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Dirty-South Blues Harp forum: wail on! >
Amp question
Amp question
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didjcripey
404 posts
Oct 24, 2012
1:26 AM
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So, I've got a great little 5watt valve amp, which i made way better and somewhat louder by building a new cab which houses a ten inch instead of the original 8 inch speaker
I remember reading somewhere that one of the biggest factors in volume is surface area of the speakers; more area moves more air which gives more sound. Given that even with low gain valves I can't get my gain past 1/4 (at full volume) before feedback, it seems to me that the amp isn't working nearly as hard as it could.
What if I made a cab with two (or more) tens, (obviously matching the impedance correctly)?
Wouldn't that shift more air and give greater volume?
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Lucky Lester
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5F6H
1397 posts
Oct 24, 2012
3:42 AM
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To a point, yes, you are on the right track, but there are some things to be aware of...
You need to consider how much acoustic feedback affects the overall picture, speaker area & efficiency alone don't give you any magic bullet as far as volume vs feedback.
If you were to, say fit 4x15" 100db+ efficiency speakers (OK, I'm pushing the concept, for purposes of illustration), your amp would most likely struggle to push the cone area and the massive sq. inch-age (is that a word?) would make it very hard to avoid feedback.
It's a bit of a balance, as with any aspect of amp/cab design.
For a given speaker motor, larger cones tend to provide more efficiency...but for a high current output section like in a typical 5W amp, I'd perhaps stick to 10", 8", or a mixture of both. I'm not ruling out 12"s but again, for a given motor, they will tend to feed back earlier than a 10", negating anything but nominal differences in loudness (though you may like the tone just fine).
As you add more speakers to a cab, every time you double the number of speakers you increase efficiency (double the loudness) and widen frequency response...but as I said before you get to a tipping point where the sheer weight of the cones makes it hard for the amp to push. I have tried champs with 1x8", 2x10", 3x10", 4x10" (all matched loads @ 4ohms or 5.33ohms)...I found 4x10" fed back the most, was overly clean & didn't give the advantages I'd hoped for volume-wise. 3x10" (one speaker at top, 2 at the bottom) loud & punchy...perhaps a bit edgy? 2x10" seemed a really good compromise. My Champ currently runs with a single 8"...because I have other, louder amps that I use if I need more volume...loudness aside, speaking purely from a tone point of view, I prefer this.
As ever, YMMV...
Part of the reason a typical 5W amp is limited volume-wise relates as much to the voltage the power tube(s) runs at & current handling of the transformers. You can make a 5-10W amp surprisingly loud & certainly giggable, if you push the voltages & efficiency all the way through the design...but this makes it cost as much, or more than many 30-40W amps! ;-) You pretty quickly get to a point with regular 5W designs where, to get significant volume increase, you simply need a louder amp...or a line out/load box & a PA. Just how much volume you need is the critical factor.
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Last Edited by on Oct 24, 2012 9:32 AM
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jbone
1093 posts
Oct 24, 2012
5:10 AM
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i admit to limited familiarity with 5w amps. but i have to ask if this amp has a pre amp section. if it does, and you have 12a class tubes in it, you may do well to experiment with cutting the gain in the pre amp circuit by swapping some tubes around. example is i have had several amps with a 3 tube pre amp. all 12ax7 tubes initially. call 12ax7 100% signal. so the way i have been taught is to leave the initial 12ax7 in p1, but then modify the signal by using 12au7's in p2 and p3. i'm not sure how much less signal a 12au7 lets past but it has significantly reduced feedback and increased usable volume esp from my single 12" silvertone.
if a 5w amp does not have a pre amp section there is likely another way to modify the signal. i do know a lone wolf harp delay has allowed me to crank a bit more volume as well.
there was a time i was trying out different eq bands and hoping to cut gain, which i did. problem was volume went with it. or tone.
to my ear the best harp tone amped comes on the line just before squealing.
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didjcripey
405 posts
Oct 24, 2012
2:30 PM
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Thanks for the responses. They make a lot of sense.
I guessed that it wouldn't be a simple answer, and that if it were viable that it would probably be done already.
5f6h: I hadn't considered the acoustic feedback. though this seems obvious now; just because an amp can go louder doesn't mean its going to feedback less. I would probably try two tens: I had a go at a twin reverb the other night with twelves, and found it sounded great on the low harps but dull with the high ones.
jbone: I've done the preamp tube swaps and found a marked improvement and also tried an eq pedal but lost tone and didn't seem to gain any volume.
My amp is actually quite loud; loud enough for a small noisy club (but perversely often not loud enough for practice with the guys I play with) and I have had good success with micing it at bigger gigs.
I like the portability and tone (I feel its my sound now), so perhaps I should use a bit of common sense and realise it aint broke so don't fix it.
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Lucky Lester
Last Edited by on Oct 24, 2012 2:30 PM
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