NAD C375BEE protection circuit activating.

[unacat]

Greetings, I recently became the second owner of a NAD C375BEE which worked fine for two weeks and now activates the protection circuit after about five minutes of playing. My speaker connections are fine with no shorting, but I think that if the cables were shorting the protection would activate upon powering up the amplifier. Any advice on troubleshooting would be greatly appreciated and I would also like to know if triggering this circuit multiple times while seeking the source of the problem might damage the amplifier. Prior to the purchase of the NAD I ran an Anthem Integrated 2 with no issues.

NAD C3375BEE
Totem Model One Signatures
REL Strata 2 Subwoofer
Ultech UCD-100
Birdland Odeon Lite DAC
VansEvers Clean Line Power Conditioner

This is plugged into a Panamax Surge Protector which is part of a surge protection package made available through my power company as I live in Florida with frequent electrical storms.
I do not know if this might be part of the issue, but my REL has developed a hum upon my introducing the NAD into my system. The REL was not powered on the last two times the protection circuit activated.
Thank you,
joseph

 

[TLS Guy]

Yes, it will damage the NAD further if the protection is activated.

I suspect you have the wrong speakers for that integrated amp. It is already damaged.

First of all NAD stands for Not Always Dependable.

That amp is rated at 150 watts into 4 and 8 ohms. Since the amp does not increase power into four ohms, it means that that amp is marginal into 4 ohms. Your speakers are low sensitivity. (84 db). John Atkinson measured the impedance of those speakers at 3.6 ohms in the mid bass. Further I note the phase angle is -ve 40 degrees below the 3.6 ohm reading where the impedance is 5 ohms. When factoring in the phase angle it makes the effective impedance 3.7 ohms at that point.

I suspect the load offered by those speakers was enough to make that NAD amp throw in the towel after two weeks.

Your NAD is already damaged, so my advice is a more robust amp. I would recommend an amp that at least increases its output 50% into 4 versus 8 ohms and preferably doubles it.

Those NAD amps are not robust.

 

[unacat]

TLS Guy, thank you for your informative reply to my post. I had my doubts about the NAD but after reading some glowing reviews and coming upon one for a very good price I thought that I would give it a try. It was very, very bright following my Anthem which had a tubed preamp stage in which I used Mullard CV2493 tubes. What type of damage would the NAD have suffered because of the impedance of the Totems? I did some research prior to my purchase and saw several postings from Totem owners using the C375BEE and they were satisfied, I believe they were mostly the Totem floorstanders. what a wonderful system in your profile, the only thing you and I have in common is the Revox B77. Again, I appreciate your reply and your wisdom. Joseph

 

[PENG]

TLS Guy, thank you for your informative reply to my post. I had my doubts about the NAD but after reading some glowing reviews and coming upon one for a very good price I thought that I would give it a try. It was very, very bright following my Anthem which had a tubed preamp stage in which I used Mullard CV2493 tubes. What type of damage would the NAD have suffered because of the impedance of the Totems? I did some research prior to my purchase and saw several postings from Totem owners using the C375BEE and they were satisfied, I believe they were mostly the Totem floorstanders. what a wonderful system in your profile, the only thing you and I have in common is the Revox B77. Again, I appreciate your reply and your wisdom. Joseph

To troubleshoot effectively, we need to know how loud you listen, room dimensions, your listening distance from the speakers. Do you have a SPL meter? The Totems do have low impedance but their maximum recommended power is only 120W so your NAD should be able to drive them to their limit without any problem, unless the amp is defective.

 

[TLS Guy]

TLS Guy, thank you for your informative reply to my post. I had my doubts about the NAD but after reading some glowing reviews and coming upon one for a very good price I thought that I would give it a try. It was very, very bright following my Anthem which had a tubed preamp stage in which I used Mullard CV2493 tubes. What type of damage would the NAD have suffered because of the impedance of the Totems? I did some research prior to my purchase and saw several postings from Totem owners using the C375BEE and they were satisfied, I believe they were mostly the Totem floorstanders. what a wonderful system in your profile, the only thing you and I have in common is the Revox B77. Again, I appreciate your reply and your wisdom. Joseph

The most likely problem is thermal damage to an output stage, but could be any number of things.

The floor standers are more sensitive, and would almost certainly draw less power from the amp.

