Loudness in smaller combo amps

[David Root]

I'm not thinking of '70s Ampegs, but generally older 2x6V6 or 2x6L6. Every now and then I'll hear about one that is super loud for its size, and they generally seem to have very good tone too. Case in point, the rather obscure '50s Magnatone 113.

What elements of circuit design/compnent selection promote this?

Highly efficient speaker and matching the OT primary impedance closely to the max Po operating point impedance value of the output tubes both seem pretty basic. Bigger iron is also a factor sometimes, but not always. Cabinet size, relative dimensions and material, maybe too? Gain architecture, fewer components in the signal path?

Anyone done any systematic work on this?

[Noel Grassy]

I seem to remember Dave Funk speaking of 'empirical studies' on this same subject. That was in his one and only book. There apparently wasn't enough space to tell us his results. I'd love to hear what he's building these days. I coveted the tone the guitarist for Dread Zeppelin consistantly had. I think quite a few builders on this site are very near if not stomping all over what was once the domain of the 'amp guru' . Pretty bitchen actually!

[RJ Guitars]

David,

This is a great topic, and obviously one of my favorites. I've been attempting to get great sound scaled down to low volumes since I started amp building. However, I'm talking about a couple watts rather than 20 or so. Let me know if you think it's the same discussion you intended for this thread. In the meantime, here is a little reading that I think starts to uncover important pieces of this topic...

rj

http://www.audioxpress.com/magsdirx/ax/ ... in2734.pdf

[nickt]

Interesting article.

Keeping that in mind a 25/30 watter is not really much quieter than a 100 watter.

Couple of other things, combos are often open backed while head type amps are usually paired with closed back enclosures. Open backed are more "right there" on stage - closed back seem to focus out in the audience. The old alnico speakers are often brighter than modern speakers and bright cuts through.

Get the feeling that a bunch of "legend" has grown up around these "really loud combos".

To illustrate - back in the good old days I remember a guy I jammed with at an audition looking totally perplexed that his marshall couldn't get on top of my AC30 no matter how far he turned up the volume or how many stomp boxes he stomped (presumably he wanted to jump up and down when he finally got on top of me ). His problem was his sound was like a washing machine - no cut, all distortion, all bass, all woof and no zing. I'm sure he just thought my amp was "really loud" - it wasn't - it was on 45% and I was trying to leave space for him!!

Anyway YMMV.

[David Root]

Thanx for your responses gents.

I'll have to review Dave Funk's book, I have it. The article is very useful too, pointing up the subjectivity involved in sound perception. Some of this may indeed be delusion too, to some extent.

However, the old adage, make it brighter to make it seem louder, only goes so far. My ears are down 10 dB or so from "normal" at 4kHz and 25 dB down at 8kHz, yet I still run into amps that sound too "bright" to me.

I think IM distortion has a lot to do with that. It is uniformly ugly. No-one talks about that much, perhaps because it's not easy to minimize without making the amp a bit too hi-fi, or sterile as some people call it, e.g. ultra-linear OT.

In a recent conversation with CJ Poulos, a leading light at the Magnatone forum, he reminded me that a low impedance power supply with bleeder resistors is a good way to get some headroom without going to higher voltages. The Maggie 113 he worked on used a 10M bleeder resistor on the preamp cap.

Strangely enough, one of my best sounding, and loud, amps is a brown Vibrolux circuit using very low ESR filter caps, two in series at each node, to get the required voltage rating. Naturally I also used 220k bleeder resistors to balance the caps, and the caps are Black Gate VKs, which are very low ESR. Perhaps I stumbled onto something just by using conventional techniques with low ESR series caps, on all nodes including PI and preamp. Of course, Fender did this on the plates years ago, albeit with higher ESR caps.

[dragonbat13]

While not having much experience with amp building I do have a good knowledge about tone (here me out on this folks!!!).

Of all the things that I have noticed that make one amp louder than the other NO MATTER WHAT THE POWER RATING are these things in this order:

Headroom
Speakers and Cabinets
Tubes
Your Specific Ears

Have you ever noticed that at a certiant point of volume nothing gets louder it just hurts more? This is your ears response to the sounds. All of our ears have different frequency response just like speakers do. Some pitches hurt more than others.

I have noticed that Headroom is more of a balance of all frequencys instead of an airy sound that I seem to hear/feel in my amps.

Speakers and Tubes have a great effect on all of the tones, we all know that.

Here are my two amps: A silverface twin that has been modded with kt66 tubes, blackfaced, complete cap job.

other amp is a half stack bone stock peavy 5150 (first type)

I only use two tubes in the twin to keep the current down for the Kt66s and because it is too loud at full power. I also have the load on the output transformer doubled to make up for the loss of two of the tubes.

The twin is more full and cleaner as you would expect. But both amps crank up at about the same volume.

Please understand that these are my opinions and If you feel I have lost my mind I understand 100%

My point is that some amps just have that "PUNCH" or kick or whatever, but what you are really hearing is that between two amps that are the same but one sounds louder is that one is more healthy.

