# Hissing from Chorus Pedal



## Robert1950 (Jan 21, 2006)

I have a 1980s Boss CE-3 chorus pedal. When I stomp on it, there is swirling hiss, not too loud, but noticable. The pattern of hiss changes as I alter the settings on the pedal. Any idea what causes this?


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## Guest (Apr 23, 2009)

Electrolytic capacitors should be changed and all solder joints touched up for a start.


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## Mooh (Mar 7, 2007)

Chorus pedals are full of venomous snakes. Have they been fed?

Seriously, chorus pedals always act weird for me. I have a Boss Super Chorus CH-1 that behaves itself so I don't screw with it. It's like the evil step-mother of effects.

Sorry I'm no help, but I am curious how this will be resolved.

Peace, Mooh.


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## wayne (Apr 8, 2009)

Make sure you're using a good quality cable before the chorus. Also, is your guitar picking up any noise?

Any noise that gets picked up before the chorus is gonna get, for want of a better word, chorused.

I'd also check on the venomous snake thing. Mooh might be on to something!

W


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## Rugburn (Jan 14, 2009)

I agree with Wayne about bad cables. I've got a cheapo cable that I use when I chain my effects, and it's noisier when I use it. Better cables lose less capacitance from point A to B. I think Konasexone might have misunderstood the question. Although, a pedal that old may be showing signs of drifting values in the circuit's components. 

Chers Shawn


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## mhammer (Nov 30, 2007)

ALL chorus pedals produce that. It's clock signal and artifacts produced as a result of clock signal. That's why its quality changes when you adjust the pedal settings.

There are two things in the design of most chorus pedals that would normally take care of this and make it a non-issue:

1) Lowpass filtering of the delay path - generally the filters are designed to allow the circuit to keep the hiss out but leave the sparkle of the strings in (i.e., rolloff is not too low, not too high). Given that capacitors are used to set those parameters, as well as the clock, and given that capacitors normally have poor tolerance (as much as 20% out), it can happen that the clock is operating withn a range that is not covered by the filtering. This can be either because the clock is a little lower, or the filter cutoff is a little higher, or both.

2) There are always two output from the delay chip. When these are combined in equal measure, they have a "hiss-bucking" (like humbucking....only a lot higher) effect. In high-end products, those two outputs will be tweaked with a trimpot to maximize noise-rejection by providing perfect balance. On the majority of chorus pedals, though, the manufacturer simply uses a pair of equal-value resistors. In the CE-3, Boss chose to use NO resistors ( http://www.synthdiy.com/files/2007/bossce-3.jpg ). I suppose you can't get more equal than that, but it also assumes that the two channels to be combined will be of absolutely identical level. Maybe, maybe not.

Clearly, in your case, you can't easily fix #2, but you CAN try and address #1. The filtering will be very involved to address, so the next best strategy is to try shifting the delay range downward a tad, by replacing C25. This sets the delay range by setting the clock frequency range. One way to test out the hypothesis in a nondestructive way is to score yourself a 10pf capacitor and just temporarily tack (solder) it on to the copper side where the pads are for C25. (My guess is that C25 is that little tan-coloured beastie just to the left of the MN3102 shown here: http://www.pedalarea.com/images/boss_ce3_board.jpg ) That will increase the combined capacitance to 57pf, and bump the delay time up proportionally. (In reality it might be different but we'll assume for the moment that the stated values are accurate) The chorus sound will be "thicker", in the sense of moving more towards Pat Metheny-like doubling. If your hiss gets worse, then clearly the issue is the mismatch of filtering and clock range, and the solution will be to nudge the delay range downward (downward meaning to shorter and shorter delays, moving towards flanger/Leslie tones rather than doubling). You can do this by reducing the value of C25. Personally, I wouldn't go any lower than 36-39pf, or else you risk losing the chorus effect and replacing it with another kind of sound.

If you are situated near Toronto, you should have no trouble finding capacitors in the 36-47pf range. Note that you can always do things like stick a 33pf and 10pf (both very common values) in parallel for a 43pf effective value (a less common value).


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