Questions about the "Simple Cab Sim" circuit?

[Jasonmatthew911]

Hi, guys...As some may know from a past post of mine, I've been working on a 2 input mixer for Guitar/Bass/Synth, with 2 separate PreAmps running on 18V, and one with an ON/OFF 3PDT switch to go through the Simple Cab Sim circuit and then to a Jensen DI Transformer to go directly out through XLR to mixer or interface for Live/Recording direct...Anyhow, my PreAmp which is a J201 going into a TL072, with a Gain stage set at 2, and the 2nd part of opamp used as a Buffer...This PreAmp gives a nice clean boost and has a lot of headroom, it's been on my breadboard for awhile now...I just recently breadboarded and fed my PreAmp into the Simple Cab Sim circuit (Built with same value components as original schematic, I used J201, 2N5087, BC550C for JFET and Transistors)...It seems to be working and sounds pretty good, though I feel it could use a little more low end...I also have it running on the 18V, but when my PreAmp goes through the Simple Cab Sim, it seems to attenuate the signal of my PreAmp a bit, also cutting lows a bit...I guess the Simple Cab Sim is more of an EQ, but I didn't expect it to make my signal a little bit weaker...Is this normal and on purpose with the Simple Cab Sim circuit?...I tested it going from PreAmp into Simple Cab Sim, into a nice Passive Switchcraft DI Box I have going into my mixer of my PA system, and when the signal reached the mixer through the DI Box it was kind of weak, with Fader at 0 decibels, I had to push the Gain up on the mixer about half way to get a loud enough signal to play with drums, also had to push my PreAmp volume beyond half way, which when I send my PreAmp directly to a guitar amp it sounds super loud even slightly below halfway...I was expecting a slightly stronger signal getting to the mixer since I have a strong high headroom PreAmp going into it, but the Cab Sim seems to weaken my PreAmp signal a bit...So I guess these are my main questions about the Simple Cab Sim circuit...

1. Is all I mentioned above normal with the Simple Cab Sim design, does it weaken/attenuate a PreAmp signal going into it?

2. What values do you recommend changing in the Simple Cab Sim to get a better Low end response, considering this would be for Guitar and possibly even Bass?...With Guitar as is, I feel it needed slightly more low end response, if it wouldn't attenuate my PreAmp this shouldn't be an issue, as my PreAmp has a bit more Low end for Guitar and Bass, as well as more Volume output on it's own Vs going through the Cab Sim which lowers the PreAmp output.

3. Can I get the Simple Cab Sim to output a stronger signal?...What would you recommend doing?

Thanks for any help in advance...Cheers!

[niektb]

Do you have the schematic for us? (or a link to) 

[Jasonmatthew911]

Do you have the schematic for us? (or a link to) 

Yea, here you go...My PreAmp schematic that goes into the Simple Cab Sim circuit...

[iainpunk]

the simple cab sim is wat my teacher would call a ''pseudo passive filter'' meaning that the active components are only used as buffers in gyrators, emulating inductors, and not as voltage amplifiers, so it is lossy, yes, that was the way it was designed. you could add a simple booster at the end to up the volume a bit.

it needs to be fed by an guitar amp simulator pedal or a real amp and loadbox, that's probably what it was designed for.

cheers, Iain

[Jasonmatthew911]

the simple cab sim is wat my teacher would call a ''pseudo passive filter'' meaning that the active components are only used as buffers in gyrators, emulating inductors, and not as voltage amplifiers, so it is lossy, yes, that was the way it was designed. you could add a simple booster at the end to up the volume a bit.

it needs to be fed by an guitar amp simulator pedal or a real amp and loadbox, that's probably what it was designed for.

cheers, Iain

Cool, I'll try a simple J201 or other simple transistor boost at the end and see how that sounds, thanks...Also, any advice as to what values to swap to get a bit more Low end response out of the Cab Sim?...To me it feels like it could use a little more low end...So far I've only tried changing the (3) .047uf Caps to .1uf...Maybe it had a bit more lows, unless it was just a mental thing, just not a big enough difference to really notice when I try one value then the other I guess...I also think I felt that the Cab Sim got a little dirtier with the .1uf...I didn't want to mess with the values too much, since the point is it's EQ sound to sound like a Cab, but it's a Cab sound that could use just a little more low end for my taste...Let me know what values I could try/swap...Thanks again...Cheers!

[Jasonmatthew911]

the simple cab sim is wat my teacher would call a ''pseudo passive filter'' meaning that the active components are only used as buffers in gyrators, emulating inductors, and not as voltage amplifiers, so it is lossy, yes, that was the way it was designed. you could add a simple booster at the end to up the volume a bit.

it needs to be fed by an guitar amp simulator pedal or a real amp and loadbox, that's probably what it was designed for.

cheers, Iain

I tried the same J201 circuit that I have going into the TL072 of my PreAmp on the output of the Simple Cab Sim and now it's a little too loud, adds a bit of saturation at higher volumes...I'm trying to keep it clean...Is there any way to lower gain slightly on the J201, or would the option be to use a trimmer coming out of the Drain leg?

