power supply help

[johndoe]

hi im very new to this ive got a "SC-480 50W Amplifier Module Kit Version 2", "POWER SUPPLY KIT TO SUIT SC-480" and "50V-0-50V 300VA TOROIDAL TRANSFORMER" all from jaycar. my goal is to make it sterio by getting another amp and power supply but i only want 1 transformer.
ive puged the transforme to the power supply but im getting 70v from the 40v - 0v (140v + - on both +-)it says i only need 40v have i got the rong transformer?
many help please

cheers

Josh from Kiwi land

[ostripper]

You should get VAC x 1.414 or in reality 68-70V dc from
your amplifier PS.

BTW- above is the Prof. leach power supply (which also uses
50-0-50 tranny.

check the secondary (3 leads- white,black, white..etc)should have
100+ VAC between the whites. That does sound like too much
voltage for 50w amps.. you need 30-0-30 Vac x 1.414 = +- 42vdc
or you might blow your amp. What you have now would work best with a 120w amp kit like the leach.
OS

[joshy]

thanks for the quick reply, as im new to this, the guy in the shop said if i wired in parrail it would work??(i think thats wat he said)
so if i get the 30v-0v-30v i would be ok? (1 transformer 2 power supplys 2 amps?)40vdc?

[ostripper]

Think the guy in shop smoked something.. If you wire the secondaries in parallel you will only get a single supply..
Is the amp single ended one, 40v power tap, or a standard
AB dual supply (V+ , V- , AND ground terminal).

IF the latter is true your best bet is to get the right
transformer 30-0-30 VAC @300VA. A picture/link is worth a thousand words (or amplifiers)I'll be able to tell in a second.OS

[AndrewT]

Hi,
a 50-0-50Vac transformer cannot be wired in parallel. The centre tap prevents parallel operation.
50Vac gives ~75Vdc and this would be used to power a 200W into 8ohm amplifier. 300VA would be just perfect for that.
The shop has sold you the wrong transformer. Take it back for full refund and ask for travel expenses.

50W into 8ohm requires about 25Vac to 30Vac transformer. This can be a centre tapped 30-0-30Vac or a dual secondary 0-30+0-30Vac. To supply two 50W channels you need between 100VA and 200VA and it will do no harm to go slightly bigger but will cost more for a very tiny performance improvement, if any.
If the amplifier is capable of driving both 8ohm and 4ohm speakers then it becomes a 100W into 4ohm amplifier and the transformer VA rating should be doubled to between 200VA to 400VA for stereo.

[ostripper]

by andrew t. :50-0-50Vac transformer cannot be wired in parallel.

That is the case with some trafo's but some of the newer one's
(antek,MCM-toriod)
have 2 CT wires [50-0-0-50] dual sec. which can be wired in this manner,
infact they even rate the secondaries wired in parallel.
Here is what he needs:http://www.antekinc.com/AN-3230.pdf

OS

[Greg Erskine]

hi johndoe/joshy,

I have built a few of these. You need a 28-0-28 VAC transformer this will give you the required 40-0-40 VDC. I would normally use two 160VA transformers but if you want to use one you should ideally get one 300VA. Smaller ones will still work but may get hotter and drop a few more volts under load. Yes, you will probably get away with 30-0-30 VAC.

I think the guy in the shop was saying to parallel the 2 PSU modules to the secondaries of your single transformer, not parallel the actual secondary windings.

The capactors in the PSU kit will not handle 70 volts for very long as they are probably rated for only 50V.

I was able to get these amp modules for $12.50 and $9.00 for the PSU modules. I was surprised at how good they sound for $22. So keep going.

BTW: Get one of the moderators to fix up your multiple usernames. It's not allowed.

regards

[AndrewT]

Originally posted by ostripper
centre tapped or dual secondary

That is the case with some trafo's but some of the newer one's
(antek,MCM-toriod)
have 2 CT wires [50-0-0-50] dual sec. which can be wired in this manner,
infact they even rate the secondaries wired in parallel.

Hi Ost,
if the two centre tap wires are connected then one cannot connect the windings in parallel.
If the two "pseudo centre tap" are not connected then it is a dual secondary transformer and the windings can be either parallel connected (if identical) or series connected ( do not need to be identical)