DC voltage when switching to phono

[colin.hepburn]

This is unrelated to Andy’s CF thread and any of the modes I have done recently to my WD CF pre

But There is a rather alarming crack when switching to and from the WD phono 2 nothing to do with my recently add CF preamp

but it happens with any pre it is connected this is an old fault as I just took it for granted it was a problem with the relay SW selector on the Nad amp i was using

Only to eliminate this thought when I started to use the WD CF pre as the loud crack is still there
any thought on this pleas

[bikerhifinut]

I'd be inclined to check if theres any DC after the coupling cap on your Phono stage. I assume its a standard CF off V3?
I have a similar issue with my old leak troughline which has reared its head and I think the coupling cap on the output has gone.
You are using a CF pre so you will have a dc blocking capacitor on the grid, therefore you probably aren't doing any damage to the valve.

OR:

the output capacitor on phono stage (C11/12 on phono3) isn't discharging any stored energy through the 1meg resistor R27/28 and when you switch to it, it's discharging through the input pot, causing the crack/thump?

I wonder if its worth metering the voltage across C11, with the phono stage out of the pre circuit and switching the PSU off and checking to see if any stored energy dissipates through the 1 meg resistor to ground.

Andy.

[colin.hepburn]

Thank Andy.

I have the older WAD phono 2 but it has most of the modes done to it output are the WD Clarity caps 2.2uf as I haven’t checked it for a time maybe there’s a dry joint at the cap or a fault cap will check out with the advice you gave

[Greg.]

Just one basic consideration. Is your selector switch make before break or break before make?

[colin.hepburn]

Originally Posted by Greg.

Just one basic consideration. Is your selector switch make before break or break before make?

Nether Greg
The SS NAD preamp is relay switched, as is the WD CF with the WD relay switcher
Its not a new problem but i thought it was a cap in the nad pre relay switched

so i just turn the volume off when switching to phono

but its only just since i started using the WAD CF i released it must by the something up with WAD phono II

[bikerhifinut]

Originally Posted by colin.hepburn

Nether Greg
The SS NAD preamp is relay switched, as is the WD CF with the WD relay switcher
Its not a new problem but i thought it was a cap in the nad pre relay switched

so i just turn the volume off when switching to phono

but its only just since i started using the WAD CF i released it must by the something up with WAD phono II

It does sound to me like a capacitor discharging across the volume pot. I don't know how the WD relay board works, does it short the input before closing the selected source relay contacts? Or does it simply close the previous source relay to ground whilst simultaneously switching over the new source relay?
Then again the phono input sockets would have been shorted to ground until selected? Would the caps charge up in that short period of time?

A.

[bob orbell]

Hi Colin, and all, if I switch from CD to Phono with the volume up, I too get a thump from the speakers, that is using Phono III and CF Pre, almost the same as yours Colin, I don't think it is a problem, I too just turn the volume down. BOB

[bob orbell]

Just put a meter on the output of Phono and got readings, after switch on, of between + 2volts and - 22.00volts, DC, never settles to a constant voltage, at switch off, the meter shows up to +27.00volts falling to 0. Strange.

[Richard]

Originally Posted by Greg.

Just one basic consideration. Is your selector switch make before break or break before make?

Yes it's the rotary switch will determine when the relays connect and mine doesn't pop. It needs to be a Shorting Make Before Break type. The RS number is 320-720.

If Colin got his from Bob could that be the problem?

Worth checking as you may be able to do it easily in situe, on the white part an S for Shorting MBB (the one you want) and NS for Non Shorting BBM,

[colin.hepburn]

Hi BOB/All
Richard I will check that out
But the DC thump also happens with the Solid-state NAD Amp which has a push button relay selector so it’s not just the CF it happens with I will try same check as bob and see if same