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Old 11th May 2010, 12:48 PM   #7861
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I want you to go through the maths again and determine how much heat will be dissipated by the 50 ohm and 10 ohm resistors when the amplifier is running at max.

The Panasonics, for the money, are very good for audio.
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Old 11th May 2010, 01:23 PM   #7862
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Quote:
I used THESE as PD mentions in one of his posts for all the small resistors.
Wrong. The ten ohms have to be 1w rated
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Old 11th May 2010, 01:25 PM   #7863
AndrewT is offline AndrewT  Scotland
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What is the maximum peak voltage that can appear on the speaker terminal?
Let's assume Vsupply is 25Vdc.
Let's assume voltage drop through the cables and devices from PSU to speaker terminal is 2V.
That leaves 23Vpk at the output.
You have 50r (100r//100r) + 10r determining the peak current through the feedback circuit.

Maximum current is Vpk/Rtotal = 23/60 = 383mA.

Power dissipated in the three resistors is
for 10r
10 * 0.383^2 = 1.47Wpk.
for 100r
100 * (0.383/2)^2 = 3.67Wpk.

These are instantaneous worst case dissipations for a +-25Vdc supply.
The continuous dissipation for all the feedback resistors will be less than a quarter of the peak figure. Each feedback reaches peak current when the other is at near zero current.

These figures are for flat out on a sinewave test signal that just reaches output clipping.
On real very loud music the peak figures will be similar, the continuous dissipations will be much lower.
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Last edited by AndrewT; 11th May 2010 at 01:34 PM.
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Old 11th May 2010, 01:33 PM   #7864
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Quote:
Originally Posted by jackinnj View Post
I want you to go through the maths again and determine how much heat will be dissipated by the 50 ohm and 10 ohm resistors when the amplifier is running at max.

The Panasonics, for the money, are very good for audio.
Jack, what's up with your site? went to look for F-5 components, nothing shows?

Russellc
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Old 11th May 2010, 01:45 PM   #7865
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Quote:
Originally Posted by Russellc View Post
Jack, what's up with your site? went to look for F-5 components, nothing shows?

Russellc
We had floods here last month and I had let some stuff get wet -- so I've been repairing equipment, plus it just takes a lot of time to assemble the kits and get them out so I am taking a breather for a while. I still have plenty of JFETs but IRF MOSFETs (thanks Vishay) are on 32 week backorder.
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Old 11th May 2010, 01:52 PM   #7866
cjkpkg is offline cjkpkg  United States
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Quote:
Originally Posted by bobodioulasso View Post
Wrong. The ten ohms have to be 1w rated
While you are quick to call me out as being wrong I simply went by the BOM's found in this and other F5 threads by PD and went by what I observed as the CMF50 resistors as posted by PD himslef HERE

And HERE

The only mention of larger 3W resistors I saw when collecting parts were R5-R8 and R11 and R12.
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Old 11th May 2010, 03:56 PM   #7867
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To big 100 ohm resistors suit relatively big 10 ohms ones.
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Old 15th May 2010, 08:03 PM   #7868
Marra is offline Marra  United Kingdom
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Please confirm whether this heatsink will be ok for one channel of F5.

Fischer SK157 300mmWx150mmLx85mm fins 0.25degrees/watt.

cvillier are your f5 pcb's and power supply pcb's still available.

Keith
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Old 15th May 2010, 08:11 PM   #7869
cviller is offline cviller  Denmark
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Quote:
Originally Posted by Marra View Post
Please confirm whether this heatsink will be ok for one channel of F5.

Fischer SK157 300mmWx150mmLx85mm fins 0.25degrees/watt.

cvillier are your f5 pcb's and power supply pcb's still available.

Keith
Those specs sounds perfect for the project.
And yes, I still have boards available. If you have more questions about my boards, please ask them in this thread:
http://www.diyaudio.com/forums/group...-new-post.html
or on my blog (see my signature).
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Old 15th May 2010, 09:17 PM   #7870
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by cviller View Post
Those specs sounds perfect for the project.
Yep, the long finning makes the difference, and probably the best you can get

I was so enthusiastic I bought 1 full meter ..... dammed expencive, and not too clever ..... I can barely lift it but base is 100% smooth, top quality
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