6v6 single ended guitar amp?

[Arn C.]

I made this amp( 6v6 single ended guitar amp) from www.angelainstruments.com a long while ago.  I was wondering how much more volume I would get from this if I used a different speaker.
I have in there now an 8" 30w  real cheap speaker.  If I use a 30 watt eminence (sp) guitar speaker(I have one), which I assume is much more efficient, would this give me a bit more volume?   Right now I can barely hear the guitar unless I am at least at half volume.   Full volume is not very loud at all.   Almost too quiet for a single coil guitar.

Any comments would be appreciated!

Thanks!
Arn C.

[Johan]

efficiency is the key here...if you have a ceramic one now, get an old alnico...they are much more efficient and much louder..
j

[Arn C.]

Thanks Much for the info.  I kinda remembered reading that efficiency of the speaker is important.  i will try the good speaker I have home and see what happens!

Peace!
Arn C.

[John Lyons]

When you say you can barely hear it at half volume you mean with other players playinf correct?
The efficiency thing is key for a low wattage amp. If you are looking at current production speakers you want to see about 100 spl or maybe more. 103 is about the highest I've seen.

How do you like the Angela amp by the way? I studied that one a while back...seemed cool.

John

[Mark Hammer]

More volume comes from moving more air.  You can move more air by: a) having a bigger surface area with which to move it, b) by being able to push harder, c) by having a speaker that translates smaller amounts of current into more movement, or some combination of the three.  How well small amounts of current are translated into piston-like movement is partially associated with magnet type, but more likely associated with the size of the magnet (and especially the distance from the magnet in the gap) and the stiffness or "compliance" of the cone and supporting structure.  Remember that magnetic force is a function of distance, and if the voice coil is sitting suspended a great distance from the magnet (which is good in some ways, because it won't rub against anything and risk friction-produced heat buildup and frying) then it will take LOTS of magnetic energy to translate into voice-coil movement.  Moreover, if the cone is stiff and heavy, it will take comparatively more energy to translate into the same amount of air movement.  That particular aspect is not a function of either magnet type or magnet size.  You can have small ceramic magnet structures with extremely efficient transduction, and large alnico or even neodymium magnets with inefficient transduction. What you look for is a generally more efficient speaker of whatever size you need.

I poked around for a compact definition of speaker efficiency and stumbled across this: "Although a speaker's efficiency rating is almost always correlated to its sensitivity rating, it is actually a different measurement. The efficiency rating for a speaker is a measure of how well a speaker converts watts of electrical power into watts of acoustical power. Most speakers have a very low efficiency rating — between 1% and 10% — so manufacturers rarely provide this information, choosing instead to list sensitivity ratings. "

"Sensitivity' is generally rated in terms of decibels at a given distance with a given power level input.  For instance, the Jensen P8R, with an 8" cone, a 200gr magnet, puts out 92.5db at 1 metre with 1W.  The P10R, with a 10" cone, and 200gr magnet, produces 95db at 1 metre with 1watt power applied.  The C12R (a much bigger speaker)  has a 270gr magnet yet produces 93.8db  at the same distance with the same power applied.  The Jensen Neo-10-100 is also a 10" speaker with a 200gr magnet, yet produces a 98.9db output level at 1 mitre distance with 1W applied.   Obviously more efficient.  So, it is somewhat possible to have a sense of potential loudness from specs.

The sensitivity is not the only factor, however.  A speaker pushes backwards and forwards.  Backwards and forwards air movement can often cancel each other, reducing audible output.  Here, cabinet properties can make a substantial difference in how loud the speaker sounds, by virtue of how effectively it can move air (without cancellations) in those parts of the spectrum where the brunt of the signal lives.  That very same Neo 10 speaker will be substantially quieter than the Jensen P8R if the P8R is in a properly designed cabinet and the Neo10 is merely suspended from a coat hanger. 

Related to this is the subjective loudness of a speaker.  Keep in mind that the human ear is not a flat audio transducer.  Some frequencies enjoy greater transduction efficiency in the ear than others.  If a speaker has noticeable resonances in those areas of human hearing where we are more sensitive, it can *seem* louder and cut through better.

Note, finally, that with great power comes great responsibility.  Big speakers that are supposed to be able to handle large amplifier outputs tend to have heavier voice coils (thicker wire, right), and heavier cones that can remain rigid despite the pummeling  When an amplifier is severely restricted in terms of power (and, having a tweed Princeton nearly identical to that Angela instruments single-ended 6V6 amp, I know whereof I speak), often a smaller-to-medium sized speaker rated at lower power (e.g., a 10" rated at 25W power handling) will be far more responsive to the types of outputs thrown at it from such an amp, than will a 15" 100W speaker.  Fast n' light is what you want.

What all of this says is that:
1) You look for a speaker that shows some serious efficiency;
2) You go for a sensible power handling rating that comfortably (but not excessively) handles what you plan to throw at it;
3) You do what you can to provide the most efficient cabinet feasible;
4) You look for a speaker that "cuts"..

[JonFrum]

First, try any guitar speaker. If it's still very quiet, then something is wrong with the amp. That amp should be plenty loud when you play alone. If it gets louder with a guitar speaker, check this list for the highest sensitivity units.

http://www.eminence.com/guitar.asp?speaker_size=12

[Doug_H]

For a single speaker setup, the smallest I would go with would be a 12". There is a world of difference in the volume between that and an 8".

