buffer/transformer question for low impedance inputs circuits

[Ucho]

Say you've got a low impedance input circuit (like a fuzzface).
Then you have a buffered signal going into that circuit.
As you may know this won't sound so good togheter, not as good as the straight (non buffered) guitar signal directly in the circuit.

Besides moving that circuit before the buffer, what solution is possibile to make that circuit see an higher impedance (like a straight guitar signal would do)?

A transformer at its input, as in Bazz Fuss Deluxe and/or AMZ guitar pickup simulation?
An "anti-buffer" transforming the low impedance from the previous buffer in an higher impedace feeding the circuit? Is there any buffer with an high output impedance (vs low as in most buffers)?
Both?

What else?

[GibsonGM]

The transformer idea would do something, a few fuzzes incorporate that into their design. Might be the best way to go about this.  I've never tried it, maybe it would sound ok?  One thing about a fuzz face, though, is that this low input impedance is really part of the design and character of the thing - by changing that, you no longer really have a fuzz face!

You can find transistor configurations offering high output impedance....whether they would constitute a buffer is questionable (they would then have low input impedance). 

[darron]

maybe see how running the signal through a large resistor at the input of the fuzz face sounds?

[Ucho]

The transformer idea would do something, a few fuzzes incorporate that into their design. Might be the best way to go about this.  I've never tried it, maybe it would sound ok? 

I've read many suggestions about the transformer idea, but actually I hadn't found anyone saying "I've tried it and it works" 

One thing about a fuzz face, though, is that this low input impedance is really part of the design and character of the thing - by changing that, you no longer really have a fuzz face!

What i'd like to accomplish is to mantain the circuit imput impedance but change the impedance of the signal going in it (I guess that 'technically' the words i've used aren't 100% correct, but you get the idea). So what i want is only to 'unbuffer' the buffered signal, so it has a similar impedance it had before the buffer (mantaining the low input impedance of the circuit).

maybe see how running the signal through a large resistor at the input of the fuzz face sounds?

I could try something similar to the bias control in some fuzzes. I wonder if that large resistor (what value anyway?) would change something about volume or tone.


Thanks for the replies.

[Ucho]

I've made a QUICK test with a 42TM018 transformer.

First I've connected lug 3 to jack input (bypass switch actually) and lug 1 to circuit board input.
I've made a quick test but i didn't noticed much difference than before the transformer was added.

Then I swapped the transformer lugs (so lug 1 to jack and lug 3 to circuit). This way it SEEMED to improve things a little. The difference between straight guitar signal into fx input vs buffered signal into fx SEEMED less noticeable (maybe, if this really works (see paragraph below) I could add some component to shape the frequency response as in AMZ Pickup Simulation article).

I underline that this is what it SEEMED to me, since i fear that some of what i think to have noticed may have been influenced by a psychological factor...
For example, is it normal the difference i thought to heard inverting the lugs of the transformer (I always used primary winding, I just inverted the outside lugs)?

I also noticed that now the wah (with added output buffer) - positioned before the fx - is less effective (again... psycho ?!?)

[Gus]

I believe it is better to think of the FF type circuit as summing junction input.

  If it was perfect it would be 0 ohms

read the grintbox thread and the simple opamp thread  http://www.diystompboxes.com/smfforum/index.php?topic=59426.0

look for the wha then FF threads "fixes"

Sometime the guitar or bass is part of the circuit.

[John Lyons]

Doug Mentioned using a large resistor after his wah signal into the Hwy 89 or FF.
I guess this would be similar to using a large input resistor in the Hwy 89 (if you are always going to use the buffer before it.)
Sure would be simple if this did the trick. Try a 1M pot and experiment.

John

[Ucho]

Concerning the wah problem I mentioned, I should point that some time ago i added an output buffer to the wah, and this way its sound was very noticeable even with dist after it.
But when today I made the test with the transformer the wah lost a lot of his effectiveness.
Maybe the transformer was "counterbalancig" (does that word even exists ) the effect of the wah output buffer.

I think I'll try the input pot (like FullClone  69 Bias control) and see if it acts better than the transformer.

Any idea about the transformer lugs connection thing i mentined?

First I've connected lug 3 to jack input (bypass switch actually) and lug 1 to circuit board input.
I've made a quick test but i didn't noticed much difference than before the transformer was added.

