Simple(?) question about Damping Factor

[Bestunta]

Hello!

I have heard that tube amps have a worse damping factor than SS amps.

This is for power amps only right?

My question is if in a tube preamp to solid state power amp scenario, the damping factor would be dependent solely on the power amp?

Thanks.

 

[gobble]

Hello!

I have heard that tube amps have a worse damping factor than SS amps.

This is for power amps only right?

My question is if in a tube preamp to solid state power amp scenario, the damping factor would be dependent solely on the power amp?

Thanks.

Correct. preamp has nothing to do with this as the measurement is about power amp to speaker load characteristics. Low damping factor can cause loose and flabby and uncontrolled bass. However according to Mr. Nelson Pass, even if overall damping factor is low the right amount of critical damping factor can extend the frequency response and improve SQ of fullrange speakers to an acceptable degree.

Tubes power amps have low DF by default.

HTH

 

[iaudio]

The low damping factor is preferred in order to not arrest the cone movement of full range speakers, afaik.

 

[gobble]

The low damping factor is preferred in order to not arrest the cone movement of full range speakers, afaik.

Yep. My speakers do have a feel of being slightly overdamped. Even the fostex bass-reflex cabinet design doc talks about this. Build a power amp with low DF is on the cards pretty soon.

Cheers

 

[Dr.Bass]

My question is if in a tube preamp to solid state power amp scenario, the damping factor would be dependent solely on the power amp?

It is a little more complicated than that. Even though preamps have nothing to do with damping factor directly it has an indirect effect. To take full advantage of all the damping your power amp is suppose to provide you need a preamp which is appropriately matched. One of the reasons why impedance matching between pre-power is so important is again this.

To illustrate, considering that one has a power amp with an input impedance of 20 kohm, in general keeping everything else constant, a preamp with an output impedance of 100 ohms will present a much cleaner tighter bass than a preamp with an output impedance of 1000 ohms. Basically the preamp with higher output impedance is not driving the power amp well enough to make its full damping factor available for delivery. These data normally is prescribed by the power amp manufacturer.
There is a general indicator that the ratio of output impedance of the preamp to the input impedance of the power amp should be 1:10...but please note that this is the least ratio to be maintained. A ratio of 1:100 is much better and desirable to start with.

Unfortunately tube preamps present a notoriously high output impedance than their solid state counter parts. For example a Shindo Aurieges preamp present an output impedance of 2000 ohms which is very high. An ideal match for this preamp would be a power amp with input impedance of 200 kohms and above. You would not find many such amps. You CAN use a power amp with low input impedance to the tune of 40 kohms but you are not using the full potential of the power amp when it comes at controlling the driver (what you call DAMPING FACTOR) with this tube preamp. There are ways to build tube preamps with low output impedance and high drive but they are normally expensive and therefore rare.
An Einstein tube preamp present an output impedance of just 50 ohms, the reference tube preamp from Octave Audio has an output impedance of 30 ohms...super!! There are more.
But all these are very expensive.

There are other matching criterion like input sensitivity, input capacitance etc but impedance is the first thing to look at.

So, Damping factor also depends on the preamp, though indirectly.

 

[gobble]

Basically the preamp with higher output impedance is not driving the power amp well enough to make its full damping factor available for delivery.

I agree about the impedance matching part affecting frequency extension. But DF is a reactionary impulse is it not? i.e depending on the signal flow back from the speaker driver to the power amp speaker terminals and the ability of the power amp to react to this signal? Isn't it possible that with a well matched pre-power combo that results in extended lower frequency - the power amp with low DF will struggle even further at controlling speaker cone movement thus making it sound more flabby and loose?

I am still learning electronics so my understanding as stated above may be incomplete, but I am presenting an argument for its sake. Hopefully the debate will help clarify our understanding even further.

Thanks

 

[Dr.Bass]

Isn't it possible that with a well matched pre-power combo that results in extended lower frequency - the power amp with low DF will struggle even further at controlling speaker cone movement thus making it sound more flabby and loose?

This is not the way to think IMO. This would mean one should not match a good preamp to a power amp because the power amp has low damping factor ??

It is not like that. Just like the power amp drives the speaker, the preamp drives the power amp. The better the drive, the better the control hence better is the way the amp behaves with the speaker. The amp is not an independent entity. It requires suitable inputs to deliver the output it is designed for. Damping factor is a part of this design as well.
I use an amp which has an input impedance of 10 kohm. The manufacturer of this amp recommends (highly) preamp with output impedance of less than 10 ohms !!! Their own preamp has an output impedance of 3 ohms. As the output impedance of the preamp goes lower its output has higher current which when amplified actually results in the amplifier's higher current delivery which in turn results in damping the speaker better (reactionary but the reaction is not independent of the preamp).

