Relay Power?

[raveonstevie]

No need to change that cap if the relays are working fine.

Also, if in not mistaken, the regulator's center leg is grounded. Left leg is input. Right leg is output.

Right?

Yes. I posted link to a photo. Can’t seem to post photos correctly.

Center lug is grounded and the output is connected to smaller electrolytic to ground.

https://imgur.com/gallery/WXxZpu8

[martin manning]

My VR is a 7805. Apparently it can regulate more than the 7.5 volts it’s rated for. My relays are switching fine. My capacitor is 1000 uf, 25 volts. I see Hoffman’s board uses a 4700 uf. Might have to change that too. There’s also a 100 uf, 100v electrolytic with negative to chassis and positive to the negative terminal of regulator.

I now have 16 volts ac going to bridge, 15 dc out, 5 v dc coming off of center lug of regulator.

A typical 7805 can accept as much as 25VDC at the input, but needs at least 7VDC to function properly. With no current draw at 6.3VAC you should get 7.5VDC at the output of the bridge rectifier. With current draw, you may not have enough voltage, but give it a try. Your transformer may have higher than 6.3VAC output at the low current demand of the relays. You could also get a low drop-out regulator, which might only require 6VDC input.

[raveonstevie]

My VR is a 7805. Apparently it can regulate more than the 7.5 volts it’s rated for. My relays are switching fine. My capacitor is 1000 uf, 25 volts. I see Hoffman’s board uses a 4700 uf. Might have to change that too. There’s also a 100 uf, 100v electrolytic with negative to chassis and positive to the negative terminal of regulator.

I now have 16 volts ac going to bridge, 15 dc out, 5 v dc coming off of center lug of regulator.

A typical 7805 can accept as much as 25VDC at the input, but needs at least 7VDC to function properly. With no current draw at 6.3VAC you should get 7.5VDC at the output of the bridge rectifier. With current draw, you may not have enough voltage, but give it a try. Your transformer may have higher than 6.3VAC output at the low current demand of the relays. You could also get a low drop-out regulator, which might only require 6VDC input.

Okay. Thanks

Would there be an advantage to using the new trans for heaters and the power transformer’s 6.3 for relays? Could this eliminate any hum since the heaters wouldn’t be connected to the power transformer, which powers everything else? I’d have to check that the new trans can power the heaters though.

New trans should be here soon. I’ll be installing it immediately.

[didit]

My VR is a 7805. Apparently it can regulate more than the 7.5 volts it’s rated for. My relays are switching fine. My capacitor is 1000 uf, 25 volts. I see Hoffman’s board uses a 4700 uf. Might have to change that too. There’s also a 100 uf, 100v electrolytic with negative to chassis and positive to the negative terminal of regulator.

I now have 16 volts ac going to bridge, 15 dc out, 5 v dc coming off of center lug of regulator.

A typical 7805 can accept as much as 25VDC at the input, but needs at least 7VDC to function properly. With no current draw at 6.3VAC you should get 7.5VDC at the output of the bridge rectifier. With current draw, you may not have enough voltage, but give it a try. Your transformer may have higher than 6.3VAC output at the low current demand of the relays. You could also get a low drop-out regulator, which might only require 6VDC input.

Several newer designs available for pin-compatible 78xx series using switch-mode circuits. Included some samples on my last Digikey order of RECOM 7812 specifically for relay power in upcoming builds.

https://recom-power.com/en/products/swi ... 1.0.html?4

Benefits are better efficiency, particularly at high input voltages, so lower dissipation etc ...

Best .. Ian

[martin manning]

Several newer designs available for pin-compatible 78xx series using switch-mode circuits. Included some samples on my last Digikey order of RECOM 7812 specifically for relay power in upcoming builds.

https://recom-power.com/en/products/swi ... 1.0.html?4

Benefits are better efficiency, particularly at high input voltages, so lower dissipation etc ...

Interesting, Ian, thanks for sharing. Still need 6.5V input for a 5V output, so may not work with 6.3VAC source, where a LDO 7805 probably would. Don't know if SMPS HF noise would be an issue or not.

Would there be an advantage to using the new trans for heaters and the power transformer’s 6.3 for relays? Could this eliminate any hum since the heaters wouldn’t be connected to the power transformer, which powers everything else? I’d have to check that the new trans can power the heaters though.New trans should be here soon. I’ll be installing it immediately.

No. I would try temporarily connecting your new transformer to the bridge rectifier (disconnect the old one first, of course), and measure input and output voltages with full load (All relays energized). If the regulator can provide 5VDC at 0V AC you are fine. If not, then I would replace the bridge rectifier with a doubler circuit on a terminal strip. In your case, you could leave the 1000uF cap in place and just add two diodes and another 1000uF cap, or take the old 1000uF out and use two new 1000uF 25V radials, which will be pretty small.

[R.G.]

Here's a tangent idea for relays in amps with essentially no additional power supply required.

OK, you're going to have to generate some additional DC, but it's super trivial.
Make a little 5Vdc. Use some circuitry to >detect< footswitch operation, not just use it to turn on/off relay power. Use submini latching relays. Use some more circuitry to take the sensed footswitch operation, and whack the latching relays into operating, then turn the coil power off. Use a resistor and capacitor to gradually store up and then hold enough of a charge to whack the relay coils to make them turn over.

I fully realize that to a dyed-in-the-wool, point-to-point-wiring kind of amp-guy, this sounds like silicon hell. But honestly, it will make that relay stuff able to operate from the most trivial of power feeds from rectified heaters. I did this kind of thing for my day job to run latching relays for bypass switching for 9V battery powered pedals. Average battery power drain was the same before and after the relay conversion, meaning the LED indicators were still the biggest power drain.

