Mods and bass version of Tonepad's speaker simulator?

[xorophone]

Hi! I'm planning to build a stereo version of Tonepad's Marshall speaker simulator soon. I might challenge myself to fit it in a 1590a too. I think I'll have to use SMD components for that (which I've never done, so it would be fun to try.) I'd love to add a switch that changes the values and makes it suitable for bass guitar. Which values would need to be changed for that? Any suggestions on what I should change them to?

I'm also interested in adding other fun mods if there are any available. The circuit is so simple on it's own, so it would be fun to play around with it a bit more.

[thermionix]

Maybe a dumb question, but what is a speaker simulator?  Seems like something is either a speaker or it isn't.  Is there a new way to vibrate the air?

[xorophone]

Maybe a dumb question, but what is a speaker simulator?  Seems like something is either a speaker or it isn't.  Is there a new way to vibrate the air?

It's basically a cabinet/amplifier simulator. I generally don't have much knowledge about amplifiers and cabinets, so I don't know why they called it that.

[GibsonGM]

A lot of the character of an amplified guitar comes from the speaker/amp's frequency response (and resonance).  You can build a circuit that will in some measure replicate the response of a decent cab.  Some models are more complex than others.

If you're ever plugged an electric guitar straight into a computer or recording console and experienced the dead, flat, crappy sound you get.....these things help that by enhancing the stuff you want, and nipping off a lot of what you don't...

[xorophone]

A lot of the character of an amplified guitar comes from the speaker/amp's frequency response (and resonance).  You can build a circuit that will in some measure replicate the response of a decent cab.  Some models are more complex than others.

If you're ever plugged an electric guitar straight into a computer or recording console and experienced the dead, flat, crappy sound you get.....these things help that by enhancing the stuff you want, and nipping off a lot of what you don't...

Exactly! Great explanation. Seems to be especially important when you're using some kind of distortion pedal. The cab gets rid of some nasty high frequencies and makes the guitar sound tighter in the bass region.

Has anyone tried Tonepad's speaker simulator by the way? Are there any other ones that you like better?

[GibsonGM]

I don't have any real preference; I don't use them much.   A member on there, "Dead astronaut", has been playing with a home-brew one...topic is "Ridiculously simple cab simulator"...do a search and check it out!
Sounds pretty good, actually...

[xorophone]

I don't have any real preference; I don't use them much.   A member on there, "Dead astronaut", has been playing with a home-brew one...topic is "Ridiculously simple cab simulator"...do a search and check it out!
Sounds pretty good, actually...

Yup, I've seen that thread before. It sounds great! I'd probably prefer to build a cab sim that I'm sure is 100% finished and polished though. I don't know. I'm just not very good at designing circuits myself, so I'd like to build something that I know I can rely on.

I guess I might breadboard the Tonepad circuit tomorrow and play around with it a bit. Do you know which values I should try changing to make it work with bass? I just have to make sure the low frequencies go through the pedal and then I can play around with the other values to make it sound better.

[thermionix]

But what if you run through a speaker cabinet simulator, then go into an actual speaker cabinet?  Does it cause an explosion?  Tear a gaping hole in the very fabric of spacetime itself?

To be completely honest, I knew what it was to begin with.  I was just being an a-hole.  I try to keep myself entertained.

[xorophone]

But what if you run through a speaker cabinet simulator, then go into an actual speaker cabinet?  Does it cause an explosion?  Tear a gaping hole in the very fabric of spacetime itself?

To be completely honest, I knew what it was to begin with.  I was just being an a-hole.  I try to keep myself entertained.

I like your style! Your "a-hole" questions are great, because that means I'll start to question it myself and learn something new! Well... maybe not from the last question...

I still want to know which resistors/caps I should replace to change the cutoff frequency of the high pass filter. Does anyone know? I'm guessing the first op-amp stage (IC1A) is the low pass filter, but I'm not sure. I'd also like to know which components to replace if I want to change the cutoff frequency of the low pass filter. I've heard people say this circuit cuts away too much treble, so I'd like to play around with that value too. Not as important as changing the high pass filter though.

