WAD Phono2 power supply.

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shane
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Re: WAD Phono2 power supply.

Post by shane » Tue Jul 04, 2017 2:04 pm

Everything drags down to the same level. 259 ht, 2.5v drop across the current supply. Bridge output dropped to 275, and about 10v dropped across the 100r resistor.

There's a couple of volts discrepancy in those figures, but I'm going from memory.
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Re: WAD Phono2 power supply.

Post by pre65 » Tue Jul 04, 2017 2:05 pm

shane wrote:
Tue Jul 04, 2017 1:55 pm
Hmmm. Choke out of circuit. Hums like a mad bugger.

Not going to be able to do any more investigations for a week now due to work schedules, but I'll look for a better choke in the mean time.
Try looking at the Hammond C clamp chokes on Bluebell web site, the DCR is listed.


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Re: WAD Phono2 power supply.

Post by shane » Tue Jul 04, 2017 2:09 pm

Thanks Phil, I'll have a look.

Nick, one thing I forgot to ask. Further back you mentioned the 50r sensing resistor but in the circuit it's 60r. Would that have any effect?
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Re: WAD Phono2 power supply.

Post by Nick » Tue Jul 04, 2017 2:12 pm

Typo, 50R will pass more current through the CCS.
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Re: WAD Phono2 power supply.

Post by Nick » Tue Jul 04, 2017 2:15 pm

May be worth increasing the 60R, 30ma is in reality far more current then you need to shunt for a circuit that’s drawing 5ma. Try 100R of 120R and see if that improves the voltages. Pulling 30ma will be pulling the supply down more possibly than it can handle. I notice you are using a blue LED, I used red, that will also increase the current you are passing as well.
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Re: WAD Phono2 power supply.

Post by shane » Tue Jul 04, 2017 5:10 pm

That makes sense. Just beginning to get my head round how the current supply works. Hope I can sort it without changing the choke. Low DCR = bigger choke = won't fit in the case!
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Re: WAD Phono2 power supply.

Post by shane » Wed Jul 26, 2017 8:50 pm

Having rebuilt the HT current supply on strip board instead of tag strip it seems to be behaving itself, and I'm getting about 20v drop across the mje350. The good news is that the 100Hz hum has gone. The bad news is that I now have what sounds like a 50Hz earth hum.

I just had a look at the build instructions for Phono3 and PSU3, and as far as I can see they have the two earth pins on the Phono3 board connected to the chassis, which is then connected via the umbilical to an earth connection pin on the PSU3 board, which in turn is connected to PSU3 chassis via a 100R lift resistor and then to mains earth. Thus, to my surprise, it appears that the chassis of Phono3 is earthed through the 100R resistor.

On my version (which is based around a Phono2 board, but they're the same to all intents and purposes), I'm using a screened umbilical which is earthed to the Phono chassis at one end and the PSU chassis at t'other. The two earth pins on the Phono board are connected to their own lead within the umbilical and thence to the common return in the PSU which is connected to the PSU chassis via the lift resistor, so the two cases and the umbilical screen form a complete earthed whole while the earth pins of the Phono board, the HT supply and heater supply returns are connected to the lift resistor.

Have I introduced a hum loop somewhere?

Obviously, the way to find out is to rewire a la PSU3, but I'm not going to get a chance to do that for a week or so, and it's humming away in the back of my mind in the mean time.
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Re: WAD Phono2 power supply.

Post by shane » Thu Sep 07, 2017 2:06 pm

Summer it seems has come and gone, peace has returned to the house and this project has been sitting on its shelf under the telly untouched since the end of July. In that time I've been pondering, and I've come to the conclusion that I probably don't have enough voltage into the regulator to make it work, especially since the gas tubes are sitting about 10v above where I want them.

Whilst I was out boating and so on, Steve was reviving his best ever amp which brought up the subject of Nick de Smith's MJSR kits. Lightbulb moment. A quick PM to Nick revealed that he had a couple of kits left, so I just spent a happy if slightly cross-eyed morning putting one together.

With its normal compliment of 40 zeners, this gives about 235v. Phono 2 wants 250, so I've substituted a couple of flying leads for the 10th diode up in the chain, for no other reason than because it's in the bottom left corner. These flying leads will go to the piece of strip board which currently holds the 6.3v heater regulator, which has plenty of room for 4 spare zeners.

Second lightbulb moment. Since D10 sits at around 50v, is there any reason why I shouldn't tap the heater supply dc lift voltage from here? It won't draw any current, but would it be likely to introduce noise?
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Re: WAD Phono2 power supply.

Post by shane » Tue Nov 14, 2017 2:45 pm

Just installed the MJSR. 250v delivered to the Phono2 board. Thank you very much.

It still hums. 50Hz, just loud enough to be intrusive at normal levels. Definitely psu related as if I cut the HT, the hum stops instantly and I get about 20 seconds of blissful music.

I’m also still getting strange voltages.

Image

The choke I’ve started off using is 15H with a DCR of 488, and I also have a 10H, DCR 212.

With the 10H choke, I get 225.7 AC at point A, the tx output, 261.5 out of the bridge at point B, 258.4 after the 100R resistor point C, 251.6 after the choke at D and 249.9 out of the MJSR at point E.

Substituting the 15H choke o get
A. 226.6 AC
B. 267.5
C. 264.1
D. 250.0
E. 248.9

In both cases the MJSR is only dropping about 1.5v and the total current draw through the 100R is about 30mA. I bit height but I can’t set the current on the MJSR.
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Re: WAD Phono2 power supply.

Post by Nick » Tue Nov 14, 2017 3:21 pm

Does the zener string have its own load resistor, or is it meant to be added?
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Re: WAD Phono2 power supply.

Post by shane » Tue Nov 14, 2017 6:24 pm

Nick’s original circuit here: viewtopic.php?t=6204 . Go to the second one halfway down the page.

Phono 2 itself draws about 5mA, so about 25mA is being shunted down the Zeners. Should be nearer 15 to 20, but not too far off.
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Re: WAD Phono2 power supply.

Post by shane » Tue Nov 14, 2017 6:33 pm

While swapping the chokes over I measured the transformer and bridge voltages open circuit. Transformer gives 236.5, the output of the bridge was 321.3.
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Re: WAD Phono2 power supply.

Post by Nick » Tue Nov 14, 2017 6:44 pm

That all sounds fine, however we dont know if those are steady DC voltages or have ripple. Try measuring the AC voltages at each point (assuming you don;t have a scope).
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Re: WAD Phono2 power supply.

Post by shane » Tue Nov 14, 2017 8:47 pm

Tomorrow’s job, dig out ‘scope from darkest recessed of shed. Then see if I can work it.
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Re: WAD Phono2 power supply.

Post by Nick » Tue Nov 14, 2017 9:01 pm

shane wrote:
Tue Nov 14, 2017 8:47 pm
Tomorrow’s job, dig out ‘scope from darkest recessed of shed. Then see if I can work it.
Make sure the scope is on AC input and probably x10 probe to protect the from end from the voltages.
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