Fw: [Harp-L] Feedback

[MARK BURNESS <markwjburness@xxxxxxxxxxxxxx>]

Joel B Chappell wrote: "One last question. Why do harp musicians want amps that 
âcolorâ the response of their instrument? I can understand the guitar folks 
looking for heavy metal distortion, but as a number of folks have pointed out 
blues harps donât usually approach those volumes and get that dirty. I have a 
Fender Passport system that is fairly flat and I have played my harps about 
6-inches away from a SM57 mounted in its stand and it sounds great, plus I see 
Buddy Green on TV and other participants in this forum on YouTube and they donât 
have a mic jammed right in front of their harp and they sound great."
Â
Aha! That'll be the highly personal & subjective matter of tone! :-) Some guys 
want a colored, heavily distorted sound (maybe all the time, maybe for just a 
few numbers where it suits)...cause they've stumbled on it, or heard on 
recordings that influenced them...other guys, who still use tube amps, still 
just find it a very practical means of getting over, perhaps looking for more 
subtle coloration in a little sag from the power supply & a littleÂenrichment of 
harmonics. Often 2 guys will get massively differing sounds from the same amp, 
just like they might from playing through the same PA, lots of guys who get a 
big, distorted "amp" sound will still get that from a PA if they were to play 
cupped to a vocal mic.ÂSome MI amps have a strong (sometimes 
pleasing/flattering) character -Âdepending on level of drive, Fenders are often 
pretty much the middle ground.ÂSometimes when I'm working on an amp I'm really 
justÂlistening for it to convey what the player does, with as few 
issues/artefacts as possible. And let's not forget the collectabillity aspect, 
amps often have a certain aesthetic quality...that biscuity, burnished tweed can 
still give you a lot of pleasure, even when unplugged from the wall ;-).
Â
Many guys who play through amps still do numbers uncupped, through a PA mic for 
variety...I can't think of many who solely play through an amp.. So, short story 
long, some do & some don't want amps that specifically "color" & if they do, it 
might not be all the time. It's not really that different to guitar in that 
respect, the same guy might be playing heavy rock through a Marshall stack one 
minute, acoustic the next...
Â
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From: Joel B. Chappell <joel.b.chappell@xxxxxxxxxxxxxxx>
To: MARK BURNESS <markwjburness@xxxxxxxxxxxxxx>; Greg Heumann <greg@xxxxxxxxxxx>
Sent: Tuesday, 3 May, 2011 16:21:57
Subject: RE: [Harp-L] Feedback


Gentsâ-
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Very, very few amps used today for harp are Class A (in fact very few designed 
in the last 50yrs), the vast majority of push pull amps are AB, idling 6L6 power 
tubes anywhere from 4W each to 20W+ per tube. Greg was using the term "saturate" 
in the generic sense of pushing them hard enough to get them to audiblyÂdrive. 

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I was referring to older guitar amplifiers that seem to be the rage today. To 
run AB1 or 2 correctly usually requires a good stiff fixed bias supply which 
runs up cost $$ so the thinking back in the day was to run cathode bias in class 
A. This is probably mostly true of home entertainment [hi-fi/stereo] amps rather 
than guitar amps.
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Class A push pull amps dissipate the same, regardless of signal, only within 
their clean RMS power rating. When pushed beyond that this does not apply.
Â
Correct, once again my home entertainment career prevailsJ.
Â
Whenever you push a push pull amp hard the bias effectively shifts towards the 
colder end of the spectrum towards cut-off and away from saturation in the 
technical sense, regarding tube plate current. As is evidenced by the presence 
of crossover notch distortion under heavy drive.
Â
Correct again and pentode gain curves being what they are you are now off the 
linear portion of the plate load line.
Â
As regards harp amps, primarily because of the limitations of acoustic feedback, 
it's usually a tricky enough feat to get the amp in question to make it's 
maximum rated power output, irrespective of whether it's clean RMS rating or 
not. With a Strat on the other hand you might easily see the typical stage amp 
make half as much again under drive.
Â
Well now this is where the speaker system comes into play. You can get 100 dBA @ 
75â out of 15â speaker that is horn loaded or in a tuned port enclosure [JBL and 
the like] with about 45 -50 Watts RMS out of the amplifiers, where you would 
need 200-250 Watts RMS, or more, to get infinite baffled speakers [Bose and the 
like] to provide the same ambient levels.
Â
What does all this really mean? Not a great deal, people tend to primarily 
choose amps because of the sound they make and manufacturersÂW RMS ratings are 
usually determined without a speaker attached (often a critical aspect of a harp 
friendly design), plus loudness of an amp is measured in dB, you might have a 
discrepancy of 2 to 4 times the volume (dB) for amps of the same wattage (clean 
RMS). So take all the numbers with a pinch of salt & trust your ears ;-)
Â
I prefer to use an audio meter set to human ear response curves in the actual 
venue. I have a Wave-Tek sweep generator and the combo is great for finding hot 
spots. On the bench I have a pair of non-reactive 125 Watt, 8 Ohm loads for 
preliminary testing on the limited repair work that I do.
Â
One last question. Why do harp musicians want amps that âcolorâ the response of 
their instrument? I can understand the guitar folks looking for heavy metal 
distortion, but as a number of folks have pointed out blues harps donât usually 
approach those volumes and get that dirty. I have a Fender Passport system that 
is fairly flat and I have played my harps about 6-inches away from a SM57 
mounted in its stand and it sounds great, plus I see Buddy Green on TV and other 
participants in this forum on YouTube and they donât have a mic jammed right in 
front of their harp and they sound great.
Â
Regards,
Joel
Â
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