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Old 21st March 2012, 07:07 AM   #3891
gk7 is offline gk7
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And ?
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Old 21st March 2012, 07:10 AM   #3892
gk7 is offline gk7
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According to Thiele and Small your DF=2 amplifier would result in a +4.5dB bass boost
on my speaker. Are Thiele and Small wrong ? Should we rename TSP to TLP (Thorsten Loesch parameters) ?
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Old 21st March 2012, 07:31 AM   #3893
a.wayne is offline a.wayne  United States
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TLP ....

T , I like it , you should accept ...............................
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Old 21st March 2012, 07:45 AM   #3894
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by gk7 View Post
According to Thiele and Small your DF=2 amplifier would result in a +4.5dB bass boost
on my speaker. Are Thiele and Small wrong ? Should we rename TSP to TLP (Thorsten Loesch parameters) ?
TSP's explicitly include the electrical damping limit as the factor Re. Set that to zero if you want to remove the limitations on damping it causes. I'm not sure if room temp supraconductors are now available as industrial wire, if they are you can wind your voicecoils with to experience a damping factor that is equal to that calculated for amplifiers.

My original point was that THD, (T)IMD, DF and co are advertising numbers, not technical engineering specifications.

THD and IMD as emotionally loaded advertising spec (who would want greater total distortion) would relate to a single and two tone FFT with the individual harmonics extracted and weighted to give us an indication of audibility as emotionally neutral engineering specification. Instead THD and IMD suggest a relation to audibility that does not exist.

Equally, Damping Factor is the emotionally loaded advertising term (who would not want better "damping"), while Output impedance with Frequency and signal level would be the emotionally neutral engineering specification. Instead "Damping Factor" suggests a relation of this to the damping of the Driver which as such does not exist.

I do take exception if people bandy uncritically advertising spec's that have no relation to real quality and proclaim designs either superior or inferior on the strength or weakness of these advertising numbers.

That is not rational, or scientific, that is just the cult of low THD and high DF...

Ciao T
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Old 21st March 2012, 09:59 AM   #3895
wahab is offline wahab  Algeria
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Quote:
Originally Posted by ThorstenL View Post
Hi,



Alas I posted earlier on an Amplifier schematic that would probably fit "low NFB" (only 14dB NFB looped around the output stage). This Amplifier is expected to have around 0.15 Ohm open loop output impedance with 0.03 Ohm closed loop output Impedance.

I will probably fit an additional circuit to synthetically increase the output impedance to 3 Ohm, which is the target source impedance for all of my personal speakers, as otherwise this solid state Amplifier would be put too much at a disadvantage regarding sound quality.

Ciao T
I find this schematic quite complexe but i suppose that i m inclined
toward simplicity , albeit not simplisticisms...

As presented it need some reworks to be a practical and reproducible
design.
Attached Images
File Type: gif THORSTEN CL GP.gif (24.3 KB, 98 views)
File Type: gif THORSTEN OUTPUT Z.gif (27.3 KB, 96 views)
File Type: gif THORSTEN PSRR.gif (28.9 KB, 96 views)
File Type: gif THORSTEN SR1.gif (21.0 KB, 97 views)
File Type: gif THORSTEN SR2.gif (19.7 KB, 87 views)
File Type: gif THORSTEN SR3.gif (16.6 KB, 24 views)
File Type: gif THORSTEN THD1-graph.gif (38.8 KB, 28 views)
File Type: gif THORSTEN THD10-graph.gif (38.6 KB, 31 views)
File Type: gif THORSTEN IMD 047.gif (38.8 KB, 27 views)
File Type: gif THORSTEN IMD1920.gif (32.5 KB, 22 views)
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Old 21st March 2012, 10:32 AM   #3896
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by wahab View Post
I find this schematic quite complexe but i suppose that i m inclined toward simplicity , albeit not simplisticisms...
The schematic ACTUALLY is quite simple. There are some aparent complications from certain design techniques.

Quote:
Originally Posted by wahab View Post
As presented it need some reworks to be a practical and reproducible design.
As I noted, compensation has not been fully worked out and may need changes. Also the feedback circuit is not completely fixed. Depeding on results I may completely remove NFB or increase it.