[Vivek]

I tried to trace the history of the SIMPLE CAB SIM

I found these links:

https://web.archive.org/web/20161111160222/https://dl.dropboxusercontent.com/u/11178619/Cab%20Simulation/simple_cabsim2%20Resistors.png


http://vulcanofx.blogspot.com/2014/02/simple-cabsim.html?m=1

https://www.diystompboxes.com/smfforum/index.php?topic=106719.0

[Vivek]

any advice as to what values to swap to get a bit more Low end response out of the Cab Sim?...To me it feels like it could use a little more low end...So far I've only tried changing the (3) .047uf Caps to .1uf

On the LTSPICE analysis, changing C2 and C4 from 47n to 120n changed the location of the 3db bump in the bass from 121 Hz to 51 Hz.  Then the response at 50Hz went from -14.5dB to +3.5 dB

Of course you could try other values for C2 and C4 in between 47n and 150n to suit your preferences. Bigger caps = more bass.





PS : I also show the way to control the steps of 2 parameters in LTSPICE using the Table command

[Jasonmatthew911]

any advice as to what values to swap to get a bit more Low end response out of the Cab Sim?...To me it feels like it could use a little more low end...So far I've only tried changing the (3) .047uf Caps to .1uf

On the LTSPICE analysis, changing C2 and C4 from 47n to 120n changed the location of the 3db bump in the bass from 121 Hz to 51 Hz.  Then the response at 50Hz went from -14.5dB to +3.5 dB

Of course you could try other values for C2 and C4 in between 47n and 150n to suit your preferences. Bigger caps = more bass.





PS : I also show the way to control the steps of 2 parameters in LTSPICE using the Table command

Thanks for the graph...Yea I tried .047uf, .068uf, .1uf and even 1uf for kicks...I settled at .1uf for C2, C4, C1...The only thing now is after adding the J201 at output of Cab Sim, it sounds clean and louder with my volume around 9 o'clock, but after about 11 o'clock it starts to saturate a quite a bit...So it's definitely adding more Gain...If I recall I think the gain added with the J201 is around 3...Maybe I just need an extra Gain of 2 max...Can anyone recommend any other simple Boost I can add with a transistor with slightly less gain than the J201 (Minimal parts)?...I really don't want to have to add another opamp to get less gain...If anyone can recommend what I can do to lower the extra gain after the Simple Cab Sim just slightly so I have a Gain of 1 or 2 would be great?

[11-90-an]

If anyone can recommend what I can do to lower the extra gain after the Simple Cab Sim just slightly so I have a Gain of 1 or 2 would be great?

Try this boost...


Remove R1, increase C1 and C2 to probably 1u, remove the volume pot, increase R2 to lower gain. prolly gonna need 1M...

OT question, the JFET in the simple cabsim... since it's used as a buffer, can it be replaced with a BJT? You would have to adjust the bias resistors R1 and R2, I think.. Overall ckt would have lower input impedance too, probably...

[Vivek]

anyone can recommend what I can do to lower the extra gain after the Simple Cab Sim just slightly so I have a Gain of 1 or 2 would be great?

You can adjust the gain of the FET stage by changing one resistor.

Or add a voltage divider or trim pot somewhere.

No need to totally change what you built just because of slightly high gain.

Gain of 1 = output is same as input. That won't help you.

[Vivek]

Right now you have

An Opamp with gain of 2
A unity gain Opamp

Speaker sim

And you felt gain was too little


So you can adjust gain of first Opamp to be 3 or 4


Or you can stick the speaker sim in between the 2 opamps

First Opamp has gain of 2
It feeds the speaker sim
Then second Opamp can be reconfigured to have gain of 2, high impedance for speaker sim and have low output impedance


Really no need for FET or BJT stage after speaker sim when you can change gain of Opamp 1 and Opamp 2 so easily.

More parts = more noise, more cost, more complexity, more things that can fail

[Jasonmatthew911]

Right now you have

An Opamp with gain of 2
A unity gain Opamp

Speaker sim

And you felt gain was too little


So you can adjust gain of first Opamp to be 3 or 4


Or you can stick the speaker sim in between the 2 opamps

First Opamp has gain of 2
It feeds the speaker sim
Then second Opamp can be reconfigured to have gain of 2, high impedance for speaker sim and have low output impedance


Really no need for FET or BJT stage after speaker sim when you can change gain of Opamp 1 and Opamp 2 so easily.

