Here the corrected image.
Try to make a "refresh" cicle into your brain folks...the "stablishment"...things we use to do without think about, polutes our minds.
It is not possible that the passive can be worse then the active..we know building and testing that each active stage distorts a little...so..not having active you will be rid from that.
regards,
Carlos
Try to make a "refresh" cicle into your brain folks...the "stablishment"...things we use to do without think about, polutes our minds.
It is not possible that the passive can be worse then the active..we know building and testing that each active stage distorts a little...so..not having active you will be rid from that.
regards,
Carlos
Attachments
Are your talking about yourselve Pavel?
oh!...i understood...many...may be others.... i see indefinite subject.
I also feel pitty with folks that never tried passive and go believing active is the solution.
Do not believe me....believe in yourself, but please guys, test your beliefs into real world not to go deliranting all life long.
regards,
Carlos
.................................
You know André..one day i will build something to listen....first i have to learn how to hold the soldering iron.
oh!...i understood...many...may be others.... i see indefinite subject.
I also feel pitty with folks that never tried passive and go believing active is the solution.
Do not believe me....believe in yourself, but please guys, test your beliefs into real world not to go deliranting all life long.
regards,
Carlos
.................................
You know André..one day i will build something to listen....first i have to learn how to hold the soldering iron.
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By chance, i was faced with a similar case in my last power amplifier. I had in my plans to include a signal attenuating pot in input, for direct connection of CD players in amplifier. The reason was that i know that many people it preffer this.
From my experiments, proved that a potentiometer connected directly between the input socket and the input of amplifier is not so easy. The input of amplifier consisted from some R-C filters ( Π or T ) before the LTP. A variable resistor (like the pot) it is tuned with those filters when its value is changed and produces unwanted signals. In the begining, i used a 50KΩ pot in input, which has an apropriate value to give a relativelly high Zin. By injecting square waves in input (i use allways square waves during the development of a project) i observed in my DSO strong overshoots during the turning of potentiometer. From luck, when i connected the signal generator (which has Zo=50Ω) directly to the input of amplifier the overshoots disappeared. After this, i found that only a pot of 1 to 1,5ΚΩ as much does not cause overshoots and oscillations. The existence or not of the input DC blocking cap (either electrolytic or polypropylene or 2,2μF or 22μF) does not matters, the result it is the same. To the report, the input impedance of my amplifier without resistor termination to GND, it is arround 15ΚΩ. The issue is found in input impedance. If we use a 50K pot, then we can have a good Zin in the cost of oscillations. If we use a 1K pot, then we can have a clean SQUARE signal in the cost of very low Zin. The solution it is a buffer between the input socket and the input of amplifier. Thus, we can terminate the input of buffer to GND with a 50ΚΩ resistor, and in the output of buffer we can place a volume pot with the correct value of 1ΚΩ. Τhe pot is connected as usually, the two extreme terminals accross the output of buffer and GND, and the wipper terminal in the input DC blocking cap. But a very small ringing remains in the rising edge of SQUARE wave. This can eliminated completelly by connecting a 220 to 270 pF cap after the DC blocking cap and GND, in the cost of increase the rise time of square wave by 0,2μs. In my case, i had an initial rise time at 60Vpp of 1,78μs and after the changes 1,8μs.
Summarizing: Against my initial thoughts that the addition of a simple level control pot in the input was nothing, this proved very complex finally. In practice, now and after 2 weeks of extra work, inside my amplifier exists as well a preamplifier powered from a special (zero ripple) seperate supply. The good thing it is that, i can use the buffers as subtracters to have and balanced inputs.
So, IMHO to connect a source like a CD directly in the input of amplifier, there is the need of a buffer to seperate the input socket high impedance from the low input impedance of the main amplifier. The buffer it is a form of preamplifier.
Of course, you can connect a CD player in an amplifier without input level controls, as you can manage the volume from the remote control. Most Hi-Fi or Hi-End comercial amplifiers does not includes input level controls. But you must be very cautious for the Ζο of CD player to not exceed the 1KΩ.
