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1
Building your own stompbox / Re: Talk Box Small Amplifier Suggestion
« Last post by Ben N on Today at 07:36:53 AM »
Do you feel like I do?  :icon_eek:
2
Building your own stompbox / Re: Name This Pedal Contest - Free Sausages....
« Last post by EBK on Today at 07:24:29 AM »
I like this idea for a pedal I am making for someone!  Maybe something like this?
I love it.  For bonus points, use the UPC of an actual product.  If it is a clone of a commercial pedal, find the UPC of that pedal.  Or, pick an unusual or funny product.  :icon_wink:

Oh, and use all capital letters.  Looks more authentically generic.
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Building your own stompbox / Re: Talk Box Small Amplifier Suggestion
« Last post by GibsonGM on Today at 07:18:14 AM »
Sounds pretty cool, Mark :)  I've messed w/them for a friend, fixing his vid camera's audio - yes, some can be pretty good little units!
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Building your own stompbox / Re: Dynamic response cab sim?
« Last post by Fancy Lime on Today at 07:10:42 AM »
I don't know, but I doubt it.

Reducing a cabinet's response to a single frequency response is a big approximation to begin with, since I doubt the frequency response is identical at all power levels, so it should really be some kind of family of curves. Plus, as you say, you can start to get non-linear behaviour too.

My guess would be that when people get into that level of detail for a cab sim, they're working in DSP land.
If we wanted to get an accurate representation of all the behavior of, say, a Mesa 4x12 with Celestion vintage 30's, then yes, DSP is pretty much the only reasonable way to do it. But for a simple analog cab sim, what I would be trying to do is something that "makes the guitar signal sound better in roughly the same way that a typical (whatever that means) guitar cab does". I'm just wondering if for that sort of thing we would even want to do anything other than frequency shaping. Or in other words, if we could design a "perfect" real cab, would we want it to compress? We certainly want it to have a non-linear frequency response, as anyone who has plugged their Marshall head into a full-range PA cab can attest.

Andy
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Building your own stompbox / Re: Dynamic response cab sim?
« Last post by bool on Today at 06:42:40 AM »
Oh, compression.
In a daw, a tri- or even dual-band comp will get you there fast; otherwise you can play with the idea of a muff-style tone control with a soft-clip pair across the lpf.
Even a baxandall tone control can be "enhanced" this way.
https://patents.google.com/patent/US5509080
6
Bootstrapping gives you higher input impedance but it doesn't solve the input noise currents of a BJT design.
To some extent it's possible to band-limit the bootstrap fb signal, in net effect diminishing the buffers' cur.noise outside of the band of interest, and this is cheap and simple to do, but fails at midrange freqs, which is where the crunch lives...
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Building your own stompbox / Re: Dynamic response cab sim?
« Last post by ElectricDruid on Today at 06:22:15 AM »
I don't know, but I doubt it.

Reducing a cabinet's response to a single frequency response is a big approximation to begin with, since I doubt the frequency response is identical at all power levels, so it should really be some kind of family of curves. Plus, as you say, you can start to get non-linear behaviour too.

My guess would be that when people get into that level of detail for a cab sim, they're working in DSP land.
8
Thanks guys for all the wonderful inspiration!!  I'm going to bookmark this thread for future reference!

Since we didn't seem to really zero in on a particular single name.... I chose "Double Trouble" as my choice.. it got 3 votes.  Great because I am a huge SRV fan, and my sweetie is a Texan.  It works.  Everybody gets a sausage!!

I made the order to fabrication this morning.. started ordering parts.  I should be ready to build out the prototype in a couple of weeks, and I will check back in on this project then!

Cheers!  Thanks again!!  You guys are great.

MC

9
Building your own stompbox / Re: Choosing equalizer bandwidth
« Last post by ElectricDruid on Today at 06:18:29 AM »
Since the bands are an octave apart, I was expecting them to be an octave wide, no? Half an octave to the left, half an octave to the right. Instead they are around 0.4 octaves wide according to Jack's calculator.

I doubt that they made the bands too narrow by accident or on purpose, meaning I am not understanding something right. Can someone help me clear this up. Understanding this seems sort of crucial for building a useful EQ.

I suspect this is to do with how Q is defined in bandpass filters. It's the centre frequency, divided by the bandwidth between the lower -3dB point and the upper -3dB point. Imagine what the frequency response looks like - typical bell curve. The part that is regarded as the "passband width" is only the bit between -3dB points at the top of the bell. Since the "skirts" of the bell actually go out quite a bit wider than that (especially for lower-order filters) you might well want to set the Q a bit higher than the raw numbers suggest to stop one band interfering with another quite so much. As usual, there's a trade-off there between having bands that don't overlap too much and having a sound which is unnaturally "peaky".

if the "virtual order" of the filter (in this case defined by the properties of the gyrator) remains the same, then Q and boost/cut are coupled. But that is the same for all EQ designs that I can think of at the moment, no?

Aside from the Rane "Constant Q" design (and probably subsequent copies) mentioned earlier, yes, that's true.

https://www.rane.com/note101.html

I think this is a bit over-played though. Saying that the Q varies with cut/boost makes it sound like the curve gets wider or narrower as you range the cut or boost. I don't think it does, really. The skirt goes out just as wide at high boost as at low boost. What happens is that because of the way Q is defined, the Q works out much lower for a low, rounded hill than a tall mountain. Doesn't mean you don't reach the foothills for both at the same place:

(or see the MT-2 curves below)

There's a picture on that Rane page that explains what a "Constant Q" EQ looks like.

Instead of "squashing" the curve as you turn down the boost, it "shrinks" it.

There's one other issue, which is the coupling between frequency and resonance. The gyrator-based EQ design suffers very badly from this, but not all EQ sections do.

For example, state-variable-filter-based EQs don't have that problem. In the SVF, resonance and frequency can be completely separate. They use 3 op-amps per section rather than the one you need for a gyrator though, so cheaper designs settle for the gyrator.

The Wein-bridge EQ used for mids in the MT-2 also provides a very constant Q as frequency is varied:


Hope these thoughts give you a few more ideas to play with.

T.
10
So -

Quote
The suggested readings in the build doc are -
Q1: C -8.5v B -0.05v E 0v
Q2: C -0.15v B -0.07v E 0v
Q3: C -8.5v B -0.15v E -0.1v

...and currently -
Quote
Trims at 100%:

Q1 - C -9.34 B -.002 E 0
Q2 - C -0.9 B -0.04 E 0
Q3 - C -3.03 B -0.9 E -0.77

Trims at 0%:

Q1 - C -9.34 B -.002 E 0
Q2 - C -0.49 B -0.03 E 0
Q3 - C -3.13 B -0.49 E -0.38

The 0.9 is close enough to 0.15, and the rest of the numbers that are also close fall in line? I'm pretty green at this, and it's my first time attempting to bias germanium. Q1 Base is still way out. Will that cause a problem?

close enough? yes. but it will probably behave better at 0.15, so just set it to that. It's within your trim pot's range.
Once that is set you can set Q3's trim pot.

Are you sure you really picked a 100k for Q1b?
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