Just picked up a Kenwood KR3090 that has the power switch issue; where the contacts wear out spoiling the switch.
On that note, I could actually hear mine arching lol
So just as a temp solution / test I've installed a normal / separate switch.
However am wondering if anyone has gone the route of installing a second relay for the mains, using the original power knob as it's switch.
The only relays I have are 12v and 24v I believe; am not sure if I need to add in a power supply just for the relay or if there is a power source of similar voltage already in the unit I could use.
Am sure you can tell by the question am not experienced with electronics; so any suggestions / alternative solutions are welcome 😀
and wow, for such a simple unit, it needs to be COMPLETELY disassembled to remove the switching mechanism....which includes GLUED in components. ugh...I guess not all vintage is a pleasure to work on lol
I just read that there is an unused part of the Mains power switch. Has anyone use it with success? Looks like a super easy swap from bottom contacts / switch to the top one.
Though am thinking ideally I use that second part of the original switch to engage a second, proper relay for the mains.
On that note, I could actually hear mine arching lol
So just as a temp solution / test I've installed a normal / separate switch.
However am wondering if anyone has gone the route of installing a second relay for the mains, using the original power knob as it's switch.
The only relays I have are 12v and 24v I believe; am not sure if I need to add in a power supply just for the relay or if there is a power source of similar voltage already in the unit I could use.
Am sure you can tell by the question am not experienced with electronics; so any suggestions / alternative solutions are welcome 😀
and wow, for such a simple unit, it needs to be COMPLETELY disassembled to remove the switching mechanism....which includes GLUED in components. ugh...I guess not all vintage is a pleasure to work on lol
I just read that there is an unused part of the Mains power switch. Has anyone use it with success? Looks like a super easy swap from bottom contacts / switch to the top one.
Though am thinking ideally I use that second part of the original switch to engage a second, proper relay for the mains.
I do it all the time to totally take the pressure off an unobtamium and ageing switch, not particularly for a mains operation, normally small signal from panel switches, but it's the exact same principle
Last edited:
am think is best route;
Am not sue if you're familiar with the unit or not; but when you do it do you just find a suitable power source all ready in the unit for the added relay?
That is the part that is holding me up; from my limited understanding / experience only thin I can think of is adding in a second power supply just for the added relay.
Am not sue if you're familiar with the unit or not; but when you do it do you just find a suitable power source all ready in the unit for the added relay?
That is the part that is holding me up; from my limited understanding / experience only thin I can think of is adding in a second power supply just for the added relay.
Yeah, research what supplies are there first , relays are available in lots of voltages, better to pick a low power version
Don’t forget your protection relay, and if you’re switching mains voltages with it, take every single precaution for safety - double heat shrink it and tie cables together to help strain relief.
If there’s no suitable supply you may have to use 78 series regulator to drop the chosen rail down closer to the relay
Don’t forget your protection relay, and if you’re switching mains voltages with it, take every single precaution for safety - double heat shrink it and tie cables together to help strain relief.
If there’s no suitable supply you may have to use 78 series regulator to drop the chosen rail down closer to the relay
Looks like there's room behind the back panel to add a switched+fused IEC mains inlet. It would mean cutting a suitable mounting hole, and then you can bypass the internal mains switch.
Ideas...
If there is an unused set of 'unknown' contacts and if it safe to do so then you could use those contacts to switch a Triac based switch. The switch contact would handle very little current but the switch construction must be suitable for mains voltages on those contacts. The contacts would have to be normal on/off and not a momentary action that only makes while the switch is being pressed.
The parts count is minimal, just the triac and an R/C snubber across it.
Nelson Pass used this approach in some of his designs such as the A75.
Just a possible idea.
If there is an unused set of 'unknown' contacts and if it safe to do so then you could use those contacts to switch a Triac based switch. The switch contact would handle very little current but the switch construction must be suitable for mains voltages on those contacts. The contacts would have to be normal on/off and not a momentary action that only makes while the switch is being pressed.
The parts count is minimal, just the triac and an R/C snubber across it.
Nelson Pass used this approach in some of his designs such as the A75.
Just a possible idea.
