Speakers, high voltages, watts, etc

[spritzer]

Almost any amp can give the voltage necessary but dynamic drivers need plenty of current for all those nasty curves on the impedance graph. The voltage is about 30v or less so that times 25 (1:25) is the voltage swing on the stators. The adapters are fitted with resistors to dissipate all extra current as heat should the volume level be too extreme.

A 350w amp will eventually melt the K1000 but not at low volume level. The amp might only be delivering about 1w at said volume level so it won't hurt the phones. As you know a basic volume control is a variable resistor that drops the voltage of the input signal from the standard 2v. The amp has a gain level that is the multiplier of the input voltage.

The current draw depends mostly on impedance and where speakers are said to have a nominal impedance of 8ohm they vary quite a bit and can be quite a bit higher and lower. Electrostatics are terribly bad at this, requiring large amounts of current in the bass and treble.

[milkpowder]

Thanks for the explanation. Sorry for leading the thread offtopic.

[MaloS]

Johnathan, here is a simple lovely not for the future:

Amp has gain. Say gain of 10, feed it 2V, it will give you 20V, feed it less - it will give you less. Volume is proportional to output voltage.

Power: depends on voltage(Vo) at the output, and impedance (Zl) of whatever you are driving. Vo^2 / Zl.

Amplifier ratings for speaker amps come in:

power into 4 ohms (Zl = 4 ohms, Vo = max amp's input * gain), power into 8 ohms (Zl = 8 ohms)...

You can make your conclusions fairly easily from here. You will notice that for example Headamp GS-1 ,voltage and gain wise is the same as most SET amps, but sure ain't driving any speakers because it will fry due to inability to handle the power output. Does not mean that if you make a SET power amp drive 600 ohms, the SET will choke, more so most likely it won't care and will just go on doing its thing. Won't necessarily sound good though.

[Duggeh]

Theres multiple gains to be considered (forgetting multiple gain stages in a power amp) unless you use a passive pre-amp, but I'm just nickpicking.

[spritzer]

There are indeed multiple gain stages but the gain in a preamp is pretty low but even some CDP's aren't operating at 2v and many output 6v differential.

[milkpowder]

Thanks MaloS. Good info.

I don't have too many issues with the way amplifiers deal with voltage and how they react to driving different impedance loads. What I am still not certain about is how current changes depending on load. High AC voltages will blow a driver right out of the enclosure and high currents will melt voice coils. Is there anything wrong with this statement: an increase in voltage leads to higher current flow. Hence increasing volume (voltage), leads to higher current flow? Or should I say increase voltage => increase current and both contribute to increase in volume.

The basic equations I'm looking at are I=V/Zload, P=VI, and the P=Vo^2/Zload. Are there others to consider? The answer is probably yes

Anyhow, you guys are saying that it is definitely safe to run something like a K1000 (Zload: 120ohm) or electrostatic adapter box (Zload: 8ohms? ) from a 10 gazillion Watt amplifier as long as the preamp is capable of finely controlling the volume to reasonable listening levels?

One more stupid question before I retire: Why don't manufactures only make passive pre-amps and let the power amps do all the voltage/current gain? I understand that some sources give off minuscule voltages eg microphones and phono, so those may benefit from a bit of voltage gain so that you can actually accurately attenuate them.

[Duggeh]

Passive pre amps make matching input and output impediences much more difficult and make choices of interconnect cables very crucial to sound quality, cable capacitance is the enemy with passive pre-amps. Some people say that passive pre amps are more transparent at the cost of dynamic sound.

Some companies philosophies are firmly in the passive camp. Notably NVA, but Richard Dunn is very different about the way he does many things, and thats the reason why he makes all of the bits needed in a system, so that you don't blow up his amps by using the wrong type of cable.

[Jon L]

Passive pre amps make matching input and output impediences much more difficult and make choices of interconnect cables very crucial to sound quality, cable capacitance is the enemy with passive pre-amps. Some people say that passive pre amps are more transparent at the cost of dynamic sound.

Unless one can afford some very serious active preamps, e.g. top models from Aesthetix, C-J, ARC, one will do better with the passive approach.

It's not all that difficult to assemble a nice passive system if you remember to avoid a few pitfalls, such as:

1. Trying to drive a unreasonably-designed SS amp with very low input impedance and low input sensitivity. Tube amps tend to be friendlier to passive preamps.