I suppose that the 90% of DIYers they use only sinus waves or music (!!!) to check their projects. Square waves, although are not related with music, are very usefull to reveal concrete technical details of the circuit, mainly the TIM distortion which caused from the wrong compensation of Cdom, the wrong compensation of the feedback loop, the wrong input filtering and the existense of the smallest oscillation.
Greetings
Fotios
From my experiments, proved that a potentiometer connected directly between the input socket and the input of amplifier is not so easy. The input of amplifier consisted from some R-C filters ( Π or T ) before the LTP. A variable resistor (like the pot) it is tuned with those filters when its value is changed and produces unwanted signals. In the begining, i used a 50KΩ pot in input, which has an apropriate value to give a relativelly high Zin. By injecting square waves in input (i use allways square waves during the development of a project) i observed in my DSO strong overshoots during the turning of potentiometer. From luck, when i connected the signal generator (which has Zo=50Ω) directly to the input of amplifier the overshoots disappeared. After this, i found that only a pot of 1 to 1,5ΚΩ as much does not cause overshoots and oscillations. The existence or not of the input DC blocking cap (either electrolytic or polypropylene or 2,2μF or 22μF) does not matters, the result it is the same. To the report, the input impedance of my amplifier without resistor termination to GND, it is arround 15ΚΩ. The issue is found in input impedance. If we use a 50K pot, then we can have a good Zin in the cost of oscillations. If we use a 1K pot, then we can have a clean SQUARE signal in the cost of very low Zin. The solution it is a buffer between the input socket and the input of amplifier. Thus, we can terminate the input of buffer to GND with a 50ΚΩ resistor, and in the output of buffer we can place a volume pot with the correct value of 1ΚΩ. Τhe pot is connected as usually, the two extreme terminals accross the output of buffer and GND, and the wipper terminal in the input DC blocking cap. But a very small ringing remains in the rising edge of SQUARE wave. This can eliminated completelly by connecting a 220 to 270 pF cap after the DC blocking cap and GND, in the cost of increase the rise time of square wave by 0,2μs. In my case, i had an initial rise time at 60Vpp of 1,78μs and after the changes 1,8μs.
Summarizing: Against my initial thoughts that the addition of a simple level control pot in the input was nothing, this proved very complex finally. In practice, now and after 2 weeks of extra work, inside my amplifier exists as well a preamplifier powered from a special (zero ripple) seperate supply. The good thing it is that, i can use the buffers as subtracters to have and balanced inputs.
So, IMHO to connect a source like a CD directly in the input of amplifier, there is the need of a buffer to seperate the input socket high impedance from the low input impedance of the main amplifier. The buffer it is a form of preamplifier.
Of course, you can connect a CD player in an amplifier without input level controls, as you can manage the volume from the remote control. Most Hi-Fi or Hi-End comercial amplifiers does not includes input level controls. But you must be very cautious for the Ζο of CD player to not exceed the 1KΩ.
I suppose that the 90% of DIYers they use only sinus waves or music (!!!) to check their projects. Square waves, although are not related with music, are very usefull to reveal concrete technical details of the circuit, mainly the TIM distortion which caused from the wrong compensation of Cdom, the wrong compensation of the feedback loop, the wrong input filtering and the existense of the smallest oscillation.
Greetings
Fotios
Hello Glowbug, for sure i am not running phono cartridge directly into a power
amplifier...level is too low and phono needs strong equalization.
Only already pré amplified line out signals from CD players, DVDs, Satelite Receivers, Television Line out connectors and so on...the most used audio sources.
For a turntable, you need, at least a RIAA equalized phono pré amplifier.
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Hello dear Fótios
I already knew, in advance what you would say...i know your ideas about...thank you very much by your important contribution here.
Karolus
amplifier...level is too low and phono needs strong equalization.
Only already pré amplified line out signals from CD players, DVDs, Satelite Receivers, Television Line out connectors and so on...the most used audio sources.
For a turntable, you need, at least a RIAA equalized phono pré amplifier.
....................................................................................................
