I recently got AT-OC9XML cartridge and I want to build op amp based MC only preamplifier that's powered from USB power bank. I decided that I use the circuit of Phonoclone from RJM Audio.
I could use DC-DC converter to step up the 5V USB voltage to 24V and use TLE2426 to split the rails for +12V and -12V.
But I'd like to keep it more simple and use rail to rail op amp. There aren't many op amps out there for audio use that are designed to be powered from only +5V. One such op amp is LME49721.
I came up with this schematic:
I have lots of those USB-C connectors so that's what I'd use. R2 and R9 set the gain. AT-OC9XML has 0,4mV output so 180 ohm would give about 55 dB of gain for 0,7x line output.
As there's no negative voltage rail DC offset would be pretty high so fairly big output cap is needed. Before I start with the PCB layout I'd like some feedback about this. I'm an electronics hobbyist for many years but I'm new to audio circuits.
My idea is to make this SMD only build that would fit in slimline Hammond 1455B1002 (100x72x19mm) case.
I could use DC-DC converter to step up the 5V USB voltage to 24V and use TLE2426 to split the rails for +12V and -12V.
But I'd like to keep it more simple and use rail to rail op amp. There aren't many op amps out there for audio use that are designed to be powered from only +5V. One such op amp is LME49721.
I came up with this schematic:
I have lots of those USB-C connectors so that's what I'd use. R2 and R9 set the gain. AT-OC9XML has 0,4mV output so 180 ohm would give about 55 dB of gain for 0,7x line output.
As there's no negative voltage rail DC offset would be pretty high so fairly big output cap is needed. Before I start with the PCB layout I'd like some feedback about this. I'm an electronics hobbyist for many years but I'm new to audio circuits.
My idea is to make this SMD only build that would fit in slimline Hammond 1455B1002 (100x72x19mm) case.
You still need a split supply as you are referencing the positive input of the opamp to ground
and the opamp cannot generate a negative voltage. You will have to bias the input ground
and the cartridge ground at 1/2 Vcc. Then your other problem would be low headroom and
overload recovery from pops and clicks.
and the opamp cannot generate a negative voltage. You will have to bias the input ground
and the cartridge ground at 1/2 Vcc. Then your other problem would be low headroom and
overload recovery from pops and clicks.
A very nice cartridge by all accounts, so why not go "all in" on a phono stage & PS.
jeff
Yes, but there are tons that are perfectly able for audio, just because the marketing dept don't claim a chip is aimed at the audio market doesn't mean much - the bottom line is always the specifications and there are a ton of precision low-noise 5V opamps targeting driving ADCs - just pick one with enough bandwidth and gain and low enough noise. Not all rail-to-rail opamps have rail-to-rail output when loaded with a low impedance - watch-out for this - many are only happy with 10k or higher load.
I've used the AD8656 a few times as an example - its got bags of output drive.