LM4780 power supply

[merlinx76]

I plan to build BrianGT's LM4780 kit but with a snubberized supply and a 19-0-19 traffo.

Would 2 power supply boards be recommended?

If I use only 1 supply board will a single bridge with 4 MUR860's(because my tranformer is center-tapped) be enough for 90W x 2 into 4 ohm speakers?

[doggy]

I put the 4780 brian gt kit together. The transformer is a plitron with dual secondaries. I left the diode bridge and the amp board together. I got 30 volts dc at v- pg- pg+ v+ The fuses keep blowing; up to 4 amp so far. The chip is mounted directly to the heat sink but the heat sink is isolated from the ground. What size of fuse do I need? Is there a schematic for wiring up the 8 diodes with the red yellow, blue grey secondaries? Red yellow serves one diode rect. and blue grey the other .

[wes-ninja250]

Are you using slow-blo fuses? If not, that's your fuse problem right there. Otherwise, try a 5A.

Wes

[doggy]

No just regular automotive fuses. Who would carry slow blow fuses?

[wes-ninja250]

Well, 20 years ago Radio Shack carried 'em...

If you can't find them locally, Digikey (www.digikey.ca) has them. Small orders cost $5 to ship, larger orders have free shipping.

Suggested Part Numbers --

3AG (1.25 x .25"):
F329-ND
F332-ND

Metric (5x20mm):
WK2263-ND
WK4860-ND
WK4823-ND
F981-ND

...The ones starting with F are worth about a buck each and are sold in groups of five. The ones starting with W are about fifty cents each and are sold individually. Hint: Order spares.

Wes

[doggy]

Thanks for the help. I got some 5amp slo blow at Active Electronics Vancouver. What a hell of a time I had to get it to work!! I finally had to have each primary feeding 1/2 of both sides of the rectifier boards.

The amp sounds great and so quiet, no on off pop, nothing! It is also bringing some new appreciation for some speakers I have.

Just for fun I by-passed one board only with some oil caps. Will plan to listen and evaluate.

[jackinnj]

my LM4780 supply:



here's the schematic:

[doggy]

Good looking power supply! I guess it's up to me tolearn more about power supplies; imho it makes a big difference in the amp performance.

In the interim I did this: added nichicon, g-luxon 4700uf directly to the boards bypassed with .001uf non polar snubber 10r+100nf metal poly cap. Sounds good.

[doggy]

One channel did not have the same clarity and bass authority. What I did was use nichicon 4700uf on one side and g-luxon 4700uf on the other all 50 v. I finally tried swithching all I could to try and discover what the difference was. The side with the g-luxon was better all around, Went and changed out the nichicons and put in the g-luxons. Result; these unknown to me luxons are way better imho. I've used nichicons before but never g-luxon.

a nice find,
cheers doggy

[Russ White]

Originally posted by jackinnj
my LM4780 supply:


here's the schematic:

jackinnj,

Thats a nice supply.

Now those are snubbers.

Cheers!
Russ