Headphone amp, Turn on pop [solved]

[Michaelaudio]

So ive build a mobile Headphone amp, which works good so far. On the Output i have the TS5A23166, that should be open durring the start up, to prevent Turn on pop. Even when the ctrl pins are pulled to Grund, i do have a verry loud Turn on pop. The Switch is normally open, so i shouldnt hear anything when powering Up, but i do and i have no Idea why.

Any suggestions?

[magic]

TS5A23166 appears to be a low voltage chip, are you sure that the initial transient doesn't exceed 5V, causing it to do something weird?
How long is the switch held open? You need to wait until all the transients in the whole signal path settle.

BTW, not sure what the purpose of U1A/U1B is supposed to be.

[Zero999]

It might be the output voltage of the amplifier is exceeding the power supply rails of the analogue switch.

Please post the full schematic and use the print screen button, rather than posting a big arse photograph of the monitor.

[Michaelaudio]

I'll post a pdf later when im Home.

The TS5A is supplied by a 7803. How ever i made a terrible mistake for the ctrl Input (way too high Voltage) BUT when i Just Connect it to ground its the same Problem. 

@magic U1 is an Input buffer, providing a low impedance source to the following stages.

Oh yes, damn. The OP amp supplie is 18V, biased with 9V on the Inputs, thats way to much for The TS5 ofc. This happens when you wanna do it "quick" bc it should be a Gift for someone.

Well i guess thats the Mistake, thanks Guys.

Would it be reliable to take a Switch that can handle the Voltage, and let it Switch on after ~2 seconds via a RC circuit?

[magic]

Those buffers drive high impedance noninverting inputs of subsequent opamps, so any difference they make is marginal.

Technically, the subsequent stage has closed loop gain, so its AC differential input voltage and capacitive input current is a little higher for the same input signal. But I don't know if the difference is enough to have a meaningful effect.

[Zero999]

The TS5A23166 is completely unsuitable. The signal from your circuit can drop below 0V, as well as go above 5V.

Use a small mechanical relay. A DPDT is ideal, as it can connect both the outputs to 0V, via a much lower resistors rapidly charging the capacitors, when they're disconnected from the headphones.

Here's an example of a suitable relay.
https://uk.rs-online.com/web/p/signal-relays/7181998

[Michaelaudio]

I more or less copied the Input Stage from Phils Lab HP amp Design, u may be right but i guess it wont make it worse

@Zero999 its a mobile amp, powered from a 9V 800maH battery, that would be too much current draw. Plus my Board dimensions cant be larger than 3x5 cm, so i have verry Limited space. It must be an ic not larger than SOIC8 footprint.

Or Just another solution, just that i have no Pop.

[magic]

You could free up some space by eliminating pointless voltage followers. Some signal relays are fairly small.

For the output, opamps with better load driving capability could be considered. Like NE5532. Or NJM4556A; beware of phase reversal with this one (very ugly negative clipping), but the preceding TL072 probably doesn't have enough output swing to trigger it. Your TL072 output drivers have phase reversal too.

And so does TL072 in the gain stage. You could reduce the amount and the ugliness of transients generated by that stage simply by using the top rail as ground (referring Vbias filter capacitor, C3 and output loads to it) and the bottom rail as a negative supply.

edit
I missed battery powered and low voltage. NE5532 at unity gain will only work to ~2V below the top rail, TL072 is similarly constrained at the bottom. Not a great choice; some 4558, LM883, MC34078 could give more, dunno about THD and power. NE5532 is a power hog and NJM4556A even more so, but you get performance you pay for. With the NJM one chip could drive both channels to over 50mA, but watch out for power dissipation. OTOH, maybe it's not too bad at 9V.

[Michaelaudio]

I'll Draw a new schematic and post it. But i cant See where i have a phase Shift, all signals are on the positive inputs of the op amps?

I'll look what i can find, maybe If i get rid of an OP it will fit.

[Zero999]

The pop can be minimised to a very low, almost inaudible level by using large capacitors for the bias voltage and input. Here's an example showing a 22mV output transient, with a slow rise time up to 500ms. It has the disadvantage of it taking few seconds to turn on and requiring physically larger parts, but they only have to be rated to 4.5V, since they only charge to half the supply voltage.

What's the impedance of the headphones? 47µF is probably a bit too low. I chose 470µF for plenty of bass. Again it only needs to be rated to 4.5V.

