EF86 contour switch has no effect?

[wiseowl]

Hi,

have just completed the EF86 channel on my 36 watt. However the contour switch doesn't seem to have any effect at all on the tone. I will admit that I have only been able to check at low volume levels so far, but would still have expected to hear some effect.

The resistor values I've used were 4M7, and the caps are :-

.022
.01
.0047
.0022
.00047
.00022


The commoned side of the caps is connected to the output of the EF86 (pin 6) while the switch common is connected to the tone and volume pots.

Any thoughts?

Thanks

Martin

[jaysg]

The commoned side of the caps is connected to the output of the EF86 (pin 6) while the switch common is connected to the tone and volume pots.

Any thoughts?

What else is going on? Does it sound okay at the moment, or very thin perhaps? It's easy to guess there's a mis-wire or a bad switch.

If I was troubleshooting it, I would disconnect the wire at the input side of all the caps (A) and the wire that connects the switch wiper to the volume pot I expect is there -- disconnect at the pot (B). Use clip leads to connect individual caps from A to B -- there had better be some differences in the bass roll-off.

Be careful of course.

[wiseowl]

My initial thoughts were that is sounded OK, with the caveat that it was at low level.

If I get your reply correctly you suggest disconnecting the switch completely and
connecting a capacitor in it's place? I'll try that tomorrow.

Thanks

Martin

[jaysg]

If I get your reply correctly you suggest disconnecting the switch completely and connecting a capacitor in it's place?

Yeah, I think you should go around the whole thing and make sure it all works fine with a .01uF. Then try some different values.

[katopan]

Yeah, the difference from one end of the switch to the other will be very noticeable. Let us know how it goes.

[wiseowl]

Found an oops. Initially the channel was put together without the contour switch, because I had some difficulty in finding a decent switch and wanted to get on and test it. I'd put a 0.01 coupling cap in circuit between the EF86 output and the vol/tone pots, I had left this in, this will have had a drastic effect on the effective range of capacitance being switched. Now I've removed it the effect of the switch is more noticeable, but I feel quite subtle between switch points.

(Edited to add.)
Also found that the 4M7 resistors I bought for the switch turned out to be 4K7! I've chopped these out and the switch is much more effective. Do I need to worry about getting the 4M7's fitted, or will it be OK without? I notice that the switch pops now on every change, I would assume that the 4M7's minimise this. Do they serve any other function?

Thanks for the help,

Martin

[rsi]

As far as I know, the resistors are only there to eliminate the switching pop. I am pretty sure you can leave them out if you don't mind the noise. You don't need 4.7 meg...I have 1 meg resistors on my switch and it works fine...no pops.

Alternatively you can buy a shorting switch which doesn't require the resistors.