The woofer, is the Dynaudio 15W75. I'm very familiar with these drivers, and they do stress amps. They are conservatively rated and their 3" voice coils can handle enormous power without distress. To produce high spl. with these drivers really heats up amps. I use these drivers in my surround speakers. The amp supplying these speakers runs the hottest. I always advise robust power for these drivers.

Your options are to get the NAD repaired and give it another shot, or get another amp. Those are nice speakers. I like those drivers, but you have to give them the whip.

 

[PENG]

The most likely problem is thermal damage to an output stage, but could be any number of things.

The floor standers are more sensitive, and would almost certainly draw less power from the amp.

The woofer, is the Dynaudio 15W75. I'm very familiar with these drivers, and they do stress amps. They are conservatively rated and their 3" voice coils can handle enormous power without distress. To produce high spl. with these drivers really heats up amps. I use these drivers in my surround speakers. The amp supplying these speakers runs the hottest. I always advise robust power for these drivers.

Your options are to get the NAD repaired and give it another shot, or get another amp. Those are nice speakers. I like those drivers, but you have to give them the whip.

I see your point about those drivers being hard to drive and could over tax lessor amps. However, if you read that particular NAD model's specs, they do have enough to drive to those relatively small Totem speakers to their limit. When speaker companies rate their speakers 15 - 120 W, they typically mean 120 W is the limit, obviously it can take much more on short bursts but not much on average or would face thermal damage.

Frequency Response	<50 Hz - 20 kHz ± 3 dB
Impedance	4 ohms
Sensitivity	87 dB/W
Recommended Power	15 - 120 W
Crossover frequency	2.7 kHz electrical and mechanical

<tbody>
</tbody>

Below is pasted from the manual from http://totemacoustic.com/en/hi-fi/compact/model-1-signature/specifications/

"Limits

Be wary of providing more power than is appropriate for your speakers and damaging them. Although
a more powerful amplifier may provide better sound, it is very important to utilize speakers within their
power-range rating to prevent damage."

Without more new info, my guess is that his amp failed on its own, not because those particular speakers. He did say his previous Anthem integrated 2 (even less powerful than the NAD 375) had no issues so I doubt he needs more power for his need anyway.

 

[unacat]

Greetings PENG and thank you for responding to my plea for advice. Sorry, no SPL meter but I live in a townhome with the living room taking half of a 14' by 28' space with the speakers on the half of the long wall effectively creating a 14' by 14' listening area with a large open space of living area to the left. I sit about 8' from the speakers which are 5' apart and listen at moderate (townhome!) levels and the NAD was literally barely cracked. I have seen figures published for this amp running down to 2 ohms and I have read of people using lesser NAD amps with the Totem Mani 2 speakers with perhaps less than satisfactory results but no self destruction. Because TLS Guy has indicated that triggering the protection mode may cause more damage I am reluctant to troubleshoot methodically due to this risk. Your further thoughts would be greatly appreciated. Again, thank you. Joseph

 

[TLS Guy]

I see your point about those drivers being hard to drive and could over tax lessor amps. However, if you read that particular NAD model's specs, they do have enough to drive to those relatively small Totem speakers to their limit. When speaker companies rate their speakers 15 - 120 W, they typically mean 120 W is the limit, obviously it can take much more on short bursts but not much on average or would face thermal damage.

Frequency Response	<50 Hz - 20 kHz ± 3 dB
Impedance	4 ohms
Sensitivity	87 dB/W
Recommended Power	15 - 120 W
Crossover frequency	2.7 kHz electrical and mechanical

<tbody>
</tbody>

Below is pasted from the manual from http://totemacoustic.com/en/hi-fi/compact/model-1-signature/specifications/

"Limits

Be wary of providing more power than is appropriate for your speakers and damaging them. Although
a more powerful amplifier may provide better sound, it is very important to utilize speakers within their
power-range rating to prevent damage."

Without more new info, my guess is that his amp failed on its own, not because those particular speakers. He did say his previous Anthem integrated 2 (even less powerful than the NAD 375) had no issues so I doubt he needs more power for his need anyway.

