Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mattjaco1 on October 03, 2023, 10:13:10 am
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I am gathering parts for a dual lite build. I want to put the channel switch on a foot pedal. What would be the best way to implement this?
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I would just install separate input jacks for the two inputs and use my Morley AB/Y footswitch. The two channels cannot be played together because they will be out of phase and tend to cancel each other out. This results in a thin sound that's not pleasant.
If the AB/Y switch doesn't appeal to you then simply replace the DPDT select switch with a relay and control the relay with a footswitch. This is probably a better method because you don't have to send the guitar signal to the footswitch.
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Thank you Sluckey for the reply. I've been looking at the Hoffman relay.. I haven't built an amp yet with channel switching. I think I will give the relay option a shot. Will the Hoffman relay hook up in the amp following the relay instructions? guitar input signal to input A on the relay, then the two channel inputs to signal out 1 & 2? One more question.. If I want to have the relay toggle switch and a footswitch jack together could i just parallel the two?
Thank you,
Matt
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Will the Hoffman relay hook up in the amp following the relay instructions? guitar input signal to input A on the relay, then the two channel inputs to signal out 1 & 2?
That's half of the wiring. But you will also have to wire up the B side of the relay with ground on the common and two jumpers to the A side. One jumper between A-normally open to B-normally closed. Another jumper between A-normally closed to B-normally open. This will put a ground on the input that is not selected, thus preventing any possible noise from the unused preamp.
One more question.. If I want to have the relay toggle switch and a footswitch jack together could i just parallel the two?
yes
If you use the existing 6.3 filament winding to feed the relay power supply, do not connect any part of the supply to ground! Let it float. This also means use an isolated 1/4" jack for the footswitch and don't connect any lugs to chassis ground.
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So in order to wire up the b side relay common contact with ground, could I use the same ground wire coming off the relay supply power board going to the toggle switch in the Hoffman diagram?
Would I need to tap it before the switch or after? I'm thinking after?
Also my power transformer has 2 6.3 taps. one is center tapped, the other is not. I will use the non-center tapped winding for my ez81 rectifier, and the center tapped winding for heaters. Which tap would be the best option for powering the relay?. I know if I use the center tapped winding i will need to float the ground at the relay.
matt
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So in order to wire up the b side relay common contact with ground, could I use the same ground wire coming off the relay supply power board going to the toggle switch in the Hoffman diagram?
Would I need to tap it before the switch or after? I'm thinking after?
REPEAT...DO NOT CONNECT ANY PART OF THE SUPPLY TO GROUND! LET IT FLOAT.
The ground for the B side common contact should come from the input jack ground lug.
Also my power transformer has 2 6.3 taps. one is center tapped, the other is not. I will use the non-center tapped winding for my ez81 rectifier, and the center tapped winding for heaters. Which tap would be the best option for powering the relay?. I know if I use the center tapped winding i will need to float the ground at the relay.
Make life simple. Connect the EZ81 filaments to the other tubes' filament string. No reason to have it separate. The original Marshall 18W and Vox AC-15 both connected the EZ81 filament to the other tube' filament string. This allows you to use the other 6.3/5v winding solely for the relay power supply. Easy peasy.