As originally posted by Danner
http://www.crownaudio.com/pdf/amps/damping%20factor.pdf
This is a good yet basic explanation of damping factor. Crown fails to mention one important factor. It is impossible to achieve the damping factor figures that they quote without some help from additional circuitry. That circuitry and help comes in the form of negative feedback. The more negative feedback that you use, the lower the output impedance. At the same time though, the more negative feedback that you use, the slower the circuit becomes. That's because there's more "error correction" taking place, which takes longer to process and more time to impliment. This is part of the reason why amps using no or very low negative feedback have slightly soggier bass response, but do SOOOOOO much better at preserving liquidity, transient response and harmonic structure throughout the other frequency regions. That is, compared to a high negative feedback design, which tends to sound dry, brittle and closed-in in comparison.
As far as the frequency response goes, an amp that is DC coupled will always demonstrate better transient response with less ringing. Many people equate bass ringing with greater bass weight, which it is, but it isn't "clean" or "real" bass. It is an artificial distortion or a "error of commission" i.e. signal introduced by a component that can't be found on the recording. On top of that, placing the DC blocking cap in series with the output not only introduces time smear, but also limits current capacity.
The drawback to not having the DC blocking cap is that the amp can leak a MUCH higher level of DC if not properly calibrated and / or if a problem develops. This can smoke ( quite literally ) your speakers*. This can happen extremely rapidly or very slowly, depending on the amount and consistency of DC leakage taking place.
The end result is that one has to choose what type of sonics they want, what type of trade-off's they are willing to accept and then fork over their cash. Sean
>
* Seeing your woofers light on fire is first extremely shocking and then "kind of cool" after the fact. One of my friends purchased a new bass guitar amp. After hooking it up to his dual 15" cabinet, the speakers literally shot flames out of the dustcaps after a short period of time. The amp was leaking a very high level of DC. After taking the amp back to where he bought it from ( Guitar Center ), they gave him another identical model.
Rather than test the amp at the store, he took this amp back home and hooked it up to one of my bass cabinets that he was borrowing. I guess that they figured that there was no chance of two amps in a row being bad. Instead of lighting the drivers on fire, this one simply sounded very distorted. That's because the DC was producing a steady-state push on the cones, causing it to act as if it was partially "bound up". The reduced excursion capacity of the cone caused the bass to sound "warbled", so they knew something was wrong.
After checking the dustcaps for heat, they found them to be noticeably warm but not smoldering. The second amp was probably putting out slightly less DC voltage AND the drivers in my cabinet were also much more robust than what he was using in his.
My friend then proceeded to return this amp to Guitar Center to get a refund. Guitar Center gave him a hard time about it initially, but gave in when he started talking about filing a lawsuit to seek damages pertaining to the other equipment that was damaged due to their negligence in selling faulty equipment. While he ended up eating the cost to repair his own speakers, he was also conscientious enough to buy me another pair of brand new 18's in case mine were damaged by the heat. While i didn't appreciate him "taking liberties" with my cabinet and a possibly defective amplifier, he obviously thought more of our friendship than i initially gave him credit for.
Between replacing his drivers and mine, that whole "new amp" fiasco ended up costing him about $750 in damaged speakers. A costly mistake on his part that i'm sure he'll never forget. Both in terms of his wallet AND in seeing his speakers light on fire : )
PS... This took place probably 15 years ago and the amps were Gallien-Krueger's. Turns out that the whole production run was defective from what we later found out.
http://www.crownaudio.com/pdf/amps/damping%20factor.pdf
This is a good yet basic explanation of damping factor. Crown fails to mention one important factor. It is impossible to achieve the damping factor figures that they quote without some help from additional circuitry. That circuitry and help comes in the form of negative feedback. The more negative feedback that you use, the lower the output impedance. At the same time though, the more negative feedback that you use, the slower the circuit becomes. That's because there's more "error correction" taking place, which takes longer to process and more time to impliment. This is part of the reason why amps using no or very low negative feedback have slightly soggier bass response, but do SOOOOOO much better at preserving liquidity, transient response and harmonic structure throughout the other frequency regions. That is, compared to a high negative feedback design, which tends to sound dry, brittle and closed-in in comparison.
As far as the frequency response goes, an amp that is DC coupled will always demonstrate better transient response with less ringing. Many people equate bass ringing with greater bass weight, which it is, but it isn't "clean" or "real" bass. It is an artificial distortion or a "error of commission" i.e. signal introduced by a component that can't be found on the recording. On top of that, placing the DC blocking cap in series with the output not only introduces time smear, but also limits current capacity.
The drawback to not having the DC blocking cap is that the amp can leak a MUCH higher level of DC if not properly calibrated and / or if a problem develops. This can smoke ( quite literally ) your speakers*. This can happen extremely rapidly or very slowly, depending on the amount and consistency of DC leakage taking place.
The end result is that one has to choose what type of sonics they want, what type of trade-off's they are willing to accept and then fork over their cash. Sean
>
* Seeing your woofers light on fire is first extremely shocking and then "kind of cool" after the fact. One of my friends purchased a new bass guitar amp. After hooking it up to his dual 15" cabinet, the speakers literally shot flames out of the dustcaps after a short period of time. The amp was leaking a very high level of DC. After taking the amp back to where he bought it from ( Guitar Center ), they gave him another identical model.
Rather than test the amp at the store, he took this amp back home and hooked it up to one of my bass cabinets that he was borrowing. I guess that they figured that there was no chance of two amps in a row being bad. Instead of lighting the drivers on fire, this one simply sounded very distorted. That's because the DC was producing a steady-state push on the cones, causing it to act as if it was partially "bound up". The reduced excursion capacity of the cone caused the bass to sound "warbled", so they knew something was wrong.
After checking the dustcaps for heat, they found them to be noticeably warm but not smoldering. The second amp was probably putting out slightly less DC voltage AND the drivers in my cabinet were also much more robust than what he was using in his.
My friend then proceeded to return this amp to Guitar Center to get a refund. Guitar Center gave him a hard time about it initially, but gave in when he started talking about filing a lawsuit to seek damages pertaining to the other equipment that was damaged due to their negligence in selling faulty equipment. While he ended up eating the cost to repair his own speakers, he was also conscientious enough to buy me another pair of brand new 18's in case mine were damaged by the heat. While i didn't appreciate him "taking liberties" with my cabinet and a possibly defective amplifier, he obviously thought more of our friendship than i initially gave him credit for.
Between replacing his drivers and mine, that whole "new amp" fiasco ended up costing him about $750 in damaged speakers. A costly mistake on his part that i'm sure he'll never forget. Both in terms of his wallet AND in seeing his speakers light on fire : )
PS... This took place probably 15 years ago and the amps were Gallien-Krueger's. Turns out that the whole production run was defective from what we later found out.