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Old 5th March 2011, 05:11 PM   #11
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Quote:
Originally Posted by djanci View Post
Interesting. Simple question: What is the output voltage of such amp with applied input signal but without speaker connected?
Trick question? With no speaker connected you have no circuit and both current & voltage are zero.

dave
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Old 5th March 2011, 05:17 PM   #12
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Quote:
Originally Posted by planet10 View Post
Trick question? With no speaker connected you have no circuit and both current & voltage are zero.

dave
Forgive me if I'm wrong, but I think he wants to know what the amplifiers voltage is without a load. As in does the voltage drop when connected to a load. A before and after?
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Old 6th March 2011, 12:28 AM   #13
djanci is offline djanci  Croatia
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Quote:
Originally Posted by planet10 View Post
Trick question? With no speaker connected you have no circuit and both current & voltage are zero.

dave
Dave, sorry, you are wrong - you still have circuit but with load that is infinitely large. Hint: open circuit for current source is like short circuit for voltage source, so think again. I must note that everything that I said before is based on my own thinkings as an electrical engineer. I didn't know about Nelson Pass experiment with current source amps so I read his "Current Source Amplifiers and Full Range Drivers" article and I'm glad that I can say that I WAS RIGHT.

In real world even voltage amplifier with lowest impedance could be considered as current source BUT ONLY FOR LOADS THAT ARE MUCH SMALLER THEN SOURCE IMPEDANCE. As speakers impedance varies from couple ohms to couple tens ohms such amp would act as constant voltage source for that load. But tube amps have higher impedance and Son of Zen even greater (16 ohms!). So SoZ could be considered as non-ideal voltage source OR non-ideal current source, basically it's the same thing.
Nelson: "Remember, you donít have to own a current-source amplifier to put this information to work. Placing R0 in series with the output of a powerful voltage -source amplifier instead of in parallel with a current source will give similar results.".

As I stated before, speaker fed by current source amp would result in some kind of auto-tunning equalizer effect - gain at speaker resonance(s) and toward HF.
Nelson: "Driven by a current source, we note that the bottom end is bumped up at resonance and the top end is increased when compared to the performance of the voltage source...We can trim the damping "Q" of the low frequency roll-off knee by trying different values for R0 (L0 = 0 in this case) until it flattens out to our taste. Most of the drivers we worked with were happy with values from about 22 ohms to about 47 ohms...Usually we also want to adjust the upper midrange and high end. Often these drivers will exhibit an upper-mid peak followed by a decline before the upper-most treble is reached. We can compensate for this by our selection of R1, C1 and L1, which can be used either to create a shelf or a dip to flatten out the response."
Nelson didn't directly mention that gain is accomplished with higher power applied to speaker at resonant freq in opposite to voltage source and therefore higher cone displacement. That's why he insist for high-efficiency FR driver. With MA drivers that could be a problem. If there is too much gain for specific speaker/enclosure configuration he add R0 in parallel to current source amp - basically converting almost ideal current source toward non-ideal voltage source. Not necessarily but the problem could also be with any speaker alignment that has two resonant systems.
Also gain in HF could be bonus for FR drivers with early drop in HF extension but with FR drivers that already have good HF extension like MA drivers you should add R1,C1,L1 for compensation.

I think that current source amp idea has great potential but until speaker manufacturers start to adjust freq response for constant current source we are in muddy waters.

Mark, sorry for going off topic. Maybe you should open new thread.
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Old 19th May 2013, 10:09 PM   #14
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I believe that the speaker using dynamic speaker amplifier should only be a voltage constant, but not current constant. Since the force of the coil depends on the current, in the extreme positions of the diffuser at a constant current strength decreases due to the decrease of the magnetic field, which leads to the growth of the third harmonic in the sound pressure. At a constant voltage reduction of the impedance in the extreme positions of the diffuser leads to an increase in the coil current, and accordingly to compensate for the reduction of force coil.
The negative output impedance equal to the resistance of the speaker wire gives an even better result.
best regards
Petr
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Old 19th May 2013, 11:48 PM   #15
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Quote:
Originally Posted by djanci View Post
Mark, sorry for going off topic. Maybe you should open new thread.
Hi Dj, Guys,
No problems, this is a separate thread so please feel free to continue debating. I'm busy most of the week so will snatch time to read the posts, as I'm reading the variety of thought with much interest

