Amp Shutting Down, need help


I have a Cary 7.250 brand new amp that shuts down after 20 seconds in my NYC apartment. I have sent the unit back to Cary where it tests fine. I have tried the unit at my friend’s apartment and his place of work and it works fine. The unit is 100% in working order. After talking to many people I was told to attach a 50' extension cord and low and behold it worked.

The good news is that I have a dedicated 20amp circuit to this outlet. My voltage reads 118 volts and Cary said that is not a problem as the unit will work between 90 and 130 volts. I have tested for voltage on the negative lead to ground and there is no stray voltage. I have also tried the unit on other outlets in the apartment and the same problem occurs.

My mono blocks and all other components work just fine. So I’d love to hear suggestions as to how to get rid of this 50’ extension cord?

Thanks in advance.
sailcappy

Showing 12 responses by almarg

Sailcappy, thanks for the additional info. A few things are not clear to me, though, which are along the lines of some of the questions Jim had.

1)If the extension cord is not being used, am I correct in understanding that the breaker on the amp trips 20 seconds after the amp is switched from standby to on/active (the rear power switch/breaker having been turned on previously)?

2)And when the extension cord is being used, will the amp play music during those 20 seconds, or does it really become active only after the 20 seconds have elapsed?

3)And as Jim asked, when the extension cord is being used do you hear the click of a relay at the 20 second point?

Regards,
-- Al
I assumed his SR conditioner would have dealt with any line noise issues ....
My instinct (based on nothing specific) is to not make that assumption, especially given that detailed design information and quantitative test results appear to be unavailable for that (and most other) conditioners.

The kind of possibility I'm envisioning is that some piece of industrial-type equipment somewhere in the building, or nearby, is putting a significant voltage spike onto the AC, that repeats each cycle, and whose characteristics are such that the conditioner is ineffective against it.

Sailcappy, is there any chance that you can borrow a different conditioner from someone? Also, if by any chance you know someone who has an oscilloscope, and is knowledgeable about how to use it, a good experiment would be to view the AC waveform on it, and set it to trigger at a level a little higher than the nominal peak of the AC waveform (which is around 170 volts). Then see if it triggers, and what it captures if it does trigger.

Best regards,
-- Al
08-11-12: Sailcappy
I have a Cary 7.250 brand new amp that shuts down after 20 seconds in my NYC apartment.

08-21-12: Sailcappy
Remember this happens AFTER [emphasis added] i go from standby mode to Active mode.
Jim & Michael (Swampwalker), I've been interpreting these and other statements to mean that if the power switch/breaker at the rear of the amp has been properly turned off while in standby mode, and the rear power switch/breaker is subsequently turned on, and subsequent to that the front standby/active switch is turned to on/active, then 20 seconds later the breaker trips (if the extension cord is not used). That is what I was asking Sailcappy to confirm, in question (1) in my first post tonight.
Would a good SPD, surge protection device, installed between the amp and the wall outlet shunt out the high voltage transients?
Don't know. The oscilloscope experiment I suggested might help answer that.

Frank -- click the "markup tags" link just under the box near the bottom of the page in which responses are composed.

Have to sign off now until tomorrow.

Best regards,
-- Al
Well, one thing that seems to be clearly established at this point is that the problem is related to inrush current occurring at the 20 second point, whether its root cause is DC offset + failure of the DC block in the amp, per Ralph's suggestion (which strikes me as a clever and plausible theory), or some other kind of power anomaly, or oversensitivity of the amp's circuit breaker (even though it has been replaced once), or whatever.

And re the SR Powercell, although there is little in the way of technical detail that is available, one thing seems clear. Its design is based on different principles than most or all other conditioners.

Jim & Ralph, do you think it might be a reasonable gamble for Sailcappy invest either $215 or $239 for one of the BrickWall surge protectors, which also provide some degree of line filtering, and include a "series surge reactor current limiter; cascaded, auto-tracking dual polarity voltage limiters; dual pulse inverters," etc., with the onset of voltage clamping specified to occur 2 volts above the waveform peak. Specs here for the 2-outlet version, and here for the 8-outlet version.

I and a number of other A'goners use one, btw, with no reports of audible side-effects that I am aware of.

