Reducing hiss in Dynaudio BM5A monitors

[lontas]

I like these speakers, but there is a slight audible hiss coming from them. It is subtle, but just enough to bug me when the rest of the room is quiet. I'm wondering if anything can be done to lower it?

Each speaker has a linear power supply with a hefty toroidal transformer. There is an 8A rectifier and then eight 1000uF smoothing caps. The amp chips (likely to be LM3886, can't tell because they are buried under heatsinks) appear to be powered directly off the smoothing caps, unregulated. There is an EQ/active crossover board that has regulators on it, however.

So then, I'm thinking of replacing those smoothing caps with low-esr types and doubling the capacitance. Would that be likely to lower the hiss, or just an exercise in futility? Should I also beef up the rectifiers to handle the larger inrush current?

For now, I won't touch the EQ/crossover. I want to be really cautious about these since they are my main production speakers. Thanks!

[._.]

I don't know about the elctrical parts have you tried moving them a bit further away?

Almost all monitors will do some kind of hiss regardless of price, I would suggest passive monitors and a good amp. There are many good and cheap amps to choose from.
If you need filters with rolloff and such you can add that in separate boxes.

[LeeYoo]

Read this post

"Hiss (not hum or buzzing) in powered speakers, no input."

[Beefy]

Read this post

"Hiss (not hum or buzzing) in powered speakers, no input."

I don't see why you were trying to cut this guys throat he was just trying to help. Apparently you know the guys problem better than the last poster but I didn't see you give any solutions.



You could try what the first poster said that might work or yeah you can replace any of the caps in there with higher quality higher value caps as long the caps aren't doing any eqing. If they are just replace them with higher quality of the same value.

If there is something I own that doesn't sound right to me I just replace the inerds with better quality stuff and normally that fixes it. In fact I don't think that has ever not worked for me. If it didn't I would just buy a piece of gear your going to be happy with.

[Matt Syson]

Hi
Hiss has absolutely NOTHING to do with capacitors, certainly not with any that you can just 'swap for better ones'.
Hiss is a natural occurrence but is made more noticable by poor design choices. Either the crossover, the power amp or maybe both have an 'issue' but it is back to the design guys for a 'remedy' unless you happen to be unlucky and have a 'faulty' unit.
Hiss can also be apparent if you have a strong source of 'RF' which is getting into the amp by it's cabling but it would most likely to appear with 'odd noises' attached (like mobile phone stuff).
Talk to your dealer if they are new units.
Any form of 'messing about' in these units will '£$%^' them up and will then be no good as any form of reference.
The LM chips are supposedly 'Hi Fi' so should not be particularly hissy, but the crossover may be problematic.
If you can't hear the hiss from say 2 feet away from the speaker then it is probably OK.
Unplug the inputs and TERMINATE them (link pins 2 and 3 of an XLR) with either a short circuit or 600 Ohm resistor and see if the hiss reduces. If it does then look to your monitor controller for the problem.
Matt S

[bassguy6]

I have the same speakers. When I had that problem, I was told to decrease (turn down) the sensitivity on the back of the speaker and turn up my ensemble. Problem gone.

[lontas]

Thanks everybody. I should clarify, the hiss is really subtle and definitely not a problem. It's just good-ol' thermal noise, and it is definitely coming from the internals of the speaker. I'm sure it is within normal operating spec. (Yes, I can hear it across the room when the room is quiet.)

But why settle for "normal" when with a little extra work you could have "awesome"? Beats dropping $3k I don't have on a new pair.

The electronics are all packed tightly together, so I realize that maybe the hiss will be unavoidable in this case. Still, I like to ask around.

[lontas]

Bassguy6 - I used to do that actually. But I noticed that engaging the pad actually reduces the transparency a little, just enough to bother me. (Probably the cheap surface mount resistors are responsible.) So now, I keep the level switch set to 0 which seems to offer the greatest clarity. The level switch did affect the hiss in my case, but the difference was so subtle that it wasn't worth the loss in transparency I experienced. They're great speakers though. I'm just being picky.

[LeeYoo]

Originally Posted by Beefy

I don't see why you were trying to cut this guys throat he was just trying to help. Apparently you know the guys problem better than the last poster but I didn't see you give any solutions.

Well, if you read all of it, you will understand that there are no solutions.
Clean hiss is a design problem. No cap mod is going to fix this.
Matt Syson has summed this up clearly.
You can try to lower the gain of the monitor as bassguy6 did, if you have enough gain. Or try to add a resistor across XLR pin2/3.
Otherwise, live with it. And make sure, you try your next pair of speakers before you buy them.
Leo..

