Filter based preamps- ACG, BassXX.....

[LukeFRC]

I was looking up options of filter based preamps, out of interest more than a pressing need for one....
Quick thread asking if anyone had tried the BassXX preamp- http://www.bassxx.de/preamps1.html

Anyone tried both?

I find it interesting that while the ACG/East EQ-2 has variable bass and treble points and no mid that BassXX goes the other way and has fixed bass and treble points and a variable mid filter. Both seem to be very differently designed in how they would be used.
Any thoughts?

I would have thought the BassXX would be easier to use, but the ACG more flexible. Ideally I guess you would have something similar to the (unavailable) EQ-1 which would have different low end filters for each pup.

[Ou7shined]

It's true that the ACG takes a little longer to get your head around if you are just used to vol/tone but by heck it's worth it in the end.

[LukeFRC]

[quote name='Ou7shined' timestamp='1325514049' post='1483793']
It's true that the ACG takes a little longer to get your head around if you are just used to vol/tone but by heck it's worth it in the end.
[/quote]
yeah, that was my thought, seems way more flexible in actually shaping whats there. Which model do you have?

[mike_zimmerman]

I'm not quite sure why the BassXX is described as a "filter-based" preamp in their description--I don't see any indication that it's any different from any other typical 3-band set up with sweepable-frequency mid control like the EMG or the East.

The ACG, and other filter-based preamps like Wal and Alembic, are a whole different ball or wax. I've owned both Wal and ACG and played the Alembics, and you really have to approach the EQ very differently.

[skelf]

Hi
I had a look at the bass xx site and as far as I can see they do not use a lowpass or high pass filter in their design. It appears to be a sweepable mid which is not the same thing. As Mike mentioned it is bassically the same principal as many other 3 band EQs. The 01 a 02 preamps make use of several filters including sub sonic filtering which removes very low frequencies from the signal which means your amp/cab don't have to try and reproduce them.

Edited January 2, 2012 by skelf

[LukeFRC]

[quote name='skelf' timestamp='1325524800' post='1483954']
Hi
I had a look at the bass xx site and as far as I can see they do not use a lowpass or high pass filter in their design. It appears to be a sweepable mid which is not the same thing. As Mike mentioned it is bassically the same principal as many other 3 band EQs. The 01 a 02 preamps make use of several filters including sub sonic filtering which removes very low frequencies from the signal which means your amp/cab don't have to try and reproduce them.
[/quote]

Yeah I couldn't work at out, though the basslab site repeatedly refers to too. Like it's a fixed freq lowpass and highpass and then a sweepable bandpass.... what I don't know is is that any different to your norman preamp design... trying to remember the preamp schematics I've seen.
But I do think the (your) ACG is a better design solution, I'm tempted!


(also makes you wonder why every pre wouldn't have a subsonic filter in it- great idea!)

Edited January 2, 2012 by LukeFRC

[jazzyvee]

I have installed two of the ACG filters in my Alembic Europa bass instead of the standard Alembic setup and this gives me a high and low pass filters for each pickup. The sound shaping possibilities are enormous and the fact that it is able to focus on frequencies lower than the Alembic one did really gives some very clean powerful lows whilst still being able to keep the clarity of notes using the high pass filter or the bridge pickup LP filter. Amazing stuff and I'm really pleased with it.

It's true you have to think very differently in terms of how you use the controls to get your tones and from my personal experience it takes quite a while to understand how to change to and from different tones quickly and in a consistent manner. You become a tweaker because even small changes in any of the controls give a significant change to the sound coming from the bass so you can make fine adjustments to hone in the sound you are seeking.

I think they are great.


Jazzyvee

Edited January 4, 2012 by jazzyvee

[GreeneKing]

If you're thinking in terms of bass, treble and mid then it's my opinion (for what it's worth) that you need to cast away such notions when using filter based pre-amps.

I've said this before but with a 2 or 3 EQ you tweak your tone, with a filter pre you create it.

Just my thoughts

[Kiwi]

I'm curious to know why a filter-based preamp? What benefits are you looking for?

I'm not sure that a sweepable mid band is the same as a band pass filter. My understanding is that band pass filters attenuate frequencies outside the selection being passed. The sweepable mid band control on a 3 band pre cuts and boosts the frequencies selected, it doesn't pass them or attenuate outside the selected spectrum.

[LukeFRC]

[quote name='GreeneKing' timestamp='1325709536' post='1486542']
I've said this before but with a 2 or 3 EQ you tweak your tone, with a filter pre you create it.
[/quote]
[quote name='Kiwi' timestamp='1325710669' post='1486571']
I'm curious to know why a filter-based preamp? What benefits are you looking for?
[/quote]

This... I find it an interesting idea of how bass guitar can and could work. I'm not sure if it is for me but having a bit of a blether about it can't hurt!
Personally I've ended up looking at loads of schematics trying to work out how filters work like this, and finding a bit about the Bassxx preamp too....

