Is the AC cord plugged in on the same side of the line as the preamp and front end of the system? |
I don't think the ground is the problem.
Here is my theory:
Right now I think there might be DC on the line. DC can cause a toroidal transformer to saturate. Now what if its not very much DC, less maybe only about .3 to .5 volts...
In standby the amp might be OK. At full power the toroid saturates and the resulting inrush blows the breaker.
By adding the power cord there is enough voltage drop and resulting reduction in current inrush that things hold up.
In other places tried there is no DC on the line.
DC is a good culprit as we are talking about multiple dwellings in a single building.
There are 3 solutions I can think of:
1) have a current inrush limiter installed ()this might allow the amp to power up but I bet the transformer will be mechanically noisy)
2) have a DC blocker circuit installed (a rectifier bridge bypassed with electrolytic caps of the right value) We are talking about $15-$20 worth of parts. This is something I would have Cary do.
3) use a DC blocker with the circuitry of 2) in it.
You could test this theory by getting the DC Blocker of 3) and seeing if it sorts things out. If it does, I would have the amp modified by Cary to have these parts installed. Its an easy fix. |
Jea48, thanks for that note. In that case, I suspect that the DC blocker circuit has developed a malfunction. It would not be missed if the AC line were clean.
Its easy enough to test for. There is someone on this forum who makes AC extension outlets that have the DC Blocker built in. Just use one of those and you would know if that's what it is.
The lack of AC grounds in the wiring is disturbing, but it should not cause any troubles with the amp. |
No. I mean the signal input of the amp. |
Hm. You could certainly try it. Anything that might drop the voltage a little would probably sort it out. We have ascertained that the issue relates to overpowering the breaker due to something to do with the incoming AC power.
It happens on any outlet in the area; its not related to which side of the line or whether there is leakage from another component. Its entirely to do with the power transformer and the incoming power.
I doubt that its a surge thing- it happens consistently. A surge would only show up occasionally. So I'm going with 'no, that won't help' in this case. Measured line voltage is fine so its not an over-voltage condition of any kind.
This is all assuming that the measurements are correct and the behaviors accurately reported!
Another possibility is a shorted current inrush limiter. A third possibility is that the breaker has developed some residual magnetism and no longer breaks at the right point- IOW its become too sensitive. Simple replacement of the breaker would solve that. Any one of these problems could be such that it would not show up elsewhere due to variables like line voltage and such.
For example if Cary put the unit on a variac when they tested it, the variac may well have functioned to limit the surge current enough so it was no worries. At the other field location, there could have been something with the wiring or the unit was plugged into a power strip with other gear already on it. Power strips only have one power cord, so there could have been a temporary voltage drop, eliminating the problem.
I like to go for the simplest answer as the best one so my thinking right now is the breaker itself is defective. |
Sailcappy, I am really sold on the idea that the breaker is at fault. Have you been using it as a power switch? Or is the amplifier designed with it being the power switch?
Either way what I would do is replace the breaker... troubleshooting from a distance is always tricky, but we can be very sure that the solution has to do with the inrush current on the power transformers. |
Sailcappy, what happens if you short the input of the amp? Does it still do it? |
All the lengthy power cord is doing is dropping the AC voltage a little over its length. But I had understood that you had checked the AC voltage and it was OK. If the voltage was high then I could see the power cord helping out. That is why I suggested other things. Any chance of getting another AC voltage measurement at the wall socket? |
Switch mode supply??! I figured this thing had a big toroid...
Clearly the current limiting of the cord is having an effect.
So what is the outlet voltage while the amp and the cord are doing their thing? Bet it does not drop as much.
Based on that I would replace the AC receptacle, and make sure the screws on the receptacle are tight!
It would be a really good idea to see how this amp behaves in another apartment in the same building...
I do not think the amp is at fault if it really is SMPS powered.
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If it has large toroids, there is no SMPS. A SWPS might look like an aluminum box inside the unit, but certainly would not sport any toroids, especially large ones.
So the theories around SMPS are not.
I still think its a good idea to try this amp in another place in the same building. Also, it would be a good idea to get the AC voltage readings from the wall when the amp is plugged directly into the wall, and also what the outlet voltage is when the amp energizes at the other end of the power cord. I'm thinking this might have to do with current inrush caused by an excessive dip in the line voltage at turn on, due to saturation in the core of the transformer caused by the dip itself when the transformer energizes.
If that is the case, it may be that replacing the outlet could sort it out.... |
Sailcappy, has anyone recommended installing a current inrush limiter? This is a device (goes inside the amplifier) that when cold has a high resistance and as it heats up, goes to a low resistance. They come in different current ratings; for example in our MA-1 we use CL-30s, two of them, which limit inrush current in the two AC circuits in the amp. They prevent the power switches from being damaged, and there are MA-1s out there made back in 1987 that still have good power switches, so these things work.
In your case they would give the power supplies a little more time to charge and obviously could keep the inrush current to an acceptable level. I think this would work much better than a long power cord, and if there are no inrush limiters in the unit, there totally should be... |
If it was harmonics, no electrician can help you. The power company can though.
Its the 5th harmonic (300Hz) that causes most of the troubles and it can cause transformer cores to become noisy. Not heard of it actually causing an amplifier to shut down, if so the problem is profound and the power company should consider upgrading the local transformer that feeds the building. |
