Bazz Fuss impedance and inductor questions

[Voltzy]

Hello all!

I have just started my DIY pedal journey and been playing around with some different Bazz Fuss type circuits. I have access to a lot of old electronics at my work and have build this pedal out of completely recycled components (except the vero and case), I ended up settled on a nice sound using two BC337 transistors in a darlington configuration.

A friend suggested I design it so the effect has a wet/dry blend with the clean guitar signal so I preceded the Bazz Fuss circuit with a Split 'n' Blend found here:https://tagboardeffects.blogspot.com.au/2012/02/split-n-blend.html it mentions there that it will not work properly with inverted signals so I added another recycled transistor (2n4400) in order to un-invert the signal at the end of the Bazz Fuss circuit which worked great.
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My only issue now is that it sounds like I have lost some of the balls of the original Fuzz, I don't believe it is the 2n4400 as I used an audio probe and it sounds the same before and after it. From my research the Bazz Fuss likes to have a high impedance input and the original home-wrecker page suggests using one side of a small audio transformer on the Bazz Fuss input. One side of the 42TM018 transformer has an impedance of 10k and according to here http://www.freestompboxes.org/viewtopic.php?p=148640#p148640 the primary winding of the 42TM019 (also 10k) has an inductance of above 2H.

I have access to lots of small (680mH) inductors that I can recycle, my question is could I achieve the same effect of the audio transformer by having fourh of these smaller inductors in series on the input?

[thermionix]

A transformer doesn't really have an impedance per se, but rather a turns ratio.  The impedance ratio is the square of the turns ratio.  But that's using both the primary and secondary.



If you use only the primary as above, it's only an inductor, not a transformer.

[Voltzy]

A transformer doesn't really have an impedance per se, but rather a turns ratio.  The impedance ratio is the square of the turns ratio.  But that's using both the primary and secondary.



If you use only the primary as above, it's only an inductor, not a transformer.

OK thank you, if I were to use that transfomer and only use the primary winding as show in the schematic, will that create a higher impedance input for the bazz fuss? I am unsure why else it would be included in the schematic.

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[thermionix]

Yes.  I'm sorry I should have quoted "One side of the 42TM018 transformer has an impedance of 10k" as I was only replying to that particular phrase.  But yeah, the series inductor adds to the total impedance the circuit input "sees."  And yes, I think you can add the 680mH inductors in series to mimic that.  There's also DC resistance to factor in, but it quickly goes over my head at that point.

[Voltzy]

Yes.  I'm sorry I should have quoted "One side of the 42TM018 transformer has an impedance of 10k" as I was only replying to that particular phrase.  But yeah, the series inductor adds to the total input impedance the circuit "sees."  And yes, you can add the 680uH inductors in parallel to mimic that.  There's also DC resistance to factor in, but it quickly goes over my head at that point.

Awesome thank you! Yes I am aware of the small DC resistance that occurs in inductors.

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[thermionix]

You quoted my "parallel" before I was able to edit it to "series"...I meant series, I guess you knew that.

[Voltzy]

You quoted my "parallel" before I was able to edit it to "series"...I meant series, I guess you knew that.

Yes I did pick up on that haha, thanks for your help.

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[antonis]

In theory, 3 X 680mH in series result in 2H equivalent inductance..

But you need some amount of impedance rather than a "bare" inductance value..

A reactive element, like inductor, exibits frequency variable impedance X_L= 2*π*L*f, hence about 1k at 80Hz, 10k at 800Hz and so on..
At low to medium frequencies, 2H inductor adds practically nothing on 100k Thicknes pot at high pot value..

Instead of messing with 3 bulk/heavy/unpredictable transformers, place a phase inverter in your clean signal path..
(an amplifier with unity gain and input impedance similar to your own Bazz Fuss should do the job..)

[Voltzy]

In theory, 3 X 680mH in series result in 2H equivalent inductance..

Upon further inspection it looks like the inductors I planned to salvage are actually 680uH which is not going to cut it...

So are you saying that if I add another unity-gain transistor similar to the 2n4400 I added at the output of the bazz fuss, but on the clean input coming from the Split 'n' Blend, then it will provide the bazz fuss with a high impedance input signal?

If I am not mistaken this will also invert the input signal, which means the darlington pair bc377s will un-invert it, so I can just move the 2n4400 from the output to the input in order to not have phase cancellation with the clean signal blend.

[antonis]

 

No, I'm saying to delete the "phase correction" transistor from Buzz Fuss output and place it to clean signal path..

Buzz Fuss (as any single/one stage BJT/FET amp) inverts signal (180^o phase difference with income/clean signal..)

If you place such an inverter somewhere on clean signal path you'll result in same phase (0^o/360^o) singnals blending/mixing..

P.S.
If you place that inverter on Buzz Fuss input you maybe increase input impedance but you also add series frequency shift which may lead to oscillation problems..
If you want to raise input impedance, place a buffer in front of Buzz Fuss..

[amz-fx]

From my research the Bazz Fuss likes to have a high impedance input and the original home-wrecker page suggests using one side of a small audio transformer on the Bazz Fuss input. One side of the 42TM018 transformer has an impedance of 10k and according to here http://www.....org/viewtopic.php?p=148640#p148640 the primary winding of the 42TM019 (also 10k) has an inductance of above 2H.

I have access to lots of small (680mH) inductors that I can recycle, my question is could I achieve the same effect of the audio transformer by having fourh of these smaller inductors in series on the input?

