Multicab SIM..my own design cabinet simulator .. it works!! cool!

[Mark Hammer]

Might I suggest a BBD splitter to create a stereo spread?

One of the nice studio tricks by folks who really know their stuff is to use multiple amps and multiple mics, sometimes involving close and distant micing.  Is that the sort of stuff that require substantial time delay, generated by a BBD, or is it really more on the order small phase delays than can be created by some simple combination of lead and lag allpass stages that creates, say, 270 degrees of phase shift over the passband.  In other words, the sort of thing that may well give you what a mic positioned equidistant to a 2x12 and 4x10 cab sitting beside each other might give you.

I guess what all of this is leading to is the possibility that a splitter feeding two such cab simulators, with maybe a very small delay (the kind that allpass stages can produce) could conceivably deliver up some of those multi-cab micing sounds, particularly given how flexible the design is.

Even without any delay inserted, the idea of being able to mimic a cab with a 12" and a 10" speaker is kinda neat.  So kiddies, start getting your splitter/mixer units ready now.

[DougH]

i know most PA accepts 1/4 plugs.. but for long cable runs, i don´t know if  XLR are a MUST, since they cancell out noise

Gotcha.

When playing live I usually plug into a furnished direct box that converts it to XLR for the long cable run.

[dschwartz]

Might I suggest a BBD splitter to create a stereo spread?

One of the nice studio tricks by folks who really know their stuff is to use multiple amps and multiple mics, sometimes involving close and distant micing.  Is that the sort of stuff that require substantial time delay, generated by a BBD, or is it really more on the order small phase delays than can be created by some simple combination of lead and lag allpass stages that creates, say, 270 degrees of phase shift over the passband.  In other words, the sort of thing that may well give you what a mic positioned equidistant to a 2x12 and 4x10 cab sitting beside each other might give you.

I guess what all of this is leading to is the possibility that a splitter feeding two such cab simulators, with maybe a very small delay (the kind that allpass stages can produce) could conceivably deliver up some of those multi-cab micing sounds, particularly given how flexible the design is.

Even without any delay inserted, the idea of being able to mimic a cab with a 12" and a 10" speaker is kinda neat.  So kiddies, start getting your splitter/mixer units ready now.

let´s google all pass stages!!!!

[dschwartz]

hmm.. if i undestood right, all pass filters are the one used in phasers.. so, if i use the filters stage of a phase 90, with no LFO, for example, it will give me a phase delay enough to feel a stereo effect?

[runmikeyrun]

so the next question: what do i need to change to adapt to bass guitar?  I'd like to sim an 18 or 2x15 cab 

[dschwartz]

hmm this is not something you adapt for bass..it means redefining the filters corner values..
i´ll search for famous bass speakers and see if i can make a bass version..

[dschwartz]

BINGO!!

i researched different eminence legend speakers..this bass version can go from 18" to 12" bass end, and top response
this is the schem:


And the new freq response (at different high end responses):


the "top" pot is 50K
the low end response varies from 100hz to 40-50Hz
the scoop moved from 400hz to 250Hz


enjoy!!

[tranceracer]

I´m so proud to present to you the Multicab Sim cabinet simulator..

here is the soundclip:

http://www.goear.com/listen.php?v=bec1880

setup: squier strat, burning crunch, multicab sim, sound card

Till 0:30 the multicab sim is off, then, i put it in, and wow!!
check the last seconds.. really cool cabinet simulation..
check the variety of kinds of speakers it can reproduce..i absolutely love it!!

this is the final schem:

NOTE: the opamp is a dual TL072/62/82 ,there´s no 4558..

adding a volume control is not a bad idea..i´m happy with just the gain control...

Awesome work Daniel!

That sounds really nice and thick good guitar work too! 

Excellent work Daniel - it looks pretty simple yet flexible. Yes?

When I recover from my submini tube fetish I'll gives this a go...........

I was also theorizing that this could be a nice addition to the Valve Caster.  I really like how the Valvie works with my amp sim.  It could make a nice all in one package.  I may just have to bread board this too! 

[DougH]

hmm.. if i undestood right, all pass filters are the one used in phasers.. so, if i use the filters stage of a phase 90, with no LFO, for example, it will give me a phase delay enough to feel a stereo effect?

Yes, that's basically the idea. I used to have an EH Bad Stone phaser back in the 70's and it had a "manual" mode where you could control the sweep manually with a pot. You could hear how it affected the sound, almost like a comb filter kind of thing, but it was static and did not sweep. You may want to allow the amount of phase change to be controlled with a pot in the same way, for different amounts of "depth" or etc. So you would still need the control elements (JFETs for example for a phase 90 like circuit) and an adjustable DC voltage to drive them with, which could be controlled by a pot. Then, for stereo run the phased signal to a separate output jack. Put the phased signal on one channel and the dry on another. You could also mix them for mono to provide a "multi-speaker comb filter" effect, which would sort of emulate how multiple speakers in a cabinet would interact with each other.

Or just use a separate phase shifter or commercial phaser that does this kind of thing and plug that into the output of your speaker sim.

[dschwartz]

i understood right, then..
i think i´ll use something like that in a rack version, a stereo version, with two cabsim modules, 4 all pass filters for one of them, and a "separation" (depth) and "pan" controls..and maybe add nice FET preamp channels before it and a XLR output.

hmm maybe a TDA7294 or lm3886, and wide range speakers and what a hell of an amp!

well, when i have the time.. and the need, for now, i´m´ pretty happy with this!!!

i think the bass version can be a great success, AFAIK there are not many of those...