Hello dear Fótios
I already knew, in advance what you would say...i know your ideas about...thank you very much by your important contribution here.
Karolus
Hi,
"Need for an preamp" is that sweet fairytale grandpa used to tell from those old days, when he was a Young boy and signal sources didn´t provide for enough signal level.
Decently constructed means not a classical Pot-circuit. Besides the rather low quality of contacts (wiper) of many pots the highish und not constant output impedance is not what we want.
But many switched resistor networks that show a constant output impedance are high in Zout value which either reduces the allowable cable length considerably and/or reduces the bandwidth too much. No wonder those sound ruther dull.
You need to design a constant Zout and low Zout(<<2kOhm) network.
When You compare such a network with and without active circuitry (which is the case with my preamp) You will find that adding active circuitry distracts from the music signal in almost any case (those cases where activation actually improved things were cases in which the in-out-impedances were quite off of the norm or where unusual long cable runs (>10m) were required).
jauu
Calvin
Agreed, since they mostly will not have listened to a decently constructed passive stage!
"Need for an preamp" is that sweet fairytale grandpa used to tell from those old days, when he was a Young boy and signal sources didn´t provide for enough signal level.
Decently constructed means not a classical Pot-circuit. Besides the rather low quality of contacts (wiper) of many pots the highish und not constant output impedance is not what we want.
But many switched resistor networks that show a constant output impedance are high in Zout value which either reduces the allowable cable length considerably and/or reduces the bandwidth too much. No wonder those sound ruther dull.
You need to design a constant Zout and low Zout(<<2kOhm) network.
When You compare such a network with and without active circuitry (which is the case with my preamp) You will find that adding active circuitry distracts from the music signal in almost any case (those cases where activation actually improved things were cases in which the in-out-impedances were quite off of the norm or where unusual long cable runs (>10m) were required).
jauu
Calvin
Zin and Zout around 40K...this is what i use as CD out can hold that
also amplifier input circuit can accept without load too much.
To use lower Zin you should ask Calvin, as he seems that knows more than i know and he can provide us some schematic.
Mine use 33K in series with the potentiometers... trimpot (33K) in the input and the potentiometer in series (50K).
As you have those resistive lines in parallel, you will have reduced total impedance that will be sensed by CD output and power amplifier input.
Mine worked fine, but for sure other ideas can be even better, i am not selling the circuit idea, i am just saying that we can do it passive, avoiding active stages..and this, obviously and super of course, must be better than active..as you have to manage resistances (impedances) only to adjust level...so....no active is needed, as you do not need to amplify nothing, you need to control.
CD output has already nice output impedance..and that impedance matches the power amplifier input (reasonable matching for several audio amplifiers..and you can tweak yours to match perfectly)... Cd output level is high...from 1 to 2 volts RMS into the modern ones..this also matches the power amplifier input sensitivity, that can also be adjusted to optimize.
In the reality, all we need is a potentiometer and a series resistance..to each channel.... inductance and capacitance is minimized using short wiring and distance between wires..small box..control box.
regards,
Carlos
also amplifier input circuit can accept without load too much.
To use lower Zin you should ask Calvin, as he seems that knows more than i know and he can provide us some schematic.
Mine use 33K in series with the potentiometers... trimpot (33K) in the input and the potentiometer in series (50K).
As you have those resistive lines in parallel, you will have reduced total impedance that will be sensed by CD output and power amplifier input.
Mine worked fine, but for sure other ideas can be even better, i am not selling the circuit idea, i am just saying that we can do it passive, avoiding active stages..and this, obviously and super of course, must be better than active..as you have to manage resistances (impedances) only to adjust level...so....no active is needed, as you do not need to amplify nothing, you need to control.
CD output has already nice output impedance..and that impedance matches the power amplifier input (reasonable matching for several audio amplifiers..and you can tweak yours to match perfectly)... Cd output level is high...from 1 to 2 volts RMS into the modern ones..this also matches the power amplifier input sensitivity, that can also be adjusted to optimize.
