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mike1762
Junior
Username: mike1762

Post Number: 16
Registered: 1-2008
Posted on Sunday, March 23, 2008 - 6:57 pm:   Edit Post

I want to make sure I fully understand the Q switch and the function of the frequency pot. Mica's post re this says "...The frequency control adjusts a low-pass filter tunable from about 350Hz - 6KHz. Where you tune the filter is the cutoff frequency. Only frequencies below the cutoff frequency are passed...When the Q switch is on, it boosts the cutoff frequency of the filter by about 8dB...". So if I understand correctly, the filter pot sets a frequency that will either be boosted by 8dB (Q on) or set the point of a low-pass shelf (Q off). Does this mean that I have a 6KHz shelf in effect when running my bass "flat" with the Q switch off? But with the Q switch on, I have no low-pass shelf (but I am boosting something between 350-6000Hz)? Thanks.
keurosix
Advanced Member
Username: keurosix

Post Number: 268
Registered: 10-2005
Posted on Monday, March 24, 2008 - 3:03 am:   Edit Post

Not exactly. You always have a low-pass filter active. You would have a 6kHz shelf if the filter was turned up all the way clockwise (at "10"). All frequencies below this point are passed through. At the dialed in 6kHz frequency, you can leave it flat with no boost 0 db no "Q", or boost it with the "Q" switch active. What you get is a peak at the selected frequency, or the "top" of the low-pass filter. This enhances the tonal effect and can produce the traditional wahwah sound (as you rotate the filter control and move the top of the low pass), or as I like to call it, the vocal quality of the sound. As you dial the filter anticlockwise, you lower the "top" of the low pass, and can get a darker sound. The "Q" switch will effect the top frequency of the filter wherever it is set. They work together. I take it you are asking about your Spoiler circuit with a 2 position "Q" switch? Other circuits for different models have 3 position switches (Series 1) or a variable pot (Series 2), for even more flexibility. Some models don't have a "Q" switch, and leave it fixed. I hope this helps your understanding.
Kris
mike1762
Junior
Username: mike1762

Post Number: 18
Registered: 1-2008
Posted on Monday, March 24, 2008 - 4:35 am:   Edit Post

Thanks for your response. Yes, I'm specifically asking about the circuitry of a Spoiler. It sounds great just "noodling" around, but I'm having some problems getting it to "sit" in the mix when recording. I think it's the exaggerated "smile" frequency response that is causing me problems (I have always played/recorded with a fair amount of midrange, but if thoses frequencies were never there to begin with...). OK, let me see if I got this right: The filter pot sets the roll-off point of a low pass filter. With the Q off, it's a simple shelf parametric. With the Q on there is a 8dB boost (narrow Q) prior to the roll-off. Is that right? I just bought a SC Standard that should be here any day now, how does the signature electronics differ? Thanks again.
fc_spoiler
Senior Member
Username: fc_spoiler

Post Number: 692
Registered: 5-2006
Posted on Monday, March 24, 2008 - 5:34 am:   Edit Post

On the SC you'll have a filter + Q-switch for each pickup and a pan pot instead of a pickup selector.
mike1762
Junior
Username: mike1762

Post Number: 20
Registered: 1-2008
Posted on Monday, March 24, 2008 - 7:05 am:   Edit Post

Does anyone know if there is some philosophy behind the decision to design the electronics in this manner? Why have a sweepable low pass filter rather than a sweepable pass filter (no shelf)? I'm finding some great sweet spots with the Q engaged around 400-800Hz, but the overall tone is too dark. The signature package may take care of this (Q engaged on the neck PU but off on the Bridge PU). Just curious.
briant
Intermediate Member
Username: briant

Post Number: 147
Registered: 12-2004
Posted on Monday, March 24, 2008 - 10:57 am:   Edit Post

I'll admit to being the dumb guy in this regard.

I have no idea what is going on with the Q switch and filters. When I got my JPJ I just sat down and played with them until I figured out what kind of sounds they made when I turned the knobs and flipped the switches. My JPJ has Signature electronics so obviously one switch and filter per pickup.

I might be over simplifying things (in my mind) since I've been using this system now for 3+ years. I do know that I absolutely LOVE the tonal variations that I can get with the Signature electronics. Hence the reason I got Signature electronics on my Rogue 5 string. :-)
glocke
Advanced Member
Username: glocke

Post Number: 342
Registered: 9-2002
Posted on Monday, March 24, 2008 - 11:41 am:   Edit Post

Dont feel too stupid Brian, some of the techie stuff makes me feel dumb also..

So, for us Homers in the crowd, if I have the Neck pickup filter set midway, say at 700Hz, all the frequencies below that will be allowed to pass if the Q switch is off. When the Q switch is turned on, the 700Hz frequency ONLY gets an 8 db boost. Right???
briant
Intermediate Member
Username: briant

Post Number: 148
Registered: 12-2004
Posted on Monday, March 24, 2008 - 12:02 pm:   Edit Post

I believe that's correct, Greg.

