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Dirty-South Blues Harp forum: wail on! >
Amp Question
Amp Question
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George Brown
4 posts
Mar 31, 2013
3:57 PM
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I have a question on Amps…actually, I have quite a few questions on amps but will save the rest for later posts.
I am new to harmonicas but have played guitar for some time. I must say that I have learned more about amps (especially from this forum) in the brief period of time I have been playing a harmonica than I ever learned playing guitar.
I really like to understand the details of how something works so here is my question for this post…from what I read most guitar amps are either Class A or Class AB. Does the same hold true for harp amps? According to an explanation of these classes on the Sweetwater website (http://www.sweetwater.com/insync/class-vs-class-ab-guitar-amps/) it notes that Class AB amps have more headroom and a tighter bass response. For an uninformed person like myself it would then seem that a Class AB amp is better suited for harp amplification. Am I correct on this?
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GeorgeB
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Rick Davis
1569 posts
Mar 31, 2013
5:17 PM
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Yes and no.
;-)
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-Rick Davis
The Blues Harp Amps Blog
The Mile High Blues Society
Tip Jar
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King Casey
4 posts
Mar 31, 2013
5:29 PM
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I was wondering when the 1st of April shenanigans were gonna kick in. :)
cheers, Mark.
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5F6H
1597 posts
Apr 01, 2013
6:09 AM
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Don’t worry about “class”, it’s a bit of an abstract concept regarding guitar/harp amps. You can be sure all amps with just one power tube are class A, because they can’t be AB, but these kinds of amps are designed to be cheap/accessible, not to be paragons of class concept.
In the Sweetwater article, the feller from Korg seems to be talking about method of bias (fixed bias vs cathode bias), whilst this does not dictate class (either A or AB can be fixed bias, or cathode biased) it is a more realistic way to assess amps.
Cathode biased amps are often said to have a more organic sound, natural compression. The majority of amps made in the early 50’s were cathode biased, so there is some feeling that they give a more “vintage” sound. They create a lot of heat, and make less power compared to a similar design in fixed bias. Examples of cathode biased amps are the Sonny Jr I&II (4x8” & 6x8” amps), Mascos, Meteor amps, Kendrick Texas Crude 35, old Gibsons (GA6/8/14/20/40/45/55/77/90 etc), Valco/National, Premier, smaller Ampegs up to the mid 60’s. These amps are sometimes preferred for recording, quieter applications & can be miced up/lined out for gigs.
Fixed bias is more efficient but a tighter sound, less compression/sag. Pretty much all amps over 35W are fixed bias. Examples of fixed bias amps are Fender Princeton Reverb, Bandmaster, Bassman, Concert, Super Reverb, Twin Reverb (in fact all Fenders with reverb), Kinder amps, Sonny Jr Avenger/Cruncher/410, HG50. Lots of folk prefer fixed bias amps for live stage work, where you need a certain amount of volume to hang with a loud band (cathode bias can work just as well in a controlled environment/restrained band).
You can see by the amps mentioned that there is no distinct preference, tone-wise, for either method regarding harp/harp players. The above is a general rule of thumb, you can record with a fixed bias amp & gig with a cathode biased amp if it so suits you.
A tech can convert a fixed bias amp to cathode bias fairly cheaply, or add a switch so you can flick between the two (standard on the Mission Chicago 32-20, but not so much recommended for modern PCB amps, due to construction/accessibility issues).
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Last Edited by 5F6H on Apr 01, 2013 7:04 AM
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George Brown
5 posts
Apr 01, 2013
6:18 AM
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@5F6H
Thanks so much for the help...I knew I was missing some points but was not sure what they were. This helps me a lot.
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GeorgeB
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Rick Davis
1577 posts
Apr 01, 2013
10:13 AM
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Yep, Mark nailed it. Sorry about the wise-ass reply above. I knew you would get good advice.
Guitar amps and harp amps do not necessarily share the same goals. When you see a guitar amp that claims "more headroom," that may not be something you want. It means the amp clips (distorts, breaks up) later rather than earlier. It means the amp is cleaner at lower volume levels and must be turned up a bit more to get dirty. It may mean the sweet spot in the amp cannot really be played because it occurs above the feedback threshold.
A few things can contribute to this: Class AB, fixed bias, type of rectifier, or the speaker you choose.
On the other hand, if you perform on stage in clubs with a blues band you may want the punchier sound with more headroom.
One is not really "better suited for harp amplification" than the other. Just a different sound. Both can sound great.
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-Rick Davis
The Blues Harp Amps Blog
The Mile High Blues Society
Tip Jar
Last Edited by Rick Davis on Apr 01, 2013 10:19 AM
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George Brown
6 posts
Apr 01, 2013
11:09 AM
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@Rick Davis
Thanks to you, too...NP on the comment considering the date. I'm old and I can take it.
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GeorgeB
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King Casey
5 posts
Apr 01, 2013
1:29 PM
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No worries Rick. After the 'serious' analysis, it wasn't such a silly response after all :)
cheers, Mark.
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