Total power is not the whole point. If he had an amp that delivered 40 watts to 8 ohms, but 80 watts to four ohms he likely would be fine. Also the independent sensitivity measurement was 84 db, which is in line with my experience. When I used my speakers, which have two of those drivers, on location, even in a small monitoring room a 100 watt amp did not produce peak concert levels, so I switched to a 250 watt amp. Those drivers have 3" voice coils with flattened edge wound wire. They are not like drive units of most domestic speakers.

As you say, the amp may have failed independent of the speaker load. However it is likely not a coincidence this used amp failed after driving those speakers for two weeks in my view.

 

[unacat]

TLS Guy......thank you for your follow up and for your further assistance with my NAD issue. I really barely ran the volume of the NAD as I live in a townhome and must listen at a moderate but still enjoyable level. There could literally not have been an opportunity for the amplifier to have been run hard enough to generate more than a very modest amount of heat unless there is another cause for a thermal damage issue. When the protection circuit activated each time it was minutes into play time and at fairly low volume as the type of music that I was playing did not benefit from playing at higher levels. Your additional attention to my amplifier issue is greatly appreciated as your technical knowledge and experience is far greater than mine. Thank you, Joseph

 

[TLS Guy]

TLS Guy......thank you for your follow up and for your further assistance with my NAD issue. I really barely ran the volume of the NAD as I live in a townhome and must listen at a moderate but still enjoyable level. There could literally not have been an opportunity for the amplifier to have been run hard enough to generate more than a very modest amount of heat unless there is another cause for a thermal damage issue. When the protection circuit activated each time it was minutes into play time and at fairly low volume as the type of music that I was playing did not benefit from playing at higher levels. Your additional attention to my amplifier issue is greatly appreciated as your technical knowledge and experience is far greater than mine. Thank you, Joseph

If you are absolutely sure your speaker wiring is beyond reproach, then you need to take your amp in for service or replace it.

 

[unacat]

Hi TLS Guy. The fellow that I purchased the NAD from drove Thiel 1.7 speakers which appear to be a difficult load, although not as difficult as the Totems. He then used ELAC speakers, although I cannot recall the model floorstanders, until purchasing a KRELL 550. i do not know if the information regarding the Thiel 1.7 speakers adds any useful information to my problem. Thanks again...Joseph

 

[unacat]

i mentioned earlier that my REL sub had developed a hum and the REL is connected to the speakers terminals on the NAD. Although the REL was not powered on the last two times that the pprotection circuit activated, is there a possibility that this might be related? Thanks, Jos

 

[PENG]

Total power is not the whole point. If he had an amp that delivered 40 watts to 8 ohms, but 80 watts to four ohms he likely would be fine.

That is not logical. NAD could have rated that amp 50W into 8 ohms, 100W into 4 ohms, and 110W into 3 ohms. That will still be the same amp. If you take the time to do the math you will agree with me, happened before..

Most double down talks are myths, unless more details are presented with such talks. Otherwise you can rate just about any power amps as doubling down at least from 8 to 4 ohms.

Also the independent sensitivity measurement was 84 db, which is in line with my experience. When I used my speakers, which have two of those drivers, on location, even in a small monitoring room a 100 watt amp did not produce peak concert levels, so I switched to a 250 watt amp. Those drivers have 3" voice coils with flattened edge wound wire. They are not like drive units of most domestic speakers.

My point is, Totem rated those speakers 15 to 120W, the model the OP owns has single 5.5" driver in it, not 2.

As you say, the amp may have failed independent of the speaker load. However it is likely not a coincidence this used amp failed after driving those speakers for two weeks in my view.

I agree that is possible, could also be a bit of both, that the second hand amp was abused before and some damage already done so finally got killed easily by those 3" voice coil drivers.

 

[TLS Guy]

Hi TLS Guy. The fellow that I purchased the NAD from drove Thiel 1.7 speakers which appear to be a difficult load, although not as difficult as the Totems. He then used ELAC speakers, although I cannot recall the model floorstanders, until purchasing a KRELL 550. i do not know if the information regarding the Thiel 1.7 speakers adds any useful information to my problem. Thanks again...Joseph

Those Thiels are 3 ohm! So that amp has had a hard life.

 

[TLS Guy]

i mentioned earlier that my REL sub had developed a hum and the REL is connected to the speakers terminals on the NAD. Although the REL was not powered on the last two times that the pprotection circuit activated, is there a possibility that this might be related? Thanks, Jos

As the sub is powered I doubt that is the issue. The only way the sub could be an issue, is if it failed and is putting a voltage at the speaker inputs. Normally a powered sub connected to the speaker terminals should draw insignificant power from the amp.