This schematic also shows the correct way to connect two op-amps in parallel. U1a is the master and U1b the slave.

[magic]

The other method works as well. It also provides 3dB reduction of output stage voltage noise, unlike yours. (Yours has 3dB current noise advantage, but source impedance is very low so it's irrelevant).

edit
Wait, no. I thought you are referring to running both amps at unity gain, driven by a separate gain stage.
But you combined gain stage and output, using the gain amp to supply half of load current. This works too, with somewhat more distortion, but less power consumption.

[Michaelaudio]

So thats the circuit now. I wanna use 2 5532 for lower distortion and Power handling. For the realay, the 072 should Work, since its coil draws only 11mA, for a few seconds.

47uF should be enough i guess, its about 13Hz with a 250ohm load, so way below any kind of frequencies in music.

For the PSU im not quite Sure. I have to Test it Out if 9V is enough, however i tested it with 15v, using a step up converter, thats nice for a stable supply Voltage, but the tiny step up i got from eBay, is noisy as hell. When i Connect the circuit to it, without Sound, its like FM when u have no Connection. Strangely, that completely is gone when music is playing (maybe bc of the load)

[Zero999]

Any switched mode converter will be noisy.

It will still make a pop, as the relay will be too slow to disconnect the headphones. It needs to be connected so they're normally disconnected and the relay activated, shortly after power up. That will mean extra power consumption, which I know is what you're trying to avoid. The op-amp's output voltage will be about 1.5V lower, than the supply voltage, so it might not switch the relay, at lower battery voltages.

What do the 10R resistors do? Are the headphones designed to be driven like that? Generally the output impedance of the amplifier should be as low as possible, to provide a good damping factor. Refer to the circuit I posted previously for the correct way to connect two op-amps in parallel and maintain a low output impedance.

Why not simply design it so there's no turn on pop? I've shown you one way with the previous schematic. Another way is to connect the headphones' 0V between two capacitors to either rail which should be closely matched.

Since you're trying to save space, there's little benefit in having a separate TL072 gain stage, followed by the NE5532 buffer. The gain is only 9.2, so the tiny reduction in distortion will be inaudible. You might use the output op-amp for the gain stage, as I showed previously.

[magic]

This looks good in LTspice but it will make nasty glitches if built with TL072 due to phase reversal. Use the top rail as ground.
edit: That version may also glitch if it's turned off and then immediately back on again, before bias filter cap discharges.

Neither TL072 nor NE5532 makes a good unity gain follower at low voltage, they clip asymmetrically some 2V away from one supply rail due to input stage limitations.

Regarding OP's circuit:
- C4 is too high, seems -3dB at 20kHz. Reduce it 10x.
- R6 could be removed, just increase R18/R19 to 10Ω each.
- Filter the bias to ground, making it simply 50% of the supply voltage is invitation for noise.
- Placing caps on opamp output typically achieves little benefit, certainly not filtering, may cause instability.

[Zero999]

This looks good in LTspice but it will make nasty glitches if built with TL072 due to phase reversal. Use the top rail as ground.
edit: That version may also glitch if it's turned off and then immediately back on again, before bias filter cap discharges.

You're right on both counts. The first won't be an issue with the NE5532, but the second will be a problem, which ever op-amp is used.

I was thinking, just couple the signal to both rails, with matched capacitors, that way there will be minimal pop, the voltage will all be pretty central, as it's powered up.

[magic]

This couples 50% of rail noise into the signal.
If the rail carries pulses corresponding to positive signal halves driven out by the output stage, those get coupled too.

Maybe some simple active circuitry could be devised to discharge the bias cap when the supply rail collapses.
BTW, it looks like the same glitch will also occur during shutdown, not only on subsequent startup.

edit
In some cases, phase reversal may be prevented by adding series resistance in front of the affected amplifier input. I recall seeing this working for a discrete PNP input stage somebody presented here. Add a diode clamping the capacitor to the supply rail and maybe it works out.

Another way is chips without phase reversal in the first place. NE5532 (but bipolar input) or OPA2134 maybe.
Although in some cases, opamps advertised as such may still have phase reversal if the inputs are taken far enough beyond the rails
This may also be a violation of absolute maximum ratings at the same time.

[Zero999]

This couples 50% of rail noise into the signal.
If the rail carries pulses corresponding to positive signal halves driven out by the output stage, those get coupled too.

