Questions about the "Simple Cab Sim" circuit?

[Jasonmatthew911]

......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.

Thanks, but I seem to need help on exactly how to use this calculator...I mean I tried putting in my values for Rf, Rc, VCC, C1, and CL under the "R Given" Tab, but I have no idea how to understand my results, nor where in results I can see the amount of Gain created by my values...I guess I'm a newb with this calculator/formulas...Can someone please help me figure out a Gain of about 2 using the 2N5088 or at least explain it to me so that I can know what results to look for using the calculator?

[PRR]

[Vivek]

Thanks, but I seem to need help on exactly how to use this calculator...I mean I tried putting in my values for Rf, Rc, VCC, C1, and CL under the "R Given" Tab, but I have no idea how to understand my results, nor where in results I can see the amount of Gain created by my values...I guess I'm a newb with this calculator/formulas...Can someone please help me figure out a Gain of about 2 using the 2N5088 or at least explain it to me so that I can know what results to look for using the calculator?

Av is the Voltage Amplification or Gain

[Jasonmatthew911]

Thanks for this, helped a lot, I tried these values and it sounded pretty clean, but didn't boost volume too much compared to sound without it, so I started to experiment with the new 6.8K resistor value, I went down to 2.2K, 4.7K, and 3.9K, I think I'm happy with the Gain volume using a 3.9K instead of the 6.8K, so maybe I needed a Gain of 3 or 4...Was that the right resistor to change to adjust the Gain?...Also, for R3 I have a 10M instead of the 6.8M, is that ok or does that difference affect the bias?

Anyhow I'm happy with the volume out of the CabSim now, but now I just noticed, that if I have the output of the CabSim (Which is using the 2N5088 Boost now) connected to the Jack that goes out to my Amp, and I also have the same output going into a simple 386 Headphone Amp (See attached schematic), when both are connected at the same time I noticed the headphone amp causes a slight attenuation to the output signal going to my amp...Seems the values at the input of my headphone amp are affecting the volume loudness to the output jack as well...I tried wiring them both with 10K mixing resistors, but with or without the extra 10K resistors the signal gets attenuated a bit when headphone amp is also connected...How should I be splitting my output signal to avoid this attenuation?...It doesn't happen when I disconnect the headphone amp from the output of CabSim, it sounds a little bit louder, more low end and more clear when I take headphone amp out...I didn't mention at the beginning of post that I was also incorporating a simple headphone amp in this design for silent jamming, but I am...I thought I was fine with my headphone amps volume, but now I noticed how it's affecting volume level coming out of my CabSim...

Any help on what it could be and how to keep the headphone amp from attenuating the CabSim output level?...Proper way to split the signal to avoid this maybe?

[PRR]

Why does your headphone amp have a 2.2k resistor at the input??

[Jasonmatthew911]

Why does your headphone amp have a 2.2k resistor at the input??

I ended up adding that resistor to help kill a slight background hum and it also attenuates the signal going into headphone amp a bit, so that it's not too loud or saturated in the headphones...I can take it out, but when I do, it makes headphone volume a lot louder (Too loud) and adds a slight hum in the background, so the 2.2K was to kind of tame that issue I guess...Should I really not be doing it like that?...Is there a better way to get rid of the slight background hum in the headphone amp?...The attenuation at the output of CabSim happens whether I have that 2.2K resistor or not...Right now I have to completely disconnect the Headphone amp from the output of CabSim in order to get the full blown sound out...I don't really understand why when I connect the headphone amp to the output of CabSim it attenuates the output going to Output jack?

[PRR]

That's significantly loading almost any source meeker than a studio mixer.

Try two resistors as an attenuator. You "should not" need less than 10K seen by LM386, so try 47K+10K.

[Jasonmatthew911]

That's significantly loading almost any source meeker than a studio mixer.

Try two resistors as an attenuator. You "should not" need less than 10K seen by LM386, so try 47K+10K.

