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Old 29th August 2012, 10:38 PM   #1531
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Originally Posted by Printer2 View Post
Just took a quick look, have something to look forward to when I get home tonight. Where did you get the SMPS and the DC to DC converter?
All from China via Taobao (like eBay), but you may be able to find them elsewhere, the converter is made for "satellite TV" and the 12V SMPS is made for LED lighting.

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Old 30th August 2012, 01:50 PM   #1532
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but you may be able to find them elsewhere, the converter is made for "satellite TV"
I did quite a bit of searching and couldn't find anything like this. I also can't see why anything for Satellite TV would require 260 volts at 60 mA.

The LT3751 chip from Linear Technology will step up a low voltage into the 100 to 500 volt range regulated at up to 100 watts. Unfortunately it only comes in two tiny surface mount packages. Their "LT magazine" has the design for a 12 to 400 volt converter. I have laid out the PC board, but it is beyond my home fab capabilities. Sooner or later I will get some made.
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Old 31st August 2012, 02:20 AM   #1533
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Originally Posted by tubelab.com View Post
I did quite a bit of searching and couldn't find anything like this. I also can't see why anything for Satellite TV would require 260 volts at 60 mA.

The LT3751 chip from Linear Technology will step up a low voltage into the 100 to 500 volt range regulated at up to 100 watts. Unfortunately it only comes in two tiny surface mount packages. Their "LT magazine" has the design for a 12 to 400 volt converter. I have laid out the PC board, but it is beyond my home fab capabilities. Sooner or later I will get some made.
"satellite TV" was the literal translation from the seller's description, and you are right, why would satellite TV STB need 260V?! Or for that matter, DVD, VCD players? Here is the link for you to take a closer look of the supply, may be someone can figure out what it is designed for? Anyway, it works great for this application, the output switches do get pretty toasty, so I may add some heatsinks to them.

12v逆变万能电源 逆变器逆变板机顶盒接收机 DVD VCD逆变万能电源-淘宝网

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Old 31st August 2012, 03:35 AM   #1534
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I don't know what it's for, but I know the circuit. The TL494 is a push pull SMPS controller IC. I made a power supply using this chip about 20 years ago when I was going to college at age 40. My design converted car battery into +/- 80 volts at enough current to run about 300 watts worth of solid state audio amps. I might even still have some extra chips around here somewhere.
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Old 31st August 2012, 03:44 AM   #1535
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Originally Posted by tubelab.com View Post
I don't know what it's for, but I know the circuit. The TL494 is a push pull SMPS controller IC. I made a power supply using this chip about 20 years ago when I was going to college at age 40. My design converted car battery into +/- 80 volts at enough current to run about 300 watts worth of solid state audio amps. I might even still have some extra chips around here somewhere.
You went to college at 40? I went at 38. I was concerned being out of school so long so I asked my brother what he thought of me going back (he took the electronic technology course in his 20's). He said it is a tough course but if need be he will help me with anything, well all except the math which he forgot. Half way into the first year I gave him heck, I said the course is 90% math. He said yeah, but I will help you with the 10%.

The funny thing is eight years latter I ended up teaching the course. Came a long way.
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Old 31st August 2012, 03:08 PM   #1536
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You went to college at 40? I went at 38.
I started at age 37. Got my bachelors degree in computer engineering at 40 then started taking my time at a masters in electrical engineering at a different school which I finished at 46. I was working full time and supporting a family too.

Many engineering schools require a potential graduate to build a "senior project" or at least make an attempt before getting a diploma. NSU required two. The first was an analog design. It was supposed to be simple, like maybe a transistor amplifier stage. The instructor asked that we write a project proposal that stated the purpose of the project, its basic specs, and the measurement criteria for those specs. Our grade would be based on the compliance to our own specs and our ability to measure them. He asked each person to read their proposals to the class and a group discussion ensued. Most were simple projects with simple measurement criteria, since there was very little analog content in the entire computer engineering program.

I stated that I was going to design and build a car stereo amp and the teachers head would hit the roof of my car when I fired it up. This was 1992 and jiggowatt car stereos were not yet common. The entire class laughed, the teacher said that it was much too complicated, but we all agreed that is was acceptable. Everyone else was 20 years old and getting by with minimum effort was the norm. I was 40 when I did this, and already an engineer. It took me a lot less thinking than most of the other students. I know because I helped a lot of them. They don't teach things like soldering and oscilloscope 101.

