Ok, but we're not dealing with PA here. I think most people here would like their subsonic filters to start no higher than 20Hz, and preferably lower.Workhorse said:
I think reproducing below 20hz is very difficult, you need VERY big
speakers... And you can't hear 20hz, only feel it ! (But is fun !)
30hz is a must, i have enough music going that deep !
Mike
speakers... And you can't hear 20hz, only feel it ! (But is fun !)
30hz is a must, i have enough music going that deep !
Mike
hi Evil, I think I have already clarified my statement about subsonic frequencies that are considered to be well below 18Hz
Hi Kanwar,
You wanted my views on inverting vs non-inverting. Sure.
For any amp an inverting configuration will effectively eliminate common mode distortion as it eliminates the common mode swings. if you have an amplifier with very simple input diff'ls this may be the way to go. For instance using a simple resistor to an intermediate regulated supply can work well for the tail. I did this in the Eidetic power amp which used a chip front end with 15V supplies and the discrete part was inverting with dual diff'l, Vas then UGS output MOSFETS in it's local loop.
Since this was an intermediate stage loading the chip I did not have to deal with low input impedance to the amp. OPA627 for the front end doesn't have issues to compensate for (except price).
I mostly always use chips in inverting mode for filters etc.. rather than Sallen&Key. There's nothing wrong with using inverting for power amps as long as the input R can be high enough not to load the peramp, etc..
Of course if it's 47K you want, feedback R's for your 36 dB are 3M, and even 1pF is -3dB at 50KHz!
You wanted my views on inverting vs non-inverting. Sure.
For any amp an inverting configuration will effectively eliminate common mode distortion as it eliminates the common mode swings. if you have an amplifier with very simple input diff'ls this may be the way to go. For instance using a simple resistor to an intermediate regulated supply can work well for the tail. I did this in the Eidetic power amp which used a chip front end with 15V supplies and the discrete part was inverting with dual diff'l, Vas then UGS output MOSFETS in it's local loop.
Since this was an intermediate stage loading the chip I did not have to deal with low input impedance to the amp. OPA627 for the front end doesn't have issues to compensate for (except price).
I mostly always use chips in inverting mode for filters etc.. rather than Sallen&Key. There's nothing wrong with using inverting for power amps as long as the input R can be high enough not to load the peramp, etc..
Of course if it's 47K you want, feedback R's for your 36 dB are 3M, and even 1pF is -3dB at 50KHz!
Workhorse said:
I will clarify my question: in an amp where no DC servo is used and a feedback cap must be used and also an input cap (by precaution to prevent any external possible DC to enter the amp) in an non-inverting amp, what should be the "-3db" cutoff low frequency?
I "consider" 20 Hz as the minimum low frequency content. Of course selecting 20 Hz would create a high phase shift and less "bass"...
Hi Mr.Greg,
Nice to hear your views. By the way what are your thoughts regarding damping factor increase in inverting mode........
Sincere Regards,
Kanwar
Nice to hear your views. By the way what are your thoughts regarding damping factor increase in inverting mode........
Sincere Regards,
Kanwar
Hi Kanwar,
I can see no valid reason for an increase in damping factor in inverting mode in an amplifier with normal gain. Your ears maybe playing tricks with you. If you sense a difference with no reason you need some (pairs of is best) golden ears and double blind.
Greg
I can see no valid reason for an increase in damping factor in inverting mode in an amplifier with normal gain. Your ears maybe playing tricks with you. If you sense a difference with no reason you need some (pairs of is best) golden ears and double blind.
Greg
something a mentor must know
Hi Mr.Greg,
We have demonstrated this effect infront of one of our friend who is a well known audio specialist in field of measurement of audio specifications, and he too measured the increase in damping. My ears are absolutely fine.
If you donot have an answer with you, that doesnot mean that other people would have defect in their ears..........
The answer lies itself in the inverting mode..... the feedback error correction directly effects the signal which is at the base of transistor along with the signal from the source. The delay is reduced and all you get is speed up response which effects the control of damping..... While in non-inverting mode the signal from source entering one transistor and the feedback is entering another, thereby providing a delay to let the control begin, but in inverting mode the signal and the feedback enters simuntaneously at the base and there is less delay hence better conrol and speed of error correction................
regards,
Kanwar
Hi Mr.Greg,
We have demonstrated this effect infront of one of our friend who is a well known audio specialist in field of measurement of audio specifications, and he too measured the increase in damping. My ears are absolutely fine.
If you donot have an answer with you, that doesnot mean that other people would have defect in their ears..........
