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Brisso57 6th August 2007 06:41 AM

Upgrading a Yamaha M-70 power amp?
Has anyone upgraded or modernised their Yamaha (class A) M-70 power amp?

If so, what did you do that produced audible or measurable benefits?



Blkorpheus 18th October 2007 06:35 PM

I've done several upgrades and mod to this unit.
  • I've bypass the old level control and solder pure silver wire from the rca inputs to the input board.

    Replaced stock fuses with silver -plated types.

    Replaced standard power cord with an silver plated IEC power inlet.

    Added Bybees to the input board.
None of these alter the timbre of unit but between the level control bypass and the bybees, more microdynamics came out and more headroom which still rivals my Adcom 555 IIs at the moment. It's an easy to mod unit but it gets hard to handle when you start modding the power and gets easily stuck in protection mode.

gni 19th October 2007 03:09 PM

Service Manuals:

Links to similar discussions:

Recently toasted my M-45 (cousin to the M-70) while adjusting
the bias (top mounted jumpers carry voltage rails). I am in the
final stages of installing a new amp module in the shell of the old

The darn protection circuit. . .very picky. The M-70 is technically more
advanced than the M-45 though.

dgm 29th September 2008 05:08 AM

M-70 protection problem
There are lots of comments about M-70 protection problems. My amp has this problem - will not switch on. It was a gradual thing as it took longer and longer to start up.
Does anyone know how to fix this - whats the usual problem?

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