I'll be using 2 VRDNs to power a BA2018 preamp. Each VRDN will have its own 230V 15VA transformer with 2x18V secondaries.
I have seen people sizing fuses by dividing transformer VA by mains voltage, and then selecting a fuse of the same or next highest value. 15VA/230V gives me ~65mA.
* Closest values offered by Mouser are 63mA or 80mA. Round up to 80mA?
* Slow, normal or fast blow for a preamp?
* Is one fuse per transformer recommended? Or can I still be safe with the transformers sharing the fuse(s) in the IEC inlet?
Muchisimas gracias in advance!
I have seen people sizing fuses by dividing transformer VA by mains voltage, and then selecting a fuse of the same or next highest value. 15VA/230V gives me ~65mA.
* Closest values offered by Mouser are 63mA or 80mA. Round up to 80mA?
* Slow, normal or fast blow for a preamp?
* Is one fuse per transformer recommended? Or can I still be safe with the transformers sharing the fuse(s) in the IEC inlet?
Muchisimas gracias in advance!
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Hi Booja30
You downscaled your transformer-specs, may I ask what led you to this?
(I‘m asking because I believe I overshot with my (two) 2 x 18V 50VA but haven’t yet verified ...)
Hmm. I found the post you're referring to, and that was a typo apparently! I definitely have 15VA transformers.
I bought these 15VA transformers assuming they'd be ok after reading about 6L6 powering his BA2018 with a wall wart and/or some other tiny PSU he had used. I really don't know what I'm doing and I'm usually following someone else's example. Don't follow my example!
I worried about my 15VA transformers being too small when I read what you had bought!
I've only soldered the PCBs (VRDNs and preamp) and haven't done any hookup or testing yet, so I really can't say how it will work out.
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Thanks for the encouragement! Based on my previous build I predict at least one more parts order in my future to finish this. Fingers crossed!
Is yours progressing ok?
Connecting the linestage... (Wayne’s BA-18, parts installed, I hope nothing else went down.)
I hesitate a bit to shoot it on.
1 channel was fine though, and this time I checked the connections twice.
But about all those „many grounds“ [emoji1], do I need to connect both channels with both halves, right? (That is 2 ground connections per linestage-channel)
Thanks again
Smokin‘ear
I hesitate a bit to shoot it on.
1 channel was fine though, and this time I checked the connections twice.
But about all those „many grounds“ [emoji1], do I need to connect both channels with both halves, right? (That is 2 ground connections per linestage-channel)
Thanks again
Smokin‘ear
Here's a tip - the locating pins on the heatsinks can be moved so that they go to the edge of the heatsink and gives you a few millimeters of additional clearance, enough to get 'normal' screws to barely not touch but you'll still want to insulate with kapton tape.
Second observation - you most definitely know when you are soldering something that connects to the massive ground plane. It just sucks all the heat you can get into it and still requires patience before the solder flows. I had my iron up to about 730F and it was still not quite hot enough for some pads. I was using 63/37 Sn/Pb flux core solder.
Lastly, any chance I might have overheated something (diode maybe?) because with a 18V AC (50VA) dual secondary, I can only get -15.0V on the negative side (an minimum of -10.5V or so) with the 2K pot maxed out. The positive rail doesn't seem to have this problem and I can easily adjust it to over 19V. I tried again with a 21V AC source and can only get -15.5V.
It's late and I'm tired so will poke at it tomorrow but fortunately all the resistors and diodes are easily probed.
Thanks to Mark Johnson and Elvee for this one!
Second observation - you most definitely know when you are soldering something that connects to the massive ground plane. It just sucks all the heat you can get into it and still requires patience before the solder flows. I had my iron up to about 730F and it was still not quite hot enough for some pads. I was using 63/37 Sn/Pb flux core solder.
Lastly, any chance I might have overheated something (diode maybe?) because with a 18V AC (50VA) dual secondary, I can only get -15.0V on the negative side (an minimum of -10.5V or so) with the 2K pot maxed out. The positive rail doesn't seem to have this problem and I can easily adjust it to over 19V. I tried again with a 21V AC source and can only get -15.5V.
