The input impedance is frequency-dependent. For subsonic frequencies, the input impedance tends towards infinity with reducing frequency. For increasing frequencies above HF, the impedance tends towards 2.2K (RF filtering). In the normal audio band, the input impedance is around 24.2K (ignoring the small impedance presented by the input transistor on the right).
In the first schematic there is a gain stage in the output of CD player capable to produce above 2 V in a load often as low as 600R
Signal then will travel through a resistor 46.900 R
Then get shunted to ground with 100R resistor
From this divider then we expect to drive the amp at very low power .
In the second case where a CD player produces 2V often to a load as low as 600R
Signal then will travel through a 46.900R resistor
Then get shunted to ground with 100R
But this doesnt matter much since our next stage is active and we can amplify the signal as much as we like but with a cost ( noise distortion and many others ) and then take it to the amplifier .
While the active stage in its output will always see an easy load like 22K stable and easy to drive ...
Now any one expects ? That any given amplifier will produce the same dynamics when its input is shunted to ground to as low as 100R next to another one that it's input is always 22K above ground ?
If i read correctly the perfect amplifier should have infinite input impedance and zero output impedance Is that correct ?
Signal then will travel through a resistor 46.900 R
Then get shunted to ground with 100R resistor
From this divider then we expect to drive the amp at very low power .
In the second case where a CD player produces 2V often to a load as low as 600R
Signal then will travel through a 46.900R resistor
Then get shunted to ground with 100R
But this doesnt matter much since our next stage is active and we can amplify the signal as much as we like but with a cost ( noise distortion and many others ) and then take it to the amplifier .
While the active stage in its output will always see an easy load like 22K stable and easy to drive ...
Now any one expects ? That any given amplifier will produce the same dynamics when its input is shunted to ground to as low as 100R next to another one that it's input is always 22K above ground ?
If i read correctly the perfect amplifier should have infinite input impedance and zero output impedance Is that correct ?
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There should be no electrical or audible difference, as far as an amplifier is concerned, whether it is being driven by a passive attenuator with an output impedance of, say, 200 ohms or by an active source with the same output impedance (other than some additional noise and distortion). This, of course, assumes that there is no audio colouration occurring in the active source.
That would be ideal, but not particularly practical.
When a system produces a perceptibly less, or more, "dynamic" sound than another from the same program, how does one determine which is the correct sound, and why?
Well to my ears and eyes this doesn't sound right 22K should be a by far easier load than 100R while also signal will struggle to pass 46.900R and then be shunted to ground with 100R
so i think that you must be loosing something from part A = signal travels through 46.900R and then get shunted with 100R But i also expect any input of any amplifier to loose something when shunted down to 100R
I trace the loss of dynamics in the specific application in exactly that
so i think that you must be loosing something from part A = signal travels through 46.900R and then get shunted with 100R But i also expect any input of any amplifier to loose something when shunted down to 100R
I trace the loss of dynamics in the specific application in exactly that
Cannot answer that there is plenty of variables in the answer
to a given system this can be tested with the one way and the other way and then you will now .
My target was to have the full spectrum in a given very low power in a system as described above .
When driven passively bass was very week seemed also to miss some part of the very low end , middle was ok but bellow average and high was half dead
After going active in the same low power all went up ok low end was rich and plenty without the lowest end missing middle woke up and high was enough very crystal and the total picture was very balanced from frequency range aspect while none of the areas seem to scream or be absent for any reason .
Hi currentflow
I don't think it's the imbalanced impedance. I suspect it has to do with the low impedance zapping the current of the input signal. Don't forget, the other end of the passive pot is to ground. This will shunt the input impedance at the differential. At low volume setting, the amplifier's input impedance will be largely determined by resistance of the wiper to ground of the passive pot.
Mike
You are looking at it wrongly. The input impedance is not the input of the passive pot. The input impedance of a non-inverting amplifier is generally taken to be the resistor at the non-inverting input to ground. For SS amplifiers, it is normally from 10K to 47K.
I understood that the sound of your actively driven system is your preferred sound, and that of the passively driven is not as preferred, however way you would describe them. My question was how you determined which system has produced the supposedly correct sound, or what the reference was? I have little interest in your preference to sound or its balance, and a preference is not subject to discussion anyways.
The only thing lost is voltage level, due to the effect of the potential divider. There will also be a loss due to the output impedance of the preceding stage forming another divider with its load.
All the impedances in a resistive potential divider do is to attenuate voltage. There can be no dynamic content changes. I suggest the effect you are experiencing is caused by something else.