 

[odyssey]

@Gobble
I think Dr Bass was trying to address drive in a system, damping factor itself has to do with the interaction between the speaker and the amp, not with the preamp.

For people who look at specs, higher damping factor does not alone necessarily contribute to better drive/bass/dynamics - take a look at the Class D amps which tend to have a high damping factor as an e.g. Also a small amount of negative feedback can be added to make the output impedance of the amp measure very low - hence leading to a very high damping factor - this does not really tell you how good the bass is.

On tube preamps and impedances - specs taken as a single value of output impedance dont really tell you much - why? The output impedance varies with frequency of the signal. Generally, they are done at 1 Khz or a few hundred hertz. However, this value can go up as much as 10x at the lower frequencies. Manufacturers such as Shindo try to give an estimate on the minimum input impedance of the amp to be used.

In a situation where the pre and power are purely resistive loads, even a pre out to power in impedance ratios of 1:1 will result in a 6 dB loss (high) but does not matter as there is typically enough gain to make up. What is important is that the drop or gain is uniform throughout the frequency range.
The output impedance of the tube preamp says nothing about the quality of music that it can produce just like the input impedance of the power amp says nothing about its quality. There are people who believe in keeping the input impedance of the power amps low so that they are less prone to picking up noise, however this depends on design as well.

cheers

 

[Dr.Bass]

@Odyssey, I am not talking about just the drive, I am talking about the damping factor also. Both drive and damping factor are functions of current delivery of the amp. The current delivery nature of the amp depends highly on the preamp as well. So, its time to reveal the source of information where I have learned this from. It was none other than Rolf Gemein with whom I had a long discussion on this topic. He was explaining his preamp philosophy and why his specs are very important for his power amp to perform optimally and as per specs. He was very clear about damping factor in particular. What makes his RG3 Turbo special is the way it makes his amps deliver the most in terms of damping factor while maintaining a good drive. According to him this is the main reason behind his design and one should adhere to this spec at least to get advantage of the current capability of the power amp.

Now it is obvious that damping factor doesnt certify anything regarding sound quality but yes Preamp does matter when it comes to damping factor going by what RG has to say.

 

[Bestunta]

Hello again,

Sorry I was unable reply earlier, but THANKS a lot really for all the comments and explanations!!

I feel a lot more confident with my system! I have a Little Dot MKIV hooked to a NAD325Bee feeding a pair of recently bought RTiA7s from Polk Audio and noticed the bass just isn't quite quite there yet. I was worried that it would have something to do with the tube to ss combo, but it is probably because of the very cheap cables I hooked it up with... I couldn't wait to wire them up so I just used some wires I had from my dvd player, which are very poor (22 gauge).

Anyway, I am off to buy some decent wires in a few days when I have the time!

Thanks again

 

[gobble]

Hello again,

Sorry I was unable reply earlier, but THANKS a lot really for all the comments and explanations!!

I feel a lot more confident with my system! I have a Little Dot MKIV hooked to a NAD325Bee feeding a pair of recently bought RTiA7s from Polk Audio and noticed the bass just isn't quite quite there yet. I was worried that it would have something to do with the tube to ss combo, but it is probably because of the very cheap cables I hooked it up with... I couldn't wait to wire them up so I just used some wires I had from my dvd player, which are very poor (22 gauge).

Anyway, I am off to buy some decent wires in a few days when I have the time!

Thanks again

Which cable do you plan to get? Also CDP<IC Cable>Preamp<IC Cable>Power matter. Only speaker cable may not help.

HTH

 

[Bestunta]

I have very limited options... I live in Macau and there are very few stores. Guess I'll believe in the wire gauge, origin, the guy from the store, and luck.

Anyway, anything will be a big improvement from what I have!

 

[odyssey]

@Odyssey, I am not talking about just the drive, I am talking about the damping factor also. Both drive and damping factor are functions of current delivery of the amp. The current delivery nature of the amp depends highly on the preamp as well. So, its time to reveal the source of information where I have learned this from. It was none other than Rolf Gemein with whom I had a long discussion on this topic. He was explaining his preamp philosophy and why his specs are very important for his power amp to perform optimally and as per specs. He was very clear about damping factor in particular. What makes his RG3 Turbo special is the way it makes his amps deliver the most in terms of damping factor while maintaining a good drive. According to him this is the main reason behind his design and one should adhere to this spec at least to get advantage of the current capability of the power amp.

