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Old 15th February 2013, 10:14 AM   #2181
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by wahab View Post
Hitachi s laterals are extremely rugged components that could
stand extreme abuses that would be lethal for BJTs with supposedely
higher power ratings.

........ a pair of 100W TDP devices is enough for 70W RMS output....

if using single pair lateral output for balanced amp..... are you saying they could also be the obvious choice for the tougher low impedance load on a balanced amp ?
meaning it would be relatively easy and simple to make a quite strong 100watt(balanced)
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Old 15th February 2013, 01:40 PM   #2182
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Quote:
Originally Posted by wahab View Post
From this extensive real world and long term testing i came to the conclusion that those devices can handle a power output that is 70% of their TDP ratings, a pair of 100W TDP devices is enough for 70W RMS output
Or from another angle :

70W/8 continuous power comes to about 100W/4 continuous.
Peak output in 4 Ohm is then 200W.
Picking 200W total Pd for the output stage enables it to handle full output in 8 and 4 Ohm.
Instantaneous output will never exceed the total Pd number, and the output stage can handle bursts in lower impedance loads.
(do not last long, and as such do not heavily load the output stage in a thermal sense)

Pd of an output device does not directly correpond to output power, but to dissipation. (wouldn't make much sense to place a d after the P otherwise )
But as an approximation, Max dissipation level is taken at half output power level : half the rail voltage is across the output device, half Vrail across the load.
But what did I mention about average/continuous Die temperature : at 50% between 25C ambient and 150C kill zone.
At 87.5C Die temperature, see the datasheet Pd/Tc gaph, allowable dissipation is 50% : a 100W device reduces to a 50W one.

So 200W datasheet Pd in devices reduce to a 100W dissipation capable output stage.
Tada : Max dissipation of an output stage that is capable of handling a continuous 4 Ohm load !

So an easy&quick way to thumb-rule check whether a 4 ohm capable Lateral Mosfet class AB output stage is properly dimensioned :
Just total the nominal Pd number, divide it by three, and compare that to the continuous output power figure in 8 ohm.

Examples ;
250W/8 Mimesis 9 : 6x125W=750W. Divided by 3 makes 250W. OK !
140W/8 Crescendo Elektor : 4x100W=400W. Divided by 3 makes 133.3W OK!

350W/8 Mimesis with 3-pair J56/K176 : Not OK.
Don't need no stinkin calculator.
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Last edited by jacco vermeulen; 15th February 2013 at 01:47 PM.
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Old 15th February 2013, 02:57 PM   #2183
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Quote:
Originally Posted by TANDBERGEREN View Post
Eight powertransformers supply all the "gadgets" and softstart and so on in this one.
1000VA X 2 transformers for the output transistors and probably a total of 16000uF on each channel. Nice.
to get the best audio performance from this amplifier, you should use a separate transformer for each channel and power consumption as large as possible.The capacitor need a small amount, maximum 2 capacitor 10.000uF for a channel.

for example: 45V - 0 - 45V/10A for the left channel
45V - 0 - 45V/10A channel.

thanks
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Old 15th February 2013, 07:35 PM   #2184
wahab is offline wahab  Algeria
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Quote:
Originally Posted by tinitus View Post
if using single pair lateral output for balanced amp..... are you saying they could also be the obvious choice for the tougher low impedance load on a balanced amp ?
meaning it would be relatively easy and simple to make a quite strong 100watt(balanced)
I didnt understand well your question , to give an exemple
the original Hitachi commercial amp circa 1978 used a single
T03 100W TDP output pair for about 75W RMS/4R and the amp
was measured by an audio magazine as 112W RMS/4R , wich
is in the hedge of the devices max current and well above
what is exctractible from a single BJTs pair.

Quote:
Originally Posted by catalin View Post
Hello Wahab,you can say from simulations if an amp performs low in therms of sound ?
Can the simulations assure us that an amp has great sound ?

As I understand the thd&imd for goldmund are decent to good ~0.01 .
But may be the thd are not a factor important to say that an amp has good sound .
So what parameters do you simulate ?
I did some sims of the GM as a comparison with Gaborbela s
project that use a similar topology although a little more complexe,
there s some significant simmed tests in the last pages.

Simulations are reliable enough but final results depend
on components choice and physical implementation.

Quote:
Originally Posted by jacco vermeulen View Post
Or from another angle :

70W/8 continuous power comes to about 100W/4 continuous.
Jacco , i agree with all your calculations set apart that i was talking
of 70W whatever the load....
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Old 15th February 2013, 11:10 PM   #2185
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Mr Wahab,

you know very well that they're not "calculations", but again a (very crude) simplification.

A complete description would include more parameters, some general, others that apply to a specific layout.
But all those just distract from the point at hand : that it's both extensive experience from many years of practice and can be evidenced on paper.

Source resistors at the Mosfet outputs would take a small part of the output stage dissipation.
Not using separate rails with higher voltage for the drivers would imply that the output can be driven less closer to the rails, leading to a higher relative dissipation of the power devices.
Phase shift between output current and voltage makes the calculation even more complex.
Then there's charging ripple on the rails, which' influence works in two directions.

