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Old 8th September 2004, 12:29 PM   #1
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Default sam's 300W or eti-466 : alternative for Vbe

Hi guys,


Having finish Mr. Holton's AV400, I intend to go for the 300W BJT amplifier at :

http://users.otenet.gr/~athsam/power_amp_300w.htm
or
http://www.alphalink.com.au/~cambie/ETI466Web.htm

1/ I think the mechanical work involve for implementing Q8 could be difficult : either too tight to get thru or too loose to get good thermal contact. I think the mounting could be a lot easier if we use BD139 (or other TO126 package) and flying leads to the pcb (just as in AV400). Can this be done and what other changes had to be included?

2/ Would eliminating the Zobel network cause any problem?

3/ What happens to R10 in sam's circuits (as R4 in eti-466)?



Tks for your input.
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Old 8th September 2004, 12:35 PM   #2
sajti is offline sajti  Hungary
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You can use BD139, without any problem. You can get better thermal compensation if You aplly the BD139 to the top of the output device (plastic case better, in this case)
Keep the Zobel network. Removing can results instability.
R10 can be apply, or not. Without it You can get hum...

sajti
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Old 8th September 2004, 12:56 PM   #3
nbcd is offline nbcd  Romania
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hy bigpanda

I would also like to build antony's 400w amp , can you help me with some things?
-i want to know if i can replace the original mosfets with irf240/9240? , how is the amp sounds? , how is the bass , which is the normal operating temperature , do i need some corections in the schematic?

Thank you!
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Old 8th September 2004, 12:57 PM   #4
nbcd is offline nbcd  Romania
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Or maybe you could give me the whole project , including a pcb

Best regards!
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Old 12th March 2005, 05:28 AM   #5
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Hi guys,

I've put this away for a while and I am back for it again.

In Sam circuits :

What are purpose of C14, C17. I have some 220u, 100V. Can they be use instead?

What are purpose of C13, C16. Do they have to be 250V. If 250V polyester are used, they take up too much space. Can I use lower voltages? I do have some metalized film 100n 250V that's much smaller in size. Can I use them?

It's quite difficult to locate R28....R31, 100R 3W carbon film. Can 50R 5W wire wound be used. If not, I might have to use 4 x 200R 2W for R28+R29 which looks sort of clumsy.

How to calculate the value for L1? I might get ready made ones from my friend. It's quite difficult to get 1mm D enamelled wire in my place (I might have to get in 100 ft roll)


Tks for your help.
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Old 12th March 2005, 09:37 AM   #6
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Quote:
Originally posted by bigpanda
Hi guys,

In Sam circuits :

What are purpose of C14, C17. I have some 220u, 100V. Can they be use instead?
C14 and C17 are for providing some local decoupling to the voltage rails.
Yes you can use 220 uF 100 volts.




Quote:
What are purpose of C13, C16. Do they have to be 250V. If 250V polyester are used, they take up too much space. Can I use lower voltages? I do have some metalized film 100n 250V that's much smaller in size. Can I use them?
C13 and C116 are for bypassing the electrolytics C 14 and C17 at very high frequencies.

They can be 100 Volts .Yes you can use them.



Quote:
It's quite difficult to locate R28....R31, 100R 3W carbon film. Can 50R 5W wire wound be used. If not, I might have to use 4 x 200R 2W for R28+R29 which looks sort of clumsy
50 Ohms wire wound must not be used because of the inherent inductance.
You can use 4 of 200 R 2 W for R28 / 29 ...
But it seems to me that 3 W, in that position , is a bit over rated...
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Old 13th March 2005, 10:42 AM   #7
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Tks Jorge,

Do you mean that the total wattage for 1 pair (R28,R29 in parallel) should be less than 3W?
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Old 13th March 2005, 11:20 AM   #8
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Quote:
Originally posted by bigpanda
Tks Jorge,

Do you mean that the total wattage for 1 pair (R28,R29 in parallel) should be less than 3W?


Where do you read the necessity of R28 , R29 to be 3 W each?

I can see nothing in the schematic you gave.

http://users.otenet.gr/~athsam/power_amp_300w.htm
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Old 14th March 2005, 02:06 AM   #9
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Hi Jorge,

I think I found more info about R28-R31 in here

http://www.alphalink.com.au/~cambie/ETI466Web.htm

Its only 1W resistors. I think I could proceed. Lots of mechanical work to do-----drilling holes.


Thanks, hope I don't have to boder you guys on this one again.
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