dorrisant wrote: ↑Sat May 25, 2019 12:37 pmKeep in mind that the relays don’t need a conventional chassis ground, they can float.
That said, look at the Silver Jubilee and take notice of relay PS. That's one example, right under your nose.
You certainly dont have to do it this way but it has been done quietly in production amps... for years. Just sayin'.
Marshall couldn't be accused of over-engineering the Silver Jubilee relay supply... half-wave rectifier, no regulation, and minimal filtering. Luckily, relays aren't too fussy.
norburybrook wrote: ↑Sun May 26, 2019 9:04 amI would imagine you just need to rectify and filter it then send it through a voltage regulator.
Use a 5v regulator and relay, or use a voltage doubler like the regular dumble board and a 12v relay if you like...Or use the regular voltage doubler board and a 5v relay and regulator as those regulators will take up to 30V IIRC.
As the voltage drop increases, so does the need for heat sinking. I'd stick to a FWB for 5V and use a voltage doubler only for 12V. Since the relay supply is taken from the chassis ground-centered filament voltage, the negative side of the relay DC will be about 4V below chassis ground for the FWB, 8V (average) for the doubler. Relay supply grounds (including the regulator tab and the foot switch jack), must be isolated from the chassis. A plastic Cliff jack is fine for the foot switch, and I would isolate the relay supply from the foot switch enclosure too.
Pay attention to what Martin said about the grounding.
I'm not 100% sure about this but I think it might be to do with the fact the heater secondary has a center tap which of course is grounded.
For a High gain overdrive switching circuit.
IMO.You really want your relay supply regulated, well filtered and ground referenced. Using a separate winding (The way Dumble did)is the safest best and quietest way to go
We messed around with several different floating relay supplies off the filaments. some were better than others but they all added some noise with the coil energized. We eventually dropped it. Again IMO if your a DIY'er and want to do it in one of your amps and are aware of the noise issues it can cause as well as someone or something accidentally grounding the footswitch,go for it As a commercial builder, I would leave the filament supply isolated.
If you have no room for another transformer you could use the 5V rectifier tap into a voltage doubler filter it and regulate it down to about 8 V with a 5V relay would be IMO a better alternative Of course the amp would have to be converted to SS rectifier.
Just Sayin
Good Luck!
Here is a diagram posted by Andy.
Tony
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" The psychics on my bench is the same as Dumble'"
Regardless of whether you power the relays from a separate transformer, a dedicated winding on the PT, or the filament string, the circuit (be it a voltage doubler or a FWB) is the same. The difference is where you put the ground reference. If you are using the filament string, that choice has been made for you.
I think I would make up a small board with the circuit below (which is a marked-up snip from a 183 schematic), and try it with the filament string as the AC source. As I mentioned above, isolate the regulator tab and foot switch jacks from the chassis. Since the voltage drop is only a couple of volts, I doubt the regulator will need a heat sink, but you could attach a small U-shaped one. If it proves to be noisy, add a dedicated transformer and move the ground reference to the output.
I strongly recommend a 5V relay circuit and a FWB rectifier as shown, since a doubler will have large current spikes and much more ripple with respect to chassis ground. DC current draw is 40-50 mA per relay (30 mA coil plus LED), AC current draw about three times that, so two relays would be like adding another preamp tube as far as the filament winding is concerned.
Tony Dorris said he has derived relay power from the filament string many times, so I'm interested hearing about his approach.
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Is it a idea to use a dc converter?
That way you can keep the rectification with a floating ground reference. The dc converter has galvanic isolation so you can put a ground reference touching the chassis without hum issues.
erwin_ve wrote: ↑Mon May 27, 2019 12:47 pm
Is it a idea to use a dc converter?
That way you can keep the rectification with a floating ground reference. The dc converter has galvanic isolation so you can put a ground reference touching the chassis without hum issues.
Yes, that should work... If it proves necessary ;^)
erwin_ve wrote: ↑Mon May 27, 2019 12:47 pm
Is it a idea to use a dc converter?
That way you can keep the rectification with a floating ground reference. The dc converter has galvanic isolation so you can put a ground reference touching the chassis without hum issues.
Yes, that should work... If it proves necessary ;^)
Like this:
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Yes, it's pretty straight-forward, and a good idea. That converter is a bit larger than needed, and I would still try without it first. I don't think the 5V FWB circuit will have noise issues, and it isn't difficult to isolate the relay voltage, even using the standard ODS layout.
Thanks Martin and Erwin. I will give it a try first without the converter and if any issues I will upgrade. Thanks Martin for listing the part numbers, indeed super helpful.
As far as rectifier board Hoffman has some very narrow ones which will fit vertically on the side of my Deluxe chassis with enough lugs to make this happen so I will get it https://hoffmanamps.com/MyStore/catalog ... g_0737.jpg
It will be simple enough to get a couple of leads out of the pilot light heaters and right before the artificial CT ground resistors (as per Erwin schematic) and adding the vertical rectifier board (pic attached).
About the grounding, a question regarding isolating the footswitch (with washers): one side of my
Jack is currently ab763 tremolo (which won’t use a relay) and the one which is for the ab763 reverb will be replaced by the overdrive (which will use a relay). Any issues in having he jack not grounded as far as the tremolo is concerned?
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The AB763 tremolo circuit requires a grounded jack since the tremolo oscillator is enabled by providing a ground from that jack. I would not try to share the trem jack with an isolated relay control jack.
sluckey wrote: ↑Mon May 27, 2019 5:33 pm
The AB763 tremolo circuit requires a grounded jack since the tremolo oscillator is enabled by providing a ground from that jack. I would not try to share the trem jack with an isolated relay control jack.
Thanks Sluckey, it will be more complicated than I thought
So I will go ahead an add a second jack for the relay. I am thinking of the Overdrive switch and a PAB. Let me know in case the relay power will be enough for 2 different relays.
Now the question is shall I go Fender style with a stereo jack (isolated), or HAD style with all those pins. I assume I cannot LED power the foodswitch with the Fender style, correct, which probably will be downside of this approach.
norburybrook wrote: ↑Tue May 28, 2019 9:59 am
I'd go HAD style, it's only a 5 pin din which isn't that big. Also having LED's to show the on/off is invaluable with something like an OD stage.
M
Thanks Marcus, I have a spare one of those 5 pins and will go as per your advice. I will look up on how to build the pedal afterwards.
Of course the amp would have to be converted to SS rectifier.
