Shure SE30 mods:

If your unit has not been serviced in the last decade or two then I would recomend replacing ALL of the electrolytic capacitors.
This is generally a noisy pre-amp, but can be quieted a bit by increasing the filter capacitors and switching to metal film resistors. The compressor can have a good squashing type distortion on vocals.
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PSU:
Replace the 220uf 40v caps with a higher value capacitance. 1000uf-2200uf 50v work well
Bypass those with a film cap
Note: A beefier transformer into a linear regulated supply + a phantom tap would be an option. There would be a lower noise floor with the linear regulator.

Board 1:
(Optional) replace c106, 110, 114 with a .1u polyprop cap like: Wima (MKP4F031003C00KSSD)
Replace the 4.7uf electrolytic capacitors (c117,113,109) with a film cap Panasonic #ECW-F2475JA
Replace c119 with a 22uf bipolar and bypass that with a film cap
Replace the 33k's on the input jacks with metal film resistors (r25,26,21,22,17,18)
Replace the 150 ohms on the input jacks with metal film resistors (r23,24,29,20,15,16)
Replace the 33k's on the volume knobs with metal film resistors (r11,12,13)
Replace the 47k's on the board with metal film resistors (r113,118,122)
Bypass c122 with a film cap

Board 4:
Bypass c413 with a film cap
replace r406 with a metal film resistor
(Optional) replace c401 and c407 with a .47u polyprop cap like: Wima (MKP1G034705G00JYSD)
(Optional) replace c402 with a .1u polyprop cap like: Wima (MKP1T031005I00KYSD)


Board 5:
Bypass c511 with a film cap
Bypass the output (c510) 220uf cap with a film capacitor
replace r518,524,528,523 with metal film resistors


Jacks:
Put in direct outs for each channel: insert a 1/4" switched jack just after the 33k resistor on the pot and before the switch.
You can take out the battery tray and put a blank pannel there to mount your output jacks or like in the picture.


Phantom: I put in another transformer into a circuit like the 48v phantom board I used for my jbl 5306 then run it into a switch which goes into a 220uf 63v capacitor
then matched 6.81k metal film resistors to pins 2 and 3 of the xlr input. Like jensen's standard microphone preamp.
www.jensen-transformers.com/as/as016.pdf
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Disclaimer: I encourage people to DIY and I'm here in a informative role.

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ModDefecation is about making equipment sound better, providing knowledge and support, repairing that awesome piece of gear, and custom builds. Send me you questions or Ideas.