Delay gate

[britt-stinker]

Hi
I was thinking about if I could ad a "gate" to a delay pedal so it will only delay the signal when the strings are hit hard. Kinda like a fuzz pedal?
I searched the forum but it was mostly noise gates it found.
I'm not a really good scematic reader, so if anyone have some layouts or anything that would be really nice.
If someone has one, can it be made switchable?(I guess it can, but will it be to hard)?

Thanks for all

[Mark Hammer]

Look for the schematic of the Boss CE-1 Chorus Ensemble ( http://www.geocities.com/j4_student/BossCE1.gif ).  before we had other ways of keeping noise from delay units reasonable, one of the strategies was to build a gate into the pedal so that when the signal dropped below a certain predetermined level, everything coming out of the delay chip (clock noise, hiss, etc.) would be gated out.  The idea was that you wouldn't notice clock noise if there was music mixed in but compared ahgainst silence, the clock noise would be objectionable.

So where is it on the schematic?  Look for Q12 (a FET), and IC3 (an op-amp).  IC3 takes its signal from the input (IC1) and boosts it ([470k+3k3]/3k3 =  gain of x143).  The network of D12 and D11 should look a little familiar to anyone who has made a compressor or envelope-controlled filter.  These provide half-wave rectification of the input signal.  In this case, however, it is set up, through R66/67 and D13, and the reverse orientation of D11/D12, to provide a voltage that is high (6v) when there is no input and low (0V) when there is input.to Q12.  Q12 and R48 (2k2) form a kind of attenuator or pot where R48 is one side of the virtual"wiper" and Q12 is the other leg.  As long as Q12 is off, the combination will behave like a pot turned almost all the way up, and most of the audio signal coming via R48 will pass.  When Q12 gets turned on, though, Q12 will provide a lower-impedance path than R48 and the signal will be turned down to darn near off.

This gate is intended to turn the volume on the delay signal almost off when there is nothing to hear, and turn it back on (by Q12 going off) when there IS something to hear.

So why am I telling you this?  Because you can use it to accomplish what you asked about.  In your case, what you would want would be a way of varying the gain of the equivalent of IC3 so that you might only turn the FET off if you were playing very hard.  You can also consider fixing the gain of that stage and placing several diodes in series with D11 (complete with a switch that short-circuits different combinations) so that several different preset voltages are fed to Q12.

Note that this circuit, since it is geared towards killing ojectionable noise, has a pretty quick onset and offset time.  You might consider increasing the value of C42 from .047uf to 4u7 of something like that to add some fadeout time.

There are other ways of doing this, but this one is known to work, pretty simple to implement (even simpler if you use a different op-amp that doesn't need the compensation components on pins 1, 5, 7), and can be added onto most delay lines of different types that I am aware of.

[A.S.P.]

read here ,
what the designer/inventor* of the R*land J*zz Ch*rus ( Ikutaro Kakehashi , the founder of B*ss himself!) had to say about it...