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So in this situation we're looking at the 100K resistor as an output pulldown, but what about the 1K? How is that reducing switch pops?

Thanks again.

I have a question regarding output resistors on circuits.  Just looking at the Bacon Bits booster as an example, what is the purpose for the voltage divider of R7 and R8?  Output signal limiting?  Even further, what about when a buffer is used on the output like in the Quasar? If you have a buffered output with a low impedance, what is the thinking in placing more resistors after it?

I wondered if it had something to do with supplying a load to the amplifier, but that still didn't make sense to me.  I probably need to delve more into my electronics textbooks to find this out but sometimes it's hard to know where to start.

Thanks for any help.

Thanks, that helps to confirm some things.  I guess what i'm wondering now is, do I still need to include the resistor between the opamp input and ground? With a Vcc/2 setup the resistor is  regulating current to the input from the 4.5v correct?

Anybody have any pointers? I'm breaking out the Art of Electronics and searching but so far I haven't seen anything for this specific application...  Maybe I posted this in the wrong section as well? Any info would be greatly appreciated.

Jeremy

Like so:

R16 and R15 set the gain for this half of the OpAmp, it's set at 4.7 (Rf/Ri in an inverting configuration, 47K/10K) The capacitor is there to control high frequencies. This stage is boosting the signal a little before the active tone stack section.

Jeremy

I've seen two different configurations for charge pumps here on Brian's site and at FSB, one with a split rail supply as seen on the Kingslayer project and also as a straigh 18v supply as seen in the Road Rage project.  My question is, I saw how using the split rail supply on the Kingslayer eliminated the need for biasing the inputs at 1/2 VDD with an inverting configuration, but what about with a non-inverting configuration such as the Tubescreamer where you use a resistor connected between the non-inverting input of the op amp and the biasing voltage?  Does this mean that the op amp doesn't need to be biased at all?

If I need to be more clear just let me know, I can include some schematics to explain myself I think.

Cheers!

I'm having the same problem with my fuzz face (Hipster) build.  I'm using 2N3904's for my build.  I can't bias below 6.7 volts with either transistor at the collector, and I'm using the correct orientation.  I've adjusted the fuzz pot all the way up, and I've used a 100kB pot just to see if I could get it to bias down. Again, to no avail.  The fuzz is very gated and won't function when I really hit the strings hard, so it's hitting the ceiling with the supply I think.  Any ideas?

Just to show what i'm doing, I've included the Eagle schematic with what I have in mind.  I took my 9v power for the boost at the end from the regulator in the delay circuit.  Will this be ok?  I've not used regulators much at all.

Any help at all would be appreciated.

I'm thinking of tacking on the IC baby board boost at the end of the CaveDweller 1, I wasn't sure if the effect ran at unity volume but I'd like to be able to boost it a little or a lot.  I guess I could use any boost on the end but wondered if this would effect the delay circuit at all.  I'll use coupling caps in between circuit stages, and I was thinking of not using the split rail supply for the boost to minimize parts count.

Anybody see any technical issues with trying this?

Wouldn't that be for a non-inverting op amp configuration?  Since I have the virtual ground connected to Pin 3 I figured that wouldn't be needed.  That's also the way the actual AC Booster is connected.

I've taken the AC Booster schematic and breadboarded it, but I removed the input and output buffers.  I've verified the wiring and checked all my voltage levels, but I'm getting a very low output signal.  At full volume there's still a volume boost, but it's not like the actual AC Booster, which I own.  I've tried three different IC's, the 4558, TL072, and the OPA2134, and all have the same volume issue.  The tone stack works like it should, and I know that tone stacks can cause loss, but if the original works just fine why shouldn't this one?  I've included the schematic to show what i'm working with.  Any suggestions?

I can include voltage readings on the IC as well.

On pins 3 and 5 i'm getting 6.8 volts
Pin 8 I'm getting 9.46 volts
Pin 4 is 0
On the output pins and pins 2 and 6 I have 6.8 volts as well.



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Cool. Very good info.  Any idea why they don't use the standard voltage level for the Vbias on the non inverting inputs of the opamp?

Thanks for the reply Brian.  I guess my next question would be, why does using the inverting input make a difference?  I was under the impression that this just changed the phase of the signal? I just wondered if I could switch around the inputs, add the filter back in, and maybe make the cap switchable to change the cutoff frequency from the normal 720 hz to something that let a little more bass frequency pass though.


And one last question, what's with the weird biasing voltage used on the non inverting inputs of the op amp?  It's not the normal half of the supply voltage level i'm used to seeing.

Just wondering, why is the typical TS mid hump filter connected to Vr left out of the Xotic pedals clipping section?  Is it because of the active tone controls after the clipping section of the circuit? And if you were to put this back into the clipping section, would it make any difference?