You need to check your sums!.
48v p-p is only 17V RMS, giving you only 36W to a 8 ohm speaker.
Using a 4 ohm (if the amp would take it) would give you 72W or so.
As you're building a mains amp, it's pretty silly to use such a low supply rail, just because you have one to hand.
Ah yes, you don't double the volts twice.
I was intending the 24v supply as a test to make sure the amplifier and speaker works, with the idea of moving up to a 36v 10A PSU at a later date.
This would give me about 80w before clipping, which is more like it.
The alternative to a cheap switching amplifier would be to find a class AB one (or higher voltage switching) and use the pair of 68v split (linear) supplies I have here.
If I put them in series, that'd be +/-68v rails, giving... 288w into 8ohm, though I don't think the transformers would survive running 4ohm - they're about 250VA each.
Decisions...
Chris
Hi all! Just a couple thoughts: amplifying guitar is way different than amplifying most other stuff. That means: 1.Limited bass response is a target. Depending on your style, you don't need much below a couple hundred Hz. Okay, quite vague... Let's put it this way: you only need to get close to 100Hz if you play strong low Heavy Metal riffs. So, there's not so much air to move - again: depending on your style - so there's good chance a 6" can do. Note: limited treble is desired too, specially for using distortion pedals. 2.You don't get linear or uncompressed. If you do, you're not going to like the sound. That means you can't go for the "musical power" of your speakers to spec your amp. The dynamic range is way lower than acoustic stuff (disregarding post-90 CDs...), and you get more harmonics than normal (again and again: depending on your style), so respect the RMS power limit. 3.Open rear cabinets help on cooling the speaker. But you have to limit the bass output not to blow the speaker on overexcursion. Watch out: the desired nonlinearities create sub-harmonics and so on, so put your limit after overdriven stages! Important question (excuse me if you pointed so already): which is your style? Best regards, Emerson
But volume is still all about moving air, and a 6 inch driver doesn't move that much air.
To get the same volume from a 6" driver as a 12" would require a LOT more power, and a 6" driver capable of much greater cone movement.
I think I have a plan.
Going to get hold of one of these Eminence speakers, and a 2nd hand graphic eq pedal (to dial the exact sound I want). Using a sufficiently large power amplifier (I have something big enough here that'll do for a test) and the limiter/mixing desk to limit the bass going to the speaker.
I was thinking of going for a ported box to improve the LF power handling of the speaker, and provide some form of ventilation. Anyone got any thoughts on that?
Chris
Going to get hold of one of these Eminence speakers, and a 2nd hand graphic eq pedal (to dial the exact sound I want). Using a sufficiently large power amplifier (I have something big enough here that'll do for a test) and the limiter/mixing desk to limit the bass going to the speaker.
I was thinking of going for a ported box to improve the LF power handling of the speaker, and provide some form of ventilation. Anyone got any thoughts on that?
Chris
Sure. What I wanted to emphasize is the need of air movement is frequency-dependant - the lower the frequency, more air should be moved. Since a guitar amp is not supposed to deliver much bass, the need for air movement is drastically smaller than, say, a bass guitar speaker. So Chris might be able to get high SPL from a small cone if he doesn't abuse on the low end - what, again, depends on his style.
Cone excursion might be a limitation, indeed. I guess wider speakers have greater excursion limits in general (though I never checked this). But, again, higher frequencies demand less excursion, and the above apply. IMHO, Chris has a chance, just will have to be happy without lots of bass.
Other things to consider: our ears are way more sensible to mids, which are predominant in most guitar styles. So the absolute SPL for the guitar can be lower than the bass and drums. Also: hardly ever the other musicians want to hear the guitar as loud as the guitarist wants - get the amp close and pointed towards you.
Another thing I forgot to mention: smaller cones tend to make guitars harsh. Have an eye on the tone character for the amp.
Best regards,
Emerson
Porting DECREASES the power handling of the speaker, a sealed box (infinite baffle) is the best for power handling, the limited space restrains movement of the cone.
Certainly the lower the frequencies, the more excursion of the cone - but guitar isn't bass heavy anyway, so it's not really that much of a concern.
But trying to get similar volume levels from a smaller speaker require MUCH greater cone excursions (simply pumping air remember), so a 6" speaker will require far greater excursion capability, and much higher powers top provide the same volume.
Not particularly, larger speakers don't need as large an excursion as smaller ones, as they pump more air by moving less.
Large excursion speakers are often smallish HiFi types, aiming to give good bass from a small speaker/cabinet, by using high powers.
I'd beg to differ there.
Assuming a steep low cut below port tuning, the port provides more excursion damping than a small sealed box - it almost stops the cone altogether at port tuning.
The maxSPL chart in WinISD (you'll have to enter the Xmax data for the driver) shows what I mean quite nicely.
Taking an 8L cabinet for both (ported tuned to 90Hz), at 100Hz the ported cabinet will run out of thermal power handling at 111dB, the sealed box runs out of excursion at 101dB.
At 80Hz, the ported does 109dB running at full power, the sealed just below 98dB (excursion limited).
