Double Bass GK MB200 for DB: overcoming baked-in tone

[Pings Bass]

I'm starting to use this backend rig for DB (why? because it's what I have!), mainly for stage monitoring, but in small places, for the whole room:

• Gallien-Krueger MB200
• Gallien-Krueger Neo 112-ii

I think it sounds pretty good with bass guitar, but I haven't been happy with it for upright. It comes off as very harsh in the high end. I tried a lot of knob twisting and turned off the horn in the cab, but never was satisfied with the results.

I use a front-end rig (HPF/EQ/DI) that feeds FOH and mons when available, and I'd like whatever amp I plug into to sound the same as FOH, basically. So I'm looking for full-range, flat-response on an amp that has a notoriously pronounced baked-in sound.

My first thought was to insert my signal after the tone-shaping circuitry. But this amp does not have an effects return jack. It has a 1/8" TRS aux in (post-EQ), but I don't want to depend on that in live situations.

So I'll want to plug from my DI into the instrument input and have as close to full-range, flat-response as possible going into the power section and out the cab.

According to spec, the "contour" switch does

• +2dB @ 50Hz
• -10dB @ 500Hz
• +3dB @ 7 KHz

in other words a big scoop, which I definitely don't want.

The EQ knobs are

• bass: +/-10dB @ 60Hz
• low mid: +6dB/-10dB @ 250Hz
• hi mid:+6dB/-10dB @ 1KHz
• treble: +/-14dB @ 7KHz

(Q not specified))

By the spec I would assume I could get close to flat if I turn off contour, put the bass and treble straight up, and turn the lo mid and hi mid up a bit I'd be close to flat... but that doesn't sound good to me! So I thought I'd put a little pink noise through it and see what it looks like on an analyzer.

Here's what the "contour" looks like with all the knobs straight up:

Looks roughly to spec! Boosts a 50hz and 7Khz and a cut a 500Hz

So I tried contour off, all knobs straight up:

That's not what I expected per spec and assumptions about the knobs! Still a little scooped, and a big high-end boost. It sounds harsh to the ear.

A very simple tweek (turning treble to about 9 o'clock) gives me pretty dang close to flat:

Closer...

I added a little low-mid, and I think I found flat or close enough for govt work

I know "just use your ear," but I need a point of departure! This gives me that. Posting here for posterity, and if anybody else is trying to get decent sound out of this amp for DB. It now sounds pretty good, I think. Punchy, but without sounding harsh. I'm playing a gig with it Saturday, and I'm pretty confident now that I can focus on music instead of knobs.

 

[KevInDaBassment]

Great info!!

Yes, I can't speak for everyone but I left that Contour switch all the F off when I had my MB200. My usual go-to for the GK EQ was some high cut, boost lo and hi-mids to about 1 or 2 o'clock and leave bass at noon. No contour or scoop stuff at all. I do love to crank the Presence knob up on the 700RB-II though, gives awesome cut and grind paired with a healthy Boost setting of 3 or 4 o'clock.

This has me wanting to grab an MB200 again

 

[Pings Bass]

This has me wanting to grab an MB200 again

It's a great little amp, I love the weight-to-power ratio, but up until today I have been struggling with getting it to sound good with upright!

 

[Ric Vice]

There was a time when the original Gallien Krueger 200MB Combo ( not the MB 200 head) sounded great with Double Bass. So did the MBS combo. The MB 200 head can sound pretty great!

 

[DoubleMIDI]

I think I remember that @fdeck has measured the MB200 for mostly flat response and posted the result here on Talkbass.

 

[fdeck]

I think I remember that @fdeck has measured the MB200 for mostly flat response and posted the result here on Talkbass.

I remember it was something like 10:00, 2:00, 2:00, 10:00.

But maybe I'll hook it up again and try Esteban's settings. Also, I now have two of these things, and it'll be a chance to see if they're different. The designs are slightly different on the inside, notably in the limiter circuit, but I don't know if the EQ ever changed over the years.

 

[jasper383]

I think I remember that @fdeck has measured the MB200 for mostly flat response and posted the result here on Talkbass.

This (10, 2,2,10) is roughly the flat setting for all the MB heads. They have a baked in scoop (which is very pleasing in certain situations), but if you wants flats, this is it.

 

[Bar Star]

Thanks for this!

Do you think you’ll have time to analyze and post the results for the Gallien-Krueger Neo 112-ii…?

 

[logdrum]

Cool, What pickup will you be using, You pumped in pink noise from a synth?

 

[Martin Beer]

I like my MB200, it's straightforward to get something I can use with it and I still haven't found a solid reason to look at something else. I always have the contour off, the two mids go no lower than 12:00 (usually up a little) and the bass and treble no higher than 12:00 (usually down a little).

 

[Pings Bass]

I remember it was something like 10:00, 2:00, 2:00, 10:00.

But maybe I'll hook it up again and try Esteban's settings. Also, I now have two of these things, and it'll be a chance to see if they're different. The designs are slightly different on the inside, notably in the limiter circuit, but I don't know if the EQ ever changed over the years.

This (10, 2,2,10) is roughly the flat setting for all the MB heads. They have a baked in scoop (which is very pleasing in certain situations), but if you wants flats, this is it.

