Phono 1 MC

[Daniel Quinn]

Cheers

[Latteman]

Daniel, I put the transformer in and it gave , by my meter, 60V ac to the rectifier and the output to the regulator is 79V dc. I will connect up to the turntable and let you know how it goes. I probably won't manage to start on the upgrade for a while as I am going down to Bristol to get re-acquainted with my 3 grandchildren. I will keep you updated with my progress.

Those voltages sound high to me ??

[karatestu]

Seem very high to me too. Should be 25-0-25Vdc after the rectifier if transformer has 18Vac secondaries wired in series with the join being 0V. The regulator will regulate it to 20-0-20V whatever the input voltage is up to a voltage difference of 37V between input and output. After that it will go pop. With a much higher input voltage than needed all you are doing is creating lots of heat as the regulator has to drop a certain amount of volts at whatever the current draw of the amp board is (I haven't measured it yet).

[floydfan]

Sounds high to me also but I am not that good with electronics. The transformer is from Daniel's P1 and I have connected it up to the turntable and it sounds fine. i measured the mains going to the transformer and it read 236, which I thought was ok as I may not have made good contact as I was being very careful not to short it. I measured the voltage going to the rectifier as 60 V. I thought that 25v and 25v in series should give me 50v ac going to the rectifier. I measured the voltage going to the regulator by connecting the probes to the solid bars coming from rectifier, so I assume the capacitors will some effect.
Excuse me if I am talking nonsense. My past electronic projects were carried out in monkey see monkey do system: the doc told me what to do and I did it with little knowledge of the theory.

[SteveTheShadow]

If there is no load on the transformer secondary when you measure it, the voltage will be high. A 10% regulation spec (which most are) will give 5V extra on each of the two secondaries going to the rectifier. Add these together and you get 10V too high, add your 10V too high to the 50V it’s supposed to be and you get 60V rms. Feed this to the cap input supply and you will get 84V coming out, which is + and - 42V . This is a difference of 22V or so, input to output on each reg chip.

[Daniel Quinn]

It worked fine for me , although I never measured it .

The boards and caps were fine as well.

[floydfan]

My system sounds the same as usual. I am just interested in what's going on. I think from what Stevetheshadow says everything is ok as I did measure under no load conditions. I will get going on the upgrade when I get back from "down South".

[Ithilstone]

Are you sure it is not 30-0-30 VTX transformer ?

[floydfan]

The transformer is a vigortronix 30VA Secondaries 0-25 0.60 A The same as was in my P1 MC.

[floydfan]

I have the parts to build a new power supply for my Phono 1 ie a 500VA Noratel transformer,Luxon 10,000 uF capacitors,a KBPC 3504 rectifier and an ABS box. Next step is to stick it all together, the transformer is very heavy so I am not sure of the best glue to hold it. I have UHU glue which the Doc said was good enough to stick the lid on but may be a bit weak to hold the big transformer in the box. I know the Doc used some sort of Bison glue but I am not sure which one. Maybe Bostick will do.
I've had another thought; I am not sure if it matters which rectifier I should use so I picked one which can handle high PD and current and hoped for the best.
Again any comments welcome