Phase exciter

[Kipper4]

What does it do?
I saw this and I don't get what it does please let me know.

http://experimentalistsanonymous.com/diy/Schematics/OOP%20Japanese%20Electronics%20Book/phase-exciter.gif

Has anybody  built it or any similar projects?
Thanks guys
Rich
Don't ask me why I'm still searching for phase shifter stuff.
I like em I guess everyone has there thing.

[Scruffie]

All pass filter - sallen key high pass filter - 1st order high pass with gain - inverter.

Cuts a lot of bass and adds high end top.

See Mark Hammers Woody for similar.

[Mark Hammer]

All true, except that the first stage can provide up to 11x gain.  When one considers the relative amplitude of what comes out of the filter stages, the direct-mix control allows for the unaffected signal to be louder than the added treble content, or low enough for the added treble to really stand out and "excite".

[Kipper4]

Thanks guys I'll look up the woody.
Tell me this though what's with the 20kB pot at the output of the exciter?
Is it a dual pot? It looks a little like it has two wipers. Offset at that.
Or should it be read as a single pot lug 1 to output of op amp. Lug3 to op amp input. And wiper to switch. So the two out of phase signals are mixed by the 20kB going to the switch.

[Mark Hammer]

What you want is Jules Rykebusch's "Harmonic Sweetener".

[Ben Lyman]

What you want is Jules Rykebusch's "Harmonic Sweetener".

Sparked my curiosity... a schematic that appeared in a magazine in the 1980's? Cool!
http://www.harpamps.com/schematics/harmswtn.pdf

[ElectricDruid]

Thanks guys I'll look up the woody.
Tell me this though what's with the 20kB pot at the output of the exciter?
Is it a dual pot? It looks a little like it has two wipers. Offset at that.
Or should it be read as a single pot lug 1 to output of op amp. Lug3 to op amp input. And wiper to switch. So the two out of phase signals are mixed by the 20kB going to the switch.

It looks to me like a centre-tapped pot. You don't see them very often, but they're handy for this type of mixing job. The middle of the pot track has a connection which can be grounded. You can then connect a different signal A & B to each end of the track, and you get A->down to 0->up to B as you move the pot. Useful. It's not the only way to do it of course...

HTH,
Tom

[Kipper4]

Well that's a first for me. Centre tapped.
More homework to do.
Let me know if your gonna breadboard it Ben.
Thanks again guys.

[Kipper4]

I do wonder what it would sound like if the output of the 14 where to be switchable between inputs 12 and 13.

Some phase cancellation. Or and intresting sound
In the below

http://www.harpamps.com/schematics/harmswtn.pdf

[Groovenut]

...

[Mark Hammer]

Having built it, I would say that it is really more appropriate, as shown, when used in a studio or similar context, fed with line-level signals.  As a guitar pedal, I think folks will find it a little hissy, given how much boost is applied to high-frequency content.  Used at line level, with pristine input signal, I would imagine it is not audiophile quality but fine for the amateur studio.  Used as a guitar pedal, it probably wants a gate of some kind applied to the harmonic-content path.

In some respects the absolute simplest thing would be if one or both of the LEDs used for clipping was bright enough, and harnessed to an LDR.  The LDR would replace the 10k mixing resistor coming off that 10k mix level pot; presumably with an appropriately chosen parallel resistor to complement the LDR.  When the input signal rises above some minimum, the LEDs would light up when clipping, and would simultaneously reduce the resistance of the LDR, such that more of the added harmonic content would get mixed in when needed, and boosted hiss would get bumped to the background when you weren't playing.

Note that I said the "simplest", not the most feasible.  Finding a red LED of suitable efficiency that would provide the required brightness to affect an LDR may be difficult.  As such, it may be more effective to make a simple half-wave rectifier, with an additional op-amp, and use that to drive an additional LED, to vary the LDR resistance.

"Maybe, but don't gates mess with the sound?", you ask.  Yes, but we're only messing with the added treble content.  The basic input signal travels unaffected through that first unity-gain stage, directly to the 2nd unity-gain stage, adding no hiss.  We're only dickering with how much additional treble (and potential hiss) gets mixed back in.  Happily, the nature of the circuit makes such a modification easy and unobtrusive.

FWIW, I think this would make it an even better studio tool too.

[Kipper4]

Envelope detector now your talking my langauge.
I'll put my thinking cap on.

"Upstairs for thinking, Downstairs for dancing."

[Mark Hammer]

Doesn't have to be terribly complicated.  All it really needs to do is dial back the "exciter" level when you stop playing.  I would imagine that even if it only drops the level of that path by 10-12db, it will make unit more usable.

[Kipper4]

Is anyone else surprised at the second unity gain stages input impedance ?

[samhay]

Rich - op-amp's can happily drive 5k/10k and the second stage doesn't directly see the input, so can't load it down.

Mark - rather than an LDR, why not try coring diodes (series, anti-parallel) as a cheap and cheerful noise gate feeding the input of the clipping stage?