In the reality, all we need is a potentiometer and a series resistance..to each channel.... inductance and capacitance is minimized using short wiring and distance between wires..small box..control box.
regards,
Carlos
Hello
read this thread with interest because I experiment with passive Pre's as well since around 10 years now.
First some remarks:
With modern sources a passive pre can be the better solution, but I prefer an TVC - transformer volume control. It should be no problem nowadays to design a phono stage which delivers the same outputlevel like "modern sources" - here a CD-Player for example - with low output impedance.
Using a passive pre, and I speak about TVC, we should have a look onto impedance mathcing and signal voltage ratio:
in the world market a passive preamp is not really accepted by the crowd, as well when you explain them the advantages pf a passive pre!
Regards
Joao
PS:
Para meus amigos brasileiros ... Mas por favor, tome contacto com o meu amigo Carlos no Rio de Janeiro, ele tem muita experiência com o TVC. Ele também esta aqui em forum sobre o nome Casouza.
Nevertheless, for my Brazilian friends ... please take up contact with my friend Carlos in Rio de Janeiro, he has a lot of experience with TVC. His user name is Casouza.
read this thread with interest because I experiment with passive Pre's as well since around 10 years now.
First some remarks:
With modern sources a passive pre can be the better solution, but I prefer an TVC - transformer volume control. It should be no problem nowadays to design a phono stage which delivers the same outputlevel like "modern sources" - here a CD-Player for example - with low output impedance.
Using a passive pre, and I speak about TVC, we should have a look onto impedance mathcing and signal voltage ratio:
- imprdance matching > power amp's input impedance ~10 times higher than source output impedance
- voltage ratio ~ 6dBV head room of the power amps input sensitivity
in the world market a passive preamp is not really accepted by the crowd, as well when you explain them the advantages pf a passive pre!
Regards
Joao
PS:
Para meus amigos brasileiros ... Mas por favor, tome contacto com o meu amigo Carlos no Rio de Janeiro, ele tem muita experiência com o TVC. Ele também esta aqui em forum sobre o nome Casouza.
Nevertheless, for my Brazilian friends ... please take up contact with my friend Carlos in Rio de Janeiro, he has a lot of experience with TVC. His user name is Casouza.
Thank you João...i will search for Cazuza very soon
If you have some passive pré amplifier, or a control box, a potentiometer array, please, post it here to help us with some real schematics.
I am not an engineer, so i have some troubles to produce those things with reasonable precision...i use to work into a try and error bases and the best instrument i use are my own ears (not so good those old days.... Ich habe 58).
Mine "thing"..works fine..but for sure a better impedance matching can be interesting.
I am here to say passive is better than active...and to invite folks to give a try on that and to say what they have perceived.
A better schematic will be very welcome.
regards,
Carlos
If you have some passive pré amplifier, or a control box, a potentiometer array, please, post it here to help us with some real schematics.
I am not an engineer, so i have some troubles to produce those things with reasonable precision...i use to work into a try and error bases and the best instrument i use are my own ears (not so good those old days.... Ich habe 58).
Mine "thing"..works fine..but for sure a better impedance matching can be interesting.
I am here to say passive is better than active...and to invite folks to give a try on that and to say what they have perceived.
A better schematic will be very welcome.
regards,
Carlos
Post 30 has errors...i could not correct because edition time is too much small
Please, dear moderators, increase editing time to at least 30 minutes.
Post 30 should be deleted, was made once again and published as post 32.
Also we cannot correct the post tittle...this is also needed...or we cannot, or i could not make it.
regards,
Carlos
................................................................................................
here you have the schematic where the CD player "see", or sense, the impedance around 22k
Please, dear moderators, increase editing time to at least 30 minutes.
Post 30 should be deleted, was made once again and published as post 32.
Also we cannot correct the post tittle...this is also needed...or we cannot, or i could not make it.
regards,
Carlos
................................................................................................
here you have the schematic where the CD player "see", or sense, the impedance around 22k
Attachments
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I have the same request like Carlos. Please...do something for this problem!