It's late and I'm tired so will poke at it tomorrow but fortunately all the resistors and diodes are easily probed.
Thanks to Mark Johnson and Elvee for this one!
And just to be sure, I followed mark hint on the pub: „many grounds“...
Darn auto-correction! I meant to write
„And just to be sure, I followed Mark‘s hint on the _*PCB*_: „many grounds“...
“@myleftear
I think it's pretty common to offer additional ground connections for convenience, but I don't think it's necessarily a hint that you need to find uses for them.
My plan is to have each VRDN assigned to strictly one half of the BA2018 board. So the input side of the VRDN would have transformer secondaries connected. The output side would have OUT+, GND, and OUT- connected to the 3 corresponding inputs on the preamp board. In addition, one of the spare GND terminals would connect to a CL60 (or similar) NTC to provide a 'floating' ground to the chassis in case of a fault.
I don't think there is any need to connect each VRDN's GND to both channels of the preamp. If you wind up with hum it might be something to experiment with, but otherwise I think it is ok to treat them as fully independent. In other words, aside from the selector and volume pot, everything else could theoretically be installed in separate chassis.
Apologies if I misunderstood the question. And you know I'm not an expert, so I would appreciate feedback from others on what I've written.
I think it's pretty common to offer additional ground connections for convenience, but I don't think it's necessarily a hint that you need to find uses for them.
My plan is to have each VRDN assigned to strictly one half of the BA2018 board. So the input side of the VRDN would have transformer secondaries connected. The output side would have OUT+, GND, and OUT- connected to the 3 corresponding inputs on the preamp board. In addition, one of the spare GND terminals would connect to a CL60 (or similar) NTC to provide a 'floating' ground to the chassis in case of a fault.
I don't think there is any need to connect each VRDN's GND to both channels of the preamp. If you wind up with hum it might be something to experiment with, but otherwise I think it is ok to treat them as fully independent. In other words, aside from the selector and volume pot, everything else could theoretically be installed in separate chassis.
Apologies if I misunderstood the question. And you know I'm not an expert
, so I would appreciate feedback from others on what I've written.
I'm going to use my VDRN (single) to power my Wayne's BA linestage. I'm pretty comfortable soldering, been doing hobby electronics for 3-4 years, but the jump to mains power has me concerned.
I have some familiarity with the standard general advice (check everything twice, solder, then check it twice more; check for stray grounds; check for loose wires which could become stray grounds; check that + and - show resistance to ground and to each other, test with low power/dim bulb before mains)
I'd appreciate a list of ways I could kill myself with this, so I can avoid such mistakes.
I notice that the power supplies in my computers usually have a safety cage around them, I don't see this as much in the photos on this forum.
Is there a "best practices" doc or resource I could consult?
I have some familiarity with the standard general advice (check everything twice, solder, then check it twice more; check for stray grounds; check for loose wires which could become stray grounds; check that + and - show resistance to ground and to each other, test with low power/dim bulb before mains)
I'd appreciate a list of ways I could kill myself with this, so I can avoid such mistakes.
I notice that the power supplies in my computers usually have a safety cage around them, I don't see this as much in the photos on this forum.
Is there a "best practices" doc or resource I could consult?
The "safety cage" on computers is to knock down stray and generated EMI by the switching power supply, usually operating up in the MHz range. The shield isn't very effective at 50-60 Hz.
I think you have a very good grasp on steps to take not to kill yourself. Main thing, don't touch anything when it's plugged in that you don't know what kind of voltage is on it.
For the VRDN I was able to find a 15 watt appliance bulb to use in my bulb tester first. This will drastically limit current flow to 125 milliamps if you are using 120 volts. After I get it to work with that, then I move upwards in bulb wattage. It will light up the bulb with this low of wattage bulb.
Be sure and wear safety glasses when you power it up the first time, just in case you got a capacitor in backwards, they can and do blow up. Usually starts with a hissing noise, if you hear that shut off power and check caps, replace any not installed correctly.
Last thing, be sure you have an easy way to shut the power off, if you don't touch it, it can't electrocute you.
This one is very good, covers a lot of ground, touches on much of what you are asking about -
Building a Gainclone chip amp power supply.
