Headphone amp, Turn on pop [solved]

[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.