I recently came upon a harman kardon 3470, looks ok physically but selling as broken. So I was looking for service manual (found) and adjustments that could be completed.
I was not able to find an idle/bias adjustment for the final power amp devices? And no DC offset adjustment either.
Just curious if others have worked on these units?
Thx.
--Joe
I was not able to find an idle/bias adjustment for the final power amp devices? And no DC offset adjustment either.
Just curious if others have worked on these units?
Thx.
--Joe
It's runs in Class B so a few miliamps of current will stop any crossover distortion.
There is no DC offset because it doesn't need any. The front end transistors are matched.
There is no DC offset because it doesn't need any. The front end transistors are matched.
So I would equate this to AB operation 🙂
Nonetheless if everything is matched and within design tolerance no adjustment would be required. I get it.
Thanks for the reply.
--Joe
Nonetheless if everything is matched and within design tolerance no adjustment would be required. I get it.
Thanks for the reply.
--Joe
Typically for an EF output stage the optimum bias current is in the 50mA to 100mA range, ie quite high - you might want to err on the lower side for cooler quiescent conditions in the amp.
That's what I was figuring. But there is no variable resistance in the driver stage to adjust. This is a fixed bias amp. In a perfect world I'm ok with this but components drift and not always in the same direction.
I checked a similar HK (3480) that uses a pot in the preceding stage so I could hack this 3470, not sure yet.
Thanks for your reply.