So I was right - it’s the even harmonics that remain? It’s 50/50 that I ever remember. And yeah, even without being Mr. Science, I remember all the ads back in the day when SS amps first came out and they would talk about Square Waves and such - so they could try to prove that their SS amps yielded the same response curve as a tube amp - yeah, right! I didn’t quite get it at the time but it was clear that they were trying to show that square waves = good…
It looks like that’s true. And for the record, brass instruments produce sawtooth waves.
Did you know that Glenn Campbell stole most of his riffs from clarinet players?
Didn’t know that specifically, but if you read interviews of any pioneering guitarist from Charlie Christian to Robert Fripp - and Campbell is a truly monster player and epic session man so fits in this category - they all cite which horn players they copped licks off of. Rock guitar stole the role of horn soloists and sections since it could be packed into a single, cheaper, more versatile (you can sing along with it) and more portable (1 person + rig vs. full horn section) and louder package that filled the same sonic space in the mix…
My personal knowledge of the latest in recording studio equipment is not up to date, but I was in a small studio recently and the owner said he had a digital preamp that had many cicuit emulation modes. You want a certain tube amp sound from a certain era, you dial it in.
Supposedly the acoustic and electrical characteristics of tube amps have been sampled and reproduced much like the sound of a grand piano or a drum kit has been.
I buy this - but, to my point above, I am very comfortable with the thought of being able to digitally emulate the “base tone profile” of an amp or instrument, but not the dynamics of the real deal. My drummer-the-record-producer uses Amp Farm software to patch in overdubs that sound like the original long after the original amp left his studio all the time. But there is a big difference between that and getting the touch-dynamic response that you get from a tube amp. I daresay, with no first-hand knowledge, that you could emulate the sound of a Steinway Concert D Grand digitally, but you wouldn’t get the same feedback-loop responsiveness that the master pianist expects when he/she plays the actual instrument…
So emulation can be used in small doses, but it can not replace the full sensory experience an artist obtains when using the actual instrument…
I don’t know enough about how tubes or audio power amps are used to say this with authority, but if you’re talking about sag in an electrical sense I would think you’re talking about the power supply. Although I’d expect the power supply is more likely to sag in a Class AB (or B, but I don’t think anyone would use one for audio), not in a Class A amp which is drawing the most power when idle.
The output transformer saturating will draw a greatly increased amount of current so that could actually be what’s causing the power supply to sag. It’s not so much to do with the tubes themselves, but is an essential part of the tube audio amplifier. Tubes are high-voltage, low-current devices. Speakers can’t handle that voltage; they need to be driven with high current for more power. The output transformer does the conversion from high-voltage, low-current, to high-current, low-voltage.
So it’s the output transformer that’s just as important to the tube amp’s characteristic feel. You could actually distort the tube itself with the transformer working perfectly below maximum, if the amp was designed that way.
As for ‘collapse’, it could mean a number of things - although speaking in connection with sag, it’s probably part of the power supply. Some power supplies will simply shut off when they are overloaded too much, to prevent damage. That’s probably something that’s not going to sound particularly good.
I understand, oh, just about none of that. ;):smack: But I can say that transformers get discussed a lot by amp geeks. There’s a company called Mercury Magnetics that has a line of “hand wound” (or whatever buzzwords sound special) transformer that “bring the big iron” and are supposedly more of a throwback to the old amps. In fact, you can buy some amps, then go to MM and get a “transformer upgrade kit” so you can swap in their stuff. They discuss all of the stuff you mention above, so I think you are onto something.
Oh, and from the geekery standpoint, don’t forget wiring: In boutique amp circles if you aren’t “point to point” (aka: PTP) don’t even try to sell your amp. Circuit boards are tone-sucks, adding physical length to the circuit since the pathways are printed on the board and can’t cross over one another. Back in the day, circuits were wired point to point - some low-paid worker physically soldered a wire from one point to the next. Apparently they used wires that could transmit the signal with less degradation AND the overall wire length was shorter since the wires could cross over each other, further reducing degradation. So all the boutique players have gone with old-school PTP construction…
…which is pretty fun since, again legendarily, folks like Hendrix and SRV favored cheap-ass, curly Radio Shack guitar cables since they degraded the signal a tad and pulled a few more highs (I guess, per tdn, this would be odd-ordered harmonics) out. So you want to avoid degradation at some points of the circuit but introduce degradation at other points - got it.
:smack:
Did I actually type "That’s a whole 'nother kettle of fish, Chachi "?
:smack::smack::smack:
The condensed version is that some of what makes the tube amp special isn’t the tubes themselves, it’s the transformer. You could make a transistor amp that with an output transformer that would have exactly the same ‘saturation’/‘sag’ feel to it. I don’t claim it would sound the same, just that it would play the same. But no one’s going to do that, because anyone who prefers a tube amp wants it to be all tube amp, plus it’d be kind of silly to design the amp that way.
With regards to the wiring, wire length inside an amp is entirely irrelevant. Wire sizing, dielectric, and other concerns might have a tiny effect, but it’s not going to be much. A properly designed circuit board would be fine, although point-to-point makes some sense if you’re dealing with large physical devices and, more likely because it’s the popular choice for these types of amps.
