PSU for Redbox Classic?

Hi guys

I have tried contacting H&K but I have had no feedback!

Anyway does anybody know if a specific polarity is needed for a PSU used to power the redbox?
As per the spec they only mention 9V - 24V DC or 9V - 15V AC, but I have tried a 12V and 9V DC
PSU and it does not power the unit, which led me to think that it might need a reversed polarity PSU?

This is for the Redbox Classic by the way, didnt know where else to post the topic

Good grief. I've only just found this after 4 years! Talk about zombie threads. Apologies to Justfine99 for the delay. Errrmm, it took some time to research the info accurately? (My story and I'm sticking to it. )

For the record, units which are described like this, that is specd with a DC voltage and AC voltage on the same socket/terminals, will be fine with either and it won't matter which way around the DC connections are made. In order to accommodate an AC voltage there must be a diode rectifier setup inside. This will then steer a DC supply to the correct configuration no matter which way round it is connected. If a manufacturer doesn't specify which way round then you can be sure that it is irrelevent, (or you have a cast iron claim under warranty. )

So why is the DC 9-24V and the AC only 9-15V? That's because when you rectify an AC sinewave signal you get out DC which is based on the PEAK value of the signal not the RMS (root mean square) value. This RMS value is the usual one used to specify the size of a sinewave signal. The 'power' of any signal is related to the 'area under the curve' of the signal's shape. Spikey signals with not much area under that curve are not as powerful as lower peak but broader signals like square waves for example. That's why our guitar sounds thicken out and become more beefy when our amps compress the peaks. A sinewave has an RMS value which is just under three quarters of the way up its curve towards the peak. The entire sinewave shape averaged out over a whole cycle is the equivalent of a DC signal of 1/(squareroot of 2)x the peak value. (That's 0.707x). The peak value at the upper and lower extremes is therefore (sqrt 2)x the RMS value. So 100V mains has a peak value of 141V and 220V mains has a peak value of 311V. A 15V RMS value is the equivalent of just over a 21V DC signal and that is what you will expect to get on your circuit's power line after you rectify it with those diodes.

As an addendum, this doesn't mean that the battery can be attached either way round. Make sure to keep that in the correct orientation.