The answer lies itself in the inverting mode..... the feedback error correction directly effects the signal which is at the base of transistor along with the signal from the source. The delay is reduced and all you get is speed up response which effects the control of damping..... While in non-inverting mode the signal from source entering one transistor and the feedback is entering another, thereby providing a delay to let the control begin, but in inverting mode the signal and the feedback enters simuntaneously at the base and there is less delay hence better conrol and speed of error correction................
regards,
Kanwar
"The answer lies itself in the inverting mode..... the feedback error correction directly effects the signal which is at the base of transistor along with the signal from the source. The delay is reduced and all you get is speed up response which effects the control of damping..... While in non-inverting mode the signal from source entering one transistor and the feedback is entering another, thereby providing a delay to let the control begin, but in inverting mode the signal and the feedback enters simuntaneously at the base and there is less delay hence better conrol and speed of error correction................ "
Ohhh goodness me, Kanwar, where do you get this stuff! I think you need a new script writer.
Ohhh goodness me, Kanwar, where do you get this stuff! I think you need a new script writer.
mr kanwar stick to your pro design , hifi precision is beyond
your grasp, the time you are talking about is beyond the audio spectrum time and you are trying to catch it with pro audio
overkill, i would think that 250khz bandwidth would do wonders
in the inverting mode for you, you dont get me?maybe your details are overkill too
your grasp, the time you are talking about is beyond the audio spectrum time and you are trying to catch it with pro audio
overkill, i would think that 250khz bandwidth would do wonders
in the inverting mode for you, you dont get me?maybe your details are overkill too
lumanauw said:
Maybe not in power amps, but surely in preamps like all Tom Evans
designs: Michell Iso and Argo, TEAD Groove, Vibe, ...
often using cheap ICs like 5532s selected for channel matching.
Hi, Kanwar,
Damping factor is related to Zamp/Zload.
Usually Zamp is determined by the output stage. Like wheter you put EC or put massive parrareled transistor.
How inverting mode can lower Zamp?
Is it better phase that make better bass (not better damping factor?)
Damping factor is related to Zamp/Zload.
Usually Zamp is determined by the output stage. Like wheter you put EC or put massive parrareled transistor.
How inverting mode can lower Zamp?
Is it better phase that make better bass (not better damping factor?)
Hi lumanauw !
Typically you achieve high dampingfactor (low Zout) by large
amounts of feedback. Depending on how good feedback works,
you get different amounts of dampingfactor.
Another reason to have flat openloopbandwidth is to have "constant"
Zout over whole audioband...
Mike
Typically you achieve high dampingfactor (low Zout) by large
amounts of feedback. Depending on how good feedback works,
you get different amounts of dampingfactor.
Another reason to have flat openloopbandwidth is to have "constant"
Zout over whole audioband...
Mike
MikeB said:
Thanks Mike.... for clarifying bits of information to other guys .....
I think Mike has made a better point of what is known to effect the damping factor that is the feedback and i only stated about the Kind of Feedback ........ and its effect.....
Mastertech you were simply an precisionist overkiller ................, thats why it is OverKilling you.............
Mr. Greg ....... I think you are in dire need of a script writer than anyone else would ever need.......thats why your scripts are not mannerfull.....If you disagree on a certain point, then simply give valid points and show some reasonableness on this forum......
Hi Mike B,
"Another reason to have flat openloopbandwidth is to have "constant" Zout over whole audioband..."
I presume this statement is suggesting that a flat open loop response (i.e. 20KHz OLB) produces a constant amount of NFB and thus reduces Zout by a constant amount across the audio band - and that this is in some way desirable?
Why?
Take a chip driven amp with 10Hz OLB and 40 dB NFB at 10KHz, therefore 60dB NFB at 1KHz and 80dB NFB at 100Hz.
If the Zout is 100 at 10KHz closed loop and 1000 at 1KHz, and a largely unmeasurable and swamped by external factors 10,000 at 100Hz for damping your bass resonances. Would this be somehow less desirable than one that is a constant 100 across the band? As you can only apply so much feedback at HF. In reality that 8 ohm figure of 100 at 10Khz - is the equivalent of a 1u27H inductance . But the typical output inductor is considerably greater than this.
I'll take the 1000+ below 1KHz every time thanks.
And you Kanwar, would you be seeing that?
"Another reason to have flat openloopbandwidth is to have "constant" Zout over whole audioband..."
I presume this statement is suggesting that a flat open loop response (i.e. 20KHz OLB) produces a constant amount of NFB and thus reduces Zout by a constant amount across the audio band - and that this is in some way desirable?
Why?
Take a chip driven amp with 10Hz OLB and 40 dB NFB at 10KHz, therefore 60dB NFB at 1KHz and 80dB NFB at 100Hz.
If the Zout is 100 at 10KHz closed loop and 1000 at 1KHz, and a largely unmeasurable and swamped by external factors 10,000 at 100Hz for damping your bass resonances. Would this be somehow less desirable than one that is a constant 100 across the band? As you can only apply so much feedback at HF. In reality that 8 ohm figure of 100 at 10Khz - is the equivalent of a 1u27H inductance . But the typical output inductor is considerably greater than this.