It's being powered from a battery, which is very clean. If the pulses from the output stage are coupled to both rails, they should cancel.

[magic]

Not cancel, but add to create a complete, attenuated, inverted image of load current. Only in a dual supply situation, only if both rails have equal impedance (including reactance).

Cancellation would occur in case of cross-conduction in the output stage.

In singe supply configuration, you first draw current from the battery, pulling the rail down, and you charge the load coupling capacitor as you drive the load. Then you pull the capacitor to ground, using the stored charge to drive the load negative. Battery current is zero in the second phase, so rail voltage is unaffected. Hence the rail carries halfwave rectified signal.

BTW, TL072 has much worse PSRR from the negative rail, so arguably that's where ground should be. Fun

[Zero999]

Not cancel, but add to create a complete, attenuated, inverted image of load current. Only in a dual supply situation, only if both rails have equal impedance (including reactance).

Cancellation would occur in case of cross-conduction in the output stage.

In singe supply configuration, you first draw current from the battery, pulling the rail down, and you charge the load coupling capacitor as you drive the load. Then you pull the capacitor to ground, using the stored charge to drive the load negative. Battery current is zero in the second phase, so rail voltage is unaffected. Hence the rail carries halfwave rectified signal.

BTW, TL072 has much worse PSRR from the negative rail, so arguably that's where ground should be. Fun

What I mean by cancel is, each rail will have the half wave rectified signal superimposed on it. Par of the signal will be fed back to the input, but it will be inverted, as the output will pull the respective rail down slightly, so all it will do is reduce the total gain slightly, due to negative feedback.

The only downside I can see with this scheme is it will compromise the channel separation. One channel will couple to the other, via the power supply rails, but is it a big deal for a headphone amplifier? Everything is a compromise.

[jonovid]

I found this 

[wasedadoc]

That reverse biases the output electrolytic half the time.  Why is that capacitor there at all?

[Michaelaudio]

@Magic. Ur right about C4, R6. R6 should be a Shirt circuit Protection. I dont exactly know what u mean with "Filter bias to ground"
Caps on outputs: do u mean the Filter caps for the biasing, or the output for the relay Driver?
Should i just get rid of the parallel Ne55 and just switch the 72 to a 5532?

@Zero999 In Ur circuit the Input is shorted to ground, but thats Not the case in reality right?
U might be right about the relay, either i could Connect the 9V directly to the relay, and then switching a resistor for the 9V to the Rest of the circuit, or find a relay that only Takes 10mA. Well i have found some, but id like to find one that i can buy on a lokal Website, id rather not pay 20€ shipping costs for a 3€ relay.

The chanel Separation shouldnt be a big deal, i dont need -120db Crosstalk or something.

[Zero999]

@Zero999 In Ur circuit the Input is shorted to ground, but thats Not the case in reality right?

Shorting the input to ground was just a convenient way to model the turn on transient response.

I found this 

That's what I'm talking about. As mentioned above, the output capacitor is no longer required. It's better if the capacitors are matched.

[Michaelaudio]

Im not quite sure how that circuit works, and what is the purepose of the resistors across both Caps that go to ground/Vcc?

I found out that 9V isnt enough for my load, either i'll have to use a boost converter, or i simply Connect the OP amps in bridge Mode. I wouldnt need an output cap, would that already Eliminate the pop noise? II would think so.

[Zero999]

Im not quite sure how that circuit works, and what is the purepose of the resistors across both Caps that go to ground/Vcc?

I found out that 9V isnt enough for my load, either i'll have to use a boost converter, or i simply Connect the OP amps in bridge Mode. I wouldnt need an output cap, would that already Eliminate the pop noise? II would think so.

The resistors balance the DC voltages on the capacitors, as the leakage currents might differ. They also provide a path for the tiny current generated by the bias and offset from the op-amp.

I don't see how you can bridge, as headphones normally have a three way connectors.

Why not simply use two batteries?

[Michaelaudio]

Oh yes, right... that doesnt work then.
2 Batteries wont fit in my enxlosure sadly.

Bluetooth speaker always using a Boost converter, that doesnt make a lot of noise. I used this one: https://www.ebay.de/itm/SX1308-Step-Up-Spannungswandler-DC-Booster-Schaltregler-Arduino-Raspberry-Pi-/253381738734?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=707-127634-2357-0

When No music is playing, the noise is fucking loud, it disappears when i Play music thou. I have to find a Regulator thats AS small as this, with a better quality. (Or somehow modify that one)

Will it be safe when i relie on ur circuit you posted before? Or will a relay be unavoidable? If so, i might get it to work that it will turn Off, before the Rest of the circuit turns on.

