Amp9 with SMPS (my first class-d) - diyAudio
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Old 21st April 2008, 09:09 PM   #1
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Default Amp9 with SMPS (my first class-d)

I made this amp for a friend. Originally I tried the Sure Electronics 4 channel board but the background noise wasn't acceptable. So I swapped in a 41Hz amp9. This has almost no background noise and is a much better amp (to my ears).
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Old 21st April 2008, 09:10 PM   #2
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Old 21st April 2008, 09:12 PM   #3
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Old 22nd April 2008, 12:17 PM   #4
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Sorry to ask, but are you gonna leave those bulk cap wirings as such? They will not serve your power reservoir with their max rate. Anyway, all the else is pity to cover under top cover. so nice...
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Old 22nd April 2008, 03:15 PM   #5
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The big white cap is the power reservoir. This is a 47000uF 40V Rifa. Additional caps on the pcb add smaller local storage.

The four caps on the left (with the thin pink wire connecting them to the pcb) are the input coupling caps. These are 7.2uF 630V MKP caps (a pair have just arrived with Davet for testing - see his thread on class-t coupling caps...). Two caps receive the left channel from the pot and two receive the right channel. These four caps then feed the four channels on the pcb, to give L+L+R+R.

This allows bi-amping within one chassis ;-)
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Old 23rd April 2008, 08:59 AM   #6
DarkOne is offline DarkOne  Slovakia
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Hi sharpi31,
nice amp.

What power supply did you use? I'm currently looking for good one to my AMP11.

Thanks
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Old 23rd April 2008, 09:06 AM   #7
col is offline col  Australia
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wow that looks cool. I made an amp with the sure electronics 4*100w. I'm too getting tired of the white noise. Is the amp9 easy to build, isn't the amp9-basc designed for SMPS?

One question: why do you have such a large power reservoir cap or even one at all? I thought they were only used in linear power supplies to smooth the ripple coming from the rectified current. Think I read somewhere that it is actually a bad thing with a SMPS.
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Old 23rd April 2008, 09:51 AM   #8
Eva is offline Eva  Spain
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Quote:
Originally posted by sharpi31
The big white cap is the power reservoir. This is a 47000uF 40V Rifa. Additional caps on the pcb add smaller local storage.

The four caps on the left (with the thin pink wire connecting them to the pcb) are the input coupling caps. These are 7.2uF 630V MKP caps (a pair have just arrived with Davet for testing - see his thread on class-t coupling caps...). Two caps receive the left channel from the pot and two receive the right channel. These four caps then feed the four channels on the pcb, to give L+L+R+R.

This allows bi-amping within one chassis ;-)

The four caps on the left are nice antennas that will do their best to pick up humm and RF and disturb the amplifier.

Physically big capacitors in the signal path should be avoided, particularly near switching amplifiers and power supplies.


The big supply capacitor is ok as long as the control loop of the switching supply does not become disturbed.
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Old 23rd April 2008, 11:11 AM   #9
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The 4 coupling caps are shielded and grounded to the chassis - won't this minimize the the interference pickup? I assumed this would be ok, but could be wrong...

How would I know if the control loop of the smps was effected by the large PSU cap (what could I measure to check this)?

Thanks for the feedback.
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Old 23rd April 2008, 11:39 AM   #10
col is offline col  Australia
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I thought the whole idea of an SMPS was that it will supply pure DC, no ripple, making the supply cap redundant, its a legacy from linear power supply era.
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