[mbrice09]

unbalanced cables can do that at times as well

[Matt Syson]

Hi
Having an unbalanced connection can NOT make something HISS more than a balanced connection. It may upset some other parameter, possibly 'upsetting' either the source gear or the 'destination', causing them to 'misbehave' but a piece of wire CAN NOT do it on it's own.
If the OP has tried turning the level control / attenuator on the speaker down and the hiss does not reduce (with NO signal cables connected to the speaker) reducing the gain of the power amp section COULD achieve something but many chip amplifiers are quite 'touchy' about use at lowered gain so you have to properly engineer any 'mod' you make not just dive in with a resistor or two.
With the input terminated (as I said above) I would be unhappy if I could hear 'hiss' or hum from loudspeakers from more than a couple of feet away. Unless you have proper test gear (signal generator, accurate meter to say 50KHz, and an oscilloscope) (and know how to use them properly) don't even think of pulling it apart.
Matt S

[Jim Williams]

This seems to be a recurring problem with active speaker designs. Many of them have it, including the revered Meyer HD-1's, the first quality self powered monitors. That put me off of those back in 1989.

For me it's inexcusable for any monitor to emit any noise at all. Hiss is a mistake of the designers, not using low noise design techniques and components.

This is why I continue to use passive monitors fed by a quality and silent power amp. There is no hiss off my tweeters, none. Stick you ear 2" away from the tweeter and maybe you can hear a tiny amount, one foot back and it's all gone, as it should be.

I don't know why you guys put up with this noise, I've had this silent monitoring path for 22 years now. It's not like this hasn't been solved a long time ago.

[tINY]

There is always a noise floor.... If the clarity is really that much worse by engaging a pad, then live with the hiss.

What is connected to the inputs of the speaker? The hiss may well be coming from the output of whatever is driving the speakers.

If it's a problem only when the inputs are unterminated, then don't do that...



-tINY

[ripple_fx1]

if you find the hiss acceptable with the input shorted, and you're certain you're not running +4 into -10, and your volume control isn't in the first or last quarter of it's throw for full throttle monitoring, and engaging the pad gets the noise floor to a level you can stomach and doesn't throw your gain structure out of whack, cook up a pad of fanciful resistors in a sauce of exotic alloys and test your SMD theory....

[LeeYoo]

Originally Posted by Jim Williams

This seems to be a recurring problem with active speaker designs. Many of them have it, including the revered Meyer HD-1's, the first quality self powered monitors. That put me off of those back in 1989.

For me it's inexcusable for any monitor to emit any noise at all. Hiss is a mistake of the designers, not using low noise design techniques and components.

This is why I continue to use passive monitors fed by a quality and silent power amp. There is no hiss off my tweeters, none. Stick you ear 2" away from the tweeter and maybe you can hear a tiny amount, one foot back and it's all gone, as it should be.

I don't know why you guys put up with this noise, I've had this silent monitoring path for 22 years now. It's not like this hasn't been solved a long time ago.

+1
I think the main part of this hiss comes from the active crossover that is used in front of the two power amps inside a two-way monitor. Please correct me if I'm wrong.
A normal amp plus a passive box uses a passive crossover.
Active monitors also could use a passive crossover, but the prices of crossover inductors and big caps are so high that an active solution is cheaper nowadays.
Even a single tweeter cap can be more than the price of an integrated amp.
Leo..

[._.]

There is also the problem with the often dual shelving adjustable filters that compensates for tabletop, nothing/freefield, against wall etc bass response, and the top rolloff/sparkle. Then you would need separate passive filters for all those functions. It would just be a big box of filters then.

Usually the only thing you want active filters for is the ~100hz region (sub/main) or if you have really massive 3/4ways, since its a big and expensive coil you need and since it can be nice to have the sub frequency adjustable both in frequency and amplitude to match the room.

Cheapest thing to do seems to be to just move the speakers away a few ft. Probably the only thing too.

[Bill@WelcomeHome]

Originally Posted by Jim Williams

This seems to be a recurring problem with active speaker designs. ...
This is why I continue to use passive monitors fed by a quality and silent power amp. ...

When I hooked up the balanced powered Cello to the Dunlavys in the mastering room I thought that the amp was broken. It was dead silent. A scary moment until the music started. Then it was glorious.

I had discussed this subject with the Lipinskis many years ago. Their claim was that powered speakers that they had checked also measured significant distortion. Subsequently they designed their speaker stand to hold the 707 and their amp.

Right now my temp system is a Bel Canto amp with smaller Duns, but I expect to go to either Barefoot 27s or ATC 25s.

I think the biggest problem here occurs over and over when it comes to dealing with hardware.... users don't know what they are doing or why, and the vendors don't provide adequate setup literature.

[tINY]

Unfortunately, I don't think there are a lot of active speakers with really good amps in them. It's a matter of what the market demands...

The one pair that was impressive in this regard was the xD system from NHT. But, they were really spendy.



-tINY