[magic]

Not cancel, but add to create a complete, attenuated, inverted image of load current. Only in a dual supply situation, only if both rails have equal impedance (including reactance).

Cancellation would occur in case of cross-conduction in the output stage.

In singe supply configuration, you first draw current from the battery, pulling the rail down, and you charge the load coupling capacitor as you drive the load. Then you pull the capacitor to ground, using the stored charge to drive the load negative. Battery current is zero in the second phase, so rail voltage is unaffected. Hence the rail carries halfwave rectified signal.

BTW, TL072 has much worse PSRR from the negative rail, so arguably that's where ground should be. Fun

What I mean by cancel is, each rail will have the half wave rectified signal superimposed on it. Par of the signal will be fed back to the input, but it will be inverted, as the output will pull the respective rail down slightly, so all it will do is reduce the total gain slightly, due to negative feedback.

Yes, what you mean by "cancel" is what I mean by "add and complement". I happen to believe that one of those descriptions is more true to fact, but at least we understand each other

Now, the rest of the post you quoted argues why this doesn't happen in single supply circuits and even with dual supplies it's hardly perfect.

[Michaelaudio]

So for the relay solution, this should do the trick.

[Zero999]

The lack of power supply voltage is more of a problem.

Why not use an op-amp with a high current rail-to-rail output such as the MC33202?
https://docs.rs-online.com/c975/0900766b816ded01.pdf

[Michaelaudio]

Even when i have the full +/- 4,5Volts, i only have around 3V Rms, but i need about 5V Rms. I guess i wont come around the boost converter.

[Zero999]

Even when i have the full +/- 4,5Volts, i only have around 3V Rms, but i need about 5V Rms. I guess i wont come around the boost converter.

Another option is to add some transformers to the output, but they'd probably be too big.

A boost converter will work, but it needs to be properly filtered, to eliminate the noise.

[Michaelaudio]

I ordered two more, to see which performs best. I tried a big cap with my current one, but that only changed the noise from high, to a low hissing. Maybe ill be more lucky with a Pi filter.

[magic]

I dont exactly know what u mean with "Filter bias to ground"

The supply rail is noisy. If you simply divide it in half to derive the bias voltage, the bias voltage is 50% (-6dB) as noisy as the supply.
To remove the noise, you filter the bias voltage with a cap to ground. Right at the resistors, before the opamp, because a cap after the opamp has little effect - the opamp will simply charge/discharge the cap in order to transfer the noise from the resistor divider to the output.

IOW, remove C17, move C18 to the input side of the opamp.

But this means that turn-on/turn-off transients will get worse.
Relay protection makes transients kinda irrelevant, if it works reliably.

edit
Generally, every capacitor between the signal path and the supply rail (not ground) is an invitation for noise. This includes load AC coupling capacitors too. OTOH, symmetric caps to both rails reduce turn-on transients. Pick your poison.

[Michaelaudio]

Ahh, now i got it. Since im gonna usw the relay method now, with the turn in delay for the Rest of the circuit, so i dont worry about more transient.

I'll See what i can do with my Regulator, i found some nice Sheets from Ti/AD for Output filtering, i'll play around with it.

[Zero999]

I dont exactly know what u mean with "Filter bias to ground"

The supply rail is noisy. If you simply divide it in half to derive the bias voltage, the bias voltage is 50% (-6dB) as noisy as the supply.
To remove the noise, you filter the bias voltage with a cap to ground. Right at the resistors, before the opamp, because a cap after the opamp has little effect - the opamp will simply charge/discharge the cap in order to transfer the noise from the resistor divider to the output.

That's only true if the signal is referenced to one of the power supply rails. Apply the signal to the mid point and the two capacitor solution is just as good.

Here's an example showing an RC rail splitter and the effect of the loading on the power supply rails. All it does is reduce the gain a little. If the power supply had a bit of noise, it would be no worse, than referencing the signal to either rail and bypassing the bias point to the rail, the signal is referenced to.

[magic]

Yeah, that's essentially the CMoy amplifier. You replaced all the biasing drama with a virtual ground. Note a complete absence of capacitors in the signal path.

