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Old 17th December 2009, 03:08 PM   #6401
jackies is offline jackies  United States
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Quote:
Originally Posted by Nelson Pass View Post
You can simply parallel output devices and it will work fine, but...
Thank you, Mr Pass for your kindness and participation!
I read this entire thread back and forth a couple times, it doesn't seem like anybody built an F5 with paralleled outputs. I have a working F5 over here and was thinking to double up the outputs and up the bias so it would have full 4 ohm driving capacity. Incidentally, I just ordered a full complement of Toshiba mosfets from the Dunhill loving person here. So I intend to try 2xToshibas instead of original 1xFairchild. Any tips/suggestions?
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Old 17th December 2009, 03:44 PM   #6402
Snokker is offline Snokker  Netherlands
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Quote:
Originally Posted by kp93300 View Post
Hi Snokker,
I checked that R11 is indeed broken measuring about 70 R now.
Do you mean I have to change Q1 to Q4?
Sorry, I have very little electrical knowledge.
Thanks

kp93300
OK, now you know R11 is broken Q3 and probably Q4 are gone also...
I assume both voltages +/- 24V are still present?
If the cause was shorting R12 I would advise to test Q1 and Q2 (like you have matched them)
And check R1,2 and R5,6,7,8 (especially if you did not overdimension them)
If you have a tone generator and scoop you can remove Q3 and Q4 and measure on the "open" gates dc and ac level. (maybe disconnect the emitter of Q5 and Q6 during measurement)
Good luck, and remember, this way you really learn how this fine amp works
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Old 17th December 2009, 07:59 PM   #6403
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Finally, i have reset the offset of my tweeter's F5.( after monthes working)
I obtain about 15mv when cold (both channels)
Stabilising to o mv / 2mv after a few minutes.
Stable after one hour or so.
Thermistors are in touch with mosfets cases + white goo.
No need to insert a cap in the outputs (but to prevent from an accident).
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Old 17th December 2009, 08:02 PM   #6404
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Quote:
Originally Posted by jackies View Post
I read this entire thread back and forth a couple times, it doesn't seem like anybody built an F5 with paralleled outputs.
I did this some time ago with 3 pairs of paralleled output devices (irfp240/9240), and it runs absolutely fine.
I am sure several other people have also done it.
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Old 17th December 2009, 08:13 PM   #6405
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Quote:
Originally Posted by bobodioulasso View Post
Finally, i have reset the offset of my tweeter's F5.( after monthes working)
I obtain about 15mv when cold (both channels)
Stabilising to o mv / 2mv after a few minutes.
Stable after one hour or so.
Thermistors are in touch with mosfets cases + white goo.
No need to insert a cap in the outputs (but to prevent from an accident).
I assume you also are using active crossovers, if not then you already have a capacitor in the tweeter's crossover which will block dc.
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Old 17th December 2009, 08:20 PM   #6406
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Quote:
Originally Posted by thanh1973 View Post
I assume you also are using active crossovers, if not then you already have a capacitor in the tweeter's crossover which will block dc.
Yes, active crossover. Tweeters are dc coupled.

Last edited by bobodioulasso; 17th December 2009 at 08:36 PM.
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Old 17th December 2009, 08:24 PM   #6407
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i will soon be able to try double pairs 2sj201 2sk1530.
Thanks to Luvdunhill.
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Old 17th December 2009, 09:17 PM   #6408
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Judging by the curves on those parts, when paralleling them
you can raise the Source resistor to 1 ohm and get greater
thermal stability yet.

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Old 17th December 2009, 09:20 PM   #6409
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And you talked about the harmonics distortion differences between parallelled and normal class a circuit Mr Pass.Which distortion is good for ears ?not disturbing one ?
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Old 17th December 2009, 09:27 PM   #6410
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Thanks for the trick, Nelson. I will do this.
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