damping factor

[racca]

One of the reasons that high damping factor got a negative rap is that it is related to high amounts of negative feedback. And during the spec wars of the late 70s going into the early 80s, negative feedback was over-applied to the detriment of sound quality, especially in budget-priced gear.

Neither negative feedback or high damping factor (or their opposites, no negative feedback and low damping factor) are a magic bullet in amp design. But some audiophiles latch onto these numbers, which is just human nature, I guess.

 

[maxhifi]

Yeah, I think once the damping factor hits about 15, it starts to become irrelevant. Less than 15 can cause audible problems, and when it gets really low the frequency response will more or less follow the impedance curve of the speakers - NOT a good thing!

 

[whoaru99]

I have a big name brand SS amp with low DF, 20, I believe is the number. The bass is anything but sloppy/loose/bloated. I'd bet most McIntosh owners would agree as well that low (relatively speaking) DF is not indicative of poor bass performance.

And no, my low DF amp isn't McIntosh, it's Audio Research 100.2.

 

[djnagle]

Carver amps have some...difficulties...due less to circuit design than to circuit layout and parts selection.

Right on Schurkey. A properly serviced Carver amp, any of them, will outlast any other amp. I just have Roland go through my TFM 45 and it is the best sounding non-tube amp I've heard and I know it will outlast me..

 

[gadget73]

Carver designs are interesting. So far, I haven't been real impressed with his preamps but the power amps are nice. The preamps just have too much processing for my liking. I have very little experience with the power amps, other than the couple of Phase Linear 700's I've had my hands in. Thats a fairly straightforward design, but the wiring layout is pretty bad.

 

[damacman]

When you start analyzing the math (like what was done on page 1 of this thread) you begin to realize that the differences between amps are not as great as this specification would lead you to believe. There is another lengthy discussion of this topic buried in the McIntosh forum.

 

[tarior]

Kenwood Sigma Drive.

 

[Superampman]

So since DF seems not to be conducive to good control, what are the parameters of an amp that contribute to the great bass definition I hear in one that is lacking in another? Or better, why or how does one excel over another when both are great amps? What are the other factors?

 

[Kingshead]

If only Bob could design a reliable amp.

Owned three Carver amps for more than 20yrs, used daily for TV and or music on average more than 12hrs a day. Only problem ever was burned out bulbs in the VU meters, sounds pretty reliable to me. Along with the amps, also owned a pre, cassette, LD player, tuner, and surround processor. Never had a problem with any of my Carver gear, maybe some people just don't treat their gear very well.

 

[tarior]

It's not for nothing that we call 'em "Flame Linear". The TFM series were actually decent enough, but I don't think Bob designed those. The Carver branded preamps and other gear seem to hold up just fine.
I'm a bench tech for a living, and I have never seen an amp self destruct the way a Carver (except for the Japanese ones) amp does.

 

[ConradH]

I think the Carver amps with the triac controlled power supplies hammer the filter caps a bit harder than normal, but the rest of the amp seems at least as well built/designed as any other. But back to damping factor...

That Crown number up in the thousands could only be achieved if they take the amp feedback right off the output connector (armchair speculation anyway). Add six inches of speaker wire, at least anything smaller than an automotive jumper cable, and that multi-thousand damping factor is history.

Also, though it's said not to be an issue, I'd always want to see a damping factor graph like Crown gives. It isn't just one number and maybe there's some impact in the midrange we could hear. I've never seen a damping factor graph for a tube amp, though the usual number given is about 15 at some low frequency. What is it elsewhere?

 

[moejr]

I would like to see a damping factor graph for my Kenwood Basic M2 Amp. Manual lists it at greater than 1000.

 

[Brian]

There was a paper from McIntosh years ago discussing the topic as there use of the autoformer yielded a low damping factor compared to other ss amps. They found in testing that as a general rule any df greater than 16 yielded no improvement. I seem to remember their autoformer based ss as had a df in the 16-20 range.

 

[Rob41]

Very interesting thread. It all has me thinking about how damping factor.....factors into my active crossover/multi amp set up. IIRC from what I've read, an active crossover set up where there is a seperate amp for each set of drivers i.e. woffers, mids, tweeters, there exists far greater damping factor than that of any passively crossed system. In particular, there is far greater control of the woofers.

Several posts in this thread cited that anything above a DF of 15 is likely unnecessary. I've included a high damping factor in the list of benefits of using an active crossover but I think I'll remove that from the list.

