power supply problem

[marcoben]

Hi,

Sorry for my initial answer.

Toroidals FEED the power supply. So i went a step back to get basis right.
2 options: be happy with what you have or change the PSU unit completely.

change........buy DIY complete kit (or have it soldered and tested...few USS extra) or buy BEST components for the price you want to spend. And solder yourself. Test the capacitators before you solder them! So you know what you have bought.....GOOD or BAD components.

Tip: make a drawing and calculate your stuff. And check again. Then your plan will work.

71 Volt on Ac= 100 volt DC after rectification (quite high already).
Or is it 71 volts DC?? ...which is 50 volts AC (before rectification).

[Mooly]

Originally Posted by madtecchy

Im sure this is in the wrong section .... "Chipamps"??

It was, but now it isn't... thanks

[marcoben]

Oke. Good luck with fixing.

Remember; everybody has burned something!
Me also; this is the way to perfection...You carry on!
I try to learn from my mistakes.

In the end; my audio sounds better and detailed!

[goodsguys]

Hi. Thanks for the replies,.

I am measuring 72.5 volts across the transformer with my Mills multimeter set on ac, 49 volts dc across the smoothing capacitors, then 96 volts dc across the two wires which go to the positive and negative terminals of the amp boards. The amp boards are disconnected for protection just in case the power supply may have been faulty. Does this appear to be okay.

I am going to follow up on your suggestion and replace the power supply, new transformer, bridge rectifier and smoothing capacitors, put the old parts on ebay as there are quite a few Quad groupies on there.

I didn't get a reply to the idea of using several small capacitors in parallel rather than one large one. Is this a stupid question?

For the transformer should i get a toroidal 35-0-35, and what should the current capacity be, There is a 2.5 amp mains fuse before the Quad transformer.

Many thanks. John.

[Mooly]

There's nothing wrong with the Quad transformer.

A 35 volt toroid might give over the voltage you want simply because it will be specified as 35 volts at max current draw. You'll have to multiply the 35 volts by the "regulation figure" of the transformer which should be quoted and will be in the 5 or 6% region for a 250va transformer.

Lots of small caps. Some prefer that approach. A practical problem is that the wiring adds fractions of an ohm here and there and could mean that the caps nearest the bridge wiring wise do more of the work. The ripple current won't be spread equally.

Toroidal transformers draw huge switch on surges and for ratings above 300va a soft start circuit is recommended to prevent random fuse blowing. A 250 va transformer would probably get away with a T3.15A fuse (time lag delay).

[marcoben]

if you measure your transformer; it gives you 1 result=corrrect AC voltage.
THis is really important. Is this one 2 pieces transformator combined together to feed 2 PSU and than 2 power amp boards. Otherwise you don get this high output on AC.

rule 1 = 100 watt RMS per amp board= 200 watt toroidal , my advice; take 2x 300 watts toroidal or 1 x 500 watt.

to get 49 volts DC= ac voltage x 2square root (ac voltage x 1,4142) with 35 volts it will give 49,49 volt DC. take 34 volt or 32 volts AC (antekinc.com) example: type AS-3434 AS versions have purple ground wire. sound better.

Try to find lowest and highest working DC voltage for Quad power amps. if it is 40-49 volts DC...try to get 44 to 45 volts DC. Then you are SAFE. And it will work.

If DC = below 50 volts ....so max 35 volts AC you can use 2x of this kit

POWER SUPPLY BOARD FOR AUDIO POWER AMPLIFIER AMP DIY KIT | eBay

i use them als to feed my L20 power amps (350 watt RMS 4 ohm)

Good luck.

First you measure and calculate.....and again.

[goodsguys]

Hi. Many thanks for all the replies.

I will post the results once the parts arrive.

Many thanks. John.