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Old 23rd June 2012, 03:52 PM   #21
tsiros is offline tsiros  Greece
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yes, that is why it will be vented, top and bottom.
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Old 29th June 2012, 03:13 PM   #22
tsiros is offline tsiros  Greece
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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!
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Old 30th June 2012, 09:31 PM   #23
tsiros is offline tsiros  Greece
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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.
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Old 2nd July 2012, 10:33 AM   #24
tsiros is offline tsiros  Greece
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I request this thread be moved in the construction subforum
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Old 25th August 2012, 10:43 PM   #25
tsiros is offline tsiros  Greece
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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
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Old 26th August 2012, 06:49 AM   #26
AndrewT is online now AndrewT  Scotland
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1 & 2 double insulated mains wiring.
3 4 & 5 twisted pair.
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Old 26th August 2012, 11:11 AM   #27
tsiros is offline tsiros  Greece
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thanks! but what about gauge and ... strandiness?
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Old 26th August 2012, 03:31 PM   #28
AndrewT is online now AndrewT  Scotland
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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.
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Old 26th August 2012, 04:26 PM   #29
tsiros is offline tsiros  Greece
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you've been of great help, andrew, thank you
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Old 13th September 2012, 03:38 PM   #30
tsiros is offline tsiros  Greece
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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?

Last edited by tsiros; 13th September 2012 at 03:45 PM.
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