 

[PENG]

Because TLS Guy has indicated that triggering the protection mode may cause more damage I am reluctant to troubleshoot methodically due to this risk. Your further thoughts would be greatly appreciated. Again, thank you. Joseph

I think if you turn the volume way down and it does not trip then there is a good chance (still just a chance), that the amp is fine and the protective system is defective. You can also try connecting the speakers one channel at a time, to see if the problem is triggered by one particular channel.

As long as you keep the volume really low, the chance to cause more damage than it is now will also be really low, though still possible.

 

[unacat]

More good news! The amplifier was in mint physical condition and during many email discussions with the previous owner ha seemed to be a pleasant and trustworthy fellow, so I made the decision to purchase the unit. Looks like I threw the wrong dart at the wrong board. is there a possibility that there could be another issue? Prior to posting on AUDIOHOLICS and being fortunate enough to receive advice from such technically savvy members I read that I could disconnect the speaker leads and power the amp as a means of troubleshooting. It has always been my understanding that an amp should never be run without a 'load'. Is this a safe method of troubleshooting? Because you indicated that triggering the protection circuit my cause further damage I am reluctant to troubleshoot unless there is a real chance that the effort may yield positive results. You seem very certain that the amplifier is damaged, correct? Be well....joseph

 

[unacat]

The reason that I purchased a new amplifier was that I found that I had to turn the balance on my Anthem way to the right speaker to balance the sound. Since the Anthem was fifteen years old I assumed that it may need repairs so I purchased the new amp. Since introducing the NAD I found that I still must adjust the balance way to the right channel. If that speaker is in fact defective, does that have the potential to be a problem that might trigger the amp to shut down? Thx...Joseph

 

[PENG]

The reason that I purchased a new amplifier was that I found that I had to turn the balance on my Anthem way to the right speaker to balance the sound. Since the Anthem was fifteen years old I assumed that it may need repairs so I purchased the new amp. Since introducing the NAD I found that I still must adjust the balance way to the right channel. If that speaker is in fact defective, does that have the potential to be a problem that might trigger the amp to shut down? Thx...Joseph

Yes if one speaker is defective it could still cause the amp to shut down, that's one reason why I suggested to connect one speaker at a time, but still keep the volume low to minimize the chance of further damage.

That NAD is a solid state amp, it is okay to not connect a load with the amp on. In fact that should be the first step. If the amp does not shutdown, then connect one speaker at a time. Again, keep the volume low, or better still, at minimum.

If you have to unbalance both amps to get balance then either there is likely something wrong with one speaker, or it is the effect of your room acoustics, or your hearing, or a combination of things. One way to eliminate the room acoustic effect is simply swap the positions of the speakers but make sure you put them in the exactly positions, other than interchanging left and right.

 

[TLS Guy]

The reason that I purchased a new amplifier was that I found that I had to turn the balance on my Anthem way to the right speaker to balance the sound. Since the Anthem was fifteen years old I assumed that it may need repairs so I purchased the new amp. Since introducing the NAD I found that I still must adjust the balance way to the right channel. If that speaker is in fact defective, does that have the potential to be a problem that might trigger the amp to shut down? Thx...Joseph

That is the most important piece of information you have posted to date. The right speaker is almost certainly defective and has shorted turns in the voice coil. That would present an almost certain dead short to the amp and cause shut down and or damage to the amp.

However, the only time I have seen that happen one of those Dynaudio drivers, has been caused by an amp failing and sending massive DC off set to the speaker.

You can test for this easily. Get an ohm meter and test the DC resistance at the terminals of each speaker. They should be identical. If you have a speaker damaged by DC offset, it will have a much lower DC resistance.

Do not swap the speakers, as you may do much more damage. Measure the DC resistance of your speakers before doing anything else.

Be wary of that Anthem amp, as if your right speaker is damaged, it is almost certain that your Anthem is defective and damaged the speaker.

The other possibility is that your sub had DC offset at the right speaker terminals, and has done the damage. However I would think that would have caused smoke.

In a situation like this you will have to be very careful not to cause more damage. You may require expert tech help to sort this out.