SSLV1.1 builds & fairy tales

[king4joy]

Salas....the man !!!

 

[merlin el mago]

Salas I want to tell you a mystery when I bring the screwdriver over and without touching the trimmer the voltage lowers two votios, when I remove the screwdriver the voltage returns to raise two volts. Exactly when the screwdriver is near 2 cm lowers 1V, less of 2cm lowers 2 volts.

 

[AndrewT]

Oscillation !

 

[Salas]

Salas I want to tell you a mystery when I bring the screwdriver over and without touching the trimmer the voltage lowers two votios, when I remove the screwdriver the voltage returns to raise two volts. Exactly when the screwdriver is near 2 cm lowers 1V, less of 2cm lowers 2 volts.

I haven't met that condition in a bib before. Is it a magnetic screwdriver?

 

[merlin el mago]

Yes.

 

[Salas]

What happens with plastic screwdriver or non magnetized metallic?

 

[merlin el mago]

Voltage also change using plastic screwdriver, also I think I have problems with CCS because set resistor 22R (I guess is too high resistor value) / 9.73V = 441mA, the load idle draws 130mA x 1.5 safety for peaks = 195mA + 70/150mA excess on top load = 345mA but in this moment I don't have other higher value of 10W resistor, I use 30VAC 30VA R-Core, 10.000uF 63V mains cap & IRF9610.

 

[Salas]

Look on oscilloscope if there is some oscillation on the rail so its your hand affecting as it comes near. See about grounding the sink if the MOSFETs are completely insulated first. But use the proper resistor also as you say you need.

 

[merlin el mago]

IRF9610 gone

 

[Salas]

Was it probably long gone?

 

[merlin el mago]

Checked the rest of semis: all are OK, changed R301 for 3R9 7W.

 

[merlin el mago]

Changed also 5K trimmer, attached pic scope set 0.1V 0.5ms. with real load.

 

[Salas]

Now what is on the scope it has a working 9610? What kind of real load? Are there any small caps across the load's rail?

 

[merlin el mago]

Yes new 9610, real load are two active xovers, each consummes 65mA idle.

 

[Salas]

Put 100uF across the rail at the xovers. Normal, not low ESR. See on scope again.

 

[merlin el mago]

I used 220uF in place of 330uF this caused the oscillation, I paralleled other 220uF to have 440uF the result in attached pic.

 

[Salas]

Very nice thin line now. You refer to C8 in the xover schematic I believe.

 

[merlin el mago]

Yes.

 

[nautibuoy]

I had a little time this afternoon and have, I think, finalised the setup and installation of my Salas BIB positive/negative supply pair.

I took AndrewT's point about transformer voltage and I've backed down the output voltages to 13V.

Everything seems very stable.

Back to the 'I think' comment; should I worry about a mismatch in the shunt current? On the negative supply I'm measuring 2.6V across R201, which equates to 382mA. On the positive supply I'm measuring 2.9V across R101, which equates to 426mA.

I'm measuring the supplies separately using exactly the same 47R load resistor (287mA load).

The circuit I'll be powering with the supplies is a 350mA load.

A 56R in parallel with R201 should more or less equalise them at the higher current if I need to balance them more closely? The mosfets have good heatsinking.

R101/R201 are both 4watt 6R8, am I correct in thinking that any parallel resistor can be of low power rating?

Thanks muchly

Ray

 

[Salas]

Try trimming for about 450mA on both. 5% mismatch won't be a problem. A higher value parallel resistor will share less power dissipation than the main one, yes.