Hello, I recently made a PCM1794 DAC. The output of the I/V circuit was set to 2Vrms. I'd like to add a headphone output jack and a volume knob here. NE5532 based headphone amplifier Are there any problems driving low-impedance earphones or suitable headphones such as HD600?
Experimenting with this circuit in LTspice, I think the power is too large.
And why do you need a high-pass filter?
Experimenting with this circuit in LTspice, I think the power is too large.
And why do you need a high-pass filter?
There are better opamps these days for headphones, if that's what you want to do.
Examples like OPA1622, etc.
And you probably do not need much gain.
C1 blocks input DC.
C2 nulls output DC, both for me optional.
C3 is not necessary, depending on which opamp, IMHO.
My 2 cents,
Patrick
Examples like OPA1622, etc.
And you probably do not need much gain.
C1 blocks input DC.
C2 nulls output DC, both for me optional.
C3 is not necessary, depending on which opamp, IMHO.
My 2 cents,
Patrick
Opamps like the NJM4556 or 4560 have good current delivery.
As Patrick says, C3 is not needed (nor is it desirable) and R4 serves no purpose. I would suggest adding a small low value resistor in series with the output to isolate the opamp from any load induced effects. Something like 10 to 22 ohm 0.25 watt.
You can also parallel the opamps in a dual package for more current delivery if needed but 99% of applications are fine with a single opamp.
As Patrick says, C3 is not needed (nor is it desirable) and R4 serves no purpose. I would suggest adding a small low value resistor in series with the output to isolate the opamp from any load induced effects. Something like 10 to 22 ohm 0.25 watt.
You can also parallel the opamps in a dual package for more current delivery if needed but 99% of applications are fine with a single opamp.
You can add a 120R resistor between opamp and item.
Then it becomes current drive, but very inefficient.
Or change to a current drive amp completely.
Patrick
Then it becomes current drive, but very inefficient.
Or change to a current drive amp completely.
Patrick
3 ohms is to low to dangle right off the end of an opamp but also remember that these things are likely extremely efficient and so need very little in the way of voltage swing across them. Even so, if they dip to 3 ohms and also likely go much higher at some frequencies then you need something purpose designed to do that... which is still simple and little more than adding a buffer. You will only need a voltage swing of a few hundred millivolts, its not like driving a 3 ohm speaker.
@Mooly I understood. The gain was so great that I completely buffered the opmap (connecting negative and output), and then connected a very large resistance to the +input of the opamp. Now in the simulation, ICC, IEE are back to sine wave as it was. As you said, iem is enough under 100mV. By the way, is it good that the icc and iee are similar to the output waveform like this? Installing a small resistor and bypass cap on the power pin also flatten the current. I wonder if it is better to have a resistor and bypass capacitor between the regulator that supplies power to the opamp or only have a bypass capacitor. Thank you so much
I would say its normal.
Post your .asc and I'll take a closer look tomorrow 🙂 but I think all you are seeing is the supply current in response to the opamps driving the resistive networks. If you look at the currents in R3 and R4 and R5 and R6 they won't be equal.
Post your .asc and I'll take a closer look tomorrow 🙂 but I think all you are seeing is the supply current in response to the opamps driving the resistive networks. If you look at the currents in R3 and R4 and R5 and R6 they won't be equal.
Howdy, new member here.
2Vrms (2.8Vpp) seems pretty hot out of the DAC- should it be this high? Most "line level" outputs are more like 2dBV (~1.2V) May not play nice in a pre-amp where that one source is twice as loud as the other inputs. All of that extra output is just going to be attenuated later.
Driving a possible range of headphones should really not be done by an op-amp directly, as they cannot source enough current. (Although this is done frequently in cheaper designs.) I don't consider the HD600 to be "low impedance"- many common headphones are in the 300 Ohm range- that's pretty typical. You probably could drive those just fine here, but it will struggle with those that are lower impedance.
For me, my much loved Philips SHP-9500 are 32 Ohms and I wanted to be able to possibly drive lower in the future, so I took I different approach. As an option I can recommend adding a transistor AB push pull buffer to the output of the op-amp that are within the feedback loop- I highly recommend Rod Elliott's ESP project 113. I built this and the sound is amazing in my 32 Ohm cans- extremely low noise on +/-15V regulated rails, breathtakingly clear and crisp. It is powerful enough to drive any headphones, and even bookshelf speakers to a near-field listening level. The gain of this project is pretty high, so be sure to follow his suggestion of the lowest gain resistor option. It has enough drive voltage so you can also connect switch-selected 120 Ohm series resistors should you like, and see which sounds better.
-Warren
2Vrms (2.8Vpp) seems pretty hot out of the DAC- should it be this high? Most "line level" outputs are more like 2dBV (~1.2V) May not play nice in a pre-amp where that one source is twice as loud as the other inputs. All of that extra output is just going to be attenuated later.
Driving a possible range of headphones should really not be done by an op-amp directly, as they cannot source enough current. (Although this is done frequently in cheaper designs.) I don't consider the HD600 to be "low impedance"- many common headphones are in the 300 Ohm range- that's pretty typical. You probably could drive those just fine here, but it will struggle with those that are lower impedance.
For me, my much loved Philips SHP-9500 are 32 Ohms and I wanted to be able to possibly drive lower in the future, so I took I different approach. As an option I can recommend adding a transistor AB push pull buffer to the output of the op-amp that are within the feedback loop- I highly recommend Rod Elliott's ESP project 113. I built this and the sound is amazing in my 32 Ohm cans- extremely low noise on +/-15V regulated rails, breathtakingly clear and crisp. It is powerful enough to drive any headphones, and even bookshelf speakers to a near-field listening level. The gain of this project is pretty high, so be sure to follow his suggestion of the lowest gain resistor option. It has enough drive voltage so you can also connect switch-selected 120 Ohm series resistors should you like, and see which sounds better.
-Warren
@wparks
There may be errors because a translator was used. That's right the HD600 is not low impedance. Anyway, I would like to see a wide range of earphone and headphone support from 8 to 600 ohms.
The problem is that I still don't know the current consumption characteristics of the Opamp. Is it okay to use amplifiers with different output stages (A, AB) on one power rail (+12V, -12V)?
Also, would you recommend installing a resistor across the bypass capacitor to form an LPF? From what I've learned, it's a good idea to keep the output impedance of the LDO low. However, in some published schematics, a resistor is installed before the bypass capacitor to increase the charging time constant.
There may be errors because a translator was used. That's right the HD600 is not low impedance. Anyway, I would like to see a wide range of earphone and headphone support from 8 to 600 ohms.
The problem is that I still don't know the current consumption characteristics of the Opamp. Is it okay to use amplifiers with different output stages (A, AB) on one power rail (+12V, -12V)?
Also, would you recommend installing a resistor across the bypass capacitor to form an LPF? From what I've learned, it's a good idea to keep the output impedance of the LDO low. However, in some published schematics, a resistor is installed before the bypass capacitor to increase the charging time constant.