Hafler DH300 Monoblock forever?

Wow, almost sorry I asked, now I can't plead ingnorance. Will have to see if I can locate someone with one to lend me. I have a plain vanilla DVM I use so I don't think that it will fill the requirement for "True RMS" readings.

On another note, I went and got some adapters to convert the 1/4" mono input jacks to allow them to accept my phone(RCA) jacks from my preamp. The newly received DH300 works but it has considerable hum through both channels (at zero volume) as soon as I plug the input leads from the preamp into the back of the Hafler. Both channels do work, so it's set up for stereo, although I have not done anything with the 2.2K ohm resistors I picked up, knowing my standard DH200 has that across the ground leg and chassis ground on the right channel. Could that have anything to do with the hum, or is it that I have some floating ground or something with these 1/4 mono plug inputs that I think are isolated from chassis ground.

R45 should be a 2.2 Ohm, 1/2W resistor. I would install that(if the 300 has none) on the right input, and see if that helps. But first: The AC plug on your amp should be ungrounded and non-polarized. Reverse(flip) it in the wall socket, before you do anything else. Then try connecting the preamp again. It's possible that the phase is reversed between the two units. If the RCAs that you bought at Rat Shack ground to the chassis: you'll have to find a way to float the right input, so it grounds through R45(if you're still humming).

thx, I screwed up and am pretty sure I grabbed some 2.2K ohm resistors at Rat Shack instead of true 2.2ohm, will need to correct that, and report back to you.

So far I tried the new DH300 and tried reversing the power plu polarity and that helped considerably, but there's still hum as soon as I plug the input cables from the pre-amp into the Hafler. I have not yet tried to ground the Hafler chassis with a jumper or anything back to the pre-amp. I'm still using the 1/4 plugs with adapters that allow me to connect my RCA phono plugs into the DH300 and the 1/4" jacks appear to have plastic mounts isolating them from the chassis. Any thoughts?

If the jacks are isolated from the chassis, try grounding one, just to see what happens, Be certain to ground the terminal that contacts with the barrel of the 1/4" plug and not the tip. Only connect that channel, with your pre. Should be a simple test to perform. Check both channels and see if the wires from the hot terminal(contacting the plug's tip), are connected to terminal #1 of the PC-6 boards. Are all your power cables and interconnects, dressed well away from one another, with none running parallel?