Baja Music Man guitar and bass onboard preamps  [documentation]

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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Andy_
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Post by Andy_ »

Hallo Manfred,

... those were the days ;-)

Maybe we should mention that this modification will not change the sound in general...

Viele Grüße
Andy

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JayGunn
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Post by JayGunn »

About this SMD version of the MM preamp, has anyone bought and populated this circuit board?
If you look at the silk screening you can see that it is missing a number of components, like multiple resistors and multiple capacitors from the bill of materials. Maybe these are added to the back side? Otherwise it couldn't really be the MM preamp this thread is about...

John

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deltafred
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Post by deltafred »

I've just built a perf board version of the preamp with a FET input buffer and fitted it in an EUB (with piezo pickups). It sounds pretty good but it does need a HPF after it because of all the lows that the EUB puts out.


I don't think the SMD board above is for this preamp, there are the wrong number of resistors and capacitors and nowhere to connect the pots. It also has + and - inputs which looks like it could be for a differential signal, like an XLR mic or line signal to single ended output.
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JayGunn
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Post by JayGunn »

Thanks for confirming my suspicions!

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Andy_
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Post by Andy_ »

deltafred wrote:I've just built a perf board version of the preamp with a FET input buffer and fitted it in an EUB (with piezo pickups). It sounds pretty good but it does need a HPF after it because of all the lows that the EUB puts out.
You should omit the fet buffer and wire the pickup directy to the circuit 8) Otherwise the treble control will not work as it should be. You pickup parameters should be in the range of the original (a resistance of about 2k points to a suitable pickup). Unfortunately there are many replacement pickups with too much output available. Although the resistance is not the problem it comes along with an improper inductance will will lower the treble frequency peak to somewhere in the midrange...

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deltafred
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Post by deltafred »

Andy_ wrote:You should omit the fet buffer and wire the pickup directy to the circuit 8) Otherwise the treble control will not work as it should be. You pickup parameters should be in the range of the original (a resistance of about 2k points to a suitable pickup).
The buffer is staying, piezo pickups need a high impedance buffer to work properly.

The output impedance of the buffer is low and the treble control works very well, I have a genuine MM with a 2 band pre so I know exactly how the treble control should work.

I also have one fitted in a bass with a resistor in series with the pickup when the coils are in series (to match the series and parallel volumes) and the treble control does not work properly unless you shunt the resistor with a suitable value capacitor.
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012

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Post by marsbel »

Could you post the circuit of the buffer? I'd be interested in trying this out on my bass. I've got plans to add a piezo bridge.

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Andy_
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Post by Andy_ »

deltafred wrote: (...)
I also have one fitted in a bass with a resistor in series with the pickup when the coils are in series (to match the series and parallel volumes) and the treble control does not work properly unless you shunt the resistor with a suitable value capacitor.
That's exactly what I wrote some posts ago ;-)

I can imagine that there is some kind of treble functionality even with the buffer but this would only be "half of the circuit".
The treble rolloff caused by the cap (that one wired to the output) should be hearable.

To say it again (of course this is not directed to you because you use a piezo): the "magic" of the circuit is the combination of the pickup's inductance and the series cap at the input. Any additional resistor (or balance pot) will dampen the circuit more or less...

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Post by bscur »

Hi, I wired up one of these and put it in a Stingray. It sounds great, but the treble is working in reverse. I used a 1megC reverse log pot and double checked the wires, but the more you turn it on the more it cuts the treble. If I roll it off all the way, it boosts the treble. It sounds great, but the pot is working backwards. I tried swapping the outside lug wires, but that sounded horrible. Any suggestions?

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deltafred
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Post by deltafred »

bscur wrote:Hi, I wired up one of these and put it in a Stingray. It sounds great, but the treble is working in reverse. I used a 1megC reverse log pot and double checked the wires, but the more you turn it on the more it cuts the treble. If I roll it off all the way, it boosts the treble. It sounds great, but the pot is working backwards. I tried swapping the outside lug wires, but that sounded horrible. Any suggestions?
If you like the sound of a reversed C slope log pot then use a non reversed A slope pot.

I seem to recall in one preamp build I didn't have a C slope pot handy so used a linear (B slope). I must be happy with it because it has been like that for about 10 years and hasn't bothered me.
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012

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bscur
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Post by bscur »

Hi,
My problem is that it works backwards. If I crank the treble knob to ten it is all the way off/cut/mellow. If I roll it back all the way it is brightest. I just want it to work like a normal tone or volume knob- the more you turn it clockwise, the more intense it gets. Somehow, it is working backwards.
Brad

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PaulBass
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Post by PaulBass »

the pot is wired wrong. thats the most common mistake. either that or you made a mistake in the circuit somewhere

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av500
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Post by av500 »

TI is stopping the LM4250 production, stock up while you can :)

https://tech.ebv.com/PCN/pcns_show.php?pcn=1502911127

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PaulBass
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Post by PaulBass »

I stopped using LM4250's when I found better opamps

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Jarno
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Post by Jarno »

It does add a bit of "je ne sais quoi" in this preamp though.
Somewhat less treble I suppose, and then there's the 50 fold (or so) reduced power drain when compared to tl072.....
"It crackles....., but that's ok"

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Jarno
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Lovepedal Eternity
Phase 100
Brown source
Fuzz Face
Flipster
Alembic F2B (tube preamp)
Opamp and FET buffers
Loads of speakercabinets and ampracks
Busy building a modular synth (ssm2044 vcfs, preamps, ADSR's, VCO's, VCA's)
Tables
Bookshelves
Basses
So many things! :D
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Post by Jarno »

To follow up, I did a layout for the Stingray preamp, which has a bit more room for film capacitors and bigger electrolytics.
Slightly bigger but still not too large:
Image
Uses SMT resistors:
Image

Let me know if someone wants a board.
"It crackles....., but that's ok"

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Post by bajaman »

:lol:
thanks man
bajaman
be kind to all animals - especially human beings

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Post by temol »

Assume I'd like to mix piezo and magnetic pickup with a bass preamp. Is it just a matter of putting summing op-amp in front of 1u cap?

T.

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Post by tommymariotti »

Hi guys,
I finished this preamp now and I mounted it in my MM Stingray.
It work well but when the bass potentiometer is at maximum it's doesn't sound.
What could it be?

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thetragichero
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Post by thetragichero »

my first thought is something contacting ground that shouldn't be (I usually don't find this out until the laaaaast pickguard screw is fastened...)

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