Q:Power Supplies for all Zen Variations?

[Peter Huang]

I built two 50W SOZ monoblocks with transformer 2500VA each some years ago. Finally I found 10-15W output is enough. Now I want to construct Zenlits and possibly other Zen variations mounted on the top plate of the existed SOZ and use the extra capacity of 2500VA transformer. I don't want to destroy the SOZ, so I arranged the power supplies as shown in the attached drawing.

I am not majored in Electronics. Is this arrangement OK?
Thanks a lot.

[AMV8]

Peter

No one else has replied so I will tell you how I would handle this.

You will have trouble if you connect the two grounds together.

I would get around that earth problem by keeping the split power supply as you have drawn it. The single ende power supply I would take from one half of the transformer. That is the mid point on the secondry and one side of the secondry and then use a voltage doubler to double the voltage. This willl automatically give you a common ground connection between the two circuits.

Don

[Peter Huang]

Hi, AMV8

I highly appreciate your kindely response.

With your idea, I wonder if the selected half of the transfomer will be unbalancedly overloaded and result noise.

I don't know what kind of trouble will happen while the two grounds are connected together.

It maybe too troublesome to tell me the principle or concept about the gounding problem, I have the heavy book "The art of Electronics". Could you or somebody tell me which section I should reference to?

Thank you very much.

Best Regards,

[AMV8]

Peter

The proposal I gave you will aviod any noise problems form the grounding.
I do not know the VA rating of your transformer, however if it is large enough the unequal loading on the secondaries will not cause any problems. ( Typical VA requirements for an aleph 30 or similar would be 400VA trandformer )
The solution I proposed simply aviods any grounding problems by using a common ground for both amplifiers.
If you have concerns then use two transformers. However what was proposed will work fine.
Don

[Nelson Pass]

I think it's OK, as long as you don't try to use both at once.

[Peter Huang]

I may want to use both voltage rails at the same time.
If I add a diode bridge as ground isolator, is it Ok?

Thank you very much.

Best regards,

[rafafredd]

I think it can be done if you use big caps to isolate the second bridge altogether. I mean, two big electrolytics in series with the second (added) bridge, like this (but much bigger caps for you application) :

[AndrewT]

Hi,
go back to post1.
The extra bridge at the top of the diagram does not work as a bridge.
It operates as a full wave rectifier.
Follow these two routes:
1 start at A- red wire to bridge - thro' diode - to load - to blue wire to ground - to centre tap B.
2 start at D - red wire to bridge - through diode - to load - to blue wire to ground - to centre tap C (=B).
Note, that neither route uses the lower half of the bridge. Only the top half gets used. You have inadvertently wired up a full wave rectifier. The highest voltage available is sqrt(2)*Vac of one secondary.

You cannot effectively use a doubler for high current loads. The voltage drops drastically as load increases and the component values rise enormously trying to cure the defect.

There is a solution.
Due to the very high capacity of the original transformer the primary has very few turns. The result is that the secondary also has relatively few turns per volt of output. It may be only 1 to 2turns per volt. 40T~=20Vac. You can get about 3Aac from each sqmm of wire. 1.6mm diameter enamelled copper has about 2sqmm and gives <=6.2Aac. After rectification and feeding a capacitor input filter the maximum continuous current is 3.1Adc.

It would be very easy to add on new secondaries for your extra amplifiers. Each extra supply would feed it's own bridge.

[rafafredd]

Yes, in fact the schematic I posted works as a doubler. But wait... There is another way over this also, if you can remove B2 and live with a little more riple on the first PSU. But... well, it still uses a doubler:

[rafafredd]

really, if you wanna use the extra current on those PSU, try another amp that needs a split psu... That´s the only way.