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!
Hi
Piercarlo
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!
Hi
Piercarlo
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
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
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.
I_F
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.
I_F
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.
Grey
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.
Grey
audio-kraut said:
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.
Hi,
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".
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".
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.
Yeah, I know, I know. You aren't alone. But I do not automatically get my hackles up at descriptions like that. Other technical stuff bugs me far more. But maybe I have not read enough issues of Stereophile.
That's funny Andrew, because for me -- it's the opposite!! Maybe it has to do with what's in the air where we are? I keep meaning to haul an amp up the side of the mountain far from electric power lines to have a listen. No 60Hz power for miles. Wonder what that will be like?
In a sailboat far at sea, with only battery power, how much shielding would you need? Of course that does not negate the questions of case connections, vibrations, etc.
AndrewT said:
That's funny Andrew, because for me -- it's the opposite!! Maybe it has to do with what's in the air where we are? I keep meaning to haul an amp up the side of the mountain far from electric power lines to have a listen. No 60Hz power for miles. Wonder what that will be like?
In a sailboat far at sea, with only battery power, how much shielding would you need? Of course that does not negate the questions of case connections, vibrations, etc.
panomaniac said:
A couple years ago I brought in a battery powered SI T-amp to demo on some multi-thousand dollar NHT speakers that belonged to a university AES sound demo room. During my presentation of class d amps (during which I demoed the SI T-amp which actually wowed just about everyone in the room when they were told the amp powering the speakers was a 10W/ch 8AA battery powered class d amp with an iPod as a source), the professor asked everyone to close their eyes and raise their hand if they heard any difference in sound quality over the next 30 seconds. Everyone closed their eyes and he then proceeded to pick up the SI T-amp and shake the living daylights out of it. No one raised their hand. While continuing to shake the amp up and down he asked everyone to open their eyes. Everyone saw what he was doing and he commented that vibration has no audible effect on the sonic quality of an amp. Perhaps his explanation was flawed because he should have stated that vibration has no audible effect on the sonic quality of a SI T-amp. Other amps have yet to be tested
For the record, the SI was in its standard injection molded plastic case.
BWRX said:
That's not a particularly good test of whether an amp is microphonic. How fast can you shake you arm? Maybe 5 Hz or so? 5 Hz isn't audible and isn't the sort of thing that one is concerned about with regard to amplifier vibration sensitivity. If he had pounded on it it would have been a better test.
The real concern is whether the sound from the speakers can induce vibrations in the amp chassis and whether those vibrations can cause audible effects. ALL amps are microphonic if the speakers are playing loud enough, close enough to the amplifier. This question, like so many others in audio, boils down to degrees.
My amp is built solidly enough and I don't listen to music so loudly that any audio induced vibration will ever be audible. A lot of consumer amps are pretty flimsy and people do strange things with them like set them on top of speakers. A lot of subwoofers come with amps built in. In such cases it makes sense to question the sensitivity of the amp to vibration.
Here's an experiment to try. Open your amp and tap on the input coupling cap (if it has one) with a pencil eraser while the amp is powered up. You'll clearly hear thumping from the speaker.
OK, so you have a microphonic amp, now what? Do magic spikes, sorbothane balls, or magnetic levitaton do any good? I doubt it. Best bet- move the amp away from vibration sources- either mechanical or acoustical.
I_F
My latest preamp is a wood construction... perfectly quiet unless I position it crappy in respect to the other hifi components....
Its not going to vibrate either... must weigh like 4kgs.
I suppose everything is down to the scale of the observer to the observed item... but if you move a wire in a magentic field you induce a voltage over it... now there is lots of dc carrying wires in an amp... all you need is to move them around in the field...might be wrong here though...just theory
Its not going to vibrate either... must weigh like 4kgs.
I suppose everything is down to the scale of the observer to the observed item... but if you move a wire in a magentic field you induce a voltage over it... now there is lots of dc carrying wires in an amp... all you need is to move them around in the field...might be wrong here though...just theory
I_Forgot said:
I'll have to try that one.
It's similar to the pot test I did. Ran 9 VDC thru the pot. Took the wiper output to my soundcard mic input via a DC blocking cap. Got no signal when thumping it.This sort of test ought to be easy to do on an amp. Set up something to vibrate it, then record the output.
Apart from vibration, perhaps there are other issues, as has been mentioned higher in the thread. Such as eddy currents induced into the case and wiring. If the case is part of the circuit, those currents might affect the musical signals.
are you saying that for you, electrical interference through the air (as against coming in through the mains) is your over-riding concern above all else?panomaniac said:
I am surprised.
I have lived in towns before my present rural location, but even here I have 6kV overhead cables just 50m away, four different Cell-phone transmitters within 2km, all my normal domestic appliances and lots of commercial road and site vehicles moving around and I am not aware of ANY airborne interference.
But, I very definately contaminate my sound by connecting the mains borne interference that comes in via the safety ground.