[LukeFRC]

So I emailed Heiko behind Basslab and asked him a few questions about his preamp as was interested, I think it is a more conventional type preamp, abet very very small and well engineered one. I found some of his views on preamps very informative in my own understanding. - I think the use of 'filter' on his website is possibly a language one. When we use filter preamp here we mean high pass or low pass filter, whereas I guess coming from german language a fender passive tone knob is also a filter....


[quote]
....
Let´s say a room has less bass and I want to compensate this, why should I want to boost a different frequency than before?
In short: I think the concept is unlogic and not very musical.

Basically all internal preamps are not real amps. Their amplification factor is 1, rarely more (EMG, maybe?)
Filter just means, you can boost or cut a specific frequency range. So these "preamps" are basically filter-based buffers..
Variable filters on the earlier East, fixed (bass/treble) on the BassXX.
Parametric control means to boost and cut, being also able to vary the frequency range.
Next step would be to modify the half-width of that range (also referre3d to as quality factor), but believe me, things get very, very unusable.

High-cut filters
Some designs have these "sort of built-in".
An op-amp with a slow slew-rate is not able to get higher frequencies right. It´s cheaper, uses slightly less power, but has a lot less less dynamics compared to the high-speed slew-rate op-amps we use. (high-speed is what they are called and not my marketing trick! ; >)
Yes we don´t use any high-cuts and leave the higher end as it is - we simply don´t boost the really high end, which many do by design (and it is called "hiss").
(Check the frequency curve of the BassXX pre at [url="http://basslab.de/"]basslab.de[/url] and you know, what I mean.)


Sub.-sonic filters
Every preamp has a sub-sonic filter by default! It is basically caused by a capacitor at the input. (Some seem to misuse this as a "feature". ; >)
Only preamps with DC-capable inputs are able to (re-)produce those sub-sonic frequencies - not many and surely not as an internal preamp.



BTW, here is a video of the BassXX in action:
[url="http://www.youtube.com/watch?v=YO-8SkgXaPU"]http://www.youtube.com/watch?v=YO-8SkgXaPU[/url]
The StepoABout has two BassXX preamps, that are just slightly modified for the Stick. (Of course, you can skip the part about the routing options.)
[/quote]

Right, the fella said I could stick this up, and for the basis of the conversation about preamps and the bassXX being realitvly unknown I thought it would be informative. I've edited it down to try and make sense, we were emailing a lot of things! He also sent a photo or two of the thing and it looks tiny in terms of size.

oh and as this isn't an advert for his product.....
http://www.acguitars.co.uk/shop/ the acg/east filter based preamp (as in high/low pass filters) are available here.
and this is the best the net has to offer in terms of videos.... http://youtu.be/egLVWZzbU-8

Edited January 4, 2012 by LukeFRC

[Kiwi]

[quote name='LukeFRC' timestamp='1325720023' post='1486776']
This... I find it an interesting idea of how bass guitar can and could work. I'm not sure if it is for me but having a bit of a blether about it can't hurt!
Personally I've ended up looking at loads of schematics trying to work out how filters work like this, and finding a bit about the Bassxx preamp too....
[/quote]
I have filters on my Alembic, with all due respect to Greeneking, I find them limiting. He and I may have different requirements however which is what prompted my question over what you are looking for. I've tended to look for something that makes a great sounding bass more versatile. The alembic is a nice sounding bass but I wish I could have more boost in the lower mids, the filter based system doesn't deliver that.

[BassBunny]

[quote name='Kiwi' timestamp='1325737676' post='1486891']
I have filters on my Alembic, with all due respect to Greeneking, I find them limiting.
[/quote]
Certainly not my experience with the ACG pre Amp. If anything there is "too" much sound shaping available and it takes some time to get your head round it. I got my first ACG nearly 2 years ago and only when i adopted GreenKings suggestion for setting it up did all become clear.
Having a filter stack per pickup is fantastic. even 2 identical pick-ups can be set up with totally different characteristics and then just blend between the 2.
I would find a global filter arrangement a bit limiting, as IMHO a global conventional system is, but the ACG 01 is a fantastic bit of kit.

[ikay]

Kiwi - "... I wish I could have more boost in the lower mids, the filter based system doesn't deliver that ..."
BassBunny - "...Having a filter stack per pickup is fantastic ... I would find a global filter arrangement a bit limiting ..."

I agree with both the above. I have an ACG with an RFB humbucker and piezo bridge going through a dual filter stack. When using just one pickup source (RFB or piezo) I find the filter is less useful than a conventional 3-band EQ. For example, to boost the low mids you need to set the low-pass filter to the frequency you want to boost, but by doing this you lose the higher frequencies. You can add back some highs using the high-pass filter but this generally leaves a 'hole' in the upper mids. The resulting sound is quite different to boosting the mids using a conventional EQ. The boost provided by the filter at the cutoff frequency also has a narrower bandwidth than a conventional sweepable mid and gives a more nasal tone at higher levels of boost.

