Carvin Bass Preamp - change frequencies?

I can't give you any kind of specifics as I have zero experience with this, but it sounds like you've probably got the same capacitor on your bass and mid knobs. You could call and ask them about it, or do some experimenting yourself, Carvin customer service has been very helpful in my experience. Which are they both doing, bass or mids?

 

You'll need the schematic and then someone to calculate out the values of a cap or two, then to solder them onto the PCB.

 

They don't sound the same. But if your rig isn't especially capable of lower audio detail because of midbass hump or fairly high cutoff I can see why you'd think that.

Actually the midrange seems to be a fairly wide bandpass centered at around 250 Hz, and the bass control seems to be shelving below 100 Hz or so.

 

I found this....

http://www.carvinmuseum.com/pdf/guitarbass/501b-activebassmodule.pdf

what is the number stamped on your circuit board? is it 501B?

by the looks of the schematic, the mid control is a plug in to the preamp (looks like they build the same board for a 2-band and a 3-band and just wack in the mid)...is your board like that?

It'll take me a little time to sort out the frequencies here...anyone a little more experienced that can do it quicker?

 

Sorry, Mark - I skimmed and didn't realize we might be talking about an improperly manufactured one. On my '98 Carvin preamp it's easy to hear the difference.

 

Mark- I have the same problem with my LB75F, so you're not crazy! The bass and mid sound slightly different, but not much. Not to mention very little boost/cut on all the eq. Overall, it pretty much sucks! The vol/pan PCB has 1997 stamped on it. I think they've upgraded since then, but I'm not sure. I'm curious to see what you come up with!

 

Ok...i've crunched the numbers...I hope I'm right...

I'm basing all of this off the circuit diagram, not even sure yet that this even is your circuit, yet, mark.

But anyway:

the frequency for the lows is 98Hz
the frequency for the hights is 8202Hz

the frequency for the mids is 161Hz!!! ok...that's just a little TOO close to bass, IMO...300 - 400 Hz would be more like it...

If it's possible, try replacing R10 on the circuit w/ a 1K resistor...this will give you a mid frequency of 301Hz...

The filter designs are T-filters through a single op-amp for all 3 bands, so: (1) there's a bit of interaction between tone pots, (2) you won't get much filtering effect (gain)

Gain for the Bass Boost is 1.1
Gain for the mid boost is 1.3
Gain for the highs is 35

Note: by changing R10 to 1K, mid boost gain is increased to 5

 

Didn't mean to hijack the thread, but I'll give it a try! I'll let you know how it turns out. Thanks, mate!

 

I love how they call the MC33179 a "dual microprocessor op amp". Maybe that's the OP's problem; he needs to get the operating system upgraded. Call Microsoft for details.

 

you're not hijacking the thread...you're sharing in the same problem...

hijacking is when you take a thread completely off topic...(something I have a bad habit of doing, myself...)

 

Ahh... okay!

Well, I popped in that 1K resistor at R10 and it pretty much did what you calculated. Now the mid sounds more like midrange! You can definitely tell it apart from the bass when tweaked. Not bad for $.99(for a set of 5- still have four left). Mark should have no problem doing this when he gets a chance. Now if we could move the bass down to 60 and the highs to 5K!

Thanks, Pil!

 

I have the 501b in both of my Carvin basses. I think the frequencies quoted by PilbaraBass are fairly close. I can hear a definite difference between the bass and mid, it isn't a huge difference.

When I first got my SVT3Pro, I compared the sound changes of the graphic EQ on the amp to sound changes made by the bass and mid on my basses. What I found was moving the 80Hz slider on the amp had about the same effect as the bass control on the basses. Moving the 150 and 300 Hz sliders on the amp was about the same the mid control on the basses.

Moving either but not both the 150 or 300 Hz sliders didn't sound like moving the mid knob on the bass. You had to move both sliders together. So, if I had to take a guess (based on my ears only, not scientific measurements), I would say the mid control on the guitar is a little above 200 Hz and the bass control is a little under 100 Hz.

If the OP can't hear the difference, the unit might be defective.

Ben

 

Ben,

Although your tests aren't very scientific, they certainly are methodical, and extremely practical....after all, it is what we HEAR that is important anyway...Well done!

it's nice to know that my calculations weren't total hogwash and actually stood up to an empirical test...

the calculations are basically quick and dirty and are taken from the stand point of the tone controls being wide-open, on this type of tone-control (similar to what you find in a big muff) the frequencies slide as you change the boost and cut.

I agree that the difference between the bass and the mid controls should be audible (we're talking almost a full octave here)....However, it is interesting that many other 3-band preamp builders use significantly different voicings to this.... for instance, the Aguilar OPB-3 uses 40Hz for bass, 400Hz or 800Hz (selectable) for mid, and 6.5KHz for treble...the OPB-2 is voiced at 40Hz and 4KHz, which is the Same as the Sadowsky (the sadowsky is boost only, however, and the Q's are different)...

I'm just making a suggestion for an easy way (at least I think easy, I still need a photo of the mid-module), to move the mid frequency up to the 300Hz range.



Regards,
Kerry

 

I was looking for the specs on the 501B...couldn't find anything...but I did get a photo...



locating the resistor and replacing is a straight-forward task...