Fotios
And I'm here to say active sound better than passive.
Carlos, your impedance calculations are wrong, also I can't imagine that you can get good SQ with that amount of resistance in the signal path.
Thank you fótios..... i really need 45 minutes or more, as i use to edit several
times to include sketches, and to correct the language, to make it more clear, to remove errors...to make a revision.
Here another sketch..and this i have made before the post be opened, not to face the timing problems i am facing.
We can adjust your passive controls the way we want..to the resistance/impedance we want.
regards,
Carlos
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I know nothing about you said fotios..i have to test and to learn/see/realise by myself...i have the scope but the generator is still travelling to brazil..so..i will check the overshots, the pulses and the timing in the future..after my generator arrive.
times to include sketches, and to correct the language, to make it more clear, to remove errors...to make a revision.
Here another sketch..and this i have made before the post be opened, not to face the timing problems i am facing.
We can adjust your passive controls the way we want..to the resistance/impedance we want.
regards,
Carlos
...............................................................................................................................
I know nothing about you said fotios..i have to test and to learn/see/realise by myself...i have the scope but the generator is still travelling to brazil..so..i will check the overshots, the pulses and the timing in the future..after my generator arrive.
Attachments
Already noticed you disagree Visser...so.... thanks a lot by your contribution
I also know my impedance calculations are wrong...the box works, and this is what interests me.... numbers are not my interest.
Calculate by yourself, if you have this interest...i think you have not..as you like active.
Build active and be happy André Visser... also, if you want to be positive, to contribute, to help forum folks, to share your knowledge, then open a thread and write there:
- "Pré amplifier, passive is bad, the good ones are the active ones, pré amplifier is needed!"
then, there you can develop a pré amplifier, or offer your ideas for the communitty, to teach us, to help us to get out from the lame of deep ignorance and so on...beeing positive you know?.. doing something people can use...disagreements helps, but not too much.
I am not perceiving positive things on you...maybe i am wrong... show us something good to the forum folks... open a thread and expose your ideas.. defend your point of views and be productive!
Work for us, and not against us.
regards,
Carlos
I also know my impedance calculations are wrong...the box works, and this is what interests me.... numbers are not my interest.
Calculate by yourself, if you have this interest...i think you have not..as you like active.
Build active and be happy André Visser... also, if you want to be positive, to contribute, to help forum folks, to share your knowledge, then open a thread and write there:
- "Pré amplifier, passive is bad, the good ones are the active ones, pré amplifier is needed!"
then, there you can develop a pré amplifier, or offer your ideas for the communitty, to teach us, to help us to get out from the lame of deep ignorance and so on...beeing positive you know?.. doing something people can use...disagreements helps, but not too much.
I am not perceiving positive things on you...maybe i am wrong... show us something good to the forum folks... open a thread and expose your ideas.. defend your point of views and be productive!
Work for us, and not against us.
regards,
Carlos
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Oi Carlos - destroyer X
here's a schematic how to insert a TVC. The impedances are quite from the practical side. I use a TVC with 10K impedance and an overload of 6Vrms.
Instead of an TVC you can use an AVC - autoformer, which in practical is only the secondary of the TVC. Much better sounding!
The TVC transforms the input impedance from the power amp and another advantage is the absence / non existing hissing from resistors.
Joao
here's a schematic how to insert a TVC. The impedances are quite from the practical side. I use a TVC with 10K impedance and an overload of 6Vrms.
Instead of an TVC you can use an AVC - autoformer, which in practical is only the secondary of the TVC. Much better sounding!
The TVC transforms the input impedance from the power amp and another advantage is the absence / non existing hissing from resistors.
Joao
Attachments
Is this a way to get rid of people that disagree with your unproven statements?
I realy don't feel an urge to start my own thread to try and convince others that my way are the only correct way.
If you want to talk BS like this, don't expect everybody else to keep quiet, do yourself a favour and first listen to equipment of these calibre before you try and convince everybody that two potentiometers are better than that. I've done my homework, even listened to a silver TVC as mentioned earlier.
Cheers
André
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