Gallien Krueger MB-500... any thoughts?

[BassMonstrum]

I did a search and found very few threads about this amp, so I thought I'd start one.

Tried one out in a music-store here in Norway and was blown away! Ran it through a GK NEO212 with a Fender Jazz bass, since I own both. Lots of headroom, weighs only four pounds and sounds warmer than my GK1001rb-II. Needless to say, I bought it! My plan is to split my signal through my Sansamp BDDI sending the affected tone to the MB-500 feeding my Mesa Roadready cab, while the parallell output goes to the pedalboard then the 1001rb and NEO212.

Any thoughts or questions?

[craig.p]

Polarity-check time.

1. Check with GK tech support (or maybe Bob G will pop in) regarding whether each GK amp either preserves or inverts input polarity at its speaker outputs. Get an answer for each one. Let us know once you have your answers.

2. Check with Tech21 tech support regarding whether the BDDI either preserves or inverts input polarity at the "output" phone jack (the one on the left).

[BassMonstrum]

Hmmm... what if I use a Boss Line Selector?

[craig.p]

If that box lets you send your signal to either the 1001 or the 500 but not to both at the same time, then you're good to go.

[BassMonstrum]

Again... hmmmm.

So to run them at the same time I need an ABY-box?

[craig.p]

You might be able to run one off the effected BDDI output and the other off the uneffected BDDI output (the one on the right). Check the BDDI manual to see if this is supported. But if you do that, then your second question to Tech21 support should be whether input polarity is either preserved or inverted at that uneffected output.

I'm assuming an "ABY box" is a box that sends an input to either one or both outputs. If so, then you don't need an ABY box unless there'll be cases where you don't want to run one or the other GK. If you want to run both at the same time, always, you might be able to get by with three phone jacks wired in parallel, inside a cheap metal box. Sometimes this works, sometimes it doesn't. For me it's worked far more often than not. Your grounds have to be solid and your amps should both be plugged into the same power strip.

[BassMonstrum]

Both amps will not be on at the same time. The "clean" rig will also be on, while the fx-rig will be kicked on whenever I need a boost, so to say. I'll probably be better off with an ABY-box. Thanks, though!

[craig.p]

Ok, but make sure you get your answers on polarity. Polarity-checking when you're using non-identical gain stages simultaneously is not optional and I'm still shocked at how few people actually go through the exercise.

[Jim C]

Craig,
Assuming you had the volumes down VERY low; couldn't you use the 9-volt battery test to check absolute polarity from the input lead starught through to the speaker?

[craig.p]

Hi Jim. First of all, 9 volts would be at least an order of magnitude too much voltage. Second, in the vast majority of cases the signal chain won't pass DC.

The proper way to do the test is with an audio generator and a dual-trace oscilloscope. The audio generator's output is connected to the amp's input and to scope channel A. Scope channel B is connected to the amp's output. (Of course the channel gain for channel B has to be set far lower than that for channel A.) If the two waveforms look the same, then the amp is "non-inverting" (preserves polarity). If the waveforms are "flipped" one relative to the other, i.e. one looks like the other's reflection in a pool of water, then the amp is "inverting" (inverts polarity).

Hope this helps.

[::::BASSIST::::]

Currently digging my mb500 alot.

[BassMonstrum]

Originally Posted by ::::BASSIST::::

Currently digging my mb500 alot.

What do you run it with?

[craig.p]

Thought I'd better add the obvious to the test scenario above: the amp's output should be connected to a dummy load as well as to the scope, unless it's an amp that doesn't mind running into an open circuit.