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NHT crossover badly damaged; what caused this?

J

jquark

New Member
Hello all,

Long time lurker here; I am hopeful someone has an answer/advice for me on this.

About 9 years ago, I was *given* a pair of NHT 2.9s for helping someone move. I have NO business owning these as I couldn’t afford them then and could barely afford them now used. For the at least the past ~year (I’m kicking myself for not checking things sooner) or so my NHTs haven’t sounded right.. I thought it was due to a move and very sub-optimal furniture positioning in the new place. Then I thought it was my NAD 2200... the output relays went and need to be replaced. I recently bought my first true hi-fi amp, a PSE Studio IV (It’s incredible) and the NHTs STILL did not sound right. After tracking the problem down to the crossover, I pull them out to find that one channel had a badly burned resistor and the other channel showed some signs of heat damage. See photos at linked album.

I then saw that the speakers I have are NOT a matched set; they have differing serial numbers.

What I would like to know is if the crossovers were damaged prior to me receiving them OR if there is anything *I* did to damage these speakers. The speakers are my most prized possession and I want to keep them the rest of my life if possible. I plan on getting the crossovers fixed (NHT is helping! They have been AMAZING). Still, any clue as to HOW such a catastrophic failure occurred? Once I get them fixed, I do not want this happening again.

Quick note: The drivers all check out fine; I measured the resistance across the terminals of each. Thank goodness the crossover took the damage.

Amplification history since I have owned them:

1) NAD 2200 in stereo

2) For about a year, I split preamp out with metal jumpers and horizontally biamped with NAD 2200 on tweeters an NAD 2400 on bass.

3) NAD 2200 developed output relay issue, then tried NAD 2400 in stereo. During this time was in a house with electrical issues (frequent black outs).

4) NAD 2400 developed output relay issue, for the past ~year or so I have run them in stereo with an NAD 3020. I know this is not enough power for them.

My listening habits are very reasonable. I do not like to push the speakers as I have had small listening rooms.

So, any clues on how to avoid this in the future? THANK YOU!

More photos at:IMG_20160608_164154304.jpg

https://www.dropbox.com/sh/hj6svl6vhwq3m9c/AADeEoU7BqVaACXDIOFnaPAOa?dl=0
 
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Here's my theory:

Perhaps the amplifier with the relay issue went DC on you and sent a huge amount of energy to the crossover board, effectively burning it up! Something had to get VERY hot to scorch the board that badly

What components (if any) are on the other side of that board?
 
I'm not at home so can't take a quick picture but I believe they were two capacitors that looked fine. Agreed on the heat, it would HAVE to be something bad DC from the faulty amp right? There is no way that underpowering (with the NAD 3020) would have done this, yes?
 
redcoates7 said:
Here's my theory:

Perhaps the amplifier with the relay issue went DC on you and sent a huge amount of energy to the crossover board, effectively burning it up! Something had to get VERY hot to scorch the board that badly
Click to expand...
That was my thought as well. The power sent to the speakers at normal (or even high - even when you think you're using a lot of power, it's still probably less than a watt except on peaks) listening levels is not near enough to cause that sort of damage. If you were underpowering (and sending them into clipping) you'd probably hear something very wrong before you burned anything up like that. Also, the 3020 has a softclip circuit which should prevent such things.
 
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Thanks all, has the NAD 2200 been known to do this? I know the output relay issue is a known problem but could a faulty output relay allow a huge DC rush?
 
Jon Bird said:
Thanks all, has the NAD 2200 been known to do this? I know the output relay issue is a known problem but could a faulty output relay allow a huge DC rush?
Click to expand...

Sure- if the relay was stuck "open" when the protection circuitry should have been closing it, that do the trick. There's nothing on the loudspeaker side that could have caused this outside of an internal short somewhere...which is highly unlikely, even after a move.Try giving NHT a call- believe it or not, they may have a crossover replacement in stock still!
 
Output relay offers protection only in the event of a failed amplifier. To get the kind of energy that that crossover saw the amp would have had to output a lot of DC. Somewhere along the line an output transistor went bad creating short and full DC went into that crossover. Amp and the relay would both have to fail to allow this to occur. Did you do this or did you receive it this way?

If the speakers sounded fine at first then I would have to assume it happened on your watch.

What did you do to repair your amp?
 
Thanks for sending this. What's absolutely nuts is that the speakers didn't sound awful; just the tweeter on one channel wasn't responding.. all other drivers responded properly with a test CD (different frequency tones).

