Nixie said:
Okay, your English is good.
You are better than me.
But, don't think that you know where my fingers are put in.
Enjoy!
Hello all! Long time since a post was sent here.
Been reading a lot over this forum and heard about this " dual inverse parallel Power Diode" safety thing we should (been strongly inclined to) build in our gainclone.
I'm a very curious hobbyist, ausiophile, DIY, jack-of-all-trades. I want o build a great AND safe amplifier. Would someone be kind enough to post a simple schematic or description and what parts to buy? I'm no veteran in electronics or audio conception at all so this is why a simple HOW-TO is needed. 🙂
Been reading a lot over this forum and heard about this " dual inverse parallel Power Diode" safety thing we should (been strongly inclined to) build in our gainclone.
I'm a very curious hobbyist, ausiophile, DIY, jack-of-all-trades. I want o build a great AND safe amplifier. Would someone be kind enough to post a simple schematic or description and what parts to buy? I'm no veteran in electronics or audio conception at all so this is why a simple HOW-TO is needed. 🙂
What has worked well for me is to buy (cheap) the GPB type diode
bridges rated at 30A, and tie the two AC lugs together and the + and -
lugs together. One goes to AC earth/chassis, the other to signal ground.
bridges rated at 30A, and tie the two AC lugs together and the + and -
lugs together. One goes to AC earth/chassis, the other to signal ground.
Great!
like this one?
https://www.digikey.ca/product-deta...ion/GBPC3506-E4-51/GBPC3506-E4-51GI-ND/754835
It does not matter wich is tied to earth and SG?
No it doesn't matter it is schematically the same. That part is fine and meets safety approval. We use what works and passes approval with the testing agencies and then stick with it.
I don't know if the inverse parallel diode bridge has been approved.
Does anyone have evidence that an approval organisation has given it their blessing?
It's nice to see N.Pass is showing approval of the diode bridge rather than the NTC shown on some Pass schematics.
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It's a bit grey area and an old issue. The AC earth ground should be
attached directly to chassis, no fooling around. The connection between
signal ground and chassis is a problem because you tend to get ground
loops when you directly attach them. A few ohms or a volt of isolation
is generally adequate for that.
The key is that the isolation should be such that a fault will trip the AC
breaker(s)/fuses without generating too much voltage between chassis
and circuit ground. A big resistor/thermistor can do it, and a 30 amp
bridge can do it.
Currently it seems that CSA is good with either.
attached directly to chassis, no fooling around. The connection between
signal ground and chassis is a problem because you tend to get ground
loops when you directly attach them. A few ohms or a volt of isolation
is generally adequate for that.
The key is that the isolation should be such that a fault will trip the AC
breaker(s)/fuses without generating too much voltage between chassis
and circuit ground. A big resistor/thermistor can do it, and a 30 amp
bridge can do it.
Currently it seems that CSA is good with either.
Is it good practice to use a diode bridge signal ground lift in each power amp and preamp or a bridge in just one of the units? In other words, one unit has signal tied to chassis ground and one unit has a signal ground lift.
A question about chassis grounding for Nelson:
The SIT-1, SIT-2, and a few other Papa designs have power supplies floating in order to generate the bias voltage for the SIT or other depletion mode FET. The RCA ground appears to be connected to chassis ground through a thermistor (inrush current limiter). Is there any concern for the possibility of transformer (toroid) failure causing a high current into the negative power supply rail? In other amplifier designs where the negative (or positive) rail is ground, there is a low impedance path to the thermister connected to the chassis which would blow the fuse in the event of a transformer failure.
The SIT-1, SIT-2, and a few other Papa designs have power supplies floating in order to generate the bias voltage for the SIT or other depletion mode FET. The RCA ground appears to be connected to chassis ground through a thermistor (inrush current limiter). Is there any concern for the possibility of transformer (toroid) failure causing a high current into the negative power supply rail? In other amplifier designs where the negative (or positive) rail is ground, there is a low impedance path to the thermister connected to the chassis which would blow the fuse in the event of a transformer failure.
if there is Donut failure, impedance between actual amp GND and most neg leg of PSU is low enough to ensure enough current to burn mains fuse
besides, role of chassis grounding circ ( as you called it), be it NTC or bridge+NTC, is to keep user alive, not necessarily amp (circuit) itself
but, let's be real, in all these years, I still didn't stumble on Donut gone so far south
besides, role of chassis grounding circ ( as you called it), be it NTC or bridge+NTC, is to keep user alive, not necessarily amp (circuit) itself
but, let's be real, in all these years, I still didn't stumble on Donut gone so far south
Not only must the impedance between actual amp GND and most neg leg of PSU be low but the resistor must be able to dissipate power long enough for the fuse to blow before the resistor itself blows.
But like you say, I have never heard of a failure in a toroid.
certainly, something will blow, fast
but still unlikely, as we agreed
(Pa did use in SIT-1 and SIT-2 TO247 4R7 (or was it 5R) resistor, 50W (by memory))
but still unlikely, as we agreed
(Pa did use in SIT-1 and SIT-2 TO247 4R7 (or was it 5R) resistor, 50W (by memory))
In the document by hifisonix linked here
https://hifisonix.com/wp-content/uploads/2019/02/Ground-Loops.pdf
which was recommended to me by another forum member, he states:
“UNDER NO CIRCUMSTANCES can you use this technique in equipment that will be powered off of old style fused mains distribution panels that do not feature RCD/GFCI systems. If in doubt: DONT USE THIS TECHNIQUE.”
Page 21, in red.
The technique he’s referring to is the bridge ground lift under discussion.
The service panel in my house has modern circuit breakers but not GFCI breakers. There are GFCI outlets in the bathrooms. (I don’t usually plug my audio amps into the bathroom outlets.)
Does anyone know the reason for hifisonix’s restriction?
https://hifisonix.com/wp-content/uploads/2019/02/Ground-Loops.pdf
which was recommended to me by another forum member, he states:
“UNDER NO CIRCUMSTANCES can you use this technique in equipment that will be powered off of old style fused mains distribution panels that do not feature RCD/GFCI systems. If in doubt: DONT USE THIS TECHNIQUE.”
Page 21, in red.
The technique he’s referring to is the bridge ground lift under discussion.
The service panel in my house has modern circuit breakers but not GFCI breakers. There are GFCI outlets in the bathrooms. (I don’t usually plug my audio amps into the bathroom outlets.)
Does anyone know the reason for hifisonix’s restriction?