One comment on the ‘square wave’ demo: Showing off a square wave is a quick demonstration of the device bandwidth. The spectrum of a square wave is an infinite series of sine waves. No physical device can make this perfectly. As it cuts off the higher frequencies you can see it in the square wave - in some cases, you get a ‘Batman’ waveform (see here for pictures of incomplete series).
So what they were likely showing was how good it was at amplifying an input square wave. However, just because it was accurate doesn’t mean that was what people wanted, of course.
What’s the rectifier do and why do some tube amps use a solid state rectifier and some use a tube?
The rectifier is used in the power supply to convert (rectify) the AC line/mains voltage to DC. Since it’s part of the power supply, it’s going to affect the sag characteristics.
Tube amp manufacturers probably use tube rectifiers because they can make the power supply sag in a particular way, and probably partly because some people who use tube amps feel all the active components should be tubes.
I also should take back what I said about a transistor amp with an output transformer. Since tubes can react differently to dips in the power supply, any sag caused by the transformer saturating will likely affect the tube in a much different way than it would a solid-state stage.
Geez, and I thought I was a tech geek. I’m way in over my head here. All I want to do is rock out, man.
I’m a little confused about the dips in the power supply. Does this mean that certain notes can actually cause a loss of power? What sort of power chord must I play to cause a brownout in Cleveland, and in what key should it be?
Only a blinded, A-B comparison test will tell us. You know, the kind the Hi-Fi mags never do.
I would put real money on an experienced player being able to tell pretty much 100% if they were playing though a valve output stage. The playing bit is important.
Gotta be quick here:
Sag. Valve power supplies (that no-one sensible uses these days) can’t alway keep up with the amp’s demands, so the voltage 'sags’s and the amp distorts.
Collapse? Never heard of it as an EE expression.
Gotta go…
I agree with **SC **regarding the *playing *part. I have totally blown the listening part in an A/B, per musicat and per my “bloody great essay” (that’s a good thing, right SC? ;)) where I state the SS amps these days can have a “base tone profile” that sounds great but they aren’t responsive in the same way. And even if you heard someone playing two amps, you might not be able to tell, but the player should be able to tell pretty quickly, again based on the responsive of the amp…
If for no other reason, tube amps respond to external effects differently. For a great many years, a player’s sound depended on what stomp boxes drove the amp to produce their personal sound. With “modeling” amps, you can’t use something external to overdrive the input stage, you pretty much get only what’s dialed into the modeler. You can still use external effects like wah’s, delays, yadayada, but overdriving a modeling amp with a boost pedal of any sort does not respond like a tube amp and most likely sounds like heck.
The thing about the volume control really being a tone control is so true. I have an old Fender tube amp (which I just recently replaced all the electrolytic capacitors in, and changed the wiring back to blackface wiring) and I live in a small apartment. Unfortunately for me, my amp only sounds good when the volume is between 5 and 6, which is pretty much full tilt. I don’t want to anooy the neighbours, and my gf HATES it when I play loud, so I don’t get to do it very often. I have to settle for the volume at about 1.5 which sounds like crap. You just don’t get the same rush. So I play less than I otherwise would and save it up for when I drag all my stuff over to my friend’s house, where we kick the women out and play as loud as we want.
Oh, and regarding my DIY amp repair/modification that I mentioned in the last paragraph…this to me is key. I like to tinker. Old tube amps (or new boutique ones) are the only kinds of amps that are easy to work on at home. No circuit boards, everything soldered together by hand, components are cheap (except transformers) and are readily available.
What I need is a 3 watt tube combo with a reverb (for cheap). Which is apparently a tall order. No, WordMan do NOT link to a 3 watt combo with reverb that sounds amazing…then I’ll have to buy it 
Bass player here, but the info about the “sweet spot” really explains what I’ve feebly attempted to relate to people complaining about my volume. The best I’ve been able to come up with is that, when my volume knob is below a certain point, my tone just sounds “choked”. Sure, the fundamental comes through, but all the tasty bits that make for “good tone” vanish. Playing below the “sweet spot” is like eating a plain hot dog on a dry bun. It satisfies my hunger but that’s it. Turning the knob up to that “sweet spot” puts the mustard on the dog.
Could you wire in some resistors to the speaker to cut down on the sound from the speaker? For an 8 ohm speaker, if you wire a 5 ohm resistor in parallel with the speaker, then wire those in series with another 5 ohm resistor, the amp will still see 8 ohms, but some of the power is being dissipated in the resistors, so the audio output will be lower. You’d have to find resistors that could handle the Watts. If it works, you could wire in a DP/DT switch to select between using the resistors or not.
**Mister Rik **- yep, that’s it.
**ZenBeam **- you can definitely stick something between the power stage of the amp and the speaker to reduce the amount of signal moving the cones. The devices are called “attenuators” and have a bit of a market simply because tone-hounds want to use their simple-circuit boutique amps at lower volumes. I mention a couple above, the Hot Plate and the Power Soak - there are a bunch; I have one by a boutique maker named Clark who specializes in Tweed amps. Since I have a Tweed myself, I figured he must know something. Anyway, since I don’t know electronics, I can’t give you specifics, but apparently there is more to an attenuator’s circuit than simply using a variable resistor to dial down the power 
but I am not sure what it is…