Variations of DC Main Filter against buzzing Toroid Transformers - what is the right?

[AndrewT]

Originally Posted by Bob Cordell

Am I correct in assuming that Bryston still bolts the safety ground to the chassis, and that that is the only place where the chassis is connected? Am I correct in assuming that a non-direct connection of safety ground to chassis (as through the diode arrangement) would never be allowed?

there is another thread running at the moment trying to get answers on this. So far no one has come out to confirm if the Disconnecting Network (which has been proved to pass Fault Current) is allowed between Chassis and Protective Earth.

[tiefbassuebertr]

Originally Posted by AndrewT

there is another thread running at the moment trying to get answers on this.

Where? Here on diyaudio?

[djk]

"Am I correct in assuming that Bryston still bolts the safety ground to the chassis, and that that is the only place where the chassis is connected? Am I correct in assuming that a non-direct connection of safety ground to chassis (as through the diode arrangement) would never be allowed?"

Yes, you are correct. The ground wire from the IEC goes to the chassis, the the diode arrangement is between chassis ground and the central audio ground.

[Bob Cordell]

Originally Posted by djk

"Am I correct in assuming that Bryston still bolts the safety ground to the chassis, and that that is the only place where the chassis is connected? Am I correct in assuming that a non-direct connection of safety ground to chassis (as through the diode arrangement) would never be allowed?"

Yes, you are correct. The ground wire from the IEC goes to the chassis, the the diode arrangement is between chassis ground and the central audio ground.

Thanks!

BTW, I think there is another issue that pertains to the Crown implementation of the DC blocker. Without the caps that Bryston uses, the diodes in the bridge will switch at the mains rate, just like diodes in the rectifier bridge in the secondary circuit. For this reason, I believe two rectifier snubber resistors should be used in the Crown arrangement. One might even argue that those bridges should be fast-recovery for the same reason the ones on the secondary side want to be. The Bryston arrangement does not have this issue because the diodes never conduct under normal conditions.

In the Bryston implementation, the electrolytic capacitors should have very low ESR and be rated for high ripple current. Moreover, that arrangement should probably not be used for amplifiers that do not incorporate a soft-start circuit. Otherwise the capacitors will be subjected to harsh turn-on current transients.

Cheers,
Bob

[AndrewT]

Originally Posted by Bob Cordell

The Bryston arrangement does not have this issue because the diodes never conduct under normal conditions.

......... not be used for amplifiers that do not incorporate a soft-start circuit. Otherwise the capacitors will be subjected to harsh turn-on current transients.

if capacitive reactance+ESR*I is greater than two diode Vdrops, the diodes start to bypass the capacitors during start up and maybe during periods of mild overload.

[djk]

I generally recommend people try the Crown method to see if it fixes their transformer buzz. You can add the Bryston details as needed.

[tiefbassuebertr]

Originally Posted by Bob Cordell

I like the Bryston circuit, and am particularly interested in the left side, where the safety ground from the line cord is connected to the main circuit ground through a resistor shunted by the bridge arrangement. I have done the same thing before in an amplifier for my own use, but was never sure if this approach would pass muster for a commercial product. If I understand the operation correctly, the resistance breaks ground loops that may occur among the safety grounds of interconnected equipment. The diode still provides safety ground protection by never allowing the circuit ground to differ from the safety ground (in a fault condition, for example) by more than 1.4V. This is why a large bridge device is presumably used. I am a little surprized that they used a resistor as large as 100 ohms. I used less than 10 ohms in my arrangement, which I think would be plenty to effectively break the ground while still maintaining a reasonably low impedance back to the safety ground.

Am I correct in assuming that Bryston still bolts the safety ground to the chassis, and that that is the only place where the chassis is connected? Am I correct in assuming that a non-direct connection of safety ground to chassis (as through the diode arrangement) would never be allowed?

Cheers,
Bob

Hallo Bob,
today I get a "Cyrus II" from Mission for checking. After opening I found a burnt/destroyed resistor and a capacitor, which must be exploded. I replace this components for the third time (and much more bigger versions than the original purchases). But I think, in one or two years the same work is necessary again.
This devices are also arranged between the safety ground from the line cord and the main circuit ground, but not shunted by an diode network (bridge arrangement - as you it call) like Bryston. But this could be the right solution also in case of the Cyrus II.

Nevertheless - for me it would be interesting to know, from where comes such large voltage/current transients between these two ground potentials?

Perhaps it must have to do with temporarily, very rare and very short but very large different earth potentials between Broadband-Cable connection for radio and TV and that one from mains voltage connection.

[AndrewT]

is CyrusII double insulated or does it have a protective earth wire connected to chassis?

[tiefbassuebertr]

Originally Posted by AndrewT

is CyrusII double insulated or does it have a protective earth wire connected to chassis?

The versions for the German marked have a protective earth wire connected to chassis (also by Cyrus ONE/I/1. But I don't know exactly, what about the other countries. In German the mains voltage connector haven't a polarity, i. e. I can pull out the wall connector, turn around and plug in in this second polarity (please note: only by the wall connection, but not by the amplifier main connections). In your country this isn't possible.
For this reason you will not find the RC network at the PCB from attachement (british version - I think), not even the PCB hole therefore.
By German versions this network is to find in line of the PCB GND wire from the electrolytic crosspoint (right of the screw, that is close by the volume control potentiometer). One end is solder to this mentioned PCB wire (electrical GND) and the other is connected to the screw (chassis GND).

[Rainwulf]

I have a question, how would DC get onto the mains line in the first place?