Which is perhaps an acceptable option, but I was mentally stuck in the realm of single supply AC coupled circuits, as suggested by the OP.

This circuit has DC coupled signal path, so potential disadvantages:
- DC offset of the source is passed to the load
- DC offset of the opamp too, at 9x gain
- in presence of DC offset, supply rails may get asymmetric due to high resistance of R3,R4
- if the two channels fail short to opposite rails, DC fault current flows through the two transducers in series

OTOH, the AC coupling of supply rails to ground saves transducers when only one channel faults or both fault to the same rail, which is surely a more likely scenario.

DC offset problems could be reduced by AC coupling between stages, like O2. Only a pair of small caps is required. This means the gain stage no longer gets to support the output stage with additional load current.

edit
Another (unrelated) disadvantage is less efficient use of the opamp's PSRR, compared to grounding the more sensitive supply.
There is also an advantage: any distortion of load coupling capacitor is removed from the signal path.

OP will have to decide which topology to choose. Last time I remember the topic of simple headphone amps, the OP was hell bent on AC coupling the load for the sake of safety/reliability and rejected all DC coupled split rail / dual rail suggestions.

[Michaelaudio]

@Zero999 isnt Ur Last schematic more or less the same Voltage biasing like i did it? I did the same thing, but with an OP amp, for a low impedance source.

I Just looked at this vid again, and i think i should be fine now: https://youtu.be/Z2GUoi63pJs

The relay should now turn on, before the rest of the circuit, and only Turn on for ~ 3 Seconds, so battery only supplies amps to the OP amps -> improving battery life a lot.

Also, i did some filtering on my converter. With a simple added RC Filter, i went from a 200mVpp noise, to 25mVpp. Thats good so far, but still audible. Ill mess around with it more, but im getting there.

[Zero999]

@Zero999 isnt Ur Last schematic more or less the same Voltage biasing like i did it? I did the same thing, but with an OP amp, for a low impedance source.

My schematic is completely different. The 0V point is at half the supply voltage, providing a +/-4.5V power supply. There won't be a turn on pop because the both the capacitors charge up at the same time and the output of the op-amp follows them.

I Just looked at this vid again, and i think i should be fine now: https://youtu.be/Z2GUoi63pJs

I haven't watched it in its entirety, just flicked through the schematics. It's much more complicated than necessary.

The relay should now turn on, before the rest of the circuit, and only Turn on for ~ 3 Seconds, so battery only supplies amps to the OP amps -> improving battery life a lot.

Also, i did some filtering on my converter. With a simple added RC Filter, i went from a 200mVpp noise, to 25mVpp. Thats good so far, but still audible. Ill mess around with it more, but im getting there.

That will work, but why is it so complicated?

[Michaelaudio]

My schematic is completely different. The 0V point is at half the supply voltage, providing a +/-4.5V power supply. There won't be a turn on pop because the both the capacitors charge up at the same time and the output of the op-amp follows them.

U have a 9V DC on the Input, Splitting it in half with the resistors. So in the middle u have 4,5 Volts, thats what u define as ur Ground. Ur "V-" is actuall ground, 4,5 Volts is ur virtual ground, setting an Offset to ur AC Signal. Or is it a real +/- 4,5 Volts supply, with the wrong Symbol at its Input?

How do i make it simplier? As u said, the relay may be too slow, so it has to turn on first.

[Zero999]

My schematic is completely different. The 0V point is at half the supply voltage, providing a +/-4.5V power supply. There won't be a turn on pop because the both the capacitors charge up at the same time and the output of the op-amp follows them.

U have a 9V DC on the Input, Splitting it in half with the resistors. So in the middle u have 4,5 Volts, thats what u define as ur Ground. Ur "V-" is actuall ground, 4,5 Volts is ur virtual ground, setting an Offset to ur AC Signal. Or is it a real +/- 4,5 Volts supply, with the wrong Symbol at its Input?

Ground just means the point from where all voltages are referenced to. The schematic I posted uses a rail splitter, or virtual ground.

How do i make it simplier? As u said, the relay may be too slow, so it has to turn on first.

If you a rail splitter, as I suggested, then you don't need a relay.

[Michaelaudio]

Yes, but im doing the same, it doesnt matter If there is an OP amp Afterwards. Also ud still have the Cap charging Via 9V to 4,5V, which would cause a Pop on the output.

