Breakthrough with WDPre3

[A Stuart]

Just thinking along different lines. When you say "In the background", is it a very very quiet high thin tinny whisper?
Which could suggest capacitative coupling between wires somewhere, regardless of correct wiring and functioning, noticeable because the CD's output may be much larger than the others, causing it to be relatively audible, but inaudible in reverse - even though I thought whole point of the relay board was to minimise wiring inside the amp.
So perhaps not inside the amp - have you tried distancing your input leads from each other? Or swapping or wiggling the input leads to see if one has a poor screen connection?
My Cyrus1 has done this crosstalk since new in 1987, and being transistor based the input impedance will be lower so less susceptible to capacitative coupling.
Alastair

[Riggers]

Hi all
It seems we have progress. I have been misinterpreting my previous tests. When I was checking for 0ohms from centre spigot to outer shell of said input or to the chassis earth post (with power off) I got on occasions a 0.L reading, which I believe now on my multimeter is an indication of no connection, because all the other readings would give a value of 000.0ohms or 000.1ohms. When I checked centre spigot to outer shell with pre3 powered up with each input selected in turn, the same inputs would give no reading whereas the rest gave me 46.5K.
The following inputs were at fault: CD left channel, Tuner right channel and Tape left channel.
Seems I have to pull the relay board off after all.
D'oh!

[Riggers]

Apologies for the consternation and pulling out what's left of your respective hairs. I think if i am correct the tinned wire connecting all the earth connections of the RCA sockets must not be soldered well in 3 positions.
Thanks all.

[bob orbell]

I do hope you have found something Phil, O.L is infinity, as you say, no connection. I too had to remove my relay board a few months back, for the second time to sort a diode that had gone short circuit, what a bummer, this time I had to fit a new one because of damage to the tracks, best of luck. BOB

[John Caswell]

Before you rip out the relay board a simple check as follows.
Pre 3 turned off, DMM set to low ohms (200) negative lead to the earth pin on the Pre3 PCB, and then positive lead in turn to all of the outer (earth) phono connectors. This should read in ALL cases 0R or very very low. The output sockets may not be included depending how your system is wired
Then with power, back on, DMM set as before, negative lead to earth pin on PCB, in turn measure between selected input phono centre pin which should read high R with all the others except "tape out" reading 0R.
If any of the phono earths read high it is possibly poor soldering on the earth tag of that socket as they should all be connected together with a single piece of Tinned copper wire from earth tag to earth tag and thence to the relay PCB. This is for each channel.
However I do not think this is a relay board earth problem because of this comment made earlier "Since it only seems to happen with one particular source (audiolab CD player) no matter which input I connect it to". I am still convinced it is an earthing problem related to the CD. Try lifting the earth on the 13A plugtop of the CD.

John

[Richard]

Hi Phil, well that could certainly account for it. Before going further I'd check again, and, before doing so, touch both meter probes together which will show you the way it should react to 0 ohms (usually showing 0.1 or similar) compared with open circuit

[Riggers]

Hi all
I (finally) after a bit of cursing managed to remove the relay board and discovered some poor soldering of the tinned wire to the three earth tags I mentioned in the previous post. Once I sorted this I checked continuity between the earth outers of the phono plugs to the earth pin and all well. I then checked the powered up unit for around 47K for a selected phono centre to earth pin and all checked out this time.
Soooo....John wins the prize.
The breakthrough still exists, so it would seem the relay board was not the cause. At least I know now that the connections inside pre3 are good (and I now know difference 0ohms and OL.)
I am convinced the CDP is the problem. Alastair, it is a quiet, distorted background noise. I can live with it so long as I don't have CD powered up and running whilst listening to another source. As a matter of interest, if I power up the quad QSP before I power up the pre, i do hear some hum. Is this because the Quad on its own is not earthed?
Cheers
Phil.

[bikerhifinut]

Followed this with interest.
Glad you have diagnosed and repaired your preamp issue.

I was wondering about the CD breakthrough, and wondered if you knew what the output resistance of it is? I ask because I have an Arcam CDP that has an output resistance/impedance of only 39 ohms. Factor that in with a 2Volt output and theres maybe the potential (pun?) still across a small resistance of a fraction of an ohm or the resistance of your interconnect and plugs which you wouldnt get to the same degree if it had an output resistanceof 600 to 1k ohms?. Don't discount this as you have 2 extra possible sources of a resistance to develop a signal potential across. In which case theres not a lot you can do.

Then again may I ask the seemingly daft question? Why would you want the CDP running and playing a disc when not listening to it? Because that to me is the only reason you can hear it playing whilst listening to another source. So whilst you have obviously solved an underlying issue with the input circuitry, maybe there isn't really a practical issue here?
I could understand the annoyance if it was the FM tuner breaking through as many of us prefer to listen to a radio that is warmed up and at its running temperature for various reasons.

I hope I haven't offended with the remarks because none was certainly intended.

Andy.

[Richard]

Originally Posted by Riggers

As a matter of interest, if I power up the quad QSP before I power up the pre, i do hear some hum. Is this because the Quad on its own is not earthed?
Cheers
Phil.

It happened with all the power amps I used Pre3 with too regardless of their mains earth. Turn on Pre3 though and it goes quiet.

I just assumed, rightly or wrongly, that when Pre3 is powered up the DC current through the primary polarizes the OPTX so one end would appear more negative to an AC signal.

I'd also like to know if the output secondary can be tied to Pre3 signal ground for single ended drive? Anyone ?

[Richard]

Off Topic but did I see your trusty stead at Wentworth today Andy?