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Old 17th June 2005, 10:15 AM   #51
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hiiiiiiii simon ..
how r u man ? ...
yup the f****** cab was built but the sound ...........
i just do anythin in that ( corssovers , bracin , sepratin the sections ... ) but the problem s sony subs ...
i ll explain the problem in my subwoofer thread ...
c u there guys ....
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Old 17th June 2005, 10:23 AM   #52
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any hi-fi preamp ? without a tone control just a volume control ...
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Old 28th June 2005, 05:12 AM   #53
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Quote:
Originally posted by Nelson Pass


IRF250's will probably work as well or better, and I observe that
for every design there is an optimum number of paralleled
devices, and often the number is greater than 1.

Hi Nelson,

I have been researching and doing calculations to compare "net" Ciss to compare number of parallel output pair devices choices vs using a single output pair device. There is one school of thinking that for mid range or tweeter amplifiers that the ideal device configuration is to use just a single pair of output devices. So far the opinion for woofer amplifiers is parallel pairs of output devices is best. I seem to recall, but my memory is not certain, reading online somewhere that parallel devices are better for woofers vis a vie damping factor. I do not recall where online I read this. I have been doing extensive reading and research which seems to differ to your very respectable knowledge and experience. I suspect from my questions to follow that you will enlighten me about why my research above has been >95% of the opinions.

My questions would be as follows when considering LF range <= 150-200Hz, MF 150-200Hz to 2-3KHz, and HF >= 2-3KHz :

1) What differences in are there in MF and HF using single VS parallel devices?

2) Is damping factor affected by number of parallel devices? If so, generally the general trend of difference.

3) Is it fair to assume that output device having a single output device Ciss of 2600pf is the same as using two output devices having a Ciss of 1300pf assuming perfectly match devices and identical devices in all other respects? I know such identical devices do not exist, I just set the context to limit the scope of the question.

4) Generally what aspects of the amplifier design that affects if a single device or the ideal number of parallel devices should be used? Is the answer generally speaking different based on amplifier class, i.e. A, or AB.

5) Generally from experience how does one determine the ideal number of devices for a given design?

6) Does the bias level chosen or designed affect any of the above questions answers?

I am not design savvy, but I can handle a little bit of technical amplifier design detail. I can handle math most of time even if I do not understand the theory of how the math models things. I am assuming the nature of my questions will only make use of basic math and application theory.


Regards,

John L. Males
Willowdale, Ontario
Canada
28 June 2005 00:12
28 June 2005 00:16 Correct typo errors.
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Old 28th June 2005, 05:37 AM   #54
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Default Re: Relevance ?

Quote:
Originally posted by quasi
With a well designed and low impedance output driver stage the effects of gate capacitance can be minimised to a negligible (non-audible) level. A low impedance drive will swamp out any variations in capacitance.

Visually this can be observed with a 10Khz full rail swinging square wave where with a well designed driver stage the effects observed are quite small. (IMO).

Cheers
Quasi,

A few questions:

1) Is there an easy way to determine looking at a design if it has a low impedance output driver stage?

2) Visually on the scope with 10KHz square wave what will one see to indicate a well vs marginal or poor driver stage design?

3) Does one scope at the output of the driver stage or driver stage output to observe the 10KHz square wave test signal?

4) Can using a square wave test signal >10KHz to < 25KHz demonstrate a well vs marginal/poor driver stage design any better or seperate well design ed driver stages subtle differences more?

5) Can you expand what you mean by "swamp" in you comment of "... will swamp out any variations in capacitance."?


Regards,

John L. Males
Willowdale, Ontario
Canada
28 June 2005 00:37
28 June 2005 00:43 Corrected typo errors
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Old 28th June 2005, 08:25 AM   #55
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keypunch,

Paralleling device is not really anything much to do with your first round of points, it simply comes down to the power handling of the devices and how much power you need to dissipate. Damping factor may be slightly lower with more devices.

Regarding the second round of questions, the impedance of the driver stage can be given a knowledgeable eye and a rough guess as to ballpark high/low impedance can be judged. This is based on transistor configuration (emitter/collector driving), standing current and to some extent the resistor values.

Looking on a scope poor results could come from any one of the stages in an amp and really you need to scope at several points (LTP, VAS, drivers and output) to see where the problem lies.

Going up in frequency of square wave may start to bring in effects due to amplifier bandwidth more. These could be a little misleading as the harmonic content of square waves is very high, so for it to be replayed properly you need orders of magnitude more bandwidth than the square wave fundamental.

To swamp something out means that e.g. the resistor applied close to the gate of a MOSFET swamps out or dominates over the track inductance thereby rendering it not a problem.
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Old 30th June 2005, 03:25 AM   #56
quasi is offline quasi  Australia
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Yep ...what richie00boy said.

The easiest drive impedance indicator (indicator only) is to look at the value of the gate to rail / gate to line resistor.

If the FET requires 4 volts to turn and 6 volts for maximum load current and the resistor is 100 ohms then 40mA to 60mA will run through the driver stage. This gives you an indicator of the drive capability.

Of course if the gate to rail resistor is 10 ohms then 400mA will flow.....but things (driver transistors) then start to get very hot.

Cheers
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Old 1st July 2005, 02:22 PM   #57
jmateus is offline jmateus  United States
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Default What Mosfets to use?

I have a question related to Mosfets.
A few years ago I bought 5 pairs of TO3 Mosfets, 2SJ50/2SK135 which
I haven't used. At the time they cost me $4.00 each as opposed to $15
they cost now.
I'm planning to build an amplifier that uses 2SJ162/2SK1058, about
150W per channel.
Are both devices compatible so I can use the 50/135 instead of these
new ones?
As far as I know they both lateral Mosfets, but I'm not sure, perhaps
you guys could enlight me.
I'd appreciate.
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Old 1st July 2005, 04:01 PM   #58
mlloyd1 is offline mlloyd1  United States
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Default Re: What Mosfets to use?

go ahead and have at it. they'll work just fine!

same die, so same specs, etc...

mlloyd1
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