Yamah p2200 setting idling current

[priscared]

Gday,
I have almost fixed my Yamaha p2200. And hopefully you guys could give me some info on setting the Idling ccurrent. I have the manual for the p2100 is it the same as the p2200? It says set the variable resistor so that across PE and E is 13mV within 30seconds, and afterwards there should be 22mV across them, is this the same as on the p2200? I dont want to blow anything up Thanks
Daniel

[priscared]

thanks

[jaycee]

You are looking to measure the current through the output transistors when there is no signal present (or signal input shorted to ground), ie the idle current.

How to do this depends very much on the amplifier design but often there will be a collector or emitter resistor attached (or both depending). What you want to do is work out the current flowing through this, usually this is done by measuring the voltage drop over the resistor. To do this you would place your multimeter probes either side of the resistor and set your multimeter to a low voltage range as the drop will be on the millivolt scale (if it is more there is something wrong!)

For example, if the drop was 20mV, and the resistor was 0.33 ohms, it'd be 0.02/0.33 = 0.0606 ~ 60mA bias

Note that if theres more than one pair of transistors in the output stage, the bias current is PER SET. 60mA is a pretty good figure per set but some people prefer higher, such as 100mA.

[markp]

It can be set the same as the p2100. It is just twice the number of outputs with the same design.

[anatech]

Hi priscared,
You will be fine with that setting. The heatsinks should run run just a little warm. There is no benefit to run the bias current higher with that design.
You are measuring the voltage drop across an emitter resistor if memory serves.

Tell us how it sounds when you are done.

-Chris

[priscared]

so adjusting that variable resistor is safe, wont break anything if i go to far the wrong way, it says start at the leftmost position but that could depend on which way u look at it, if i get it the wrong way could it break anything.
THanks
Daniel

[jaycee]

Yes, if you turn it too high you will be setting a massive idle current through the transistors which will eventually blow them due to overheating - although you should notice the heatsink getting scorchingly hot before any permanent damage is caused.

[anatech]

Hi priscared,
If the controls are roughly in the same position as the working channel, then leave them and power up with a variac. I think there is a surge resistor in this amp (could be wrong) that gets shorted after a moment when power is turned on. Short it out so it doesn't overheat during testing.
Compare bias currents at around 60 -70% rated AC. Monitor the new channel as you bring the power up. Stop if it gets too high. Alternatively, use a light bulb (around 100W) in series with the AC supply. You still need to short out the surge resistor.
Set the new channel's bias to the same level as the old channel. Once you reach full rated AC, perform the bias proceedure in the manual.
-Chris

[priscared]

If i hook up the amplifer when i get my new outputs installed (waiting for em) and put the ac input in series with a 100w globe. Then set the variable resistor to the same position as the workin side shoould be no problem, if i go to far the 100w globe will protect it? how? i cant figure this, will i see it get to hot or what? The transistors that is. Thanks
Daniel

[anatech]

Hi Daniel,
The 100W lamp will limit the energy into the amplifier. Anything is possible when adjusting the bias though. Don't run the control right to one end or the other. If you can't reduce the bias to the correct level, then something else is wrong.
Remember, new doesn't mean good or defect - free. Always use your common sense.
-Chris