CJ MET1: two different units experiencing loud popping and crackling sounds. One I think I know why...

[scottm_dj]

Hello all . So I have an interesting saga with the CJ MET1-- folks familiar with the unit please bear with this lengthy post First and foremost, this is got to be one of the nicest pieces of audio equipment ever made...just beautifully designed

Anyway...I first picked one up maybe a half dozen years ago as a UK transplant that had the power supply changed to US voltage. It worked great for quite some time...then one day on turn on it started popping and crackling dangerously on the main speakers. I quickly changed out a tube on a crackling speaker but it did it again so I shut it down permanently as it seemed to be something other than the tube involved...

In the interim, I was always suspected the voltage change so I found & picked up *another* MET at a great price for my analog setup (as well as an Audio Research MP1) before these classics are gone completely!)--and this MET had the upgraded caps. I put all new tubes that came with it in & fired it up and had slight rushing out of one of the channels and another slightly crackling channel.. But you can very easily tell the clarity difference in the upgraded model.

So...just yesterday after living with the slightly rushing (and LOW crackling) channels for about 6 months...in a bit of haste, I think I sadly committed the cardinal sin of CJ tubes. I know enough to at least have the unit on standby if not fully off before messing with the tubes, but somehow in a somewhat brain haze I blame on a stressful work week , being only on *mute* I pulled and replaced the left rear tube. Not smart. By the time I realized it wasn't on standby, I shut it down. When I fired it up that same huge popping noise went through my subwoofer this time (better than main speakers though!) which is not the channel that I pulled. As with my original, the noise is SO loud no matter what volume you have it's not something you can troubleshoot very long. I do plan to pull out an old speaker I don't care about to check which channels are affected in both units

So...if you do a general search on tube components, you see that most of the times you can actually change out tubes while a component is on...but I don't think that's the case with this particular CJ preamp. I think it needs to be on at least standby or you can do buffer damage. In this case, does anyone know why *another* channel would be affected than i pulled, and what overall damage I may have done by doing that? Interesting that they're both having the same issue, even though the "live" tube was only pulled on the second one and I can't imagine a bad tube alone would have that much concerning noise. Can any gurus here anyone shed any light on what might be going on?

By the way, I think it's pretty well known that the two best analog multi-channel preamps in history are the MET1 and the Audio Research MP1 (rare SS device from them). Maybe it has to do with thie synergy with my McCormick HT5 amplifier (and about 10db higher gain too), but the AR can't touch the sound of the Conrad Johnson in my setup. The MET is so much more natural & fuller sounding then the more clinical AR. Hopefully I can revive it (second one) without too much expense after that really dumb move.

Thanks for reading!

[AnotherJohnson]

So...if you do a general search on tube components, you see that most of the times you can actually change out tubes while a component is on...but I don't think that's the case with this particular CJ preamp. I think it needs to be on at least standby or you can do buffer damage. In this case, does anyone know why *another* channel would be affected than i pulled, and what overall damage I may have done by doing that? Interesting that they're both having the same issue, even though the "live" tube was only pulled on the second one and I can't imagine a bad tube alone would have that much concerning noise. Can any gurus hear anyone shed any light on what might be going on?

I don’t know where you’re searching to find the advice that it’s ok to change tubes in a powered device. That’s the problem with the internet. Lots of information, but no distinction between the good and the bad.

This is NEVER a good idea.

As for what damage you’ve done, if you’ve seen or smelled smoke or heard a pop, you’ve probably got some blown resistors or caps. You might be able to see them on inspection.

I would not encourage you to remove casework and look because I am concerned for your safety. It does not sound like your background is adequate for the task.

Low hanging fruit is to look to see if fuses have blown, and once fuses are confirmed good, to then replace the tube set. But before doing this, unplug the unit and set it aside until power supply caps have bled down. If you know what you’re doing, you can accelerate the bleed down with a snuffer stick and a good ground sink. Work with one hand and stand on a nonconducting mat to avoid becoming a ground path.

