Circuit explinations

[BJF]

Hi,

Here's a little circuit explination:

Well as you can see in the circuit it has a voltage controlled input, by means of the resistor in series with the input. As this is varied it aslo affects the base response as it works as a filter as well and the 1M resistor works as a resistans multiplier actually just a part of damping at minimum fuzz so the pot appears to be twice as big.
This makes also minimum noise at minimum fuzz- this is explanied in the original article
..
This circuit does not run on maximum gain but has a a couple of feedback systems that makes the circuit stable using many different types of transistors and also feedback system to control excess noise.

To get more gain out of the circuit the input resistor as noted 47K Ohms in the FF2,8% can be 2K0 Ohms.
This gives more gain at the maximum setting of Fuzzcontrol.

For those familiar with OP-Amps. This two stage amplifier works similar to an inverting configuration allthough the gain equation is different and also the open loop gain is very low compared to an OP amp, but I mention this to give a view of what the Fuzzcontrol does as if you'd view changing the input resistor.

The circuit is a basic application of a two stage transistor amplifier to get higher gain and higher input impedance than a single transistor.



As you can see in the original articles when using bipolar transistors the base to emitter doide is used since that junction is made to be progressive in tenths of the total forward voltage.

Of course you can use J-fets or Mos fets connected as diodes as well with slightly different results.

I have built very few but some of these using the transistor of the day in the true spirit of the Folk Fuzz- use what you can and what sounds good

Have fun
BJ

[mills]

Thanks!

One thing I was wondering about was the 100k resistor to ground that's connected to the base of Q1 and the 100k feedback resistor (I think... don't have the schematic here)? Does that just reduce the amount of signal that feeds back? I've seen it in a few other fuzz circuits, and it always seems to make things a little more gated-ish?

[BJF]

Hi
Ah, R3, that resistor is part of the bias system and it sets the amplifier DC working points. It does the contrary of making a gating effect. Let's say the circuit would work without this resitor but then for desired DC resistor R4 would need to be adjusted.
These two resistors carry mostly a DC function.

For a very rough explination:
What sets open loop gain is the product of the Collector loads divided by the Emitter loads, simply put and so as a rough measure of gain would be 10/0,09x10/0,099=111x101=11211 times
which gives roughly 80dB of open loop gain, but the actual AC gain through the circuit is defined mostly by the input divider formed by the fuzzcontrol and R2 and R3 and the dynamic inputimpedance of T1, T1iZ. R3 and R4 appear in parallell with the dynamic inputimpedance of T1, the latter that depends on device used and its hie and hfe. Let's say that T1iZ would be in the order of 15K and that parallelled with 50K (of R3 and R4 in parallell) which gives about 11K. So therefore the influence of R3 on final gain through circuit is minimal.
Ah yes I realize that I should not have mentioned 'loop' because it could give false ideas, mea culpa!

Now the circuit works like this that first signal enters through a divider network and then it is amplified by the transistors.

The gain through the circuit as seen from the base of T1 to the collector of T2 is in the circuit set so that if hfe of both transistors is higher than about 100 any excess won't be used for AC amplification but will be used for DC stability,which means that as long as the hfe of either transistor is at least 100 or higher as in perhaps hfe=400 maximum gain will be defined by the internal feedback systems to about the same, while if hfe is lower than 100, let's say you will be at the mercy of the transistors, while the circuit in terms of DC will accept hfe's from about 30 to 800, which makes it possible to use a rather large number of transistors whithout the circuit havocing.
This type of circuit is many times more stable than say the type used in fuzz faces,which is a circuit, that totally relies on the transistors ........ and the source impedance.....

Now the actual gain through the circuit as seen from the input to the collector of T2 cannot be calculated without knowing the source impedance- such is also the case for a fuzz face but this circuit will stay a whole lot more within reason and can be driven by a low impedance......
A rough measure would be that as the source impedance enters the divider and affects the division, and if a median value of guitar pick up's impedances the gain would be about 46dB or about 200 times using R1=47K. if R1=2K then gain might be raised 10dB to 56dB

Interesting,isn't it?

The reason I mentioned inverting OP amps is that varying the input resistor gives the same effect.

FF for bass I am thinking possibly a capacitor could be put across R4 to dampen treble a bit..
If R2 =2K then definitely increase C1 to 1uF

I've copied this post from another thread that is fitting
Hi,

This is the Folk Fuzz 3,5%. To get higher gain and lower noise I use T1=BC550C and R2=2K0. I'd use a 2N1306 for T2 but for T3 and T4 I've used either complementary PNP/NPN or an N- or P-FET connected as diode( hook the drain and source together and you'll get a diode). Various variants of connecting CMOS transistors also works and if you'd like the unit to double as a booster connect a switch for the clipping section as described in the instructions for Folk Fuzz 2,8%.
The capacitor of 150pF is the main rolloff: for use with guitar choose a value between 47pF to 180pF. I'd use a very low noise silicon transistor in position one to keep the circuit stable and also to give the highest gain aswell as giving the highest signal to noise ratio. For position 2 I'd prefer a germanium as this is the 'colouring' transistor put very simplified.
The 2N1306 is one of the last generation of germaniums and just as germaniums finally got rid of plague of popcorn noise and poor gain and high leakage they also became too expensive as compared with the silicon alternatives. There are few numbers of these last generation germaniums. If needed I can post a list of numbers.
There are a couple of million transistor types while they all belong in families. Many of these were originally made for a product most often forgotten these days and so Phillips had their own partnumbers for instance. In view of this there are about 30 types that are high quality germanium NPN transistors.
I have choosen carbon resistors for such positions that are noncritical in terms of noise and just as sidenote carbonfilm resistors burn when overloaded to create an open circuit while metalfilm resistors create a short when burned.This is maybe a subconcious thing guiding this as there would be no risk of overload in the circuit

