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Brady Ridgway's Fuzz_Face (guitar "fuzz" circuit) simulations

 
Edited

Brady Ridgway uploaded some files to the Temp folder, which are now inside "Fuzz_Face_+G.zip".
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But Brady forgot to send a message here.? Brady, please READ the group's guidelines on its main webpage.? After uploading something, it is crucial that you compose and send an actual message here to this group, telling us what you did.? You forgot to do that.
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Everyone else, here is the file Description that Brady used with his uploaded files:
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I am a beginner. I have uploaded two circuits, both of the classic Fuzz Face, which differ mainly in the power supply. Apart from the LT1054 and its components, the circuits are, I believe, identical. Graphing the voltage in most of the circuit produces very similar results, with the losses in the LT1054 being the cause. However, the current through the final capacitor C1/C3 (unfortunately I haven't indexed the circuits the same way) is completely different, as is the voltage at 'Vout'. Would someone please explain what I am missing?
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Some of us here will remember the Fuzz Face.? It is a guitar "fuzz" circuit.? If I remember correctly, it simulates poorly in LTspice, suggesting that the circuit works differently than SPICE simulations suggest.
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Andy
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Brady wrote, "However, the current through the final capacitor C1/C3 (unfortunately I haven't indexed the circuits the same way) is completely different, as is the voltage at 'Vout'. Would someone please explain what I am missing?"
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By observation:
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What you are missing is a load on Vout.? Without any resistor from there to ground, the DC voltage at that node is indeterminate (unknown).
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Also, there would be zero current through that capacitor.
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I haven't run your simulation yet.? It is a really bad idea to modify your "standard.bjt" file by adding new models to it.? In this case, the only transistor is the AC128, and it would have been far better to just include the .MODEL statement for that transistor, either on the schematic itself, or in a separate file.
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Your "standard.bjt" file has two AC128 models in it.? That is yet another problem.
? ? .MODEL AC128 PNP(IS=20.66u BF=229.6 BR=14.66 NF=1.133 NR=1.140 VT=25.5m VAF=19.68?
? ? + ? VAR=88.28 IKF=463.0m IKR=241.5m ISE=2.190u ISC=7.546u NE=1.796 NC=1.364 RB=1.885?
? ? + ? RE=306.4m RC=1.727u CCB=100p)
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.MODEL AC128 PNP(IS=5u ISC=1u ISE=200n IKF=3 ITF=1
+ ? NC=2 NE=1.5 BF=90 BR=5 RB=7 RC=0.2 RE=0.1 vaf=40 var=40 CJC=250p CJE=80p TR=5u TF=1u
+ ? FC=0.5 eg=0.72 VJC=0.4 VJE=0.4 VTF=4 MJC=0.333 MJE=0.333 XTB=1.5 XTF=6 XTI=3 Vceo=16
+ ? Icrating=1 MFG=GERMANIUM-TYPE)
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Which model did you want your simulation to use?? It can't use both.? Choose one and delete the other.
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Andy
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I can't find the standard.bjt upload.

On 2025-03-11 17:41, Andy I via groups.io wrote:
Brady? Ridgway uploaded some files to the Temp folder, which are now inside "Fuzz_Face_+G.zip".
?
But Brady forgot to send a message here.? Brady, please READ the group's guidelines on its main webpage.? After uploading something, it is crucial that you compose and send an actual message here to this group, telling us what you did.? You forgot to do that.
?
Everyone else, here is the file Description that Brady used with his uploaded files:
?
I am a beginner. I have uploaded two circuits, both of the classic Fuzz Face, which differ mainly in the power supply. Apart from the LT1054 and its components, the circuits are, I believe, identical. Graphing the voltage in most of the circuit produces very similar results, with the losses in the LT1054 being the cause. However, the current through the final capacitor C1/C3 (unfortunately I haven't indexed the circuits the same way) is completely different, as is the voltage at 'Vout'. Would someone please explain what I am missing?
?
Some of us here will remember the Fuzz Face.? It is a guitar "fuzz" circuit.? If I remember correctly, it simulates poorly in LTspice, suggesting that the circuit works differently than SPICE simulations suggest.
?
Andy
?
--
OOO - Own Opinions only If something is true: * as far as we know - it's science *for certain - it's mathematics *unquestionably - it's religion

Virus-free.
 

On Tue, Mar 11, 2025 at 01:56 PM, John Woodgate wrote:

I can't find the standard.bjt upload.

It's inside the .ZIP file.
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Anyway, you don't need it.? Just copy-and-paste one of the two AC128 .MODEL statements in my previous message.
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Brady had uploaded two schematics and his standard.bjt as three separate files.? I moved all three into one .ZIP file.? He should have done that, but I took care of it for him.? I did not think it was a good idea to leave the file "standard.bjt" out there in the open, so it is in the .ZIP file now.
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Note to everyone:? DO NOT move Brady's standard.bjt file to LTspice's component library folder, which would replace LTspice's own standard.bjt.? That would mess up your LTspice installation.
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Andy
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Brady,
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Here's a better explanation for the difference you saw.
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Plot the voltage at the top of R1, which is the supply voltage for the fuzz circuit.
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In the "original" circuit, it stays steady at -9.000 V.? It was at -9 V already at the very start of the simulation, because V1 is a pure DC source.
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In the "+G" circuit, the same voltage point starts at 0 V, and then ramps towards -8.5 V over the first 7 ms or so.? This has a profound effect on the voltage on the right of R2, which connects to the output coupling capacitor.
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In the original circuit, the voltage V(N001) starts at -8.51 and pulses to -9.0 V occasionally.
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In the modified circuit, the same voltage (now V(N002)) starts at 0 and sweeps towards -8 V as the regulator powers up.? That ramp couples through the capacitor to Vout.? That is the reason for the difference you saw.
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If you run the simulation using ".tran 0 50m 10m", the displayed difference appears to be much smaller because the ramping portion in the first 10 ms is ignored.? However, a large DC offset remains.? That's because of the lack of any load connected to Vout.
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Andy
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One more thing to mention here:
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Because LTspice finds the lack of a load (DC path) connected to node Vout, it "corrects" the omission by adding a small conductance (large resistance) there.? It has to do that because it can't solve for the circuit's voltages without it.? Every node must have a DC path to ground.
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With GMIN connected there, there is a little current through the output coupling capacitor, rather than zero as it would be in theory.
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Andy
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Apologies for the mis-steps. Thank you very much for taking the time to explain everything so clearly. I will restore the standard.bjt file and follow your suggestions with regard to the circuit and simulation.?

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