Noisy Audio Output

Thread Starter

kemuelgersonb

Joined Mar 18, 2019
34
You can't use any "Bridge-Amp" with only 3-Wires,
regardless of whether it's a Digital, or, Analog, Amplifier.

All Headphones that I know of only use 3-Wires.

If You want more Volume .............
You will need to supply more Voltage to ANY type of Amplifier that You want to use.

A simple and cheap "Dual-Op-Amp" will blow your ears off "if" You Power it with at least ~12-Volts,
and do it with extremely Low-Distortion, ( if You choose a high-quality Op-Amp ).
.
.
.
So in my case there's no workaround using the existing components or amplifier that I have? I am limited to a Li-Po battery which has 4.2V max. Do you know any headphone amplifier that is more compatible?
 
Sorry where did you get that info? I am using a 16 ohms headset. Any ideas how to measure a clean sine wave output? Do I need a LPF?
The specs are in the datasheet. Sorry, I wrongly said 0.33W when it is 0.53W.
Then its low distortion output with a 3.3V supply into a 16 ohms headset is 0.28W which is extremely loud and will damage the headset and damage your hearing.

The PAM8403 is class-D that switches its outputs back and forth at 260kHz that you cannot hear. The inductance of the headset presents hardly any load at 260kHz. The datasheet shows an LC filter if you need one to prevent radio interference.

The PAM8403 amplifier is designed to drive both wires of speakers but headsets have one wire of each earphone grounded.
Then do it like this:
 

Attachments

Last edited:
I already mentioned the valid work-around to the balanced output back in the third paragraph of post #33. That is to use a transformer in each output. The cheapest isolation transformers can be those dual filter chokes used to stop line noise. Just use it as a transformer instead of a choke. Some will work much better than others.
 

LowQCab

Joined Nov 6, 2012
2,044
The subjective results that will be obtained depend heavily on the Specifications of the Headphones.
Not all Headphones are created equal, there are vast differences in Efficiency and Fidelity,
not just Impedance differences.

The only "work-around" that I know of using this Switching-Amp is by using 2 Transformers.

Otherwise, if this were my situation,
I'd use 4-Quad-Op-Amps, DigiKey p/n MCP6294-E/P-ND, ~$2.19 each, ( in-stock ).

It's somewhat wasteful of Battery-Power when compared to a Switching-Amp,
but You can't hurt it,
it makes 95% of the Power,
and it has extremely low Distortion.
.
.
.
Low-Voltage Headphone Amp FLAT .png
 
I think the opamp will not be loud enough with a 3.3V supply even with six of them in series with 160 ohms and in parallel.
80mW into 16 ohms is a voltage peak of 1.26V. The current peak is 79mA.

Six 160 ohm resistors in parallel is 26.7 ohms that when in series with a 16 ohms earphone reduces the power in the headphone to only about 17mW.
 

LowQCab

Joined Nov 6, 2012
2,044
We don't know anything about the Headphones that will be used.

The Resistors on the Op-Amps insure that no matter what gets hooked-up to the Output,
it won't hurt the Op-Amps.
They can run maxed-out, all day long, with any outside Load, even a Short-Circuit to Ground.

If the user knows what he is doing, and pays attention to the Load-Impedance,
the Resistors can be eliminated,
which with a set of ~80-Ohm Headphones might give around a ~20% bump in power output,
( that's less than a 1db increase in output, which will be almost unnoticeable ).

The Circuit keeps things simple and bullet-proof.

Virtually all commercial Receivers with a Headphone-Jack have current limiting Resistors on the Outputs,
that doesn't mean that they are absolutely required,
but they're not a bad idea either, not all headphones are created equal.
There is no "standard", or even "average" Impedance for Headphones.

Few, ( if any ), "Ear-Buds" can withstand 1 full RMS Watt of Power for very long.
.
.
.
 
I suggested rewiring so as to have fully independent connections for each side. It seems that must be way beyond what anybody is able to do. But that would be a simple solution.
 

Thread Starter

kemuelgersonb

Joined Mar 18, 2019
34
Update : Removed pop noise by adjusting the FW. Longer delay for mute and shutdown.
Used 220uF tantalum caps for output DC blocking, improved the bass but still not "loud" enough.
Will adjust Rin to 18k below.
 
I am still wondering about what sort of noise. Hum, buzz, hiss, rumble, oscillation of some type, or maybe just distortion products. Or possibly white noise. Or even cross-talk from another signal source.
 
Try checking with a different set of headphones first.Check the resistance at the plug, one meter lead on the sleeve, to the Tip and the Ring. If the two sides do not read very similar resistance then there may be a cable problem. Let us know the resistance when you are done measuring.
 
Top