Gentlemen have great fun
BJ


Again I did fail at posting the schematic and if someone more skillful at such things would please post that to this thread?
Gentlemen thanks

[mills]

Interesting stuff. Thanks for the explanation!

[BJF]

Hi

At your service

Now if somebody would be so kind as to post a schematic to this thread I'd be happy to go through effects of various modifications.

Have fun and thanks
BJ

[mills]

Hi Bjorn,

I missed your last post, but if you can find the time I'd love to read your explanation of some modifications. I've picked up a really basic textbook to do some learning about transistors, and circuit design... but your explanations are always interesting and easier to read.

Thanks for the guidance and suggestions so far!

[BJF]

Hi Mills,

Hm let's see:

The first step I'd take would be to listen and then decide what I'd like to remove or reduce or increase removal of-removing is usually more powerful than adding as any add on's will make more noise and introduce more problems and when stacking many filters there can be side effects, while sometimes adding is the best choice.

The hard part for me is that I don't know what you'd like to do.Also I have not played the Folk Fuzz on bass, but will as soon as I get a speaker cabinett to handle an Ampeg SVT that I have access to.

All parts designations are from the above schematic that is of the Folk Fuzz 2,8 %.

I think there is on line a schematic of Folk Fuzz 3,5% at http://www.fuzz.se under articles and Fix Ljud.

Let's see for bass perhaps try lowering R3 to 2K0 and increasing capacitor C1 to 470nF-this will give more fuzz at extreme end of FUZZ control and try getting a 1M C ( reverse log) for that. This modification will also give more low end.

Try excluding T3 and T4 for less fuzz effect

Try increasing the value of the Tonecontrol cap to say 68nF for a deeper range of the tonecontrol.



Try also moving the bases of T3 and T4 to junction R11 and terminal 3 Volume pot and the tone control cap which will shift what gets most distorted.

Try connecting a capacitor 4n7 across terminals 3 and 1 of the Volumecontrol for a fixed treblecut and increase value if turnover frequency is not low enough.

If you try any of this please let me know what you think and any further observations you make which will help me to come up with maybe something close to what you'd like from this basic circuit

Have fun
BJ

[mills]

Hi Bjorn,

Thanks for taking the time to reply. I haven't really been looking for anything more out of the circuit... it sounds great, and is about the fuzz range I expected. Not too crazy, but not too mild. I mostly thought I'd post the circuit to see what thoughts you had to share, and incase anyone else was interested in asking about modifications. I'm just always interested in trying to figure out a little more about the workings of these circuits... so thanks!

I do have a bit of a question though, you've suggested a few places where treble can be cut. Do you mostly tune by ear for that sort of thing, or does the circuit and design goal really determine which method you're going to use to cut a frequency? I can usually see the difference of cutting frequencies out before or after the distorting stages, but in the folk fuzz you've suggested a cap across R4, and I think that a cap across the collector and base should cut some treble too... I still get a little confused with changing frequencies in feedback paths and am not sure what the benefit of cutting treble here would be instead of cutting it later.

I guess in the end, I'm just trying to figure out if its possible to get clipping or fuzz without feeling like the bass response is gone because of the incresed harmonic content... not specifically the folk fuzz, but it seems like a simple circuit to start learning on. It always seems to me that a simple treble cut makes things sound too muffled, but a blend or active bass boost is more complicated than it needs to be. I think that if you want clipping then there will have to be at least a little bass lost, but I've played pedals (mostly yours) that don't sound muffled, and keep most of the bass there. So, I really appreciate the comments about improving bass response without just adding a bigger lowpass filter somewhere!

I like the suggestion to move T3 and T4 to after the tone control, but its such a simple thing I feel a little rediculous about not noticing that. Its little things like that that once I've been shown, something clicks into place and inspires new ways of looking at circuits I've seen before. Otherwise, I think I'm going to play with R3 and the Fuzz pot and see what that does. So far I have the tone pot controlling the input cap, and just put a fixed resistor for the post gain treble cut. The circuit actually lets a lot of the low end through with the bigger input cap and I'm really enjoying it.

[BJF]

Hi Mills,

I tune by ear. I listen for what I think is a useable range on all controls and play a while and hear how notes and chords ring a cling together and decay aswell as their attack and the balance of treble.
When tuning for bassguitar I have had test bassists that have benevolently lent me both their ears and playing skills- I watch listen and learn.

At your service
BJ