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Need opinion on good 3000+ amp
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<blockquote data-quote="hispls" data-source="post: 8798712" data-attributes="member: 614752"><p>Which might as well be promises of rainbows and unicorn tears. The following is from the Zed Audio manual AND is assuming 4 ohm drivers. Numbers get far worse real-world when you run even lower impedance.</p><p></p><p><em>MYTHS, MAGIC AND FACTS</em></p><p><em>Damping Factor - This amplifier specification has been blown out of all proportion. What</em></p><p><em>it means is the ability of the amplifier to resist a change in it’s output voltage. The formula</em></p><p><em>is DF= Speaker Z / Amplifier output Z (where Z is impedance). So many manufacturers</em></p><p><em>have claimed ridiculous, and often false damping factors. A damping factor of 1000</em></p><p><em>implies that the output impedance of the amplifier is 0.004 ohms (4 ohm load). The only</em></p><p><em>way to attain this figure is to apply masses of negative feedback (or use positive</em></p><p><em>feedback) and too much feedback makes amplifiers sound harsh and clinical. Also</em></p><p><em>damping factor changes with frequency. The lower the frequency the higher the DF</em></p><p><em>number. Typically the DF can be ten times larger at higher frequencies.</em></p><p><em>Let us take this amplifier whose output impedance is 0.004 ohms (Zout). The speaker</em></p><p><em>circuit is a series circuit and the following impedances(resistances) are in series with this</em></p><p><em>0.004 ohms. Let us assume that this DF measurement was made at the amplifier’s</em></p><p><em>speaker terminal. The first extra contact resistance is the speaker wire to the speaker</em></p><p><em>terminal (WT ohms). Then there is that of the wire itself for two conductors (W). Next is</em></p><p><em>the contact resistance of the wire to the speaker terminal (WS). Next there is the contact</em></p><p><em>resistance of the wire from the speaker terminal to the voice coil (WV) and lastly there is</em></p><p><em>the DC resistance of the voice coil itself (DCR). So what we have is a series circuit with</em></p><p><em>the following resistances in series and adding up. WT+W+WS+WV+DCR+Zout.</em></p><p><em>WT,W,WS,WV and Zout are very small indeed. Certainly less than 0.1 ohms. Whoa, look</em></p><p><em>what has happened the EFFECTIVE DAMPING FACTOR has been reduced from 1000 to</em></p><p><em>40 by just taking into account those pesky unavoidable contact resistances. Now for the</em></p><p><em>cruncher, remember that the DCR is also in series and is typically 3.2 ohms for a nominal</em></p><p><em>4 ohm speaker. So we must add 0.1+3.2 = 3.3 ohms and now EFFECTIVE DAMPING</em></p><p><em>FACTOR is now a magnificent 1.212! (4 divided by 3.3)This is the real world. We see that</em></p><p><em>the DCR of the speaker swamps all other resistances in the speaker circuit and the 0.004</em></p><p><em>ohms amplifier output impedance is almost meaningless. It has been found that a DF of</em></p><p><em>about 20 is quite sufficient to dampen the voltage spikes from the speaker. An eye opener</em></p><p><em>this one is it not? Good tube amps sound marvelous - low damping factors!!</em></p></blockquote><p></p>
[QUOTE="hispls, post: 8798712, member: 614752"] Which might as well be promises of rainbows and unicorn tears. The following is from the Zed Audio manual AND is assuming 4 ohm drivers. Numbers get far worse real-world when you run even lower impedance. [I]MYTHS, MAGIC AND FACTS Damping Factor - This amplifier specification has been blown out of all proportion. What it means is the ability of the amplifier to resist a change in it’s output voltage. The formula is DF= Speaker Z / Amplifier output Z (where Z is impedance). So many manufacturers have claimed ridiculous, and often false damping factors. A damping factor of 1000 implies that the output impedance of the amplifier is 0.004 ohms (4 ohm load). The only way to attain this figure is to apply masses of negative feedback (or use positive feedback) and too much feedback makes amplifiers sound harsh and clinical. Also damping factor changes with frequency. The lower the frequency the higher the DF number. Typically the DF can be ten times larger at higher frequencies. Let us take this amplifier whose output impedance is 0.004 ohms (Zout). The speaker circuit is a series circuit and the following impedances(resistances) are in series with this 0.004 ohms. Let us assume that this DF measurement was made at the amplifier’s speaker terminal. The first extra contact resistance is the speaker wire to the speaker terminal (WT ohms). Then there is that of the wire itself for two conductors (W). Next is the contact resistance of the wire to the speaker terminal (WS). Next there is the contact resistance of the wire from the speaker terminal to the voice coil (WV) and lastly there is the DC resistance of the voice coil itself (DCR). So what we have is a series circuit with the following resistances in series and adding up. WT+W+WS+WV+DCR+Zout. WT,W,WS,WV and Zout are very small indeed. Certainly less than 0.1 ohms. Whoa, look what has happened the EFFECTIVE DAMPING FACTOR has been reduced from 1000 to 40 by just taking into account those pesky unavoidable contact resistances. Now for the cruncher, remember that the DCR is also in series and is typically 3.2 ohms for a nominal 4 ohm speaker. So we must add 0.1+3.2 = 3.3 ohms and now EFFECTIVE DAMPING FACTOR is now a magnificent 1.212! (4 divided by 3.3)This is the real world. We see that the DCR of the speaker swamps all other resistances in the speaker circuit and the 0.004 ohms amplifier output impedance is almost meaningless. It has been found that a DF of about 20 is quite sufficient to dampen the voltage spikes from the speaker. An eye opener this one is it not? Good tube amps sound marvelous - low damping factors!![/I] [/QUOTE]
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