Tír Na HiFi

Just a thought.
I had a loan of some Croft Valve amps many years ago while my Gamut D200 was in Hospital. I hooked them up temporarily in my kitchen just to get a feel for them and I had a hum. I didn't think too much about it and moved them to my usual set up, no hum. I looked into it and it turned out the amp was picking up from the kitchen equipment.
Is your system on the same line as other household equipment? You could try turning off some of your appliances just to rule out them out.

Derek wrote: ↑Sat Feb 17, 2018 3:34 pm Just a thought.
I had a loan of some Croft Valve amps many years ago while my Gamut D200 was in Hospital. I hooked them up temporarily in my kitchen just to get a feel for them and I had a hum. I didn't think too much about it and moved them to my usual set up, no hum. I looked into it and it turned out the amp was picking up from the kitchen equipment.
Is your system on the same line as other household equipment? You could try turning off some of your appliances just to rule out them out.

Was it a Series 4? Can you remember the preamp?

Cyndale's setup is Croft Series 4 monoblocks in tandem with Croft Super Micro A (AFAIR) and Croft mc head amp feeding an LP12/Lingo and Quadral Chromium 8's plus Rel sub.

Valve total : 41 valves approx.

Transformer total : 10

With all the equipment plugged into the block except either the pre or one of the power amps there's no hum. Plugging either of the others in = HUM

One suggested solution was to disconnect the earth from one of the amp plug. No hum.....

Obviously a solution that's frowned on but.......would the interconnect take the earth path anyway?

Over to the experts :)

Derek wrote: ↑Sat Feb 17, 2018 3:34 pm Just a thought.
I had a loan of some Croft Valve amps many years ago while my Gamut D200 was in Hospital. I hooked them up temporarily in my kitchen just to get a feel for them and I had a hum. I didn't think too much about it and moved them to my usual set up, no hum. I looked into it and it turned out the amp was picking up from the kitchen equipment.
Is your system on the same line as other household equipment? You could try turning off some of your appliances just to rule out them out.

Funny you should bring this up, I saw another cable connected into the back of the socket I use for the HiFi and I sussed out that the immersion is connected to that socket. The immersion hasn't been used for over 12 years, even so I was thinking of disconnecting from the socket just to see.

Fran wrote: ↑Sat Feb 17, 2018 2:33 pm Is the preamp active or passive?


Are you confident opening up the bottom of the amp where there are lethal DC voltages - not like AC these are much more dangerous?

Not confident but reasonably capable. What were you going to suggest?

Opening it up and having a look to see how signal ground is bound to mains earth

Fran wrote: ↑Sun Feb 18, 2018 11:07 am Opening it up and having a look to see how signal ground is bound to mains earth

Are you talking about signal ground - phono or loudspeaker?

Cyndale wrote: ↑Sun Feb 18, 2018 1:24 pm

Fran wrote: ↑Sun Feb 18, 2018 11:07 am Opening it up and having a look to see how signal ground is bound to mains earth

Are you talking about signal ground - phono or loudspeaker?

In some way signal gnd is connected to mains earth on all amps
That's both rca gnd and speaker return/gnd
So probably need to look into all of them but maybe just one will cure the hum
Don't kill yourselve ☺

Just an update...

I am using Van Den Hul interconnects (ground at one end only), meant to go headamp (ground) to preamp; preamp (ground) to power amps.

So I reversed them all, no change.

Then I tried moving the preamp as far away as possible (the lengths of the interconnects) from the power amps, no change.

Now, with one power amplifier on and nothing else, no hum. Turn on the preamp and the hum comes back.

I checked the preamp and the earth of the mains cable is connected to the base of the preamp with a screw, then a small green wire goes from that earth point to the transformer.

I haven't got round to turning the power amps upside down to have a look at what way the mains cable is earthed inside.

Not sure I know how an interconnect can actually work if ground is only connected one side as that would mean there's no return path
Maybe it's shielded to gnd one side ?
Mains earth is connected to chassis that's normal it's how chassis and mains earth is connected to signal gnd that interests us
If both power amps is on and preamp off is there hum?

nige2000 wrote: ↑Mon Feb 19, 2018 9:08 pm Not sure I know how an interconnect can actually work if ground is only connected one side as that would mean there's no return path
Maybe it's shielded to gnd one side ?
Mains earth is connected to chassis that's normal it's how chassis and mains earth is connected to signal gnd that interests us
If both power amps is on and preamp off is there hum?

Regarding Van Den Hul, it's all there in their literature about the interconnect grounding.

Here is a link...

http://www.google.ie/url?sa=t&rct=j&q=& ... sqbaePgL8n


Anyway, here is the latest that is happening....

Disconnect earth on right power amp only and I only have hum on the left power amp

Disconnect earth on left power amp only and I only have hum on the right power amp

Disconnect earth from the preamplifier and disconnect the earth's on just one of power amps (it can be either) and absolutely no hum, go figure.