These kind of reasons are the reason that I will never own another solid state amp but I will give a modern tube amp a chance. I love the fact that everytime I plug in I might get a new sound depending on how the amp feels that day!!!!!!!

[Normster]

My guess is that there are two things that influence how loud an amp is; transient response and the frequency that's emphasized. A good example of the latter is the Express. It's only about 35 watts, but seems VERY loud because it has so much focus on the upper mids.

Transient response (if that's the right phrase) in the lower mids really gives an amp some punch...a different kind of loudness altogether. I've built several Dumble-style amps that had sweet tone, soft attack, and notes that seem to swell. These amps never really seem loud. OTOH, I've built a few (mostly HRM) that are very fast with notes that just seem to slam into your chest. These amps always seem to be louder, even at the same volume with the same tone settings.

[dartanion]

I think that it has a lot to do with each person's ears and what each amps has for innards and speaker(s)/cab.

Each person's ears are different and perceive tone differently as well as their response to SPL.

My 69 SFTR is hella loud, and not noticeably less loud with 2 tubes removed. Fresh cap job made it noticeably louder. Very comparable to my 2205 in perceived loudness, but the more present mids in the 2205 make it seem louder at times. My 210 5E3 build is really loud for it's smallish output, but the speakers are 100 db @ 1W 1M. Same thing will my 18watt builds. Very loud when used with high efficiency speakers. They all can make your ears ring but the big difference is the lack of headroom in the low output amps. Loud yes, but quite distorted. Loud clean is not their forte'.

[David Root]

I hear headroom, transient response, speaker efficiency, individuals' ears, cabinet size/dimensions and tubes.

I think the "loudest" amp I ever heard is a '71 SF Twin owned by Jason Lollar. He was testing a prototype Rickenbacker toaster type pickup design with a huge horseshoe magnet at the time.

Totally clean, Max Headroom was here. It had great transient response too, bass, mids and treble. You could physically feel the "snap" to it. And it wasn't anywhere near dimed either.

I think that great headroom and transient response originate in the power supply through a generous design philosophy and appropriate component selection. Not saying other factors, particularly gain architecture from the PI through the power tubes and OT, aren't important, they are, but the PS is the raw diamond and the rest is the way it's cut, so to speak.

[jelle]

Yeah I agree, the power supply enable the tubes to behave the way they do...just increase voltage and filtering and the amp is totally different all of a sudden. Tubes are just working with what the powersupply gives them.

Jelle

[mlp-mx6]

Yeah I agree, the power supply enable the tubes to behave the way they do...just increase voltage and filtering and the amp is totally different all of a sudden. Tubes are just working with what the powersupply gives them.

Sometimes it is a current-delivery limitation also, and a different power xfmr can make ALL the difference.

[dragonbat13]

Its Ironic to me that my twin is a 72 or maybe a 73. I lean more towards 72. Anyway, from what Dave wrote I will say that it is one of the loudest 100 watt amps I ever heard. Then I wore it out so bad that I thought I had ruined it. Then I learned about tube amps and did a cap job and such, and the amp is CLOSE to what it was when I first got it ( I have had the amp since I was 15 and now I am 31 and maybe/most likely my ears are different now. In any case if you can get some numbers off of the twin you are talking about (Dave) and I can get some numbers off of mine maybe I can help you.

I did not understand your question to its fullest extent until you described my amp to a tee. I know what you are talking about.

I dont have the experience that some of you folks have when it comes to tube amps,

But I have the desire!!!!!!

[dragonbat13]

I forgot to mention I have all the parts that I pulled out for the cap job also, I can also get some pics of trannys or whatever yall need for this subject.

Just for the record I fixed my friends Ultraliner PR today. The reverb went to the dogs. Bad tube. I used the normal channels tube to test the reverb tube. I am gonna send him a handfull of tubes to mess with to get him interested in working with these amps to his advantage.

[dragonbat13]

I forgot to mention I have all the parts that I pulled out for the cap job also, I can also get some pics of trannys or whatever yall need for this subject.

Just for the record I fixed my friends Ultraliner PR today. The reverb went to the dogs. Bad tube. I used the normal channels tube to test the reverb tube. I am gonna send him a handfull of tubes to mess with to get him interested in working with these amps to his advantage.

[David Root]

The '71 Twin I referred to is not mine so I don't have any numbers off it but I doubt it's significantly different than dragonblat's '72.

I believe this is the AA270 schematic, which is not high plate voltage, unlike the earlier SF amps, but the iron is identical (AA769, AC568) and substantial.

I have no personal ownership experience with SF or BF twins, but maybe those who do could comment.

The loudness phenomenon is not limited to amps with SS rectifier and big iron however, some examples are frequently smaller tube rectified combos from the '50s or early '60s. One I recall, the so-called Martin amp, which I think was built by DeArmond in that period and sold briefly by Martin when they dipped their toes in the electric guitar market, did have an exceptionally large power transformer, for example.