Audio Research Reference 150 - buzzing input transformer

It's possible the power supply electrolytic capacitors may need replacement, especially after being idle. There could also be poor mains power with a DC component causing the buzzing and subsequent damage.

What @noromance said. ✅️

Check the bias first to be sure that you are within range.

As i read the other post, cause was a melted washer.

You can check this as the rest of them.

If it was dc the buzzing should be audible on start and not appearing after some time.

Not necessarily. The traf may loosen up as it warms up allowing the DC to cause audible vibration.

If it was dc the buzzing should be audible on start and not appearing after some time.

Ok, i understand your point and it may be only that.

💩 happens and it’s frustrating when it does. But I’ve never heard “poorly designed” in the same sentence with Audio Research. Fixing the issue is worth it because ARC stuff sounds great. 

If it's the presence of DC, it must have happened quickly with permanent damage on the transformer. After I took it to a friend's place, it behaved the same even after plugging it into a power plant. And it would be interesting if this was the only piece of gear being damaged. My LS16 preamp works great, there's also slight buzz but I think it's normal. It's only audible when I place my ear right above the mesh cover. 

@audphile1 yes, it does sound pretty amazing 🙂

Is it expensive to replace those capacitors? I'll definitely have them checked if possible. 

Sorry to hear about your issues! If it happens at another home, it's not DC.  However even very good transformers do sometimes delaminate and cause this buzzing.

🤣… yeah, poorly designed… coming from another engineer. Very typical. They are, in general, an argument I’ve bunch that criticize anything they didn’t design. I would ignore that comment.

Sorry to hear about the transformer noise. It will probably be easier to replace the transformer. I have a power transformer that hums all the time, but it never changes, so I just turn it up a little more. 😃

Very likely it can be DC backwashing into your AC- it makes transformers buzz and hum. PS Audio made a Humbuster to take this out and Emotiva makes an outlet strip to do the same. Both work well. DC can come from a refrig, coffee maker etc. 

Thanks, the transformer will be replaced soon. 

I'm just thinking what kind of precautions I can take so it doesn't happen again. It was quite expensive, plus shipping, custom fees and mainly, it takes time. 

I have a separated circuit for the living room sockets (not for the audio only, yet) but I'd say the power in my apartment is quite stable. 

If there's DC present it doesn't damage the traf immediately, or does it!? My guess is it can get loose but it would take some time, even weeks, right?

iFi and and Van Alstine make a DC killing product:

(Personally, I'd go with the latter ...)

@filipm

I have bought a second hand ARC REF 150 power amplifier (non SE, KT120 tubes) and there was a buzzing noise coming out of the input transformer after few hours.

If this started upon initial use have you discussed this with the seller? Did he know of the problem and not disclose the condition? If so I would try to have him help with the repair or try to get a refund.

Just guessing here but did ARC ever sanction use of the KT150 in the REF150? If not perhaps the previous owner was using these tubes and they caused the problem?

I have taken the amplifier to a friend, a reputable tube amp engineer. He told me the input transformer must be replaced and also that in his opinion it was poorly designed.

No idea of the design but a simple search here seemed to find this particular model had its fair share of problems.

@jetter Yes, we have split the new traf cost 50/50.

We're not sure how that happened. It worked fine for several hours when plugged into a cheap Dynavox filter. Then I got a proper cable that reached the wall outlet and listened for the whole evening. The buzz initiated after several hours at first. I turned it off, let it cool down, plugged it back into the filter and the buzz was still there. Maybe it was just a matter of time and it was just a coincidence that it happened after plugging it into the wall. 

Also, it was mid August, super hot weather. I placed the amp into a custom made MDF cabinet with a space of two inches on the sides, opened back, opened front, semi-opened top (there's a shelf with preamps and TT about 20 inches above). The mesh never got hot, maybe even the LS16's mesh cover gets warmer. 

I didn't really listen to it for more than an hour and half until I got the power cord.

Thanks for asking.

I'd like some advice what to check so I can listen to it with ease. 🙂 

@jetter I have even asked the ARC if they recommend using KT150's in this model. They said definitely yes. Not in REF110 though. I was planning to get a set of KT150's when these KT120's reach their limit.  

I don't think this amp ever tasted KT150. The previous owner was a second owner and he has many amps. He said this one has been sitting in a box for some time. 

@filipm 

I'd like some advice what to check so I can listen to it with ease. 

Perhaps the individual repairing your amp can give you an educated guess of what caused your problem and recommend how to avoid a similar occurrence. 

From your description of your cabinet, it sounds like your amp had plenty of space to breathe and was not overheating, especially as your mention the top was barely warm (surprising to hear as I would have GUESSED it to be toasty even in "regular" use).

Hopefully someone here will address the problems that can occur with your house/apartment's power, i.e., too much or too little voltage, DC in the lines, etc. just in case that is a problem.  All over my head and happy listening.

The ARC REF150 manual says that the operation temperature is about 40 degrees of Celsius. Of course the tubes are much warmer but the chassis was always about that.

So the traf is finally replaced. I just had a first listen. 

Does anyone know how hot the input transformer can get? I have left the cover off so I can touch the transformer. I guess it gets to about 80 degrees of Celsius after 2 hours. The output transformers are quite cool. The volume wasn't loud.

Tannoys D700's are connected at 8 ohms, bi-wired. 

It works without any problems of course, I'm still a little nervous. Thanks!

Is there anything that can cause the transformer to overheat and melt inside? The noise was caused by a vibration of the plates inside the transformer. 

Does anyone know how hot the input transformer can get?

@filipm To the first comment (sorry I didn't catch this earlier), to my understanding ARC uses 'EI' core transformers for their power transformers (its not an 'input' transformer).

Over time, the bolts holding the transformer together (not the ones that secure it to the chassis) can loosen up. This is because they are insulated from the transformer by nylon washers, which shrink over time. If they get loose enough, the transformer can rattle. I suspect, since the amp was running this whole time, that simply tightening these bolts (there are four of them) would have solved the problem.

EI core transformers are quite resistant to DC on the power line. It takes quite a lot to make them rattle. Toroid transformers OTOH are quite sensitive!

Live and learn...

Regarding the second question its normal for the power transformer to run warm. 80C is fine. If the transformer gets so hot you can't touch it that's bad, but 80C is acceptable.

@filipm

Better get a cook’s (meat) thermometer, like the ones sold at Ikea, to be sure.

@atmasphere

I still have the old transformer in a box over here - it seems there’s only one set of long bolts (at least those that could have been tightened).

I have been running the amp opened with the new transformer - without the top cover. I check the temperature time to time, I can touch it anytime, even after a long playtime but I can’t hold my hand on it for more than 4-5 seconds.

// I even checked with ARC, they said it was alright. Hope it lasts for long, I'm going to replace the tubes for a set of KT150's soon.

Thank you.

I still have the old transformer in a box over here - it seems there’s only one set of long bolts (at least those that could have been tightened).

Those are the very ones.