WAD Phono2 power supply.

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shane
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#91 Re: WAD Phono2 power supply.

Post by shane »

Will do!
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#92 Re: WAD Phono2 power supply.

Post by shane »

Hmmm. Perhaps it’s just a figment of my imagination. AC voltages are

B. 5.75V
C. 1.63V
D. 9mV
E. 5mV

The scope on point C agrees. This is .5V/div. , and on point E it gave the same waveform a bit rounded off at about 1mV. Crap photo but you get the drift.

Image
The world looks so different after learning science. For example, trees are made of air, primarily. When they are burned, they go back to air, and in their flaming heat is released the flaming heat of the Sun which was bound in to convert air into tree.
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#93 Re: WAD Phono2 power supply.

Post by Nick »

Where is your 0v point connected? Can you show the actual wiring and connections especially where the 0v point is in relation to the link between the bridge rectifier and the -ve of the first cap?
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#94 Re: WAD Phono2 power supply.

Post by shane »

The HT bridge, caps and 100r resistor are all mounted on strip board with short jumper leads to the choke. The strip board also carries bridges and caps for two 9V supplies, one for the heaters and one for a relay that connects the two 9V transformer windings together. There are two umbilicals to the other chassis which contains the Phono2 board, the MJSR board and the heater voltage reg.
One umbilical carries the heater supply with its screen connecting the two chassis earths. The other carries the HT and the leads connecting the switch to the relay, with its screen acting as the 0V HT return. This is isolated from the chassis and connects the earth terminal of the MJSR board to the 0V rail of the stripboard. The 0V stripboard rail is connected to mains earth via a 100R resistor.

Image

Image

The HT budge is just visible above the gap between the second and third caps, and the 0V connection is just out of sight on the edge of the board next to the left hand cap. You can just see the yellow and green lead which goes off to the earth lift resistor.

Point B is the top leg of one of the bridge diodes, point C is the top of the 100R resistor which is mounted vertically right next to the bridge, point D is the output terminal of the choke and point E is the output terminal of the MJSR board.

When I took the voltages and ‘scope readings earlier I was using a 0V terminal on the Phono board as the earth ref and putting the scope probe on point C, the 100R resistor. Moving the earth ref to the 0V connection on the strip board gives the same voltages but a rather different waveform on the scope. Again, crap photo.

Duff bridge?

Image
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#95 Re: WAD Phono2 power supply.

Post by Nick »

That looks like the cap charging current. What you need to make sure is that the wires from the bridge go to the +ve and -ve of the first cap and nowhere else, and everything from that both +ve and -ve come from the cap. The idea is that the charging current in the first cap will create a voltage across the wires, if you are connecting ground in one of those wires, you will see that voltage. Ideally, the -ve terminal of the first cap will be the star point. If not connect the -ve of the first cap to the negate of the 2nd cap and make that the start earth point. Think in terms of current through wires and what you are calling 0v.
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#96 Re: WAD Phono2 power supply.

Post by shane »

Looks like I might need to ditch the strip board in that case. Bit of a rethink needed.

Leaving the hum aside, is the fact that I’m only getting a couple of bolts drop across the MJSR board significant?
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#97 Re: WAD Phono2 power supply.

Post by Nick »

Well, the voltage dropped across that will be the input voltage - the zener voltage.

Generally I would avoid strip board for power supplies. point to point or PCB gives you better control.
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#98 Re: WAD Phono2 power supply.

Post by shane »

It’s going to be a week or two before I’ll have time to do a rebuild. Meanwhile, as ever, thanks Nick. Your help is invaluable and much appreciated.
The world looks so different after learning science. For example, trees are made of air, primarily. When they are burned, they go back to air, and in their flaming heat is released the flaming heat of the Sun which was bound in to convert air into tree.
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#99 Re: WAD Phono2 power supply.

Post by shane »

Would there be anything to gain from increasing the values of the three 100uf caps?
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#100 Re: WAD Phono2 power supply.

Post by Nick »

100uf will probably be more than enough. The larger the values, the more the peak charging current (and the shorter time over which the spike happens), if you want to increase any, leave the first one as it is and increase the later ones.
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#101 Re: WAD Phono2 power supply.

Post by shane »

Sorted!

I got a bit disillusioned when I finished this thing and couldn’t get rid of the hum, so it’s been sitting gathering dust for two years whilst the music’s been handled by a Pi courtesy of Tidal and IDAGIO.

Today though, I looked at it staring at me from under the telly and tried to remember what was inside and why it might not be behaving. The main thing I remembered was that the statistical voltage regulator (thanks Nick/Jack) hadn’t been measuring correctly. Took the lid off and measured again and V-in was only about 1v above V-out, at around 245v.

The quoted HT for Phono 2 is 240v, but I figured it probably wouldn’t hurt to drop it a bit, so I took three diodes out of the zener chain. After a brief twiddle of the regulator pot , bingo! 250V in, 238V out. Nick’s leaflet with the MJSR suggested that it should drop 12 -15V so I’m in the right place.

Back to the sitting room. Plug in. Warm up. Blissful silence!

Took a while, but I got there. Sounds nice, too.
The world looks so different after learning science. For example, trees are made of air, primarily. When they are burned, they go back to air, and in their flaming heat is released the flaming heat of the Sun which was bound in to convert air into tree.
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#102 Re: WAD Phono2 power supply.

Post by IslandPink »

Excellent !
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#103 Re: WAD Phono2 power supply.

Post by Mike H »

Yep. :thumbleft:

So simple as it turned out.
 
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