Even with two pickups I can see that a single/global filter is somewhat limiting in what it can do.

The filter-based approach really comes into it's own when you have two pickup sources each with their own filter stack. Set the filters up with different characteristics (the more different the better), blend between the two pickups and you have access to a vast palette of sounds. The tone creating potential is virtually limitless. However, the complex interactions between the filters are difficult to fathom and finding particular sounds is largely a matter of experimentation. Small tweaks to the filter settings or the blend can result in dramatic changes to the sound. Great fun but not that easily tweakable in a live environment.

Edited January 5, 2012 by ikay

[John-E-Retro]

[quote name='LukeFRC' timestamp='1325512203' post='1483752']
I was looking up options of filter based preamps, out of interest more than a pressing need for one....
Quick thread asking if anyone had tried the BassXX preamp- [url="http://www.bassxx.de/preamps1.html"]http://www.bassxx.de/preamps1.html[/url]

Anyone tried both?

I find it interesting that while the ACG/East EQ-2 has variable bass and treble points and no mid that BassXX goes the other way and has fixed bass and treble points and a variable mid filter. Both seem to be very differently designed in how they would be used.
Any thoughts?

I would have thought the BassXX would be easier to use, but the ACG more flexible. Ideally I guess you would have something similar to the (unavailable) EQ-1 which would have different low end filters for each pup.
[/quote]



In truth all EQs use filters.

Briefly, the difference between those termed filter based EQs compared to what we think of as conventional:

CONVENTIONAL: Tends to be based on a straight line flat frequency response, where the controls allow it be bent away from that flat line, in order to contour the desired response.

FILTER BASED: More a case of opening up filters to allow the desired parts of the frequency spectrum through, and where a reference flat setting does not really exist, as such.

GreenKing's take makes sense - I've said this before but with a 2 or 3 EQ you tweak your tone, with a filter pre you create it.

Looking at the published curves, the Basslab falls into the conventional category.

I believe there's quite a lot more detail on Alan's website about the use and operation of the 'filter based type'.

[Kiwi]

Even in a stack per pickup system, options are similar when using just one pickup as they will be with a 'global system'. You're kind of stuck with using two pickups for maximum flexibility.

I like the roll off of treble that I get with the Alembic and with the Alembic Q circuit I had on the Pentabuzz for a while. I also like that the filter boosts frequencies along a narrow band at the shelving point (my Alembic has Series 1 Q switches to control the boost rather than Series II CVQ knobs).

I'd still prefer the mids being controlled independently though. A 2 stack filter (hi/lo pass) with sweepable mids would be interesting.

Alternatively, they're just different tools with different purposes.

[LukeFRC]

[quote name='John-E-Retro' timestamp='1325757498' post='1487039']
In truth all EQs use filters.

Briefly, the difference between those termed filter based EQs compared to what we think of as conventional:

CONVENTIONAL: Tends to be based on a straight line flat frequency response, where the controls allow it be bent away from that flat line, in order to contour the desired response.

FILTER BASED: More a case of opening up filters to allow the desired parts of the frequency spectrum through, and where a reference flat setting does not really exist, as such.

GreenKing's take makes sense - I've said this before but with a 2 or 3 EQ you tweak your tone, with a filter pre you create it.

Looking at the published curves, the Basslab falls into the conventional category.

I believe there's quite a lot more detail on Alan's website about the use and operation of the 'filter based type'.
[/quote]

Thanks for the input john,
interesting thread this!
Has anyone with an ACG got the time to make a wee video showing off their bass? (or if these exist on the web already can you stick them up on this thread)

[skelf]

There was a good one in this thread but it has been taken down. He may still have it might be worth asking.

[url="http://basschat.co.uk/topic/161706-sold-acg-recurve-six-string/page__p__1461796__hl__acg__fromsearch__1#entry1461796"]http://basschat.co.uk/topic/161706-sold-acg-recurve-six-string/page__p__1461796__hl__acg__fromsearch__1#entry1461796[/url]

[ikay]

[quote name='Kiwi' timestamp='1325759120' post='1487069']
I'd still prefer the mids being controlled independently though. A 2 stack filter (hi/lo pass) with sweepable mids would be interesting.
[/quote]

kiwi, doesn't your Noll 3-band parametric do pretty much exactly that? http://www.noll-electronic.de/sites_d/tcm_3p_spezifik.html

[Kiwi]

Its a basic three band parametric eq with cut and boost of 15dB, although I've had Klaus make a few tweaks to the Q and bandwidths for each control. The mid and low bands crossed over at the sweetspot in the mids on my bass before I had him move that crossover lower. Like I said above, its great for dialling in those mid and low frequencies that make a good bass sound better. I'd be happy with a hi-pass filter on it for the treble too. The only draw back is that it requires a 9 pin jack socket which can be a pig to retrofit on instruments that don't use a jack plate.