Turtlerock Forum

I'm pretty sure this is a ground loop issue, but I can't really get my head around it...

When I use my Quad 402 amplifier in conjunction with my Crane Song Avocet (i.e. sound card > Avocet > amp) I get a very loud buzz through my speakers, however, if I bypass the Avocet (i.e. sound card > amp) the buzz disappears.

Is this a classic ground loop scenario? Should I look into isolating the signal with something like the Radial Twin-Iso? Any other solutions?

Cheers

I would start by disconnecting the earth at one end of the cables between your Avocet and your amplifier.

I tried running it through a DI with the ground lift switch engaged, is that the same thing? That didn't work.

Not sure whether this is relevant or not, but the audio signal is travelling via XLR from the Avocet into a custom 4-pin DIN cable with XLR ends, then into the amp. Since it winds up going through 4 pins, that means it's an unbalanced input right? I don't think the XLR DIN cable is standard (it's usually DIN to RCA), so is that possibly what's causing the buzz?

What ever the problem is it won't be the avocet

So assume something else can not comment on your
Din plug thingy cant even visualize it

But you can run unbalanced into the avocet
On channel two if I recall so there is a solution their as well

start lifting audio
Earths and if you get frazzled .. Well drop one side of the
Signal run it unbalanced and see what's what

Why aren't you running digital into the avocet any way?

I had a similar problem with a Shadow Hills Equinox balanced out feeding a unbalanced Perraux power amp. I tried many solutions including balancing transformers but ended up using a balanced Bryston power amp . That solved all the problems.

the Quad is unbalanced in, yeah?

The Avocet is balanced out. yeah?

If the Quad has a five pin din socket for inputs then the middle pin will be ground. Try wiring it unbalanced to the Avocet only using hot and ground, ie leave the cold wire from the Avocet floating. If no cheese, try the opposite. connect the left and right cold wires from the Avocet to the ground pin on the DIN of the Quad and the hots to the two input pins. Leave the ground wire from the Avocet floating.

Is the quad mains grounded? ie chassis measures 0 ohms to the earth pin on its mains plug? Or is it a earth pin free plug ?

Chris Wright wrote:I'm pretty sure this is a ground loop issue, but I can't really get my head around it...

When I use my Quad 402 amplifier in conjunction with my Crane Song Avocet (i.e. sound card > Avocet > amp) I get a very loud buzz through my speakers, however, if I bypass the Avocet (i.e. sound card > amp) the buzz disappears.

Is this a classic ground loop scenario? Should I look into isolating the signal with something like the Radial Twin-Iso? Any other solutions?

Cheers

Chris,

Is this a Quad 405-2 current dumping amplifier?

T

Thanks for the replies so far. Sorry I've been slow to respond.

waitup wrote:I would start by disconnecting the earth at one end of the cables between your Avocet and your amplifier.

I've tried this and it didn't change anything.

rick wrote:Why aren't you running digital into the avocet any way?

Just haven't gotten around to trying this, and don't yet have the necessary cables. I don't think it's on the input side of the Avocet as the buzz occurs even when I cycle through inputs and select the digital ins on the remote. Seems to be between the Avocet output and the amp input.

rob wrote:If the Quad has a five pin din socket for inputs then the middle pin will be ground.

The Quad has a 4-pin DIN socket, i.e. no ground pin, they're unbalanced inputs.

rob wrote:Is the quad mains grounded? ie chassis measures 0 ohms to the earth pin on its mains plug? Or is it a earth pin free plug ?

Yeah the Quad is mains grounded.

zenelectro wrote:Is this a Quad 405-2 current dumping amplifier?

This is a Quad 402 current dumping amplifier. Not a 402-2.

the input is on a 4 pin DIN and is unbalanced. .... There has to be one pin that is the "ground" of the amp.
So what I suggest is you wire pin 2 of the CS out to the hot of the 402 and pin 3 of the CS to the ground of the 402. Then leave pin1 of the CS floating

Could one of these bad boys sort out the issues?

http://www.groupdiy.com/index.php?topic=50730

Sammas wrote:Could one of these bad boys sort out the issues?

http://www.groupdiy.com/index.php?topic=50730

Shouldn't really be necessary.

The Avocet has a fully balanced / floating output stage. This is a SS OP stage with transformer like behavior.
Both + and - OP's need to be connected to Quad. The Quad IP is another matter, a lot of them have multiple
(power / signal) grounds. Some were apparently also susceptible to oscillation and RF sensitivity.

I would try what Rob suggested. If that doesn't work, connect Quad IP ground to chassis - if it is separate,
this was a recommended mod on some models (by the designer).

Failing that, put an oscilloscope on it, might even be oscillating.

When I plug the DIN Y-split XLR ends directly into the Avocet I get this sound through my speakers-

https://soundcloud.com/chriswrightaudio/quad-402-interference

Got it sorted. Turns out the pinout on the 4-pin DIN was jumbled with ground going to hot.

Thanks for the help everybody. Amp sounds great too!