Suitable Wadding for SE Labs/EMI Oscilloscope Power Converters? - UK Vintage Radio Repair and Restoration Discussion Forum

Chris55000 · 16th Jun 2022, 1:49 pm

Just a quickie one!

Can anyone recommend any sound–deadening wadding to use in SELabs SM111/SM113 Oscilloscope DC–DC Converters that whine like a stuck pig?

I've been looking around but all I can find is "audiofoolery–priced" rolls of the stuff for lining daft speaker cabinets!

I'm looking for this in reasonable small quantities!

PS!

Is it worth trying to reduce the capacity C6 across the primary of the d.c. – d.c. converter transformer to get it to run at a higher frequency?

Chris Williams

G6Tanuki · 16th Jun 2022, 2:43 pm

I guess the problem is 'magnetostriction' in the transformer?

Not familiar with this particular 'scope but could you consider 'potting' it in resin? If not resin, what about slooshying the transformer windings with the brown Gorilla Glue?

WME_bill · 18th Jun 2022, 10:57 am

SM111 power unit whistle.
I agrre with G6Tanuki. Magnetostriction. I have tried clamping the transformer down to the PCB and the elements of the core tightly, Also experimented with changing the oscillation frequency. All to no benefit.
But slugging it with insulation does work very well.
I use the lightweight fibreglass insulation used for attic insulation. A higher density version is used for sound insulation. But the attic version can be stuffed in hard and deadens the sound very well.
On this scope, the whole power supply is in a separate shielding box, so I have stuffed it full and clamped the whole lot back. Glass fibre is an insulator too.
I found amply enough fibreglass insulating my attic- one handfull!
wme-bill

16th Jun 2022, 1:49 pm	#1
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,874	Suitable Wadding for SE Labs/EMI Oscilloscope Power Converters? Just a quickie one! Can anyone recommend any sound–deadening wadding to use in SELabs SM111/SM113 Oscilloscope DC–DC Converters that whine like a stuck pig? I've been looking around but all I can find is "audiofoolery–priced" rolls of the stuff for lining daft speaker cabinets! I'm looking for this in reasonable small quantities! PS! Is it worth trying to reduce the capacity C6 across the primary of the d.c. – d.c. converter transformer to get it to run at a higher frequency? Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 16th Jun 2022 at 2:00 pm.

16th Jun 2022, 2:43 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,014	Re: Suitable Wadding for SE Labs/EMI Oscilloscope Power Converters? I guess the problem is 'magnetostriction' in the transformer? Not familiar with this particular 'scope but could you consider 'potting' it in resin? If not resin, what about slooshying the transformer windings with the brown Gorilla Glue? __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

18th Jun 2022, 10:57 am	#3
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Suitable Wadding for SE Labs/EMI Oscilloscope Power Converters? SM111 power unit whistle. I agrre with G6Tanuki. Magnetostriction. I have tried clamping the transformer down to the PCB and the elements of the core tightly, Also experimented with changing the oscillation frequency. All to no benefit. But slugging it with insulation does work very well. I use the lightweight fibreglass insulation used for attic insulation. A higher density version is used for sound insulation. But the attic version can be stuffed in hard and deadens the sound very well. On this scope, the whole power supply is in a separate shielding box, so I have stuffed it full and clamped the whole lot back. Glass fibre is an insulator too. I found amply enough fibreglass insulating my attic- one handfull! wme-bill Last edited by WME_bill; 18th Jun 2022 at 11:04 am.