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Old 15th February 2012, 06:53 AM   #81
JBL4435 is offline JBL4435  Germany
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Quote:
Originally Posted by UKToecutter View Post
JBL,
Please correct me if I'm wrong but I would have thought that as long as Q1 and Q2 are thermally coupled then that should be enough as the other pair are in parallel.
Not sure about this. Some experts may comment.

Quote:
Originally Posted by UKToecutter View Post
Can somebody explain to what the advantage of paralleling these devices is?
Will there not be an effect on the input impedance?
Andy
You need more driving current with 6, 8 or 10 output pairs. Some REAL experts may comment on this.
Nelson recommend it together with changes in the feedback loop in the Turbo article if we use more output pairs (page 14)

Another question:
Will you produce these boards?

Last edited by JBL4435; 15th February 2012 at 06:57 AM.
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Old 15th February 2012, 08:36 AM   #82
a.wayne is offline a.wayne  United States
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Chassis is more expensive than outputs , it should be easy to do mono if boards are l/r , 4 pr / ch is an optimum balance of sonics /power /heat ....
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Old 15th February 2012, 02:00 PM   #83
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Hope you realise that using TO-247 dual cathode diodes for a 2x4 parallel output stage is bad economics.
+$45 for stereo, in comparison to cheapo TO-220 that also handle 2x15A each .

TO-247 lead holes are only interesting for a twit who bought them by the thousand.
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Old 15th February 2012, 02:33 PM   #84
a.wayne is offline a.wayne  United States
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Noted ......
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Old 15th February 2012, 02:59 PM   #85
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Jacco,
are the BYW99W200 candidates?
Curves seem to match.
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Old 15th February 2012, 03:33 PM   #86
a.wayne is offline a.wayne  United States
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Wait for his BOM ....... .........
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Old 15th February 2012, 04:00 PM   #87
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I don't think a Schottky would be recommendable
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Old 15th February 2012, 04:06 PM   #88
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Thanks Jacco.
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Old 15th February 2012, 04:12 PM   #89
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For making a jokey ?
(would be a first time)

Anyway, for a bad example : http://www.vishay.com/docs/88892/mbr60100.pdf

Requirements would be :
- Low resistance (duh)
- Vf preferably higher than 0.5V at ~zero current
- Smooth transition

Moi, i'd thermally couple the diodes (plus select matching ones from stinking stash)
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Old 15th February 2012, 04:33 PM   #90
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2 big questionS
Supose you pay attention to what Papa said and don't use more than 50W dissipation on each of the mosfets.
Amplifier is suplied by positive and negative voltages of +25 and - 25 V
Example 25 V rails 2 A (this is the easy DC bit)
and supose that your amplifier clips at about 2 volts from the suply rails 23 V

Each rail contribute half the current or current is = 2 X bias current to stay in class A

Now the speakers aledgedly have impedence as low as 4 Homs (alegdgedley or just to make things simple)

What would be the current needed to stay in class A for 25 V rails

And for 35 V rails ?

50W dissipation = 1.4 A bias on each more or less

As soon as route mean square came up I get flied so can somebody do the mats for me please.

Real question
1) Do one realy need 4 mosfets on each rail for 35 V rails?

2 )How low can your speaker impedence be if you have 35 V rails and bias for each rail is set at 5.5 A ?

3) do one need to stay in class A till the amplifier clip?
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