OD/Clean

halfbackstrat · Post by **halfbackstrat** » Thu Jun 02, 2011 8:41 pm

Hey guys, i'm writing up the parts list for a 124 build, this would be my first Dumble Build.
Project is going great so far, i've spent the past few months researching the electrical physics related to valve amplifiers. I've been able to answer all the questions after extensive research and reasoned logic. But theres one thing thats confusing me about the 124.
The OD/Clean and PAB relay's. These are Footswitch controlled through the relay circuits, i understand this.
Now i realise there are switches on the back to switch to manual control, but where are the manual controls? As of course there are only 3 switches on the face of the Dumble.

I should mention i know this forum is frequented by real pro's and i feel a bit bad asking a question that is probably quite simple.
But i've had a good search online and i wouldn't ask if i wasn't totally stumped.
Thank you for any feedback you can give me.
Matt

stelligan · Post by **stelligan** » Thu Jun 02, 2011 8:58 pm

Welcome! The switches on the back just serve as a substitute to actuate the relays when the foot switch is not plugged in. Or as a duplicate or override when it is. Notice how pins 2 & 4 on the foot switch jack are applied to the manual switches. Good luck with your build.

halfbackstrat · Post by **halfbackstrat** » Thu Jun 02, 2011 9:05 pm

So if no XLR controller is connected then the manual position is Overdrive engaged and pedal is clean only?

Thank you for the warm welcome!

stelligan · Post by **stelligan** » Thu Jun 02, 2011 9:17 pm

You may do both Boost and OD with either the manual switches or foot switches. SO you get clean, clean + boost, OD, OD + boost with fingers on back or feet on floor. They're each other, brother......

halfbackstrat · Post by **halfbackstrat** » Thu Jun 02, 2011 9:36 pm

Right so the Pedal side of the switch is off, without the XLR plugged in. Thank you so much man.
Really appreciate you taking the time for a newbie like me.

talbany · Post by **talbany** » Thu Jun 02, 2011 9:45 pm

halfbackstrat wrote:Right so the Pedal side of the switch is off, without the XLR plugged in. Thank you so much man.
Really appreciate you taking the time for a newbie like me.

FWIW..If you use an on off on DPDT switch for the rock jazz you don't need a separate PAB manual switch as this does the same in the off (center position)..Dumble did this on 124 as part of an upgrade and disconnected the rear PAB switch

Tony

diagrammatiks · Post by **diagrammatiks** » Thu Jun 02, 2011 11:18 pm

plenty of room for a push pull pot connected to the manual on the front as well.

hans-jörg · Post by **hans-jörg** » Fri Jun 03, 2011 8:22 am

Hi,
I gave the former (because useless to have 2 of them) PAB switch at the back the "chance" to switch my RNFB from V1. The right switch at the right place for that IMO

Hans-Jörg

Structo · Post by **Structo** » Sat Jun 04, 2011 4:07 pm

I should add that when you turn those back panel switches on, they actuate the relays.
So if you have LED's on the footswitch, they will light up as if the footswitch was pressed when you use the back panel switches.

The back panel switches can help if you have to trouble shoot and you don't feel like plugging the footswitch in or other reasons.

Also, the PAB switch is not wired to where it will work right as shown in the #124 layout.
There is a ground missing on the PAB switch.
Here is a layout that I have edited a few things.
Check out the OD/PAB switches to see what I mean.
Remember that #124 has slide switches, not toggle switches.
So for toggle switches, you would flip the wires on the terminals.
In other words the ground goes on the bottom terminals.

On my amp I put the Mid Boost on the footswitch as well.

martin manning · Post by **martin manning** » Sat Jun 04, 2011 5:11 pm

Structo wrote:I should add that when you turn those back panel switches on, they actuate the relays.
So if you have LED's on the footswitch, they will light up as if the footswitch was pressed when you use the back panel switches....

Not with the original wiring. There is a separate wire carrying the 12V supply for the LED's in the footswitch, and they will not come on unless the stomp switches are closed.

Structo · Post by **Structo** » Sat Jun 04, 2011 6:08 pm

Really?
Must be the way I have my footswitch wired then.

I believe this is the way I have my foots witch wired.

When I throw the switch on the back panel, it lights up the corresponding LED on the footswitch.

halfbackstrat · Post by **halfbackstrat** » Sat Jun 04, 2011 8:13 pm

Thanks for that info Tom, I had read something before about errors in the layout's provided. So i have worked exclusively from photographs of 124 and the circuit diagram. I was going to replace the slide switches with SPDT switches which i think should serve the same purpose. Really i don't want to use a foot pedal at all, as i won't be using the amp live, i might revert to a foot switch if i did a no compromises amp, but seeing as this is my first build it's probably not worth it.

As a matter of interest, i live in the UK, so obviously the current power transformer, 022756 from at Fender Twin/Showman, isn't suitable as this is a 120V transformer. The mains in the UK is 240V. What is the transformer of choice for replacing the current transformer.
Also is there any other modification to the amp i would need to do for the UK? I can't see anything or any reason why, but i thought i should ask incase i have missed something glaringly obvious.
Thanks

martin manning · Post by **martin manning** » Sun Jun 05, 2011 1:18 am

There are export versions of the Fender Twin Reverb power transformer available from Hammond (made in Canada, and sold by, among others, Antique Electronic Supply in the US) and also from Mojo Musical Supply. Mercury Magnetics also has appropriate voltage models. Tube Amp Doctor lists this one: http://www.tubeampdoctor.com/en/shop_Tr ... an_100_111 Of course the relay supply transformer will have to be 240VAC too.

I'd wire it for the footswitch and put the jack on the rear panel. The footswitch itself can be left 'til later if you like.

Tom, the difference in your wiring is in the amp, rather than the footswitch, I believe. The way you have it would be useful- it'll tell you from the footswitch if the manual switch is on.

jestaudio · Post by **jestaudio** » Sun Jun 05, 2011 9:02 am

[quote="halfbackstratThe mains in the UK is 240V. What is the transformer of choice for replacing the current transformer.

Thanks[/quote]
I used the hammond 291dex which works a treat in my build, try http://www.bluebellaudio.com/ ,very helpfull and very quick to deliver

halfbackstrat · Post by **halfbackstrat** » Sun Jun 05, 2011 9:22 am

Thanks very much for that link jestaudio, i think i will use the 291 FEX from that site as it has the exact voltage ratings that are specified on the schematics, 6.5V 320V and 60V.

Thanks for your reply Martin, I think i agree with you, the best course will be to wire as standard with the XLR socket and use the sliding switches (SPDT switches in this case) as on/off instead.

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