Small Stone LFO amplitude?

[gez]

Does anyone happen to know the amplitude of the Small Stone’s LFO waveform? (peak-to-peak)

Alternatively, does anyone fancy scoping it and letting me know?  I’d do it myself if it weren’t for all my breadboards being full.

Thanks

[puretube]

free information block:

[gez]

Now that's what I call service!!!  

Thanks a million PT, just what I need to know.

[puretube]

free information block:

[gez]

you`re aware of the hyperbolic character of the waveform

To tell you the truth, I'm having difficulty understanding how this particular LFO works.  At first sight it looks like a simple relaxation oscillator, but I can't see any mechanism to flip between thresholds.

I'll have to redraw it, perhaps then it'll make more sense.

If those measurements you gave are taken from the emitter of the Darlington buffer, how come the OTA's used for the phase stages aren't fried?  With only a 100R resistor, surely the max. Iabc for each device is exceeded?  I'm obviously missing something here...

Puzzled  :?

[puretube]

free information block:

[gez]

anyway: use those voltages, and be sure to stay well under 2mA for 3080 or 13700...

I'm using 13700s in a slight variation of the stock OTA phase stage, but with a non OTA LFO.  It works, but sounds quite different to the Small Stone (though an accidental blunder resulted in something that made me a very happy bunny, so I'm not complaining!).  

Although I like what I've got, I'd like to tweak the thing to see if I can get it to sound more conventional too, but need to do some number crunching so that I can see what the differences are (not too sure if it's my modified phase stage that makes it different, or the chip)...that damn LFO has me stumped though!  Anyone want to scope it for me?

[R.G.]

Guys, that's a current output LFO, not a voltage output.

[puretube]

right - that`s why the mentioned series-resistors are in there...

[gez]

Guys, that's a current output LFO, not a voltage output.

I was starting to come round to this way of thinking (I'm slow), but still don't understand the finer points of the set-up.  

What I want to know is does the transconductance of each OTA stage, when the current provided by the LFO's output is at its lowest, drop to a level such that gain in each stage is less than unity? (or would be if you ignored/pulled the parallel cap)

Presumably the current source provides greater scope for change in Iabc than a voltage source could deliver? (headroom limits 'depth' available)

[gez]

you`re aware of the hyperbolic character of the waveform)

The LFO of the SS schematic I have shows the single amp version, but is this the double one you mentioned?

http://home-wrecker.com/ross_phaser_black.png

Managed to clear a board and scope this.  I think what I saw was 'hyperbolic' (my memory of geometry lessons at school is a little sketchy!) - ramp up, ramp down, but with concave sides? (round troughs, pointy peaks)  Clever circuit!

I'm now starting to understand why I had 'problems'...pity all my problems aren't as good!

[puretube]

free information block:

[gez]

ps: waveform should look like handwritten " w "-s  ......

Yup!  

Thanks for the link to that thread, I don't think we were on line then so I missed it (we'd just bought a computer that month!).

Interesting circuit, output of amp 2 provides its own bias current, so transconductance varies during course of the ramp up/down - compressed at bottom (round), stretched at top (pointy).

Presumably, amplitude can be changed by varying the 270k to first amp's bias input.  I'll have to mess about with this to see how it affects the waveform.