[petemoore]

  Neodynem [spell check passed over] tend toward very clean sound, too clean for my tastes, excellent Lbs. per amount of air pushed, but really will not break over smoothly {IME}.
  Ceramics have come long way tonewise IIUC, I use Alnico's, have had heavy ceramics that sound great too though.
   What Mark said. cone weight/structure, close tolerance of coil to magnet has it's advantages and disadvantages, tends to be trickier to 'do' and not touchy-touchy, hence more expensive generally.
  If you have a heavy cone/coil structure, stiff suspension...it might be about 1/3 to 1/4 as 'loud' as a really effecient speaker.
  Greenbacks and Jensens have always sounded loud and good, nice breakup, different types of course, I have an Alnico Blue [expensive], but there are many great choices of speakers.
  Check out some small amp forums and read speaker reviews...the really great sounding, responsive loudspeakers don't seem to go on sale as often.

[brett]

Most speakers have a very low efficiency rating — between 1% and 10%

Too true.  A lot of noise equates to very little energy.  I still remember my surprise back in high school physics (1977) when I worked out that a stadium full of people yelling for 1 minute don't produce enough energy to boil a cup of water.
Imaging if speakers were also rated for their OUTPUT.  Speakers would get ratings like 100/1.2W and 250/4W, and I suspect those funny-looking chrome-plated monsters that go in cars would get ratings like 800/2W.

[aron]

Doug is right. I would get a WeberVST speaker if possible. Not too expensive but they sound great!

[Dan N]

That little amp should rock with any working speaker.

The schematic shows no decoupling caps on the 12AX7 cathodes. If you have a 25uf/25v electro laying around, try soldering it across the cathode resistor on the first stage. There should be a nice increase in volume. If you like it, put one on the other preamp cathode and give it a listen.

[bancika]

I've got one weber sig8 in my princeton (also 6v6 single ended) and it's very loud

[WGTP]

Based on my research, the Celestion G12H and the Eminence clone of it, the Wizard, are the most effecient 12" speakers.  That excludes the Celestion Century that has Neo.   

[Arn C.]

Wow, you guys rock!   A lot more info.   The amp is super clean, no hiss, no hum, nada!!!!!!   To me with the cheapo speaker in there, it may sound like about 2 watts maxed out.  I do have a, I think, an eminence 30 watt , 10" speaker that I will try also.  I think I also have a 12" guitar speaker in a cabinet I buit (sealed back).  I will also give this a try.  The 6v6 single ended amp is in a cabinet I made, it is open in the back.   I built this quite a while ago, and then it also was not real loud, and I swapped out every tube in there at least once with known good ones.  So, I believe it has to do with the speaker.    Tonight I will try it with another speaker and also the speaker cab I have.

Dan, thanks for the tip on the electros!

Peace!
Arn C.

[Mark Hammer]

Though a sealed cab will sound the bassiest, compared to an open-back cab, ideally you want to port the bass to the front such that more bass energy "escapes" in the direction of the listener.  I suspect a bass reflex design will give you more volume than a sealed or open cab will.  Of course, the key is to figure out the dimensions and properties of that port - something that amp-builders tend not to spend much time on.

I have an old JBL 2110 8" speaker in my Princeton.  It was considerably more efficient/sensitive/loud than the stock 8" Jensen it came with.  I suspect that if I ever get round to cab-ing the 12 Jensen I have in the garage and using that , the Pricneton will be even loiuder.

[bancika]

Also you could try 1uF non-electrolytic caps across cathode resistors. I avoid electrolytes as much as possible in signal path...

[JonFrum]

   I built this quite a while ago, and then it also was not real loud, and I swapped out every tube in there at least once with known good ones.  So, I believe it has to do with the speaker.   



Peace!
Arn C.

Possible, but if the speaker doesn't help that much, check the grid resistor on the 6V6 and make sure it's the full value - 220K and not 22K for example. It's a common error, and it sends much of your signal to ground. Also make sure the 100K plate resistors are not 10K - same issue. I have a 1 watt amp with an 8" Weber Sig, and it's pretty loud compared to my Celestion GH12-30. Not as good or as loud, but the difference isn't that great.

[IGR]

I´ve built similar amp two years ago, up to this day several times modded, tonestack only. Finally I´ve decided to stay by AC30 tone control. At end is 6L6 pentode, as OT serves Hahn mains transformer 240/12 V( 30W). The box is for 10" speaker quite voluminous W/H/D-400,350,280mm, back half open, vent 150/150mm, speaker Eminence Legend LE10-358.  This amp tonally perfect correspondes to Telecaster,deep twangy bass,bright treble IMHO better than commercial mass product. When I´m playing with drummer and bass (RolandCube100) have no problem with my volume level, sligt buried reserve have yet.

[Mark Hammer]

Just as an aside, in the 60's and 70's, most reference works on audio would indicate that "room-filling sound" could easily be achieved with 4W if the speaker, and cabinet design, was efficient enough.  Not necessarily pain-inducing, mind you, but loud enough that you could not simply talk over it.  Given that one need roughly 50W pumped into the same speakers to produce double the perceived loudness of 5W pumped into those very same speakers, 5W can, in theory, be VERY loud....if the speaker and cab are designed for max efficiency.

[IGR]

I agree completely to Mark. I remember a test, running my handmade SE (5W described above) thru serious 4x12 stack, it kicks really ear splitting wave, at least for player with 10 ft cable direct to the amp!