2. Driving the system with poorly designed output stage. Often, improperly designed tubed output stages of CDP/DAC's will have way too high output impedance and not enough current.

3. Many people combine the pitfalls #1 AND #2, AND use garden-hose cables with tons of capacitance, AND use low-sensitivity, zig-zag impedance speakers. No wonder they have NO dynamics with passives.

[MaloS]

You can go by those equations for the most part Jonathan. Just keep in mind the fact that impedance will vary with frequency, there are two types of amplifiers, current and voltage based (well ok, main type, speaker that works by amplifying power is also plausible, but increasingly complex). Current amplifier will increase obviously current, and subsequently voltage, voltage amplifiers boost voltage and subsequently current. V and I at any given moment are related by impedance, but if you want to talk over times longer than infinitely short you have more things at play. Amplifier ratings are providing with maximum average power output more or less, not account for spikes, frequency variants, roll-offs and blah blah.

In short - the equations I listed there are what you as a user should be concerned with being careful over. Everything that goes on from there is for madmen (or spritzer).

[spritzer]

I'm not crazy, I'm just special!

The adapters normally present a fairly benign 8ohm load and while they do require a bit of current it's voltage they need and they get that from the first watt or two. You can continue to push them but I've seen way too many burned up diaphragms in my time to ever do it myself.

I fully agree about the passives and while a top level system should be active there are simply too many compromises at lower price levels to consider going active unless you are dealing with impedance issues or long cable runs. TVC's are a clever way of controlling the volume as you gain some current as you lower the voltage but there is a whole lot of wire in the signal path.

[milkpowder]

^^

I'll fully assimilate what's been said tomorrow morning.

Another slightly off-topic tangent: Malo, you mentioned current-based amps. Naim Audio is the first company that comes to mind (my mind anyway, since I spent a decent amount of time listening to them). Their power ratings are low and they boast high current design. Low wattage + high current = low voltage. In that case, how do the speaker diaphragms move? How is current related to displacement of the speaker cone? I've always been taught that it's the voltage (amplitude) that makes the cones move because the magnitude of the induced EMF is proportional to the rate of change of the magnetic flux linkage (to be understood inversely, in the case, since it's the change in EMF producing a change in magnetic flux linkage), a phrase I was made to remember when I was doing physics in high school

This is great physics revision:D

[MaloS]

EMF = Electro-Magnetic Flux

Magnetic fields are induced strictly by moving charges. I.E. Current.

Oh, and for amusement I guess. Take 100 watt amplifier (decently powerful, ditto?)

P = V^2 / R (I am going to use resistance, not impedance just for this example).

Let R = 4 ohm, so like 100 watts into 4 ohms. V^2 = 100 * 4 = 400.

Oh shit. 100 watts into 4 ohms is only 20 volts...

Current-based amplifiers are far more resistant to highly reactive loads (i.e. impedance

that varies alot with frequency). That generally means the flat response is easier to achieve.

(easier is a relative term).

I guess I should show the easiest way to think about all of these things. Dynamic driver is basically an inductor with a magnet in the middle. Magnet produces a field, which has influence on charges. The current going through the inductor wire will basically be charges that will be moved depending on the direction and strength of the current.

Planar drivers are 2 stators surrounding a diaphragm. The stators are the ones with the current, in opposition. The introduced field by those, this time magnetic (a magnet actually produce electrostatic field), will move the diaphragm, which has charges in it.

Disclaimer: Corrections requested if I am wrong here somewhere, this is my understanding of the subject...

[Duggeh]

It's not all that difficult to assemble a nice passive system if you remember to avoid a few pitfalls, such as:

1. Trying to drive a unreasonably-designed SS amp with very low input impedance and low input sensitivity. Tube amps tend to be friendlier to passive preamps.

2. Driving the system with poorly designed output stage. Often, improperly designed tubed output stages of CDP/DAC's will have way too high output impedance and not enough current.

3. Many people combine the pitfalls #1 AND #2, AND use garden-hose cables with tons of capacitance, AND use low-sensitivity, zig-zag impedance speakers. No wonder they have NO dynamics with passives.

Its not knowing the input impedance or sensitivity of my power amp that makes me hesitate. Richard Dunn basically offers his products on a trail-sale basis though, so at worst, I'd only be out the cost of return postage...