Boss Chorus/Phaser

The Dark force of dance batzman at
Mon Mar 9 13:24:41 CET 1998

Y-ellow R.G.
At 01:52 PM 3/6/98 -0600, R.G. Keen wrote:
>>However, from what I remember about making them stereo, the technique was 
>>to feed the dry channel to one output and the wet channel to the other.
>As I remember, the trick is to add the wet signal to the dry one for
>one of the stereo channel, and subtract the two for the other channel.

The Chorus I have must be the CE-1. I think the CE-2 was already stereo. You
are essentially correct. To create a pseudo stereo image is simple in
essence. Except you need to be able to get hold of the wet signal from the
BBD prior to it being mixed back with the output. To "Chorus" a signal, you
delay it by a varying amount. Then mix this signal with the dry signal. This
creates what is called a comb filter. So called because it has many peaks
and troughs resembling a hair comb. However if you invert this signal and
feed it to a second copy of the dry signal you will cancel and accentuated
the opposite of the previous comb. Thus in the left channel, a given
frequency may be boosted but in the right it will be attenuated. (Canceled)
The left and right channels will be a compliment of each other but contain
different information. Though the energy levels will be roughly the same.
Your ears here an evenly spread image but they tell you it's stereo.

It's interesting to note that a great many el-cheapo multi FX units, such as
the Alesis boxes also use this approach to give a stereo image. The Effects
processing is all mono but the output is inverted and Canceled with the
original in the opposite channels. This is particularly easy with effects
such as reverb. 

Pseudo stereo uses a subtle stereo chorus effect. Though my unit was stolen
some years back, I built such a BBD test bed which can be seen on my site.
The thing is that I'd like to convert this Boss mono chorus unit to a stereo
one. It'd be more useful that way.

But I'm still looking for a circuit to the PH1a Phaser. Which is completely
dead. Although I don't like Phasing all that much, I'd just like to fix it
up some time. You'd think with everyone putting FX circuits on-line these
days, someone would have posted the PH1A but it seems a rare beast.

Thanks in advance.

Be absolutely Icebox.
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