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Chip Amps Amplifiers based on integrated circuits

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Old 17th December 2004, 02:04 PM   #1
Aunkst is offline Aunkst  United States
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Default Another One

Built in an old case I had. New faceplate. Speaker Termilals on front because this goes on a narrow shelf next to the desk.

Xfmr is only about 80VA 20-0-20 No heatsink, bolted to the case sides. These will never be run hard. nor could they with the small transformer.
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Old 17th December 2004, 02:05 PM   #2
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front. Volume control, some day.
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Old 17th December 2004, 03:21 PM   #3
Aunkst is offline Aunkst  United States
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I tested this amp with the computer outputs. and I hear a HUM in the 200hz region. Definatly not 60hz. The hum is clearly audible at several feet away. but not over bearing.

The hum is only present when both RCAs are connected. If I disconnect either one The sound stops.

There is no hum when I run it off of the AV preamp in the living room, nor is there any hum when there is no input connected.

Is this a faulty sound card? I have never noticed this with any other amp I had run off the computer.

It is also not a grounding problem with the amplifier. I changed the grounding scheme several times and the hum never changed.
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Old 17th December 2004, 03:37 PM   #4
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In my opinion you seem to have pinpointed your problem with those two connectors: there seems to be a loop.

What I think you should do is disconnect one of the grounds and that's it.

The loop is probably coming from the source.


Carlos
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Old 17th December 2004, 04:10 PM   #5
Aunkst is offline Aunkst  United States
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I aggree that that would work however that seems to be a band-aid that is only necessary for use with the computer. Wouldn't it be better to fix the source?
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Old 17th December 2004, 08:15 PM   #6
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Is there metal under/behind the wood touching the RCA's? You could have a grnd loop there if so.
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Old 17th December 2004, 11:00 PM   #7
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It's 120 Hz hum -- you are using a full wave bridge rectifier.

The wall of the cabinet is not remotely adequate to conduct the amount of heat generated by a chipamp. You need a heat sink.

The transformer doesn't look adequate. The one you are using looks to be from a 10 or 15 watt stereo -- this will overheat and fail.

the diode board should have a greater clearance between itself and the bottom of the chasis. Consider putting a sheet of mylar underneath the diode board to prevent accidental contact with the chasis.

i would tackle the diode board first --you don't want to be dead before you have a chance to enjoy the music.

consider using 2 10,000 uF capacitors, with a rating about twice the transformer voltage (i.e. if the transformer is 24-0-24 V, the caps should be rated for 50V) right after the diode bridge -- this will accomodate most line voltage swings.

(edit) run the leads from the power supply along the rear of the chasis to the amplifier boards. run the input leads along the floor of the chasis. twisted pair should be OK
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Old 17th December 2004, 11:29 PM   #8
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Default well actually..........

Quote:
The wall of the cabinet is not remotely adequate to conduct the amount of heat generated by a chipamp. You need a heat sink.
I disagree - if you're not driving the amp hard, and your transformer voltage is fairly low, you don't need much of a heatsink at all. See pics of my Mini-Clone that runs on a 16V transformer. The case is very thin aluminium, but even then it barely feels warm, even when I play it the loudest I ever will...

Quote:
The transformer doesn't look adequate. The one you are using looks to be from a 10 or 15 watt stereo -- this will overheat and fail.
Suck it and see. If the transformer doesn't get too warm, when you run the amp at your max. listening level, you don't need to change it.

Quote:
i would tackle the diode board first --you don't want to be dead before you have a chance to enjoy the music.
I agree that this needs to be done, but would suggest that the 20V from the transformer secondary isn't very likely to kill you. -Especially if your chassis is grounded as well.


Just some opinions based upon my experiences..

Steve
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Old 17th December 2004, 11:47 PM   #9
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Default Re: well actually..........

Quote:
Originally posted by BlackDog


I disagree - if you're not driving the amp hard, and your transformer voltage is fairly low, you don't need much of a heatsink at all. See pics of my Mini-Clone that runs on a 16V transformer. The case is very thin aluminium, but even then it barely feels warm, even when I play it the loudest I ever will...
What are those uninsulated wires eminating from the transformer on the Miniclone?
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Old 18th December 2004, 05:24 AM   #10
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Default extra windings

Hi jackinnj,

The 'bare' wires aren't quite bare. It's magnet wire, which has a thin layer of enamel insulation as it comes. The extra wires are an additional 10 ten turns of wire that powers the LED on the front panel. It produces around 2 volts if I remember right. --- Some people on here have mentioned that putting LEDs on the amp supply rails adds noise, and this was suggested as a win-win way of doing it.

Steve
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