ARC Ls 15 Schematic - diyAudio
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Old 28th August 2008, 05:28 PM   #1
ingemar is offline ingemar  Sweden
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Default ARC Ls 15 Schematic

Hi all.
Thinking about to upgrade my preamp,but to this i need a schematic.Is it some nice person who can provide me with one??
Kindly/Ingemar
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Old 29th August 2008, 02:50 PM   #2
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Default LS-22 schematic - very similar

http://www.mcmlv.org/Archive/HiFi/AR-LS22.pdf

The LS-15 and LS-22 are very similar. I'm pretty sure they share
the same PSU which is fairly complex. In fact, the PSU is about
80% of the schematic!

On thing you'll notice is the Cathode Follower is direct coupled
to the gain stage. The coupling caps keep the elevated cathode
voltages (north of 90VDC) away from output. Those coupling
caps are a critical component - if they fail, 90V+ DC gets sent
downstream to the connected component (hopefully, not a SS power amp).

I dont think there's ALOT you can do to tweak here. You could
theoretically change out the dual-triodes to reduce gain ; but
you are still limited by the B+ and filament supply current limitations.

What you *COULD* pull off, however, would be to install
CCS's into the cathode circuits. The negative supply is more
than competent to do this. Putting in the CCS's would only require
jumper-bypassing some on-board resistors.

The CCS would improve symmetry ; but I dont think there's alot
it would do for PSRR as the PSU's in this box are already over-engineered! A CCS, however, WOULD make it much easier
to dinker with other tubes. That requires more analysis of how
much B+ current you can work with.

- Jim
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