Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: RobBozic on September 03, 2012, 10:17:44 pm

Title: How to wire up a cathode bypass cap as a footswitchable boost
Post by: RobBozic on September 03, 2012, 10:17:44 pm

Hi gents,

Need help on how to wire up a cathode bypass cap as a footswitchable boost. I was looking at the Sommatome Overdrive 35 amp & it has a footswitcable boost which I'm sure is the V2a cathode bypass cap on a JTM45 / Plexi circuit. That amp is set up with a switch or a footswitch to activate it.

My amp already has it set up on a switch but I'd like to make it footswitcable as well.



Thanks in advance
Rob

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: kagliostro on September 04, 2012, 01:32:19 am

Quote

My amp already has it set up on a switch but I'd like to make it footswitcable as well.

if in your amp is already present a panel switch for that function you can add a relay which contacts are in parallel with the panel switch

Doug has very good documentation about that

http://www.el34world.com/projects/relay_switch.htm (http://www.el34world.com/projects/relay_switch.htm)

you can also read about this argument on this tread (see pages 4 and 5)

http://www.el34world.com/Forum/index.php?topic=14201.200 (http://www.el34world.com/Forum/index.php?topic=14201.200)

K

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: TIMBO on September 04, 2012, 03:11:07 am

Hi rob, If the cap is engaged into the circuit by connecting it to ground (as a bypass cap usually are ) and you already have a sw. that does this then all you need is a sw. in a pedal setup that does the same as the sw. on the amp.  :icon_biggrin:

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: RobBozic on September 04, 2012, 03:55:09 am

Timbo,

I want to know how it's done, exactly as it is in the Sommatone amp, with a switch (as currently done in my amp) and with a pedal footswitch.

I'm not good with pedal footswitches, therefore I'm hoping someone has a schematic I could follow.

Thanks
Rob

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: tubenit on September 04, 2012, 06:13:08 am

And some more relay switching information from the ARCHIVES:

http://www.el34world.com/Forum/index.php?topic=14348.0 (http://www.el34world.com/Forum/index.php?topic=14348.0)

With respect, Tubenit

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: sluckey on September 04, 2012, 06:48:52 am

You may not need a relay at all. It 'may' be this simple...

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: jjasilli on September 04, 2012, 10:08:39 am

In the background, the posters are implying that there are 2 potential issues to be aware of:  ambient noise & switch popping.  These problems might or might not arise in any particular build. 

Noise: If you run the cathode cap wires outside the amp, they might pick-up ambient noise and inject it into the signal path.  This issue could vary from venue to venue.  A relay solves this issue.  The cathode cap wires stay inside the chassis; only the relay wires exit the chassis.  (But note that the electromagnetics of the relay, and/or its lead dress, could also introduce noise if not located properly.)

Switch popping: Operation of the SW could cause a pop (regardless of whether a relay is used or not.)  If the cap is switched in/out at its top, the cap itself might squelch any pop.  Sluckey offers an alternative: a 1M R across the SW's.

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: kagliostro on September 04, 2012, 01:36:44 pm

I agree with Jjasilli about the possibility of noise recovery if the cathode is connected to the switch on the pedal without a relay

however Sluckey experience is very large and if he tell something I think it will be good practice to give a try to his council

than if you get noise from the cable, to add a relay is always possible

K

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: RobBozic on September 04, 2012, 05:14:14 pm

Thanks guys,

Great advice there. I found a pic of the Sommatone amp internals and I'm going to post it when I get back from work today.

Thanks again
Rob

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: HotBluePlates on September 04, 2012, 09:18:03 pm

You might be able to use a FET in place of the mechanical switch, and use the footswitch to control the gate.

But someone more familiar with solid-state should chime in on that plan.

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: RobBozic on September 05, 2012, 05:01:28 am

Here's the gut shots.

It looks really simple, I guess as per Sluckey's schematic.

Rob

Title: Re: How to wire up a cathode bypass cap as a footswitchable boost
Post by: Colas LeGrippa on March 02, 2016, 11:46:34 am

sluckey's schem works perfectly , no noise, effective.

Colas