Awesome, thanks!...Those 2 resistors worked perfect, and now at least I'm not loading the source (I'm attaching updated schematic with the 2 resistors added just to make sure this is what you meant)...If not, let me know...

I still have the issue that my Headphone Amp is causing my CabSim output to attenuate...It still sounds pretty good with headphones connected to the CabSim out, but as soon as I disconnect the Headphone Amp, the CabSim output to my amp sounds noticeably louder and better...This is the last thing I need help figuring out, then my design will be done and working as intended, and I can finally finish up my PCB design...Anyone have any idea how I should be splitting the signal out of the CabSim so that the Headphone Amp doesn't attenuate any of the signal when it's connected to the CabSim out??

[PRR]

[Jasonmatthew911]

Thanks, this works, but it does saturate my signal sooner in the Headphones...I tried replacing the 47K with a 10K to see if it attenuated a little more signal so that it doesn't saturate so soon in the Phones, but I didn't notice much of a difference by changing the value of the 47K resistor...Would this be how to attenuate a little more or should I try something else for a tad more attenuation?

I also wanted to mention, that while I was trying out my circuit through the headphone amp, outside of my house they're doing a small construction and they have some power tools connected to the electricity of my house, and everytime I heard the drill being used, it added a slight noise in the background of my sound...When the drill stopped, the added noise also stopped...Why does that happen exactly?...Is it because my circuit and drill are both connected to the electricity of my house, or maybe there's an issue in my house electricity/isolation, or could it be because my circuit isn't completely shielded in a Box yet, or not having a fully regulated power supply?...I'm using an 18V / 1A Dunlop Power supply...I'm curious as to why this happened?

Lastly, so no one has any idea why when I have the Headphone amp connected to the output of my CabSim, it slightly attenuates my output signal that goes to my Amp???...If I disconnect the Headphone Amp, the CabSim outputs a slightly louder output signal to my Amp...I'm really confused as to why it's happening

[FiveseveN]

I tried replacing the 47K with a 10K to see if it attenuated a little more signal

Other way around: higher resistance means lower maximum volume.

Why does that happen exactly?

The motor induces voltage spikes in the mains which get through your PSU's filtering and/or are radiated along with the "mains hum".

Lastly, so no one has any idea why [...] it slightly attenuates my output signal

Others have already noted how it is loading the output with a (much) lower impedance.

[iainpunk]

a lot of power tools use DC motors, and they have brushes and commutators. the commutator spins around and has multiple contacts to work together with the brushes as a switch. when the brushes break the connection with a contact of the commutator, the current through the coil connected to the commutator can be high enough that there will be a spark jumping across the 2 contacts, this works like a wide bandwidth transmitter of noise.
guitars are really efficient at picking up such noise.

cheers, Iain

[Jasonmatthew911]

I tried replacing the 47K with a 10K to see if it attenuated a little more signal

Other way around: higher resistance means lower maximum volume.

Thanks for clearing that up for me...I might be able to work with the 47K or slightly bigger, cuz 100K attenuated too much...I have to see if I have any in between values like 68K.

Lastly, so no one has any idea why [...] it slightly attenuates my output signal

Others have already noted how it is loading the output with a (much) lower impedance.

Ok, so basically if I want to connect my attenuated Headphone Amp with the out of my CabSim I have to live with the slight attenuation on my other outputs?...Is there any way around this, or are my options either live with it if I want an attenuated Headphone amp, or use with an unattenuated Headphone amp if I want the full blown output level of the CabSim?...If these are my only options, then I guess I'd have to live with the slight attenuation, because without attenuation the 386 Amp is too loud and saturated to be pleasant/usable...Please let me know if there's anything else I can change to still get the full-blown sound from CabSim and attenuate the input of my 386 Headphone Amp at the same time...Thanks again for all the help...Cheers!