I am not sure precisely what you are simulating and what Iq 152mA X 2 is meant to mean?

Each Output BJT requires nominal 120mA Iq, the precise amount will depend on testing the completed design. It also seems the compensation may need a few lead compensation Cap's and maybe a few pF miller, this will have to be worked out.

Also, I have realised later that one capacitor better had one connection shifted. The one bridging the 56K resistor in the input current mirrors collector needs to be shifted to connect the two gates of the J-Fet VAS buffer... Not sure it will make a difference in the simulator though.

Ciao T
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Old 21st March 2012, 11:13 AM   #3897
dvv is offline dvv  Serbia
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On the subject of simple vs complicated, I'd say that's a VERY relative, as Thorsten beat me to the punch.

As I see it, there are two basic layers to every device - the essential audio circuitry and the auxilliary circuitry.

For example, overvoltage/overcurrent protection circuitry in my case will add 18 components, which are, under normal operating conditions, 100% wasted, as they actually do nothing. You can remove them and nothing will happen. They are there "just in case" some dummy short circuits the outputs, or has a brilliant idea of connecting two sets of 4 Ohm speakers which go way below 4 Ohms and then tries for full power.

As I see it, they are still a must - just in case. Their cost in comparison with possible damage is totally insignificant, but I have seen many burnt out amps with their "protection" fuses intact. Nothing is as fast as a transistor.

Or the DC servo circuit. It also adds 14-16 components, but has a crucial role to play - in comparison with AC coupled units, one with a DC servo will look more complex, given that it can be replaced by just two capacitors. However, when you factor in the additional circuitry needed to null the DC offset, things begin to change, as at least three, and typically more like 6 or 7 additional components get into the picture.

Lastly, there's the DC and thermal protection circuits. For reasons of sheer lunacy, much of the DIY community feels they somehow impair sound quality and choose to leave them out. I see this as a downright stupid move, that's sticking your head in the sand and hoping for the best. Some choose to show it, some set it aparat; I show it because my concept is that of a power amp module, i.e. everything right there, so you can parallel amps to whatever number takes your fancy. But that's my choice, it has its pros and cons, just like every other choice.

The point is, if one is careful and chooses to have it all, the resulting schematic will appear to be very complex, because all these auxilliary circuits will add around 50% more parts over the actual audio circuits.

If you feel that say 4 22uF caps are better than one 100uF cap, before you know it, your schematic starts becoming complex.

I would rate Thorsten's schematic, bearing in mind it's just a preliminary one (with much of, as he put it "housekeeping", NOT included), as complex as it needs to be for the required results. About middle of the road.

If anything, I'd ask him to add another pair of output transistors, not because he really REALLY needs it, but again, to be on the safe side. Those devices lose 1.43 Watts of power per every degree centigrade over 25 deg, ambient, meaning that if somebody start to misuse it, it will get hot rather fast and its effective power dissipation will be reduced quite significantly, to less that 100 W per device - that's assuming he has mighty heat sinks, and he's going to need them if he takes up his upper limit of biasing. Anyway, his amp is his business, but I sure would include a fourth pair, and I use mighty heatsinks (probably the same as Thorsten's, mine are Fisher of Germany too).

If you think I am simplifying things, just let me know and I'll post some REALLY complex schematics of otherwise well known and well regarded products, which I guarantee will change your concept of the word "complex".

Last edited by dvv; 21st March 2012 at 11:25 AM.
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Old 21st March 2012, 11:23 AM   #3898
wahab is offline wahab  Algeria
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Quote:
Originally Posted by ThorstenL View Post
Hi,



The schematic ACTUALLY is quite simple. There are some aparent complications from certain design techniques.



As I noted, compensation has not been fully worked out and may need changes. Also the feedback circuit is not completely fixed. Depeding on results I may completely remove NFB or increase it.

I am not sure precisely what you are simulating and what Iq 152mA X 2 is meant to mean?