I never repaired the NAD 2200 and 2400. When the relays went, I kept them in the closet and moved to the NAD 3020. I recently replaced the 3020 thinking that the poor performance was from the lack of power in the 3020. Only when the new amp sounded significantly better with my NHT 1.5s did I do the frequency test and found the tweeter not responding. I feel ridiculous not picking up on this sooner.

I still have the NADs. I have a multimeter. Is it possible to test the transistors while still on the board?
Last night, I checked the DC current AFTER the relays ( I now know I should check before the relays, will do tonight) and it was measuring under 2 mV both channels. I find this low value strange. The only thing I did was deoxit on the relay contacts... when I turn the amp on, they now "click" on like they should.

Any other tests to run? THANK YOU!
 
redcoates7, I have called NHT and an sending in the crossovers to them. They have been simply amazing! I just want to make sure that I do everything I can to not damage the speakers in the future....
 
satellite65 said:
To me it looks like a bad connection has been arcing, not an overload of any kind.
Click to expand...

Do you mean bad connection on the speaker terminals or something internal?

There are 4 binding posts per speaker (for biamping). I do not have the original jumpers so I am using speaker wire connecting the highs and lows in phase (+ to + and - to -).
 
Bad connection at the base of the 4 pin connector. As low as the burn is I'd say it was a bad solder joint from the circuit card to the connector.
 
satellite65 said:
Bad connection at the base of the 4 pin connector. As low as the burn is I'd say it was a bad solder joint from the circuit card to the connector.
Click to expand...
Interesting... I will check when I get home. The other channel also shows a lot of heat at this same connector (NOT burned like this but major hotspots). I will check when I get home... should I just look for a loose solder joint?
 
The PCB material was burnt by heat. The wires in the connector show how hot it got. The insulation shrunk from the heat. The white wire itself is looking burnt. Possibly broken solder joint. The resistance of the connection goes up. The power applied now is turned into heat. Have seen this over the years at work. Electronic tech . Bet the bottom of the PCB is worse. Also the wiring will have to be redone at the cut wires. New pins and connector needed to mate up with the new crossover. Not sure about the 2 wire connector.
 
If you are not comfortable effecting repairs on your two board I would gladly test everything and recap/ replace what needs to be done here. You cover shipping both ways and I would offer the rest at no charge.

I just got done with a 46 piece recap of four x-over boards, so skill is not a problem just would like to help and be neighborly to a fellow member.
DC
 
The above post is a really generous offer from a very experienced speaker guy. If NHT is fixing them cheap or free, then by all means, but if not, you would have no worries with dc270.
 
dc270 said:
If you are not comfortable effecting repairs on your two board I would gladly test everything and recap/ replace what needs to be done here. You cover shipping both ways and I would offer the rest at no charge.

I just got done with a 46 piece recap of four x-over boards, so skill is not a problem just would like to help and be neighborly to a fellow member.
DC
Click to expand...


This is UNBELIEVABLE!! DC270, an absolutely amazing offer and I am sitting here in disbelief and happiness. Thank you!

I have spoken with NHT and they are going to take a look at the boards. My hope is that they can get them all back to spec and perhaps just replace with something they have in stock. If NHT comes back with a "sorry" or want to charge something serious, I will take you up on your offer. I HOPE you enjoy beer or bourbon (living in TN) OR something else because I can't let you get away with fixing them for free. I'm grinning ear to ear, what an amazing day!
 
Just to be clear, in no means is my going with NHT any disrespect to you DC270! I have just been very impressed with the service and time NHT has given me (Bob Hopkins has been SO nice) and I want to give them a crack at it. I am SO relieved that there will be a way forward no matter what. I really miss listening to these!
 
Jon Bird said:
Just to be clear, in no means is my going with NHT any disrespect to you DC270! I have just been very impressed with the service and time NHT has given me (Bob Hopkins has been SO nice) and I want to give them a crack at it. I am SO relieved that there will be a way forward no matter what. I really miss listening to these!
Click to expand...

No problem, just would like for you to have an alternate option if needed. Even I come across some things I just do not feel comfortable doing. Example, I sent both my uni"Q" twtr/mid assembly back to KEF America as I could not find the correct twtr and mids for a proper repair. Anthony H. at KEF America was mystified when he got them as they were parts he had not seen as well- but is still going to make them right!

If I can help you later on just set us up with a private conversation- I am always glad to help anyone here.
DC
 
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