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New bass guitar preamp


 
11/6/2004 6:16 AM
Le Basseur New bass guitar preamp
Hi all,  
Just got this Warwick Thumb bass guitar and the owner is heavily complaining about the low quality of the internal preamp on this bass-too noisy and the corrections (2-band) are too deep and too high for his needs (the preamp itself is a little encapsulated rectangle,so no intervention here).He asked me if I could make another on-board preamp-corrector for this particular instrument.He'd like a 3-band active EQ if possible,maybe even a mid-parametric one.  
Any links and/or ideas,please?  
Thanks,  
Le Basseur  
PS  
I know,must be a discrete components' thingie,(...puah!) but I can't put some tubes in that carved space on the back of the bass!;)
 
11/6/2004 9:26 AM
Albert Kreuzer
email

quote:
"I know,must be a discrete components' thingie,(...puah!) but I can't put some tubes in that carved space on the back of the bass!;) "
 
 
Why not?  
 
http://www.takamine.com/?fa=cooltube  
 
And for other discrete thingies look here:  
 
http://www.runoffgroove.com  
 
or even here:  
 
http://www.albertkreuzer.com/preamp_onboard.htm  
 
Cheers,  
Albert
 
11/7/2004 1:28 AM
Le Basseur Thank you,Albert!
Very interesting lectures,indeed!  
The Takamine thing was the biggest surprise.When you wrote "..why not?",I thought about an active bass preamp using some of those sub-miniature or pencil tubes,but the cold 12AU7 is an entirely new stuff for me.The Takamine preamp looks very sophisticated and hard to imitate from a DIY level but even so,does anybody know something more about cool tubes?I'd really appreciate any other info about this principle,thanks!  
The runoffgroove site is also interesting but it doesn't contain any onboard schematic info...useful documentation though,as I said.  
Last but not least,your JFet preamp is the most valuable info I got so far (aside of scopeboy's schemos) and,even though it's made as a "JB"-style (wich isn't the exact match for this Warwick' needs because it has a PB-split style on the neck,a JB-style on the bridge and 4 pots),it's a place to start.  
Once again,thank you and keep them coming!  
Le Basseur
 
11/11/2004 3:35 AM
alpha Re: New bass guitar preamp
In terms of design, there's not an awful lot of difference between a large proportion of bass preamps. It boils down to a few cap values which set the control frequencies - this is about choice of frequencies as opposed to quality.  
 
Find the treble cap on the board and increase it to taste. This will lower the treble frequencies.  
 
Find the bass cap on the board and decrease it taste. This will raise the bass frequencies.  
 
If you can send me JPG pics of the board I will be happy to trace the circuit for you and I could even give you some part value recommendations - it's a fairly straight forward task.
 
11/11/2004 5:10 AM
Le Basseur
email

Thanks for the reply alpha,  
What you're saying is OK and I thank you for offering your help,but unfortunately the preamp itself is not on an open PCB (in that case,I'd have made the mods/tweaks a long time ago exactly as you said) but in a little sealed rectangular plastic case.The sealing material is epoxy so I don't have any chance to get to the circuit-there are only the pots and battery wires to be seen.  
However,was thinking of a complete replacement of that preamp because there are some obvious flaws about it,the worst being the imparted "tonal character" (lately,I found out that those old MEC preamps were made using opamps,wich,opposed to JFets,explains why my ears are bleeding;) ).  
In the meantime,I'll get as a gift a brand-new 3-band with parametric mids preamp made by Noll Electronic (all-round JFet SMD) from my cousin who reacted unexpectedly fast:D to my complaints and bought it.For now,"the case is closed"!:)
 
11/11/2004 7:44 PM
alpha
Hmmm, bummer.  
 
Externally raising the bass frequency and lowering the treble aren't possible without another "hook point" into the circuit. You can often (not always) put a cap in series with the treble pot wiper to *raise* the treble frequency, and a cap across the ends of the bass pot to decreasing the bass frequency - both are in the opposite direction to what you want!  
 
Good luck with it just the same.
 
11/12/2004 1:38 AM
Le Basseur
Thanks,  
This is a fast-and-easy one!  
I'll try it in a few days,just before the installation of the new preamp.However,I'd not throw away the old MEC and if the tweak sounds acceptable I'll give it to one of my younger fellow bass players who'd want active EQ.  
Regards,  
Le Basseur
 
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