Yamaha PM180 mixer voltage question.

[Brinxter]

Hi guys
My yamaha PM180 mixer has a broken Yamaha NE80100 opamp in the output amplifier. Since these opamps are pretty hard and expensive to come by, I want try to use another opamp in there. I have some spare opamps with the same footprint that I would like to use, but they are rated up to +/- 20V and the mixer runs on +/- 22V. So my question is this, what would be the best way to drop the voltage to +/- 18V on only the opamps on the output amp card, or is it better to drop the voltage from 22V to 18V from the psu?

 

[dom]

Could try just a low-voltage series Zener diode (4-5V or so) and a shunt capacitor on each of the rails (1 - 10 µF or so, depending on the amplifier load).

The Zeners won't need a large package or any heatsinking assuming your new op amp only draws 1-10 mA or so.

That's the simplest, lowest parts count solution.

If you need good load regulation on the ±18V rails, then you could put in a couple of three terminal regulators instead, but that's more green-wiring bodge work. The load regulation of a Zener is probably good enough for most applications.

 

[Bo Deadly]

Unfortunately there isn't a really good solution here. A 4V drop is quite a lot. If you changed the 1K8/10K to like 2K2/4K7 it might get the rails down to 18V but then you would be dropping that extra 4V across the pass transistors which significantly bumps up their power dissipation. Too much I would think. It would probably get really hot and eventually the transistors would get burned up inside and fail. Depends on what sort of heat sinking is going on. Dropping the rails at the amp with something like zeners might work but you might need to shunt some current and add bigger caps to get the right drop and low noise rails. It would be a lot easier to just get a high voltage op amp.

 

[Whoops]

Hi guys
My yamaha PM180 mixer has a broken Yamaha NE80100 opamp in the output amplifier. Since these opamps are pretty hard and expensive to come by

Can the NE80100 opamp be fixed?

is it a Discreet Opamp?

 

[Monte McGuire]

The power isolators already on the PCB can be reworked to provide a regulator for a lower voltage amplifier. The parts on each rail are a series 10Ω resistor with a 47µF shunt capacitor. A pair of reverse zeners, perhaps 17V, can be placed across the 47µF caps and the series 10Ω resistors can be increased to 100Ω parts, able to dissipate 1/4 watt. It would also make sense to increase the shunt caps to 470µF. On the whole, this will probably be simpler than shoehorning three terminal regulators in there, and should work just about as well. The extra heat in the 100Ω resistors needs to be handled, but it's only 1/4 watt, so it won't be terribly difficult.

 

[Brinxter]

Thanks for the replies guys I have gotten my hands on a "new" NE80100 opamp