[Zero999]

Yes, but im doing the same, it doesnt matter If there is an OP amp Afterwards. Also ud still have the Cap charging Via 9V to 4,5V, which would cause a Pop on the output.

You're using a single supply non-inverting amplifier topology, which uses the negative side of the power supply as the ground. The circuit I've shown, uses half the power supply voltage as the ground.

Here's a couple of schematics showing the difference between a single and split supply.



In this case, the TLE2426 can be used, that way the large capacitors are no longer needed.
https://www.ti.com/lit/ds/symlink/tle2426.pdf

[Michaelaudio]

I cant see how the "Split supply" circuit could work. If ud apply a signal to it, it would cut the sinewafe in half. The -6v still isnt -6V, its ground, therefore If i feed a Signal to the Input, without biasing it, it cant work.

[Zero999]

I cant see how the "Split supply" circuit could work. If ud apply a signal to it, it would cut the sinewafe in half.

The split power supply circuit works fine. In this case, the signal is AC, so the biasing resistors only carry a tiny circuit. The capacitors need to be large enough to pass the AC signal, but similar sized capacitors would be needed for the signal supply circuit.

The -6v still isnt -6V, its ground, therefore If i feed a Signal to the Input, without biasing it, it cant work.

Ground is just a reference point, from where all voltages are common to. It doesn't have to be the negative side of the supply. It can be the positive. Here's an example showing two 9V batteries in series, with the ground reference, in the middle, on the negative and on the positive.

[Michaelaudio]

I know, its just the definition, how u define ground. But if u now connect lets say ur phone to the input, ur input ground of the circuit is at 4,5Volts, while ur Phone ground is at 0V. So u biased the ground, Not the signal path so to speak. Isnt that a Problem?

[magic]

TLE2426 can be used, that way the large capacitors are no longer needed.

Another advantage: higher peak output at low frequencies.
A disadvantage: load driving efficiency decreases by 50%.

I know, its just the definition, how u define ground. But if u now connect lets say ur phone to the input, ur input ground of the circuit is at 4,5Volts, while ur Phone ground is at 0V. So u biased the ground, Not the signal path so to speak. Isnt that a Problem?

Only a problem if there is some external connection between the phone's ground and the negative of the PSU, for example through mains-powered chargers with three prong plugs.

[Michaelaudio]

I'll try that out in my current Board, If the pop is gone then, i can just use that board how it is, and focus on the psu noise.

[Zero999]

TLE2426 can be used, that way the large capacitors are no longer needed.

Another advantage: higher peak output at low frequencies.
A disadvantage: load driving efficiency decreases by 50%.

Good point. The capacitors are charged in series and discharged individually, like a charge pump, which halves the voltage, rather than doubling it.

I know, its just the definition, how u define ground. But if u now connect lets say ur phone to the input, ur input ground of the circuit is at 4,5Volts, while ur Phone ground is at 0V. So u biased the ground, Not the signal path so to speak. Isnt that a Problem?

A circuit can have different grounds, which isn't a problem if they're not connected. The mains has protective earth/ground and neutral serves as the 0V reference for the circuit. Another example is a device connected to the mains via an isolated switched mode power supply: the 0V ground on the secondary, is completely different to the mains neutral.

[Michaelaudio]

So ive tried it Out and it works, i still have a slightly pop tho. I dont know If its bc of my quick and dirty test, or if there will be Always a slightly pop. If so, the question is, If i will have this with the relay solution too.

[Zero999]

So ive tried it Out and it works, i still have a slightly pop tho. I dont know If its bc of my quick and dirty test, or if there will be Always a slightly pop. If so, the question is, If i will have this with the relay solution too.

Did you try matching the capacitor values?

It's very difficult to eliminate the pop. I've done this before, using the relay method and there was still a tiny pop.

The question is: is the pop acceptable? I'd say if it's not uncomfortably loud, it's good enough.

[Michaelaudio]

U mean If i changed them to 100uf aswell? Or if i changed all caps to the Same value?

Acceptable yes, but the perfectionist inside me still going nuts
I guess ill do it like this: Make the circuit like ur suggestion with the ground biasing and add the relay method. Ill at first, only solder components without the relay circuit. If it works without, great, If not, i still can solder in the relay. Not much more work and im on the safe side then.

[magic]

In a DC coupled amplifier you will inevitably have some pop due to offset voltage, even if you use a relay.
The opamps may generate additional transients during startup. A scope is your friend here.

