Looking for a simple analog mic monitoring / sidetone circuit

[Headlab]

Hi all

I'm looking to build a simple device that I can put between my headset and my PC's built-in soundcard that will inject the mic signal into the headphones. The headset is closed-back, and I find myself yelling unnecessarily when things get loud. This can be enabled in Windows via software, but the latency is problematic. I know there are plenty of interfaces out there that incorporate this feature (some are dirt cheap), but it would be fun to build it myself.

The mic capsule is an electret. As for power, 5V is easily available via USB, and this can be increased with a small boost converter if necessary.

I'm envisioning a simple single-ended mic preamp for the capsule and then a mixer to add it to the existing amplified headphone signal. Does this sound about right?

 

[Tubetec]

The mic signal would need to be mixed in before the headphone amp ,
a small 4 ch audio mixer would probably do it although you'll still need the electret capsule pre-amp'd .

Heres an electret preamp thats phantom powered ,

https://www.ebay.ie/itm/254884630092

 

[Headlab]

Okie dokie. Thank you for the link, but I'd prefer to build this myself . So looks like I'll skip the integral sound card's (probably not great) mic pre and headphone amp.

For the mic pre, would something like an NE5534 (100x gain, adjustable) do the trick? Are there any special considerations I need to take into account for splitting the amplified mic signal to the headphone amp as well as the sound card line in?

Headphone amp could be anything from a simple cmoy or a TPA6120 for more grunt.

 

[Chrisfromthepast]

This seems to share some of the same design constraints as a party line intercom system.
Check this out: ComClone2-Home
The supply is 30v, which will be different from your project
You don’t need much of the top half of the schematic, and you do need to account for the fact that your input is stereo. But your three sub-circuits are there.
The author describes each sub circuit on another page, could be helpful.

 

[Headlab]

Thank you, Chrisfromthepast! That will definitely be helpful.

 

[Tubetec]

Soundcard/computer mic inputs usually provide a few volts to energise the capsule .
What ever kind of amplifier circuit you end up using you will need to provide this bias voltage to get sound .
Splitting the output of the mic pre between the two inputs shouldnt pose any problems .

 

[Tubetec]

Heres a simple electret mic pre using a 5532 op amp ,

http://www.next.gr/circuits/Electret-mic-pre-amp-l20780.html