Basic LM4780 amp

[tsiros]

yes, that is why it will be vented, top and bottom.

[tsiros]

as of yet:

i've ordered a 120VA 2x18V 3.33A toroidal, four 10mF 50V capacitors (2 per channel, if necessary i'll get more later), two rectifier bridges, the LM4780 and a pcb for it

i'll be giving it +-25V, that's supposedly 30W per channel at 1%THD, i won't be using more than 10W though and usually it will be at 1W.

now i need a <0.7C/W heatsink and the various thingies (caps, resistors, wires, connectors, fuses, fuseboxes, switches etc)

any comments suggestions or warnings would be most welcome!

[tsiros]

I need some help determining the values of Rf and Ri for the amplifier.

are those the usual feedback resistances that determine the gain of an opamp based amplifier?

if so, i might be able to determine their values.

[tsiros]

I request this thread be moved in the construction subforum

[tsiros]

Ok so maybe my previous questions were stupid or elementary, i don't know...

now i have an other question

What kind (single/multi strand, other), gauge and type (shielded, unshielded, twisted pair, other) wire should i use for the various connections?

1. from mains socket to power switch
2. from switch to power transformer
3. from transformer to bridge rectifier
4. from rectifier to LM4780 PCB
5. from pcb to speaker terminals

thanks for any and all input

[AndrewT]

1 & 2 double insulated mains wiring.
3 4 & 5 twisted pair.

[tsiros]

thanks! but what about gauge and ... strandiness?

[AndrewT]

1 & 2, maybe 0.5sqmm
3 & 4, maybe 0.75sqmm or 1sqmm
5, 1sqmm or 1.5sqmm
I would use stranded for all. Makes it much easier to do twisted flow and return.

[tsiros]

you've been of great help, andrew, thank you

[tsiros]

ok so i completed it
earth connector is connected to middle of symmetrical transformer and also connected to ground, between the smoothing caps :


-Vcc---)|---GND---)|---+Vcc

however i get buzz. i shouldn't be getting this much buzz. the usb is with ferrite core. the signal wire is high quality shielded.

this, (lm4780) amp has lots of buzz.

the other amp did not have the connection between plug earth and middle of transformer. it was DEAD QUIET.

question: what will happen to the lm4780 if i DISconnect the connection between PLUG EARTH ("E") and MIDDLE of TRANSFORMER, but KEEP the connection between middle of transformer and GROUND on PCB?