Why do some amps sound "hollow"?

[K4JC]

And by hollow, I mean it sounds like someone is talking through a drainpipe! It sounds horrible, and I wonder if it's due to design flaws, certain brands, or what? I am going to be looking for an amp to buy one day, and I definitely don't want one that makes me sound like I'm inside a hollow tube!

[W7ETA]

One hopes the amp is operated in its linear range.  If it is, then crappy audio in means crappy audio out.

If the amp is loaded past its linear range, and you have crappy audio in, why then, you have crappy audio with the added delight of crap all over the airwaves.

WB2WIK wrote a nice article about how to adjust your mic gain and "processor".  

If I remember correctly Tom W8JI has a nice article on loading an amp: http://www.w8ji.com/loading_amplifier.htm

Get a good mic for your rig, adjust the mic gain, turn off the processor, load amp correctly, and as long as you don't have excessive RF in you shack, you will sound great.

73
Bob

[W7ETA]

Ooops.  I forgot to mention you'll sound great unless you decide to distort your audio with mic equalizers.  Then you can create a hollow sound with reverberating audio.

73
bob

[K0BG]

If the true facts were known, the majority of amateurs overdrive their amplifiers. As Steve Katz, WB2WIK would say, all knobs right! These include way too much microphone gain and/or compression.

Another segment buy peaky microphones, and then a bunch of ancillary hardware to go along with them.

The results speak for themselves; enough IMD to satisfy any ego!

Alan, KØBG
www.k0bg.com

[K6AER]

I have never heard a HF amplifier that made the audio sound hollow.

I have heard splatter, IMD distortion, flat toping, electronic bias distortion, hum, high voltage arching and the proverbial sudden 13 dB of gain loss but never a hollow sound.

Maybe you were hearing phase distortion from multipath signal arrival.

[KM3F]

I would say that you don't know what you are hearing and blame it on an amplifier.
An amplifier is 99% of the time a single stage circuit and cannot produce time delay long enough to be heard and has no effect on fed bandwidth from the tuned circuits or the active devices.
However, if some form of digital processing is being done at the radio and/or audio input to the radio, then high SWR or feedline RF getting back into the audio can produce all sorts of results that is amplified by the linear.
I have heard it on the Flex radios.
Garboge in garboge out!
An amp may make it worse but is not the real cause.
This is where the terms good engineering practice come in in part 97.
Run a clean station and these things are seldom an issue.

[AA4PB]

all knobs right!
-----------------
Isn't the goal to make the wattmeter read as high as possible? :-)

[WW5AA]

The hollow sound is a secondary audio response caused by line delay when an amp is over driven. This is also heard and seen on a scope when a transmitter has a large key-up overshoot. Some folks just like all the knobs to the right and their buddies will tell them they are "booming" in.

73 de Lindy

[K6AER]

Given a RF amplifier has at best 180 degrees (one half of a cycle at the resonate frequency) of phase change from input to output that is minuscule at audio frequencies. Also for a hollow sound you would need phase cancellation at the 2000-3000 Hz audio range. Where is the second audio path for this to take place?

Blaming the RF amplifier of bad audio other than general amplitude distortion is a misplaced concern.

[WB2WIK]

Next time you hear a "hollow sounding" amplifier, ask the other operator to turn his amp off and see how it sounds.  I'll be it sounds the same way, just a bit weaker.

The sound comes from the rig, not the amplifier.

An amplifier can surely add distortion if it's not operated properly, but it can't create "hollowness."

[K4JC]

Thanks for all the replies. It seems to me that the "hollow" sounding stations are (mostly) using amplifiers, but it's probably just a coincidence. Maybe poorly adjusted audio processors, or something along those lines. But now I can go QRO with one less thing to worry about!

[K4DPK]

I hear quite a number of stations such as you describe, and almost invariably when I ask them how far they are from the microphone, they answer in the range of ten to eighteen inches.

When you are successful in getting them to close-talk the mike and back down to a suitable level on the mike gain, the hollowness disappears.

I guess they see this on TV or something.

Having said that, I remember one guy who asked for an audio report, and I told him it sounded like he was speaking through a piece of pipe.  He said "Doggone, how did you know?"  

He really was.... because he had moved the mike across the room to avoid picking up fan noise from his amplifier.

Takes all kinds.

Phil C. Sr.
k4dpk

[W7ETA]

Great story!

[W3LK]

I'm with Phil.

Close talking a mike (either hand held or a boom mike) with reduced mike gain will eliminate the overwhelming majority of funky-sounding audio problems.

73,

Lon - W3LK
Naugatuck, Connecticut

[RADIOBOB]

Well, lets see if we can put this to bed.

You have been given some of the very best answers you will find.  Re – read them.  Don’t try and fudge the issue.  99% of the time what you are hearing is OPERATOR ERROR.  You are trying to make “QRO”, into the issue, it’s not.

The chance of an amp “QRO”, in your words, sounding “BAD” “HOLLOW”, is probably less than 1 %.  Other than that, the poor/awful/bad sound you hear, is from the equipment ( driving the amp “QRO” ), and the adjustment of said equipment by the operator.  Now the amp could be effected by RFI, but that sound is usually pure distortion, not “HOLLOW”

Since you had to ask the question, it is safe to assume that you are new to the hobby/HF bands/ and to amplifiers, or as you termed them “QRO”.

So, since you are still getting your “sea legs”, here’s what you need to do, so you won’t have a problem with “QRO”.

1. Please read very carefully, the section of your owners manual, for your transceiver, on how to adjust the transmitter.

2. DO NOT, use any special, EXTERNAL, processors, EQ’s, or microphone amps.

3.  Talk at the mike, not to the side of the mike.

4.  Keep you face 12 inches or closer to the mic, 6 inches or less would be better.

5.  Until you get use to using everything, DO NOT, use the speech processor.

6.  Use the correct mic for the radio.  That does not mean going out and buying some over priced, hyped up, gilded, mic.  Use the mic’s the factory recommends.  They will all sound just fine, when the radio is adjust correctly.

7.  Think about buying a solid state amp.  You will have more protection aginst blowing up the amp.  Unless you pay attention to what you are doing you will run the risk of over driving a tube amp, risking costly damage.

8.  Remember, this is ham radio.  If you goal is to sound like your favorite FM DJ, or like some national news anchor, then you need to apply for the correct FCC paper work, and use the proper broadcast equipment.  There are many reasons ( hundreds ),why ham radio will not sound like your favorite FM station, or TV anchor, the most basic of which is it wasn’t engineered to sound that way, period.  A good number of the people that sound “HOLLOW”, think THEY sound just great.  They don’t.  Almost every radio out there can be made to sound very, very good, using basic mics, and proper adjustments.

Want to sound crappy, just god back up to number 1 and 2, and forget about them.

Lastly, go back and read:

http://www.eham.net/articles/8069

http://www.w8ji.com/loading_amplifier.htm

Now if you feel tic’ed off GOOD.  Please don’t come back here re-asking the same question, in some re-phrased way, or re-worded.

DO, go back and re-read all the answers to your questions.  If you do, then running “QRO”, will not be a problem.

Want to sound bad, have a bad QRO signal, well then just ignore all the replies, and do it your way.

Good luck in the contest.