Here's a link to the tonepad project: http://tonepad.com/project.asp?id=72


Edit: Also, why is there an asterisk beside the 1M resistor on the second op-amp stage? Does that mean it's a value I should play around with? Can't find an explanation of it anywhere.

[PRR]

> which resistors/caps I should replace to change the cutoff frequency

On almost any R-C filter problem:

Leave the resistors alone!! They are picked for proper impedance scale, sometimes DC biasing.

Change the caps. Bigger makes lower. Keep cap ratios the same. Double the uFd is one octave lower.

[xorophone]

> which resistors/caps I should replace to change the cutoff frequency

On almost any R-C filter problem:

Leave the resistors alone!! They are picked for proper impedance scale, sometimes DC biasing.

Change the caps. Bigger makes lower. Keep cap ratios the same. Double the uFd is one octave lower.

Thank you for mentioning that! I'll leave the resistors alone.

[maggotron]

Leave the resistors alone!! They are picked for proper impedance scale, sometimes DC biasing.

Change the caps. Bigger makes lower. Keep cap ratios the same. Double the uFd is one octave lower.

I wondered that too! I want to make a cab sim for bass, with switch for bass & guitar. Just input caps. What about D.I. out? What is that about?

EDIT: So, a DPDT switch that changes both input & output caps? Called "bass" and "lead"?

[maggotron]

Leave the resistors alone!! They are picked for proper impedance scale, sometimes DC biasing.

Change the caps. Bigger makes lower. Keep cap ratios the same. Double the uFd is one octave lower.

I wondered that too! I want to make a cab sim for bass, with switch for bass & guitar. Just input caps. What about D.I. out? What is that about?

EDIT: So, a DPDT switch that changes both input & output caps? Called "bass" and "lead"?

EDIT: So, what is difference between an "OUT" and an "XLR OUT" and why one over the other? I use my Bad Monkey for bass guitar & love it, it has a jack out for mixer desk with some "poor man's" cab sim, but it works. Can I do better on a piece of vero?

[xorophone]

Leave the resistors alone!! They are picked for proper impedance scale, sometimes DC biasing.

Change the caps. Bigger makes lower. Keep cap ratios the same. Double the uFd is one octave lower.

I wondered that too! I want to make a cab sim for bass, with switch for bass & guitar. Just input caps. What about D.I. out? What is that about?

EDIT: So, a DPDT switch that changes both input & output caps? Called "bass" and "lead"?

A D.I box basically converts a guitar signal into a line level signal. D.I boxes and speaker simulators seem to often be combined, but the Tonepad one is just a speaker simulator.

Yes, I guess you'd use a DPDT switch, but I don't know where the filtering is occuring in the circuit. I'm pretty sure there's an active high pass filter in the circuit and that means you'd have to change the capacitor value on that one too. I've breadboarded the circuit, but I couldn't get it to work right now. I'll take a look at it again tomorrow if I have time and start experimenting with different values.

Leave the resistors alone!! They are picked for proper impedance scale, sometimes DC biasing.

Change the caps. Bigger makes lower. Keep cap ratios the same. Double the uFd is one octave lower.

I wondered that too! I want to make a cab sim for bass, with switch for bass & guitar. Just input caps. What about D.I. out? What is that about?

EDIT: So, a DPDT switch that changes both input & output caps? Called "bass" and "lead"?

EDIT: So, what is difference between an "OUT" and an "XLR OUT" and why one over the other? I use my Bad Monkey for bass guitar & love it, it has a jack out for mixer desk with some "poor man's" cab sim, but it works. Can I do better on a piece of vero?

I'm guessing the "OUT" is a 1/4" mono jack. Those have two poles (+ and ground), while XLR jacks have 3 poles (+, - and ground). With 3 poles you can use a balanced audio signal and thus reduce noise if you're using long cables. If you don't know what a balanced audio cable is, I strongly recommend watching this video for an explanation: https://www.youtube.com/watch?v=5ENXqMJvvdo

[anotherjim]

As the tonepad info uses no part numbers, it's tricky to call them out.
To begin with the .047 (47nF) at the input can be doubled to .1 (100nF). 'though 220nF will allow full range
The .0033 (3.3nF) going into the second amp, also try double that - maybe 6.8nF.
Those should deepen the bottom end and low mids about an octave.