Regards,
-- Al
Sounds like a plan to me, except that my instinct would be to avoid configurations in which the Brick Wall and the Power Cell are used in series. If you are using both, have them both plugged directly into the wall.

Also, given the small difference in price between the two versions of the Brick Wall, I think it would make sense to get the 8-outlet version. That would give you the flexibility to experiment with what gets powered from where.

Regards,
-- Al
Is the Brick Wall Surge protector something that should be installed prior to the SR Power cell or just after the SR Power Cell and the Cary? Right now I have two plugs on my outlet one goes to the SR Powercell (which has my OPPO, Theta Pre-Pro, 2 Red Dragons, Runco and Sonos) and the other goes to the JL Sub.
I had been envisioning that the Brick Wall would replace the Power Cell altogether, if it in fact solves the problem. It would plug into the wall outlet, and (assuming that you purchase the 8 outlet version) everything else would plug into it (aside from the JL sub, if its current requirements and those of everything else total up to exceed or to be uncomfortably close to the Brick Wall's 15A rating).

There would be no harm, though, in experimenting with other configurations that utilize both the Brick Wall and the Power Cell, with the amplifier powered via the Brick Wall and some or all of the other components powered via the Power Cell.

Regards,
-- Al
Sailcappy, Ralph is referring to seeing if the problem occurs when the input connectors of the amp have shorting plugs, such as these, on them.

If you don't have any, you could pick up some RCA plugs at Radio Shack and solder their center pin and the ground sleeve connections together.

Alternatively, you could connect RCA cables to the amp, leaving their other ends unconnected, and WHILE THE AMP IS TURNED OFF stuff some aluminum foil into the unconnected ends of the cables to short the RCA center pin and ground sleeve together. You would want to make sure that the foil is securely in place, so that it won't dislodge when you turn the amp on, and to be careful to not let anything or anyone touch the RCA plugs while the amp is on (and for a minute or more after it is turned off).

I'm not sure what possibility Ralph is envisioning in suggesting that experiment, though. Perhaps that the current surge that occurs at the 20 second point is causing a transient to couple to the inputs of the amp, and to then be amplified to excessive levels, somehow resulting in the breaker tripping.

Regards,
-- Al
When i get the Oscilloscopes what should I be looking for? Is there a setting I should use?
I described one of the things that should be done in my post dated 8-18-12. Also, you should look for any major distortion of the 60 Hz waveform. Ideally it should look like a close approximation of a 60 Hz sine wave. If you see anything questionable try to photograph it, and post the photo at one of the free online photo-sharing services, with a link to it here.

As far as settings are concerned, there are a great many of them, so try to have Ken guide you through this. Also, of course, be cautious of the fact that you will be connecting to a potentially lethal voltage.

Sorry that the Brick Wall didn't help. Before selling it, it may be worth your while to compare sonic results between it and the SR, powering the entire system from one and then the other.

Regards,
-- Al
Jim -- I don't see the 117V being indicated as a minimum. I would assume it is intended as a nominal value.

Best regards,
-- Al
Jim just called this thread to my attention, by posting in another thread I was participating in.

Sounds like he and Metro have made many logical suggestions, and I'm pretty baffled as well. But here are a couple of thoughts:
08-14-12: Sailcappy
I had my friend who is knowledgeable about power test the lines and he confirmed that the polarity is correct vs. the small and large slots. He also noted that none of my outlets in my apartment are wired to ground it seems the ground is left to the junction boxes alone.
08-15-12: Sailcappy
It seems that none of my outlets have separate ground wires. I will call Cary today to discuss.
1) What does this mean? Does it mean that the safety ground pin on the outlets is not connected to anything, so that the safety ground pin on the amplifier's power plug is not connected to ground through the power wiring? If so, that would be number 1 on my list of things to focus on in relation to the problem. It would also be a serious code violation and a serious safety hazard.

Perhaps the design of one of the amp's various self-protection mechanisms is such that it is not happy if the amp's chassis (which can be assumed to be connected to the AC safety ground pin on the power plug) is not properly grounded. By attaching the 50 foot extension, capacitance between the three conductors in the extension cord will result in the addition of a significant amount of capacitance between the amp's chassis and AC hot and AC neutral, which conceivably could lessen the sensitivity of the protection circuitry to the ungrounded or improperly grounded condition of the chassis.