I'll take the 1000+ below 1KHz every time thanks.
And you Kanwar, would you be seeing that?
Hi lumanauw !
Typically you achieve high dampingfactor (low Zout) by large
amounts of feedback. Depending on how good feedback works,
you get different amounts of dampingfactor.
---------------------------------------------
feedback is good for a whole lot more things mr mikeb
what are you telling to mr lumanauw that your "depending" is more
solid than his statement
Typically you achieve high dampingfactor (low Zout) by large
amounts of feedback. Depending on how good feedback works,
you get different amounts of dampingfactor.
---------------------------------------------
feedback is good for a whole lot more things mr mikeb
what are you telling to mr lumanauw that your "depending" is more
solid than his statement
I still dont get it. If in one amp, the RE and RC anywhere in any transistor involved is the same value, how come inverting and non-inverting has different gain factor or different feedback factor? If the OL and CL gain is the same, the feedback factor should be the same, shouldn't it?
Hi Amplifierguru,
Have you ever looked at the impedance characteristics of an amplifier when it does not have constant feedback.
Unless the NFB factor is level with frequency the open loop gain was not flat, and the output stage does not react phase linearly with regards to loudspeaker generated back EMF.
I would rather have less NFB and less damping, but a non-inductive output characteristic.
It takes all sorts to make a world !
Cheers .......... Graham.
Have you ever looked at the impedance characteristics of an amplifier when it does not have constant feedback.
Unless the NFB factor is level with frequency the open loop gain was not flat, and the output stage does not react phase linearly with regards to loudspeaker generated back EMF.
I would rather have less NFB and less damping, but a non-inductive output characteristic.
It takes all sorts to make a world !
Cheers .......... Graham.
Hi !
Lumanauw, you are right, feedbackfactor is OL / CL.
I see the advantage of invertingmode in not having commonmode
inside the LTP. In invertingmode the voltageswing of LTP-emitters
is only half the errorvoltage, in noninvertingmode it's nearly
identical to the inputvoltage. The ability of an amp to "ignore"
this effect is the CMRR.
But i prefer to use both outputs of the ltp, this eliminates most
of this commonmode-problem.
amplifierguru, yes i meant that flat OL-gain gives constant NFB
over the audioband, resulting in much more constant Zout.
The dampingfactor does not only have audible effects for bass,
this applies also to tweeters. An undamped speaker produces
more sonic around it's resonacefreq, and much less at it's lowest
impedance. To sad that it's nearly impossible to simulate that,
as speakers are mechanical parts.
I just made the experience that my amps constructed with more flat
openloopbandwidth have much less of the typical solidstate glare
or bright sound. I researched a lot to understand this, but was not
able to reproduce this effect in sims. This effect is not subtile,
i am speaking of several DBs change in trebles.
So, i am convinced that this effect is created in the speakers,
but i am not EE, only hobbyist, i might have told bullshid.
Mike
Lumanauw, you are right, feedbackfactor is OL / CL.
I see the advantage of invertingmode in not having commonmode
inside the LTP. In invertingmode the voltageswing of LTP-emitters
is only half the errorvoltage, in noninvertingmode it's nearly
identical to the inputvoltage. The ability of an amp to "ignore"
this effect is the CMRR.
But i prefer to use both outputs of the ltp, this eliminates most
of this commonmode-problem.
amplifierguru, yes i meant that flat OL-gain gives constant NFB
over the audioband, resulting in much more constant Zout.
The dampingfactor does not only have audible effects for bass,
this applies also to tweeters. An undamped speaker produces
more sonic around it's resonacefreq, and much less at it's lowest
impedance. To sad that it's nearly impossible to simulate that,
as speakers are mechanical parts.
I just made the experience that my amps constructed with more flat
openloopbandwidth have much less of the typical solidstate glare
or bright sound. I researched a lot to understand this, but was not
able to reproduce this effect in sims. This effect is not subtile,
i am speaking of several DBs change in trebles.
So, i am convinced that this effect is created in the speakers,
but i am not EE, only hobbyist, i might have told bullshid.
Mike
But just how much of this is contributed by the amp's output impedance? There could be many orders of magnitude difference between low and high frequency output impedance and yet it could still be totally swamped by the resistance of the wire etc.MikeB said:
It is possible to simulate it. The whole electromechanical system can be represented very accurately by a purely electrical equivalent circuit (or by a purely mechanical 'circuit', if you wanted). I do this sometimes when experimenting with unusual amps to see how they behave with real loads. With a little maths you can see what the resulting frequency response out of the speaker will be.MikeB said:
Flat open-loop response is certainly an alluring idea, but I'm not convinced that it is really necessary. I have never been able to discern any particular audible advantage to such designs.
- Status
- Not open for further replies.