OPEN LOOP Bandwith and Slewrate are correlated, that's what i wrote. Please, read correctly and/or learn.
Open loop bandwidth is an envelop curve, witch shows the max gain an amp is able to provide for each frequency.
To understand how bandwidth depend both of the open loop bandwitch and gain factor of an amp, please, read:
Gain?bandwidth product - Wikipedia, the free encyclopedia
To understand what is slewrate, please read: Slew rate - Wikipedia, the free encyclopedia
TIM, (also called slewrate distortionis produced when the amp is not fast enough to follow the correction signal, please, learn or try to understand.
Please read some books and try not to confuse DIYers here with YOUR wrong assertions.
And, by the way, please, learn in the same time how to post in a non aggressive and disagreeable way, and not be ridiculous.
Sorry if you are offended, but what you write is just not correct. I suggest Bob Corddel book, not wikipedia.
Bandwith and Slewrate are NOT correlated.
TIM is not result of Negative Feed Back, but in most cases is result of not enough high Slawrate, by the way,for 100W amp 50V/usec is more then enough. What means the amp is not fast enough, low Slewrate??
Don't bee angry, but you are wrong.
dado
Well, let says that they are two different ways of looking at the same thing.
Please, somebody can explain Dadod the difference between Open Loop bandwidth and bandwidth ?
Here is a slew rate nomograph that shows how much slew rate is required.
I think Dadod knows what the difference between open loop bandwidth and bandwidth is.
I have participated in threads where we also discussed if it is more beneficial to raise the open loop bandwidth or go for massive gain in the bass. Unfortunately we did not find an agreement so i gave up.
I think Dadod knows what the difference between open loop bandwidth and bandwidth is.
I have participated in threads where we also discussed if it is more beneficial to raise the open loop bandwidth or go for massive gain in the bass. Unfortunately we did not find an agreement so i gave up.
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Joachim, i don't realy understand your monograph with *fixed values*. For several reasons.
One is TIM and IM continuously *reduce* as much you are reducing the slewrate of an amp.
On the amp i was comparing Voltage feedback with so called "cureent feedback", same schematic, i simulated (and measured) the followings, with the same closed loop gain:
Square waves (gives an idea of the slewrate): http://www.esperado.fr/images/stories/SSA-Crescendo/square2.gif
Harmonic distortion: http://www.esperado.fr/images/stories/SSA-Crescendo/distortion-curves.gif
IM: http://www.esperado.fr/images/stories/SSA-Crescendo/distortion-curves.gif
Bandwith: http://www.esperado.fr/images/stories/SSA-Crescendo/response2.gif
(Simulation is interesting while it lies only on calculations, so: theoretical.)
On my point of view (i hope it was the same you tried to defend) there is no doubt slew rate is the goal, as i said, not massive increase of the gain of an amp. My religion since decades. The reason to live of the SSA.
One is TIM and IM continuously *reduce* as much you are reducing the slewrate of an amp.
On the amp i was comparing Voltage feedback with so called "cureent feedback", same schematic, i simulated (and measured) the followings, with the same closed loop gain:
Square waves (gives an idea of the slewrate): http://www.esperado.fr/images/stories/SSA-Crescendo/square2.gif
Harmonic distortion: http://www.esperado.fr/images/stories/SSA-Crescendo/distortion-curves.gif
IM: http://www.esperado.fr/images/stories/SSA-Crescendo/distortion-curves.gif
Bandwith: http://www.esperado.fr/images/stories/SSA-Crescendo/response2.gif
(Simulation is interesting while it lies only on calculations, so: theoretical.)
On my point of view (i hope it was the same you tried to defend) there is no doubt slew rate is the goal, as i said, not massive increase of the gain of an amp. My religion since decades. The reason to live of the SSA.
I wrote OPEN LOOP Bandwith, you argue about Bandwith. Am-i not clear ?
Slew rate is just a method to evaluate the open loop bandwith of a closed loop amp. Done for that. To measure the slewrate, you need to over saturate the amp, for there is no influence of the gain factor. *Just the switching time*.
That's exactly what i said from the beginning: "Result of not fast enough Slewrate ... in a closed loop amp." (Consequence of delays, distortions and phase turn of the feedback signal due to slow response ).