Thanks
Mark.
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Old 26th May 2013, 11:10 PM   #16
TiMBoZ is offline TiMBoZ  Australia
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Default Speaker Driver Q and amp damping factor

Here's something that I thought was a rule of thumb with amp and speakers in layman's terms:

With a valve amp ideally, you would want speaker/drivers with low Q, like <0.3 (to compensate/offset lower damping of valve amp)

With S.S you might want speaker/drivers with higher Q: >0.3 because amp S.S generally provides more damping

What do people think about this? Reasonable/logical, True or False, over simplification, matter of personal taste/preference...comments?

Last edited by TiMBoZ; 26th May 2013 at 11:17 PM.
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Old 27th May 2013, 01:46 AM   #17
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Quote:
Originally Posted by djanci View Post
Ufff, all amps are designed to be constant voltage source and likewise all drivers are designed to give flat(desired) freq response when applied constant voltage.
.

Hi Djanci, Guys,
Thanks for your input, but please show all members your sources to back up your claims.

Member Djanci's post 13 has referenced Nelson Pass, useful and informative, but please include the web-links to these sources, or state the publications from which they came. Give members the opportunity to read/check/interpret and evaluate references for themselves.

I'm all for debate but I'm not in favour of statements made to look "factual", or being argued on any authoritative basis, unless they come with a well researched credible references.

Anyone is welcome to offer their opinion/thinking and beliefs but if the debate moves to a "statement making phase", such comments that come without researched sources, will generally carry less credibility.

One of the best features of the Markaudio section on Diyaudio is that most contributors recognise the benefits to all when comments are technically accurate (much as possible) and easy for others to understand/follow. This way, everyone benefits in better knowledge sharing and we stay better protected from misleading information, trolling and similar.

Thanks
Mark.

Last edited by markaudio; 27th May 2013 at 04:04 AM.
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Old 27th May 2013, 02:11 AM   #18
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Quote:
Originally Posted by TiMBoZ View Post
Here's something that I thought was a rule of thumb with amp and speakers in layman's terms:

With a valve amp ideally, you would want speaker/drivers with low Q, like <0.3 (to compensate/offset lower damping of valve amp)

With S.S you might want speaker/drivers with higher Q: >0.3 because amp S.S generally provides more damping

What do people think about this? Reasonable/logical, True or False, over simplification, matter of personal taste/preference...comments?
Hello Tim,
As interesting set of thoughts. They are an "over-simplification" but you've done the right thing by using the suggestions to encourage more thinking. Many thanks for doing this.

Cheers
Mark.
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Old 27th May 2013, 04:31 AM   #19
TiMBoZ is offline TiMBoZ  Australia
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Ok, I don't mean to categorise/pigeonhole drivers by any singular specification; '0.3' is kind of just a general sort of arbitrary number to explain the idea.

For example; take a solo Mozart flute motif/phrase: the precise stop/start, the timing of the rhythmical punctuation of the flute notes express the 'musicality' of the phrase as much as the harmonic realism, clarity etc. So for me they're should be some tension, control/damping in the component and in between the components.

Just from my listening between S.S vs. valve amp. Just for myself - I love the 'sound' of valves, but prefer the 'feel' of S.S. This is the best way I can explain it. How does one explain/express this more technically? Is it in T/S parameters like 'Qts' and damping factor of an amp?

I guess the goal (for me) is to try to find a happy medium. I'm interested in defining/understanding the factors/parameters/measurements that determine the 'feel' of sound; numerical definitions for dynamic articulation, rhythmical punctuation - this is something I'd like to understand better. In context of dynamic/coil speakers.

Last edited by TiMBoZ; 27th May 2013 at 04:59 AM.
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Old 27th May 2013, 06:03 AM   #20
TiMBoZ is offline TiMBoZ  Australia
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Here's another way of expressing it: Driver 'compliance' and mating a very compliant driver to a low damped amp. Is this generally, a good idea? Or a matter of taste? whether it sounds 'good'?

Or should there be a good balance between driver compliance and amp damping?

Is there a singular parameter that expresses driver compliance?

that feels better, got that off my chest. Thnx
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