Did I blow my mid-bass woofer?

[ZolaIII]

I don't know but if you did manage to demage mid woffer then rest also took a good beating.

 

[johnsen88]

This all happened a few years ago for my friend and is second hand, IIRC he was told that some about the architecture/design of Crown was not compatible with the Focals and he got a different amp as a result.

Oh, so there are such compatibility issues as well? But I have used this amp all along with an older Focal model(bought at around the same time when this Power Amp was released) and there was no problem. Both worked well together. The dealer suggested their pairing(NAD and Focal) because they worked well. Any idea what he got later?

 

[Timcognito]

Oh, so there are such compatibility issues as well? But I have used this amp all along with an older Focal model(bought at around the same time when this Power Amp was released) and there was no problem. Both worked well together. The dealer suggested their pairing(NAD and Focal) because they worked well. Any idea what he got later?

I seem to remember Cambridge? I think Focal would be the best source of advice there. I'm a hoobyest and an electronics expert.

 

[kemmler3D]

A decent non-technical way to test if speakers are damaged is to play tones (not too loud!) and listen for anything odd. As you noticed with the double-bass, it made a distorted sound.

Sweep through the range with this and if you don't hear anything wrong with tones or music you may not have any damage.

You can also record the output with a mic and REW to check this more closely, if you are so inclined.

 

[Jaxjax]

Oh, so there are such compatibility issues as well? But I have used this amp all along with an older Focal model(bought at around the same time when this Power Amp was released) and there was no problem. Both worked well together. The dealer suggested their pairing(NAD and Focal) because they worked well. Any idea what he got later?

So you have a multimeter on the way to test DC offset.? Thats a good older NAD amp but could have had something let go.

 

[johnsen88]

A decent non-technical way to test if speakers are damaged is to play tones (not too loud!) and listen for anything odd. As you noticed with the double-bass, it made a distorted sound.

Sweep through the range with this and if you don't hear anything wrong with tones or music you may not have any damage.

You can also record the output with a mic and REW to check this more closely, if you are so inclined.

I will be doing this again, properly. I ran a test tone track earlier when the speakers sounded distorted. Did not pay close attention to each speaker a single was in a state of panic. I need to determine now if other drivers are damaged as well and this will be first step before I open anything up. I have planned to check the drivers physically after this with a multimeter. I have not used one in my life and am just reading about it usage before putting them to use.

The miniDSP mic is on its way. Will do the mic + REW recording when that comes in.

 

[johnsen88]

So you have a multimeter on the way to test DC offset.? Thats a good older NAD amp but could have had something let go.

I got it earlier today. Now I am reading up on the resources available online to begin measuring. I will be measuring the speakers first before attempting anything with the amplifier. Any guidance would be helpful and appreciated.

The amplifier is well regarded amongst many. Not the best in the world but it's packs some true power for it is worth. I am afraid some issues are inevitable with time. Some units were sent in for overheating and whereas others have been working flawlessly for decades. My unit was sent in for inspection to be cleared of any issues before operation. If anything, the techs might have passed it as fit for use without being thorough with their checks. I put it to use with a set of bookshelves which were of little value to make sure all was working well before plugging them to my main set of speakers. All ran well for a month and this happened. I listen at low volumes and always for max 2 hours, every two days or so.

I will have to determine the root cause of this before putting it to use again. Replacing the drivers without weeding out the real cause of this is a recipe for another episode.

NAD is helpful with anything technical. I have reached out to them.

Also, parts are available according to Focal. Now I have to make a careful decision.

 

[Clmrt]

The good news is that they have spares! They confirmed it when I wrote to them asking about its availability. I guess it would be a 1-1 switch. My concern now would be if such damage spared the other two, namely, the tweeter and the woofer. How do I even know if those are fine?



Well damn. I am hearing these horror stories of power amps destroying speakers. It is really frustrating to see this happen when you are extra careful. I am not sure what exactly went wrong at my end but this happened after a good month into usage. What is even more annoying is the very fact that the Power Amp was sent to the agent for servicing and given the all-clear to be used.

Speaker repair businesses should have test equipment to measure driver parameters. They can detect voice coil rub and can compare drivers against each other to ensure they are operating identically.

If you can't find such a resource, Parts Express sells speaker evaluation products and software. You get the best value from this if you have access to the drivers' TS parameters from the factory.

 

[johnsen88]

Speaker repair businesses should have test equipment to measure driver parameters. They can detect voice coil rub and can compare drivers against each other to ensure they are operating identically.

If you can't find such a resource, Parts Express sells speaker evaluation products and software. You get the best value from this if you have access to the drivers' TS parameters from the factory.

Clmrt, I am looking to diagnose this from a consumer level. From my readings here and elsewhere, I gathered that it is possible to determine the condition of these drivers through measurements taken with a mic and REW software. I got myself a UMIK mic and will be using the REW software. Is this the setup you are referring to?

The one thing I need to compare this to would be the drivers' TS parameters- this is something I need to get from Focal but am not sure what is the industry practice when it comes to obtaining such data from manufacturers. Do you think they will share this with their customers? There are no measurements taken for my speakers afaik. I checked with Amir on this as well. He has measurements for the Chora 816s but not my Chorus 816v.

 

[Clmrt]

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[johnsen88]

So you have a multimeter on the way to test DC offset.? Thats a good older NAD amp but could have had something let go.

I did a quick check with the multimeter for the DC offsets. I took the readings an hour after the power amplifier was powered ON. The readings were identical the next day when I repeated this. The next day, measurements were taken immediately(2-3mins) after it was powered ON to see if there was any difference. They were the same though. Also, the readings on the multimeter took a few seconds to stabilise. But when they did, they remained without fluctuation.

The measurements are as follows:

Speaker binding post A:

Left channel - -1.4 mv
Right channel - -2.8mv

Speaker binding post B:

Left channel - -1.4 mv
Right channel - -2.8mv

The heatsinks on both sides felt equally warm. However, I made another observation. When the amplifier was switched ON(after a week), it took about 4 minutes for the relay to click in and emit the green light for usage. The last time this happened was when I got it serviced after storage and put it to use. The next day, it took 10 secs to get ready. I am wondering if this is normal.

 

[AnalogSteph]

However, I made another observation. When the amplifier was switched ON(after a week), it took about 4 minutes for the relay to click in and emit the green light for usage. The last time this happened was when I got it serviced after storage and put it to use. The next day, it took 10 secs to get ready. I am wondering if this is normal.

This sort of issue is not unheard of. It may indicate that the electrolytic capacitor determining turn-on delay has seen better days and developed excessive leakage current. Some preliminary investigation on the schematic would be advisable. If you want to reproduce the problem, look for suitable probe points for DC offset preceding the protection relay inside the amp that could be accessed quickly, even though I suspect there'll be nothing concerning on either channel and changing the suspect cap itself would rectify the issue. (The capacitance value is generally too large to be easily replaced by a film cap, unless it's <<10 µF. The best choice will be a quality cap of normal ESR and a generous voltage rating up to 50/63 V.)

BTW, speaker terminals A and B are usually connected to the exact same power amplifier, so it is not surprising that the respective readings for the left and right channels would be identical. Readings in the single-digit mV are well in the green.