# Optional cab sim bypass Emu Amp?



## Prefectingfjords (Sep 9, 2020)

Has anyone modded the Emu Amp sim to allow for bypassing the cab sim?  I’d like the option to run into a different cab sim.

The stock config has “center”, “classic”, and “off-axis” for SW1.   I’d like to change either the “classic” or “off-axis” to be a “bypass” for the cab sim but still be able to use the other two options.  Is there an easy way to do this with a jumper?


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## daeg (Sep 9, 2020)

Scroll down and look at S1A and S1B. Signal is going right-to-left...


*Up / Off-Axis*
At S1B the 4.7n and 6.2k form a HPF for -6db/oct rolloff below 5.4khz.
At S1A the 22n and 100k form a HPF for -6db/oct rolloff below 72hz
The 22k bypass resistor lessens the overall impact of the filter.

*Center / Center*
At S1B two 4.7n and 6.2k form a HPF for -6db/oct rolloff below 2.7khz.
At S1A the 22n and 100k form a HPF for -6db/oct rolloff below 72hz
The 22k bypass resistor lessens the overall impact of the filter.

*Down / Classic*
Removes the aforementioned filters from the circuit.
Signal only goes through the 22k bypass resistor.
A 22k resistor to ground is added to form a voltage divider with the 22k bypass resistor.

So there you have it... Classic is _already_ the 'bypass' mode. It just adds an extra resistor to prevent an audible volume jump.


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## Prefectingfjords (Sep 9, 2020)

This is EXACTLY the info I needed.  Thanks so much.  This is my first build where I’m trying to truly understand the circuit design before just following the build doc, so I really appreciate the info.

one follow up question, the Emu faceplate has the off axis option as “Down” and the “Classic” option as “Up” which looks reversed from the actual GT2 and Sin amp layout.  Do I have that right?


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## daeg (Sep 9, 2020)

Prefectingfjords said:


> This is EXACTLY the info I needed.  Thanks so much.  This is my first build where I’m trying to truly understand the circuit design before just following the build doc, so I really appreciate the info.



The Sansamp pedals are about as complex as a distortion circuits get. There are 40 page threads out there of smarter people than us doing their best to analyze them, so don't beat yourself up if this one goes a little over your head.

In the future, I'd recommend heading over to ElectroSmash to read a few circuit analysis articles they've produced over the years. They have the Tubesceamer, DS-1, Rat, Klon, Rangemaster, FuzzFace - all with graphs from simulation software. It's just the right amount of info to learn more than you'd ever get from demos, forums or product descriptions, but still be brief and accessible.


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## daeg (Sep 9, 2020)

Prefectingfjords said:


> one follow up question, the Emu faceplate has the off axis option as “Down” and the “Classic” option as “Up” which looks reversed from the actual GT2 and Sin amp layout.  Do I have that right?


 
We'd have to look at the pinout of the slide switches to figure it out. I've never built one of these (I have the cheap Behringer clone and never use it), perhaps Mr. PCB can chime in.


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## Prefectingfjords (Sep 10, 2020)

daeg said:


> The Sansamp pedals are about as complex as a distortion circuits get. There are 40 page threads out there of smarter people than us doing their best to analyze them, so don't beat yourself up if this one goes a little over your head.
> 
> In the future, I'd recommend heading over to ElectroSmash to read a few circuit analysis articles they've produced over the years. They have the Tubesceamer, DS-1, Rat, Klon, Rangemaster, FuzzFace - all with graphs from simulation software. It's just the right amount of info to learn more than you'd ever get from demos, forums or product descriptions, but still be brief and accessible.



That’s a great suggestion, I’ve seen the electro smash articles recommended before and it’s about time I spend some time with them.  Thank you for the advice and info!


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