Yet another Woody question

[alparent]

I was planning on building the Woody.
Searching the forum I came across Oliver Alex mods . (And Mark seams pleased with them.)

It's now working on a single 9v battery. So you get +4.5v and -4.5v

I also read there are some noise issus with the Woody? Did Oliver's mods fix that?

Would powering Oliver's version with a 9v+ and 9v- (using a max1044 to keep it a single battery unit) help with noise at all?

If so .................. how would I do that? Would using the max1044 to generate 18v and just feeding that to Oliver's layout work? (Would I need to change the value of the caps or resistor of Oliver's power section?)

Or is it better to use the 1044 to give me 9v+ and 9v- and use the power section on Mark's original Woody?

IF using 9v+ and 9v- actually give me any advantages 


Thanks.

[~arph]

Olivers version has more filtering so it is less noisy. On a side note, the fact that it now uses a single 9V supply means that it runs of 0-9V, not +4.5 and -4.5

The negative supply became 0V, the GND became +4.5V (usually referred to as Vref)  and the positive supply is +9V. That is how single supplies are done with opamps. And how most opamp circuits in pedals work.
I hope this makes sense as I'm not really good at explainging this.

One thing is sure, the power arrangement is not affecting the noise. So using -9V and +9V is not an advantage here.

[alparent]

Makes perfect sens Arnoud.

But you are stile only getting 4.5v of headroom on each side of the Vref? Right?

If that's good enough for our effects (is it? What if a have line level input?) why are some using bi polar then? Is it just to get more headroom?

I think I'm missing something 

[~arph]

Yes it is about the headroom. Single supply gives you 4.5V pp. (less of course, opamps are not ideal)
Since guitar input levels are so low (100mV), this is more then enough.. Guitar amps don't like signals 4.5V pp. very much either.

Line level is higher indeed, but not 4.5V pp either I believe. This pedal is intended for guitar, the split supply would be better for line level applications.

Note that the Woody  is now also commercially available for about $35. Biyang electronics are selling it. I believe it's called the AC8 "Woody". I have one. They are good quality.

[alparent]

OK so if I'm building something that calls for +9v and -9v (projects from Anderton books) Would I be OK supplying them with only +4.5v and -4.5v ?  As long as it's only for low level input.

What happens if I run out of headroom?    Distortion?

Is a signal coming out of a preamp considered line level?

[~arph]

1) Well, it depends if the components used have enough voltage with +-4.5, but in theory: Yes.
2) If you run out of headroom you will get distortion.
3) I don't know honestly. I'd say, yes.

[Mark Hammer]

There is not much gain applied to the part of the signal that has the greatest amplitude (the bass).  Much more gain is applied to the treble, which normally has a fairly small amplitude on its own, when it isn't riding on top iof the bass.  If lots of gain was being applied to the whole signal, one would be correct in being concerned about whether 9V gives as much headroom as +/-9v.  Since the biggest chunk of the overall signal is not being "slammed" against the upper and lower bounds of where the chips can swing, and since the objective of the pedal IS to generate clipping in the treble portion, using a single 9v battery does not really get in the way of the overall objectives of the circuit.  So, if you have a layout for a +/-9v version and don't mind the "inconvenience" of a bipolar supply, build that.  And if you have a layout for the 9v version, build that.  What's probably more important is using sockets for the op-amps and aiming for the chips that provide lowest noise in that context.

Oliver's mods were specifically to improve noise and bandwidth, so if the Biyang pedal follows his modifications, then it ought to be a decent-sounding pedal.    As an aside, I've been pondering a simple wayto insert some partial gating into the design so that quiet passages do not result in audible background hiss.

Although Guitar Fetish's new line of inexpensive pedals are effectively repainted Biyang pedals (with a few mods in several instances), in discussion with GFS president Jay Abend, he indicated that he would not carry the "Woody", out of consideration for me (he's gotten steamrolled by larger companies himself, so he feels my pain).  So, any commercial purchase will have to be from Biyang themselves.

In theory, dynamic headroom is increased by use of a) chips that have wider voltage swing, and b) larger supply voltage.  The basic idea is that if you take an average and maximum AC signal of voltage X, and apply Y gain to it, the result should remain below the maximum voltage swing permitted by the chip and supply.  Depending on pickups, number of strings plucked, guitar volume setting, and playing style, a pedal might receive a signal ranging anywhere from 20mv to as much as a volt.  If the audio portion of the circuit is one applying a gain of 2-3, then a 9v battery feeding an op-amp that can swing to within 1.5V of the rails (in this case, it can go from 1.5v to 7.5v, or +/-3v) still provides relative safety, with respect to clipping.  If the gain is 10x, then high output pickups and powerchords will likely result in clipping if using a humble 9v battery.  If the intent of the circuit IS to generate clipping, then that becomes less of a problem.  Indeed, the venerable MXR Distortion+ generates significant clipping even without any diodes!  As near as we can tell, that within-the-chip clipping, which is then clipped again by the diodes, is part of the character of the pedal.  generally, op-amp datasheets will state the maximum voltage swing.  For example, the datasheet for the Fairchild NE5532 states that, with a +/-15v supply, the typical voltage swing is +/-13v.  So that's 2v from each extreme of the supply voltage, meaning that we can ony expect a clean output signal (or at least one that isn't dirtied by the chip itself) of +/-2.5VAC from the chip (9v, minus 2v from each side = 5v = +/-2.5v).

[~arph]

Thank you for the right technical explanation Mark.

As a matter of fact I just recalled that the Biyang woody is not the Oliver Alex version, but rather Marks version converted to a single supply. So it's a bit in between. The extra filtering is definately not in there.

Nice of Jay Abend to not put out the Woody, but I have mixed feelings about the steamrolling, since he is now doing others what was done to him. There is a nice dutch saying for this, which I am sure has it's english counterpart. It goes:
"Wat u niet wilt dat u geschied, doe dat ook een ander niet." 
Basically: What you don't want to happen to yourself, don't do that to someone else either.

[alparent]

I know the Woody story    sad!

So if I take the TL074.  the specs say +/- 12v pp at +/- 15v supply.......so -3 pp

So if I use a single 9v battery(4.5v above Vref and 4.5v below) .......... I get 3v pp right?

How much V can a active pickup or a preamp give out?

I'm trying to get this right 'cause I want to build some effects in Anderton's book. I got a bunch of MAX1044 (Did I buy thew mfor nothing?  ) but if a certain effect doesn't need it I wont use it. But if it does......

And I don't want to have to ask each time..........I want to learn  

On a side note .............. what happens to all the effects we are building with single 9v if it's used with a guitar with active pickups? Will you get distortion? So you have to turn your guitar volume down?

[Mark Hammer]

Don't worry too much about levels and headroom limitations in the pedal itself, because whatever clean headroom is lost when you hit a pedal with active pickups is also likely to be severely lost when your signal hits the front end of the amp!

Actually, arph, jay has been really nice about it.  I have to commend him.

[alparent]

So I can build all of Anderton's effects with just a 9v batt by giving it +4.5 and -4.5v?

So I bought all those 1044 for nothing then?

[Mark Hammer]

No, they are still useful. One of the things one has to do when using a single-ended supply and Vref is you have to bias each stage appropriately.  Use of a true bipolar supply permits you to totally ignore all that biasing stuff.

Is it a "simpler" circuit when using +/-9V?  Not necessarily, but then not necessarily more complicated either.  If you have a viable PCB layout, then it pays to consider the overall nuisance factor, of which finding or making a +9v layout is certainly a part.