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Old 13th March 2006, 06:32 AM   #91
ACK2005 is offline ACK2005  Taiwan
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Default Speaker impedance and sensitivity

Mnnn..

Does SEWA work well for speaker with impedance 6-Ohm
and 87dB sensitivity??
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Old 13th March 2006, 09:28 AM   #92
Mad_K is offline Mad_K  Norway
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Tyimo; You can do that if you want, but it doesn't really matter as Q2 is simply a current source. I use the same type as it is practical, but if you have both types I would probably do it like you described to save the hard to get 044's

ACK2005; SEWA is set up to give 7WRMS into both 4,6 and 8 ohm loads. If 7W is enough on 87dB speakers depends a lot on your listening habits and listening room. I would recommend a speakers from 93dB and upwards. That being said I have lived with ~87dB speakers and 5W amplifiers over long periods of time..

edit: if you build it with 30V rails and 2,5-3A bias you will be able to get about twice the outputpower from the design. I think this will be more suitable for your speakers. This requires very good thermal management though
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Old 13th March 2006, 11:45 AM   #93
Tyimo is offline Tyimo  Hungary
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Hi Mad!

Thanks!
Quote:
I would probably do it like you described to save the hard to get 044's
It is the reason why I asked. :-)

How can I bias the SEWA V.1 to 2,5-3A, if I use 30V rails?
Change R12-R16 to near 1 ohm?

Tyimo
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Old 13th March 2006, 01:03 PM   #94
Mad_K is offline Mad_K  Norway
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Quote:
Originally posted by Tyimo


How can I bias the SEWA V.1 to 2,5-3A, if I use 30V rails?
Change R12-R16 to near 1 ohm?

Tyimo
You got it. Bias is BE drop of Q3 (0,6V) divided by the paralelled value of R12-16. Say you want 2,5A. 0,6V/2,5A=0,24ohm. 0,24*5=1,2ohm for R12-16.
You also need to change R1 to 5K6 to get the DC operating point just right as I said in post#72
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Old 13th March 2006, 03:30 PM   #95
Tyimo is offline Tyimo  Hungary
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Thanks Mad!!!

Tyimo
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Old 1st April 2006, 08:21 AM   #96
ACK2005 is offline ACK2005  Taiwan
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Default Different voltages

What is the difference between +22V/2A-CCS and +30V/2A-CCS?
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Old 1st April 2006, 08:27 AM   #97
Mad_K is offline Mad_K  Norway
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About twice the power output in 8 ohm, and about the same in 4 ohms
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Old 1st April 2006, 05:30 PM   #98
ACK2005 is offline ACK2005  Taiwan
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hi

>would consider a LC (+LC) or a regulated supply to get the rails >somewhere around 30V with 3A bias.

Well, how about parallel MOSFET 2A x 2 (for Q1 and Q2 both)?
So, there will be four transistors.

For two parallelized MOSFETs, is it better to use two sets of BC550+R12~R16, one for each MOSFET? or,to use one set of BC550+R12~R16 for both MOSFETs?

I may add a switch to select the current flow through CCS.
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Old 1st April 2006, 11:36 PM   #99
JCM is offline JCM  United States
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I love that design !

It seems like the heatsinking is modest - which I think is good, not to have to have some - anvils - attached to the case. It is because of the fan ventilation you were able to get by with those heatsinks, I think ?

I find myself planning to avoid complex designs, it seems there is no reason for it, since 5, 10, 20 watts can be had with good Class A, and since I plan to use efficient speakers.

And yet I was surprised how much volume a flea powered (about one half to one watt ) amp I cooked up gave with a pair of speakers I guessed were not real efficient at all - especially the bass, using my little tone controls - it made a mockery of the bass performance of some commercial hi fi amps, the kind found in hi fi shops. (Of course, those use extremely skimpy reservoir caps, and sloppy RC tone controls.)

I look forward to any future designs you come up with.
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Old 4th April 2006, 01:05 PM   #100
Mad_K is offline Mad_K  Norway
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Sorry about the late reply, but I've been very busy lately.. You COULD paralell the fet's for improved heat dissipation. To do this, you simply put them in paralell, but with separate gate and source resistors. If you keep the original source resistor value, you will have twice the bias (4A)
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