A peculiar problem's occurred today. I've finished putting together two HD Placids for my dual-mono setup. All went fine, adjusted resistors up to the right values, connected up to the transformer & all lights up correctly. Adjust output voltage to 5.2V. Adjust shunt current to 0.35mA. Connect to spare Buffalo and nothing. Voltage drops to 1.8V. shunt current disappears. No amount of twiddling with the variable resistors has any noticeable effect.

I've tried resoldering everything, checking the components for correct positioning, connecting up the original Placid (which works fine & powers up the Buffalo). Now I'm completely stumped. Both HDs have the same problem so I really don't know what to do now.

Here are a couple of photos -





Any help would be much appreciated, and please be gentle, I'm still a newbie to all this DIY stuff.

Thanks for the speedy reply Russ. But when the HD Placid's connected up to the Buffalo, altering VR1 has no effect. Should I therefore try upping the CSS current before connecting up? I've packed my kit away for tonight so can't try this until tomorrow.

Well, I've managed to get both Placid HDs working, but I'm still not sure how!

I think part of the problem is to do with the Vishay variable resistors, which have been behaving in a very peculiar way. This morning I started from scratch - readjusted the resistors before attaching to power. These required considerable adjustment, despite me not turning them very much from their original settings. Powering up, with no load, I adjusted the voltage up to 5.2V, but the adjustment was really hair-trigger. It seemed to settle, than I watched the meter climb over the course of a couple of minutes, up to over 9V. Then a few touches, probably only a turn, of the resistor & it dropped down to 3V. At this stage I wondered if I had a poltergeist on board...

I left it all to settle down with the power on for half an hour, then noticed the voltage had crept up to nearly 5V. I then adjusted it quite normally to 5.2V. The power adjustment resistor also behaved in a rather erratic way. I adjusted up and down for a bit before it seemed to settle.

OK, time to connect it up to the Buffalo and success! Adjusted the shunt current, all seemed well.

I had the Buffalo, plus HD BP Placid, Legato 3.1 and transformers mounted on a board which I use to test everything. I'd last used this about a month ago, with a standard Placid, and ran it for a few days to burn things in.

Plugged into the system, played a track, and - horrible distorted, very quiet sound. Damn. Then i noticed the Buffalo's LEDs were dim, and one went out... Back on the table, the voltage had dropped to 3V or so, no shunt current. Readjusted. Left to settle. Reconnected up. Lousy sound again, but Buffalo still lit up OK. On the bench. HD Legato still measured OK. Checked previously working HD BP Placid, voltage well down, no shunt current. Starting to despair. readjust, reconnect, check all connections. Unable to adjust voltage beyond 13V on positive side. Despair crept in...

I won't bore you with the rest - resoldering , swapping units, crying, etc.

Anyway, it all appears to be working & has been playing music for the last couple of hours, sounds really good. I really don't know what to make of all this but I think, once the dual-mono setup is running properly, I'm going to replace those flaky variable resistors with fixed-value ones. Or is there something else at work here that I don't understand?

Hmm I do not understand what you mean with " Headrooom " ?