wood amplifier box, you may as well pray to whatever God you worship for that will get you as good an answer as any.

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Old 3rd February 2007, 02:48 AM   #5
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Another thought to ponder: The definition of a generator can be either stationary metal in a moving magnetic field or moving metal in a stationary magnetic field.
Thin metal moves easily in a sound field. If that metal is close to a signal trace--like for instance the bottom of the chassis--it can react with either AC or DC (signal or rail, respectively) magnetic fields surrounding the trace to create weak secondary AC signals in the trace.
This can be taken either as an argument against using ferromagnetic material (e.g. steel) for the chassis, or for using thicker--hence more rigid--metal. Or both. Most high end gear uses thick aluminum. Most cheap mass market stuff uses thin steel. Am I saying that this is the one and only reason why cheap equipment sounds inferior? Don't be silly. Of course not. But it's a contributing factor.
Obviously this isn't a major problem. It's a detail to be attended to after all the big stuff has been taken care of.

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Old 3rd February 2007, 02:50 AM   #6
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Quote:
appear more "liquid" and "open" toward high frequencies with an overall playing more quiet and less "transistor like"

when I hear those words - I shudder, think of stereophile and crawl back into my sceptic's lair. Those words evoke the same reaction as someone scratching a blackboard.
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Old 3rd February 2007, 09:01 AM   #7
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Quote:
Originally posted by audio-kraut



when I hear those words - I shudder, think of stereophile and crawl back into my sceptic's lair. Those words evoke the same reaction as someone scratching a blackboard.

If I put those word between quoting marks there is a reason...

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Old 3rd February 2007, 11:08 AM   #8
Pano is offline Pano  United States
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Quote:
Originally posted by audio-kraut
I shudder, think of stereophile and crawl back into my sceptic's lair.
And responses like that give me the willies.
Come on A.K. Leave the cave and join the fun.

What's wrong with subjective descriptions of audio? Is music objective? You just play the notes and basta? Why not just type it all into a midi sequencer, then? Where is nuance, where is emotion?

Let's be fair to Piercarlo, he wasn't asking what brand of shellac to use on his wooden amp case - his question is legit. He's asking if the case can influence the circuit, thus the sound.

The case can be, and often is, a large part of the circuit. It serves as the ground for much of the signal. Can we deny that cable layout and shielding make a difference in how a circuit works? What about all those contacts between case and wiring that make up such a large part of an amp? Do better contacts make for better sound?

I have yet to hear proof that vibration makes a difference in solid state amps, but there are reasonable arguments as to why it "might."*

The case is a very large part of the amp. It may pay to be careful how it is used in the overall circuit. I can't be considered a perfect ground plane. It may be a very good one, or it may not. Not to mention how well it keeps noise both in and out. All things to consider.




*I once did a test to see is those crazy high dollar wooden volume knobs might actually be of benefit.
I.E., are volume pots microphonic? My conclusion was no, they are not, even when hit with a hammer.
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Old 3rd February 2007, 11:23 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
Quote:
The conclusion is simply to use a metal box and ground the amp properly and there will be no "box sound" issues.
I don't agree.

Mounting the amp in a metal box that is safety earthed will make a difference to most amplifiers.
The steps required to make the noise floor of the safety earthed version as low as the noise floor of the uncased "floating audio ground" version are extensive.
I have never yet managed to make a cased stereo amp as quiet as an uncased mono floating ground amplifier.

The raised noise floor DOES have an audible effect, particularly during quieter moments in the music and even in some of the "details" of the louder moments.

The box creates a "box sound".
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Old 3rd February 2007, 12:53 PM   #10
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Quote:
What's wrong with subjective descriptions of audio? Is music objective? You just play the notes and basta? Why not just type it all into a midi sequencer, then? Where is nuance, where is emotion?
sorry to threadjack a bit...

panomaniac, those descriptions are usually not about the music - I have no reservation to react to music completely emotional., and I do.

Those words (liquidity, blackness....etc) are mantras to describe the supposed (and in the case of speakers very often real) characteristics of a piece of electronics.
The abuse of those words by some magazines sets me on edge, where electronics and the effects of tweaks are endowed with almost magical qualities.

'Nuff said.
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