Rectified question

[kyrochan]

What????
How is possible that the voltage after my rectifiers (kbpc3510) is of 20V DC while the trasformers secondaries are at 24VAC??? ...and sensible AC voltage is misured at the rectified outputs?

[Giaime]

Well, you can't measure voltage just after a rectifier without filter caps. You'll get a strange waveform that's not recognizable by neither the VAC test or the VDC test of your multimeter. So the VAC shows that you still have big ripple in your supply without caps, and VDC senses that the strange waveform might have some DC components since it is all-positive.

Add caps and you'll see..

[kyrochan]

Thank You, grazie,
Why it happends?
Se la risposta è difficile e vuoi usare l'italiano fà pure... =)

[Giaime]

Sorry for not italian members but...

Ciao! il problema è che la forma d'onda subito a valle del rettificatore ha sia componenti alternate che continue. Continue perchè non va mai in negativo, quindi ha una componente continua pari al valore efficace della sinusoide in ingresso (Vpeak / rad(2)), alternata perchè non è ancora livellata è c'è molto ripple. Quindi solo il (o i) banchi di condensatori possono risolvere la soluzione... Casomai prova a darci un'occhiata con un oscilloscopio, oltre a ciò che ti ho detto, ci troverai anche molto rumore in alta frequenza (risolvibile parallelando ai condensatori di filtro dei buoni condensatori di piccolo valore - diciamo 100nF - in plastica). Ricorda di non fidarti delle letture del test VAC del tester - in fatti quello che fa è far passare la corrente attraverso un banco di diodi, quindi ogni componente continua passerà inosservata e verrà misurata dallo strumento! Inserisci sempre un condensatore di plastica dal generoso voltaggio in serie al DMM quando misuri in alternata... Sennò ogni componente continua falsa la lettura...

What are you building? Let us know!

[kyrochan]

I'm not so in the measuring instruments I have to study for my measurement exam.... AAARGH...

This is my PSU scheme at the moment any idea to improve it?

It feeds a SE single stage Pass' Zen Amp in its second revision, in this revision the Zen don't use a regulated PSU, in my opinion reguleted psu is a contraddiction in terms for Single Stage amps...I think the fet should be strictly near as possible to the trasformer... this project uses only 2 fet one for the amplifier stage and the other beetween the xformer and the other fet, the first fet is used as costant current source to feed amplifier section that works in a pure class A.
The regulator in the following version of Zen amp is needed only to prevent the poor quality of 220 electric net...
The strange thing is that to obtain similar audio results in the zen series with regulated PSU you should go ahead untill the version 5 when the zen become pushpulled and its Psu section become heavier....
So i'm going to think that probably if I reach a regulated and stable 220 before the xformers it could be the final mantra experience in ZenAmp I also prefer the second version of this amplifier becase it don't care of input impedance it is really low (1kohm) but with a "thoughted" preamp this factor should not be a problem...

Any idea to have a stable rocking 220 before the transformer?
Any idea for a good pre?

[Giaime]

Hi! I saw you also on www.videohifi.com!

What is that second rectifier bridge in the schematics? I can't see its purpose. For me it's not good since it is rectifying some secondary current and send it to the earth ground. You cannot do that: between the amp chassis and earth there will be a voltage (because there's current passing, and real wires have finite resistance): not good! If there's a purpose, let me know...

To get a steady 220VAC, get a line conditioner. Go on www.audiocostruzioni.com, there's one for sale.

For a good pre, check www.tnt-audio.com. On the "Autocostruzioni" page, you can find a simple tube pre that seems to be good sounding. If you don't want to do this, I still strongly suggest you a tube pre.

Ciao!