Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Solid State => Topic started by: jojokeo on May 11, 2015, 11:52:23 am
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One can have a relay that does switch and has the correct voltage and that relay can still induce a significant amount of hum. I have had that happen! That is the reason I suggested bypassing the relay switch as illustrated in the previous schematic about trouble shooting.
Is your jack for the footswitch isolated from the chassis?
T - what did you find was the cause of relay hum in your experience? What did you do to correct it?
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It actually has happened twice.
First time it was sloppy wiring, poor grounding scheme, layout & not using enough shielded wiring. Even after all that, it was not nearly as quiet as Doug's relay system. it was a single relay & always had some hum. Considerably more then I have using Doug's with 3 relays.
2nd time, it was the same company as the first time (not Doug's) & it was a multi-relay system. I tried all kinds of fixes and then gave up, removed the relay system and installed relay parts that I got from Doug. That resolved it. And this was prior to Doug's current relay system which is GREAT and worth the cost, IMO.
With respect, Tubenit
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Perfect, thanks! So the relays being between the turret board and pots is not an issue then? And make sure to use Doug's relays and power supply scheme? I'm going to be inserting a couple relays into existing designs - one a 'Wreck express and the other one of my past builds "DumbleWatt".
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For switching, do you simply use a 1/4" jack type DPDT or whatever? Do you have them set up for both toggle on the panel and footswitch both? Have you incorporated LEDs at all?
It was 5 years ago almost to the day where we began our Dumblish first forays at about the same time. Fresh after reading Designing Tube Preamps... I went in a direction trying Merlin's idea of alternately cascading hot & cold biased stages into each other then into an 18watt PA section. The only Dumbley thing about it was switching in the cascaded stages deal and the front end was pseudo tweedy. It was originally called BumbleWatt.
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Lots and Lots of relay and relay jack info here including photos and schematics, etc ............
http://el34world.com/Forum/index.php?topic=14348.0 (http://el34world.com/Forum/index.php?topic=14348.0)
When I have used two relay switches, I use both toggle switches and a stereo jack that is insulated from the chassis. The foot switch I use has LED lights already built into it. Last build, had the foot switch jack on the back and the mini-toggles on the front panel.
With respect, Tubenit
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Thanks T! In just skimming things it appears that the big lesson is to not ground the relay system power supply, footswitch connection(s), and even LEDs. It all has to be contained in it's own little ground system away and seperate from the amp's grounding system!???
(I definitely don't want to chance blowing a $100+ PT)