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Old 6th August 2007, 06:41 AM   #1
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Location: the leafy west of Brisbane
Default 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?


A speaker-builder's parable: "That burned down, fell over, then sank into the swamp. But the fourth one stayed up. And that's what you're going to get, Lad, the strongest castle of all."
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Old 18th October 2007, 06:35 PM   #2
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Default M-70

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.
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Old 19th October 2007, 03:09 PM   #3
gni is offline gni  United States
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Service Manuals:

Links to similar discussions:
Yamaha M-45 Blown Output Transistors
Yamaha M-45 Power Meter Mods

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.
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Old 29th September 2008, 05:08 AM   #4
dgm is offline dgm  Australia
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Join Date: May 2006
Default 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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