[admin]

Never ever change tubes while the unit is powered on. I would also recommend waiting 30 minutes for caps to discharge before working on any component in the system. Not only can you kill the unit if it's powered on and you do this kind of stuff, but more importantly the unit could kill you. There can be very high voltages coming from those caps and just because the "mute button" is on, doesn't mean that the rest of the circuits are not powered. Matter of fact, they surely are including the tubes.

As for what happened when you pulled that tube, who knows. I would start with a visual inspection of the circuit board and components looking for any burn marks, bulging caps, etc...

And of course the unit should be totally off AND unplugged when you do this.

Hope this turns out well. The MET is truly unique in that CJ never really pursued multichannel components. I also agree with you that I really like its design.

[scottm_dj]

Thanks for the responses (albeit a few somewhat snide in nature) I obviously did not do that on purpose and no I didn't research the internet to see if that task could be done before I did it more like after I inadvertently did to see if that's typically able to be done with tube components. IE hoping for the best So...yes I'm "qualified" to open it up and take a look see...

I did not smell any burned components and as far as I can tell the channel was still working just loud crackling & popping but on a different channel)...so doubtful it's a fuse. I have it completely disconnected now and will carefully open it up and see if I see anything obviously amiss and go from there. As I said, I have a test speaker that I don't mind blowing up where I'll try each channel for about10 minutes and see which one(s) have an issue. Even before all this, the other rear channel was notably ticking during quiet passages.

I'll try their service tomorrow to see what they think but I've heard that's not what it used to be, even in just contacting them. If I have to send it in that's the way it is. It's not like the Acoustic Research MP1 I also have is a slouch, it just doesn't sound as good (or fit as well!) in my setup as the CJ.

[scottm_dj]

Here's the internals of the MET. The motherboard is just as tidy here as the outside. Although of course I draw the line getting underneath the tube cage, but everything else looks (and smells) okay including fully intact fuses as I suspected. One of the caps denoted by the arrow does seem to be a little malformed ends...not sure if that has any significance to anyone here? If you quick-save the picture, you can really blow it up for detail.

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Just for an interesting aside, take a look at the internal design of the Acouatic Research MP1 where it's a completely different layout. That pure Class A device uses 6 individual PC-like channel boards instead... which I actually had to reseat one due to apparently rough shipping. Got to love UPS these days.

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[admin]

Don't take offense, I assure you that nobody meant disrespect but safety is the most important thing and touching some of the insides of these units while plugged in can kill you. Be safe.

Lot's of the higher end home amp manufactures use the design of vertical boards for each channel. I think it makes design easier and cheaper. Emotiva uses similar designs in their unit. If memory services you can pretty much order as many channels as you want and they just put these vertical boards in (it's been awhile since I looked at it so I may be wrong).

As for that bulging cap. I would really be looking closely at that. It's hard to tell from the picture but if there is obvious deformity, I would agrue that it should be replaced.

[AnotherJohnson]

He can think it’s snide to point out his lackadaisical approach to electronic box troubleshooting or to advise him that it does not appear to be a strength.

It’s his ears, his gear, his bank account, and his life that he is handling.

“Here. Hold ma beer, an’ watch this!”

Maybe I’m overly concerned, but I don’t know where you go to find advice to R&R tubes in a powered unit. Seems like one of those Darwin Award categories. After you go there, Appalachian Emergency Room might be the next stop.

This stuff deserves at least a modicum of respect. It can kill you.

[scottm_dj]

I'm a little confused because it sounds a few think I opened the case and mucked around with the inside while it was still powered & live. The only thing I did while it was live (inadvertently) is change out the tube-- wearing gloves at that--which I don't think is going to blow me up. Full disclosure is the mute button on the remote has an issue where it doesn't always power down when you hold it (stays on mute only) and I didn't notice at the time because it was during the day that the tubes were still actively lit... but anyway yes definitely my fault & dumb. But there's no way they would make something accessible from the outside that a child could possibly get to (if you removed the guards pulling a tube in this case) a dangerous to yourself process. Of course what it does to the equipment internals is a different story.

