Breakthrough with WDPre3

[Riggers]

Hi all. This is an issue I noted when I was doing a test on my pre3 with all sources connected and powered up, namely turntable (via WD phono3), tuner, cd and cassette deck. As I switched between the sources to check they were all connected I could hear the cd source in the background of the other sources. I tried connecting just the cd to a different input, it sounds fine on its own but once I connected another source and had both playing, I could still hear some "breakthrough" from the cd source in the background of the input source that I had selected.

I was just reading an old post from Peter Comeau regarding the use of the relay board and the un-selected sources being shorted to prevent just this problem. Since it only seems to happen with one particular source (audiolab CD player) no matter which input I connect it to, I was wondering what might be happening. As I only (usually) listen to one source at a time, I usually only have one source powered up at any one time so I s'pose it probably doesn't matter anyway.
Cheers
Phil.

[John Caswell]

Hi Phil,
Not sure what is causing this, as theoretically as the input is shorted when not selected there should not be a signal path.....However I suggest that you look at the earthing arrangements for the CD player and also the earthing arrangements pre to main amp. It does sound like a strange earthing problem. Are you able to borrow another CD player from someone to see if is only the Audiolab CD that causes this?
I have/had a similar problem with a massive "splat" garage fluorescent pickup which was eliminated by connecting both the power amps and the preamp together with something akin to 10mm earth cable.

John

[pre65]

I'm not using my Pre3 at the moment, but I seem to remember having the same problem.

[bob orbell]

Hi Riggers and all, I agree with John, this must be a earth issue and I feel that the culprit is the Pre III, if built correctly, with no power applied, IE, the PSU switched off, there should be 0 ohms between any input and earth which will kill any signal, dead, if that is OK then put your meter between any input and its outer connection, this also must be at 0 ohms, this may show a problem. BOB

[Riggers]

Thanks Bob, I'll disconnect the pre3 later this week and check as you have said. I did do checks like this at build completion time and it did seem to test ok, ie 0 ohms. I wondered if it was the CD player as the problem arises with only this source no matter which input I connect to.
The one thing about the CD player which is different to the other sources I use is that it is an earthed appliance whereas the tape deck and DVD player are not.

[bob orbell]

John is your man on this, he has a wealth of experience that most of us do not poses, however I still think that your Pre III is at fault. BOB

[bikerhifinut]

Originally Posted by Riggers

Thanks Bob, I'll disconnect the pre3 later this week and check as you have said. I did do checks like this at build completion time and it did seem to test ok, ie 0 ohms. I wondered if it was the CD player as the problem arises with only this source no matter which input I connect to.
The one thing about the CD player which is different to the other sources I use is that it is an earthed appliance whereas the tape deck and DVD player are not.

The only Issue I could think of with earthed equipment would be a possible "hum loop" but I am sure the Audiolab equipment will have a proper grounding scheme to avoid that issue.
I'm with Bob here, a simple check across the sockets with the power off will ascertain if there's any open circuit relays. You can do that without opening the case and use the meter probes on the RCA sockets.
I take it that you have tried the CD player in all the other sockets? The bleedin' obvious I know so apologies in advance.

Andy.

[Richard]

Hi Phil,

What power amp is your Pre3 connected to and is it earthed? I connected mine once to an un-earthed power amp (experimental ) and it tuned all sorts of strange signals.

I realised that as Pre3 output is transformer coupled, with no signal ground connecting its output to the power amp, there were 2 big coils of wire (the OPTX secondaries) hung on the power amp inputs acting as search coils.

Anyway this might jog a train of thought. As the others say the un-selected inputs should be shorted so it would be worth shuffling your cdp and Pre around to see if the signal is induced rather than conducted.

[John Caswell]

Hi Phil,
OK, so that we don't go chasing our tails you need to try another CD player before anything else.
Then we can try to sort things out.

John

[Riggers]

Hi All
I did the checks to the Pre3 today. I verified that the Audiolab CD is the only source that the problem occurs with. I changed its input from "CD" to "AUX" and had the same background music from the CDP when listening to an other input source.

I also did the continuity checks from the different inputs to ground with the pre3 unpowered and got 0ohms each time.

Not being an electrical engineer i'm not sure if there is some ground loop issue with the CDP, (btw I don't have another I can borrow). Also BTW my tuner is an earthed appliance as well but has no such breakthrough issues.

At the end of the day the gear i have sounds great (connected to a Quad QSP for the time being, hopefully I can get my mitts onto a wd88VA in the near future....) and considering that it is an unusual event for me to have all connected sources powered up at the one time I might just try not to think about it ;-)

Thanks all for your help.