Royal Filter

[StephenGiles]

Think about this one, I'll get back tomorrow.
Stephen

[puretube]

quote: "goodness, gracious, great balls of fire!"

where`d you get that from? very educative - thank you, sir!

[swt]

wow stephen!!. That looks like a really simple microsynth. have you tried it?. Does it work for guitar?. Thanks for sharing!!

[gez]

That looks like a really simple microsynth

Not really a synth, just 2 parallel multi-feedback (bandpass) filters swept by an envelope follower.  Filters have different value caps so it probably has a voicey sound to it (similar approach used in the Bass Balls circuit).  

Interesting circuit though, thanks for posting...

[StephenGiles]

Bad news swt, we've finished the dulce de leche! Still we'll get a can of it at the Anglo-Argentine Society Asado next week. Now, the filter.......my simple understanding of the beast is this: when a note of sufficient strength is plucked, pin 14 of the 324 goes high to a voltage set by the Start frequency pot. The voltage then falls, I suppose as the capacitor made up of the 2 elctrolytics discharges at a rate set by the sweep time pot until it reaches the low state voltage set by the Stop frequency pot. The trick is that if the stop frequency is set higher than the start frequency, you get a reverse sweep - just like in the Microsynth. All basic EH stuff is it not Puretube?

To take this one step further, and I expect Puretube to burn some midnight oil on this! - what if we had some additional circuitry which sets in real time, the maximum voltage normally determined by the Start frequency pot as a measure of the strength of the input signal? Perhaps not very well explained - what we get from this sweep generator is a ramp voltage independent of the input signal level, so no ripple in the sweep generator. So what I want to do is preserve the ripple free sweep generator, but have the facility to control the start voltage from the guitar by the strength of note played.

Over to you!

[puretube]

S & H  the env-voltage...
:idea:

[Mark Hammer]

I don't think you folks out there have an appreciation of how many of these filter designs Steve has come up with and just exactly how long he has been working on these.  One of the first ECFs I built was actually a project that Steve had published in Electronics Today well over 20 years ago.

This one combines what is essentially the filter complement of the Anderton Bi-Filter Follower with the envelope generator of the E-H Microsynth.  In this instance, the "envelope" is not one that tracks the guitar itself, but rather one that is caused/prompted by the guitar.  That has good and bad aspects, or rather a different sort of feel.

What it WILL do is provide much more flexibility in terms of the kind/form of filter sweep produced as well as the timing.  With the usual sort of half-wave rectifier that I almost invariably recommend tweaking with respect to attack and decay parameters, any appreciable increase in attack time comes along with a reduction in sensitivity, and consequently amount of sweep.  In this instance, as long as the note is strong enough to trigger the envelope generator, sweep speed is independent of any additional differences in picking strength.  The start/stop nature of the envelope generator is capable of producing a broad palette of upward and downward-sounding sweeps.  

Where this sort of arrangement may not be to everyone's liking is that it is not quite as dynamically responsive to playing.  You can't nudge a bit of sweep for most of the bar and whack the strings for a big sweep on the downbeat.  That's not better/good or worse/bad, just a different sort of device/approach that may or may not fit your plans.  In the other hand, it's not like making one of these and one of the dynamic types is mutually exclusive.  After all, our urge here is to have one of everything! :lol:

As JC Maillet brilliantly noted, the Anderton LDR arrangement has the interesting property of providing natural compression at the same time as it sweeps.  This occurs because the LDR and the 47k resistor ahead of it form a voltage divider.  As the LDR resistance goes low, the filter sweeps higher, but the level is attenuated.  Fortunately, the arrangement does not produce a significant drop in level, but what it does do is smooth out the volume over the sweep so that it doesn't sound quite as jarring.  Personally, I like it but I understand how it isn't what everyone wants.

Steve, I'm curious why the decision to opt for compensated op-amps (TL070 + 22pf cap) for the filters.  Any particular strategy there that you'd like to share?

