Penfold Autowah

[Kipper4]

http://hammer.ampage.org/?cmd=lt&xid=&fid=&ex=&pg=7
schematic in the above.

I havent reread all the article. I was wondering if a lm358 would make a suitable sub for the ca3130? Anyone

Also
If decoupled why couldn't we just use a Jfet buffer in the place of the 741 chip.

Thanks for any insight you may offer.
Rich

[duck_arse]

rich, what is it I allays says? no subs. the article says 'output to ground nearly and input mega high Z' due to the R values. so 'yes' on the 358 at the output, but 'no' at the bipolar 358 input. but don't quote me, try it and see.

probably a modern cmos rail-to-rail output oppy would sufice, LMC6482 (dual) like.

[StephenGiles]

This was one of Uncle Penfold's "simple" circuits, so simple in fact that I'd wager a Flanger Hoax schematic against all of the songs you can sing, that that your suggested opamp subs could duplicate the big ripple problems in this autowah with no problems at all!

[Kipper4]

Thanks guys maybe I'll let sleeping dogs lie and just use the suggested componants then.

You know me and ripple Stephen.....

[anotherjim]

Is it just me, or were all those UK magazine projects designed to use parts that Maplin just happened to stock? Back when Maplin actually stocked stuff that is.

I like TLC272 dual CMOS as its easy to get. A useful alternative to the 358 as well as a sub for early CMOS parts.

[Mark Hammer]

The 3130 has to be externally compensated.  I can't speak to how crucial to the performance of the circuit that is.

[Kipper4]

Externally compensated. How please?
Thanks guys.
My build is underway. I'll report back.
This has been put off for several years, with the chip just sitting there glaring at me.

[duck_arse]

the capacitor the you fit across pins 1 & 8, (offset null and strobe, the pins are dual function) the phase compensation pins, compensates the internals. I've never had an explanation of how to select the cap value to provide what compensation I could understand, but that's what it is.

the LM301 was also uncompensated, like the LM308, and others. the LM741 and most of its descendants had the compensator internalised.


glaring chips? just put on shades.

[Kipper4]

Thanks Duck.

I hide most of the glaring componants in a lead box and only show them the light of day when Nelson gets his eye back...............
No Sunnys required.

[Kipper4]

The build is done.
It's passing signal and wah'ing.
I need to go over all the nodes to check everything.
Take voltages and test it. Then I'll post up the info and a layout.

[stringsthings]

Sounds interesting.  Might have to build me one.
Back in my vero days, I built a few Penfold circuits.
His books have some good info in them.

[ElectricDruid]

Wow, this takes me back. I built several of these back in the days Maplin sold a full kit for it. The PCB was an utterly bizarre shape, very long and thin, so I used to etch my own and use those instead. I still have two or three of the original Maplin PCBs in a box somewhere.
The 13700 filter is excellent, but I remember adding extra resistors at the ends of the Frequency pot on my layout, since it went from somewhere below subsonic to somewhere above dog whistle/bat confusing. The resonance is brutal when turned up and can burst your speaker cones. The other thing about it is that it's an state variable filter, so there's a unused bandpass output at the output of the first OTA stage.
The envelope detector is very basic and is the obvious place to make improvements, but it always worked fine. A full wave rectifier would be my only "want" in this circuit.

Tom

[Kipper4]

Yer Thanks Tom.
I think I just smoked my freq pot. It glowed orange from inside and smells like a bag of new transistors.
Can you remember what value R you used on the freq pot?
Did you put it in series from V+?

[rutabaga bob]

Maybe it would be best to find the suitable range for the frequency pot, measure the setting along with any add-on resistor, and hard-wire a resistor of proper value in place of the pot.  Did you try a larger value for the frequency control?

[Kipper4]

I replaced the freq pot with a 100k B value.
After a short brain fart. Input jack to output plug etc. Don't ask.....

It's sort of works like it did before and the voltages are almost the same as yesterday.

At least i think I havent fried the ca3130. That thing costs silly money compared to a TL072.
I know it's only a fiver but that's expensive for a dip chip IMO. Plus I only have the one.

I'm gonna play with it later and see if i can make it play well.
I think it's expecting a much larger signal than guitar. So I'll have a diddle with the RV1 too.

[anotherjim]

A lot of RP designs have lower input impedance than we like nowadays, often around 100k. Might be enough to lose some treble from the guitar which a filter needs to make the most of. I have a suspicion that the designers test guitar may have had an onboard buffer -  it was the fashion back then.

[Kipper4]

Top Idea Jim.
I'll give that a whirl too.
Meantime heres the layout I made and used.

[ElectricDruid]

Yer Thanks Tom.
I think I just smoked my freq pot. It glowed orange from inside and smells like a bag of new transistors.

Oooooopppss?

Can you remember what value R you used on the freq pot?
Did you put it in series from V+?

I can't remember, but I've probably got some notes somewhere. I'll try and have a dig and see what I can find.
Yes, I had one at both ends, I think - from +V to the pot and from the bottom of the pot to ground.

T.

[stringsthings]

At least i think I havent fried the ca3130. That thing costs silly money compared to a TL072.
I know it's only a fiver but that's expensive for a dip chip IMO. Plus I only have the one.

Tayda sells these for about a dollar.

http://www.taydaelectronics.com/ca3130ez-ca3130e-ca3130-ic-operating-amplifier.html

[Freppo]

I built this one on vero a couple of years ago.
Pretty cool  sounding, but the controls are a bit odd.

I made a vero layout for it here:
http://www.parasitstudio.se/stripboard-layouts/penfold-auto-waa