More parts = more noise, more cost, more complexity, more things that can fail

You forgot that I have a J201 going into my Opamp, and I think that adds a Gain of 3, then I have a Gain of 2 in my Opamp...I didn't need the 2nd stage of Gain in the opamp because as a PreAmp alone this was more than enough...My PreAmp sounds good by itself and with other pedals, so I don't want to mess with it, plus it is loud enough...The problem is that when I feed this same PreAmp into the Simple CabSim, the sound comes out weaker than my PreAmp alone, meaning the CabSim is weakening my sound...That's why I need the extra boost/gain after the CabSim, but I don't seem to need much, as I added my J201 with the same 1K and 15K resistors for proper bias after the CabSim and it works well up to about 9 o'clock, after that there's a bit too much saturation, so just too much gain...If a Gain of 1 after the CabSim puts me back at the output volume level of my PreAmp before it goes into the CabSim then that would be perfect actually...I'd like the volume out of the CabSim to at least match volume level of my PreAmp on it's own, so that I don't feel a volume drop when I switch the CabSim on, as there will be a 3PDT switch to either send my PreAmp sound direct to a Jensen DI Transformer or turn CabSim On and send it to the DI...My PreAmp is clean but powerful and after about 3 o'clock is when a bit of saturation starts, so if I add more gain to my PreAmp it will get dirty too soon, I'm trying to keep my PreAmp clean and as a clean boost...If I feed anymore gain into the CabSim I'm pretty sure it will receive a saturated sound rather than clean, and it won't sound clean at the output...Therefore I think I just need a Gain of 1 or 2 at the Output of the Simple CabSim...

What value resistor do you say I can use for my J201 at output of CabSim, and what about the proper bias so that it sounds good?

[deadastronaut]

Have you tried other cab sims...?

On my own lengthy cab sim quest i tried lots on breadboard including this one and to be quite honest none of the popular and not so popular did it for me at all,  the circuit sim graph might say it looks ok, but the reality of actual sound when it comes to playing it is very  different. Imo...

In the end i had to go with what my ears were telling me.....thats just my 2p of course....

It ended up being the " astro sim".

Have a search.........as you were... 

[Vivek]

https://www.hamerfanclub.com/forums/topic/87873-cab-sims-what-they-sound-like/


Comparison of many different Cab Sims

[Jasonmatthew911]

If anyone can recommend what I can do to lower the extra gain after the Simple Cab Sim just slightly so I have a Gain of 1 or 2 would be great?

Try this boost...


Remove R1, increase C1 and C2 to probably 1u, remove the volume pot, increase R2 to lower gain. prolly gonna need 1M...

OT question, the JFET in the simple cabsim... since it's used as a buffer, can it be replaced with a BJT? You would have to adjust the bias resistors R1 and R2, I think.. Overall ckt would have lower input impedance too, probably...

Thanks for the suggestion...I just tried this Boost like you said, except with 1M for R3 and 470K for R2, cuz I don't have 6.8M, I have 10M, but not sure why go so big...With these values this Boost seems to be slightly cleaner/more usable than my J201 after the CabSim...I also tried 1M for R3 and R2, but that may not be giving much gain...So R2 and R3 values determine the Gain I assume?...Would 1M at R3 and 470K at R2 = a Gain of 2 or 3?...Would 1M for both R2 and R3 equal to a Gain of 1 or 2 maybe?...Also, are these size values fine, or would smaller values = less noise?

[Vivek]

http://paulorenato.com/index.php/electronics-diy/104-transistor-amplifier-calculator

[Jasonmatthew911]

http://paulorenato.com/index.php/electronics-diy/104-transistor-amplifier-calculator

Thanks, but I really didn't understand how to use this calculator in excel...If you can help me calculate a Gain of about 2 with the 2N5088 Boost circuit I'd really appreciate it.

[Jasonmatthew911]

If anyone can recommend what I can do to lower the extra gain after the Simple Cab Sim just slightly so I have a Gain of 1 or 2 would be great?

Try this boost...


Remove R1, increase C1 and C2 to probably 1u, remove the volume pot, increase R2 to lower gain. prolly gonna need 1M...

OT question, the JFET in the simple cabsim... since it's used as a buffer, can it be replaced with a BJT? You would have to adjust the bias resistors R1 and R2, I think.. Overall ckt would have lower input impedance too, probably...

Hey, so which resistors determine the Gain in this simple boost circuit...Is it R2 & R3 or is it R3 & R4, or is it R2,R3 & R4?...I've been changing R2 & R3 and it's been changing my Gain, but I ask because I was also sent a Transistor Calculator where R2 doesn't exist, the calculator only has R3 & R4...Can someone please clear this up for me?...Thanks.

[PRR]

......Can someone please clear this up for me?...

There are many ways to skin a horse.

The calculator link in reply #16 does not cover this case.

However for a mere gain of 2 the #16 calc and circuit may be a better plan.