New (to me) opamps

[JTEX]

I tested an OPA2310 the other day to see if it makes sense as a headphone amp, given its high output current capability (150mA) and very low idle current (~165uA per channel). Great for battery power! Only problem is that it doesn't take more than a 6V supply. But a low quiescent voltage regulator can take care of the that.

It's funny, I contacted TI to ask how they feel about this use case, since the datasheet doesn't give any performance data for such heavy loads (most common headphones and earbuds are between 16 and around 50 ohms or so). After many back-and-forths, they admitted they never officially tested it with loads below 600 ohms or so, so I was basically on my own.

I'm pleased to report that it does a great job. I got 150mW out of it into 16 ohms, and 110mW into 32, at less than 0.5% THD. That is really, really loud! More so than many dedicated headphone amp chips, while consuming quite a bit less idle power.

Caveats: to get the lowest THD (below 0.5%, typically <0.1%) you must use it in a non-inverting configuration (inverting doubles THD), and at unity gain. Any additional gain increases THD, so you're better off adding a separate gain stage before a unity-gain OPA2310.

Which brings me to the second opamp I discovered: OPA313. Would make a suitable gain stage before OPAx310. Also a low voltage part (<6V), but it only draws 50 microamps while having a 1MHz bandwidth and significantly less noise than a TL062 that draws 4x as much juice.

/endbraindump

 

[Feral Feline]

Thanks for the info.


This is the sort of ding-etje that's up @Passinwind 's alley — any additional findings, Charlie?

 

[Passinwind]

Thanks for the info.


This is the sort of ding-etje that's up @Passinwind 's alley — any additional findings, Charlie?

I'm still playing catch up on optimizing for the OPA205 family in low current onboard preamp builds and battery powered pedals, and then using the small Traco power bricks for +/-15V power in pedals. But a headphone output for a new PEQ/Preamp/DI pedal is on my to-do list, so I'll definitely be checking out Jerry's suggestions.

 

[JTEX]

I'm still playing catch up on optimizing for the OPA205 family in low current onboard preamp builds and battery powered pedals, and then using the small Traco power bricks for +/-15V power in pedals. But a headphone output for a new PEQ/Preamp/DI pedal is on my to-do list, so I'll definitely be checking out Jerry's suggestions.

Don't people mostly use AC adapters to power pedals these days? In which case super low power is not really important... Might as well use something like an LM4808 if you can spare 1mA idle. It's also a max 6V part, so it would need a regulator.

 

[jubal81]

These are pretty interesting. I've been looking at options for driving a reverb tank and I haven't been able to setting on one yet. I don't like the headroom for most of these as most new stuff is designed for 5V-ish supply.

I like the TI series of bridge tied amps like the LM4876. They're AB, small, cheap and have good specs. The gain is adjustable with an external feedback resistor.

 

[Passinwind]

Don't people mostly use AC adapters to power pedals these days? In which case super low power is not really important... Might as well use something like an LM4808 if you can spare 1mA idle. It's also a max 6V part, so it would need a regulator.

I'll definitely check it out, and 5V power is super easy to come by these days, thanks. For my own pedal use cases battery power is mainly just an open mic thing for when I need quick and dirty EQ correction without messing with someone else's amp or FOF settings too much. Doing a more extensive multi instrument pedalboard right now using a power bank with a Cioks C4 to distribute various voltages, which is working great. Wall wart clutter sucks, but distributed line power is even worse on the floor IMO.