Help with PS under load.

DF96 · 2012-11-19 1:00 pm

Do we yet have a circuit diagram of exactly what the OP has done? Without this we are all fumbling in the dark.

Mooly · 2012-11-19 1:11 pm

DF96 said:
Do we yet have a circuit diagram of exactly what the OP has done? Without this we are all fumbling in the dark.

Post #9

Unregulated supply with a 47uf reservoir cap and possible wiring problem of centre tap if it happenes to connect to the zero volt line.

JForged · 2012-11-20 3:48 pm

Hi Audio peoples.

OK, I am still waiting on the correct cap but I did with two 480uf's in series to get close.

Also I have some more pictures for you guys.

Here is the PS in the case.

An externally hosted image should be here but it was not working when we last tested it.

Here is my breadboarded rectifer. Looks ugly but i'll dress it up when it goes in the case.

An externally hosted image should be here but it was not working when we last tested it.

And here are the readings on it. The ripple doesn't occur until I put a lamp or some other kind of load on it.

An externally hosted image should be here but it was not working when we last tested it.

So it looks like even with the larger cap I am still getting ripple. I have yet to modify the rectifier section with a regulator but will probably be doing that when I have some time this evening. I know that some ripple is probably unavoidable but any time I connect an audio circuit to this I can hear the heavy modulation.

DF96 · 2012-11-20 4:01 pm

Assuming this has to drive the valve heater as well as the 'HT', a 47uF is almost no smoothing at all. Two 480's (470's?) in series is 240uF, which will give you about 7V ripple. To get below 1V pk-pk ripple you need 1500uF. The regulator can then clean this up.

Find out how to do a ripple calculation. It involves calculating the charge removed fromthe cap for each mains half-cycle, then dividing by the capacitance.

JForged · 2012-11-20 5:37 pm

Thanks DF96. I plugged in three 480 uf in parallel and the ripple was greatly reduced but now has movement to it.

Also, my scope will not see it under DC at this point only under AC. Anyone suggestions as to why this is.

I am relatively new to electronics and extremely new to scope operation.

Mooly · 2012-11-20 6:32 pm

JForged said:
Thanks DF96. I plugged in three 480 uf in parallel and the ripple was greatly reduced but now has movement to it.

Also, my scope will not see it under DC at this point only under AC. Anyone suggestions as to why this is.

I am relatively new to electronics and extremely new to scope operation.

The only way you will kill all the ripple is either with a regulator (although we're not sure there is enough "headroom" to work with for that) or an active ripple filter.

The scope is essentially just a voltmeter, always remember that. So the reason you can't see the ripple on the DC is because the DC voltage drives the trace off the screen. When you AC couple the scope you are left with just the AC component riding on that DC voltage which makes it possible to see and measure easily.

JForged · 2012-11-21 5:27 pm

Thanks Mooly.

Drifting off topic here a little bit, I have been digging around in the manuals for the 'scope trying to find a way to include some kind of reference grid or markers that sow the voltage at certain levels. Do you know if this is possible on any scopes?

Mooly · 2012-11-21 5:38 pm

Just looking at your pictures. So the scopes an "add on" for a PC ? I've never used one like that tbh so I don't know although it looks like you can read voltages off from the "settings" panel

I use the traditional CRT display type with graticule etched on the screen.

JForged · 2012-11-21 5:40 pm

Yea, I'd like to get one but money is tight. This was a usb scope for about $200. I'd like to get a nice techtronik scope some day.

Mooly · 2012-11-21 5:44 pm

I still think an analogue scope takes some beating and would take one any day over a digital. Bandwidth is everything, the one I use is a 100Mhz dual trace which is great for audio.

http://www.diyaudio.com/forums/head...le-ended-class-headphone-amp.html#post2075959

Mooly · 2012-11-21 5:51 pm

Like this one,
Hung Chang 5510 Oscilloscope 100 MHz 3 Channel | eBay

They call it a three channel here... it is really in all fairness and it can actually display up to 8 traces if you put a bit of spin on the description.

JForged · 2012-11-23 12:19 am

That would certainly be nice. Wife and I have a kid on the way so no new toys until we find out what kind of $$ we are talking about with the kid.

Back to the PSU.

After adding 2200uf of smoothing everything looks much nicer.

Thanks folks for all of your help. I'm on to the speaker forums for help with my next dilemma.

Mooly · 2012-11-23 7:44 am

That is looking better. Has it cured your hum or do we need to do a bit more work on that. Ideally it should be silent.

JForged · 2012-11-23 6:52 pm

Hi Mooly,

Very little hum if everything it turned all the way up with no signal. Running at normal listening levels with audio it is all sonic joy. Tis much nicer now. Thanks!

Mooly · 2012-11-23 6:58 pm

That's great

And if you ever feel the urge to try and reduce it a bit more....... you know what to do

Help with PS under load.

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