Now, the ported cabinet is much smaller than the optimal ~15L, but still takes the sealed box to town.
Combine that with the fact that, using two ports, you can get convection cooling for all the internals, and I can't see why anyone would use a sealed cabinet.
Chris
Chris, which is your style? Most good guitar cabs are open back, while some are sealed, and I can't recall of a ported one (I don't know as many, though). A sealed can add some bottom, and a ported can add some more, but do you really want more bottom? That's why I'm asking your style. Depending on what you play, more bottom will harm more than help. OTOH, good cabs use 10" to 15" speakers. With 6", design path might have to change anyway... Best regards, Emerson
Neither can I, there really doesn't seem any point for guitar, but it's common for bass combo's though.
I'm usually playing rhythm guitar a band - open chords, usually clean (if my amp manages it). Having some mechanical power handling (and ventilation) would be of use, I feel.
At practice today, the 10" open backed speaker was waving the speaker cloth around when I hit a chord (the cloth itself moved maybe 0.5"). Again, the amplifier was pushing out square waves. Sounded awful, in the best possible way. Sorta like the guitar(s) in I Love Rock and Roll by Joan Jett. Crunchy, "gritty", etc etc.
There is need for some bass output. I'd rather have a speaker efficient at producing bass and turn the bass down in the pre-amp section (saving amplifier power, speaker heat, etc) than try to boost the bass to make up for cancellation due to an open backed cabinet.
Chris
At practice today, the 10" open backed speaker was waving the speaker cloth around when I hit a chord (the cloth itself moved maybe 0.5"). Again, the amplifier was pushing out square waves. Sounded awful, in the best possible way. Sorta like the guitar(s) in I Love Rock and Roll by Joan Jett. Crunchy, "gritty", etc etc.
There is need for some bass output. I'd rather have a speaker efficient at producing bass and turn the bass down in the pre-amp section (saving amplifier power, speaker heat, etc) than try to boost the bass to make up for cancellation due to an open backed cabinet.
Chris
Right, so your style really demands some bass. Keep in mind that, depending on amp design, big excursions can also be a result of very low or even infrasonic subharmonics. Since you play clean, chords will not do that much, but chords picking can make the speaker jump around a lot.
I'd go for sealed then. The extra bass for ducted cabs can be detrimental to the guitar sound. Plus, they don't control excursion below resonance, and you definitely will have signals below resonance.
Agree. For many styles, the bass loss do good to the guitar sound - and the front/rear interferences also please many players - but it's not the case when you do need bass. Do use means to control subsonics at the output, though.
Best regards,
Emerson
yeah, I know not to take video clips really serious
but after listening to quite many, I found the best to be
6V6 SE
EL84 SE
6L6 SE
EL84 PP
(and in that order)
and pretty loud too
but louder than that, I think TC electronics digital reverb or modulator sounded like it might be good
I guess its true when they claim a tube amp sounds pretty good on overdrive
but from what I heard, only the tiny ones get it absolutely right
and maybe even only the best of them
but after listening to quite many, I found the best to be
6V6 SE
EL84 SE
6L6 SE
EL84 PP
(and in that order)
and pretty loud too
but louder than that, I think TC electronics digital reverb or modulator sounded like it might be good
I guess its true when they claim a tube amp sounds pretty good on overdrive
but from what I heard, only the tiny ones get it absolutely right
and maybe even only the best of them
But that's not a fair assumption with a guitar amp. In fact, Fender and Vox guitar amps have +15 dB boost in the low end, centered way low around 30Hz. Marshalls offer a more modest
+6 dB boost at 100Hz.
You'll also find your choice of speakers that will work in a reflex cab extremely limited by the high Qts common to most guitar speakers.
Why, pray tell, would they put so much boost so low? This just seems like a completely bonkers design choice, especially when many Fender amplifiers feature open backed cabinets.
Having tried a few of Marshall's cheaper amps, I can say I'm not keen on their clean sound. Too much bass.
The amp I use mostly at the moment has bass cut centered around 100Hz (turn the bass all the way up, it gives a flat response), and an open backed cabinet. Sounds nice enough.
The speaker I'm planning on using is a 6" pro midbass (Qts ~0.5), goes nicely in a vented cabinet of around 12L, but can be made to go 8L by playing with the port tuning a little.
The amplifier I'm basing my design around has a steep low cut from 200Hz.
Chris
its probably the hifi/BSC frequency you should be concerned about, roughly from 100hz to about 500hz
sure, some like a thin screaming sound rather than a more full bodied
and apart from the choise of driver type, it also interacts with your choise of guitar pickup
but as you go up into higher SPL, you might want to turn that effect down a bit
and I think you have to clearly distinguish between the nature of different kinds of sound
just now seen distortion effect unit with 7 frequency bands, all individually adjustable
might be a cool thing
apparentlty its also possible to adjust distortion so that it only sets or increase when playing harder
distortion, reverb, delay, etc
you wont get much good sound without
that is, if you ears can take it
sure, some like a thin screaming sound rather than a more full bodied
and apart from the choise of driver type, it also interacts with your choise of guitar pickup
but as you go up into higher SPL, you might want to turn that effect down a bit
and I think you have to clearly distinguish between the nature of different kinds of sound
just now seen distortion effect unit with 7 frequency bands, all individually adjustable
might be a cool thing
apparentlty its also possible to adjust distortion so that it only sets or increase when playing harder
distortion, reverb, delay, etc
you wont get much good sound without
that is, if you ears can take it
Speaker choices
So, the main design criteria of this amplifier is small, and loud.
