Circuit for headphones?

General project help for Adafruit customers

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
robcranfill
 
Posts: 142
Joined: Wed Feb 13, 2013 4:14 pm

Circuit for headphones?

Post by robcranfill »

Hey, all :-)

I am building a project based on a Feather RP2040 that emits audio (via the audiopwmio library and an Adafruit MAX9744 amplifier) and I've got it working fine, but I'd like to be able to work on it without bugging my wife, and use headphones some of the time.

I found this page from "TodBot" that then refers to this Twitter thread and this little circuit diagram.

This seems quite suitable for my purposes. Anyone have anything different/better/simpler? (Hard to imagine anything simpler!)

Any ideas appreciated!

/rob

User avatar
sj_remington
 
Posts: 994
Joined: Mon Jul 27, 2020 4:51 pm

Re: Circuit for headphones?

Post by sj_remington »

The circuit linked has high output impedance, and would probably not drive headphones with useful volume.

User avatar
robcranfill
 
Posts: 142
Joined: Wed Feb 13, 2013 4:14 pm

Re: Circuit for headphones?

Post by robcranfill »

sj_remington wrote: Thu Jan 19, 2023 2:17 pm The circuit linked has high output impedance, and would probably not drive headphones with useful volume.
Ah, yes, I see now that, of course, that is just a line-level output, suitable for input into an amp of some sort.

Any ideas how to drive a set of headphones? I've looked here at Adafruit but see no modules with headphone out.

User avatar
robcranfill
 
Posts: 142
Joined: Wed Feb 13, 2013 4:14 pm

Re: Circuit for headphones?

Post by robcranfill »

Could I use an Adafruit stemma speaker by un-hooking the speaker and wiring in a headphone jack? That is, just using the amplifier part of this breakout?

User avatar
sj_remington
 
Posts: 994
Joined: Mon Jul 27, 2020 4:51 pm

Re: Circuit for headphones?

Post by sj_remington »

If you don't want to use the 20W amplifier with the headphones, this tiny stereo breakout would work: https://www.adafruit.com/product/987

It is a good idea to use a voltage divider when connecting headphones to an audio amplifier designed for speakers. Overview here: https://[email protected]/h ... p-adapter/

(REMOVE the @ in the link, added to get around the forum censor).

User avatar
robcranfill
 
Posts: 142
Joined: Wed Feb 13, 2013 4:14 pm

Re: Circuit for headphones?

Post by robcranfill »

sj_remington wrote: Thu Jan 19, 2023 3:19 pm If you don't want to use the 20W amplifier with the headphones, this tiny stereo breakout would work: https://www.adafruit.com/product/987
I think maybe you are under the same mis-impression that I was: the Adafruit 20W amp that I am using does not have any headphone output. The description does repeatedly refer to the “headphone jack” but this is for input, not output. I made the same mistake and was disappointed to realize this after I ordered it. So here I am. :-]

User avatar
robcranfill
 
Posts: 142
Joined: Wed Feb 13, 2013 4:14 pm

Re: Circuit for headphones?

Post by robcranfill »

sj_remington wrote: Thu Jan 19, 2023 3:19 pm It is a good idea to use a voltage divider when connecting headphones to an audio amplifier designed for speakers.
I guess ideally, rather than retrofitting a power amp to work with headphones, if I could just create the appropriate circuitry for a dedicated headphone amp, that might be preferable. But thanks for the link!

User avatar
sj_remington
 
Posts: 994
Joined: Mon Jul 27, 2020 4:51 pm

Re: Circuit for headphones?

Post by sj_remington »

the Adafruit 20W amp that I am using does not have any headphone output.
No misunderstanding there. That was why I brought up the resistive dividers. The usual approach is to connect the high resistance end of a divider to each of the speaker outputs, and the taps to the input leads of the headphone jack.

This assumes a common ground, and now that I look at the schematic of the 20W amp, that may not be advisable, as there is none for the push-pull speaker outputs.

Indeed, the best solution is a dedicated stereo headphone amp.

Locked
Please be positive and constructive with your questions and comments.

Return to “General Project help”