I know that with the bridge pickup only and the switch turned off I can roll back the filter about 1/4 turn and suddenly my bass sounds like a Jazz bass on steroids.

Or bridge pickup only with the switch turned on I can roll the filter back a bit and get a very nice P bass type sound.
mike1762
Junior
Username: mike1762

Post Number: 21
Registered: 1-2008
Posted on Monday, March 24, 2008 - 12:51 pm:   Edit Post

Greg,
I think that is correct. The "issue" for me is that the filter always (Q on or off)sets the breakpoint for a low pass shelf. I can dial in a nice 800Hz "punch", but I lose all the frequencies above that...thus the "dark" tone.
tbrannon
Senior Member
Username: tbrannon

Post Number: 680
Registered: 11-2004
Posted on Monday, March 24, 2008 - 1:00 pm:   Edit Post

Mike,

I only own one Alembic bass and it's signature equipped, but my gut feeling is that you are going to REALLY like the signature setup.

Having a filter+Q for each pickup and a pan knob allows you to dial in that 'punch' on one pickup and then use the other pickup to add top end or a thumpy dub bottom... then just use the pan to blend the two pickups until you find what you're looking for.

Toby
bob
Senior Member
Username: bob

Post Number: 833
Registered: 11-2002
Posted on Monday, March 24, 2008 - 1:09 pm:   Edit Post

Without meaning to be picky about terminology, I'd like to try to clarify a few things here.

First, it really is not appropriate to use the term "shelving" when describing these filters. A shelving filter, or tone control, will raise or lower all frequencies beyond a particular point, by a fixed amount. For example, it might reduce all frequencies above 3 kHz by 10 dB. In contrast, the low pass filter has a roll-off slope beyond the set frequency, such that higher frequencies are reduced at the rate of 12 dB per octave (doubling of frequency). In other words, if the filter frequency is set at 3 kHz, then 6 kHz would be reduced by 12 dB, 12 kHz by 24 dB, and so forth.

Second, while these filters may be "parametric" in some literal sense (since you can adjust the frequency and Q parameters), they are really very different animals from what most people would think of when you talk about a parametric equalizer.

Here is exactly what you can do with one of these low pass filters and a three position Q switch:

filter

The graph in the lower right shows what the Q switch does. In the high position, it gives you a sharp peak at the set frequency position, while in the off or 0 position it allows the filter to roll off smoothly without a peak, and the middle position gives you a modest emphasis. Note that in all positions of the Q switch, you still end up with a 12 dB roll-off above the set frequency. Q simply determines whether you get an emphasis, and how much, at that frequency.

Changing the frequency setting shifts the roll-off point (and the peak, if Q is engaged) right or left, as shown in the upper right. So as you lower the frequency, you are eliminating more of the highs, and more drastically than if you were turning down a shelving treble control.
keurosix
Advanced Member
Username: keurosix

Post Number: 270
Registered: 10-2005
Posted on Monday, March 24, 2008 - 2:32 pm:   Edit Post

Thanks for clearing this up Bob, the diagram really shows what words have a tough time describing. Mike, I think Toby says it best that with 2 filters you can combine a low centered filter on one pickup with a high centered one on the other, and get a variable blend with the pan pot. However, even with only one filter, I have never had it sounding too dark for my tastes. In fact, the Alembic circuitry usually has way too much high end for my liking, and I find myself backing off on my preamp treble settings to compensate. Also, if your strings are dead, you can get some life back just by setting the filter higher to allow more highs through. Maybe this could be a contribution to the dark sound you preceive - are your strings old? Also, you may get more gain from the guitar by adjusting the pickups closer to the strings, or using the trim pot inside the control to get more overall gain. Happy experimenting!
Kris
mike1762
Junior
Username: mike1762

Post Number: 22
Registered: 1-2008
Posted on Monday, March 24, 2008 - 3:56 pm:   Edit Post

Thanks guys. Bob, the diagram really helped. I don't want to sound like I'm complaining about the tone (heck, on every other guitar I own I just put everything on 10 and get my tone from the amp), I just wanted to get an understanding of how it worked. Like I said, the Spoiler doesn't have a bad sound when playing by itself, but I'm having real issues getting it to sit in the mix when recording. I'm going to have to invest in a good pre-amp (right now I'm running through an ART Pro Channel then straight into the board). Hopefully my SC will be here soon and I can try out the Signature electronics.
davehouck
Moderator
Username: davehouck

Post Number: 6376
Registered: 5-2002
Posted on Tuesday, March 25, 2008 - 5:42 pm:   Edit Post

Thanks Bob; great description!
glocke
Advanced Member
Username: glocke

Post Number: 343
Registered: 9-2002
Posted on Wednesday, March 26, 2008 - 2:22 am:   Edit Post

Yes, thanks Bob. That clears up alot. It is probably the most useful explanation Ive seen.

