Noisy, unusable phonostage

[Aardvark]

Hi all,

A while ago I scratch built a Hagerman Cornet valve phono stage. It turned out to be very musical while having a bit of a mains hum that was not just about audible when not actually playing music. This was with a MM cartridge with a healthy 6mV output. However I changed cartridge to one with a lower output and, having to turn the wick up a bit more, the hum got intrusive.

The original build was a tad rough and ready so I set about separating out the earths, HT from heater from signal. Now it's really very quiet except when I connect the input leads from the turntable. At this point it starts buzzing like an angry Bumble Bee.

It's completely unusable. I've tried different arms, cartridges, earths connected and disconnected - nothing changes. I've been in and out of the box so many times. I can't find anything wrong. It's both channels so it's some point of commonality, probably not a fault on one of the channel tag boards.

Anyone got any thoughts?

TIA

Circuit here - http://www.hagtech.com/pdf/cornet.pdf

[Andrew]

What version of the Cornet is it? There have been several. Early ones were less refined, I believe, although once fettled sound very good.

Might be good to post an image of the innards so we can see what's going on.

Alternatively, if you are close to someone who is good with phono's then it might be worth taking it along to them and perhaps offer them a few beer tokens by way of thanks, assuming they can sort.

Andrew

[Nick]

Has the turntable out got a separate earth wire?

[Mike H]

Any chance of a diagram to show how the earths have been changed? That's problee where it all went pear-shaped by the sounds of it ~ OK before, rubbish after....

Also, is it AC or DC heater supply?


 

[david C]

I have a cornet which doesn't cause any hum problems at all,

there is one connection from the pcb to an earth post on the chassis, the arm and Garrard chassis are connected to this,

[Aardvark]

Apologies to all for not coming back sooner and thanks for all your responses. I will be getting back to it soon.

Its gone on the back burner for the moment as "my hobby room" has suddenly acquired a new title - "our spare bedroom". I am now putting down a new carpet and bed so am having to rearrange all my bits and bobs. In the meantime I've bought Soulminer's PreII and PSU over the road so quality vinyl sounds will soon be heard again.

David - I scratch built it from the circuit diagram on tag boards, not on the Hagtech pcb. The parts layout and wiring paths are all my own and clearly not of the first order!

Mike H - its a DC heater supply - 1N5821 followed by CRC.

Andrew - AFAIK its the very 1st incarnation without the cathode transistors.

I will get around to posting pictures and fully expect I have made a healthy number of newbie errors which will no doubt induce much drawing in of breath through teeth when seen

Anyway, back to the furniture removals.

[Mike H]

What it is to have a "domestic life"