power supply problem

[Hairy Harry]

Hi Ken (et al)

I don't have the xpander schematic... but the Oberheims I've
seen (like matrix 6) have a main LINEAR supply (with the big
honkin' transformer) and a small "inverter" to generate the
high voltage needed for the Vacuum Fluorescent display...

If this is the case... then the BIG transformer is the Linear
supply... and the little one is for the display only...

H^)  harry

BTW: The higher the frequency the switcher runs at, the smaller
the magnetics (for the most part). Some old switchers didn't work
at very high frequencies...


>From: Kenneth Martinez <kmartinez at bency.com>
>To: synth-diy at node12b53.a2000.nl
>Subject: Re: power supply problem
>Date: Tue, 21 Nov 2000 08:21:46 -0700
>
>I'm happy to report that my Xpander is working correctly again...symptoms
>were that it failed the DAC MONO test on the Service page, and there was a
>waivering in the pitch of all VCOs and self-resonant VCFs, and it failed
>the tuning routines...I eventually discovered that the -12V portion of the
>power supply was passing an inordinate amount of ripple...thanks to all
>those on synth-diy who gave suggestions - it turned out that filter cap C8
>was open and so wasn't filtering at all, which is perhaps why the 7912
>started to fail - replacing both of those corrected all problems.
>
>I'm still trying to get a grasp on the benefits of switching power
>supplies...Harry said transformers are smaller...my Xpander supply has one
>big transformer whose output is regulated & feeds the switching circuit,
>which drives a smaller transformer... and the first transformer is just as
>large as what's used in a linear supply.  So - is the difference that the
>big transformer in the switching supply somehow generates less heat than
>the one in the linear supply?
>
>

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