...Wierd Turn On...

[petemoore]

I have an effects circuit, that sounds great.
 After I hit a relatively loud note, it 'gates into on' mode.
 The Switch seems an excellent one, a 3PDT, new, tests good...
 It seems to be an internal switching on, like an amp stabilizing to bias or something, show none of the typical, misconnection type symptoms...
 The OA's measure consistant good voltages.
 It can go for extented periods without turning on [after an off/on bypass cycle, it is consistantly 'quite' off, a small gated signal may pass]..until a sufficient input level is reached [a Medium attack bar chord turns it on...the transition from the odd off state to stable 'on condition marked by a small transient gating period..about 1/3 second duration]
 The consistancy of the on/off oddities is altered slightly by using different batteries...the new Duracell measuring 9.2v.
 During an extended odd' off condition, extensive gentle wiggling of wires etc. was done, as was general tapping on the board and switch...
 I haven't a clue why this condition exists today, it just seems to be like some kind of in circuit latching effect...for lack of a better description.
 It' is a Minibooster, and an SD-1. Worked perfectly yesterday...
 Any Ideas are welcome.
 I'll simply type 'cold solder here', but it doesn't exhibit any usual symptoms of that, and exhibits behaviour that I feel strongly is 'in circuit' related....

[Alex C]

I thought this was going to be some sort of "fet.ish confession" or something (not that I suspect you of being the type, Pete   )


Alex

[R.G.]

You likely have either a weirdly bad cap or a weirdly bad opamp. There are other possibilityies, but without putting it on a bench with a scope on it, I can't sort them out.

Your description is the classic one for misbiasing. If the signal stays "on" for a while, there's a cap somewhere holding the circuit in conduction. In the mu amp circuit in front, the cap could be the one between the two JFETs or the bias bypass cap.

Actual schematic and typical voltages might help.

[strungout]

Hmm that sound like something I'm getting with the EQ section of RDV's pedal (from you, R.G.), a sort of gate effect witht he same symptoms described. I stuck a Burr Brown in there (getting oscillation with TL072) and the effect was even more pronounced, like the signal if "fighting" it's way thru... I'ma check those caps tomorrow.

[petemoore]

After posting I saw the two sides to my title.
 Fruedian humor I guess...looked a little funny, even though these days what could possibly percieved to be a 'wierd' turn on
 Oops...please don't elaborate...my definition of wierd is wierd enough, anything wierd-er, and we'll have to find a new, wierder word for wierd
!!!