For example: Are the active stages in the chain capable of satisfactorily driving their loads? Are the interconnecting leads between the source and pre-amplifier as well as between the pre-amplifier and the main amplifier making a good connection and of low resistance? Are all the power rails in the active stages adequately decoupled?
you are laying a multiaspect issue ...
I am 50 , I repair amplifiers since i was 13, i own east electronics for more than 30 years , small repair firm that now days with 4 more people working with me we repair between 1000-1500 audio devices per year, To do that except parts we have investments above 30.000 euro in testing equipment which obviously know how to operate .
Sub division of east electronics is a rental dpt that operates sound systems PA rentals for live shows , Dj sets and so on for crowds up to 1000 individuals .
At the specific tests all devices have been developed and tested over very long periods of times, even though given designs like P3A and P37 and given sources like a CD 63 KIS
So i think you can take my opinion as valid😱
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Now i am at the stage to pretend that i have never seen this post ...Just missed it ...
You talk about 'zapping the current' of the input signal. Agreed, but only in a uniform way. For a network to modify dynamic content, it would have to do it selectively. Purely resistive attenuators, no matter how they are configured, surely don't have that ability?
Don't take my post the wrong way. I'm not questioning your ability to repair amplifiers - it's just that I'm running out of suggestions that may explain your experiences.
LTP stage in the input of one amplifier is a live part ...Even though just a few parts behind, anything that happens behind it will have some impact in the performance .
People have spent ages discussing the behavior of one ******* capacitor in the input Why Mundorf plays better than silmic or worst than this and that ....
Does this also apply to your voltage divider rule ?
Or by the same logic we have to think that all 4u7 capacitors in the input will play exactly the same as long as the value is 4u7 ???
Sorry i don't get it
It took me 2 years of occasionally testing to chose input capacitor for my P3A ( value was always 4.7uf )
People have spent ages discussing the behavior of one ******* capacitor in the input Why Mundorf plays better than silmic or worst than this and that ....
Does this also apply to your voltage divider rule ?
Or by the same logic we have to think that all 4u7 capacitors in the input will play exactly the same as long as the value is 4u7 ???
Sorry i don't get it
It took me 2 years of occasionally testing to chose input capacitor for my P3A ( value was always 4.7uf )
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Quote:Originally Posted by east electronics View Post
headroom ...what a magic word ..... Quote
Funny that.
If the source is the same, and the load is not detrimental to either. A passive pot has almost limitless headroom, than a pot with a buffer.
Which equals even better dynamics??
Cheers George
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Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
headroom ...what a magic word ..... Quote
Funny that.
If the source is the same, and the load is not detrimental to either. A passive pot has almost limitless headroom, than a pot with a buffer.
Which equals even better dynamics??
Cheers George
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
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Then current flow let us suppose that both my repair skills are fine and my construction skills are even better ...On your behalf though you should know that both P37 and P3A are for starts proven designs and second due to the simplicity of the circuit are very tolerant and very forgiving in this type of mistakes ... So NO that wasn't the issue ...
I think that the reason for such a long argument is that actually nobody bothered to do this cause in a way is useless .
P3A will happily produce 60 Watts so who will bother to run this amplifier all day long only to use 0.25W while from time to time might use 30-40W
So i think experience on the very specific application must be very low One that was not happy with the sound at such a low power just crunked the level a bit and all was fine .
Been trying to operate my system with the ZCA from Mark at first never liked the sound ( no mater how it was driven ) and second with the ZCA lost the ability of 30-40W if needed once in a while
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Funny ??? Yes George Got some more funny things :
In the other thread i was almost "accused" for behaving like the man who sells active preamps for living ...
Do you actually sell light speed attenuators ???
Cause if you do and these also behave like passive pots in such a low listening level then i might done some harm to your business with my thread which wasn't my intention
Sorry for that !!!
In the other thread i was almost "accused" for behaving like the man who sells active preamps for living ...
Do you actually sell light speed attenuators ???
Cause if you do and these also behave like passive pots in such a low listening level then i might done some harm to your business with my thread which wasn't my intention
Sorry for that !!!
It's all about the facts, and you've been shown them numerous times at the other thread, and probably here too, not that I could be bothered to read this one. As you said to post it here instead, so I did.
Cheers George
Cheers George
taking as a fact that a 4UF capacitor is perfect is simulator procedure in real life each and every one of them will behave different only the differences will be too small to determine with instruments , personal taste will have to do something with that while real life tests either require HD analysis instruments or long term listening tests ... I actually have both !!!
so by the same logic zapping signal with 100R to ground in simulator might appears absolutely no problem but it seems to me that in real life will not be the same ...
so by the same logic zapping signal with 100R to ground in simulator might appears absolutely no problem but it seems to me that in real life will not be the same ...
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