Also curious as to why 3/4 of a quad 324 was used for the envelope generator and a half a 4558 was used for the input stage.  Together, they make up an entire quad op-amp or a pair of duals.  Deliberate, or the product of trimming back on a larger design where the (here) unused portions found gainful employment without editting the part labelling?  Some comment here might save some folks who take things a little too literally a few headaches.

Finally, this design has all the mod possibilities inherent in the BFF itself.  For instance, you can:
a) stagger the filters by using various (matched pair) values of caps for the upper filter (e.g., 3n3, 2n2, etc) in addition to the 1n5 shown (though 1n5 gets you a nifty kind of swept phase-shifter sound which is great for rhythm guitar)
b) build in a loop or fuzz between the input stage and filter stages for processing a more harmonically righ sound
c) adapt the passive output mixing arrangement to have variable blending of the two filters or the filters and straight signal

Steve....her majesty IS amused.  Well done.

[StephenGiles]

Hi Mark - thanks for your kind worrds. I used TLO 70s because I had some (from Steve Daniels) - no other reason. The answer to your point about the 3/4 of 324 aand 1/2 of the 4558 was to see if anyone suggested the other half of the 4558 could be used to build in a distortion section. The remaining 324 amp I left for use with additional circuitry requested in my previous post, but would probably be no good for a S & H as Puretube suggested. I'm off to mow the grass (yard!!) so perhaps someone will have come up with a revised circuit by the time I get back.

[bwanasonic]

Bad news swt, we've finished the dulce de leche! Still we'll get a can of it at the Anglo-Argentine Society Asado next week.

Just CAREFULLY simmer an unopened can of sweetened-condensed milk in some water for a couple of hours and allow to cool before opening. Never personally had one explode, but be careful.

Kerry M

[StephenGiles]

......and lots of sugar I believe! Trouble is, I keep hearing my dentist say "no sugar between meals" in a Dublin accent!
Stephen

[puretube]

S & H  the env-voltage...
:idea:

of course the env-voltage of a "real" follower!
(you could use that quarter 324 for peak detector,
and a FET for "holding");
maybe an extra "trigger" is needed, too?

getting complex....

and now: invert the "LED-drive-voltage" *,
increase the second filter`s caps
to almost the same value as the first`s:
voila: "Talking FolloWah"  :wink:

(* of the 2nd filter)

oh, yes, you could play with the "Royal`s" detection/sweep circuit
and add some pots for attack/decay/sustain/release   ...

[StephenGiles]

.......the sweep generator formed by IC2, IC1D and their associated components. With the system at rest, no current flows through R4 into IC2 (CA3094) pin 5. This results in the transconductance amplifier portion of IC2 being effectively disconnected from its darlington emitter follower output stage, hence the voltage at IC2 pin 6 follows pin 1, which is at the voltage set by R7 - STOP FREQ, and buffered by ICId (324).When .........is struck, IC2 is energised by the current into its pin 5 and becomes a voltage follower, forcing pin 1 to equal the pin 3 voltage, set by the START FREQ control. The pin 5 current soon ceases to flow, however, and the voltage at pin 1 decays through R10/C4 to the STOP FREQ voltage.........

Similar circumstances to part of my circuit - so more to think about Puretube!

[puretube]

will look if I got a printed MS schem somewhere tomorrow;
actually I intended to check out the tracking filter of it, firstly...

:?:  :idea:  :?:  :!:

[puretube]

calling Stephen:
was it this thread, I wanted to look for the following S&H Env-Foll., for:
http://www.uni-bonn.de/~uzs159/envf.html ?

sorry - took a while...  :oops:

[StephenGiles]

Thanks Ton - looks interesting.
Stephen

[troubledtom]

bump , just couldn't let this one die
      - tom
it was on page 5

[puretube]

don`t worry Tom & Joe:
unlike @ H-C, threads don`t go down the drain here...

(only in the OT lounge, if not replied within 1 month...)

[Paul Marossy]

What is that 324 chip - meaning what's the full designation of the chip? Well, while I'm at it, what the heck is it?!

[puretube]

LM...

[Paul Marossy]

I thought that was an LM324.