 

[bowtie427ss]

Several posts in this thread cited that anything above a DF of 15 is likely unnecessary. I've included a high damping factor in the list of benefits of using an active crossover but I think I'll remove that from the list.

Maybe "improved damping factor" would be a less contentious statement.

Regardless of the numbers involved, eliminating the passive crossover components from between the amplifier and woofer is going to change the impedance ratio between amp and load....................... that ratio IS the damping factor.

 

[Audiovet]

It has been pointed out several times that the classic DF definition is just about meaningless, in that it ignores the quite major contribution of the driver voice coil resistance in the total circuit. But, with due respect, how difficult it is to override an idea once ingrained ....

My effort at bringing this truth across is by a sharp look at the real voice coil resistance of practical drivers - practical in that most members can easily measure it. That might bring reality home.

I have never measured voice coil resistance for an 8 ohm driver as lower than 5 ohm. On average I find values in the vicinity of 6 ohms; it varies slightly with the brand. Several 4 ohm drivers I have measured linger in the 3,0 - 3,6 ohm region.

That means that the lowest voice coil circuit series resistance (in the 8 ohm case), will be 6 ohms. Thus even if amplifier output impedance plus cables plus what else amounts to zero, the damping factor actually indicative of to what degree a driver is damped (practical DF), cannot be much higher than 1,3! (This excludes the fact that the voice coil circuit ompedance can be quite higher than the d.c. figure. Voice coils operate under signal conditions, which exibits an even highr series impedance.)

This explaines why for generally DFs per classic definition above values of 10 or higher have negligible effect.

It explains why the (audible) frequency response of any half decent amplifier can hardly be influenced audibly by by the loudspeaker load variation, funny loudspeakers excluded. (One presumes amplifiers with 'dfs' of at least some 15; I have not noticed anything lower than that; on the contrary. Low DFs associated with tube units are often touted as the main reason for mellow or whatever flavour of sound; I fear the main reason must be looked for elsewhere, mainly so or at least to a large extent.

Going further, one can point out that tube amplifiers using at least UL output stages can easily have 'DFs' of some >20. For the figures-thirsty, it is moderately easy to achieve figures of some 50, or several 100 with certain measures - if such would be of any practical consequence whatsoever.

 

[evsentry3]

Another thing to consider....

Many woofers are over damped. "Loosening" the control could allow them to ring more naturally.

I've seen it said that the modern quick woofer "thwack" sound is the result of too tight of control actually cutting off the recorded continuation of the ring of the bass drum, for instance.

Ever set next to a big drum and listen to how long it continues after a single hit?

That's kind of the idea of this thought...that you're curtailing a natural tail out of sound when you get too tight of a driver suspension and too high of a DF amplifier.

Validity? Who knows.... It certainly would be individual to the amplifier/speaker combo and how the driver and cabinet volume was executed.

EV3

 

[Ken Boyd]

I think I know what you mean but to further expound, the matching you speak of is not that the 8 ohm tap has 8 ohm impedance thus "matches" an 8 ohm speaker.

It's that the 8 ohm tap has the correct turns ratio to put the as-designed plate load on tubes through the reflected load of an 8 ohm speaker. The 8 ohm tap winding itself likely has much lower impedance than 8 ohms (but considerably higher than typical SS amp output impedance).

Some older tube amps have what appears to be a variable damping factor, yet you say tube amps match the impedance. I recall some of the older Fishers having a feature called Zmatic, does that simply change the output impedance on the output transformers. That same amp also has a switch to select between 8 ohms and 4 ohms for speaker impedances.

Personally I don't know why anyone would want to purchase a SS amp that sounds like a tube amp. Is not the goal of any good amp to not have any sound just to amplify the source? If I want a good SS amp I want it to not have any sound, if I want a good tube amp, I really don't want to hear it either.

 

[bowtie427ss]

practical in that most members can easily measure it.

Yet, it is a static measurement.

Where DF counts is not a static situation. It's an environment where power and acoustics(acoustic load and cabinet tuning) play a significant, and reactive role.

 

[tarior]

Maybe "improved damping factor" would be a less contentious statement.

Regardless of the numbers involved, eliminating the passive crossover components from between the amplifier and woofer is going to change the impedance ratio between amp and load....................... that ratio IS the damping factor.

True enough, but the eq requirements for operating a driver with out passive crossover components opens up a whole new can of worms. Especially with tweeters and mids.