3 band (selectable mid) vs 4 band fixed
You guys were super helpfull with my previous dilemma concerening some design considirations for my bass preamp. So here my next hurdle.
I can't decide between a 3 band EQ with selectable mid frequency or a 4 band with fixed frequencies (80 shelf, 360, 900, 2k shelf). It's an all tube EQ. 3 Band will give a bigger boost/cut dB range, but that's not really an issue. i don't like to use an EQ as an effect.
So, there it is. What would you guys like on your pre amp??
Both designs work well for me IF the center points of the mids are chosen well. Your bass and treble shelving and upper mids are right on the mark for me, but the low mid control is centered too high IMO (similar to the 4 band Markbass amps). Moving that down to the more 'meat area' of a bass low end (maybe 150 or 200), and then lowering the start point of the bass shelving just a smidge would be perfect for me.
I don't know how difficult or expensive it is, but I was always very impressed with mid controls like used on the EBS amps, where the Q was tighter when cutting (1/2 octave) and fatter when boosting (full octave), which works great with how bassists tend to use these controls (i.e., boosting of a tonal reason, and often cutting to take care of 'issues').
To answer your specific question, I greatly prefer two well voiced mid controls than a single semi-parametric. Of course, I PREFER two semi-parametric mids, but that wasn't an option:p
Thanks for the extensive reply! The lower mid frequency is still under debate at the moment ;). The 'EBS' solution sounds awesome. I've always held them in high regard, but didn't know their EQ's worked that way. Thanks for that. But the pre-amp being full tube limits the design flexibilty, without resorting to very complex passive circuitry. Something I try to avoid with this design. The technical limits also prevent me from going down the 'two semi-parametric route'. The mids are already influencing eachother.
I lean towards the fixed 4-band myself, but the poll already suggests the 3 band is more popular! Interesting.
The EBS thing is pretty cool. Just FYI, they use a single band of semi-parametric mid in the 360/660 series of amps, with that 'variable Q' when cutting versus boosting. One other cool thing is that if you take the mid level to full cut, the Q narrows to a notch for feedback control with DB or to deal with a very specific frequency problem.
I would prefer the four band over the three band, even with three-band mids being semi-parametric.
I like as much EQ and as tweakable as I can get it the EQ. I like fully-parametric EQ's with adjustable Q's. 5 band please.
I'd rather have 4-band fixed assuming they are at the right places. I think something like 40-120-750-2K is about right (so agree with Ken on dropping your low mid target. Whatever they are on the current Tecamp Puma is pretty spot on. Invariably if I'm using eq to deal with a room I'll need to worry about being too fat/boomy (low mid) while also needing cut or being too strident (hi mid). Having only one mid eq doesn't give you that flexibility.
Unfortunately, a lot of 4 band EQ's have center points that I hate. I greatly prefer sweepable mids or selectable mids so I can pick my own favorite point.
4 band with fixed frequencies (80, 360, 900 2k)
Those are not good frequencies for a bass preamp.
I have 2 preamps that I like.
1 - the east j-retro with the mid sweep function
2 - the Audere the the bass, treble, high mid, and low mid knobs.
Agreed that it's all in the preamp voicing. In theory the three-band preamp with sweepable mids should be more flexible than the fixed four-band. But if you happen to like the voicing of the fixed four-band, then you probably don't need any more flexibility.
I have an Audere four-band in several of my instruments. I don't recall the frequency center points just now, off the top of my head. But I do know that the overall voicing suits me just fine.
Audere's frequencies for the 4 band are 172 shelf, 200, 800 and 1920 shelf. I agree my low mids need some considiration and experimentation, but I'm pretty set on my high mids and highs. Audere's bass seems a bit high though...
+1 in that an upper mid control somewhat around a half octave 1K center point is probably the most useful knob on an amp.... either dialing out ganky upper midrange for a more 'hi fi' tone (as we use that term on TB), or adding that top end grind to a J or P.
