Cry Baby Original

[Goodrat]

I just saw. Check email. Tina is spice by Texas instruments. (I think).

[Gus]

http://www.diystompboxes.com/smfforum/index.php?board=41.0

[PRR]

> Tina is warning me most of my parts are not connected.

I don't know TINA.

In PSpice, a rash of no-connection often means there is no AGnd node (analog ground). While real circuits always can work un-grounded, SPICE needs ONE point to call "zero" to get started.

If you use a GUI layout tool (we used to type netlists on punchcards), sometimes stuff that looks connected isn't. PSpice Schematic puts up a "!" when you hover a line-end where it will make a connection. I have seen other tools make it very hard to get connection.

___________________________________________

> not sure what all goes into what we call Q

In this case, Q is basically Series Resistance. What you see on your ohm-meter.

It can be Core-Loss.

An ideal coil has zero series resistance and infinite parallel resistance.

If the whole system were perfect, the resonance would be infinitely high and infinitely narrow.

OTOH a low Q gives a small wide boost which does very little.

We don't want infinite boost (clip) and we don't really want infinitely narrow (the peak would go through a harmonic too fast to hear, or could not be set on a harmonic easily).

With modern varnish the parallel resistance will be infinite-enough for our uses.

Jiggling magnetism in iron causes a drag. This has an effect similar to a parallel resistance. The way the Wah circuits work, there's already considerable parallel resistance, so core-loss may be a minor detail.

We can't buy superconductors, so all coils have series resistance. The usual Wah's self-resistance is small, an emitter-follower. So coil series resistance may have large effect.

We can make series resistance as small as we want (Q as high as we want) simply by making the coil (and wire) larger. See Rick's monster stack. Of course that costs money. We usualy buy only as much Q as we need. Unfortunately the series resistance is often not specified in coils sold to the Wah market.

[Goodrat]

I got it. There was a rogue resistor at the top of my page. I've learned a few trick with it today and got a wah circuit working. Connections are good now too.
I am pretty sure this is the same as spice.
Very interesting. I can see the distortion just like I can in the unit and I'm finding ways to center it and maybe even with more gain.

http://www.ti.com/tool/tina-ti

[joegagan]

thanks paul. the inductor R is very important in the way the wah acts in spice. the  'bad' inductor that ken fischer was referring to was probably the 80s one that measures over 250 ohm, 5 or 6 times larger than the  ' good' range.

[PRR]

> larger than the  'good' range

Thanks. It would be nice to know what is the "good range". You are suggesting 40-50 Ohms, with 250 way-out (yet still marketable)?

Rick's doughnut-stack is probably much less than 40 ohms. It may not matter, since there's another ~~30 Ohms or more in the circuit. And a very high Q may still be useful. A too-high Q (low resistance) coil can always be broadened by adding a few dozen ohms of simple resistor. This means you "paid too much" for your too-good coil, but in DIY that's not a problem. (Make a million of them and you will be pinching every penny, less core, smaller wire, and no added resistor).

[joegagan]

correct.
the morley wah inductor measures 12 ohm, and their factory schematics actually spec 12 ohm.
some people like wahs that have inductors as low as 10 ohm, but the ' classic' inductors that a lot of people like fall into the 35 - 50 ohm range, boomerang EL Rad and the thomas stack of dimes for example.

i can make 12 ohm sound pretty good, but i have found it near impossible to make a wah sound good once it gets over 100 ohm. alternately, series R can be faked in as mentioned. the TDK 70s inductors in thomas wahs fall into two groups.: 14- 18 ohm, and 144 ohm.

[Goodrat]

This is where I am now. I don't need the output gain stage anymore.
No more distortion, the signal is more centered  and the gain is slightly higher than it came with.
http://www.rickviola.com/images/WahResult.jpg

[Goodrat]

Here is with original values.
http://www.rickviola.com/images/WahOrig.jpg

[joegagan]

very nice!

[Goodrat]

With the older values, it looks like the older values have more gain on the analyzer sweep, but looking at the scope, you see it is because it is distorted.
The new values have 0.8V more swing at top and bottom.
The frequency of the generator is slightly different to find the highest output of the pot at 50% with the component differences.
There is an odd distortion on the new when the pot is all the way to bass (not shown in these pics), but that end is not usually used.
But what's  cool is, I see the exact same results on the bench. That impressed me.
I'm glad I took the time to try the program.

[Goodrat]

One more tweak. Adding the 47K vocal mod and lowering the input resistor a little, boosts up the high end, but just enough so not to distort the mids.
I could play with this forever and never get it perfect. With no output gain stage, everything is too critical.
http://www.rickviola.com/images/WahResult2.jpg

[Goodrat]

I had some great changes today, but it wasn't matching what I got on the bench. I tried setting the Q1 collector to half the Vcc (lowering Rc) and I was able to get more gain with Re on the simulator. On the bench, I was over driving and the collector voltage was higher that expected. Maybe something is not right with the transistor specs. I'm just going in circles now.