But audio is AC coupled so its usually unimportant, especially at unity gain at line level! But yes if you want DC coupling for some reason using a FET opamp is wise.
You can't count on that if 'equipment modders' are at work removing output coupling caps in source components. Worst case the DC offset from a unity gain 5532 stage with something as low as 47k input resistor can still be quite a few tens of millivolts.
Looks like we think alike in suggesting FET is the way to go here.
That's why you should always AC couple at any audio input(!). And probably the output too. Capacitor-phobes think otherwise of course, but hey every microphone used to record music is either a capacitor (condensor) or uses (unipolar) electrolytic coupling capacitors in the phantom power circuit and they haven't noticed(!)
The point is that source devices have their own output capacitor that would just connect in series with the input capacitor and create a more aggresive filter.
I wouldn't count on that. I always put an input cap on the input. You never know what you're connecting to. And you can get a super good quality film cap that's not going to degrade anything at all, one or two microfarads, and then you'll always be safe no matter what the source is. I always use a 2.2 uf Wima on the input, and make sure I have ultralow DC coupled offset on the output.
My point is that capacitors connect in series with each other and your 2,2uF becomes an 0.9uF capacitor which changes the rc filter characteristics
What are you assuming is at the output of the preceding stage? Assume it is another 2.2 uF, which is very low and very safe to assume. It is probaly quite a bit more in most cases, if present.
So 2.2uF in series with 2.2 uF on your input yields 1.1uF total. With a 47k impedance that yields an f3 at 2.8 Hz. That is in the weeds and neither your speakers nor headphones will ever get close to that frequency. I don't see a problem at all with a 2.2 uF coupling cap in this instance. It will work fine AND protect whatever follows it from unwanted DC or voltage offset. It's safe thing to do.
Play with the math yourself.
f = 1/(2*pi*R*C ) Don't forget R is in ohms and C is in farads. so 2.2uF =s 2.2/1000000.
So 2.2uF in series with 2.2 uF on your input yields 1.1uF total. With a 47k impedance that yields an f3 at 2.8 Hz. That is in the weeds and neither your speakers nor headphones will ever get close to that frequency. I don't see a problem at all with a 2.2 uF coupling cap in this instance. It will work fine AND protect whatever follows it from unwanted DC or voltage offset. It's safe thing to do.
Play with the math yourself.
f = 1/(2*pi*R*C ) Don't forget R is in ohms and C is in farads. so 2.2uF =s 2.2/1000000.
Could also move rv1 in front of u1b and you also need to make sure that there's no DC offset coming out of U1B going into the power amp unless the power amp has a blocking cap itself.
Here is what i built:
im also intrested in the value of the biasing and if 100k is too much and if i could add an 100k resistor on the input or even add an switch to switch between diffrent input resistors.
I found this schematic on google images becuse i was too tired to make my own, the changes i made is no R9 100k R6 and R5 and 100uF C6.
I found this schematic on google images becuse i was too tired to make my own, the changes i made is no R9 100k R6 and R5 and 100uF C6.
TL072 data sheet page 36 "Place 0.1-μF bypass capacitors close to the power-supply pins to reduce errors coupling in from noisy or
high-impedance power supplies. For more detailed information on bypass capacitor placement, see Section 9.6."
high-impedance power supplies. For more detailed information on bypass capacitor placement, see Section 9.6."
You are using a single ended supply here so should add a blocking cap to the output or else you will be feeding DC to your power amp.
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i will you can even see two of these blue capacitor things in the picture with one of them being the output cap, im probably gonna add an volume control potentiometer before the output decoupling capacitor like this: (asuming the first triangle is the buffer/preamp and the 2nd one is an unspecified power amplifier [ignore values])
Wasn't the whole point of the buffer to have it DC coupled and get away from coupling caps, which introduce high pass filters and uncertain interactions with varying value resistances in subsequent stages?
i dont know at this point what it does, my original idea was to isolate the volume potentiometer in some way.
i also just opened up the toslink dac and removed the ouptut capacitor and resistor from it.
i also just opened up the toslink dac and removed the ouptut capacitor and resistor from it.
The Toslink DAC probably needs the output capacitor to block DC voltage. But, it was setup for an input resistance of 100k minimum (15.9 Hz cutoff). That would even be marginal. Use this high pass filter calculator . You want the cutoff frequency to be much lower than 20 Hz, because you want phase shift in the audio band to be minimal. For usual solid state 10k loads, they typically use a 10uF coupling cap, which gets the cutoff frequency down to 1.59 Hz. It doesn't need to be that low.
With pots, there is a fixed resistance facing the coupling capacitor, when AC coupled. The high pass filter will then have a fixed cutoff frequency. The wiper connects to the following stage. Buffers after the pot do help a great deal, in my experience.
If you want to DC couple, as in your original idea, you would use JFET input op amps and dual supplies for lowest DC offset. I would also use adjustable regulators (e.g. LM317/LM337), so that you can get the rail voltages symmetrical. Buffer-pot-buffer arrangement.
I just use a PGA2310 based volume control. I like it. They are not available on Ali any longer. They now have the improved (assuming) MUSES72320 units. You get remote control. Not very DIY. There are some DIY projects here using the MUSES72320 or MUSES72323.
With pots, there is a fixed resistance facing the coupling capacitor, when AC coupled. The high pass filter will then have a fixed cutoff frequency. The wiper connects to the following stage. Buffers after the pot do help a great deal, in my experience.
If you want to DC couple, as in your original idea, you would use JFET input op amps and dual supplies for lowest DC offset. I would also use adjustable regulators (e.g. LM317/LM337), so that you can get the rail voltages symmetrical. Buffer-pot-buffer arrangement.
I just use a PGA2310 based volume control. I like it. They are not available on Ali any longer. They now have the improved (assuming) MUSES72320 units. You get remote control. Not very DIY. There are some DIY projects here using the MUSES72320 or MUSES72323.
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