At the end of the term the other students demonstrated their projects in the lab, then we all gathered in the parking lot for my demo. The amp had one 80 W amp for the 15 inch sub and 4 X 30 W amps for each door speaker. This was all installed in a tiny 80's vintage Dodge Omni with about 2 inches of room between the occupants head and the roof.

I put in a CD that is dead silent until the bass drum stomp followed by some screaming lead guitar. I got an "A"!

I have since stolen all the amps from the project (for guitar amps), but the case and power supply remains somewhere. I could rewind the secondary of the transformer, but it is far too big for this application. I need to dig it up and figure out what I did, making circuits smaller (electrically) is usually far easier than making them bigger.

The TL494 is still available in DIP and SOIC for easy breadboarding. SMPS circuits don't like flying wires on perf board though, a well thought out PCB is usually needed.

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The funny thing is eight years latter I ended up teaching the course.
I had a "discussion" with one of the teachers in my masters program. The class was TV systems engineering, and the teacher had no clue how a modern NTSC TV worked (this was 15 years before DTV). I wound up taking over the class, which wandered into the details of syncronization and just what information was hidden in the vertical blanking interval or AM modulated on the FM sound carrier. These details were needed to put a "broken" cable TV signal back together. I never saw so many people taking notes in class.
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Old 31st August 2012, 04:51 PM   #1537
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Just taught for one term but the students appreciated that I spent 20 years in plants (years just operating production equipment and 5 as a tech) and had real world examples to back up the theory. The college decided to put some engineers that only designed electronics (good teachers for electronics though) to teach an industrial controls course (none of them set foot on a shop floor). One course we teach is on valves, when taking over the course the instructors wanted to know why it was necessary (why teach mechanical technology, the stuff the electronics mates to). I was to put my teaching aspirations away and get them up to speed on how to teach the course, good enough to teach the instructors but not to be made one myself, only a Technologist, not an Engineer. I went back into industry instead. The students were really pissed.

On a guitar related note I wanted to see what all the fuss was about with the volume control interaction with the Fender 5E3 Deluxe. Took some 1M pots and subbed a 51k resistor for the tubes, one channel not driven, the other with a 10V supply as the signal. The pots were duals and I used one half of it across an ohm meter in order to rotate the pots to the exact spot in my tests, originally used a the numbers on a Fender skirted knob to determine the amount of rotation.

Click the image to open in full size.

The left axis is 1000k full scale and 10V, the bottom is rotation in knob numbers. The two plots close together is the resistance of either side of the pot. The top trace is with the driven side at full rotation (amp channel on 10) with the un-driven channel stepped through its range. The black dashed like is the driven channel's output with the other channel at zero (basically a 1M resistor across the driven channel). The blue trace is with the un-driven channel at '10' while stepping through the numbers with the driven channel.

As can be seen the big complaint with the 5E3 is that most of the volume change is in the first quarter of rotation and then not much else. I am surprised the loading of the second pot full up did not drop the output even more. Not sure what would happen with real tubes in place of the 51k resistors, just not set up to breadboard the circuit right now so I did this quickie circuit. Maybe in winter I will give it a go.
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Old 4th September 2012, 11:17 PM   #1538
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When you are all done compare it to a 10-30 watt Toa amp from ebay like the BG series. You can pick em up for well under $75. No tubes in there but I'd be surprised if it doesn't beat the home built units described here. I know I strayed off the topic a little.....sorry
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Old 5th September 2012, 01:16 AM   #1539
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Originally Posted by cjkersh View Post
When you are all done compare it to a 10-30 watt Toa amp from ebay like the BG series. You can pick em up for well under $75. No tubes in there but I'd be surprised if it doesn't beat the home built units described here. I know I strayed off the topic a little.....sorry
You do realize these are guitar amps don't you?
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Old 5th September 2012, 03:21 AM   #1540
cjkersh is offline cjkersh  United States
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Yep I got that, and I'm familar with good guitar and keyboard amps. I'd really like to see the comparison. The Toa is a general purpose commercial amp not really designed for a guitar amp per se, but I'd love to hear the comparison. DIY on a shoestring vs an inexpensive good quality redily avalable amp. I've used them for small keyboard and guitar setups in a pinch and have been plesently suprised. Just basic treb. bass controls no effects....
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