[DougH]

Yeah, if you don't draw the line somewhere, pretty soon you're building a full-blown rack mount amp emulator.;-) I've thought about combining one of my distortion pedals with my cab sim- then I wake up and realize I like pretty much *all* of my distortion pedals with my cab sim. So I prefer to keep it simple and modular, and combine/rearrange my building blocks at my whim. That's one of the advantages of building pedals instead of rack "systems" in my opinion- ultimately there is more flexibility. But the 2 differently tuned cab sims for stereo and phaser ideas are good ones, even if they don't all need to be combined in one box. There are a lot of good ideas in this thread- and a lot of different ways of implementing them. (I would love to try the comb-filter/phaser idea at some point).

[dschwartz]

hmm a separated pseudo-stereo box is not a bad idea, i concur!

with a tl074 and 4 fets (or optos) looks like an easy build...

[Xavier]

I have attempted a perf layout for this circuit, which I think is more than interesting.............next one in my to-build list

http://www.aronnelson.com/gallery/main.php/v/Xaviers-shrine-of-noise/Layouts/Policab+simulator.gif.html

Please let me know if you find any error. i have used 2x single opamps, I guess it should work, otherwise please correct me

[runmikeyrun]

thank you very much for the bass version and perf layout- i will get going on this someday soon!

[CLAAS]

Hello,
on the perf board C9 is 4,7nF,
NOT 47nF.

[dschwartz]

HEY that´s a cool perfboard.. but is not quite right..

Actually, the name is "MULTICAB SIM". and the FINAL shem is this one:


The opamps are just 1 TL072/82 or any dual opamp (even though 4558 didnt work, but probably was a bad chip)
I added the input resistor, and the output coupling filter..
The twin t filter is also now up to date (47n caps)

this is my first build of it:


any questions, please ask, i´ll be glad to answer

BTW: i simulated a pseudo stereo effect with all pass filters, and it works pretty good!!

[DougH]

Nice looking build!

[dschwartz]

haha yeah, i love the design i did.. kind of give you an idea of what it is

[Mark Hammer]

The phase-shift I mentioned is a little more complicated than Doug makes it out.  Normally, allpass/phase-shift stages either apply increasing amounts of phase-shift as frequency increases or as frequency decreases, depending on the configuration.  There are two basic configurations: the more familiar one in which a cap goes to the noninverting input and a variable resistance goes to ground, and its complement in which the cap goes to ground and the resistance goes where you're used to seeing the cap.  One is referred to a lead and the other lag, though I honestly can't remember which is which.

If you look at just those components (the R and C), you'll realize that one is a highpass filter section (series C, and R to ground) while the other is a lowpass section (series R and C to ground).  The highpass form provides a path that offers less resistance to the signal as frequency increases.  The lowpass form offers less resistance to the signal as it decreases in frequency.

The trouble with using only one type is that, while phase-shift does equal time-delay in a way, if the phase-shft imposed only increases or only decreases with frequency, they you end up with what is referred to as "group delay", where the phase-relationship between large portions of the spectrum is so staggered as to disrupt their "psychoacoustic connection" with each other.  The analogy I like to use is that of considering how hard it would be to pick out familiar faces in a crowd or group photo when everyone's nose is digitally moved 1cm to the your left and every left eye is nudged 5mm over to the opposite direction.  The overall relationship between the components of any complex pattern needs to be preserved for that pattern to be recognized and emerge from against the background noise.

What you want to achieve is a given amount of phase-shift that is equal across the entire spectrum.  There are a number of ways you can do this, I suppose.  One of them is to have a series of complementary stages that apply a known amount of phase shift below a given point and above a given point.  The basic version would be a lead stage plus a lag stage, with the cap values calculated to provide complementary action (this means that the 3db down points are staggered to add up appropriately).  keep in mind that phase shift is cumulative (it sums up across stages) So, if the phase shift gradually increases from 200hz up to a point at 3200hz where it maxes out at 90 degrees, then the complementary stage should be such that it gradually provides more phase shift as you move downward from 3200hz until it maxes out at 90 degrees around 200hz.  You end up with (in theory) 90 degrees below 200, 90 degrees above 3200, and the sum of both stages between those two points.

Sebastian in Argentina (who uses the handle here of STM) has done a number of designs intended to provide a relatively flat-bandwidth phase shift across the spectrum.  These are primarily for the purpose of introducing small fixed full-band delays for producing through-zero flanging using only one BBD, but they will also work for the purpose of mimicing a pair of speakers set slightly apart.  In principle, it may seem easier to just use a BBD to produce a very short flat-response delay, but you have to factor in lowpass filters and other noise considerations.  It can end up being easier and more compact to use a wee bit of phase-shift.

[dschwartz]

well, for the test i did with all pass filters (4 in a row), mixing dry signal left, and wet signal right, it sounded pretty good. you can fee how the sound spreads to stereo..
On the transien analysis, i got over 1.5ms of delay at 1kHz, and AC analysis gave me a pretty flat response with a low cut of 40Hz (more than enough for guitar). The phase shift goes from 90° at 40Hz, to 650° at 1kHz and 720° at 4kHz.

I used basically a P90 style filters, but i changed the filtering caps to 22nF and the resistor to ground to 33K..

having the bass response less delayed is not so bad, cause the ears feel stereo spread more over high frequencies than low freqs..
I experimented with a feedback resistor, but i didn´t notice a change..