"- Turn the Input and Threshold control all the way down (CCW). Inrush current upon power up is very high, and it will definitely damage the control amplifier"
Is is the same with Fairchild? I was looking at the manual of the original 670 and another clone and there is no such warning.
FWIW; there is no such warning of this kind within the UTA UnFairchild manual that I know of. After two years of use I've never turned the knobs CCW before power up/shut down and I've never had a problem.
Last Edit: Aug 27, 2019 23:06:15 GMT -6 by drumhead57
It's going to result in lots of broken units because most people are just going to start twiddling knobs and without ever reading the manual.
If the plan is going to be to leave it powered on most of the time, then it seems like temporary power outages are going to damage the occasional unit in a home studio environment.
No unit will be broken. No need to leave it turned on.
Would be great to know about how the damage could be avoided. Even if you always make sure to follow the procedure, the power cut could cause the unit to be turned back on with the knob in the wrong place or you simply that one day when coffee has not started working just forget about it and turn it on with the knob in the wrong place. I am sure some sort of a UPS that will not return the power after a cut could work to avoid turning the unit back on after the outage. Then I wonder if there is a risk if you turn the knob too fast?
The Fairchild uses a 5A mains fuse. Such a high value was used only to stand the huge inrush current needed to feed all that cold filaments and charge the big caps, since back in the day s slow blow fuse was still not avaliable (I believe it was in the eighties)
The disadvantage if using a such big fuse is that any eventual subsequent malfunctioning will blow the circuit before the fuses shorts out.
We decided to use a smaller slow blow mains fuse to protect the inner circuit. For further protection in the unfortunate case you forget this suggestion of turning down the knobs a soft start circuit in the control amplifier and NTC's surge protection has already been implemented on all units, in other words, you can power on the unit with the knobs anywhere and it won’t damage the control amplifier
The manual was made before I made this changed thus is outdated and you have nothing to worry about, I will be editing the manual this week