Suggestions needed - Stereo in > mono out w/ auto-pan

[motterpaul]

I have a guy who wants me to make a pedal for his stereo bass.

It has two pickups like a Fender Precision - split for low & high strings (he plays a six-string).

He has it wired with separate outputs for each pickup - and he wants a box with two pickup inputs that will alternately auto-pan them. Then he wants the signal summed in mono (basically, it is an effect where the output is the low and high strings alternately).

Does anyone have any ideas?

Basically, I see it like a stereo input chorus circuit, with no modulation, and mono out.

[Neil mcNasty]

I'm not absolutely sure what you are saying here, since your reference to a Chorus without modulation, is simply a dry signal passing trough. (Chorus is one dry signal, mixed with a vibe/pitched signal. So if you take away the pitch modulation, the result is a normal dry signal)

I suspect that he is talking about, is a active "panner" between the two channels.
And then we are talking a Stereo Input Tremolo with a dual channel LFO (one of them inverted) that merges the output signal to mono.
The result of his idea would be: that his top 3 strings drop out and the other 3 are audible, and vice versa, and this is something that potentially  could result in "missing notes" when playing, unless the LFO tempo of the panner/tremolo is very fast and does not bring any channels to complete silence.

I suspect that this is a product that will not function anything near what this bass players thought it would... (Sorry for stating this, but my experience is that musicians without technical knowhow and fancy instruments, do indeed come up with a lot of stupid shit when they realise that they can stuff custom built. But most importantly: it might be a project that goes on forever, consuming way too much of your time, since the customer actually does not know exactly what he wants, but just throws out ideas in order to get a "custom pedal". This is the main reason that I no longer do any custom builds)

But as a start: I would ask him to hook up two tremolo pedals (one for each channel), merge them in a mixer.
That way he can see if he can get them to work against each-other, and thereby consider if that is anyhow similar to the idea in his head...
Because this is what he is describing as his idea: a dual LFO that removes the sound of one pickup and raise the other, every other time in an automated fashion with speed control.
If this is near what he wants, then proceed to the next step and designing a dual LFO/Channel tremolo that merges the signals at the output. After all a panner is actually just a stereo/dual channel LFO with one LFO signal inverted...

[motterpaul]

Thanks for the reply. I totally agree with you that I wouldn't like the sound of this effect - but then again it isn't my place to decide. The sample he sent me is nothing I would ever listen to - but whatever.

I used stereo chorus (not mono) as an example since I knew you would then get the idea - which you did. I didn't really know how else to describe it because most "autopans" or "tremolos" do not keep two signals separate but equal - which is why I chose a stereo input (not mono) chorus to describe it.

(BTW: what you describe as chorus is what I would call flange - but it doesn't matter. I don't really know that much about tremolo pedals since I still think of tremolo as what Fender used to put into 1960s amps. )

The idea was two signal inputs that can be mixed together into mono by alternating inputs, but they are not SUMMED together into mono to play together at the same time, electronically speaking. I knew there would be an LFO involved since something has to set the autopan at an audible rate.

Anyway - I was hoping something here might do something like what I described.

[Neil mcNasty]

Here is a pretty nice schematic of a Tube Stereo panner that shows how you can do it.
If you look upon each tube-section as a separate preamp with their own separate inputs, the rest would be the dual LFO needed for this kind of panning modulation.
If you break the link that feeds the input to both tube-sections, and rather put the link at the output instead, you will actually have what you need/what he asked for...


Regarding tremolo: the effect is simply an automated version of someone turning the volume up and down, repeatedly and very fast. Doing Tremolo on a stereo signal with an inverted LFO for one of the channels, makes the Tremolo into a Panner. This is what happens with the circuit above.
The Tremolo has been given two channels of preamp, and a inverted LFO wave, so that one channel fades down at the same time as the other fades up. Resulting in a movement of sound from left to right.

Chorus is pitch modulation blended with direct signal, and if you take away the direct signal and keep the pitched signal, you have got a Vibe/Vibrato effect.

Your Flanger comment made me aware of one slight mistake in my description of Chorus: in addition to pitch modulation, there is also an extremely short delay involved on one of the signals.
And this last detail is actually the effect called Flanger.
The first "flanging" ever done, was to record a signal from one tape reel to another, then line them up and while playing them back simultaneously in synch, you would slightly touch one of the reels to decrease or increase the speed slightly to put them slightly out of synch, resulting in an offset between them, which then is resulting in overlapping frequencies, and this the effect we know as a Flanger.
The modern Flanger delays the signal, and then the LFO changes/modulates the "gap" between them in a cycle.

[motterpaul]

Thank you Neil...

Yes, I am aware of the story of Flanging, allegedly first done at Abbey Road although George Martin disputes that.  So do the former owners of Gold Star studios in Hollywood (where I have also recorded) who say they used it on the Ventures song "Telstar"

BTW: in the days of "pancakes" (open reels of tape you could buy with no metal sides because it was cheaper) you would grab a pair of "flanges" to lock the open tape down on the deck - hence the name "flanging" - yeah, I go back pretty far. These days if you try to play a lot of analog masters you had better find some flanges first, because a lot of recording was done on pancakes. Of course, all the best analog masters have already been transferred to digital because tape does erode.

But - moving on - Thank You so much for the layout. I will have to look into it and see what I can learn. In mind I see a 555 as a possible LFO controller.

[Neil mcNasty]

555 LFO?
Here you go: