L20 AMP。use only two NJW0302G - Page 2 - diyAudio
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Old 24th October 2011, 07:22 PM   #11
sajti is offline sajti  Hungary
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It's hybrid amplifier.

Sajti
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Old 25th October 2011, 03:46 AM   #12
ljm_ljm is offline ljm_ljm  China
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Quote:
Originally Posted by AndrewT View Post
the 107W is an average power prediction for driving an 8r0 resistor load.

This 107W cannot be used to determine whether the transistors will survive driving an 8ohm speaker when the devices start to warm up or worse get hot.

I will give you free starter:
A two pair output stage driving 200W into an 8r0 resistor, will get warm. Calculate what temperature the device cases (Tc) will be for your average power dissipation in each device.
From the Tc that you determined, calculate the Pmax that the devices can dissipate.
Is this average dissipation more or less than the DC (continuous) power rating for the device operating at that Tc?
Is this average more or less than the 100ms one shot power rating for the device operating at that Tc?
Is this average more or less than the 10ms one shot power rating for the device operating at that Tc?
Is this average more or less than the 1ms one shot power rating for the device operating at that Tc?
Is this average more or less than the 100us one shot power rating for the device operating at that Tc?
Now that you are into short term one shot transients, you must consider not the average dissipated power but the instantaneous peak dissipated power.
Next stage is to repeat those comparisons using resistor loading and instantaneous Pmax, to all those temperature de-rated SOA limits.
Finally, the difficult bit, you need to examine what effect changing from a resistive load to a reactive load does to the average P and instantaneous Pmax and use this information to make all those comparisons again.
Manually this is a lot of work.
David Eather shows a manual method for doing this.
Benson gives a spreadsheet to convert the manual method to computer assisted for mosFET output stage.
There are other computer assisted methods available to Members.
Start with Eather so that you can understand what it is that you need to know to make the assessment that you originally asked for.

Welcome your comments.



L20 can be installed transistors to 4。

OR 2 。

OUTPUT + -60V. 6.6 OHM

use a small aluminum。yes, it's very hot. I added a small fan. Not hot.
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Last edited by ljm_ljm; 25th October 2011 at 03:50 AM.
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Old 25th October 2011, 05:37 AM   #13
ljm_ljm is offline ljm_ljm  China
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note
: L20 Only blue PCB
Other counterfeit will use inferior components, pay attention to recognize
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Old 29th October 2011, 01:37 PM   #14
ljm_ljm is offline ljm_ljm  China
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SCH
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Old 14th August 2012, 10:24 PM   #15
xslavic is offline xslavic  Moldova
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So c1 should be 1uF and c2 2.5nF-3nF to make it work
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Old 15th August 2012, 08:21 AM   #16
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
R2 C2 form a low pass filter
C1 R4 form a high pass filter.
Your suggested values give a narrow passband.
Use the normal filter formula to find your roll off frequency.
F(-3dB) = 1 / 2 / Pi / R / C
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regards Andrew T.
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Old 16th August 2012, 03:32 PM   #17
sajti is offline sajti  Hungary
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Location: Vác, Hungary
The minimum configuration I have checked was 2 pairs of NJW0xxx, with +/-63V. It was OK, even with 4ohm resistive load, but the distortion was increased by 20dB with 4ohm load compared to 8ohm load.
And it needs very heavy protection, and sometimes shut down itself with 4ohm reactive load.

Sajti
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Old 27th December 2012, 05:54 PM   #18
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i use both L20 and L20SE.

power output in real life situations is the same.
i use 4 ohm transmissionline speakers.

on the picture you see the speaker protect kit "unactive". I have ordered a new power supply. the ones i bought did ........MELT!

Sound is great.

don forget to change the 10uf into ....silmic 2 or nichicom muze versions....upto what you like!!!
sounds less metallic and more natural. differences easy to hear with classical music..violin etc...

i use in my preamp 2x jantzen superior z-cap + PGA2310

Best regards,
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Old 27th December 2012, 06:20 PM   #19
jaycee is offline jaycee  United Kingdom
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As AndrewT says, if you want to use only one pair of output devices, the maximum voltage should be +/- 35V. Anything more will cause the transistors to fail when driving a 4 ohm load hard.
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Old 27th December 2012, 09:13 PM   #20
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Default pics L20

mine both L20 and L20SE are at 33VDC (24 volt + rectification).

i kept voltage quite low so with same power more ampere available to L20.
my toroids both deliver 24 ampere.
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