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Advise on amp

vco1

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I currently own a Cambridge Audio 840A amplifier with an 840C cd-player and Focal Profile 918 speakers. Have it for almost 9 years and overall I'm happy with the sound quality of this set. However, the transformers in the 840A amp (sometimes) hum like crazy. Even when using an ATL DC Blocker. The DC Blocker was able to get the amp quiet at moments (while before it was humming 100% of the time), but I guess the power in my neighborhood is of such bad quality that even the ATL is not always able to remove all DC. The hum can (sometimes) be heard from up to a couple of meters distance. And I'm actually sick of it.

So I'm looking for a new amp (and matching cd player). Obvously, I'm a bit reluctant to buy yet again an amp that has huge toroidals inside. I might end up in the same situation as I'm now.

Saw a good deal on a Denon PMA-1600NE, but it kind of looks like a step back from the 840A.

Any opinions and/or suggestions? Budget for the amp preferably max €2500/$2500. The Denon PMA-1600NE would be €1000 (usually €1699).
 

Jim Matthews

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The DC Blocker was able to get the amp quiet at moments (while before it was humming 100% of the time), but I guess the power in my neighborhood is of such bad quality that even the ATL is not always able to remove all DC. The hum can (sometimes) be heard from up to a couple of meters distance. And I'm actually sick of it.

Setting aside the improvements available at lower cost in today's market -
What is physically under the 840a?

If a transformer is "humming" it may induce vibration into the supporting shelf. Some of my noisier high output amps had transformers that benefitted from tightening mounting bolts.

If it's actually in your power line, modern amp designs with a "wallwart" DC transformer might provide relief.

****

In my limited experience, verification of AC mains ground was a valuable (and inexpensive) first step.

Forgive me if I'm suggesting what you have already attempted, but established practice requires some fundamental conditions be satisfied, first.
 
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vco1

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Setting aside the improvements available at lower cost in today's market -
What is physically under the 840a?
The cd player is under the amp. And under that is a quite sturdy and heavy sideboard made of think wood. When I put the amp straight on the concrete floor the hum was there too. The amp has to be on top as it gets quite hot.

Forgive me if I'm suggesting what you have already attempted, but established practice requires some fundamental conditions be satisfied, first.
Your suggestions are appreciated. And I understand why you're asking these questions. I have a feeling though that there's little I can do about the humming of my amp. Although I have no scientific proof, I do think it's DC on the mains, since the DC blocker did bring a change. Did A-B tests, and the hum returned when I removed the blocker from the powerline. So it's not that there was no DC at that moment of the day. The only things I didn't do (yet) are replacing the transformers in the amp or measure the DC component on the mains. First because of the money, and the latter because I lack the skills and most likely an electrician wouldn't know what I am talking about. Besides, it seems to be a difficult thing to measure to start with.

I am very cautious in replacing this amp though. The sound is good. And the last thing I want to do is spend money on another noisy amp. But like I wrote, the hum is (relatively) loud and annoying.
 
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vco1

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I'm in The Netherlands. The 2500NE looks like a good amp. Unfortunately is much more expensive here (€2699). And only available in silver. Though that's a minor thing.
 

Jim Matthews

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I am very cautious in replacing this amp though. The sound is good. And the last thing I want to do is spend money on another noisy amp. But like I wrote, the hum is (relatively) loud and annoying.

This is precisely my concern. If you have someone that could lend you an amplifier, that might verify the line noise.

Most interference in domestic power lines comes from motors (such as Air-conditioning compressors) cycling on and off.

I would be very surprised(in a modern country) to find DC offset in your power grid. If this is a recent development I suspect Summer weather increase the use of "noisy" equipment connected to your power lines.

It is an unfortunately common problem.

https://www.audiosciencereview.com/...s/powerline-network-interference-noise.15708/
 

gasolin75

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Mabye a used Michi (rotel) or ROTEL RA-1592, the mkII is a little over your budget
 
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vco1

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Thanks for all the suggestions so far.

Does anyone have experience with the Denon PMA-1600NE and DCD-1600NE? Would it be a downgrade from my 9 year old Cambridge Audio 840A and 840C?
 

Willem

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I am also Dutch, and to be honest the power grid in our country is rather good and clean. I have never experienced any issues with any gear, from ultracheap to Quad or Luxman. Is there anything special in your location, like proximity to a power hungry industrial plant or a solar panel park? Have you tried to use the amplifer somewhere else? Is the transformer humming/resonating physically, or is it a 50 Hz electrical hum in the output signal? Are you sure it is not a ground loop?
 