I meant protection diode in my earlier post, I can’t edit it now, not sure how it came out relay 😀
I've have a google for protection diode; I couldn't make sense of protection relay and was picturing that I may need two relay and what configuration it would be lol so thanks for the clarification / effort to correct typo.
Thank you so much for the suggestions, am going to try and go this route as it would leave the operation of the unit the same and looks to be a good learning project.
The relays I have pulled / in the used parts bin are from protection circuits of more modern amps.
This amp is only 40 watts TOTAL (20w a channel) so even with powering the unit on with speakers connected there is not much "pop"; that was just playing and seeing / learning. I don't intend to have the speaker and power switches independent just incase I forget power up / down two step sequence lol
will post follow ups since you all were so kind as to reply.
that said, appreciate is my first modifying / adding in a circuit project 🙂
(pulling power out of existing supplies in the unit kind of scares me, but would be super satisfying to accomplish)
Thank you so much for the suggestions, am going to try and go this route as it would leave the operation of the unit the same and looks to be a good learning project.
The relays I have pulled / in the used parts bin are from protection circuits of more modern amps.
This amp is only 40 watts TOTAL (20w a channel) so even with powering the unit on with speakers connected there is not much "pop"; that was just playing and seeing / learning. I don't intend to have the speaker and power switches independent just incase I forget power up / down two step sequence lol
will post follow ups since you all were so kind as to reply.
that said, appreciate is my first modifying / adding in a circuit project 🙂
(pulling power out of existing supplies in the unit kind of scares me, but would be super satisfying to accomplish)
Yes TON of room in the amp and back panel.
That is along the lines of initial thinking, however even though the amp is very low power (40 watt total I believe) I prefer the power on first, then speakers connected. That is the sequence of the original switch as well.
As best I can reasonably do would like it to be same sequence....that said am now thinking about the time to engage mains power if done through a relay; hopefully they're "fast".
You've got 33v rails in this , you could easily drive a 36v DC relay off that without any extra circuitry , just that protection diode to fit and Bob is your relative.
So take your relay supply straight off one of the large 6800uF reservoir caps (be careful to observe the right polarity whichever you choose)
So take your relay supply straight off one of the large 6800uF reservoir caps (be careful to observe the right polarity whichever you choose)
I think I'll look to pull that switch this evening. pretty sure I read people managed to do so without remove the whole assembly.
If I do get it out will post a pick of it's contacts...was surprised that I could actually hear the arching; so I envision a miniture mess of semi melted metal with multiple points of once fused / welded connections.
hmmm...this is turning into a great intro into electronics.
So I just read about triacs, and that they physically switch off at zero point of waveform and can be robust enough and still super small?! A mod suggestion am reading says the off power consumption is super low as well.
I think someone in this thread mentioned them as well.
am not to sure yet but seems one of those can be used and that means I don't need to power a relay / have concern for protection diode and all that. Sure there is no satisfying relay click but it seems a less mechanical way of switching.
So I just read about triacs, and that they physically switch off at zero point of waveform and can be robust enough and still super small?! A mod suggestion am reading says the off power consumption is super low as well.
I think someone in this thread mentioned them as well.
am not to sure yet but seems one of those can be used and that means I don't need to power a relay / have concern for protection diode and all that. Sure there is no satisfying relay click but it seems a less mechanical way of switching.
This is how Nelson does it. It is a classic triac configuration using a small switch for on/off. When off there is no power consumption as such apart from leakage. The snubber network across the triac will pass a tiny current and it is important that any caps are rated for continuous mains use. That usually means a "Class X" type of cap.
Safety Capacitors First: Class-X and Class-Y Capacitors - Technical Articles
Safety Capacitors First: Class-X and Class-Y Capacitors - Technical Articles
Attachments
I once fixed a switch contacts in a drier (part of the cycle program) with a TO-220 TRIAC and gate resistor ~150 Ohms. This took the current off the contacts and it never failed again. I didn't even heat sink it, just hung off the switch.
I obviously wasn't paying attention yesterday 🙄 , you obviously won't have the 33V rail if the unit is off 😀
I blame the belgian beer I had
I blame the belgian beer I had