TNX to all! I'm a bit surprised because til now i've supposed that sound of enclosures, box and similar was a quite academic rather than real question and I've thought what happen to me was dued mainly to my clumsies. But is not so. Especially GRollins and AndrewT gave in thread some considerations which are excepionally in touch with many thoughts I've worked out in order to catch the essence of this curious and stimulating problem. Which appear to be just neglected but absolutely NOT unknown.
Til now I've conducted some experiments only on some old and cheap CD players (2 Philips, 1 Sony and 1 Pioneer). With the partial exception about a Philips CD600 (which come in the session yet modified), experiments a modifies left untouched the internal circuitry and concentrate mainly on rearranging the enclosures from an electrical viewpoint.
Philips enclosures are all plastic with metal reinforcement (especially top covers) which don't play any explicit electrical task (there are unconnected from all, even from the main ground); screening function reely on the ground plane existing on the upper side of PCB
Sony and Pioneer instead are mounted in a metal enclosures which act as a general shield.
Although the final result from a sonic viewpoint is extremely similar for all four CDP, the strategy of modification was quite different in the two kind of CDP.
Philips required the *adjoint* of a second ground plane, connected to the ground output, which cover the downside of the PCB. In the case of CD600 this auxiliary ground plane was obtained connection the bottom metallic cover to a ground; in the case of CD471 (the other Philips I own) the second ground plane was obtained glueing on the bottom of plastic case an aluminium foil (cut from a kitchen reel) and connecting it to the output signal grounds with a clip.
Sony, Pioneer and, I suppose, any other equipment with the same kind of enclosures (jap consumer style), required instead a systematic breaking of electrical continuity of the metal components of enclosures (top and bottom covers, rear panel and, if metallic, front panel).
Rear panel was connected on the output signal ground via a dedicated piece of wire (*not* via the outer ground ring of RCA pinout!). Bottom cover was left connected to a single ground point (on PSU) insulating or lefting they open any other connection to circuit ground.
The edges where top, bottom and rear covers meet and joint were insulated with insulating tape. Hence electrical continuity between panels was assured by a *single* screw lefting the others insulated or unmounted.
The mains trasformer was remounted electrically insulated from the bottom cover of the enclosures to decouple magnetically the former from the latter.
CONCLUSIONS - The modified equipments were of cheap type i get around; the same kind of tweaking may be done (and was done by a friend) on a low priced dvd-all standards players which can be found on big stores without any adverse advice.
In all the cases the sound has *inequivocally* (and somewhat unexpectedly!) changed. Here if the sound changed for better or for worse is not a question; the question is the changing *itself* due only to a rearrangement of ground *external* to the ground really pertaining the active circuits (from schematic and topological viewpoint, nothing is changed from before the tweaking).
Hi
Piercarlo
Til now I've conducted some experiments only on some old and cheap CD players (2 Philips, 1 Sony and 1 Pioneer). With the partial exception about a Philips CD600 (which come in the session yet modified), experiments a modifies left untouched the internal circuitry and concentrate mainly on rearranging the enclosures from an electrical viewpoint.
Philips enclosures are all plastic with metal reinforcement (especially top covers) which don't play any explicit electrical task (there are unconnected from all, even from the main ground); screening function reely on the ground plane existing on the upper side of PCB
Sony and Pioneer instead are mounted in a metal enclosures which act as a general shield.
Although the final result from a sonic viewpoint is extremely similar for all four CDP, the strategy of modification was quite different in the two kind of CDP.
Philips required the *adjoint* of a second ground plane, connected to the ground output, which cover the downside of the PCB. In the case of CD600 this auxiliary ground plane was obtained connection the bottom metallic cover to a ground; in the case of CD471 (the other Philips I own) the second ground plane was obtained glueing on the bottom of plastic case an aluminium foil (cut from a kitchen reel) and connecting it to the output signal grounds with a clip.
Sony, Pioneer and, I suppose, any other equipment with the same kind of enclosures (jap consumer style), required instead a systematic breaking of electrical continuity of the metal components of enclosures (top and bottom covers, rear panel and, if metallic, front panel).
Rear panel was connected on the output signal ground via a dedicated piece of wire (*not* via the outer ground ring of RCA pinout!). Bottom cover was left connected to a single ground point (on PSU) insulating or lefting they open any other connection to circuit ground.
The edges where top, bottom and rear covers meet and joint were insulated with insulating tape. Hence electrical continuity between panels was assured by a *single* screw lefting the others insulated or unmounted.
The mains trasformer was remounted electrically insulated from the bottom cover of the enclosures to decouple magnetically the former from the latter.
CONCLUSIONS - The modified equipments were of cheap type i get around; the same kind of tweaking may be done (and was done by a friend) on a low priced dvd-all standards players which can be found on big stores without any adverse advice.
In all the cases the sound has *inequivocally* (and somewhat unexpectedly!) changed. Here if the sound changed for better or for worse is not a question; the question is the changing *itself* due only to a rearrangement of ground *external* to the ground really pertaining the active circuits (from schematic and topological viewpoint, nothing is changed from before the tweaking).
Hi
Piercarlo
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