Speaker - terminal connected to the AC line?
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From: stratus46 on 25 May 2010 01:23 On May 24, 7:35 am, "William R. Walsh" <wm_wa...(a)hotmail.com> wrote: > Hi! > > > Got schematic? > > I have the complete service manual for the unit. However, it doesn't > seem to show any connection between speaker - and the AC line. > > That's not to say it isn't there. I have yet to spend a lot of time > looking at it, as right now I'm dealing with a bat that is somehow in > the wall of my house. > > William Are you sure of that? I just looked at the schematic of my Technics SA-160 receiver and there it is. R791 3.3Meg 1/2 Watt from the neutral side of the power input to ground (polarized power plug). This _may_ happen physically near the speaker terminals simply because the power and speaker switches are grouped together. On the schematic it's shown on the primary side of the power transformer, not at the speaker connections. G²
From: Meat Plow on 25 May 2010 09:50 On Tue, 25 May 2010 02:30:29 +0000, Paul G. wrote: > Probably a guess, but I suspect the mystery part is a high value > resistor as Phil stated. Its purpose is for "leaking" any DC static And Paul G wins the contest! Go claim your prize, a date with Phil Allison. The resistor is there to protect the amplifier from static discharge. Said static could build up while wiring up the speakers or even after they are wired scooting them around on the carpet.
From: William R. Walsh on 25 May 2010 10:33 Hi! > Probably a guess It's as good as anything to me. It certainly does not show up in the schematic, nor the parts list. > Its purpose is for "leaking" any DC static voltage that could > build up in the circuit. That would probably happen > if you were connecting a speaker up, and you were charged up > (could be anywhere from a few volts to tens of thousands of > volts). So that's got me thinking... Perhaps this serves to protect the hybrid module from such things? It's my belief that the hybrid power amplifier is already something of a delicate part. I've noticed already that this receiver also contains additional relay/ outboard circuit protection against failure of the hybrid possibly putting a power supply rail on a speaker. Earlier and other models did not do that, instead relying on ineffective protection measures built into the hybrid module. Maybe the Technics/Panasonic engineers were trying to improve the reliability of their design? I've seen a lot of these receivers that were dead, usually as a result of hybrid module failure. > Touching the case or metal knobs of your amp when you > are charged, may also stress components in your amp, especially > if the case isn't grounded (has a 2-wire cord). It's not...there is only a two wire, non-polarized cord set. > Be very careful replacing these components.... should that > capacitor or resistor fail, you could die. You should be very > concerned about the reliability of these parts. I don't have any reason to believe the resistor itself is bad. The front of the receiver and all of its controls are plastic. > That current depends on your electrical code.... values are > from a few microamps to a few hundred microamps. The service manual for the set explains tests that can be run to determine if the leakage is within specification. It would definitely appear to be well within specifications. As with you, I can usually feel a tingle from even very low current leakage sources. I much prefer using test equipment to resolve any uncertainty, anything else could result in a nasty surprise at the least. I have not noticed anything from this set, and have no reason to believe there is any problem. > Any current greater than a few hundred microamps, and I'd > retire your amp. Fortunately, I do not think that this will be a problem. The unit seems to operate safely in every regard. If anything, I will probably be replacing the main filter capacitors as a precautionary measure. The power supply section of this receiver runs hot and the original filters are ~23 years old. They work fine now, but I do not want a problem. William
From: GregS on 25 May 2010 11:05 In article <pan.2010.05.25.13.50.51(a)gmail.com>, Meat Plow <mhywatt(a)yahoo.com> wrote: >On Tue, 25 May 2010 02:30:29 +0000, Paul G. wrote: > >> Probably a guess, but I suspect the mystery part is a high value >> resistor as Phil stated. Its purpose is for "leaking" any DC static > >And Paul G wins the contest! > >Go claim your prize, a date with Phil Allison. > >The resistor is there to protect the amplifier from static discharge. >Said static could build up while wiring up the speakers or even after >they are wired scooting them around on the carpet. I think I have added resistors like that to my circuits. It can help but is not foolproof. A static charge to the amplifier metal will occur regardless of resistance to AC ground. It can help prevent transformer arcover. greg
From: Meat Plow on 25 May 2010 11:36
On Tue, 25 May 2010 15:05:59 +0000, GregS wrote: > In article <pan.2010.05.25.13.50.51(a)gmail.com>, Meat Plow > <mhywatt(a)yahoo.com> wrote: >>On Tue, 25 May 2010 02:30:29 +0000, Paul G. wrote: >> >>> Probably a guess, but I suspect the mystery part is a high value >>> resistor as Phil stated. Its purpose is for "leaking" any DC static >> >>And Paul G wins the contest! >> >>Go claim your prize, a date with Phil Allison. >> >>The resistor is there to protect the amplifier from static discharge. >>Said static could build up while wiring up the speakers or even after >>they are wired scooting them around on the carpet. > > I think I have added resistors like that to my circuits. It can help but > is not foolproof. A static charge to the amplifier metal will occur > regardless of resistance to AC ground. It can help prevent transformer > arcover. > > greg Nothing is foolproof. My reference was strictly static discharge via speaker wires. Since the resistor is not in the schematic from what I understand, it must be a factory fitting after a trend was spotted in warranty repairs. Maybe the output device is sensitive to ESD augmented by the output circuit design. |