Dave, any chance we could have that put in the FAQ section of the boards?
davehouck
Moderator
Username: davehouck

Post Number: 6385
Registered: 5-2002
Posted on Friday, March 28, 2008 - 7:07 pm:   Edit Post

It's been added to this thread in the Must Reads section.
jakebass
Junior
Username: jakebass

Post Number: 42
Registered: 7-2007
Posted on Saturday, March 29, 2008 - 6:37 am:   Edit Post

I don't know exactly what technically is happening in terms of frequency manipulation, although I have a reasonable idea (some seem to really understand what they are doing with Q switches)
Whichever way, I have played around and recorded to play back the sounds that I really like and then taken a picture of the settings with the camera on my cell phone and named them. Pbass, Jbass, back pick up, Jimmy Johnson etc etc.
I suppose its a bit long winded but it means I can look up the best sounds I have found when I have time to really listen (ie when the studio is not costing the producer 1500 for the morning)
Jake
tbrannon
Senior Member
Username: tbrannon

Post Number: 709
Registered: 11-2004
Posted on Saturday, April 12, 2008 - 6:47 pm:   Edit Post

Mike,

I'm assuming that your SC arrived- what are your impressions now that you have a bass with 2 filters to compare with?
dfung60
Advanced Member
Username: dfung60

Post Number: 315
Registered: 5-2002
Posted on Sunday, April 13, 2008 - 4:52 pm:   Edit Post

I'm not sure exactly what Ron W's motivations were in developing the original Q circuit was, but you're all aware that in addition to his work at Ampex, he operated a recording studio as well, so he had access and experience with high-powered studio gear.

I wouldn't be surprised if the motivation were to develop a very characteristic alternative to the very simple conventional controls that were common at the time.

The Series filter is a low-pass filter that does something a passive filter can't do - it adds a very strong resonance around the corner frequency. That's what that pointy peak on the frequency response curve is in the old diagrams above. The basic flavor of the circuit is a regular low-pass filter. When you turn "down" a conventional low-pass tone control, you're sweeping the frequency of the filter downward and filtering out the highs. There's no bump at the corner freq, so the highs just sort of disappear. This is how the Series circuit works when the Q switch is turned to the 1st (or "most off" position) or a CVQ is all the way down.

When you flip the Q switch to one of the other positions, the EQ opamp is creating a pretty huge and narrow boost right at the corner frequency. If you turn the Q to the 3rd position and rotate the filter knob, you're shifting the corner frequency as before, but the resonant peak is shifting around with it and you'll perceive that as a "wah" effect if there's any output in it's range.

The circuit is not working like a parametric EQ, but, if you've used one before, tuning a parametric is often like what you hear using the Q-circuit - you boost or cut in a narrow, specific range, then slide it around to find where you want it to act, then drop the level and bandwidth to refine your tone.

So, with the addition of the Q-switch, you keep everything you had before (switch in pos #1) and get something new and totally different, but relatively easy to use.

There probably was some temptation to put a full pararmetric EQ on board, but it's more knobs, and more complexity in explaining how the controls interact to somebody who's not a gearhead. Same with having a bandpass rather than low-pass filter - useful for some, but a confusing knob that makes your bass freqs disappear for many. The sophisticated user can add a parametric or bank of parametric EQs in their signal chain, but everybody benefits by a simple to use knob that does something really unusual but doesn't screw up your tone too much no matter what you do.

Just a guess,

David Fung
mike1762
Junior
Username: mike1762

Post Number: 40
Registered: 1-2008
Posted on Monday, April 14, 2008 - 6:29 pm:   Edit Post

Toby
I REALLY love the SC. Having a filter per PU and a blend control makes it much more...flexable. But what I'm really jazzed about is the short scale. You can really motor-scooter around on it. Since this post I have also aquired a Series I. Until I got my Alembics, I had NEVER used the tone controls on my guitars (just put everything on 11 and go for it). For that matter, (other then my FJ) I never bought a bass with anything other than a bridge PU. I'm really having to learn a whole new approach to bass playing (having a blast doing it!).
tbrannon
Senior Member
Username: tbrannon

Post Number: 713
Registered: 11-2004
Posted on Monday, April 14, 2008 - 7:32 pm:   Edit Post

0 to 60 huh? from a no fiddle approach to a Series I (tone tweaker heaven) in very little time.

Glad to hear you're enjoying what Alembic brings to the table. Be sure to post some pictures in the showcase threads when you have the opportunity.

Toby
ajdover
Senior Member
Username: ajdover

Post Number: 612
Registered: 11-2003
Posted on Monday, April 14, 2008 - 7:52 pm:   Edit Post

Here's what I do. I fiddle with all the knobs and switches until I find the tone I like. I make a mental note of it. Then I dial it in when I need it. Graphs and charts both scare the bejesus out of me and bore me. To me, it's all about what you hear. That's how I approach my Alembics - I tweak it until I hear a tone I like, simple as that.

I'm not casting aspersion on those who take a more technical bent to such things - far from it. I just think that some folks might get too involved in the techical end of things as opposed to the more "natural" end of things, namely, you know a good tone when you hear it, regardless of technology. That's how I personally approach my Alembics, and it's worked for me thus far.

Alan

(Message edited by ajdover on April 14, 2008)

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