In a ideal perfect amp with no feed back, and a limited slewrate and bandwidth, just high frequencies will be not reproduced. No IM generated.
To give an image, it is like in a car accident. Damage is caused with the speed in correlation with the slow response of the driver. More the speed is high (hf ), more you need fast (slewrate) reflexes ( feedback).
No, 50V/µs is not more than enough on my point of view. Distortion and phase response will be greatly better with faster slewrates. See pictures in my previous post.
Easy to understand: The signal across the amp. If the amp is not fast enough (slew rate) to follow-it you will have a great differences between the original signal and the signal at the output. When you apply feed back, those errors will feed the amp with higher level correction error signal, that the amp will not be able to follow again, worsening the situation.
End of this endless controversial and useless discussion on this subject. Known from decades, and perfectly described by the authors you are referring too, among many others.
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Esperado, i have looked at your modification of the Crescendo and you got lower distortion
after the modification.
Concerning if i have a priority of CFB against VFB that is not easy to answer in an absolute way out of context. My power amp and my preamp use current feedback, my phono has a current conveyer input stage with 75usec transimpedance and an active second stage with VFB. So i have at least one stage of voltgae feedback in the chain and it sounds great.
The TSSA though that i build gives me the best sound so far i had in my system.
Is it the speed, is it the spartanic simplicity, is the the PSU and how i build it ?
I can not tell. What i can tell is that it sounds very clean although it has distortion in the 0.1% range at higher level. I knew already that my hearing is not particular sensitive to low order harmonic distortion since i participated in the Klippel test. I scored in the middle group at around 1% TH low order weighted. Since then i know that the hunt for ultra low distortion is fruitless, especially when the amp gets very complex and a lot of PN junctions are in the chain.
after the modification.
Concerning if i have a priority of CFB against VFB that is not easy to answer in an absolute way out of context. My power amp and my preamp use current feedback, my phono has a current conveyer input stage with 75usec transimpedance and an active second stage with VFB. So i have at least one stage of voltgae feedback in the chain and it sounds great.
The TSSA though that i build gives me the best sound so far i had in my system.
Is it the speed, is it the spartanic simplicity, is the the PSU and how i build it ?
I can not tell. What i can tell is that it sounds very clean although it has distortion in the 0.1% range at higher level. I knew already that my hearing is not particular sensitive to low order harmonic distortion since i participated in the Klippel test. I scored in the middle group at around 1% TH low order weighted. Since then i know that the hunt for ultra low distortion is fruitless, especially when the amp gets very complex and a lot of PN junctions are in the chain.
The nomograph is from the Elliot sound pages and he is very concervative in terms of required slew rate. There are more examples when you google the article. He comes to the conclusion that a 10W amp needs only 2V per usec
to swing the highest audible tones.
I have some other ideas about speed. One of my teachers was Joseph Manger and the Manger driver resolves better when it is driven by a fast chain. It has to be a stable chain though. Incredible extention with oszillation is not good ether although such a chain can sound very exiting in terms of detailing. It is just too much and ultimatively tiring.
to swing the highest audible tones.
I have some other ideas about speed. One of my teachers was Joseph Manger and the Manger driver resolves better when it is driven by a fast chain. It has to be a stable chain though. Incredible extention with oszillation is not good ether although such a chain can sound very exiting in terms of detailing. It is just too much and ultimatively tiring.
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In the early 70th, (1971) i was working as one of the two engineers in the research and development office of the most important French hifi manufacturer. We where so aware of those slewrate questions that we where the first to use Planar power transistors (new at this time on the market) for their higher speed.
And guess what ? Our amp was ... current feedback with no compensation cap in the feedback line.!!!
A French guy has recently made a restoration of this amp:
https://plus.google.com/photos/109296933751482509949/albums/5624648973530419217?banner=pwa
Measured performance by this guy:
2X50W RMS in 8 Ohms. (200w peak)
0.05% THD,
flat at 20 000 hz.
Rare at this time, specialty for a consumer level equipment low medium priced with a SSS (so simple schematic).
You will notice the protection circuit and the volume made of a 24 pos switch (resistances array), making a constant source impedance without the noise of a potentiometer.
