In reading your post regarding feedback problems and not being able to crank enough volume to cut through the mix brought back memories of similar experiences for me.
I also use an Underwood pickup on my 3/4 German Bass and run it through a GK MB 150, I used to keep the amp in close to me (within 4 -5 ft) while playing on stage.
Discovered that the other guys could hear the bass real well at the other end of the stage and were always saying "turn it down".
With some experimentation moving the amp around and angle placement I discovered that I can actually lower the volume required on stage and reduce any tendency for feedback by keeping the amp in behind me and up to 15 ft away pointing on a 45 degree angle or so.
Just getting it away from the bass makes a huge difference and I believe it allows the sound waves to fatten up prior to you hearing them.
Incidently I line out off the back of the amp with a 1/4 to XLR adapter and always have the sound man keep the bass out of the monitors using only the amp for my monitor.
I've played some pretty loud stages and never seemed to have a problem getting the volume I need in this configuration.
I did buy an Ergo Electric Upright and I use it on stage as well, feed back is not an issue at all with this bass and you can basically park the amp on top of the bass however... again the sound is not as good for me when the amp is right there beside me and I've found that the distance and angle thing is the important ingredient.
With the Ergo I actually have to turn the volume output level knob up about 2 numbers more than is required with the Acoustic in order to run approximately the same volume on stage from the amp. I don't adjust the Volume swithc on the GK which as you know is on the pre-amp side of the amp, doing so overdrives the sound board and it ends up clipping. I've set this knob at a 3 and have never had to go higher with it in either application (acoustic or Ergo).
The Output knob I usually run around 10oclock with the acoustic on stage and around 12oclock with the Ergo.
As far as eq settings I don't adjust them at all when switching bass's from acoustic to EUB and I get a great sound from both.
Prior to plunking down a huge amount of money I would suggest trying the amp movement thing. If your still having a problem and are determined to go to an EUB don't be afraid to go the Ergo route at $700 US dollars it is a good deal for the money and the bass plays really well.
Yep there are lots of EUB's out there that are likely better but their price's are a heck of a lot higher, in order to justify the difference in money they should sound exactly like a DB acoustic and being as the Ergo sounds as close as I've heard and it is so easy to play I don't believe the value is there.
If your getting big bucks for playing bass then go ahead and go after a Clevinger, Azola or Eminence but I don't think your going to hear 3000 dollars difference.
I've tried the Eminence and the sound was not as good as my Ergo but it sure is a pretty bass, I've used an Ampeg Baby bass and got good sound but the damn thing was impossible to keep in tune on outside stages.
I've heard the Clevinger and love the sound out front in the house and ditto for the Azola but then again the folks hearing the Ergo out front in the house usually say they can't believe how much a stick with strings sounds like a regular Upright bass.
Good luck............ hope this helps.
