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argonrepublic 28th January 2013 08:00 PM

STK4044 Power up.
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I bought these PCB with all components installed. I would like to know more about powering these. At 100 watts RMS into 8ohms per module, I was told that ideally I would use a torroidal 38-0-38 250VA.
I do not need that much power. Would I reduce the voltage, current or both to make them around 50 Watts RMS. I would prefer not to attenuate and at full power, be the loudest that I will ever use with a nearfield monitoring situation. I would also like to know what signal power I need to drive these. The PCB has 2 STK4044XI. My hopes are to use this pair to bi amp speakers.

PetruV 8th February 2013 04:59 PM

most probably stanadrd computer out signal will do it

Mooly 8th February 2013 05:14 PM

I would follow the data sheet for all the circuit details.

Perhaps aim for around -/+45 DC which suggests a 30-0-30 tranny. The AC voltage will be higher at low load anyway. 50 watts RMS/8ohm is 28 volts RMS or 40 volts pk/pk.

Power up initially with a bulb tester... just in case there are any construction errors... it could save damaging the STK's

The "signal power" (you mean voltage) needed for full output depends on the values of the feedback components. Thats the 56K and 560 ohm in the application circuit. They give a gain of (56000+560)/560 which is 101. So for 28 volts RMS output you need to apply 28/101 which is 277mv RMS. In practice that means line level and a passive volume control.

argonrepublic 8th February 2013 05:45 PM

Can I expect good results from these modules? I would like to drive a Dynaudio 17w75 from one module and a dynaudio D28/2 from the other. I am hoping to exceed the quality of my Blue sky that used Tip 35 and Tip 36. I do not need much power. I am always attenuated while working at my desk.

Mooly 8th February 2013 06:05 PM

I think they should be fine sonically. The internal equivalent circuit shows a quasi-complementary output (two npn) so that bodes well for sonics.

argonrepublic 8th February 2013 06:47 PM

I am learning very much today. I have a few transformer lying around. I plugged one in and found it to have 30-0-30. I was feeling lucky! When I plugged in directly, My voltage went up. I had about -51 and +51. I thought that the light bulb was current limiting but obviously causes voltage to drop as well. I have another transformer here. It is 22-0-22. Would that be too weak to audition these Amps?

Mooly 8th February 2013 06:51 PM

The bulb is for limiting and as such will drop some voltage as current is drawn.

22-0-22 is perfectly fine, and you may find it gives all the output power you need in actual use. Probably around 40 watts RMS.

An added bonus is that the lower the supply voltage and the less heatsinking you need.

argonrepublic 8th February 2013 07:18 PM

I have supply hooked up. It is sitting at -31Vdc and +31Vdc. All of these little details were so unexpected! I really thought that It would come easier than this. Then again, the reason that I left the automotive field to learn elcetronics was that I needed the stimulation. These recent projects have been far from swapping visibly scorched components and getting lucky 51% of the time.
Thanks so much!

argonrepublic 8th February 2013 08:22 PM

WOW!!! This is my first finished circuit of any significance. It sounds like I am running out of current when I run it at higher levels. I am notiving more high frency energy than all of the other amps I have used on My Tag band 2 ways. Is it possible that something is lacking or is this the transparency I have been looking for?

Mooly 9th February 2013 06:19 AM

Without hearing it :) I wouldn't like to say what you are hearing :D

The next step would be to use a scope and confirm all is as it should be, but assuming you haven't access to one there are still a couple of things to check.

The power supply. Having confirmed it all works, I'm assuming your running it on full mains power now without the bulb. So check the rail voltage with your meter as you turn the volume up. The power supply should hold up without the voltage sagging.

The other thing is to check the grounding layout, In particular I would make sure that the speaker returns go directly back to the power supply and not to any points on the PCB.

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