Porter - a headphone amp for musicians

[neighborhoodcircuits]

Hi all,

I'm launching my first-ever product on Crowd Supply, and thought you might be interested in taking a look: https://www.crowdsupply.com/neighborhood-circuits-llc/porter

In short, it's a headphone amp that is designed to make it easy to use your own effects pedals. Most other headphone amps out there plug straight into the guitar and come with a number of built-in effects. That's nice and all, but I really wanted to use the effects that I or my friends had built, and toggle them with my feet (since my hands are kinda busy). I think it's much more effective to practice the same way you would play live (hence the "for musicians" part).

Porter has a bunch of other nice features, like a belt clip, a rechargeable battery. and a line-in for playing along with a song or backing track.

Please have a look and let me know what you think!

[neighborhoodcircuits]

FYI, I am also working on documenting the design on Hackaday: https://hackaday.io/project/196611-porter

[floobydust]

Looks really good. For something like this, I add ESD protection because headphones, guitars, walking around makes a lot of static electricity which nails IC's and damages them.
It's the male end of the 3.5mm or 1/4" jack when jacking in, zaps it. From the other end of the cable.
This could be at least a series resistor to the first TL072 input, or clamp diodes. A pair of clamp diodes like BAT54S or BAV99 from the headphone out to the +/-5V rails.

[bob8819]

 You need to make him pretty.

[neighborhoodcircuits]

Looks really good. For something like this, I add ESD protection because headphones, guitars, walking around makes a lot of static electricity which nails IC's and damages them.
It's the male end of the 3.5mm or 1/4" jack when jacking in, zaps it. From the other end of the cable.
This could be at least a series resistor to the first TL072 input, or clamp diodes. A pair of clamp diodes like BAT54S or BAV99 from the headphone out to the +/-5V rails.

Thanks! I was thinking along similar lines for the production unit - likely an input RC to cover both ESD protection and RFI rejection.

[madires]

Have you considered adding an LC filter after the boost converter (for the 5 V rail) to mitigate the typical issues when running linear audio amps with SMPSUs?

[neighborhoodcircuits]

Have you considered adding an LC filter after the boost converter (for the 5 V rail) to mitigate the typical issues when running linear audio amps with SMPSUs?

Good question. I assume you're referring to the ripple from the switching converter getting to the headphones and causing various kinds of problems (EMI, excess power dissipation, weird nonlinear effects)? I haven't specifically measured that yet, but for now we can look at what the datasheets say.

The boost converter shows about 10-20mVpp ripple in typical applications, with that ripple in roughly the 1MHz range (could be 500k-2M from the specs). The power amp doesn't have gain or PSRR specs going out that far, but it does show the gain falling off sharply after 100kHz, and the PSRR is about 60dB at 30kHz. Can't really extrapolate from those points, though I'm not seeing anything that would immediately make me worried. It's also worth noting that the power amp has its own ~500kHz charge pump to generate a negative supply, and the manufacturer doesn't suggest any particular mitigation for that, either.

Only way to be sure is to measure it, though. Thanks for the suggestion!

[madires]

Load changes are of particular interest. With a changing load the converter's PWM ratio changes too, which can sometimes lead to audible interferences.

[floobydust]

What delay? Are you a bot?

[magic]

ChatGPT isn't the sharpest tool in the shed.
Very poor performance today

[themadhippy]

Delay on a headphone amp? just wot every muso wants

[floobydust]

It's REVERB you want, not delay, not AI fuzzbox distortion lol