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Author Topic: Adding a variable Contour control on GK MB Series?  (Read 1160 times)

ziggyzipgun

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Adding a variable Contour control on GK MB Series?
« on: June 06, 2016, 10:28:06 PM »
I have a Gallien-Krueger MB110 that I really like, but I wish that it had the adjustable Contour knob of the MB200 head instead of the on/off Contour switch.  Are the circuit boards similar enough that it could be modded? 

Enzo

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Re: Adding a variable Contour control on GK MB Series?
« Reply #1 on: June 07, 2016, 05:28:44 AM »
The boards need not be similar, it helps if the circuits are similar, but even then, it is just a matter of identifying the part of the circuit in any amp that does the contouring, and then decide how to make it variable.

it would be helpful if you posted schematics.  All my various 200MB schematics show it with a switch.

However, looking at a number of them with switch, and others with control, it appears that the switch is a SPDT, with the center as the output to the rest of the amp, and the end poles are at the outputs of two separate tonal paths.  The contour control models have a very similar circuit except instead of the ends of a SPDT switch getting those signals, the ends of a pot get them, with the wiper taking the place of the switch common.

So as a simple experiment, you could remove the switch and wire a control in its place on some wires, and see if it works as you like.  If it does, then you'd need to mount the control in there somehow, in place of the switch.

ziggyzipgun

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Re: Adding a variable Contour control on GK MB Series?
« Reply #2 on: June 07, 2016, 09:50:32 AM »
My mistake - I was thinking of the MB500 and larger models that have the Contour knob.

Would you happen to know the value and taper of the pot used in those model?

Thanks for the quick and thorough reply!

ziggyzipgun

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Re: Adding a variable Contour control on GK MB Series?
« Reply #3 on: June 07, 2016, 09:47:31 PM »
I found the schematic for the MB500 Fusion head, which uses a 500k linear taper pot.  I'll give it a shot, but does anyone have any experience with the GK-style contour/"voicing filters" that are used on a lot of bass amps?  Any suggestions?

I actually bought the MB110 while searching for a better quality/higher wattage amp similar to the Crate BX25 combo, which I've had around for years and years but only recently tried reamping guitar through and was blown away.  The Crate has a "Shape" knob and an on/off switch for the Contour, and 100% sounds very similar to the GK, but I keep it at 50% and it sounds great. 

Enzo

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Re: Adding a variable Contour control on GK MB Series?
« Reply #4 on: June 08, 2016, 12:03:06 AM »
The pot idea should work in any of them, but the pots vary, I saw one was 2k, and other 10k.  SO it might matter the value in a specific model.  Try the 500k, if it works well, great, if not, then try say 50k or 10k or 5k and see if any work better than others.