any major flaws in this schematic

joesphanlu

Member
2016-02-07 5:59 pm
hey guys, i saw this schematic and i'm currently building it, is there any major flaws in it?

Parts:
P1______________47K Log. Potentiometer
(twin concentric-spindle dual gang for stereo)

R1_______________4K7 1/4W Resistor
R2______________12K 1/4W Resistor
R3,R4___________33R 1/4W Resistors
R5,R6____________4R7 1/4W Resistors

C1_______________1µF 63V Polyester Capacitor
C2,C5__________100nF 63V Polyester Capacitors
C3,C6___________22µF 25V Electrolytic Capacitors
C4,C7_________2200µF 25V Electrolytic Capacitors

IC1__________NE5532 Low noise Dual Op-amp
IC2___________78L09 9V 100mA Positive Regulator IC
IC3___________79L09 9V 100mA Negative Regulator IC

D1,D2________1N4002 200V 1A Diodes

J1,J2__________RCA audio input sockets
J3,J4__________6mm. or 3mm. Stereo Jack sockets
J5_____________Mini DC Power Socket
 

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milliganp

Member
2010-08-24 9:16 am
Input bias flows through pot

The input bias current for the first stage is flowing through the input level pot. At maximum impedance and worst case bias of 800nA this will 37.6mV and with forward gain of 3.55 this gives -133mV output offset.
Also having DC flowing through the pot will mean probable wiper noise (crackle) as you change level.
 

Arty

Member
2011-02-24 5:04 pm
hmm i think this would pick up any nearby radio station perfectly...
should not there be some pf range value caps at input, from input to ground at least?
and sortha i would add a 100 ohmish resistor at the output of the opamps..
just in case of that funky feeling.

dunno.
it may be absolute correct but i don't quite like this schematic.
i mean the looks of it is just "alien".
 
I bet it's just another of those funky (being kind) "Red Circuits" , at least it looks like it.

"Designed" by somebody who obviously has too much free time, most are clearly unbuilt/untested , may or may not work, and in general have design flaws which would be obvious and corrected *if* they were actually built and tested.

Doubts expressed above are very reasonable: pot may scratch, offset will be high (acceptable on speakers, not on headphones) , WHY does it have DC gain?

As of "adding 100 ohms to the output" ..... why?
Those Op Amps have higher than normal current capability and can drive headphones , they're popular in that use; the 4.7 ohms shown is enough.

That said, there's a ton much better headphone amp circuits out there (cough cough DIYA Headphones section ;) )
Headphone Systems - diyAudio