Each Output BJT requires nominal 120mA Iq, the precise amount will depend on testing the completed design. It also seems the compensation may need a few lead compensation Cap's and maybe a few pF miller, this will have to be worked out.

Also, I have realised later that one capacitor better had one connection shifted. The one bridging the 56K resistor in the input current mirrors collector needs to be shifted to connect the two gates of the J-Fet VAS buffer... Not sure it will make a difference in the simulator though.

Ciao T

Unfortunately , my free simulator has limited nodes number
so i simulated with two pairs of output devices , each pair
being biaised at 152mA for a total of 304mA quiescent current.

The load is increased to 12R to compensate a little for
the absent third pair , albeit at those high bias currents it makes
little difference in respect of the relatively low simulated output level.

A classical dominant pole compensation works better in this amp ,
about 22pF from the VAS collectors to their fets drivers gates,
while at the same time increasing the two 100K local loop FB resistors
to at least 1M.

Phase response will be correct , IMD 400/7K is significantly lower
wich is important since this measure is way more significant than
the overkill 19+20K tests.

The use of a full fet cascode is useless , the upper pair can be replaced
by bjts with no change in the perfs.

Also , the fet differential input pair must have no more than 8/12V Vgd
as generaly the drain/gate leaking current rise very sharply above those values.

Last edited by wahab; 21st March 2012 at 11:43 AM.
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Old 21st March 2012, 12:04 PM   #3899
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by wahab View Post
Unfortunately , my free simulator has limited nodes number so i simulated with two pairs of output devices , each pair
being biaised at 152mA for a total of 304mA quiescent current. The load is increased to 12R to compensate a little for the absent third pair , albeit at those high bias currents it makes little difference in respect of the relatively low simulated output level.
Ahh, okay, now it makes sense. Maybe even drop another pair and use 16R, if it helps to preserve the rest.

Quote:
Originally Posted by wahab View Post
A classical dominant pole compensation works better in this amp , about 22pF from the VAS collectors to their fets drivers gates,
while at the same time increasing the two 100K local loop FB resistors
to at least 1M.
Not going to happen. This creates the usual amp with the usual results. Not interested.

Quote:
Originally Posted by wahab View Post
Phase response will be correct , IMD 400/7K is significantly lower wich is important since this measure is way more significant than the overkill 19+20K tests.
I see around 0.05% IMD for 25W/8R equaivalent, or -8dB. I am not very perturbed. I know you want to see -90dB, but that is your goal, not mine.

Quote:
Originally Posted by wahab View Post
The use of a full fet cascode is useless , the upper pair can be replaced by bjts with no change in the perfs.
As the circuit uses essentially a Hawkesford cascode with a bootstrapped CCS feeding is, this is indeed so. However someone already put the Fet's there, so I'll keep them. ;-)

For anyone building from scratch BJT's are indeed fine.

Quote:
Originally Posted by wahab View Post
Also , the fet differential input pair must have no more than 8/12V Vgd as generaly the drain/gate leaking current rise very sharply above those values.
I don't have the curves for the 2SK246, however lowered drain current reduces the gate leakage.

Here the input Fet's are running at maybe 0.2mA (which means we will have around 2.2V reverse bias on the input diodes, which has it's own rewards) and I'm estimating maybe 5nA at the set 25V appx., so nothing to loose sleep.

Also, if your Sim program is free, would you mind sharing the Schematic/Models and a download link, so others can play too. This schematic could be a good exercise to illustrate the trade-offs in amplifier design, different compensation schemes, feedback schemes and levels and so on.

One could see how much difference cascoding the VAS makes for example. Who knows, we may even find two completely separate versions that offer different tradeoffs. I make my optimisations and you do yours.

Ciao T
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Old 21st March 2012, 12:06 PM   #3900
gk7 is offline gk7
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Quote:
Originally Posted by ThorstenL View Post
...
My original point was that THD, (T)IMD, DF and co are advertising numbers, not technical engineering specifications.
...
If you donīt like the term "DF" feel free to invent your own. But DF _is_ a well defined number and the impact on bass response can be calculated,
simulated, measured and is audible. What else do you want ?
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