PPI PC21400

[mike49504]

I got the driverboards for this amp.. The orginal driverboards have 2 large transistors on them maked.. BF722 and BF723

The new boards the large transistors are marked BF720 and BF721

Wondering will the new boards work??

[Pioneer621]

They share the same datasheets so I would say it will work fine. Looks like the only difference is the BF720 & BF721 are rated for slightly higher voltage so should not be a problem.

Always a good idea to check the datasheets, & still if in doubt, ask.

[mike49504]

Ok got the new driverboards installed..

Now i get 0.01 volts on both channels so im sitting good there..

The bias pots are still fully counter-clockwise..

Where should i set the Bias in this amp??

[1moreamp]

Measure the V drop across the emitter resistors. And watch your total current draw from the 12 volt supply. make sure the power devices are tightly clamped for this part of your service. You might have to use alternate clamp bars like Perry recommends.
No one I know has the correct bis idle spec so you must use total currant draw off the power supply at 12 VDC. read it with no bias, and then add bias to each channel so the amp idles at its correct 12 volt current draw. try to make sure both channels get equal bias. And verify this by reading V drop across the emitter resistor sets, and individually each resistors...Best advise I can give you other then using a O scope to set it along with all of the above. O scope will require the amp be driver at 250 Milli-watts and 1 watt and full power and at different frequency's across the 20 to 20K band. Looking for notch distortion, and the such and checking bias V drop both cold and hot soaked....hope this helps some....C


PS the DC offset will vary as you adjust output bias upward, so you will need to do a bit of back and forth adjusting the DC offset adjustment. Something to do with thermal drift of the SIP modules as they heat up from forward biasing the outputs...