Now it is obvious that damping factor doesnt certify anything regarding sound quality but yes Preamp does matter when it comes to damping factor going by what RG has to say.

Its possible that you heard him wrong or it didnt come across correctly since he isnt fluent in english. His new RG2 which he raves about highly actually has an output impedance of greater than 100 ohms. Damping factor itself is defined as the ratio between the speaker impedance and the output impedance of the amplifier. where is the preamp in this equation?

cheers

 

[keith_correa]

Damping factor itself is defined as the ratio between the speaker impedance and the output impedance of the amplifier. where is the preamp in this equation?

Quite right. Damping factor involves only the source [relative to the speaker] output impedance and the rated impedance of the loudspeaker.

 

[sidvee]

As I understand damping factor is a constant function of the amp. and not really variable in regards to the source or load and I have noticed audibly it makes a difference only when the speaker represents a difficult load.
cheers
Sid

 

[Dr.Bass]

I have had this discussion with two of the other members audio_engr (Arup) and Bombaywalla (not on this forum). Both of them use Symphonic Line Kraft power amps. They too have discussed this aspect with Rolf and got the same understanding. Preamp does have an impact on how effectively an amp damps the speaker. It is one of the major criterea of design of their preamps. The 100 ohm output impedance of the RG2 is on the higher side and obviously has its own share of compromises which is understandable considering that it is the most entry level preamp from S-L.

 

[entsurgeon]

well i agree with dr bass for following reason-
most specifications provided are mean of varying values over the range... thus , a pre amp will affect the way current inside the amp is produced under different situations.

 

[Dr.Bass]

CORRECTION:
After some discussion on this thread, I did some further reading and research on damping factor. It did turn out that damping factor should not depend on the preamp. I am also a bit confused now because RG's correlation of preamp output impedance to the damping factor seems somewhat gray to me now.

All I can assimilate is, when power amps have high damping factors, their preamp requirement could become more specialized and that should be taken care of.
And, I infer this way by the logic that, having high damping factor is of very little use if the bass is loose at the amplifier output. It will sound loose anyway, damping factor cannot help here. Now, the looseness of the bass can very well be because of electronic mismatch between the preamp and the power amp (impedance matching and all that). To make sure this does not happen, one needs to take care that the preamp is matched to the power amp requirement. Then we have clean bass available amplifier output and it now comes down to the damping factor which will keep the speaker in check reproducing the bass lines accurately. I guess this is what RG would have meant.

Thanks to Odyssey for pointing this out !

Answering OP's initial question, I still think you need to take care of pre-power matching if you are expecting clean bass from your speakers. Cannot rely on damping factor to do the job alone.

 

[kanwar]

Damping Factor = Load impedance/ Amplifier output impedance

DF decreases with increase in Frequency, for example if you have 1000 DF at 100hz, at 10khz it will be less, the reason for this is the amount of negative feedback available at high frequencies is less than available at low frequencies due to the compensation network in the amplifier to make it stable.

For further reading have a look at this:-

http://www.crownaudio.com/pdf/amps/damping_factor.pdf

regards,
Kanwar

 

[gobble]

CORRECTION:
After some discussion on this thread, I did some further reading and research on damping factor. It did turn out that damping factor should not depend on the preamp. I am also a bit confused now because RG's correlation of preamp output impedance to the damping factor seems somewhat gray to me now.

All I can assimilate is, when power amps have high damping factors, their preamp requirement could become more specialized and that should be taken care of.
And, I infer this way by the logic that, having high damping factor is of very little use if the bass is loose at the amplifier output. It will sound loose anyway, damping factor cannot help here. Now, the looseness of the bass can very well be because of electronic mismatch between the preamp and the power amp (impedance matching and all that). To make sure this does not happen, one needs to take care that the preamp is matched to the power amp requirement. Then we have clean bass available amplifier output and it now comes down to the damping factor which will keep the speaker in check reproducing the bass lines accurately. I guess this is what RG would have meant.

Thanks to Odyssey for pointing this out !

Answering OP's initial question, I still think you need to take care of pre-power matching if you are expecting clean bass from your speakers. Cannot rely on damping factor to do the job alone.

Dr. Bass

Great to see a frank revision. Not from the point of "I told you all along..." but it keeps other people with similar perspectives informed.

By default I would go for a preamp that suits my subjective tastes and with lowest Zout and highest Zin and with ratios for Power Amp Zin matching as close to 1:10 and also the wallet - one cant go wrong there can we?

Cheers