I also waited well long after it being disconnected (several hours) to remove the top and look inside for a visual inspection, but I'm certainly not going to touch anything cuz I definitely don't know what I'm doing there.

I sent an inquiry to CJ to see what they think. In the interim I'm going to use a scrap speaker and check each channel one by one to see what that shows. The AR MP1 is a great piece also...but I already miss the tube sound (and McCormack system synergy) of the CJ.

[admin]

It certainly would be great to get this up and running. Again, the MET1 is a really interesting unit in the CJ lineup.

Don't worry about the tube changing while the power on. We all do dumb stuff from time to time. I don't have to tell you about how I thought my new DAC was broken because I couldn't turn it on when pushing the power button. It ended up that I just have to push the button for a full second or so for it to register... but dang I was close to sending it back!

Regardless, keep us informed of the progress.

[scottm_dj]

Amusingly dumb task: I put a cheap 6 1/4" adapter on a 3.5" headphone plug into my Exasound DAC several years ago. When I extracted it, part of the adapter remained INSIDE the unit and is still there to this day-- I couldn't get enough of a grip on it with needle nose to remove it. Luckily I don't use the headphone jack on there but still... probably should have used a higher quality adapter...

So here's a closer up shot of those capacitors, and that one definitely looks deformed so I bet that's at least part of the culprit. Again...I was having issues prior to this so could be unrelated (and the cause of those), but that appears it definitely needs to be looked at. Inquiry into CJ...

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[admin]

Yes, I would definitely replace that cap if I were you. Whether that is the cause of the underlying issues I am not sure sure but my general policy is that anything that looks defective should be replaced.

BTW- you may be able to use a screw extractor to get the old headphone plug adapter out.

[AnotherJohnson]

FWIW, that CJD cap does not look bad to me. You may want to lift it and measure it, rather than replace it. I’ve seen similar that were new.

FWIW #2, admin, pressing the button for too short a time on your Holo May KTE will not damage anything. R&R of tubes in a live circuit is far more dangerous. Ask JF.

You could change my name from AnotherJohnson to Mudge (short for Curmudgeon), if you like. But I think your forum has an obligation to not encourage seriously bad practices.

Of course we hope the OP will solve his problem. But we should not give the impression that all you need to know is where your phillip’s head driver is before you get into casework. Again, ask JF.

[scottm_dj]

AJ, I appreciate all your advice. I spoke to one of my very handy friends local friends and he suggests I get this which is kind of right in line what you were talking about where we can test the caps... But first task is to test all the channels one at a time on a secondary system with a scrap speaker to see which of them are actually affected. 10 minutes per channel should let me know what's going on. I'm also very much wondering why two different units (only one having the live tubes pulled) are having the same popping issues.

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[admin]

I think narrowing the issue down to a channel or all channels is going to save you a lot of troubleshooting time. If it indeed just a single channel that is causing the problem, that will narrow the faulty component down considerably.

As for that cap. It still looks funny to me. It may be fine, but I would definitely test it.

[AnotherJohnson]

AJ, I appreciate all your advice. I spoke to one of my very handy friends local friends and he suggests I get this which is kind of right in line what you were talking about where we can test the caps... But first task is to test all the channels one at a time on a secondary system with a scrap speaker to see which of them are actually affected. 10 minutes per channel should let me know what's going on. I'm also very much wondering why two different units (only one having the live tubes pulled) are having the same popping issues.

I think it comes back to the idea that you have more than one failed tube. A new tube set might clarify things.

Testing with expendable speakers is definitely the way to go.

