Highway 89 input impedance

[Ucho]

Hi!

Some time ago i built Doug Hammond's Highway 89 (which sounds GREAT as some of you already know) that i love.

I noticed some "problems" when i use it after a buffer, similar to some fuzzes (when used after a buffer).
(i used quotes for "problems" because actually it works ok, it doesn't sound bad, it's just that it does suond different and not as good as when plugged directly to the guitar).

So the question: does the Highway89 (which has the Brian May Treble Booster as its first stage) has a low input impedance?

If so, would a transformer placed at the input (as in Bazz Fuss Deluxe,  AMZ Guitar Pickup Simulation article) be a solution?

[snoof]

I have a similar prob with my BSIAB, when I run my Boss BluesDriver in front of it...

[Ucho]

I have a similar prob with my BSIAB, when I run my Boss BluesDriver in front of it...

I also have a BSIABII, but it doesn't seem to have problems with buffers before it ....

[Ucho]

Sorry for bumping, but anybody can tell me if the input impedance is 1M (because of R1) or less?

What about the transformer on the input?

Here's the schematic

[John Lyons]

The impedance is low because the 22K is in parallel with the 1M. Calculate this and see what it is.
I'm not sure about the transformer thing before the 89...

The Hwy 89 is like a fuzz face in that the low impedance gives it it's sound.
Try to put the 89 first in the chain, it's designed to be fed from a guitar only.


John

[Ucho]

Thank you for answering again.

Actually, if we have to consider R1 and R4 in parallel for input impedance, then it will something very near to 22k (maybe a little lower if i did the math right) which seems very low (maybe i made a mistake?!)

I cannot use it as first in chain because i'm using Tillman's FET preamp cable as buffer (also sometimes i'd like to use a comp, a booster, or a wah, in front of HW89).

Reading the Guitar Pickup Simulation article on AMZ and the Deluxe Bazz Fuss one on HomeWrecker (and Tim Escobedo's page) I thought about the transformer (42TM018)

The transofrmer on the input helps preserve the unique tone of the circuit when preceded by a buffered effect

[...]

The most peculiar is the transformer winding on the input. I added it at the suggestion of Jack Orman , to counter the effects of using low output impedance devices in the signal chain before the fuzz, which had a tendency to kill the tone of the fuzz. I don't know why it works. It just does.

Now I only need someone to confirm me that "it works" (not actually on HW89, even on other fuzzes or low input impedance effects)

Maybe I can only change the input resistor (R3 = 1k) to a bigger value (10k or more)... will this affect also input volume?

Maybe I shold just stop bothering you and try it... 

Thank you again John, I really appreciate

[jakenold]

I've had this problem before, so I've been very interested in this thread.

If you'd want to make an universal solution, then how about adding a buffer to the circuit, in front of the input, with a transformer between the buffer and the circuit input? That way we have a known impedance that we can match with a single transformer, instead of having to worry if we're gonna use the effect alone one day.

Now to the thing I'm unsure about - the transformer we need, should it change the output of e.g. the FET-buffer from Jack Orman's site to something like 250K-500K. How do we make these calculations? Like the output impedance of such a buffer?

mfg Jake

[Ucho]

I really don'y know how to make those calculations.

About the buffer+transformer solution, is it to have a "constant effect" driving it with an already buffered (low impedance) signal vs straight guitar signal? Maybe just a buffer (without transformer) with an high putput impedance...

And, will the output impedance of a transformer be different if driven by a buffer vs straight guitar signal?

Anyeay, in the next days i'll try installing a 42TM018 and see what happens. Obviously I'll report. 

[John Lyons]

I'm not really sure what to do but in thinking out loud what we need to do is have a 1Mish impedance at the input, which gets knocked down to 250K-500K at the Hwy89s input, which is what most guitars are putting out.

The 89 was designed for passive pickups Doug says. It seems that the buffer and transformer would be the only way to do this.
As long as the Hwy 89 sees 250K-500K then it should sound as it does when being fed straight from a guitars pickup.

This is a little over my head, maybe we should post this as a buffer/transformer question for low impedance inputs circuits. it would get more attention..or at least would be more direct...

John

[brett]

but in thinking out loud what we need to do is have a 1Mish impedance at the input

Ahhh. This a perennial issue. This and other pedals (e.g. the fuzzface) get some of their cool tone from their low input impedance.  It you raise the input impedance, it will sound like it has a buffer in front of it all the time (i.e. thin and trebley).

Why not add a switch to the buffer so that you can lower its input impedance to 22k?

Although it is possible (in theory) to stick coils (transformers) and capacitors in front of the circuit to emulate a pickup, it's hardly worth it, as the alternative is so simple and effective. 

[Ucho]

Thank you guys, I really appreciate you're trying to help

It seems that the buffer and transformer would be the only way to do this.

So a "normal" buffer followed by a transofrmer, as jake said, both inside the HW89?

Why not add a switch to the buffer so that you can lower its input impedance to 22k?

Did you meant the output impedance of the buffer (going in the input of HW89)?
Is it possible to have just a buffer wich will raise impedance (vs lowering as in most buffers) at its output (feeding then the HW89 input)?

Although it is possible (in theory) to stick coils (transformers) and capacitors in front of the circuit to emulate a pickup, it's hardly worth it, as the alternative is so simple and effective. 

I'm also wandering if a transformer will change the 'tone'...
What is  the simple and effective alternative (sorry, i'm dumb  ) ?

This is a little over my head, maybe we should post this as a buffer/transformer question for low impedance inputs circuits. it would get more attention..or at least would be more direct...

Yeah, I think you're right. I'll make an other thread with a more general question (eg not specific to HW89) so maybe others can read and hopefully answer.




Thank you John, Jake, Brett