I am using two Placid HDBP power supplies to power my assembled as shipped Legato. Dual BIII's connected to Legato.

Jumpers J1 and J2 removed on Legato. Jumpers J3 and J4 installed so one HDBP powers the left channel, one powers the right channel and SE/headphone out. Sometimes when powering up for the first time, the right channel is garbled. It requires another power up for it to work. I tried another Placid HDBP I have, same thing happens.

Initially I shunted ~ 50mA for both R and L channel supplies. Pos and neg output set to 14.85v when warmed up, ~15 when first powered up. Now I am now shunting 90-100mA on the right channel/SE supply and sometimes I still don't get the right channel powered up on first power up. Voltage will read low on pos/neg for right channel supply when first powered up, like 7v, 5v, etc. Next power up I may get full voltage and mA.

Is their any difference with powering the SE stage from the left channel side versus the right? Anything I am missing?

Thanks for reply Russ.

When I wired the trannys I tired to keep the AC wiring close in length. That is closest tranny to furthest PS. There is ~ 2- 2.5 inches difference in AC wiring to Placid HDBP's. The DC wiring is shortest for the Placid HDBP running the extra load of SE section.

Primary wise I have three short harnesses off the line AC input connected to two trannys each.

OK, just curious, does it have something to do with the relay on the Legato?

Edited by user Tuesday, April 2, 2013 5:43:53 AM(UTC)  | Reason: Not specified

This pic is accurate for power supply and tranny placement. Originally had two ver 3.1 Legatos but wanted discrete output, SE and headphone back. That is when I decided to power single Legato with two HDBP supplies. Jumpers J1 and J2 removed, J3 and J4 installed.

Using switch on back of IEC/filter (not pictured) to power unit on. Line in off IEC/filter is 14 gauge black/white. Three 16 gauge black/white leads soldered to line in 14 gauge leads. Each pair 16 gauge leads attach to two trannies each, one 15va and one 30va.

30va trannies mounted across upper part of angle aluminum. Looking at it first closest 30va it powers HDBP at right. Second 30va powers HDBP at left.

This is rather interesting. Way before my "ripple on output" threat (and before I modded the Placid) I experienced almost the same behaviour - only difference to yours is that I'm powering a single Legato (with buffer) with only one Placid HD.

I have set my HD to shunt around 100mA @+-12V.

When I power up, the negative rail always gets to -12, but the positive hangs ~5-7v.

I have narrowed the problem down to one channel. When powering the left channel it works. When powering the SE section it works. But when powering the right channel, excessive current draw at the positive rail occurs holding it down.

Now, here comes the really interesting part. Due to the nature of the shunt supply, it can safely survive a shot on the output. When the problem is present, if I quickly short the positive (5-7v) rail to gnd and release the short - it ALWAYS comes up as expected. 10 out of 10 times.

All el-caps on the problematic channel has been lifted to rule out a semi shorted cap, no difference.

The problem isn't the Placid HD. It lays somewhere in the Legato.

Now, what can cause the one channel to behave as described ?

What I would do to get to the bottom of your issue, is power the circuit with a series regulator (like LCBPS) and measure the actual current draw of each rail for each channel.

That will help you narrow down where to look. :)

yes if you have one that bad it may smoke once it gets unfettered current. :) But hey then you will know what to replace. :)

No smoke detected.

Surely it is as current problem. I did shunt to little. I'll try to balance it, enough to startup and no more than the heatsinks are up to remove.

Thanks Russ. Always a pleasure.

It was now I did it.

Problem is, that I have to shunt such a large an amount of current to be able to start up the thing, that the steady state shunt current afterwards tends to be to much for the heatsinks (and for my comfort).

"Inrush" current in the fets ??? (no).

BTW, with the LPBPS the Legato starts up as designed, using aprox 190mA @ 12v. I have set up the Placid to ~300mA, with this it doesn't start every time.

Edited by user Thursday, May 2, 2013 3:31:27 PM(UTC)  | Reason: Not specified

I just need to wake up!

The output voltage was to low, somehow this condition kept down the positive rail.

Changing this to +-14.8v shunting 270mA it just works flawlessly.