Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

[Audioguru]

The Chinese kit had a 5V1 Zener diode for D7 since it used TL081 opamps. The new opamps use two diodes in series instead. A Zener diode is used with reverse polarity but you installed the two diodes backwards also with reverse polarity. Reverse the two diodes so that their cathode ends are at the negative voltage and they will limit the voltage to -1.3V. On a multimeter a 1N4148 diode should measure 0.6V to 0.7V on Diode Test, your "894" is too high.

 

[bushtech]

In the photo above the cathode ends of the diodes are pointing to the negative afaik. Am I wrong?

The 894 reading is the reading over the 2 combined diodes

 

[Audioguru]

The photo shows the cathodes of the diodes at the cathode end of the old Zener diode D7. But a Zener diode is used in reverse mode, ordinary diodes are used in forward mode. Yours are backwards so turn them around.

Use an ohm meter to measure the pcb trace that connects the anode of the D7 zener diode to pin 4 of U3. That should be the cathode ends of the diodes.

You measured "894" but what? Volts or Ohms? The two diodes in series should measure about 1.2V to 1.4V of forward voltage on a diode test when not in the circuit.

 

[bushtech]

Thanks a mil Audioguru. Looks like it's working now. Getting -1.4V on pin 4
The 894 will be 0.894V measuring across both D7 diodes with DMM in diode function. When I pulled the diodes to swing them around I measured them and and I did get about 1.2 V

 

[bushtech]

St. Edd

My beta version of transformer winding, now giving 12.1V AC

Now where do I go from here? Just a bridge rectifier or is more required? The meter draws <20mA and requires a supply of 4.5 to 24V

 

[Audioguru]

When you feed 12.1VAC to a bridge rectifier then at a low current the output of the bridge rectifier is pulses of about 15.7VDC. The meter probably needs smooth DC so add a 100uF/35V capacitor to the output to smooth it.

 

[bushtech]

Brilliant Audioguru Thanks

In my meagre supply of electronic components I have 220μf 35V caps. Will that work?
Then for a dummy like me, how do I wire it up, in series in the positive line?

 

[Audioguru]

220uF will be fine as a filter for the 15.7V pulses. Connect its (-) wire to the (-) wire of the bridge rectifier and connect its other wire to the +15.7VDC that you are smoothing.

 

[bushtech]

Great, thanks a mil Audioguru

 

[bushtech]

Display working great with independent transformer winding, bridge rectifier and 220μf smoothing cap:

Thanks again 73's de Edd and Audioguru

 

[bushtech]

Audioguru
I think the power supply might be working now but I am still scared that the opamps might have been damaged during my short circuits saga.

Here is a set of voltages taken of the opamps in circuit:
Both pots set to zero



Please have a look if these Voltages are as expected.
Bit dubious about U3 pin 7 at 32V and U3 pin 5 at -1.1V

Thank you for your endless patience. Hoping we can put this saga to bed soon

 

[Audioguru]

Your meter looks nice and bright and your voltages are good and normal.
U3 pin7 is fine at the unregulated voltage of 42V minus the 10V of zener diode D13.
U3 pin5 is fine because it does not have an offset adjustment pot.

 

[bushtech]

Thank you so much for all the help Audioguru.

Now for the tricky job of shoehorning it into a box

 

[Audioguru]

The heatsinks need air circulation. I can't remember if you are mounting the heatsinks outside the box or if you are using a fan.

 

[bushtech]

I am going to be using a fan and shooting for forced air ventilation straight onto the heatsink. Will be posting some photos

 

[bushtech]

Heatsink mounting:

The idea is that the fan is going to blow into the box straight onto the 2N3055's. The heatsink will be insulated from the rest of the box so all air goes onto the heatsink and forced up and out:

 

[bushtech]

Do you place your fuse before or after the main switch, ie between power plug and main switch or between main switch and transformer?

 

[bushtech]

Progress report

My build so far. Still need to pick up a 10 turn pot on Wednesday, so front panel on hold. PCB will be mounted vertically between transformer and big cap. Sure would appreciate it if somebody would tell me if I'm making some monumental stuff up somewhere

 

[Audioguru]

The fuse should be in series with the electrical input and the on-off switch that feeds the transformer.

 

[bushtech]

Thanks Audioguru
Fuse between power plug and switch in live line. I am using a double pole single throw switch so I am switching the neutral as well.

Question: Now that the power supply has been weaned off the series lamp I am blowing 0.75A slow blow fuses when I switch on. Is this the correct rating of fuse? Power at home here 238VAC.

And the fuses say ATE + some logos and CQ on one side and 0.75A 250V on other side (Glass fuses btw) Are they slow blow?

Thanks