[Amps] Acoustic Noise Comparison

Fri Jun 22 07:14:44 PDT 2012

On my home built 2 x 8877 amplifier I have a low power switch that turns the
fan and blower down to tick-over on long-term standby and it is as quiet and
my PC. They go to full speed when I TX or when I throw a front panel switch.
As there is only 100 watts of heater power being dissipated in stand-by this
approach works well. Should have done it years ago. I also have a switch on
the separate PSU but this only gets used when operating JT65.

I work from my shack and need to have the amplifier on ready for any opening
when and if they occur.

Works brilliantly.

Chris G3WOS

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Carl
Sent: 22 June 2012 15:03
To: audioguy at q.com
Cc: amps at contesting.com
Subject: Re: [Amps] Acoustic Noise Comparison

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 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
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>
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