Hey guys,

Just finished two Placid HD BP 2.1 boards and both exhibit the same issue: the negative voltage is approx. -2.88V at startup. It seems the exact same issue that miero encountered a couple of months ago.

Upon warming up (<1 minute) the output voltage suddenly rises to the normal value (-14.9V) and remains stable from then on. The problem occurs again after the board has cooled down completely.

The +ve side of both boards, as well as two Placid HD2.1 (non-BP) boards I built, function perfectly well.

All solder joints are double-checked, including the opamps. Of course I can try miero's workaround (replacing R8B by 100R) but that leaves me wondering why both my BP boards (and miero's) are affected on the -ve side while most people don't have this issue. I'd say opamp failure seems rather unlikely...

All parts are stock, except for C1A/B, the resistors, and a larger 225VA 2x15VAC toroid.
TP_VREF- is -1.70V (-2.49V after brief warm-up). TP_VREF+ is 2.49V.

Thanks a lot for your help :)

Yes, load unconnected.

Hi Guy's,

I have my Placid HD BP V2.1 playing now.
After careful adjustment with the load connected I adjusted the Placid to 55mA Shunt Current and 14.81V
(I can't find the exact recommended voltage. What do you use?)

But when powering the LH channel onto which the new Placid is connected gave a very weak signal.
When checking the voltages I also measure around 2.88V on the - channel.

TP Vref- was approx. 1.65V.

After a little adjusting of the voltage and current I hear a kind of "Click" like a small relay and all voltages were normal again.
TP Vref became 2.50V again and output 14.81V....

If you are using a TPA output stage, the click comes from the relay getting the proper voltage and therefore engages.

Ok I will increase the Shunt Current. With the extra extra large coolers it must be no problem.

I will also increase the voltage to 15V more precise.

Miero had a bad IC, don't you think there is a bad badge of OPAMP's installed on the Circuit Boards?

My other HDBP V2.1 doesn't have this kind of problem. It was delivered earlier than my recent HDBP.

Best regards,

Jordo

OK, more people with the same problem, all with -2,8V on the negative rail. I'd say that sort of eliminates construction errors.

I'm using 402R fixed resistors for an output voltage of +/- 14.8-14.9V.
Increasing the shunt current doesn't solve the problem, since the load is not connected and (almost) all CCS current (approx. 2x300mA) is already shunted.
The problem also occurs when the load (Legato) is connected, as is the case with Jordo and Martin H.

Unfortunately my understanding of the working of the circuit is too limited to really identify the cause of the problem, I only see the symptoms.
(I still feel it is related to the temperature since I can only reproduce it when the boards are cooled down completely.)

Hopefully someone has good ideas :)

I don't believe it could be a bad batch... nobody seems to have problems on the positive rail.

@ Stunts: O, he had it on the Positive rail, that's a different OPAMP indeed.

@ AVR300: I might try to do so if it re-occurs frequently.
I just experienced it one time today at start-up.
I hope the higher Voltages and Currents might prevent this of happening.

Thx!

Jordo

I understood nobody has problems with the +15V, only the -15V is affected, as was also the case with Miero (correct me if I'm wrong). The opamps are identical on the positive half and the negative half (OPA209, marked IC1 and IC2), only the PNP and NPN transistors are different (marked QPx and QNx).

Do they have the same p/n's?
I thought I saw different 'Legs' connected to similar components than on the other side so I figured it must be another model OPAMP.