But keep in mind that (I don’t think) you can’t turn off some of the channels, so you need a load on all of them. You might put an 8 ohm 50 Watt power resister on each channel not being tested. I’ve used two 16 ohm load resistors in parallel to simulate 8 ohms with good effect.

Move the speaker as required to isolate the problem circuit(s).

In the end, you could have an intermittent cold solder joint OR a bad tube socket to deal with.

It sounds more like bad tube, bad tube socket, or cold solder joint than bad cap. Those are very high quality plastic caps. They will last a long time in normal service. They’re not like electrolytics that bulge or bubble on failure.

A great expendable speaker is the used PSB Alpha. They are inexpensive and decent quality.

It would be a shame to do further damage in troubleshooting. Running any tube amp with no load is asking for trouble.

[admin]

The MET1 is just a preamp. So it will only have RCA outs. AJ mentions that running a tube amp without load should not be done. I agree. Due to the unknown condition of the MET1, I would not hook it up to an expensive amp at this point. I would probably just use some $30 receiver off of ebay/craigslist and run the MET1 outputs into that and have the cheap receiver run some cheap speakers. Or maybe even just get some cheap self powered speakers to make it that much easier.

[AnotherJohnson]

The MET1 is just a preamp. So it will only have RCA outs. AJ mentions that running a tube amp without load should not be done. I agree. Due to the unknown condition of the MET1, I would not hook it up to an expensive amp at this point. I would probably just use some $30 receiver off of ebay/craigslist and run the MET1 outputs into that and have the cheap receiver run some cheap speakers. Or maybe even just get some cheap self powered speakers to make it that much easier.

Good points. Is it possible that the problem is in the coupled amp? Crackling and popping is often a sign of problems in the first gain stage of the amp.

[admin]

The MET1 is just a preamp. So it will only have RCA outs. AJ mentions that running a tube amp without load should not be done. I agree. Due to the unknown condition of the MET1, I would not hook it up to an expensive amp at this point. I would probably just use some $30 receiver off of ebay/craigslist and run the MET1 outputs into that and have the cheap receiver run some cheap speakers. Or maybe even just get some cheap self powered speakers to make it that much easier.

Good points. Is it possible that the problem is in the coupled amp? Crackling and popping is often a sign of problems in the first gain stage of the amp.

First step is isolate the faulty unit. So if that has not been done, AJ makes a really good point as that is where it should all start.

[scottm_dj]

Wow this board is so enlightening. I had no idea that you have to load all channels on a M-Ch tube preamp or there could be trouble. I've been running my ARC preamp on two channels for a month before I moved it out to the main room, but that's not a tube model from them...

just use some $30 receiver off of ebay/craigslist and run the MET1 outputs into that and have the cheap receiver run some cheap speakers. Or maybe even just get some cheap self powered speakers to make it that much easier.

I got the first part covered. I have an old Denon mini receiver and speakers for it literally lost the tweeter so only has a woofer so perfect to test if I get any noise (so far heard only from subwoofer during my brief after-listening). But obviously it's only a two channel setup so if I do that I better make a pretty quick test with only two channels under load at a time. Unless I want to dig out my secondary 100lb Sherborne 7-200 amp beast to hook it up through that. Which is a big...no.

Ironically, I have powered speakers as well but they happen to be Elac Navis model--which are far from expendable In fact this 100% analog model from speaker guru Andrew Jones is about as good as you can get powered...

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[scottm_dj]

I also did some digging looking for the original for sale ad because I thought I remembered it showed the insides to see if the capacitor was like that prior. I did find it and it does appear to show that the dented sides were there previously.

Here's the actual ad, and if you look at the internals picture you can clearly see that capacitor looking the same. Also, you can see the tube branding of the extra tubes...so are those Mullard tubes renamed?

Oh...and finally you can see the just ridiculously great deal I got on it a few years back ...especially with the Teflon cap upgrade included and even the power cord was a souped-up audiophile version. Fully working it's probably worth double this now!

https://www.usaudiomart.com/details/649 ... amplifier/