SEWA - Seven Watt Amplifier

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#362
Hello Tyimo, I'm back from my vacation now. I've had pcb's made for BOSEWA/Aleph L 1.2 , but I haven't had time to actually build/test it.
As I am in the process of moving to another apartment/giving it a serious makeover I have very little time left for anything else. Looks like it's going to be like this for at least a couple of months 🙁
 
#363
Hi Mads!

As I am in the process of moving to another apartment/giving it a serious makeover I have very little time left for anything else. Looks like it's going to be like this for at least a couple of months
Click to expand...

I know this situation from end of the last year and I wish you the bests!😀

Only one theoretical question: how could I calculate the output power for the choke loaded SEWA (or better to say OTA)??

I would like to use:
120mH 0.5R EI core Choke
+24V supply
8R load

I only know: 24V/8R=3A bias

and on 20Hz the choke has 15ohm resistance.

Greets:

Tyimo
 
#367
Re: Re: Sewa and z=15 Ohm?

Mad_K said:



In that case you should use 24VAC transformer for 30VDC+ rails. You can also lower the bias to 1,5A 😉
Click to expand...

I have transformers with 30VAC secondaries, from zen v.1. This would give me 34V after Pi filter. Is that too much?

What I shuld change to get 1.5A bias? Can you suggest exact values? I hope I don't ask too much 🙂

Thanks!
 
#368
Re: Re: Re: Sewa and z=15 Ohm?

ticovski said:


I have transformers with 30VAC secondaries, from zen v.1. This would give me 34V after Pi filter. Is that too much?

What I shuld change to get 1.5A bias? Can you suggest exact values? I hope I don't ask too much 🙂

Thanks!
Click to expand...


34V is nice. Bias is defined by the 0,6VBE from CCS transistor divided by the CCS Source resistor(s) 😉
 
#373
Just to be sure and not to burn something 😎

For Bias of 1,5 A - R12 to R14 should be 0,4 Ohm. So, to achieve that I need 2 resistors of 1 Ohm in series parallel with two resistors of 1 Ohm, also parallel to those in series? Right? If yes I am ready for shopping 😀
 
#377
I have thought of using SEWA to drive a RIBBON in a triamped 3-way system
The loss of gain in Sewa is maybe compensated by higher efficiency of the ribbon

Any comments on that ?

Hard to explain - but how much higher efficiency is needed from a midrange driven with SEWA - to align with a woofer driven with amp with normal gain ?
 
#379
Ryssen said:
Is it possible to use a trimpot to set the current trough the amp,I mean if I use rather small heatsinks.Where could I use the pot?🙄
Click to expand...


Bias is set by the value of R12-16. If you can find a 1 ohm 3W multiturn pot, you can insert it there and have adjustable bias 😉 Another option would be to use a switch to short out some resistors.
 
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