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Revisiting some "old" ideas from 1970's - IPS, OPS
Revisiting some "old" ideas from 1970's - IPS, OPS
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Old 1st February 2017, 11:20 AM   #1831
jwilhelm is online now jwilhelm  Canada
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Quote:
Originally Posted by AndrewT View Post
the fuse rating for inductive loads like motors and transformers is 3times the maximum operational current.
A 230VA 230Vac transformer has a maximum operational current of 1Aac.

The fuse for starting that transformer would be a 3A fuse.
A close rated fuse would be a 1A fuse.
You might find that the 230VA transformer will start up repeatedly over many years on a 2.5A fuse.
Try a 2A fuse and you will probably find it fails within a few weeks, or months.
Try a 1.25A fuse and it may start once, or twice and then it fails.
Try it.

For domestic audio power amplifiers and the way they demand current from the mains transformer, I find I can reduce the close rated fuse considerably (when I don't have the correct fuse rating in stock) and it can operate upto clipping with very loud music and the undersized fuse does not blow.
It's down to averaging of the current flows and what heating they generate in the fuse wire.
I agree with what you are saying about being able to run a lower rated fuse on the inlet. I just go by industry standards. Here the standard is 125% and slow blow fuses. I use Antek transformers normally and if you look at their test criteria (and if you can believe it), 125% of input current isn't an issue at all. We are on 120VAC here, so our current is double what you are accustomed to. This actually works out in our favour for selecting appropriate fusing availability wise.
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Old 1st February 2017, 11:27 AM   #1832
jwilhelm is online now jwilhelm  Canada
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Originally Posted by AndrewT View Post
A 3phase motor will operate reliably including start up, on far lower fuses than 3times.
Single phase motors are hard on fuses.
Three phase (600V) is what I'm normally dealing with here, but even for single phase we normally calculate 125% of FLA of the motor. Our standard practice is also to never run a motor at FLA too. You learn a whole new respect for grounding practices with 347V mains voltage present also.
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Old 1st February 2017, 10:04 PM   #1833
evanc is offline evanc  United States
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Revisiting some "old" ideas from 1970's - IPS, OPS
Jeff, I gather from your post that it would be better if I connected both the heatsink and the supply ground to earth. Easily done. I would guess that since the amps I am using have the audio ground connected through opposing diodes and a resistor that a simple wire from supply ground and heatsink to the ground wire from the power inlet would be OK.
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Old 1st February 2017, 10:12 PM   #1834
jwilhelm is online now jwilhelm  Canada
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Any exposed metal (heat sink) should be connected directly to earth ground with 14AWG wire. The supply/main audio ground should be connected to earth ground through a loop breaker. This will keep the supply ground fairly close to earth ground potential, while still minimizing the chance of ground loops. I normally use a 30 amp bridge for a loop breaker with no noise.
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Old 1st February 2017, 10:13 PM   #1835
evanc is offline evanc  United States
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Revisiting some "old" ideas from 1970's - IPS, OPS
Will do...
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Old 2nd February 2017, 08:58 PM   #1836
Ampi is offline Ampi  Germany
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Do you use a 30 amp rectifier bridge as loop breaker?
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Old 2nd February 2017, 09:02 PM   #1837
jwilhelm is online now jwilhelm  Canada
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Originally Posted by Ampi View Post
Do you use a 30 amp rectifier bridge as loop breaker?
Yes. The 30 amp bridge is pretty standard for a loop breaker.
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Old 16th February 2017, 02:25 PM   #1838
vzaichenko is offline vzaichenko  Russian Federation
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Revisiting some "old" ideas from 1970's - IPS, OPS
Arrow In memoriam of and inspired by the good old Sansui BA-3000

In general, I'm not a big fan of so called "blameless" topology, considering it sort of "too classic", thinking of something more "interesting", like current drive, feed-forward, etc.
However, there are some amplifiers, being a kind of a benchmark of their time. For me, one of such products is Sansui BA-3000 - a deliciously sounding bulky device, introduced in 1976, I was lucky to come across in the beginning of 80'-es. It was a real High Fidelity experience. So, I decided to play with its model, based on the modern active devices, introducing a few mods, mostly aimed to achieve very clean clipping behavior.

The model actually performed even better than I expected. Low distortion, very good profile (mostly H2 + some H3), excellent stability margins. It's definitely not the fastest one, however around 45V/uS slew rate is fine, bearing in mind all the other qualities - highly accurate clipping, symmetric rise/fall time, low noise, rather high power (200+W @ 8 ohm with +/-70V rails). Very low (among the most of my designs) ULGF = 520KHz, that still does not harm - overall "speed" of the circuit is fine.

The design is rather simple, easy to layout on a single side board for etching (slowly working on it). So, I consider it as a good DIY project.

I plan to split the whole thing in 2 boards, just kind of the same way the original BA-3000 is arranged (output devices are placed on the separate board), allowing the driver board to be placed a little bit away from the heatsink.

Hi-res schematic is attached in PDF.
I can also share a Diptrace file if somebody is interested to come up with alternative layout.

Isn't it cool?
Attached Images
File Type: jpg 00 BA-3000 04.jpg (51.8 KB, 712 views)
File Type: jpg 01 Tribute-3000 Sch.JPG (148.9 KB, 721 views)
File Type: jpg 03 Feedback loop analysis.JPG (93.9 KB, 694 views)
Attached Files
File Type: pdf 01 Tribute-3000 Sch.pdf (71.0 KB, 206 views)
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Old 16th February 2017, 02:49 PM   #1839
padamiecki is offline padamiecki  Poland
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Dear Valery!
Cool, indeed, why not NS OPS?
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Old 16th February 2017, 03:09 PM   #1840
vzaichenko is offline vzaichenko  Russian Federation
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Revisiting some "old" ideas from 1970's - IPS, OPS
Hi Pawel, it will perform even better with NS-OPS, however, even as is it's going to be very good - much simpler though
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