Schematic Request - Mesa Boogie Caliber 50+ Footswitch

[chaos2k]

I've tried building a replacement footswitch for a Mesa Boogie Caliber 50+ using two standard switches (the switches connect ground to wire each and have a LED+matching resistor in parallel to the switches). I.e. it's the dumbest switch possible. Both switches are identical and one goes to Lead/Rythm and the other to EQ.

Unfortunately it's not as simple as that it appears to me. Here's what's currently wrong:
- The EQ switch appears to work correctly but the LED isn't glowing. I suppose this is due to wrong resistor value for the voltage the Amp puts on the circuit.
- The Rhythm/Lead switch behaves weird. The LED switches correctly but it will always go into Lead mode - eventually. When I put it from Lead to rhythm the LED turns off (and stays off) and for a second I hear the sound change to Rhythm mode. But then it slowly switches back to Lead mode, only louder than before!

I suppose some magic cap/resistor combination is needed on both switches. Does anyone have a schematic for a Mesa Boogie Caliber 50+ Footswitch or could open up theirs and send me a pic?

I could find some schematics for the Amp, but none of them contained the footswitch I'm afraid. And Caliber 50+ replacement Footswitches are apparently hard to get by in 2015....

[52 Bill]

I couldn't find a schematic for a 50 caliber plus that had a dual foot switch, they all showed single ones.

Looking at a DC5B schematic with a dual foot switch, it shows the foot switch as an led in series with the switch. Closing the switch grounds the end of the led. Try that and see if it works.

[chaos2k]

Thanks for your reply Bill!. It's actually two independent switches with independent wiring going out to two Mono jacks. The official Mesa switch probably just houses them in the same case. I can't tell for sure because I haven't seen any yet :-(

The Manual (http://www.mesaboogie.com/media/User...ber%20Plus.pdf) actually says that the EQ Footswitch is a standard "ground type" switch, so that's why I suppose it works more or less the way it should.

Wiring the LED in series with the Rhythm/Lead switch.... might try that. Any chance this may damage the Amp?

As far as schematics goes, would it be a safe bet that Mesa re-used the footswitch design on other amps? Thinking of it, the functionality of the switch should be the same as the push/pull gain pot on the Amp so looking at that part of the circuit might give some insights... But not all editions of the Caliber 50 had the push/pull pot I think.

[52 Bill]

Well then scratch the series led switch.

The standard Boogie foot switch is as you wired it with an led and series resistor across the switch contacts, so that the led is turned off when the switch is closed. The normal resistor value is 3K3 ohms.

I don't know how the eq foot switch jack is wired, so it may or may not work with the led.

As for damaging the amp with the series led, it is more likely that you will damage the led. If the hot of the switch jack can safely be grounded, then grounding it through an led will not damage the amp.

[chaos2k]

The resistors in my switch are apparently only 470Ohms. Will swap and then check. Meanwhile I found a good source of Mesa schematics here: Free Mesa Boogie Diagrams, Schematics, Service Manuals :: Schematics Unlimited

These say 3.3k as well (the studio caliber 22+ schematic has a Ld/Rhythm switch section. A comment in the schematic says 8-10v for Rhythm 3v for Lead. I will try to find a 3.3k resistor and a multimeter and will report back.

[chaos2k]

I just want to confirm that 3.3k Ohm is the correct resistor value, channel switching works perfectly now. Unfortunately I can't say the same about the EQ, the switch works fine but the LED isn't glowing. I suppose it either needs to be wired in series or it needs a different resistor value (no idea how much Volts the Amp puts on the jack - will have to find my multimeter to measure it).

Thanks for bringing me on the right track!

[52 Bill]

Unfortunately I can't say the same about the EQ, the switch works fine but the LED isn't glowing. I suppose it either needs to be wired in series or it needs a different resistor value (no idea how much Volts the Amp puts on the jack - will have to find my multimeter to measure it).

I don't know how the eq switch jack is wired. It may not have any voltage on the jack, so the led may not ever work.

See if you can find a schematic that shows how the eq switch works.

[g1]

Here's 2 different 50 cal. schematics (6BQ5 or 6L6 versions). Sorry the second one is a doc file, I don't know how to extract the image, hope it works for you.
It shows 7.8V at EQ footswitch jack to turn on LED.

[chaos2k]

Hi g1 thanks! The .doc schematic does indeed show 7.8v but my Multimeter didn't show any potential (0v) between the two pins of the EQ switch... (with the switch open). I even wired my multimeter in series to check if there's any current going when the circuit is closed but apparently there's none either. How does the EQ switch work at all (on an electric level)? It does indeed change the EQ on/off, so there must be some effect of opening/closing the circuit. Please bear with me, I'm only a software engineer with a basic understanding of circuitry...

So what I was wondering if the Amp does not power the EQ switch, I could hook up a battery to it do drive the LED. The switch has 3 lugs and connects either 2 in the on/off (latched) position. It's currently wired to connect 1&2 but I could hook a simple 9v Battery+LED+Resistor circuit to 2&3. Only downside there is that the LED could be on even when the switch is not connected to the Amp....

Would it be possible to design a circuit where I can hook up the battery+led circuit to the switch so that the LED is only enabled when the switch is engaged and plugged in?

[chaos2k]

Hang on a second... might they actually run the actual signal out to the switch and back? Don't have an Oscilloscope to check.... but that would explain how it works. In any case, I'm still wondering if I can get the LED to work with the SPST switch in there
+ a battery.

[52 Bill]

Hang on a second... might they actually run the actual signal out to the switch and back?

Yes, it might be the grounding circuit of the inductors that is sent out to the pedal. If you look at the schematics there usually is an ldr that grounds or ungrounds the eq circuit. The foot switch may be in series with the ldr, so it wouldn't have any voltage on it.

You could create a self powered switch with an led, but to keep the battery voltage out of the audio circuit, you would need a two pole switch, one for the audio and one for the led.

[g1]

Does your EQ supply match this drawing? There should be 8V on the 3300uf cap, then through the 470ohm to the footswitch where there should be 7.8V.

[52 Bill]

I think that the EQ foot switch is separated from the rest of the foot switching so that it would not interfere with the channel switching when the amp is set to auto mode and not require a special jack.

If the circuit is ungrounded by the foot switch, it would work regardless of whether the EQ was turned on by the front panel switch or by the auto function of the channel switch.

[g1]

Here's a pdf for the 6L6 version schematic:
http://music-electronics-forum.com/a...-schematic.pdf