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vco1

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We have an elevator in the building (but there's no relation between the elevator moving and the hum). There's a factory at about 400m (as the crow flies). And like in so many other places there are quite a few houses with solar panels nearby. Not on my building though. So the situation is probably not ideal to start with. That being said, the hum has been there way before there were any solar panels.

I haven't tried the amp at a completely different location. Only across the street (more or less). And there it's humming too. Years ago when the amp was out for service for this issue, it was returned telling there was no noticeable hum.

Today I opened up the amp yet again. Trying to pinpoint the culprit. What I did notice was that the hum got (a bit) less when I turned down the volume completely, muting the output. So I assume most hum is coming from the main transformer. There's also a smaller one; don't know what that's for, but I assume to keep it powered up in standby mode.

There is no difference if I put the amp in a different place in my apartment. Also no difference if anything is connected or not. The signal is clean, both to headphones and to speakers.

Not sure if it's relevant, but the amp gets quite warm (not hot) when it's just powered on, but not playing. And I think the temperature is not always the same: sometimes it seems to get noticeably warmer than other times. No matter if it's in active use or not (but obviously fully switched on).

Finally, I read many messages on the net that (some) hum from a big toroidal transformer is considered normal. For what it's worth it. I prefer my equipment to be silent. But perhaps I'm a bit too demanding?
 

UniPolar

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VCO1, from my experience, those toroidals are mounted using a rubber or silicone insulator on top and below. There also is usually a metal 'cap' on top through which a metal bolt is used to secure the transformer to the chassis.

IF there is enough room, you can add an additional layer of insulation material to both the top and bottom of the large toroid.. From the online pictures, it's hard to tell if this would be possible or not..... But the extra 'damping' should further reduce the hum

As for the the smaller toroid mounted on the rear plate.. Since it is much smaller, you can 'unmount' it ( with the power off ) and then power on to see if it may be the source of some of the hum.

In a similar thought, you could unscrew that large bolt on top of the main toroid leaving it in place and power the unit on without the bolt or nut in place and see if the hum is reduced....

That is a nice amp, which it sounds as if you like it so maybe a little 'tweaking' will reduce or resolve this issue.

Good luck..
 
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vco1

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So I tightened the bolt on the big toroidal. And, lo and behold, the amp was absolutely quiet for over a week. Daily.

Until yesterday that is. When the amp started humming like crazy again. Immediately after I switched it on. Ceteris paribus. That is, on my side nothing has changed. To give an impression, when it was quiet I could barely hear a faint hum when I put my ear on the amp. Right now, I can hear it buzz with my headphones on (but no music playing, luckily) at 1m/3ft distance. It must be something external. And I think it's the 'quality' of the power, whatever that may be.

When the amp was quiet, I forgot about the idea of buying a new amp. If it stays humming like it is now, I'm sure it's time for something new. Something without a huge toroidal transformer. Looking at 2 Audiophonics MPA-M400ET's and a MiniDSP (either DDRC-22D or SHD).
 

gasolin75

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rubber feet grommets under the amp, torodial ? Like improving vibrations from a spinning harddrive.
 

Roland

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Connect a wire from the gnd terminal earth on the back panel to a mains plug and you’ll cure your hum.
 
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vco1

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Thanks for all the suggestions. It's appreciated.

As to why 2 amps? I thought monoblocks would be nice. Just for a change. And I can put them out of sight next to the speakers. Don't like to have a stack of all kinds of different size and color devices in sight. Also don't think the Audiophoncs devices are particularly beautiful. Yes, I'm that picky. ;-)

Rubber feet, etc. won't help much. If anything. The hum comes from inside the amp. Even if I would hold it in my hands, it'd still be audible. As far as I can hear nothing resonates, except the transformer.

I can try a ground wire. But this is not ground hum. It's not coming from the speakers. It's not anywhere in the signal path. It's not related to any connected components. It's coming from the inside of the amp. More particularly, from the toroidal transformer. After all things investigated I'm pretty sure about that.

Either the design of the Cambridge 840A is really weird, or some external factor causes the humming. Since the amp can - and is - absolutely quiet at times. But when it isn't, it's emitting a really a loud hum. Constantly (i.e. the whole day, for days in a row, etc.). I've basically given up on finding a solution. I don't see a pattern. And I've tried everything I could do myself (DC blockers, tightening bolt, switching off other equipment in my appartment).
 
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