Leak Stereo 70 noise at switch off

[Robin_D]

Hi all.

I have a 1971 Leak Stereo 70 I've owned from new and is still in use in my study one or two days a week.

Recently when turning it off I get a noise through the speakers that I recognise from time at EMI in the late 60's as being a capacitor cause issues.

I have a circuit diagram, and have started to look to replacing all the high capacity electrolytics. 1250uf 100v in the PSU, 2000uf 50V in the output stage and 500uf 64v and a couple of 500uf 64v that I've yet to identify where they are in the circuit. I also have a worn pot on the volume, but that's easy to sort.

Two questions if I might.
1. What would you good people suggest I replace these with please?
2. Should I also replace the smaller value electrolytic's while I'm at it. I think there's a dozen or so on the daughter boards.

Anything else I should be looking at?

Thanks in anticipation.

Robin

[Silicon]

I would start with C8 and C9, the 0.01uF capacitors across the mains switch contacts.

Class X2 safety certified capacitors are normally recommended in this situation.

A 'snubber' circuit could be used instead as an improvement over the original capacitor.

It consists of a capacitor and resistor in series, encased in plastic.

[Sideband]

Originally Posted by Robin_D

Recently when turning it off I get a noise through the speakers that I recognise from time at EMI in the late 60's as being a capacitor cause issues.

What sort of 'noise'? Is it a thump or crack from the speakers when switching off or is it a softer noise like 'rustling' that dies away after some moments? The former is probably the snubber across the switch, the latter could be drying out electrolytics.

[Robin_D]

Hi and thanks for the replies.

I get a thump when powering up, but have had that for 20 years or so. The power off noise is a swishing noise for 2 to 3 seconds.

[Robin_D]

Hi.

It seems I should replace the C8 and C9 to take out the thump and C34L and C34R for starters.

For C8/9 will https://www.mouser.co.uk/ProductDeta...CKr%2FXyReE%3D do?

The electrolytic's are still proving a challenge. Any suggestions for a source for 2000uF 50V or better please?

[snowman_al]

Originally Posted by Robin_D

The electrolytic's are still proving a challenge. Any suggestions for a source for 2000uF 50V or better please?

Modern capacitor values are different.
2200uF and 63 volts is closest and you need the 'snap in' types. They will be much smaller in size than the originals. Not sure if yours are 30mm or 35mm diameter? You can use 3300uF and 100 volts no problems, see next.

When / if you replace C6 and C7 (1250uF) no need to use two caps, just use a single 3300uF 100 volt type.

The replacement value for the 500uF types are 470uF and so on. No problem using higher voltage types.

Look at 'Farnell', CPC and Radio Spares for supplies.

Manual enclosed if you d not have it already.

[Robin_D]

Thanks for that. I have the circuit diagram, but not the rest of the manual.

Thanks also for the tips on the components. My C34's are 35mm diameter.

[Sideband]

Originally Posted by Robin_D

I get a thump when powering up, but have had that for 20 years or so. The power off noise is a swishing noise for 2 to 3 seconds.

The thump at switch-on is normal. Both of mine do that and always have done. The 'swishing' noise is not and could well be capacitors as suggested. Is it on both channels? If yes, it's probably power supply since that is common to both channels, if only one channel then you only need to concentrate on the PCB associated with that channel. I believe they are marked L and R respectively. You could also try swapping the L and R PCBs over and see if the swishing noise changes channels as well.

[Robin_D]

Main capacitors now changed. Swishing noise completely disappeared. Thump at switch on significantly reduced.

Thanks for your help.