Candidate PT For Mono Chipamp (LM3886)?

[mydementia]

This one's on clearance at PartsExpress...
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=129-075&ctab=14#Tabs
Will it work?
Looks like it has a pair of secondaries 16-0-16 rated at 0.5A on each side... I can't tell how much current the LM3886 'wants' from the data sheet... I see plots with supply voltage vs current - these currents are all in the 60mA range... then I see the 7A min in the table at the beginning...

Thanks in advance!!
Mike

[teemuk]

The current draw depends on the amount of output power as follows:

I = SQRT(P/R)

Where P = output power and R = speaker impedance. For details concerning the amount of output power check the graph titled "Output Power versus Supply Voltage" at page 14. Remember to convert the "average continuous" output power rating to peak power by multiplying it with 2. The result of the equation will be at least few amperes.

The currents in the mA range are quiescent currents (meaning how much current the amp draws at idle when its "doing nothing"). The chip begins to limit output current after 7A.

The VA rating of the transformer - calculated by multiplying the total secondary voltage (in RMS) with current - should be at least 1.5 x the output power – preferably even two or three times higher. 2 x 16V times 2 x 0.5A is only 32VA and it isn't going to cut it. Minimum for a 60W amp is about 90VA and recommendation is about 120 – 180 VA. You can skimp on the rating if you invest in filter caps with more capacitance.

[darwindeathcat]

Hey there, I went over to the description of that tranny at partsexpress. It actually has THREE secondary windings, one of which is 35VAC at 4 amps (VA = 140). It does not specify that that winding is center-tapped, however. In fact it is very vague about the center-tapped-ness of the whole thing, except for the winding you mentioned (16-0-16 at .5 amp), but, looking at the picture, there are A LOT of black wires hanging out there, and only a few colored wires (in the wire harness). So IF some of those black wires were the center-tap for the 4 amp secondary, THEN this sucker would work for an LM3886. Of course you would not be getting 60 watts out of it, but maybe something like 40 watts (i did not bother to do the real math)...