The caps between the rails and grounds should be equal in value, but I doubt that obsessive matching to <10% will make any difference.
The two supply rails come up simultaneously at approximately the same rate, that should be enough.

[Michaelaudio]

Maybe i can make it from a small pop, to a tiny pop.

So this would be the design now.

[Zero999]

Maybe i can make it from a small pop, to a tiny pop.

So this would be the design now.

C13 & C14 are far too small.

The AC coupling capacitors are no longer needed. The output capacitors can also be omitted, but can help to reduce the pop, so I've kept them in. If you do include them, they should be non-polarised. If you don't have non-polarised 47µF capacitors, connect two 100µF capacitors back-to-back, to make a 50µF non-polarised capacitor.

The 10R output resistors aren't required. All they do is limit the output voltage swing and reduce the damping factor, which emphasises the headphones' resonant frequency, making them sound boomy.

The relays should switch a low value resistance in place of the headphones, rather than an open circuit, so the bias voltages settle quickly.

All of those 100nF capacitors do nothing. C13 and C14 provide all the decoupling required at audio frequencies.

Here are some modifications.

[Michaelaudio]

Okay, changed the Output and coupling Caps. The 100nF should stay, they are for stability reasons, close to the ICs, nerly recommend in every datasheet, so they should stay.

What about R7, R15? I placed them to discharge the output cap.

[Zero999]

Okay, changed the Output and coupling Caps. The 100nF should stay, they are for stability reasons, close to the ICs, nerly recommend in every datasheet, so they should stay.

Keep them in, if it makes you feel more comfortable. They certainly won't do any harm, but won't make any difference, unless the layout is very poor, as C13 & C14 dominate. This isn't a high speed digital circuit, with fast rising and falling edges.

What about R7, R15? I placed them to discharge the output cap.

The relay will do that, when the power is first applied.

[BrianHG]

If you want to get rid of the pop and eliminate the mechanical relay in the above schematic, use 2 of these solid state relays in series with the headphone jacks:

https://www.digikey.com/en/products/detail/toshiba-semiconductor-and-storage/TLP170AM-V4TPL-E/12390883

Tie 1k or 10k to the output caps before the OPTO-Relays to GND, and switch on the 2 opto-relays around 1 second after power-up.

Alternately, you can use the opto-relays to short the output to GND rapid discharging the DC filter caps, however, you may hear a tiny very low volume pop during power-up with this reverse logic.


Remember to wire the 2 relay LEDs in series so you only need 5ma to drive both together.

If price isn't a concern, you can go from 0.3ohm down to 0.05ohm, though, nothing will beat a mechanical relay.

[Michaelaudio]

@BrianHG Thats also a nice Idea, but a bit late, couse i already have the relay and the shipping costs would be Higher than the IC costs.
Layout is also nearly done, should be fine this time.

[magic]

Okay, changed the Output and coupling Caps. The 100nF should stay, they are for stability reasons, close to the ICs, nerly recommend in every datasheet, so they should stay.

Keep them in, if it makes you feel more comfortable. They certainly won't do any harm, but won't make any difference, unless the layout is very poor, as C13 & C14 dominate. This isn't a high speed digital circuit, with fast rising and falling edges.

C13 and C14 are AC coupled inductors, not capacitors.

https://www.eetimes.com/op-amps-in-small-signal-audio-design-part-3-selecting-the-right-op-amp/
CTRL+F 100 nF

I see no reason to cut corners with such cheap components, particularly if the OP doesn't even seem to have much test equipment available to verify performance and stability. OTOH, you don't need a separate cap for each IC - they can be shared if two chips happen to be placed next to each other.

[magic]

Layout is also nearly done, should be fine this time.

Don't send it for manufacturing yet, you forgot about input biasing resistors after C2, C7.

Again, I see no point of R14. Just increase R12 and R13 to 10Ω - same level of isolation from the load for each opamp, better isolation between the opamps (less idle current due to different offset voltages), lower overall output impedance.

[Michaelaudio]

Oh, yes, thanks. I'll Just move R2, R9 behind the Cap.

I also forgot to remove C4, C9, there are also Not needed.

I removed R14 in my layout, like Zero said too.

[Michaelaudio]

I got my PCB and assembled it, it works well so far. The relay method is pretty bad tho, i have a double Pop, pretty loud. It is a small pop now, but a lot better than before. 👍🏻

Problem is still my switching Regulator, but thats for another threat.