You maybe don't need to touch the top end response. I think you can control that if needed just as well anywhere before it, even use the guitars tone. A lot of old bass cabs were dead over 3kHz while modern ones try for full range.

That thing has a really low input impedance at 27k (why!), so make sure whatever is driving it has a really low output impedance.

Thing is, "suitable for bass" could mean a lot of things. Speakers from 10" up to 18". Cabs sealed or various forms of port or reflex. Drivers from ribbed paper guitar style to plasticated with metal domed PA types with added tweeters, so the simplest & easiest thing you can do is just let more lows through.

[xorophone]

As the tonepad info uses no part numbers, it's tricky to call them out.
To begin with the .047 (47nF) at the input can be doubled to .1 (100nF). 'though 220nF will allow full range
The .0033 (3.3nF) going into the second amp, also try double that - maybe 6.8nF.
Those should deepen the bottom end and low mids about an octave.

You maybe don't need to touch the top end response. I think you can control that if needed just as well anywhere before it, even use the guitars tone. A lot of old bass cabs were dead over 3kHz while modern ones try for full range.

That thing has a really low input impedance at 27k (why!), so make sure whatever is driving it has a really low output impedance.

Thing is, "suitable for bass" could mean a lot of things. Speakers from 10" up to 18". Cabs sealed or various forms of port or reflex. Drivers from ribbed paper guitar style to plasticated with metal domed PA types with added tweeters, so the simplest & easiest thing you can do is just let more lows through.

Thank you! Sorry for the late reply by the way.

I don't really care if it doesn't fully emulate an amp. I just want to let the bass frequencies come through. If it sounds bad I can experiment a bit with other values too.

I've never really understood impedance. Should I change the input impedance? How? What is considered a low output impedance?

[anotherjim]

What do you plan on plugging into it? Can't advise properly without knowing.

The 27k input resistor represents the input impedance. 27k is too low by a factor of at least 20 to be directly used with a passive guitar. Increasing resistor values by enough with this circuit will also increase noise. It ideally needs a high impedance buffer in front to use with passive guitars.

It has been hacked from another design, providing a cab simulated D.I. output from an amplifier.  If your bass is active, it would probably be ok with just the capacitor changes.

As you say you don't have need of amp simulation, that's ok, but for anyone else - some amp simulator pedals are meant to drive guitar amp clean channels which have high input impedance, and so some of these don't have particularly low output impedance. These would be adversely affected plugged into this cab circuit as it is.

The cab sim output is right out of the last op-amp, so it has a low output impedance and should be able to drive any line input directly.


I think this scheme is the same...

[PRR]

> some amp simulator pedals are meant to drive guitar amp clean channels

The TonePad doc files says:
"...useful for straight recording into a line input or mixing desk."

> I think this scheme is the same...

That one lacks an output cap so is throwing DC at the mixer.

Because a "speaker" (real or emulated) can be connected either way, I see no shame changing the first opamp to non-inverting, so it can be hi-Z input. As you say, this may not be needed in all cases, but can be handy.

[anotherjim]

I was referring to amp simulator pedals (the circuit under scrutiny is a cab sim only). Those meant for feeding guitar amp clean channel and give it the flavour of a different amp - like the "Plexi Drive". These do not have cab simulators of their own. Maybe those would be best called "amp channels"?
Some may think that adding this cab circuit in its own box would be good way of making a full D.I. solution. I've seen some of these amp channels with 10k or more in the output & some with passive tone networks right at the output. They would not work well into 27k.

Good catch for the lack of DC blocking cap on the scheme I linked. It seems to have been forgotten after the output line driver used in the Marshall original. There is a 22uF cap on the original feeding an XLR with resistor balancing.

[pee-j]

hi,

just for reference, I'm adding this schematic version, with the output cap,
I don't remember the source where I downloaded it from..




okay, another one, from Tonepad (this one has only a 1uF output cap instead of 10uF or 22uf):