power supply question for SI T-AMP

michelevit · 19th October 2005, 08:48 PM

I just received my SI T-AMP and have begun playing with it
last night. I am powering it using alligator clips connected
to a sealed lead acid 7 amp hour battery.

This afternoon I went to my local electrocnics junkyard and found
a 12 volt dc wall wart for 6 dollars. I was happy, but returning
to my desk I plugged it in and found that it actually outputs
15 volts DC!

Is it safe to use on the SI T-AMP? I am having too much fun with
it and hate to pop and blow smoke on me.

Thanks for your reply in advance.
I hope to pull it all apart this weekend and begin fabbing a case for it.

primopyro · 20th October 2005, 06:52 AM

well the wall wart isnt regulated is why...

its 12 volts dc but at how many ampers? lets say its 12vdc 500mah... well when you introduce 500mah of load then the unit will be producing 12volts, until then unloaded its going to be around 15-17vdc

so either grab a regulated one, or introduce its specified output load and your set.

michelevit · 20th October 2005, 09:35 PM

its a 1 amp wall wart.
what kind of resister do i need to indtroduce a 1 amp load?

thanks again for the advice.
mv

Tweeker · 21st October 2005, 04:00 AM

12R. V=I*R. Absolute max voltage listed for the TA2024 is 16V. If you use a resistor across the wart to drop the voltage, your going to be eating up alot of the warts capacity. Also itl get hot, resistor would need to be ~20watts.

It idles at about 70ma so dont expect the SI to drop much voltage when its on. Idealy your transformer would be somewhat more than 1000ma. If you have any a smoothing capacitor or two across the wart will help. Observe polarity.

T-AMP PSU concerns.

BWRX · 21st October 2005, 06:25 AM

Quote:

Originally posted by michelevit
what kind of resister do i need?

I'd say to use a 15-20ohm 2W minimum resistor to be safe. The T-amp doesn't draw much current at low to moderate listening levels. That shouldn't drop too much voltage unless you really push the amp.

Tweeker · 21st October 2005, 06:29 AM

Wouldnt a 20ohm resistor dissipate 7 watts or so, or am I missing something?

DonoMan · 21st October 2005, 06:39 AM

http://www.linear.com/pc/productDeta...40,C1055,P1358

BWRX · 21st October 2005, 04:27 PM

The power dissipated in the ressitor is equal to the current squared multiplied by the resistance. At low to moderate levels the amp should only draw up to maybe 300mA average. So, ok. Perhaps the resistor rating should be a bit higher, 5W or above, but you can get away with smaller ones if testing at lower levels. If you try one with too low a power rating and it gets really hot just remove it from the circuit and replace it with a higher power one.

Tweeker · 22nd October 2005, 06:43 PM

I see the problem, I was looking at putting a resistor in parallel as a load to drop the rails rather than in series. I think using a 180 ohm resistor as a load in parallel might be a better solution than 15 ohms in series. The 15 ohm resistor would seriously soften the power supply degrading the performance.

The amp draws 70ma at idle, the resistor would draw a tad more, you could test what the rails are with the resistor across them, and they should be that much lower with the amp connected. If it doesnt drop them enough, figure out what load would be needed to drop it from how much it did drop. <14V is fine.

pjburnhill · 7th November 2005, 11:07 AM

Ehm,

I must've used unregulated power supply, since I plugged it in and turned it on and it made noticable humming noise for a while (about 5 mins) and then went silent and the light went off. Now it won't turn back on again.

So, does anyone have any ideas how to get it running again or is it not worth it? Any idea what should I replace?

19th October 2005, 08:48 PM	#1
michelevit diyAudio Member Join Date: Aug 2004 Location: .	power supply question for SI T-AMP I just received my SI T-AMP and have begun playing with it last night. I am powering it using alligator clips connected to a sealed lead acid 7 amp hour battery. This afternoon I went to my local electrocnics junkyard and found a 12 volt dc wall wart for 6 dollars. I was happy, but returning to my desk I plugged it in and found that it actually outputs 15 volts DC! Is it safe to use on the SI T-AMP? I am having too much fun with it and hate to pop and blow smoke on me. Thanks for your reply in advance. I hope to pull it all apart this weekend and begin fabbing a case for it.

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20th October 2005, 06:52 AM	#2
primopyro diyAudio Member Join Date: Oct 2005	well the wall wart isnt regulated is why... its 12 volts dc but at how many ampers? lets say its 12vdc 500mah... well when you introduce 500mah of load then the unit will be producing 12volts, until then unloaded its going to be around 15-17vdc so either grab a regulated one, or introduce its specified output load and your set.

20th October 2005, 09:35 PM	#3
michelevit diyAudio Member Join Date: Aug 2004 Location: .	its a 1 amp wall wart. what kind of resister do i need to indtroduce a 1 amp load? thanks again for the advice. mv

21st October 2005, 04:00 AM	#4
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	12R. V=I*R. Absolute max voltage listed for the TA2024 is 16V. If you use a resistor across the wart to drop the voltage, your going to be eating up alot of the warts capacity. Also itl get hot, resistor would need to be ~20watts. It idles at about 70ma so dont expect the SI to drop much voltage when its on. Idealy your transformer would be somewhat more than 1000ma. If you have any a smoothing capacitor or two across the wart will help. Observe polarity. T-AMP PSU concerns.

21st October 2005, 06:29 AM	#6
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	Wouldnt a 20ohm resistor dissipate 7 watts or so, or am I missing something?

21st October 2005, 06:39 AM	#7
DonoMan diyAudio Member Join Date: Feb 2005 Location: Massachusetts	http://www.linear.com/pc/productDeta...40,C1055,P1358

21st October 2005, 04:27 PM	#8
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	The power dissipated in the ressitor is equal to the current squared multiplied by the resistance. At low to moderate levels the amp should only draw up to maybe 300mA average. So, ok. Perhaps the resistor rating should be a bit higher, 5W or above, but you can get away with smaller ones if testing at lower levels. If you try one with too low a power rating and it gets really hot just remove it from the circuit and replace it with a higher power one.

22nd October 2005, 06:43 PM	#9
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	I see the problem, I was looking at putting a resistor in parallel as a load to drop the rails rather than in series. I think using a 180 ohm resistor as a load in parallel might be a better solution than 15 ohms in series. The 15 ohm resistor would seriously soften the power supply degrading the performance. The amp draws 70ma at idle, the resistor would draw a tad more, you could test what the rails are with the resistor across them, and they should be that much lower with the amp connected. If it doesnt drop them enough, figure out what load would be needed to drop it from how much it did drop. <14V is fine.

7th November 2005, 11:07 AM	#10
pjburnhill diyAudio Member Join Date: Nov 2005	Ehm, I must've used unregulated power supply, since I plugged it in and turned it on and it made noticable humming noise for a while (about 5 mins) and then went silent and the light went off. Now it won't turn back on again. So, does anyone have any ideas how to get it running again or is it not worth it? Any idea what should I replace?

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