[Amps] Acoustic Noise Comparison

Fri Jun 22 09:02:38 PDT 2012

> 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 have been fairly fussy about quiet ever since I started to suffer
with Tinnitus ( ringing in the ears ).  Loud noises - or even medium
noises over periods of time - exacerbate the condition.

   A few years ago, my wife wanted a Honda Element.  We found one, went
and got it, I drove it 100 miles home.  My ears rang for three days! 
Road noise in the Element is extreme.  That's why I got the Dynamat
material.   I basically took the interior apart and pasted this stuff
to the sheetmetal.  Dynamat is not a sound absorber, it is specifically
designed as a resonance killer.  Sound absorption takes different stuff
- I guess it's what Jim calls "fuzz".

   ETO did pay some attention to the sound of the blower.  They rubber
mounted it, and ran it off 95VAC, courtesy of a 25V winding on the big
power transformer, connected out of phase.   In receive/idle it's
more air than is needed - the amp idles very slightly above room
temperature.  I'm thinking a two-speed arrangement with either a resistor
or
a little transformer, switched by a relay.  Depends on how much power
is involved in driving the motor.  From a space perspective the resistor is
better - there's not much space in that cabinet, and space needs to be
saved for a filament transformer for a possible future 3CX800 conversion. 
OTOH, a bucking transformer won't create (much) more heat.  There would
need to be some sort of timer to make it flow full speed for a while after
stopping transmit.  I guess I'd do that with a 555 and a logic gate -
IF ( we are in transmit or the one-shot is running ) THEN fan=full speed.
and the one-shot would kick off when you go from transmit to receive.

                        - Jerry Kaidor, KF6VB

>
> 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 at q.com>
> Cc: <amps at 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 at rogerhalstead.com>
>>> To: <amps at 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
>>>>>> _______________________________________________
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>>>>>> Amps at contesting.com
>>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>
>>>>
>>>>
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