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Old 18th March 2013, 08:44 AM   #11
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Hi

I would not be unusual at all to have to run an earth external wire to the case of an ungrounded case.
I have had to do this on more than two times in the past depending on the installation.

Cheers

Anthony
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Old 7th May 2013, 11:01 AM   #12
mesc is offline mesc  Norway
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Hello

I'm practically finished with both my amps now, and I'm NOT dissapointed anymore (couldn't remove the "thread icon").
Very happy in fact. There isn't any noise hum/whatever anymore, it was the other equipments fault.

Though I am starting to regret going xlr. I was thinking of adding an rca input but I'm not sure how to implement it. When RCA in, should "-" and "gnd" be shorted? How best have both options?

Thanks for the good amp
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Old 7th May 2013, 11:35 AM   #13
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Hi

Great to hear your amp is working well now.
To unbalance the input of the nxV300 amp
Short the inverting input to signal ground and connect the + input to the RCA.

Cheers

Anthony
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Old 7th May 2013, 11:48 AM   #14
AndrewT is offline AndrewT  Scotland
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I have "updated" an old amp and added xlr inputs.
Pin1 to Chassis.
Pin2 to +IN of amp
Pin3 to -IN of amp, which also happens to be Signal Ground.

I added 47pF from 1to2 and from 2to3 and from 3to1. That effectively gives me differential mode RF filtering and common mode RF filtering on the input right next to Chassis so that it is effective to VHF.
I have conventional RF and DC block filtering at the amp PCB.

I had been planning to do this to a variety of my amps. I've started.

I did enquire a few weeks ago about this but got no useful replies.
Today, I found it in Ott page603 fig15.16a
Earlier he had stated that the inherent inductance in the cable/s was sufficient to make these "at Chassis" filters effective.
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Old 7th May 2013, 12:48 PM   #15
mesc is offline mesc  Norway
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Quote:
Originally Posted by The Saint View Post
Hi

Great to hear your amp is working well now.
To unbalance the input of the nxV300 amp
Short the inverting input to signal ground and connect the + input to the RCA.

Cheers

Anthony
Yes I suspected as much. But was thinking about having both options. Would I need a switch to select between xlr and rca?
I tried using a "xrl - rca" cable before. The cable internally shorts pin1 and 3 so I thought i would be ok but it didn't work..? I was thinking it had to do with my input caps, I have one on both "+" and "-". So it would probably have to be shorted after the caps, at the board.
Is that right btw, to have two dc caps in xlr?

Quote:
Originally Posted by AndrewT View Post
I have "updated" an old amp and added xlr inputs.
Pin1 to Chassis.
Pin2 to +IN of amp
Pin3 to -IN of amp, which also happens to be Signal Ground.

I added 47pF from 1to2 and from 2to3 and from 3to1. That effectively gives me differential mode RF filtering and common mode RF filtering on the input right next to Chassis so that it is effective to VHF.
I have conventional RF and DC block filtering at the amp PCB.

I had been planning to do this to a variety of my amps. I've started.

I did enquire a few weeks ago about this but got no useful replies.
Today, I found it in Ott page603 fig15.16a
Earlier he had stated that the inherent inductance in the cable/s was sufficient to make these "at Chassis" filters effective.
Interesting, though not sure I need filtering, would it help with ground loopish problems? Did you use ordinary cheap ceramics?
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Old 8th May 2013, 08:13 AM   #16
AndrewT is offline AndrewT  Scotland
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Ceramics are probably the most effective @ vhf and beyond. So, yes.

Some Balanced Sources will plug straight into the XLR arrangement I have described.
Some will benefit from adding a resistor into the cable feeding Pin3.

I wonder if there are some Source types that are not compatible with my arrangement?
Any help forthcoming?
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Old 8th May 2013, 08:46 AM   #17
mesc is offline mesc  Norway
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Quote:
Originally Posted by AndrewT View Post
Some Balanced Sources will plug straight into the XLR arrangement I have described.
Some will benefit from adding a resistor into the cable feeding Pin3.
Was you amp not designed for xlr input?

My connections are as yours, except I don't connect pin1 to chassis directly. Pin1-2-3 are connected to the corresponding 3 pins on Anthony's modules, and I find that the gnd (pin1) pin is connected through to chassis ground.
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Old 8th May 2013, 10:34 AM   #18
AndrewT is offline AndrewT  Scotland
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No, I have just one balanced Source and will be building some balanced Power Amps soon.
I want them all to be compatible.

The XLR addition will allow a balanced input to be inserted between the XLR and the unbalanced Power Amplifiers. I can use a balanced input transformer (I have 6 from a previous Group Buy) for very long cables, or I can use Cordell's jFet based bal to unbal active circuit.

PIN1 MUST be connected to CHASSIS right next to the input socket, by the best RF connection.
PIN1 MUST NOT go via a torturous route to PCB and then on to Chassis.
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Old 8th May 2013, 11:04 AM   #19
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by mesc View Post
Was you amp not designed for xlr input?..........
no.
Quote:
I have "updated" an old amp and added xlr inputs.
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Old 8th May 2013, 01:03 PM   #20
AndrewT is offline AndrewT  Scotland
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There is no need to ground the PSU Zero Volts at the same point as the PE wire is connected to the Chassis.

Normally we expect to see the PE wire connected to Chassis very close to the incoming mains cable using a short wire connection.

The PSU Zero Volts can be connected to Chassis anywhere else that is convenient to the Circuit. The Ground Plane effect of the Chassis will ensure that any Fault Current will find the lowest impedance route back to the mains distribution board via the PE wire.

Artificially increasing the impedance of the Return Path for the Fault Current will INCREASE the voltage of the Zero Volts with reference to Ground during the Fault incident. Using a wire connection from PSU Zero Volts back to the mains PE connection to Chassis must, almost by design, result in a higher impedance.
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