6ak6-tone-experience?

[bob p]

I went to a gig (as an audience member) to see a guy that owns two of my amps as well as a little Mesa Subway Blues that I modified (his smallest amp). I asked the sound guy which amp he liked the best.?. He said "The little one".

Sound Guys -- It's like they're in a damned Union.

[Justin Thomas]

I went to a gig (as an audience member) to see a guy that owns two of my amps as well as a little Mesa Subway Blues that I modified (his smallest amp). I asked the sound guy which amp he liked the best.?. He said "The little one".

>:[
Quoting from the guy in "Happy Gilmore":
"JACKAAAAAAASSSSS!"

On another note, it's hilarious when you show up with a "toaster" amp & plug it into a 2x15. They think the size of the speakers makes it more powerful or something.

Justin

[bob p]

They think the size of the speakers makes it more powerful or something.

well, they do. it's about matching the speaker:air interface to the impedance of air.

[Gnobuddy]

The same Printer2 who is already featured in this thread for his 6AK6 amp, also had a thread in which he reported measurements using first one,and then two, identical speaker cabs; I think first one and then both speakers were wired to the same solid-state power amp, driven by a white noise signal. An SPL meter showed a 6 dB increase in loudness.

The interesting part is that paralleling the two identical speakers draws double the power from the amp - but that only accounts for a +3 dB increase in loudness! The other 3 dB increase had to come from the increased speaker efficiency due to having twice the cone area as before.

I think this sort of efficiency increase (from increasing cone area) only happens at frequencies low enough for the wavelength to be much bigger than the speaker diameter. For a 12" speaker with an effective 11" piston diameter, the sound wavelength equals the cone diameter at about 1200 Hz. Most of the fundamental frequencies in guitar music are under 664 Hz (12th fret on the high E string), so most of the sound energy is indeed at wavelengths much bigger than the speaker diameter.

-Gnobuddy

[bob p]

the principles you're describing are well known. acoustic engineers refer to the phenomenon you're describing as "mutual coupling" between drivers. the math actually says that mutual coupling only occurs if the distance between the center of each adjacent driver is less than lambda/2 (one half wavelength).

think about diffraction ... but occurring backwards.

for mutual coupling to occur between 2 or more drivers they have to be reproducing the same signal, in phase, with a common axis of projection. the combined signal will propagate on-axis as if it were a single waveform with the multiple drivers behaving as if they were one driver with their composite surface area. the larger driver is more efficient in matching the impedance of free air at those frequencies.

it's important to note that these coupling effects only occur on-axis, and for signals that are of adequate wavelength relative to the center-center distance of the drivers.

the coupling effect is directional; the coupling occurs on-axis. the on-axis coupling actually occurs independent of the driver spacing, but frequency dependent combing will occur off-axis. as the wavelength of the signal increases relative to the distance between the drivers' acoustic centers, the off-axis angle at which mutual coupling continues to occur will increase.

the effects are only practical at frequencies below ~ 500 Hz because of the physical size of the loudspeakers. if the speaker-speaker distance is > 1x lambda the gain in SPL will be +3dB. if the speaker-speaker distance is 1/2 lambda then mutual coupling occurs at that frequency and the gain in SPL is +6 dB.

[Gnobuddy]

the principles you're describing are well known.

Oh, I know. Just keeping it relatively simple and non-technical.

There is a lot of physics from classical optics (diffraction and interference) that is quite directly relevant to speaker systems using multiple full-range drivers. And some odd gaps in our thinking about them when it comes to musical instruments, audio, and speakers.

For instance, why does everyone seem to understand that "line array" speakers should stand upright, but continue to place two speakers horizontally, side-by-side, in 2x10 or 2x12 guitar amps ? That is a recipe for severe beaming in the horizontal plane, exactly where your audience is spread out!

Same thing for those "sound bar" speakers that are supposed to go under your TV to provide the centre channel. That's a line array, placed horizontally, so it beams like a searchlight in the horizontal direction, and gives decent acoustic dispersion in the vertical direction. Exactly the opposite of what is actually desired! That sound-bar should be standing upright under your TV, not lying on its side.

I have actually seen one bass guitar cab which placed its two speakers vertically, one above the other. It stood on its small end, tall and upright, like a vintage home Hi-Fi speaker. Whomever designed that speaker system got it right! (Unfortunately, I don't remember the brand.)

-Gnobuddy

[bob p]

bass players are actually pretty good about orienting their speakers vertically. the guys at talkbass are huge proponents of the vertical arrays. as much as i agree with it, i can't get over how funny a skinny vertical 4x12 stack looks with a wide head balancing on top of it.


at least Leo was smart enough to place the 2x10 speakers at an angle in the early 50s V-front super.



as far as the soundbar speakers go, they're just an add on that fits underneath or on top of your TV. they do it that way for the acceptance factor. nobody's wife is going to want a vertical post speaker sticking out on top of the TV.

[Gnobuddy]

bass players are actually pretty good about orienting their speakers vertically. the guys at talkbass are huge proponents of the vertical arrays.

In my experience, generally speaking, bass players seem to be a lot more willing to abandon tradition when something new and improved comes along. Guitar players tend to cling to the past, whether or not it makes sense.

i can't get over how funny a skinny vertical 4x12 stack looks with a wide head balancing on top of it.

There's an easy fix for that, start making narrow heads!

at least Leo was smart enough to place the 2x10 speakers at an angle in the early 50s V-front super.

