How to drive 8 pairs of MJL21193/94? - Page 2 - diyAudio
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Old 17th March 2009, 09:03 AM   #11
fotios is offline fotios  Greece
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Quote:
Originally posted by sajti
I think to use 200mA bias, or higher
Do you mean 200mA Iqs per output device?!!
That is amazing if it is true! You will exceed the "extreme class AB" operation, for which - according to my experiments - a 50mA Iqs per output device it is enough.
I am wondering where you want to go. Near class A?
If yes, you have to use a ton of supply xformers and heatsinks!

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Old 17th March 2009, 09:08 AM   #12
sajti is offline sajti  Hungary
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Quote:
Originally posted by fotios


Do you mean 200mA Iqs per output device?!!
That is amazing if it is true! You will exceed the "extreme class AB" operation, for which - according to my experiments - a 50mA Iqs per output device it is enough.
I am wondering where you want to go. Near class A?
If yes, you have to use a ton of supply xformers and heatsinks!

Fotios
No. 200mA bias for the driver. For the output stage I planned to use some 100mA for each output device. I have 2 pcs of 350mm long heatsinks, with forced cooling, and 1500VA toroid transformer, for each channel.

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Old 17th March 2009, 09:15 AM   #13
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Quote:
Originally posted by sajti
I have lot of NJW0281/0302 (about 70pairs).
Smarter to use them both as drivers and as output devices if you have so many.
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Old 17th March 2009, 12:51 PM   #14
sajti is offline sajti  Hungary
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I put together the 1st version. Due the file is too wide here, you can see if follow the link

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Old 17th March 2009, 04:53 PM   #15
AndrewT is offline AndrewT  Scotland
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A pair of output devices with an Re of 0r1 requires 260mA for optimal ClassAB bias.
Reduces to 114mA with Re=0r22 and to 53mA with Re=0r47.

Multiple pairs need these bias currents per device.
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Old 17th March 2009, 05:17 PM   #16
sajti is offline sajti  Hungary
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Quote:
Originally posted by AndrewT
A pair of output devices with an Re of 0r1 requires 260mA for optimal ClassAB bias.
Reduces to 114mA with Re=0r22 and to 53mA with Re=0r47.

Multiple pairs need these bias currents per device.
This means:

308W dissipation with 0R1
140W dissipation with 0R22
65W dissipation with 0R47

but higher emitter resistance increase the takeover distortion.

But You find the reason why no values on the emitter resistors...

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Old 17th March 2009, 05:28 PM   #17
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by sajti
...but higher emitter resistance increase the takeover distortion....
What is the question?
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Old 17th March 2009, 05:30 PM   #18
sajti is offline sajti  Hungary
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Quote:
Originally posted by AndrewT
What is the question?
Nothing. I just wrote two different point of view...

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Old 17th March 2009, 05:45 PM   #19
AndrewT is offline AndrewT  Scotland
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AKSA will not agree with you.
He has adopted 0r47 for Re in many of his amp designs and retail offerings because he believes that value of Re is optimum for his style of amplifier.
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Old 17th March 2009, 06:24 PM   #20
sajti is offline sajti  Hungary
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But John Curl will agree. I have not that much experience. Another issue is the power loss on the emitter resistors, what I want to kepp as low as possible

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