SEWA - Seven Watt Amplifier

[renjiish]

dear madk
i have two transformers with rating 18volts/80VA . i want to make an SEWA with lower power rating. i will be happy if i can get a 5 watts power output . shall i lower the bias current, so i can use these transformers. what is your opinion
regards
renjish

 

[Mad_K]

Lower the bias to 1,5A and make shure your transformers have some ventilation To get 1,5A bias, use R12=0,4ohm. (R12A-E=2R).

 

[aetosa]

I can't understand what's happening. I've double-triple (and more...) checked the PCB in conjuction with the diagram, but nothing found.
V+ = 22,5 V, BUT when I connect it to the SEWA, it falls to 8V!!!
I seen no shortcircuits, no mistakes on the PCB.
PCB= Rev.1
Diagram=Rev.D
Differences=R6(I put 1k, by Rev.D) R2(100K, by Rev.D) R9(100K, by Rev. D)
C7, which I have not put it yet.
Is there something else should change?

 

[aetosa]

Except that it falls from 22.5 to 8 V afteer connection with the supply,
Q1 gets hot while Q2 is cold

 

[aetosa]

Here is PCB and parts, except capacitors:

 

[Mad_K]

What is the voltage across the 0,47R in the supply?

 

[Mad_K]

Did you use BC550C (or npn with same pinout)?

-Seems to me you are using too small a transformer and that it collapses under the heavy current draw? What is the VA rating?

 

[aetosa]

The transistor IS BC550C. I ve soldered it correctly (the pins I mean). I've checked it a lot of times.
Transformer: !8V, !.4 A.

 

[Vix]

Aetosa,

If I got it correctly, you have a 18V, 1.4 A tranny??

That's a problem, you need a much bigger transformer. I am using a 200W transformer for one channel of SEWA.

regards,

Vix

 

[aetosa]

Yes, correct.
Do you think that's the reason it's falling at 8V (from 22.5V) after I connect it to the supply?

 

[Vix]

Hi,

Yes. The only way for you to find out is to connect a bigger transformer, or, find two 12v car batteries, connect them in series, so you get 24 v and measure.

 

[Tyimo]

Chokes question

Hi Choke Masters Circlotron and Fuling!

I need your help to make a minimum 120mH 3A chokes!

I found a workshop wher they could make the EI core chokes, but they need the:
- EI core size
- gap distance
- turns number
- wire diameter

I think about a 300VA EI transformator core with 0.25mm gap and ca. 200 turns of 1.5mm2 wire. What do you think?
Could you help me and give some info????

Greets:

Tyimo

 

[Fuling]

300VA EI transformator core with 0.25mm gap and ca. 200 turns of 1.5mm2 wire

Sounds good.

 

[Tyimo]

Hi Fuling!
Thanks for the answer!

Sounds good

I hope that it will sounding good!

Tyimo

 

[Fuling]

I hope that it will sounding good

I´m sure it will!

Resistors across the choke (27 ohms or so) might help if you get problems with ringing on the square wave test.

 

[Tyimo]

Resistors across the choke (27 ohms or so) might help if you get problems with ringing on the square wave test.

Thanks!

Greets:

Tyimo

 

[hoktuna]

Mad k is it possible to buy pcb`s from you?

 

[Mad_K]

Yes, I have some Rev.C boards available, look here:
http://www.diyaudio.com/forums/showthread.php?postid=989085#post989085

 

[hoktuna]

I will be very happy if i can buy 4 pcb`s
I have no e-mail at home but on my work on monday.
hans-olof@bennstroms.se
Or sms your address on 0703506696.
I send you the money and my address.

 

[Tyimo]

Hi Mads!

Don't you want to make a PCB for the Atlantis MM pre??
I like your PCB design style!

Greets:

Tyimo