EQ Bypass

[jwkelley]

I would like to have some way to bypass the tone controls on a Series II bass without bypassing the entire preamp. Has anyone tried this?

[adriaan]

Keep the filter wide open, and the Qs fully closed. That should give you a fairly unadulterated signal, with a minor boost around 6.5 kHz.

[jwkelley]

Thanks, Adrian. It sounds to me that, in the case of my bass at least, that setting may have a bit more than a minor boost. Having a bypass switch is certainly the way to know for sure. I've spent hours trying to get natural sounding tones from this bass. I have this luxury when I'm at home, but not so much while I'm standing on stage. The EQ is extremely versatile and I'm sure there is a setting that comes close to a natural sound.  
 
With the amp systems I have, I can plug in any of my other basses (including the Series I) set flat and get a nice sound. In my experience, an Alembic bass doesn't need a lot of EQ in order to sound amazing. The fact is, in the case of this '89 Series II, it really needs a lot less.  
 
So I would like to leave all of the electronics in place and in tact, and simply bypass the state variable filters with a switch. Aren't some of the newer basses offered with an EQ bypass switch? I need to be able to do it on this bass.

[serialnumber12]

i dont think series basses can go passive, however alembic did make a bass with no control knobs on the bass it just had the 5 pin jack.does this sound like what you're after?

[terryc]

Correct me if I am wrong(I am sure someone will LOL) but the sound you get is already the natural sound, the filters enhance the frequencies coming from the strings at each fret.

[jwkelley]

All good points. And yes, the low impedance pickups probably must have a preamp in order to have sufficient level to drive the front end of the amplifier. However what I was after is a means for bypassing the equalization portion of the preamplifier. Granted, this may not be a realistic goal since the EQ section is integrated into the preamp as a whole. A glance at a schematic diagram would reveal the extent to which it might be possible.
 
Perhaps the idea of 'natural sound' is too subjective. What I had intended by using the term was something like 'a fair reproduction of the acoustic qualities of the instrument'. To my way of thinking the meticulous layering of woods, crafting of shapes and resonant cavities, and all of the many other aspects that contribute to the creation of a properly vibrating instrument is the difficult part - the part which Alembic does without equal in the world. But in my opinion, introducing electronic resonances tends to adulterate the response of the instrument and its pickups. Don't get me wrong. Like everyone else, there are times when I really like doing that. But I don't necessarily want to be forced into it. :-)    
 
This particular instrument, it seems to me, may have spent too much of its 23 year life in the case. It's 'natural' tone still seems to be evolving slowly as I play it, and it continues to get better as it seemingly becomes more accustomed to the vibrations. Or it could be that I'm imagining all that. ;-)

[edwin]

Well, I have been able to compare SII pickups with and without the tone controls and with the Q backed off all the way and the filters wide open, it's very very similar. Without being able to switch back and forth, I don't know that it would be possible to hear a difference.
 
There is a way to do this, but it's not trivial and in my view, not really worth it. YMMV.

[elwoodblue]

One thing I might be tempted to try is to
adjust the gain trimpots to a low setting,
(and maybe lowering the pickups a tad?).
 
Just make a note of where they are( or take a pic)
if/when you want to backtrack.
You might be able to quell a couple electronic resonances .

[serialnumber12]

sounds like he needs a stethoscope type of mic/pickup installed into or onto the alembic to experience the true acoustic nature of those exotic woods with out the bass being turned on
 
(Message edited by serialnumber12 on May 14, 2012)

[elwoodblue]

I think Zappa had a piezo installed in his SG neck to catch those woody tones.  
 I call your stethoscopes and raise you a DeArmond 900 :
(apologies for the tangent jwkelly)

[mica]

I sent you the schematic, you should be able to take the output off the preamps, and I know you are clever!

[jwkelley]

I managed to successfully bypass the EQ, and now it really does give the natural sound I have been hoping to hear from this bass. It sounds best without any bumps or dips in the response - in my humble opinion.  
 
Thanks for the invaluable help, Mica. The pickups made a world of difference. You were right that the hum coil isn't perfectly matched to them. But I think I'll be able to find a reasonable balance using the gain controls.
 
Is there such a thing as a break in period for a bass? Do you think that playing an instrument has an effect on it?

[edwin]

Do you have it set up with a bypass switch or are the filters just out of the circuit? I've thought about doing a bypass, but I find that I use the filters constantly, at least on my SII equipped Starfire.

[jwkelley]

Hello Edwin -  
 
At the moment I just have it bypassed. It would probably require a 4-pole double throw switch to make it switchable. I think all it really needs are a couple of old fashioned tone controls. It's a bit of a dilema.

[adriaan]

According to this thread, #16 and #17 had passive tone pots, so it's not unheard of. There is another thread where Michael talks about the differences in sound, but I haven't found it yet.