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The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
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Old 12th September 2019, 08:52 PM   #541
xrk971 is offline xrk971  United States
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The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
I typically use an NTC like 8D-20 between IEC line and trafo primary. That works pretty well as it has about 10ohms resistance cold. Takes about a minute to warm up to 0.5ohms nominal value once hot. Simple and passive.
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Old 12th September 2019, 11:18 PM   #542
astromo is offline astromo  Australia
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Originally Posted by xrk971 View Post
I typically use an NTC like 8D-20 between IEC line and trafo primary. That works pretty well as it has about 10ohms resistance cold. Takes about a minute to warm up to 0.5ohms nominal value once hot. Simple and passive.
From Post #1, Advantages:
Quote:
7. As icing on the cake, the SLB provides a smooth slow ramp up to prevent mains current overload and tripping fuses, plus, it eliminates turn on speaker pop
.

xrk971, so you're recommending an NTC as well? Contradiction? What's the nuance?
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Old 12th September 2019, 11:24 PM   #543
jhofland is offline jhofland  United States
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Perhaps I can help. Without some sort of soft start there will be significant currents required to charge the main caps in the SLB. The output of the SLB, on the other hand, does have a ramp up due to the relatively long risetime of the control voltages that are part of the of the so called capacitor multiplying circuits.
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Old 12th September 2019, 11:48 PM   #544
Shawnstium is offline Shawnstium  United States
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The components of an electronic inrush current limiter and cap Mx are very similar, however the 60,000uF of CRC filtering is before the cap Mx. If you’re using a small (<300) VA transformer you can probably get away without using a soft start method, but the current surge is still stressful to your fuses and transformer.
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Old 13th September 2019, 12:14 AM   #545
xrk971 is offline xrk971  United States
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The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
The NTC reduces in rush current to energize the magnetic core of the trafo. Also, as Jhofland mentioned, the bulk caps before the cap Mx need to charge up.
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Old 13th September 2019, 12:15 AM   #546
astromo is offline astromo  Australia
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Originally Posted by jhofland View Post
Perhaps I can help. Without some sort of soft start there will be significant currents required to charge the main caps in the SLB. The output of the SLB, on the other hand, does have a ramp up due to the relatively long risetime of the control voltages that are part of the of the so called capacitor multiplying circuits.
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Originally Posted by Shawnstium View Post
The components of an electronic inrush current limiter and cap Mx are very similar, however the 60,000uF of CRC filtering is before the cap Mx. If you’re using a small (<300) VA transformer you can probably get away without using a soft start method, but the current surge is still stressful to your fuses and transformer.
Got it. Thanks.

Item 7 that I quoted could go with a reword to avoid misunderstanding. Ideally a wiring overview, typical schematic for those coming in cold..
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Old 13th September 2019, 05:23 AM   #547
Dadbeh is offline Dadbeh  United States
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Originally Posted by xrk971 View Post
You can go as high as 32v, but don’t exceed it. (Maybe 2v or so above might still work, but 32v or less is guaranteed safe).
this is the excellent instructions that came with the gainclone LM3886 that I am building and it clearly says that the power supply vontage can be as high is +-42v just like I originally said, is it possible that the 32v was for the LM3875? the instructions are so detailed that it is hard to think there is a mistake there. instruction pdf file is attached.
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Old 13th September 2019, 05:51 AM   #548
Vunce is online now Vunce  United States
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The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
Dadbeh,

If you reference the Texas Instruments data sheets for the Overture amplifier series LM3875, LM3886, etc...
The absolute max voltage with input signal is +/-42v. You would never want to run these chips that high. No “extra” power, but a lot of extra heat
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Old 13th September 2019, 11:53 AM   #549
xrk971 is offline xrk971  United States
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The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
Go by manufacturer’s data sheet which says max supply (with signal present on inputs) is 84v absolute or +/-42v.

These can be run single supply with output cap, which is why they say an absolute voltage.

https://media.digikey.com/pdf/Data%2...DFs/LM3875.pdf
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Old 16th September 2019, 09:31 PM   #550
Shawnstium is offline Shawnstium  United States
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Quote:
Item 7 that I quoted could go with a reword to avoid misunderstanding. Ideally a wiring overview, typical schematic for those coming in cold..
Don't forget that input fuse too!
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