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Old 25th January 2010, 04:53 AM   #1
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Default negative effects of high frequency filtration?

My X600.5 amps normally sound awesome. But sometimes the sound would, inexplicably, turn too warm with the treble noticeably rolled off and the bass loose and weak; transients become smeared despite the fact that stereo imaging will remain intact. This can last hours. I've begun to wonder whether this might be related to amps' built-in high frequency noise filtration. Any thoughts?

p.s. My amps are plugged directly into their own dedicated circuits so load shouldn't be an issue. I've tried other preamps and source to no avail. Removing the power conditioner the frontend equipment is plugged into can reduce the problem but not completely.
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Old 25th January 2010, 06:24 AM   #2
gootee is offline gootee  United States
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Well, maybe it's because there's NOT ENOUGH high-frequency filtering.

Any RF that gets in can and will be rectified by any PN junctions it encounters. That can potentially change DC bias setpoints, mucking things up. Maybe someone or something nearby, or even something on the power grid, occasionally causes a strong RF signal, for a few hours.

Inputs are not the only places that RF filtering is needed. Outputs and AC and DC power circuitry are all "inputs", for RF.

"Minimalism" in circuit design might have its place. But one should not ignore RF filtering, if good audio reproduction is desired. How high do you think the bandwidth needs to be, for "perfect" audio reproduction, anyway? I do not believe that lowering the bandwidth from a high RF frequency to a lower RF frequency could be noticeable.

Also, since your problem is perceived intermittently, I doubt that it could be from "too much" HF filtering (although the intermittence of the effect still leaves open the possibility of not enough HF filtering).

It could also be something in the circuit that is only marginally stable, either thermally or with respect to high frequency oscillation.

Or, and this is a bit of a stretch but it just occurred to me, it could even be something electro-chemical, in yourself. (OK it's late and I'm a little "punchy".) Intermittent problems can be difficult to diagnose! Heck, it could even be an insect or a rodent that is sometimes attracted by the heat from the amplifier, nestling itself into a sensitive area of the circuitry. Or maybe it's a mechanical thing, like a cracked solder joint (or an interconnect) that usually makes good-enough contact but is sometimes heated or jarred just enough to move just enough to change its resistance just enough to be noticeable. Or maybe humidity or ambient temperature could even be affecting it (or the phase of the moon, or the tide, or sunspots, or...). Seriously though, "just in case", and since it's relatively quick and easy, I would re-seat all of the plugs and jacks, and treat them and all of the switch contacts, etc and probably also pots if they're not sealed, and any internal non-soldered interconnects, with the appropriate Caig product, such as De-Oxit for things like contacts, plugs, jacks, etc, and then maybe some of their other products for certain materials, such as gold connectors, plastic pot elements, et al. Check caig.com. You'll wonder how you ever lived without it.

Edit: I didn't notice that you said "amplifiers", as in plural. That changes everything. If both of them are affected the same way, at the same times, it's obviously something external to either of them, that causes both of them to change similarly. That tends to point to 1) not enough HF filtering and an intermittent RF source, or 2) something nasty happening on the power grid, or 3) you or something in the surroundings.

Last edited by gootee; 25th January 2010 at 06:29 AM.
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Old 25th January 2010, 01:06 PM   #3
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Default oops

Sorry didn't mean to suggest that HF noise filtration is a bad idea -- should've worded my original post better! What I meant to ask is whether filteration could, under certain situations, leave the kind of sonic imprint I described? What I also don't understand is why removal of the power conditioner from the frontend equipment's power path would improve things.

The problem is very obvious when it occurs -- my wife can hear it too. I've also ruled out connectivity having cleaned all electrical contacts thoroughly.

Last edited by 5spheres; 25th January 2010 at 01:33 PM.
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Old 25th January 2010, 03:23 PM   #4
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The X600.5's don't have much in the way of filtering, just
about 10pF, so I wouldn't expect that to be the issue, besides
the fact that it is intermittent.

Most intermittent effects are bad connections. I would start
by checking and re-seating every interconnect and cable in
the signal chain.

And then I would check the tweeters on my speakers.

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Old 25th January 2010, 05:39 PM   #5
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Quote:
Originally Posted by gootee View Post
Inputs are not the only places that RF filtering is needed. Outputs and AC and DC power circuitry are all "inputs", for RF.
...
2) something nasty happening on the power grid
Very good!
It's sometimes overlooked that an output can serves as input for RFI.

If the problem comes and goes, power supply can be the issue. Often people describes that it sounds better late evenings or during weekends when there is less disturbances on power grid.

Quote:
Originally Posted by 5spheres View Post
What I also don't understand is why removal of the power conditioner from the frontend equipment's power path would improve things.
A change in how your equipment is grounded?
The X600.5 are monoblocks, right? Do they get power feed from same location as preamp, or other outlets in your room?
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Old 25th January 2010, 07:27 PM   #6
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Quote:
Originally Posted by Audio_se View Post
A change in how your equipment is grounded?
The X600.5 are monoblocks, right? Do they get power feed from same location as preamp, or other outlets in your room?
The X600.5 are powered by two separate circuits fed directly from the breaker panel. The frontend equipment is connected to a power conditioner on another circuit.

I've tried cleaning/replacing all signal and power cables but that didn't help.
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Old 26th January 2010, 09:59 PM   #7
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I noticed that my AC can sometimes reach 127-128V (before load). Might this explain the excessive warmth and treble/bass rolloff that I hear?
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Old 27th January 2010, 02:43 AM   #8
gootee is offline gootee  United States
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Quote:
Originally Posted by 5spheres View Post
I noticed that my AC can sometimes reach 127-128V (before load). Might this explain the excessive warmth and treble/bass rolloff that I hear?
I am sorry. I am not at all familiar with those models. Do they have regulated power supplies? If not, then "maybe". Perhaps you could try to correlate the "episodes" with the power grid voltages.
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Old 27th January 2010, 09:36 AM   #9
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Quote:
Originally Posted by 5spheres View Post
The X600.5 are powered by two separate circuits fed directly from the breaker panel. The frontend equipment is connected to a power conditioner on another circuit.

I've tried cleaning/replacing all signal and power cables but that didn't help.
I'm thinking of issues with ground loops. I would try to run everything from same outlet, just to try. Assuming you can without overloading the outlet.

But I might be walking on thin ice here, downloaded the X600.5 manual and found:
Signal ground is isolated from chassis, safety ground, to reduce the incidence of ground loop noise. The presence of a safety ground will not degrade the audio signal chain.
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Old 30th January 2010, 07:24 PM   #10
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Okay I monitored changes in my system/sound closely this week. There was only one bout of "intermittent warmth". It happened when the line voltage was 124V -- a bit higher than average. The temperature of the heat sinks on my amps was feeling a little hotter than usual. (According to the manual, the steady state temperature of the heat sinks is related to the voltage of the incoming AC.) I'm ruling out dirty contacts because I had just cleaned every conceivable electrical contact in the signal / power path throughly with pure alcohol the night before.
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