Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Curranm on January 25, 2018, 08:55:09 pm
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OK, SO i have a new two channel build that I am trying to get the hoffman relay switch to work in. everything is wired properly EXCEPT for the relay between the two channels. IF I wire the amp up for the clean channel or the distortion channel things are wonderful. BUT I am getting bleed through when I wire the two volume controls to the separate sides of the relay and out to the FX loop input. HOW would I wire this beast up to get me the channel switching with no bleed through? I am feeding the clean stage off of the 1Va buffer coupling cap, BUT I can wire this thing how ever I want, its my amp................. :)
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Do you have a drawing to show us?
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here you go, sorry I was at work all day
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well I have tried a few other ideas with the relay and I am failing due to my lack of knowledge. grrrrr
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here is another try with a fail. more detail schematic and relay in the middle
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RAGE failure! damn it I have re-wired this darn thing so many times my head is spinning. here are pix. from schematic to reality I am screwing something up. the relay is not switching at all right now so I don't know what that means........
the red wire is feeding 5vDC to the relay board Pin 16.
pin 1 is going to the TIP of the FTSW jack.
pin 13 is coming off of the coupling cap of V1.
Pin 4 is feeding into the FX loop input.
Pin 11 is coming from the gain control of the distortion channel and the 470K/500pf, 470K/1000pf switch set up.
Pin 6 is feeding distortion volume control.
Pin 8 is coming from the EQ input of the clean channel.
Pin 9 is feeding the clean volume control.
the ground wire from the power board is connected to the non switching ground of the ftsw jack
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did a little battery switching test on the relay, and it is not switching. I do not hear a physical click when I hook up a little 9v to the diode. is there a way to test for a bad relay?
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With a relay that small you may not be able to hear it click. Try this... Use a medium size screwdriver. Hold the tip of the screwdriver firmly on the body of the relay. Put your ear firmly on the end of the handle. Operate the relay. Can you hear it now?
To test the relay, make sure you have +5vdc across the diode when energized. Positive will be on the cathode of the diode. Also, measure the resistance of the relay coil. Should be 125Ω.
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You "can" check the relay in-circuit. "Closed contact" should be under 1 Ohm. "Open contact" will really be whatever is connected to the relay, but here it is all high resistance (if that pot is not on zero). Oh, the amp will buzz/squeal with ohmmeter leads on high-gain points, use a dummy load or long wires to the speaker on your neighbor's land.
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Curranm - I see a few potential issues:
* Not sure why you're using a 9v battery to test the relay - are you no longer getting 5V from your supply board? That's the first bit to get working again
* Assuming your 5v supply is ok, remove the relay and check for connectivity between the supply connections on the relay board and the pins (i.e. pos with pin 16 and neg with 1) and test the supply connections with your on/off switch to make sure that's working
* If that checks out, you may have damaged your relay. They are sensitive to excessive heat and looks like you did some soldering with it installed (melted plastic on the relay). May be too late for this one but in future be sure to remove the relay before soldering - I learned that lesson the hard way myself
* Another suggestion for future - install the turrets vs soldering directly to the eyelets. Looks like you may have some excess flux and stuff that could be problematic. The turrets will help with your wired connections and you won't have solder on the board. Doug will do that for you for couple bucks if you don't have turret press.
Once you get your switching diagnosed and working again, you'll need to address your bleed over issue, and my solution would require two relays. You'll need a dedicated relay for the volume feeds to your FX. The one side (pins 4-8) leave as is, but pin 13 will go to ground, and you'll run wires from 6 to 9, and from 8 to 11. I usually wire these underneath the relay board. That way you'll ground the signal from the "off" channel so it won't bleed over to the "on" channel. Second relay you'd then only need half of it to switch V1 per your schematic. May be other solutions but that works great for my builds.