Then I swapped the transformer lugs (so lug 1 to jack and lug 3 to circuit). This way it SEEMED to improve things a little.

Should it make a difference or not?



Thank you guys.

[brett]

This topic comes up many times, and Gus or RG or I or any one of many others have answered it again and again.
I think that Gus is saying something so simple that it isn't being believed or maybe the importance of the statement isn't obvious when he says

Sometimes the guitar or bass is part of the circuit.

(Please note that I'm not trying to be rude or obnoxious here, I'm just trying to convey the importance of the statement. Maybe we could call it "Gus' law" or something.).

If we think about how easy it might be to emulate the electronic characteristics of a pickup further down the chain (with inductors (ie coils and transformers), resistors and capacitors), we find that it is not easy (because of the electronic complexity of the pickup).  That's not to say that some good tones can't be achieved with these other circuits, but it is unreasonable that simple ones can emulate the originals (such as pickup -> fuzzface).

Furthermore, as best as I understand them, the input stage of effect pedals are usually simple in electronic terms (usually dominated by a fairly constant resistance, whith maybe a little capacitance).  Therefore, they are easier to emulate than the pickup.  For example, a useful approximation of the first stage of the fuzzface is a 22k resistor.  So a buffer with 22k of input impedance will give some (but not all) of the tonal changes seen at the input to a typical germanium fuzzface.

All comments and feedback are welcome.
cheers

[Ucho]

I understand the sometimes-the-guitar-is-part-of-the-circuit thing, and I'm not expecting to achieve the same tone/behaviour of direct guitar-fx with inductor-res-cap (or whatever else), but only a similar sound or however an improvement over the guitar-buffer-fx thing. I just want to reduce a litte the changement in tone caused by the low output impedance buffer before the circuit.

Anyhow, the issued circuit is not a fuzz face but the Doug Hammond's Highway89, but maybe the "Gus' law"  is still valid.
I mentioned the fuzz face only as a famous example of a low input impedance circuit.

Saying this I don't mean i don't appreciate your words, indeed I thank you for trying to help and pointing me to technical cues that will help improve my still limited knowing of these things.

Anyhow, with the use of the transformer it seems that i'm getting some improvement, now i'll try other solutions to se if things can even get better.

Sorry for asking again, about the transformer connections, is input-lug1-lug3-circuit different than input-lug3-lug1-circuit?

[Gus]

Jack and R.G. have posted about input R IIRC.  Jack had something in the past using a transformer as an inductor to do a better sim of a guitar IIRC

http://www.diystompboxes.com/pedals/3tran.JPG

The 10K between the buffer and fuzz section is a VERY CRUDE sim of the guitar just resistance to help get the gain of the first transistor of the fuzz section in a nice range.  It does not sound like a guitar to FF type circuit

A better way would be a humbucking inductor(mu metal case would be needed for non humbucking) of a measured pickup inductance value with maybe an added resistor.

FWIW I built an inductor for a friends guitar it was a copy of the Gibson L6 (BL) circuit.  I looked at a L6 an noted the inductor looked to be wound on a plain 1/4 20 Bolt!  I wound a humbucking two chamber inductor with a 1/4 20 a washer glued to the middle and a nut glued to the bolt at the end I used tape to wrap the threads.  I handwound a inductor of about 1.7H IIRC.  I will look for my notes.
I used my metal lathe set to slow and just filled the chambers.

One can wind simple inductors.

[Ucho]

Jack had something in the past using a transformer as an inductor to do a better sim of a guitar IIRC

If you're talking about Jack Orman and his Guitar Pickup Simulation article on AMZ, that was exactly where i took the idea from.
By now I've only used the transformer withouth the resistor and the capacitor, but maybe i will add them.

About the 10k input resistor, I think i'll try with a pot and see how it behaves compared to the transformer.

Thank you Gus 

[Gus]

 Thanks for the link to Jacks page

Has anyone measured the inductance of the 42tm019 at under a 1v (inductance changes with signal level)?  I need to look for my notes I measured some guitar pickups in the past I think they were over 1H.

I would think the transformer and a series resistor will sound better than just the resistor

For people that sim take the circuit from Jacks page use a voltage source the in and the out to the input of say a FF type circuit  sim it then change the inductance.  Single coil vs Humbucker, guitar vs bass.......