[Jasonmatthew911]

Hey, I was wondering, before I even try it...What if I put the attenuator resistor/Pot at the output (Pin5) of the 386 Headphone Amp instead of the input, so that the input of Headphone Amp doesn't load/attenuate the output of the CabSim?...I probably shouldn't even be asking this, cuz if I attenuate at output I guess I would be attenuating a saturated sound due to the extra gain it will output from the 386, so I might be answering my own question here ...I imagine I'd lose the clean sound and would only be attenuating nasty saturation...Any other ideas how I can remedy this final issue I'm having?

[FiveseveN]

What if I put the attenuator resistor/Pot at the output [...] so that the input of Headphone Amp doesn't load/attenuate the output

How would that eliminate the loading? A 386 has 50 K input Z, right?

I don't remember all the elements and details of your build because there's a lot of text description and not one complete schematic, but IIRC you have plenty of options:
- Instead of boosting then attenuating, take your headphone amp signal before the booster.
- Buffer the headphone amp input so it has an impedance similar to the other input.
- Make a proper headphone amp with less gain and proper input Z (this is not what the 386 was designed for).

[Mark Hammer]

I put together the Runoffgroove Condor cab-sim the other day, using Pablo de Luca's PCB layout.  Fired up great first time out.  It provides a gain control and output attenuation to match levels and achieve optimal S/N.  I thought it sounded decent.

[Jasonmatthew911]

What if I put the attenuator resistor/Pot at the output [...] so that the input of Headphone Amp doesn't load/attenuate the output

How would that eliminate the loading? A 386 has 50 K input Z, right?

I don't remember all the elements and details of your build because there's a lot of text description and not one complete schematic, but IIRC you have plenty of options:
- Instead of boosting then attenuating, take your headphone amp signal before the booster.
- Buffer the headphone amp input so it has an impedance similar to the other input.
- Make a proper headphone amp with less gain and proper input Z (this is not what the 386 was designed for).

Awesome thanks!...I guess I'm gonna try taking the signal before the Booster to headphone amp...I'll also try the Buffer at the Headphone amp input to see which result I like better...

I 'd also be up for making a proper headphone amp if you can recommend a fairly simple headphone amp with minimal parts, since I lack room on my PCB Board size due to the rest of the circuits, and it would be great if the Headphone amp can run on 18V or 12V since I'm using L7812 regulator, I guess it can be 9V since I also have L7809 regulators, but usually the higher voltages give more headroom which I also prefer...I don't do Bipolar supplies...I have no idea of such a simple headphone amp, that's why I'm using an LM386 I guess...So any simple recommendations that would sound better than the 386 would be great...Thanks again!

[Jasonmatthew911]

What if I put the attenuator resistor/Pot at the output [...] so that the input of Headphone Amp doesn't load/attenuate the output

How would that eliminate the loading? A 386 has 50 K input Z, right?

I don't remember all the elements and details of your build because there's a lot of text description and not one complete schematic, but IIRC you have plenty of options:
- Instead of boosting then attenuating, take your headphone amp signal before the booster.
- Buffer the headphone amp input so it has an impedance similar to the other input.
- Make a proper headphone amp with less gain and proper input Z (this is not what the 386 was designed for).

Hey, so I ended up taking the CabSim signal before the Booster, then going into a simple TL071 Buffer at the input of the 386 Headphone amp...Everything is good now, and I'm not loading my CabSim output anymore, so It sounds even better now...I think the CabSim sounds very natural...Let me know if you or anyone has a better/fairly simple headphone amp that I could maybe try if it doesn't have a Bipolar supply and can operate with 18V or 12V regulator.

BTW, I tried powering my Pre-Amp, headphone amp, CabSim/extra Boost with (2) 9V Batteries in series for 18V just to see if it would work alright, but I ended up getting a nasty saturated/fuzzy sound...I suppose the batteries don't have enough mA current for so many circuits...I guess this will have to run strictly on 18V power supply...Or should all of these circuits be able to operate on (2) 9V Batteries?