This requires a driver with (due to the small diaphram) plenty of Xmax, and a reasonably low Qts so that a small cabinet may be used and still get a reasonably flat response (a pre-amplification 7-band graphic eq pedal will be used, so neutrality is of importance).
These all stack up against having a driver of high sensitivity, so lots of amplifier power must be used. Of course, the driver must be able to stand the power for prolonged periods.
A design choice was that I use a ported box. These provide (around port tuning) lots of excursion damping, and provide greater efficiency in the low frequencies. This would mean less amplifier power used (giving greater headroom), and the smaller excursions mean everything gets an easier time. The port would also provide some cooling (a port at the top and bottom would allow convectional cooling), improving speaker power handling (marginally), and, more importantly, prolonging the life of any electrolytic capacitors used.
The contenders are...
FaitalPRO - Professional Loudspeakers Made in Italy
Speaker Detail | Eminence Speaker
Fane International Ltd Loud Speakers
The Fane driver was immediately discounted for its high Qts (making it unsuitable for ported cabinets) and small X-max (limiting maximum output below ~300Hz).
The Eminence driver was initially favourite, as Eminence has a reputation for reliable drivers. It had sufficient Xmax and power handling to go rather loud. The power test had an 8 hour duration, so there's decent thermal management there.
The Faital Pro driver has a claimed greater power handling (at 260w peak, 60w more than the Eminence), and will also operate reasonably in a 5L ported cabinet (the Eminence needs more like 8L minimal to get a decent response to ~80Hz). Combined with the greater excursion capability, this will probably be the driver of choice.
More to come on some other design choices later.
I'll write up all the rest of the design considerations another time, might even make a wiki of it.
Cheers,
Chris
So, the main design criteria of this amplifier is small, and loud.
This requires a driver with (due to the small diaphram) plenty of Xmax, and a reasonably low Qts so that a small cabinet may be used and still get a reasonably flat response (a pre-amplification 7-band graphic eq pedal will be used, so neutrality is of importance).
These all stack up against having a driver of high sensitivity, so lots of amplifier power must be used. Of course, the driver must be able to stand the power for prolonged periods.
A design choice was that I use a ported box. These provide (around port tuning) lots of excursion damping, and provide greater efficiency in the low frequencies. This would mean less amplifier power used (giving greater headroom), and the smaller excursions mean everything gets an easier time. The port would also provide some cooling (a port at the top and bottom would allow convectional cooling), improving speaker power handling (marginally), and, more importantly, prolonging the life of any electrolytic capacitors used.
The contenders are...
FaitalPRO - Professional Loudspeakers Made in Italy
Speaker Detail | Eminence Speaker
Fane International Ltd Loud Speakers
The Fane driver was immediately discounted for its high Qts (making it unsuitable for ported cabinets) and small X-max (limiting maximum output below ~300Hz).
The Eminence driver was initially favourite, as Eminence has a reputation for reliable drivers. It had sufficient Xmax and power handling to go rather loud. The power test had an 8 hour duration, so there's decent thermal management there.
The Faital Pro driver has a claimed greater power handling (at 260w peak, 60w more than the Eminence), and will also operate reasonably in a 5L ported cabinet (the Eminence needs more like 8L minimal to get a decent response to ~80Hz). Combined with the greater excursion capability, this will probably be the driver of choice.
More to come on some other design choices later.
I'll write up all the rest of the design considerations another time, might even make a wiki of it.
Cheers,
Chris
this 8" Fane looks cool
Fane International Ltd Loud Speakers
you should remember that a BR design looses all control of the driver below tuning frequency
but a very small closed box could be your friend
I would have suggested to put a fan in, fore the cooling, but I guess not
again, I doubt its wise to tune a BR to such relatively high frequency, but thats just my personal opinion
some of these pro drivers are designed to take a lot of heat
at least I would not make it major design parameter
I doubt a closed box will be a problem
we are not talking about big woofers being fed with a thousand watt
make it apperiodic, with acoustic 'relief'
Fane International Ltd Loud Speakers
you should remember that a BR design looses all control of the driver below tuning frequency
but a very small closed box could be your friend
I would have suggested to put a fan in, fore the cooling, but I guess not
again, I doubt its wise to tune a BR to such relatively high frequency, but thats just my personal opinion
some of these pro drivers are designed to take a lot of heat
at least I would not make it major design parameter
I doubt a closed box will be a problem
we are not talking about big woofers being fed with a thousand watt
make it apperiodic, with acoustic 'relief'
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