Good points Jim plus my shack is never quiet what with a PC, the xcvr with a
small fan always on the finals heatsink, fluorescent lights backround hum
and sometimes a radio on an AM or FM station.
I also have always used headphones to operate, even as a teenager. Am I a
typical or atypical operator?
Carl
KM1H
----- Original Message -----
From: "Jim Barber" <audioguy@q.com>
Cc: <amps@contesting.com>
Sent: Thursday, June 21, 2012 10:11 PM
Subject: Re: [Amps] Acoustic Noise Comparison
> And that's where we have to be careful.
>
> I work on dampening and otherwise normalizing enclosures and spaces for
> artsy designers, so if there's a measurable resonance in a waterfall
> decay display when excited by a high-energy signal, I feel compelled to
> fix it. To me, the 76A cabinet rings like a bell. To someone else it
> might sound acoustically dead. It's a matter of perspective.
>
> Can the "average guy" tell the difference between an acoustically
> treated amp blower/case and an untreated one? Absolutely. Will that same
> "average guy" care, or perceive it as an improvement? That's a different
> question.
>
> My .02,
> Jim N7CXI
>
> On 6/21/2012 6:58 PM, Carl wrote:
>> My 76PA 3 holer is almost silent, same sheet metal
>>
>> Carl
>>
>>
>> ----- Original Message -----
>> From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
>> To: <amps@contesting.com>
>> Sent: Thursday, June 21, 2012 9:05 PM
>> Subject: Re: [Amps] Acoustic Noise Comparison
>>
>>
>>> On 6/21/2012 2:43 PM, Jim Barber wrote:
>>>> Spot on, Jim.
>>>> The 76A and the 78 suffer from both vibration and turbulence, with the
>>>> effects compounded by resonances in the sheet metal cover.
>>>
>>> My "old" 76A is almost silent with no vibration in the cover.
>>> For those that do vibrate, a simple piece of tape on the top of the
>>> center partition should quiet it as it has to vibrate against something.
>>>
>>> If the fan vibrates bad enough to make the case vibrate enough to make
>>> noise I'd check the squirrel cage to make sure there is nothing going
>>> for a ride. Those fans are very sensitive to any foreign material...
>>> like bugs. I can lay my hand on the case while the fan is running and
>>> feel no vibration and that thing is so old that any rubber is long gone.
>>>
>>> And for Jim? Mig welding from a spool is often an exercise in futility
>>> and frustration. Heat and speed are critical and I'd not weld anything
>>> to the cover anyway.
>>>
>>> 73
>>>
>>> Roger(K8RI)
>>>
>>>>
>>>> Better blower mounting and fuzz would help a lot, a scattering of
>>>> braces
>>>> in different lengths (where they'd fit) under at least the cover top
>>>> would help them help.
>>>>
>>>> Some may not believe this, but after bracing, bead-blasting and
>>>> powder-coating the top cover with heavy wrinkle-black helps at least a
>>>> little with the cover resonance(s).
>>>>
>>>> My .02,
>>>> Jim N7CXI
>>>>
>>>> On 6/21/2012 9:28 AM, Jim Brown wrote:
>>>>> On 6/21/2012 10:12 AM, Jerry Kaidor wrote:
>>>>>> Still playing with my "new" Alpha 78.
>>>>> No experience with that amp, but some components of motor noise are
>>>>> vibrationally coupled to the desk or shelf that the amp sits on. I've
>>>>> reduce that component of the fan noise in my Titan 425 amps by setting
>>>>> the RF deck on soft foam padding. There are no vents on the underside
>>>>> of
>>>>> that amp, so I'm not interfering with cooling.
>>>>>
>>>>> I bought all of my 425s used, and one of them came with a power
>>>>> transformer that made a lot of noise. The problem was loose windings,
>>>>> so
>>>>> I jammed some shims between the windings and the frame to kill the
>>>>> vibration.
>>>>>
>>>>> Another component of fan noise is air turbulence, and the components
>>>>> are
>>>>> higher in frequency. Higher frequency components bounce off of hard
>>>>> surfaces (like walls and shelves) and into the room. We can kill those
>>>>> reflections (and thus some of that noise) by placing soft materials
>>>>> (what we acoustic consultants generically call "fuzz") on those
>>>>> surfaces. Obviously this should be done in a manner that doesn't
>>>>> interfere with cooling.
>>>>>
>>>>> 73, Jim K9YC
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps@contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>
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