Suggestions on a bass amp tone stack?

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roberto
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Re: Suggestions on a bass amp tone stack?

Post by roberto »

You can use the mid pot like in framus cobra eq:
http://www.framus.de/media/manuals/Amps ... bra_V1.pdf

or like jcm800 bass amps:
http://www.drtube.com/schematics/marshall/2001pre2.gif

or.. there are many mods to the baxandall eq to add a mid pot. :wink:

The reason I've use a passive eq is that many basses have active eq on board, so often it's just too much. :wink:
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Bob-I
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Re: Suggestions on a bass amp tone stack?

Post by Bob-I »

roberto wrote:You can use the mid pot like in framus cobra eq:
http://www.framus.de/media/manuals/Amps ... bra_V1.pdf

or like jcm800 bass amps:
http://www.drtube.com/schematics/marshall/2001pre2.gif

or.. there are many mods to the baxandall eq to add a mid pot. :wink:

The reason I've use a passive eq is that many basses have active eq on board, so often it's just too much. :wink:
I found an article on duncan's site as wel that shows a Bax with a mid.

I think I can do a simple Bax with minimul changes in my latout too. Most of the components can go right on the pots. 2 caps on the bass knob with a resistor to ground and a resistor to the output of the first gain stage. resistors on the treble pot with a cap to ground and a cap to the output of the gain stage.

Very cool idea. I'll give it a try and post the results.

BTW, I don't use any active EQ on my basses. My #1 bass is a P-Bass replacement body a friend of mine finished for me with a Mighty Mite fretless neck. It has a standard P-Bass PU from GFS and a pair of piezo's under the bridge with a blend knob between them.
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Bob-I
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Re: Suggestions on a bass amp tone stack?

Post by Bob-I »

Roberto, thx for the suggestion on the Bax. I like it.

The Bax was easy to implement and sounds great overall. I get far better control over the deep low and a nice bright punch on the highs. I can still control the mids by adjusting the bass and treble at the same time, less of both, more mids, more of both, less mids, then just adjust the volume to balance it out.

I'm having one minor issue in that the bass control is most effective between 2:00 and wide open. Between off and 2:00 is almost no change, then it comes on suddenly.

I'm using the attached values
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roberto
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Re: Suggestions on a bass amp tone stack?

Post by roberto »

Bob, happy to ear you like it!
If you have used 1M log pot, just try to invert the way it's connected.
This should fix the problem.
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Bob-I
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Re: Suggestions on a bass amp tone stack?

Post by Bob-I »

roberto wrote:Bob, happy to ear you like it!
If you have used 1M log pot, just try to invert the way it's connected.
This should fix the problem.
But wouldn't that also reverse it's function?

I'd suspect I need a 1MRA pot.
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Bob-I
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Re: Suggestions on a bass amp tone stack?

Post by Bob-I »


Thx Roberto. The layout on the left is very close to what I did. I put R1 and C1 on the board where the FMV caps were before, and I use a 1MA pot for bass. Maybe if I try the 500KA the control might be more linear.
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Structo
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Re: Suggestions on a bass amp tone stack?

Post by Structo »

Yes I think you will get a better range with the smaller bass pot instead of that off/ on type thing.
Tom

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j-po
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Re: Suggestions on a bass amp tone stack?

Post by j-po »

A crazy idea if you want a lot more effective controls - use dual pots: Tone stack on the first row on pots - gain stage - another tone stack on the 2nd row.
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roberto
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Re: Suggestions on a bass amp tone stack?

Post by roberto »

well, I think an 80dB eq is too much.. :wink:
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Bob-I
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Re: Suggestions on a bass amp tone stack?

Post by Bob-I »

roberto wrote:well, I think an 80dB eq is too much.. :wink:
:lol:

This Bax is giving me like 20DB+- that's plenty.

I modded again last night. I changed the bass caps to .001u and .005u, from .001 and .01. This raised the knee on the bass control more into a range you can hear. The 500K pot works ok but it's still mostly effective on the upper half of the range. Treble control is very effective the way it is.

Here's a pic. I need to make a new faceplate. You can see the empty eyelets where I removed the FMV tone stack, and most of the Bax is on the controls, except for the one resistor and cap. No, the screen filters are not missing, it's UL.
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roberto
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Re: Suggestions on a bass amp tone stack?

Post by roberto »

You can use the mid pot to add mids this way:
[img:381:431]http://amps.zugster.net/images/articles ... -boost.gif[/img][img:413:383]http://amps.zugster.net/images/articles ... curves.gif[/img]
Just put a 1MA pot instead of the switch: you'll have a midboost by pot.

Or a 100kB pot in series with a 100k resistor instead of 180k resistor: you'll have a midboost contour.

EDIT 2020:
images are no longer available online, so I attach my copies of those images here.

Mid-Boost.jpg
Mid-Boost-plot.jpg
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Last edited by roberto on Sun Jan 05, 2020 11:10 am, edited 1 time in total.
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Bob-I
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Re: Suggestions on a bass amp tone stack?

Post by Bob-I »

That's very cool.

I added the 1M pot and a 470pF and 100pF in parallel. I tried several values caps and this seems to work best. the 470pF alone was not very effective, a .001uF (1000pF) was almost in the same range as the treble control, the 570pF (measured 590pF) conbination seems to be the best.

This really worked out great. The Bax tone stack really is much more effective for bass than the FMV and it's easy to implement.

Roberto, you're a champ!!
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Structo
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Re: Suggestions on a bass amp tone stack?

Post by Structo »

Did you keep the 10K mid resistor?

I tried a 5K resistor in the TSC and it seemed to add more bass control.
Tom

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Bob-I
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Re: Suggestions on a bass amp tone stack?

Post by Bob-I »

Structo wrote:Did you keep the 10K mid resistor?

I tried a 5K resistor in the TSC and it seemed to add more bass control.
Yes, I tried from 22k to 2k, 10k seemed to be the best sounding.

Gotta love the TSC. I just don't know how to get additional ckts into it like Roberto is doing.
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