The treble shelf start point is a matter of design goal. Your low shelf start point (and I assume some lo passing) is great for a more 'bright' sort of top end control. On the other hand, a very high shelving start point can act nicely as a lo pass filter, eliminating the 'metal' from the top end of a cheaper tweeter, or adding that touch of 'sparkle' that slappers like.
Same thing to me with the low end. I like the 100-200hz low mid control (a bit wider Q), which is where the meat of the low end of the bass is to my ear, and then a quite low shelving start point of the bass control that again can act a bit like a hi pass filter, being more useful to cut flub that boost anything (although it can also be used as a 'loundness' type control at low volumes).
Anyway, again, really depends what you are trying to do and your target. For a more vintage tube pre that will make the passive P and J guys happy, a high input impedance, a relatively high shelving bass control, a mid mid and upper mid control, and a lower start point treble (i.e., just as you have your 4 band spec'd) might be just perfect for many.
Here is another idea (and I don't know if it is possible), but if you keep your bass, upper mid and treble as it is, and just include a switch to toggle the low mid between 'lo mid and mid mid' (e.g., 150 and 400 or whatever), you would pretty much cover the waterfront, and still keep the pre simple for those looking for a more classic front end.
I'm pretty much with the other guys here regarding center points. I'd also rather have a fixed 4 band in good spots. I get alomg pretty well with older GK eq's. 60,250,1k,4k. I can use a 3band just fine but prefer having 2 midrange controls, that's where all your tone is. In the GK example, the lowmid adds fat without adding woof. The high mid adds attacks/cut through or takes out ganky, honky stuff without losing "beef" in the sound. With a 1 band sweep, I could do one of those things but not the other at the same time. The treble is set low enough to at least have some effect on cabs that don't have tweeters, dropping it to 3k wouldn't hurt either.
A lot of it has to do with how your amp sounds aside from eq too. Take an old bassman or b15 and they sound great without all the adjustment knobs.
However, with the GK case, their cut/boost are asymmetrical. I have an MB200 which is great for a tiny rig of doom/practice etc, but I wish they provided more boost. Here are the specs for their EQ:
Bass: +/-10dB @ 60Hz
Low-Mid: +6dB/-10dB @ 250Hz
High-Mid: +6dB/-10dB @ 1KHz
Treble: +/-14dB @ 7KHz
I think most of their amps are similar in this regard.
Two things I would change for the mids. One, make the mid cut/boost symmetrical, like +/- 12 dB. For a passive fretless I like more boost in the 800 - 1000 Hz range to bring out the tone and the +6 dB doesn't quite get there for me. Second, I would provide a mid-shift for each of those ranges, like with a push-pull pot, maybe Low-mid: 125/250 Hz, High Mid 500/1000 hz. Would add very little complexity to the design but provide significantly more flexibility particularly with the adjusted cut/boost range.
Just my thoughts. So I guess my choice would be carrots, but that choice isn't available. :D
Thanks guys. Really helpfull insights and ideas.
In contrary to the poll's results, I'm going for the fixed 4 band. I did some more experimenting and listening today and lowered the low mid to 200Hz. Bass is still at 80Hz (3dB point, actual max is lower offcourse), high mid around 900Hz and treble around 2kHz (like the bass, 3dB point at 2Khz, but max value much higher). Ranges from +6dB to -10dB (like the GK). Not by choice per se, but due to technical (tube) limitations. Although I strongly believe this range should be more than enough. I'm going to use the EQ for (subtle) changes in tone, not as an effect. I really like basic tone af amp and can't think of a reason why I would need more range.
The reason for sticking with the 4 band is because, like some of you mentioned above, a good 4 band with proper center frequencies is more flexibel then a 3 band with variabel mid. It was one thing I liked about my old Markbass LMII. I had direct access to the rumble, the oomph, the nasty and the sizzle.
I might consider the idea of adding the option the change the center frequencies of both low and high mids somehow. I'm not a big fan of push/pull pots (expensive and hard to come by in the values and configuration I need), but as some of you might recall, the way Lakland did it on their 44-02 bass might be nice. There was a DIP switch to choose the mid frequency inside the battery compartment. Clean, simple and flexible at the same time.
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