(I'm an attacker if I copy a few lines. When I write a sentence, I'm a bad joker. When I post six pages, I'm bound to be carried out of this thread in tar & feathers. )
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Old 15th February 2013, 11:31 PM   #2186
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Quote:
Originally Posted by jacco vermeulen View Post
in tar & feathers.
and rubber, don't forget the rubber.
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Old 16th February 2013, 12:38 AM   #2187
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Quote:
Originally Posted by quanghao View Post
to get the best audio performance from this amplifier, you should use a separate transformer for each channel and power consumption as large as possible.The capacitor need a small amount, maximum 2 capacitor 10.000uF for a channel.

for example: 45V - 0 - 45V/10A for the left channel
45V - 0 - 45V/10A channel.

thanks
There will be Separate transformers for each channel.
Today there is one 625VA for each, wich is too small.
I have two ways to alter this.
Either buy two 1000VA (will give me 9A for each channel, Or just add two more 625VA, wich will add up to about 11A for each channel.

If I choose the 1000VA transformers, I will have to buy a pair of transformers wich is around 25% more costly than two extra 625VA transformers.
The 625VA transformers will then be in house, but the 1000VA transformers will still be in Poland. Freight from Poland for theese transformers probable would buy me yet another extra pair of 625VA.

My choise: Another pair 625VA transformers. And about 11A available.

The capasitor bank is determined.
Original idea was a pair of 10000uF onboard the amplifiers, in addition a pair og 1000uF + 2X20pcs 470uF. Still for each channel. A total of 60000uF each channel. There was to be extra filtration, either via inductor, or via a form of PTC-reactive element. (Bulbe)
The 470uF is dropped out of the planning, but the first 10000uF is replaced by 2X22000. Theese will be closer to the rectifier.
Va some resitive or inductive devices the rails will be fed to the amplifier boards, where the onboard 2X10000uF sits, and provide the peak pulse capability.
This arrangement I have used for tears and years on PA Amplifiers (Up to 500W/channel) with good results.

Until anyone can convince me this is a bad idea, I will build it this way. But pleaswe come forward i anyone have some well funded reasons I should not.
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Old 16th February 2013, 12:48 AM   #2188
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Quote:
Originally Posted by jacco vermeulen View Post
There's not much sense in comparing the MM9/9.2 with the MM29.
(and I have no idea what's inside the Mimesis 29M )

The Mimesis 29 uses TO3P devices in the output stage, 6 pairs of J162/K1058.
(Mimesis 28 has 4 pairs per channel of those)

For those who missed the very unusual way the heatsink is attached to the case of the Mimesis power amp (MM29 in this example)=>
Agree.

GM9.2 is thew reference here.

For those of You who realy know: Is the output transistors on the 9.2 isolated from the heatsink, or have the just made this arrangement for attaching the heatsink to make it possible to mount the transistors directly to the heatsink, no mica between?

I have used such configuration to several PA-amps where the heatsink has been totally covered by the cabinet, no danger of having it shortcirquited to anyting on the outside, neither any danger for being in touch with potensially dangerous voltages on outside areas.

Would further improve the C/W, wich can be a good thing.
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Old 16th February 2013, 12:50 AM   #2189
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Originally Posted by jacco vermeulen View Post
When I post six pages, I'm bound to be carried out of this thread in tar & feathers. )
Some of us would the clean You up, and gently throw You in again.
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Old 16th February 2013, 09:39 AM   #2190
wahab is offline wahab  Algeria
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Quote:
Originally Posted by jacco vermeulen View Post

A complete description would include more parameters, some general, others that apply to a specific layout.
But all those just distract from the point at hand : that it's both extensive experience from many years of practice and can be evidenced on paper.

Source resistors at the Mosfet outputs would take a small part of the output stage dissipation.
Not using separate rails with higher voltage for the drivers would imply that the output can be driven less closer to the rails, leading to a higher relative dissipation of the power devices.
Phase shift between output current and voltage makes the calculation even more complex.
Then there's charging ripple on the rails, which' influence works in two directions.
Undoubtly you are right but solving constrained equations , although
not difficult , is quite boring on a DIY perspective , best is to oversize
the things reasonably and it will spare yourself quite some maths hassle
and unreliability issues , after all only commercials designs are "optimized"
to save costs as much as possible , squeezing the last (perhaps) available cent..

Quote:
Originally Posted by TANDBERGEREN View Post
There will be Separate transformers for each channel.
Today there is one 625VA for each, wich is too small.
I have two ways to alter this.
Either buy two 1000VA (will give me 9A for each channel, Or just add two more 625VA, wich will add up to about 11A for each channel.

Until anyone can convince me this is a bad idea, I will build it this way. But pleaswe come forward i anyone have some well funded reasons I should not.
Unless you need a PA amplifier an option is to stick with what you
have at hand , 625VA/channel is good enough for 450W RMS/channel
on a permanent output power , 500W RMS/channel can be reached
by a musical program without being as power consuming seen from
the power supply.
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