Nelson Pass Amp Camp Amp #1 questions

[MrRadish]

Hi all, I hope this is the right place to ask this. I bought a secondhand DIY Camp Amp #1 a while ago and recently tried using linear power supplies with it. I'm getting some odd results though and would like to run this past those of you who actually know what you're doing with electronics ('cos I sure don't). This is just plugging stuff in, no actual DIY.

1. Running with the original (19v 4.7A) SMPS supplies the amp sounds great and I have no issues.
2. When I plug both linear supplies in (Maplin test bench supplies with front meters) turning up the voltage on one also turns up the voltage on the other. If I reverse the wires on both the same thing happens. If I alternate so red to black on one and red to red on the other the ammeter hits the end stop hard and is presumably a short (yes, I actually tried that...)
3. If I just have one PSU switched on or plugged in then both channels play normally. The same is true when using the SMPS.
4. If I run the LPSU at 12v the power consumption is about 200mA and everything works. If I turn the voltage up towards 19v the ammeter start to run away ahead of me and hits the end stop (3A). I switch it off at that point so don't know what happens next.
5. Using one or both SMPS the power consumption according to my AC regenerator doesn't change: it's pretty consistently 57 watts above that for my sources, with a little more after first switch on.
6. My first experiment with the LPSU had connectors with metal ends. I've now switched to connectors with plastic ends but I get the same results.

My questions:
Is it safe to have two PSU plugged in and switched on at the same time. It's obviously worked fine for at least three owners using the SMPS, so I'm asking theoretically. I think the amp sounds a little weaker with one, but I may be imagining it.
Is it safe to run the amp at 12v, or will that damage anything?
How many amps should the amp be fed at 19v if running from one supply? I have a 19v LPSU that can put out 5 or 6 amps I believe, but I'm not willing to try it unless that should be fine (it cost more than the Maplin supplies).

Any comments or abuse welcome. I don't expect a warranty with a DIY amp so I'm not bothered (and being able to run it off one PSU is actually a bonus), I just want to make sure it's electrically safe.

[Barry]

Hi all, I hope this is the right place to ask this. I bought a secondhand DIY Camp Amp #1 a while ago and recently tried using linear power supplies with it. I'm getting some odd results though and would like to run this past those of you who actually know what you're doing with electronics ('cos I sure don't). This is just plugging stuff in, no actual DIY.

1. Running with the original (19v 4.7A) SMPS supplies the amp sounds great and I have no issues.
2. When I plug both linear supplies in (Maplin test bench supplies with front meters) turning up the voltage on one also turns up the voltage on the other. If I reverse the wires on both the same thing happens. If I alternate so red to black on one and red to red on the other the ammeter hits the end stop hard and is presumably a short (yes, I actually tried that...)
3. If I just have one PSU switched on or plugged in then both channels play normally. The same is true when using the SMPS.
4. If I run the LPSU at 12v the power consumption is about 200mA and everything works. If I turn the voltage up towards 19v the ammeter start to run away ahead of me and hits the end stop (3A). I switch it off at that point so don't know what happens next.
5. Using one or both SMPS the power consumption according to my AC regenerator doesn't change: it's pretty consistently 57 watts above that for my sources, with a little more after first switch on.
6. My first experiment with the LPSU had connectors with metal ends. I've now switched to connectors with plastic ends but I get the same results.

My questions:
Is it safe to have two PSU plugged in and switched on at the same time. It's obviously worked fine for at least three owners using the SMPS, so I'm asking theoretically. I think the amp sounds a little weaker with one, but I may be imagining it.
Is it safe to run the amp at 12v, or will that damage anything?
How many amps should the amp be fed at 19v if running from one supply? I have a 19v LPSU that can put out 5 or 6 amps I believe, but I'm not willing to try it unless that should be fine (it cost more than the Maplin supplies).

Any comments or abuse welcome. I don't expect a warranty with a DIY amp so I'm not bothered (and being able to run it off one PSU is actually a bonus), I just want to make sure it's electrically safe.

Does your linear power supply have sufficient capacity? You say when using a SMPS your AC regenerator shows a power consumption of 57W. With a supply voltage of 19V, a power consumption of 57W implies a current of exactly 3A - the limit of the ammeter scale on the LPSU.

[MrRadish]

Does your linear power supply have sufficient capacity? You say when using a SMPS your AC regenerator shows a power consumption of 57W. With a supply voltage of 19V, a power consumption of 57W implies a current of exactly 3A - the limit of the ammeter scale on the LPSU.

I don't believe the Maplin ones do, I think they're rated up to 2.5A (although I'm not sure at what Voltage that was listed). I was only using those as I had two identical ones, so I'll switch to something else if it's just 3A overall. Does using two PSU (presumably in parallel) double the current output so they provide 1.5A each, or does it not work like that?

[Barry]

I don't believe the Maplin ones do, I think they're rated up to 2.5A (although I'm not sure at what Voltage that was listed). I was only using those as I had two identical ones, so I'll switch to something else if it's just 3A overall. Does using two PSU (presumably in parallel) double the current output so they provide 1.5A each, or does it not work like that?

No, I don't think it is quite as simple as that. Perhaps a member who is also a power supply expert can help?

[struth]

No its not that simple, but can be done. Jez might know the correct method.. i would be inclined to just get a bigger linear supply

[Arkless Electronics]

It sounds as if you will need a bigger power supply... but just one! Trying to put voltage sources in parallel will usually end in tears... Get a single supply of 6A or more. Or are you trying to run it with a PSU per channel? This should work...
Don't short power supplies etc like you did! If using PSU's without short and overload protection you would have killed them instantly!!

[Arkless Electronics]

Oh and if there are 1000's of uF of caps already fitted in the amp as smoothing caps I would expect little difference from changing PSU's...

[MrRadish]

It sounds as if you will need a bigger power supply... but just one! Trying to put voltage sources in parallel will usually end in tears... Get a single supply of 6A or more. Or are you trying to run it with a PSU per channel? This should work...
Don't short power supplies etc like you did! If using PSU's without short and overload protection you would have killed them instantly!!

The Camp Amp is supposed to be dual mono with two PSU, but this one has been built into one chassis. That should be fine and they should still be dual mono, but clearly the PSU connectors are linked in some way (maybe at the power switch). The Maplin test bench supplies are pretty resilient (thankfully) but not quite powerful enough, so as we've worked out its 3A max I'm running it off a single HDPlex PSU instead. I'm not sure it's an improvement, but that may be because I've not used this DC cable before so I'll give it a while before deciding what to do next. The LPSU is slightly noisier through the speakers than the SMPS though, with the cheap SMPS being silent.

[Arkless Electronics]

Well obviously the DC cable is critical

There should be no noise from a good LPSU running correctly. If you know how to then separate the power connections in the amp so you you have two completely independent channels. The Maplins supplies should handle one channel each then.

[MrRadish]

Well obviously the DC cable is critical

There should be no noise from a good LPSU running correctly. If you know how to then separate the power connections in the amp so you you have two completely independent channels. The Maplins supplies should handle one channel each then.

I might be able to handle that, but I'll leave it running as it is for now. It's consuming 87 watts at the mains, which is to be expected being a linear supply, but I need to keep a check on how hot the PSU gets as it's pretty toasty right now.