2-band bass guitar onboard preamp

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Hi guys,

First post, new member. I build bass guitars as a hobby, the whole shebbang right down to the pickups. I now want to build a preamp.

I'd like to have an active 2-band preamp that fits onboard and runs on one or two 9 volt batteries. I've done soldering before and I can read schems. The building part should be fine but I don't know anything of the theory part.

I've seen albert kreuzer's preamp on the net, it seems very nice and I hear good things about it but it only has one tone knob. Would that be easy to change for treble and bass knobs?

Does anyone have schems of 2-band bass preamps that fit the bill that should work well?

thanks for the help
 
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Hi displaced Phil! ;) ,
Welcome to the forum! I bet the weather is nice down in Oz.

Just wanted to welcome you here. I'm sure others can help with what sounds like an op amp or discrete solution. Which way are you more comfortable? What levels do you want to see?

-Chris
 
http://www.albertkreuzer.com/preamp_onboard.htm
Basic design. The tone stack can be any design available, it soesn't really matter. Btw, do you want separate tone controls for each band? Anyway, these circuits are so simple that almost any combination will work :) And if you feel unsure about inventing things, download some simple SPICE simulators to make sure the new circuit will operate like it should before even building it :)
Good luck
 
Thanks for the input guys. I'm prefectly fine with the kreuzer preamp if a baxendal can be put in place of the tone pot.

Only problem is, I don't know jack about how to do that. that's why I was hoping one of you guys might have a similar circuit around that would fit the bill where I would only need to solder up components based on the schematic

Anybody feel like giving me a newbie's course on how to stick treble and bass pots on that circuit? :blush:
 
Here's one that I have used for many guitars and basses. You can easily change the EQ points for guitar or bass.
 

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I've built about 20 of 'em, and they sound great. You can use a NE5532 or better for lower noise, but the LF353 works pretty good. Under normal use, the battery lasts a long time. I normally make mine unity gain, or a slight gain so it doesn't overload effects or amps.


Here's the "big brother" with a 3 band EQ. I've only built one of these. It's very nice.
 

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I really like that 2-band preamp Brion. I'd like to try building it. Do you have any photos of the end product? I'd be curious to see that.

I can easily find the 50k pots for the treble and bass but I've never seen a 10k pot in a guitar-type pot (like cts pots) where did you find yours?

I'll have a look at all the components and try to scrounge them up. i think i'll definitely be playing around with that in the next week.

If you've got any other usefull tips or tricks or even pcb or perfboard diagrams i'd love to see it/them too :D

thanks again
 
I'm afraid I don't have any photos at the moment, but maybe I could take one in the next few days. I used dry transfer direct etch on the ones I etched and made a few on copper clad perfboard too. both ways are pretty simple. The most difficult thing was to find a place for the battery before they came out with the externally accessible battery holders. I usually just routed a cavity behind the pickguard for it.

As far as the 10K pot, I get most of my electronic supplies from Mouser Electronics. http://mouser.com/

Actually, the value of this pot isn't critical and a 50K would probably work. It should be audio taper though, while the tone pots should be linear.
 
Questions Questions Questions

Hi All,

I am building a Les Paul type thing, I am thinking of using the three band EQ version of Brion55's design, so I use all four pots (for vol, bass, mid and treb), with a push switch on one pot to dial in extra gain

The alternative is the two band version with a variable gain pre-amp (so the pots would then be vol, bass, treb and gain)

So my questions are:-

For the first alternative above, could you have a switchable gain level on the pre-amp, so you can flick a switch and dial in additional gain (for soloing)?

For the second, could RG2 be a pot so you can vary the gain level? If so, would any other modifications be required?

Any help and advice appreciated.

Cheers
 
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Re: Questions Questions Questions

Scummer said:
For the first alternative above,

use the switch to change resistor value in the feedback network.

Usually dropping another resistor in parallel with the feedback resistor (-in to ground, not the o/p to ground) should give you a gain boost, but it shouldn't overload the opamp or anything, so keep the value sensible.

If you're trying to vary gain using a pot you would need to ensure that if the pot decides to go to heaven at any point in time (wiper not conducting or wiper turned fully one way or the other) the minimum feedback ratio is maintained through fixed resistors, usually in series and parallel with the pot.
 
A volume "boost" switch would be very useful. You would still have control over the volume with the volume pot, so I would think another pot would be redundant. Please keep in mind that the input circuit can provide a HUGE amount of gain by just changing the resistors. Be careful not to go too far, or all you'll have is distortion - not a very nice distortion either. Another useful alteration is a "Mid shift" to select the center freq of the mid control. Or even a "Mid sweep" control if there is room. I have included the schematic below.
 

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Hi

I have added a DPDT switch to let you choose between two different gain levels, and have worked out how to fit it all onto a bit of 21x21 veroboard (approx 5.25cm x 5.25cm) which should fit in the space available. As you can see, I am not using the version with the mid-sweep (not enough space for all the pots.....)

Any advice on:-

1) RG1A and B values? I need a small but significant boost for soloing, but I am not sure if Vg is a linear measure (i.e if the value is doubled, does this actually mean the thing will be twice as loud?)

2) As I am not using the mid-sweep, what are the suggested values for the two resistors?

In both cases I can just experiment with different values, but I would appreciate any suggestions.

Cheers
 

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