And the "physiological filter" following at each volume position the evolution of the Fletcher and Musdon curves.
You will notice the star design of the hp tracks on the board, feedback strait from the HP output point, which had generated many remarks and questions from concurrent engineers at this time (why those two parallel tracks coming from the same point ?), prove we where aware of what happens in a feedback loop and what is the impedance of a track with current ) .
This guy made praise about the sound of this amp, 40 years later !!!
May-be i'm not confusing things so much, result of my own experiments and experiences and not things collected in books?
So many hours measuring, experimenting, trying to discover and understand the phenomenas
May-be i'm simplifying too much my explanations, but, as we are not on a scientific forum, i try to make the things understandable to everybody, even non electronically experienced.
I would like to add, that, arguing again audiophiles (= in the desert) from so many years about the benefit of feedback and influence of slew rate, i was so delighted, reading Bob Cordell's articles years later, to see that it had reached exactly the same conclusions than us.
Reason why an Op Amp behave much better when used inverted.
And even overshoot on square waves
If you can design the inverting feedback input stage/ pole to do not introduce any delay or additional distortion, there will be no difference i presume
Reason why an Op Amp behave much better when used inverted.
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I am completely with you in this. I accept that SSA or modified Crescendo sounds exceptionally good, but techically very high Slewrate of SSA could not be reason for that.
VFB or CFB both type of the amps could sound equally good if designed correctly.
I have JLH 80W amp(modified by me as original had a hum and stability problems) and I like the sound very much, could be lateral fets reason for that? The distortion is higher then in my TT amp and still it sounds so good.
Regarding discution abouth if it is more beneficial to raise the open loop bandwidth or go for massive gain in the bass I do not have fixed oppinion abouth it. I have the amps of both type and I don't hear any differece. All I have read about it lids to non importance of wide open banwidth.
dado
I like the TSSA because the Lateral Fets are with the drains at the output. I think that way the amp is more stable into capacitive load and no VAS is needed. I see that as a modulated current source and Lateral Fets are very good constant current sources. The output impedance is then lowered with the current feedback. I have high sensitivity speakers and use the TSSA only over 80 Hz so i do not need high damping factor. I tried it wideband too with a big transmission line speaker and got great bass. i laready reported about the "massaging effect". A transmission line of cause does also not need a high damping factor because it has a quite flat impedance curve in the bass, at last in a damped line of correct proportions. Not that my dynamic speakers have much capacitance.
I even terminate the speakers with a Zobel that has the same characteristic impedance at HF as my cables to prevent HF ingress. It works particular well with low inductance, high capacitance cables.
Maybe there is more to that interface distortion problem then we think. Non of the commercial companies i know publish measurement of the whole chain, amp-wire-speaker, but that is what we hear.
I even terminate the speakers with a Zobel that has the same characteristic impedance at HF as my cables to prevent HF ingress. It works particular well with low inductance, high capacitance cables.
Maybe there is more to that interface distortion problem then we think. Non of the commercial companies i know publish measurement of the whole chain, amp-wire-speaker, but that is what we hear.
JLH 80W MOSFET amp has 0.22 ohm at the output so there is no high damping factor and still I like bass produced by it. I have closed box loudspeaker with not so efficient bass driver(Scanspeak 18W/8545-00) and the bas is so good. I was thiking to add 0.22 ohm resistor to my TT amp(very high DF) as aditional louspeaker output and in this case I can choose low or high damping.
dado
Never accept, never suppose. Experiment by yourself. ;-)
It is very easy to build a VFB feedback version of the symmetrical SSA (tuning feedback cap compensation on the VFB) and to compare both sound and performance.
About my Crescendo, just the feedback differ.
So you can conclude sound difference is mainly due to the slewrate difference.
Plus, but in a minor way, the suppression of the harmonic distortions generated in the inverting input carrying feedback signal in the VFB version.
Meaning that amp? I got one still going strong. Using it for when everything else is under planning or cruel operations.
Built on 80's L bracket modded PCBs that skip the 0.22R and speaker line fuse originals. I should add it and see what happens at a point I guess. Will reserve it for when the devil will find work for idle hands to do, and that is very British being a Morrissey lyric too.
