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Chip Amps Amplifiers based on integrated circuits

Chip amp power supply- a beginners guide
Chip amp power supply- a beginners guide
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Old 7th January 2010, 10:21 PM   #521
Tripmaster is offline Tripmaster  United Kingdom
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Originally Posted by audio1st View Post
Hi Richard,
Glad to hear it still clicks. Once the relay has clicked that should short out the resistor and will no longer be in circuit, leave it on for awhile and the resistor should cool down. Turn off before touching though...
Will do
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Old 7th January 2010, 10:32 PM   #522
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If it is OK you can unscrew and remove the 1u5F cap, cut the wires near the board and remove the 100k resistor near the input.
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Old 7th January 2010, 10:37 PM   #523
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Ive just done that and the resistor is cold, excellent!

I'll remove the other parts tomorrow...time for bed.

Thanks for your help Barry
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Old 8th January 2010, 12:29 PM   #524
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47r 15W as the soft start resistor on a 240Vac mains systems is a little low on dissipation for a short time delay.
The 15W rating is far too low for a long time delay.
Either fit two 15W resistors in series or shorten the bypass time delay for 240Vac working.

I use 50r 50W (10r 10W * 5off in series). They don't get warm.
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Old 8th January 2010, 12:46 PM   #525
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Originally Posted by AndrewT View Post
47r 15W as the soft start resistor on a 240Vac mains systems is a little low on dissipation for a short time delay.
The 15W rating is far too low for a long time delay.
Either fit two 15W resistors in series or shorten the bypass time delay for 240Vac working.

I use 50r 50W (10r 10W * 5off in series). They don't get warm.
Hi Andrew

Thanks for the tip. The 47R resistor only gets slightly warmer than body temperature, and then cools quickly.

Do you think I can still get away with the 1.6T fuse in the IEC mains inlet? I now have 600VA for the amps and a 30VA soft-start transformer.

Thanks
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Old 8th January 2010, 01:38 PM   #526
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fit the T1.6A fuse and see how long it lasts.
If it's less than a month then increase the rating.
If it's more than a year it might be worth reducing the rating.
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Old 8th January 2010, 06:40 PM   #527
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I've reconnected everything today, although its a bit of a rats nest. I'll tidy this up later. With everything connected the bulb filament barely glows...so a real improvement.

Click the image to open in full size.

I ran into a slight problem when I was checking the DC offset with a 10R resistor. I noticed the output on the left hand channel was 162mV, this used to be under 5mV. The right channel displayed 1.5mV

I traced the problem back to a poor connection on the V+ side of the power supply, with this corrected the DC offset returned to its normal level.

Here's hoping I don't run into any further problems...
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Old 9th January 2010, 10:06 AM   #528
AndrewT is offline AndrewT  Scotland
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Hi,
the output offset is normally checked twice.
First with the input shorted and the output open circuit.
Secondly, remove the input short and connect the source component, still with the output open circuit.
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Old 10th January 2010, 08:40 AM   #529
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Hi,
the output offset is normally checked twice.
First with the input shorted and the output open circuit.
Secondly, remove the input short and connect the source component, still with the output open circuit.
Hi

I've wired up a couple of shorted RCA plugs (ground to signal wire) and I am about to measure the DC offset.

I have one quick question before I start. If I plug the shorted RCAs into the amps input sockets and measure the offset from the speakers terminals, with no volume attenuator connected, will the amp run at full volume, and if so will this damage the op-amps? (long sentence)

Thanks
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Old 10th January 2010, 10:29 AM   #530
AndrewT is offline AndrewT  Scotland
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the shorting plug at the input ensures you have Rs=0r0 and that Vin=0mVac=0mVdc
The amplifier is OK in this mode.
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