SEWA - Seven Watt Amplifier

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SCD

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Joined 2003
From the fellow that organised the group buy this was sent to help me in my decision. I hope I made the right call.:

"Those Conrads (# MF-35-151) has a dissipation factor of 0.21°K/W and it means if the dissipating power is 72 W as a maximum, one of those sinks will rise in temperature by 0.21 x 72 = 15.1° K (C) above ambient. If ambient is 25°C heat sink temp. will be ca 40-41°C."

As long as the power dissapation requirements of the SEWA is in a reasonable range things should be okay, I hope? What is the dissapation requirement for the SEWA is the question?

Thoughts or Comments please
 
Mad_K

Mad_K

Member
Joined 2002
dzoli said:
Hi Mads,

Yesterday a new baby born.
:). My SEWA is almost ready. The first listening test was impressive. I use an opamp pre now. I'm waiting for your BOZ pcb getting available. Tonight I will post pictures.

Regards,

Zoltan
Click to expand...

Nice to hear Zoltan ;) BOZ pcb has been revised, but has been put on hold because I'm in the middle of making over a new apartment. I suspect there will enouogh interest if I made a separate thread for this pcb buy, but for now it will have to wait. I'm attaching the revised DIY files for the single sided version of Rev.2:
 

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A

aetosa

Member
Joined 2006
Sorry to interrupt your conversation, but I have a few questions for SEWA.
I,ve built it, one channel only, and it does not sound loud enough. In fact, compaired with another 7 watt amp I have, SEWA sounds like 1 watt.
For Preamp I use this: http://sound.westhost.com/project37.htm
For transformer I use one 18V at 1.5 A .
Also, considered that it draws 2A current, why do we need 8 A for the transformer?
 
Mad_K

Mad_K

Member
Joined 2002
aetosa said:
Sorry to interrupt your conversation, but I have a few questions for SEWA.
I,ve built it, one channel only, and it does not sound loud enough. In fact, compaired with another 7 watt amp I have, SEWA sounds like 1 watt.
For Preamp I use this: http://sound.westhost.com/project37.htm
For transformer I use one 18V at 1.5 A .
Also, considered that it draws 2A current, why do we need 8 A for the transformer?
Click to expand...


Does you preamp have enough gain?
You'll need about 20dB. And you'll need about 8VRMS outputswing to get 7WRMS.
It your preamp can swing 6VRMS, SEWA can deliver 4,5WRMS into 8 ohms. (P=Vrms*Vrms/8)
Minimum transformer for a one channel SEWA is 18VAC 100VA (18V@5,6A) ;)
You need a larger transfomer because of the AC/DC conversion, losses and overheating. Plus a larger one sounds better (lower losses, impedance, regulation)
What is your V+ voltage and voltage at the mosfet Source?
 
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aetosa

Member
Joined 2006
You'll need about 20dB. And you'll need about 8VRMS outputswing to get 7WRMS
Click to expand...
8VRMS=8*1.404=11.23V PeakV. Correct?
Does that mean the preamp has to swing from 0 to 11.23 V Peak?

Also, my preamp has a Voltage gain of 10db.
For the rest of your questions I'll look on monday and will tell you.
Forgive me for my naive questions. I'm trying to learn about amps, reading the book of Millman-Halkias, but to tell the truth there is much I don't understand. Too many complicated equations, diagrams...:bigeyes:
 
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