I'll bet he was simply trying to use as little wood as possible for the cabinet, and never had a clue about the acoustic aspects of the design. Leo never stopped thinking like an accountant!

nobody's wife is going to want a vertical post speaker sticking out on top of the TV.

No, but the solution is simple: raise the TV, install the vertical centre-channel soundbar underneath it.

Even better, of course, is to toss the soundbar, and use a proper speaker speaker enclosure under the TV for the centre channel. You won't have to raise the TV as high, and you won't have to deal with the crappy sound quality that usually goes with a string of 2" drivers in a long pipe enclosure with poorly damped organ-pipe resonances.

Me, I just use two-channel stereo sound, with one monitor (speaker) on each side of the TV. The centre channel often takes away too much of the stereo image for my tastes.

-Gnobuddy

[walkman]

I’m also in agreement that 1 or 2 watts is way to loud in many dwellings, with standard guitar speakers.

The Yamaha THR5 I use for low volume practice is great for bedroom level playing but after a little playing there is still the feeling I need to turn it up a notch so that it feels loud in the room and give the right vibe.

The speaker section has 2.5” or 3” speakers, that would not be super efficient and a ported cab.

Has anyone experimented much with this size of speaker and cab?

[Gnobuddy]

And two years after walkman's post...

In 2018 I designed and built a roughly quarter-watt, all-tube guitar amp. I used a a 6AQ6 triode, and a little 9-pin triode/pentode, the 6JW8. The 6AQ6 is the input stage. The triode half of the 6JW8 is the second stage. And the pentode half of the 6JW8 is the output stage, running single-ended with a 22k Fender Reverb transformer as the OT.

The pentode in the 6JW8 was designed for small-signal use. But when I tinkered with its datasheet, I found I could make it work with a 22k OT and roughly 170 volts DC power rail.

Output power is a thundering one-quarter-watt (!) or thereabouts. That's estimated, I never measured it. However, plugged into the stock speaker in my 65 Princeton Reverb reissue, using the PRRI only as a speaker cab, the little 1/4 watt amp is more than loud enough for apartment use. Actually, overdriven tones are a bit too loud!

I posted to a thread on DIY Audio as this amp came together first in my head, and then on my workbench. In case anyone wants to read along, start with post #13 in this thread: https://www.diyaudio.com/community/t...ortion.326999/

While I breadboarded and played through this little 1/4 watt all-tube amp, I never built a permanent final version. My final amp schematic shown in the thread linked above works great, but there is still room for tinkering. In particular, it was a bright little amp, and I found myself always turning the treble knob down to zero. I designed a simple one-knob tone control to tame that tendency, but never built it. The tone control schematic is at the very end of the thread, though, if anyone else feels like building it and trying it out.

That was in late 2018.

A year and a half later, the COVID-19 pandemic took over our lives. After the word "lockdown" became a part of all our lives, it became mandatory for me to find a way to play electric guitar at volume levels no louder than a typical TV.

Our weekly music jams also went online, so I had to find a way to get my guitar sound into my computer, so I could stream it via the video chat service we user for our jams.

Not wanting to mic a speaker in my living room every week, I designed and built a (solid-state) guitar speaker/cab emulator, which could take the speaker output signal from the little 1/4 W amp and turn it into a line-level audio signal. It worked, but wasn't perfect.

About that time, I heard about the wonderful little Fender Mustang Micro ( https://www.youtube.com/watch?v=0CoMsSJlv4U ). It already includes a guitar speaker/cab sim, as well as several great-sounding effects and amp models. There are no tubes in the Mustang Micro, of course, but it sounds better (to my ears) than many actual tube amps.

For at least a decade, I've been finding that all affordable DSP/modelling guitar amps sounded bad. But with the Mustang Micro, that has changed. That Cosmo Music demo sold me - at least to my ears, this little amp is full of excellent sounds. I got a Mustang Micro immediately, and I run its output into a little audio mixer for our jams. Vocal mics and a little drum machine also go into the same mixer. A cheap USB guitar cable takes the mixer output and feeds it into a cheap and compact little Raspberry Pi 4 computer running Linux, which is just powerful enough to work for our online music jams.

I've also tried running the output of the Mustang Micro into several different pairs of small powered speakers, partially answering walkman's question. What I found is that many small powered speakers sound awful - there is a huge "hole" in the frequency response between the tiny woofer and the dirt-cheap tweeter, and that hole makes guitar sound dull and muffled. But eventually I found a decent pair of small powered speakers, and they work very well with the Mustang Micro.

Not too long after I got my Mustang Micro, I stumbled across another amazing little product, the wonderful Flamma Preamp ( https://www.youtube.com/watch?v=TtorO8ugiAE ).

The Flamma Preamp isn't fully self-contained like the Mustang Micro, and has no onboard effects. Adding a few of my other guitar pedals (reverb, delay, modulation, etc) produces excellent guitar sounds - and, once again, the output is a line-level signal that can be run into any powered speaker.

So, after a decade of trying to design and build low-power tube guitar amps to get good electric guitar tone at apartment-friendly volumes, I succeeded with the little 6AQ6/6JW8 amp. And then two solid-state modelling devices came along that work even better!

Anyway, as far as I'm concerned, the problem is now essentially solved. With the Mustang Micro, you can use either headphones or a small powered speaker pair. With the Flamma Preamp, you need a headphone amplifier to use headphones, or a small powered speaker pair. Both produce very good (again, to my ears) sounds that I don't find lacking.

-Gnobuddy