2) I'll repeat Jim's question about how the extension cord is coiled. And an experiment I would suggest is to compare results between when it is in a coiled state and when it is stretched out as much as possible, with as much spacing as possible wherever different parts of the cord have to run in parallel with each other. That will lower the cord's inductance, and thereby reduce the filtering effects it will provide at noise frequencies. (The effects of the cord's inductance at 60 Hz will be negligible either way). So comparing results between the coiled and uncoiled configurations might help us to rule out or rule in power line noise as being related to the problem. I don't think we can totally rule out that possibility at this point, even though the problem occurs when the SR conditioner is used.

Good luck!

-- Al
Jim, I didn't see your last post until just now; sorry. I guess it must have gone up just a few seconds before my last post.

You've offered lots of good thoughts and suggestions. My only further comment is that while I'm not particularly familiar with magnetic breaker characteristics, I'm skeptical that relatively low order harmonics are to blame. The reason I say that, and I could be wrong, is that I doubt that the inductance of a coiled 50 foot extension cord would be significant enough to have much effect at those kinds of frequencies. Keep in mind that the inherent inductance of each individual conductor (hot and neutral) will be significantly reduced by the fact that the other of those conductors is in close proximity. Coiling will increase the inductance, of course, but it will be multiplying an amount that is much less than if just one of the two current-carrying conductors were present in the cord.

So my guess, and as I say I could be wrong, is that as I suggested earlier there is some sort of higher speed transient that is present, that repeats each cycle and that is being reduced by the extension cord's inductance. Or, alternatively, perhaps the capacitance between the safety ground conductor of the extension cord and the other two conductors is providing some sort of filtering action at high frequencies, or is somehow affecting something in the amp by adding capacitance between the chassis and the AC inputs.
08-20-12: Sailcappy
I just spoke with my friend who works for the power company and we agreed on the following:

1. Regardless of the problem with my buildings power we know they will not fix it.
2. It seems to me that some type of power regenerator is needed.
3. What do you recommend that just has one input and one output?
4. Should I go digital or analogue?
Why invest in a power regenerator, and perhaps risk introducing side effects that on occasion have been reported to result from them (such as compromised dynamics), when you already have a solution that appears to work adequately?

And if a regenerator is to be selected, it would seem preferable to first have as good an understanding of the cause of the problem as possible. Meaning, IMO, that the measurements and experiments suggested by me, Frank, and Jim should be addressed first. Such as the simple ground measurements Frank suggested, the comparison I suggested of results with the extension cord coiled and uncoiled, and the suggestions in Jim's last post.

Otherwise we're taking a shot in the dark. Which we may end up taking anyway, but it would be prudent to minimize that likelihood as much as possible.

Regards,
-- Al
Hi Jim,

Yes, I did look at the manual. As you realize, though, it does not appear to provide enough information for us to infer answers to the questions in my previous post.
If the unit is in active mode and power is removed, it will remain activated when power is restored.
Yes, I noticed that both in the manual and in one of your earlier posts. But what I'm mainly looking to establish at this point is what the amp's normal turn-on behavior is, in the situation where the breaker had been turned off only after standby mode had been entered.

Which relates to your point about inrush current. It is not clear to me when the major inrush current normally occurs. Does it occur:

(a)When the breaker is turned on, assuming that the amp had been left in standby mode when it was previously turned off. Or,

(b)Does it occur when the amp is switched from standby to active? Or,

(c)Does it occur 20 seconds later?

A related thought that occurs to me is that I would not assume that the voltage drop that was observed as the breaker was tripping was due to inrush current that normally occurs at that point. It seems conceivable to me that contact bounce occurring in the breaker as it tripped might have resulted in inrush current and voltage drop that would not occur at that time ordinarily. So the voltage drop might have just been a consequence of the breaker tripping, rather than reflecting a large inrush current that may have caused the breaker to trip. Or perhaps some sort of inductive kickback effect from the power transformer or a relay was responsible for the voltage drop, given especially that the amp was not designed with the expectation that it would normally be powered down from the active state by means of the breaker.

Just some thoughts.

Best regards,
-- Al