Yes, the 680 microH that you have will be too low in value for proper operation. The inductance needs to be much higher. Most any small 10k:10k (or 10k:600) transformer should do the job, even if it is not the Mouser part.

The original article on the design that suggests using a small transformer is here: http://www.muzique.com/lab/pickups.htm

Best regards, Jack

[poiureza]

My understanding is that the transformer helps to mimic pickup behaviour in case there was a buffered pedal in between the guitar and the bazz fuss, thus basically shelving off the highs and recovering some emphasis on a resonant frequency.

If you're playing guitar straight into the bazz fuss circuit then the transformer coil won't do much.
At least that's what I experienced.

And to be honest, when I put the bazz fuss after a buffered pedal, the transformer coil doesn't do much besides shelving off the highs.  I don't really experience any balls recovering

[Voltzy]

when I put the bazz fuss after a buffered pedal, the transformer coil doesn't do much besides shelving off the highs.  I don't really experience any balls recovering

Oh right how interesting, it feels like before I had installed the buffer effect into the pedal the fuzz was huge and nasty where as now it sounds like the gain knob has been turned down half way (if I had a gain knob).

Here is a rough sketch of what I have built:



The 15k res and 50nF shunt cap on the fuzz input form a low pass filter of around 245Hz (I hope), so when you say shelving off the highs I assume you mean it cuts them somewhat, which I am already doing with the low pass filter so I don't know if it would actually help.

No, I'm saying to delete the "phase correction" transistor from Bazz Fuss output and place it to clean signal path..

OK now I understand what you are suggesting, I should move the 2n4400 and its two 10k resistors from the end of the fuzz to in between the split 'n' blend and leg 3 of the pot? Will this help?

I am beginning to suspect I am hearing the original fuzz tone through rose-tinted headphones, hopefully I will get a chance tonight to build the original Bazz Fuss again on my breadboard and I will compare the two.

[Voltzy]

I built another bazz fuss, without the extra phase inverting 2n4400 and the buffer/blend and compared the two and it does have a lot more fuzz and bite to it.

I thought that maybe I had not biased the phase inverting transistor properly, so I upped the collector resistor to 50k and left the emmiter resistor at 10k... And it did develop a more fuller sound but not the same crunch as the original circuit. I suspect it was boosting the signal a little. I was getting around 6.5V on the collector and 0.6V on the emmiter.

Could it be the 100K blend pot is actually letting through some small amount of clean signal, even when it is turned all the way to the fuzz side? Is 100Kohms enough to completely block the clean signal?

I will be picking up a small mouser audio transistor with a 10k winding tomorrow after work hopefully this fixes the problem.

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[antonis]

No, I'm saying to delete the "phase correction" transistor from Bazz Fuss output and place it to clean signal path..

OK now I understand what you are suggesting, I should move the 2n4400 and its two 10k resistors from the end of the fuzz to in between the split 'n' blend and leg 3 of the pot? Will this help?

I suggest something like this:
(more or less..)



Items marked with red asterisk may be omitted in case of 33k input impedance for phase shifter is acceptable..
Clean Volume Pot may be part of 100kA dual gang one, also used for Buzz Fuss output Volume..
In case of you want to also use the low-pass filter for clean signal, split signals after the filter..
(cut-off point should be calculated taking in mind further effects impedance..) 

Use of active FET splitter, like above posted, is left upon your taste..

edit: 50nF cap ground erased by mistake..

[fryingpan]

Frankly I'd rework the pedal to work well with whatever impedance at the input, equipment which is sensitive to impedance is a pain in the arse. I suspect that reworking the input filter may suffice, and anyway, instead of using just the primary of a small transformer, I'd rather actually use the transformer as such, it can be an interesting idea. Maybe at the output instead of the input too.

[antonis]

instead of using just the primary of a small transformer, I'd rather actually use the transformer as such

Have you asked your guitar coils..??

[fryingpan]

instead of using just the primary of a small transformer, I'd rather actually use the transformer as such

Have you asked your guitar coils..??

Well the sound will change due to both inductance and capacitance (and, depending on where it is placed, on possible core saturation). My Epiphone Jack Casady has a transformer wired after a low impedance pickup (it measures around 13 ohms, not kohms, I think), it drastically changes the sound and it's actually nice (makes the sound warmer and thicker). Trying a small transformer (with a low primary to secondary ratio, such as 1:3, or selectable ratios even) after an input buffer (= low output impedance) could have nice effects on the sound. At the output it's probably even more interesting.

[Voltzy]

Use of active FET splitter, like above posted, is left upon your taste..

Ah I see now, you were suggesting I remove the splitter all together, thank you.

If I had a non-inverting effect instead of the Bazz Fuss, then could I wire the effect output to leg 1 and the clean signal coming straight from the input jack to leg 3 with the output jack to leg 2, and it would work the same way? Why even have a FET splitter, what does it even do?

I am still going to pick up one of these transformers and I am thinking of recording some short clips to compare the different circuits.

[antonis]

If I had a non-inverting effect instead of the Bazz Fuss, then could I wire the effect output to leg 1 and the clean signal coming straight from the input jack to leg 3 with the output jack to leg 2, and it would work the same way?

As far as we only deal with signal(s) phase, yes..
(see below..)

Why even have a FET splitter, what does it even do?

It settles to "equilibrium" possible currents difference due to different paths impendance..
(it actually makes each path input(*) to be "seen"  from other path's output(*) as a high impedance one..)

(*) Splitted signals should be considered in pararell so any individual input "sees" it's own load in parallel with other individual inputs impedances - same also stands for outputs on blending point..)