Here's what I get with 10,2,2,10:

 

[Pings Bass]

Thanks for this!

Do you think you’ll have time to analyze and post the results for the Gallien-Krueger Neo 112-ii…?

As suspected, it's voiced similarly to the head (boost at 7K). Here's what I get with a Rode NT1A, which is pretty flattish, horn on cab set to "normal"

turning the horn all the down gets rid of the harsh 7k peak (x-over is at 5K I think):

NT1A response curve per manufacturer:

Cool, What pickup will you be using, You pumped in pink noise from a synth?

I use a David Gage Realist Copperhead. Pink noise is a downloaded WAV.

 

[Pings Bass]

I gotta disclaim that I am not an audio engineer, though I've played one at work.

Cheers to anybody who can replicate or dispute these findings. The paint dots I put on the amp will scrape off.

My test setup:

• WAV audio file played on phone, cast to Chromecast audio device, one mono channel split off to instrument input on the amp*
• direct out from amp (set to "pre" for control, "post" for testing)
• mic level input to interface
• record 8 second clip in Logic Pro X, playback with MultiMeter plugin (would love if somebody could tell me how to analyze in real-time with logic built-ins)

*I oughta skip the chromecast step because chromecast probably transcodes the audio to mp3 or worse; that shouldn't impact the pink noise too much, but it's one variable that can be eliminated

Gain staging is tricky because the amp doesn't have a clip light or any kind of input indicator. The curves I got looked the same at medium and high levels. Anyhoo I'm gonna practice my bass now. This was fun, but a lot of work to get to square 1!

 

[Pings Bass]

help I've fallen in a rabbit hole and can't get out

So to compensate for the very bright cabinet in addition to the very bright baked in tone AND the piezo honk, I've turned the horn all the way down and gone extreme on the knobs treble and hi-mid on the amp. Also note I'm running an @fdeck HPF pre, set to 35hz (I will usually adjust that up depending on the room, but wanted to take it mostly out of the picture here).

you know what, it sounds pretty good! I wouldn't normally go so extreme on the knobs, but this rig has a serious bias toward the sizzle end of things.

To verify my ear I mic'd it with a Rode NT1a from about 2' out, recorded a 12-second clip, then turned off the amp and mic'd the bass the same way.

I prolly oughta back off lowmids and give back a little tweeter, but this is my starting point for sure. And I swear I practiced a little

 

[Wasnex]

I have a suggestion. Don't turn the horn off, but dial it back so that you don't hear it on-axis. The 12 will be a bit beamy in the high range. The idea is to use the horn to widen dispersion in the range were the 12 becomes beamy, rather than to brighten the tone. Depending on the horn, dispersion is probably 50-60 degrees conical.

I suggest pulling the tweeter to see what model it is. I know the P-Audio PHT-406 was used extensively in GK.

Product page: https://paudiothailand.com/product/pht-406/

As you see, the PHT406 does not have a peak at 7K. However, the amp's Treble control is centered at 7K.

 

[Wasnex]

I have an older GK 700RB/112 combo. To be honest, I think it works better for upright than bass guitar. I would expect the MB200 into a NEO 112 to be pretty similar.

 

[sean_on_bass]

i use the same pickup and generally settle on contour being off and cutting some bass and mids, but dialing it in to the room i am playing in. at low volumes that works pretty well, but at higher volumes i don't care for the sound that much and struggle to get something i can say i like.

on a few occasions i have also simply let the EQ at 12 o clock but switch on contour. it scoops out alot of the mids that i dont like.

 

[Pings Bass]

I have a suggestion. Don't turn the horn off, but dial it back so that you don't hear it on-axis. The 12 will be a bit beamy in the high range. The idea is to use the horn to widen dispersion in the range were the 12 becomes beamy, rather than to brighten the tone. Depending on the horn, dispersion is probably 50-60 degrees conical.

There is a passive crossover at 5k I believe so this doesn't make sense to me . The horn and 12 should roll off/on steeply at that point, right? Usually there's a dip at the crossover point each driver stays predominantly in its lane, right?

I have turned the horn back on to get some of the energy above 5k, which is almost completely absent with the horn off.

 

[Wasnex]

The horn and 12 should roll off/on steeply at that point, right?

Pretty sure the woofers run full range. This is true for most woofer + horn bass cabs, but not all. My impression is the ceramic 12" in my GK combo starts to roll off before the horn comes in...but this is not because an LPF is applied. It's just the natural response of the driver.

If I understand, this plot is with the tweeter off.

It looks like the woofer is starting to cut off just below 4K leaving a hole before the tweeter comes in at 5K. Also it looks like the woofer response drops by about 20dB from 4K to 8K. AFAIK GK uses 18dB/octave filters.

If you dial the horn back an appropriate amount, you should get something like this:

I cut and pasted the horn response into the plot with the horn turned off. The dipped dash just below 4K is the first dash from the pasted horn plot. I aligned it with the same dash for the woofer plot. So this dash is in the same position on the original and the edited version.

 

[Pings Bass]

Gig report: it worked out pretty good to turn the treble and hi-mid the f down. I recommend it