I can flesh this out if anyone is interested. If everyone is horrified by the mention of circuitry, I'll let it lapse.

[dorrisant]

Do tell. It's always better to find other ways around problems.

[R.G.]

I spent a few moments sketching this out. My immediate thought was to do it with a microcontroller; a $0.75 14 pin chip could maybe do four footswitches and the corresponding latching relays in the one chip. But that's programming (albeit in BASIC, and trivial) and so I decided to see if I could do it in CMOS and MML (Mickey Mouse Logic) for those who avoid programming. Turns out, I can.

The foot switches are probably latching, so they switch on with one press, off with the next. There are a few single coil latching relays that can work directly from this with a capacitor, resistors, diode, etc. I don't trust that much. So I did a simple circuit to detect a foot switch change in either direction. One XOR gate with one input fed from the switch and the other input fed through a resistor and cap from the switch will generate a pulse from each switch transition. The pulses will all be about the same width.
I took this "Hey! Something happened!" pulse and ran it into a toggle flipflop (half a CD4013). The flipflop obligingly changed state exactly once for each switch flip, The 4013 has two outputs, opposite in phase. So when one is high, the other is low. So one is "You relay, you be on now." and the other is "You relay, you be Off now." Great for non-latching relays. But we want to only power the coils for a short time when the footswitch changes. I messed with the RC on the input XOR to get its "something changed now" pulse to be 50mS long. And I fed the output of the flipflop and the "something changed now" pulse into an AND gate. The output of the AND gate is a pulse high (to 5V that is) for only 50mS on every other input switch change. Another AND gate on the other output phase gets one pulse out for 50mS. These pulses are the right logical enables for the opposing coils on a two coil latching relay. They go right into the base/gate of a darlington or MOSFET to actually run the coils.
That's for one footswitch. It uses up 1/4 of a 16 pin XOR chip, half of a CD4013, and half of a quad AND gate chip. The practical thing to do is to use the remaining parts to make a second footswitch-relay-latcher. So three 14-16 pin ICs make the gating/control logic for two footswitches, with two XOR gates left over. Add two more ICs and you get four footswitch controllers with five 14-16 pin ICs.
This is all CMOS, so the logic itself pulls microamperes. You could run it all from a zener diode and resistor; of course, a TO92 5V regulator works too. The outputs are MOSFET or darlington pulls to ground. This can be run from whatever rectified DC you make the 5V from, without regulating. Especially since you're going to put a resistor and an electro cap to slowly charge up the supply for flipping relays. This means that there are no big pulses pulled out of the DC for the thing at all, only a second or so to recharge the bulk caps for the relay coils.
I have a little more work to do on it, but it runs fine in the circuit simulator, just like the earlier version I did. It's feasible.

[gktamps]

Very interesting!

[didit]

Hello --

Several newer designs available for pin-compatible 78xx series using switch-mode circuits. Included some samples on my last Digikey order of RECOM 7812 specifically for relay power in upcoming builds.

https://recom-power.com/en/products/swi ... 1.0.html?4

Benefits are better efficiency, particularly at high input voltages, so lower dissipation etc ...

Interesting, Ian, thanks for sharing. Still need 6.5V input for a 5V output, so may not work with 6.3VAC source, where a LDO 7805 probably would. Don't know if SMPS HF noise would be an issue or not.

Yep, SMPS reputation for spraying HF EMI around is cause for concern. My limited experience with recent products is almost entirely positive. Certainly I'll be testing before putting any into a 100+ hour amp build project. The broad application for point-of-use design in low voltage high current digital (e.g., <2V @ 50A is not uncommon) has upped the game on a few fronts, including well tested canned solutions with clean EM and various newer diodes with excellent specs for low Vf. Diodes with less than half the typical voltage drop, for example venerable IN400x, are cheap and readily available. Propose with careful component selections one can safely squeeze >7V from nominal 6.3VAC so long as loading is sensibly and comfortably below true transformer secondary current specs.

Designing for power at a higher voltage results in lower current, which helps all around -- hence adopting 12VDC any relays, and similarly generally when fussing with DC heaters.

I'm now taking some inspiration from R.G. with his latching relay approach too. Will watch that with interest.

Best .. Ian

[raveonstevie]

Okay. It’s working. I got sidetracked yesterday. Had to change an alternator. Not in my amp. My amp doesn’t have an alternator.

I might post a sketch or photo later. Right now I’m just relieved. Will be really cool to fit the chassis into the cab right. After I finish tweaking. Love the amp. Sounds awesome. About to the tackle volume loss with PAB on overdrive.

Thanks for your help. I’ll go back to read the new fangled way of switching in a bit. I’m definitely open to it.

[raveonstevie]

I broke this little relay. Guy told me he got it at Jameco. Is jameco not in business? I haven’t searched Mouser or Digikey yet. Anyone know where I can find these? Thanks

[img] https://i.imgur.com/eG6V8Mn.jpg[\img]

https://i.imgur.com/eG6V8Mn.jpg

[T Wilcox]

Its just a 5vdc coil mini relay. I think Omron would be the popular brand which you can get for $8 on amazon or get a 10 pack for $12 of these....
https://www.amazon.com/Electrical-Buddy ... NrPXRydWU=
Ive been using these with no problems

Todd

[dorrisant]

I have some.

[raveonstevie]

Thanks. I don’t need one yet. I’ve got it going with clean/dirty switch and PAB.

I guess my EQ is the “classic” and I find it kind of odd. Unless my circuit’s wrong but I’ve checked it.

I only have one guitar right now - Epiphone Dot with Sheptone pickups (very bright). Right now, I like the EQ set with bass and mids all the way up and treble on about one. Kind of weird but I love it. I have to find out how my amp reacts to other guitars though. Might be getting a Strat soon.