Dansette Hifi Mystery

[Ian Russell]

Can any one shed any light on this mystery?
In one of the photos you will see a crocodile lead connecting the controls bracket of a Dansette Hifi amp to the amp chassis.
This cures a hum which is present with the volume at minimum.
However, if I replace the crocodile lead with a permanent lead the hum increases slightly. I've tried different leads but the only one which cures the hum is the crocodile lead!
Can anyone think of an explanation?

[GrimJosef]

With hum pickup the exact path in space that the lead follows can matter. If you find a temporary layout that works then you should try running the permanent wire along the same path (same route, same end point).

Oh, and I did chuckle when I saw the words 'Dansette' and 'hifi' in the same phrase .

Cheers,

GJ

[Edward Huggins]

Could be an earth loop to the Garrard AT6 deck plate?

[Nuvistor]

The green permanent earth wire in the photo is very close to the on/off switch, if you move it away does it help, if not then has GJ states, make the temp fix permanent.

[Ian Russell]

Originally Posted by GrimJosef

Oh, and I did chuckle when I saw the words 'Dansette' and 'hifi' in the same phrase

I suppose Hifi should be in inverted commas.

[crackle]

Have you added a 3 core cable when it was originally a 2 core mains cable?
It may help if you put all earth connections to each chassis (controls, amp, deck) onto the same point, possibly the amp chassis, along with the mains earth.

Mike

[ms660]

Originally Posted by Ian Russell

I suppose Hifi should be in inverted commas.

The Dansette Hifi MKII was ultra linear PP according to the schemo I'm looking at...I think the ECL82 version was as well.

Lawrence.

[Herald1360]

In this case, isn't "HiFi" actually the model name?

It was one of their classier models, ending up with an AT6 and p-p ECL86s.

Edit: Nobody beats Lawrence to the draw,

[Ian Russell]

Yes 'Hifi' is the model name. This one has 2 x ECL82.

[Station X]

Having repaired one I can confirm that it is Ultra Linear.

[emeritus]

Proximity to a mains cable does seem the likely cause. Many years ago I fixed the hum in a friend's record player by re-routing the screened lead from the pick-up to the amp that had been lying in contact with a cable carrying mains.

[GrimJosef]

One of the really annoying features of 50Hz hum is that it can come from more than one source. If you're unlucky you can start out with one badly routed piece of wire partially cancelling the effects of another one - two wrongs almost making a right, if you like. The set is delivered to you with the customer complaining about the small amount of uncancelled hum. You notice one of the badly routed wires and, since you understand these things, you move it to a place where it picks up much less hum. Lo and behold, the cancellation is ruined and the total amount of hum now gets much worse ! I've banged my head quite hard against this once or twice .

Cheers,

GJ

[Edward Huggins]

Both the Dansette "Hi Fi" ECL82 and ECL86 versions were UL. We may laugh as to the oxymoron of Dansette and Hi Fi, but back in the middle 1950s, the Margolins did make a (very rare) wooden console mono record player with a 3 valve amp, 3 speed changer and an 8" speaker and which would have probably sounded quite decent in it's time.

[Hartley118]

Originally Posted by Edward Huggins

Could be an earth loop to the Garrard AT6 deck plate?

I agree Edward. If a hum problem changes when an earthy connection is rerouted, it's very unlikely that the hum is being picked up electrostatically, but likely it's induced magnetically due to AC current circulating in an earth loop. Would that be the mains transformer I see next to the susceptible earth connection? If so, it could be the main source of the induced field.

As Edward suggests, if as usual the deck metalwork has its own earth connection and then maybe the amplifier earth also finds its way to the deck via the cartridge wiring, that could be the source of the loop. One earth connection may have to go.

Martin

[ukcol]

As well as the considerations above make sure that your wiring is as Pic 1 below.
That is the screen cable to the pickup is connected to chassis at the amplifier end only AND a separate cable is connect between the turntable chassis and the amplifier chassis.

Do not use the pickup cable to connect the turntable chassis to the amplifier chassis (as in Pic 2) as this will cause hum.

Do not connect both ends of the screened (as in Pic 3) as this will also cause hum.

[ukcol]

Just a safety warning.

Anyone reading my post no 15 above should be aware that connecting the turntable chassis to the amplifier chassis would be very dangerous if, unlike Ian's "Dansette HiFi", your machine employs the live chassis technique.

[Edward Huggins]

I seem to remember that, as wth the Dansette "Bermuda", these have trailing leads to 3 phono sockets at the back of the cabinet for "EXT LXS", "STEREO" and "TAPE". These are notorious for inducing hum and, what's more, they were rarely ever used.

[Station X]

That matches the circuit diagram.

https://www.vintage-radio.net/forum/...d.php?t=129365