Presonus Bluetube makeover

[moonbird]

Hello all -

The subject of the Presonus Bluetube mic preamp was mentioned in another thread as a possible subject for mods. To get the ball rolling - kevinkr offered these suggestions :

"I replaced the original quad op-amps with National LME49740 - see here: LME49740 - Quad High Performance, High Fidelity Audio Operational Amplifier

The supply in this thing is one of the real weak points IMO and a separate toroid and full wave rectification of the rails would be a real enhancement. A separate winding for the tube would be good too."

thx to all --

[kevinkr]

Here's that link again since it did not copy over correctly to the new thread:
LME49740 - Quad High Performance, High Fidelity Audio Operational Amplifier

These parts are SOIC (surface mount) so some skill in their replacement is required.

The 12AX7A in mine was Chinese, nothing special. I replaced it with a vintage Mullard..

Again I have no idea what effect these changes will have on the sound of this mic pre as I have not yet used it to record anything.

The tube in the Bluetube pre is really there to add some distortion, err, warmth in the signal path. This isn't a tube mic pre in any sense.

One thing worth considering as I pointed out in another thread is power supply improvements. A nice toroid and an entirely outboard supply providing +/-15V or so and 60V for the tube would be worthwhile I suspect. The supplies are mostly regulated, but IIRC there is nothing special about the circuit, and because a wall wart (18VAC) is used as a source all of the supplies are half wave.