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Audio Research Reference 150 - buzzing input transformer

Hello everyone, 

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. I have detected the noise appears as the amp fully warms up - after about an hour. It goes pretty loud within another 30-45 minutes.

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.

I live in Europe so I didn't have the chance of sending the amp to the factory, nevertheless, a new transformer is on its way and I'll get it fixed by an authorized dealer and service. 

I was also told that the problem may happen again and that I should get rid of the amp. 

My question is whether any of you had similiar problems and what the cause can be. I really love the sound of this amp and of course I'd like to keep it. I'd also like to do as much as possible to keep the amplifier safe. 

I have found a very similiar discussion here on Audiogon, I have messaged the OP and he replied he had his transformer replaced afterall - 

 

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. 

 

My speakers are Tannoys D700, they go down to 3 ohms and I can imagine they are current hungry even tho their sensitivity is 92dB. They worked well with a Classe CA-200 but the ARC sounds a lot better of course. I'm planning of upgrading the speakers in about a year but for now, I'm still very happy with these, it's always a pleasant surprise when I upgrade any piece of gear. 

I have asked the ARC company whether the speakers won't be a problem for this kind of amp. They ensured me I'd be fine and that they test their gear with much more difficult loads. 

The amp never got too hot when I placed my hand on the top of the chassis, the tubes were measured and they're fine, about 1100 hours on them. The amp wasn't in use for a few years before I bought it. 

Thank you for any suggestions.

128x128filipm

Showing 2 responses by jetter

jetter
2,972 posts
 

@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.

 

jetter
2,972 posts
 

@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.

 

 

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