Power-One power supply mod

[bushtech]

Audioguru: Please have a look at my first post on this thread for a look at a dual rail supply But if this is very unusual am I wasting my time building a dual rail supply? It certainly would have been useful when I built my quad opamp version of the muffsy phono preamp. Instead of stuffing around with 2 x9V batteries soldered and taped together


Well, considering that Liquibytes and the Chinese designs share a common ancestor, I'm wondering if there is any advantage in buying the chinese kit and modifying it a la the improved design, or is that a slippery slope I will be venturing on.

 

[Audioguru]

I have made many preamps but they all used a single positive supply without a negative supply.
All opamps will work from a single positive supply if the input is biased at half the supply voltage and coupling capacitors are on the input, output and feedback.

The preamp uses plus and minus 12V at a very low current. It can easily use plus 24V at a low current.
Why do you need plus and minus 30V at 3A?

 

[bushtech]

lol. I didn't even know that, I just followed the muffsy design which called for 2 rails.

Well we have now moved very far from ordering a $5 supply from China and sourcing some ancillaries to having a pcb made (at a cost which is still unknown but it won't be as low as $5) buying all components and sourcing all ancillaries. I suspect I am looking at a 10 fold price increase.

Need to review this

One alternative is buying Chinese kit and following Kokotov's fairly detailed build and then accepting and setting the power supply to supply a max of 1.5A. It will be a very good learning experience. And, heh, anything that can go wrong on this board has already happened to somebody somewhere and dissected ad nauseum

 

[kellys_eye]

If you purchase TWO power supply kits and they are built as 'isolated' outputs (i.e. no common ground) then you can chose which wiring method you like and either use them singly, in series (additive) or as a +/- source as you wish simply be wiring the output terminals accordingly.

When constructing them either use two separate transformers for the AC input or a single transformer with two individual AC output windings.

 

[bushtech]

Thanks kellys_eye. Very good idea. Can probably do some fancy footwork with dpdt switches an suchlike.

Still pondering this lot.

 

[bushtech]

Well, the plot has thickened to pea soup consistency. I am busy eyeing this version which comes with a display. I see they have lowered their sights to 28V and 2A. Interestingly it uses an A1941 power transistor and no IC's. The good old 7824 still there which I suppose could be changed to a 7812 to drive a normal PC fan.

https://www.banggood.com/0-28V-0_01...-p-1060253.html?rmmds=detail-left-hotproducts

Busy checking to see if this an update of a design, a regression to an older design or a completely new design. Whichever I just hope it doesn't have any problems of the original design.

@Audioguru: You are familiar with the old design to the point where you are probably sick of it. Please give this a glance and see if anything catches your eye. Thanks

 

[Audioguru]

The new Banggood power supply has no ICs so its voltage and current regulation must be awful. There is a "doc" file about it which might have some detailed spec's but my pc no longer has Microsoft Word program to see it.

Yes, I am sick of the original old power supply circuit. I have dealed with it for 13 years.

 

[bushtech]

Thought so lol. Libre office opens it, but anyway it just contains instructions about the display set up.

Sad to hear that it's regulation is probably awful.

More navel contemplation required

 

[bushtech]

Update time:
Well, after a lot of headscratching I took the plunge and ordered the el cheapo kit from China (Audioguru: stop banging your head on the desk) Partly because it's cheap and that's rather a large factor in a retired guys life, and partly because I think that it will be a very good learning experience for me. I will be leaning heavily on paulv and kokotov's blogs for guidance re upgrading resistors, IC's etc.

Will take a couple of weeks for the stuff to arrive.

I have found a nice toroidal: http://www.communica.co.za/Catalog/Details/P4292902673 I have never played with a toroidal before. They say nothing about input so I hope it's 220V in. Will have to phone them Monday.

 

[Audioguru]

The voltage from the little transformer is too high for the opamps in the cheapo Chinese kit. but then the opamps will burn out before the overloaded little transformer burns your house down.

 

[bushtech]

@Audioguru.: Thanks for replying. I am sure you are dreading what this thread could turn into.

Are you talkig about the transformer I chose?
I am battling to make sense of the massive amount of info on these power supplies. I am planning to replace the TL072's with TLE2141's. With what little I understand after wading through pages and pages of stuff I thought this would solve that problem

 

[bushtech]

And I am planning on using calibration trimpots to limit how high the Volts and Amps can go.

 

[Audioguru]

Banggood do not know Engrish or they do not know anything about this kit. It IS NOT the original Hyland kit, instead it is a new one with a display. I have not seen its schematic or its parts list. The photo does not show any opamps.
The original Hyland kit costs almost nothing and uses the horrible Greek circuit.

The little 50VA toroidal transformer will burn up when it powers the new kit and the output of the kit is 2A.
The peak voltage from the transformer is 1.414 x 30V= 42.4V that the rectifier bridge uses to charge the main filter capacitor. When the DC output of the kit is 2A then the transformer must supply 42.4V x 2A= 84.8VA.

 

[bushtech]

Thanks Audioguru. Should I then rather be using the one output leg of something like this: http://www.communica.co.za/Catalog/Details/P1308330058

 

[bushtech]

Oh and I have ordered the original Hyland/Greek kit not the new one

 

[Audioguru]

The voltage from the 2x25V transformer is too low at 25V and it is too high at 50V.
You need a transformer that produces 28V at 119VA or 30V at 127VA.Then if the circuit is modified to the latest improvements it will reliably produce 30VDC at 3A. But I do not think the larger more reliable parts will fit on the Chinese pcb.

 

[bushtech]

Thanks Audioguru, now I have something to go on. Which components are you thinking of.? I am quite a good McGyver.

 

[bushtech]

Apologies for this question but is there any leeway in the VA numbers?

 

[bushtech]

This is the closest I have got so far: http://za.rs-online.com/web/p/toroidal-transformers/6719135/
I don't know if the 120VA is per leg or total

 

[hevans1944]

Looks like its 60 VA per secondary winding, or 4 A at only 15 VAC. That's waay too small for a 30 V, 3A power supply. See @Audioguru post #36.

Want some (more) advice? Scrap the idea of using Chinese parts or kits. Find a decent schematic for a dual-output laboratory bench power supply of whatever voltage and current you require. Order the necessary parts, including any "specialized" ICs, from a reputable electronics distributor. Breadboard it, design a PCB and have the PCB manufactured (China okay for that... usually). Mount everything in a nice case with a real power cord, switch, and fuse or circuit breaker. Add bells and whistles, like digital or analog panel meters, 5-way binding posts for outputs, slide-out ground straps for the binding posts. A year from now when you have it finished you will have something you can be proud of and a useful tool for your electronics hobby.