Dr. Imbabi’s DIY Power Supply?

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GlidingDutchman

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Joined 2007
#1
Hi there

Dr. Imbabi’s DIY Power Supply?

I searched all over for a link to this PSU and the only one I found here is a dud!

Anybody have the schematic or a live link to it?

I am looking into building a similar PSU but would like to check it out.

It is for a Lenco L75 turntable (with a shaded pole motor)

T-I-A

D
 
#4
GlidingDutchman said:
Cromodora - you've got mail... 🙂


What do you think of this?

http://www.norre.dk/TTPSU/TTPSU.html#Downloads|outline

D
Click to expand...

Interesting design, one concern is the issue with distortion of the output sine, I am not sure whether that is actually an issue or not, but I would probably replace the first order LPF with a 2nd or 3rd order filter if I were concerned.
 
#5
kevinkr said:


Interesting design, one concern is the issue with distortion of the output sine, I am not sure whether that is actually an issue or not, but I would probably replace the first order LPF with a 2nd or 3rd order filter if I were concerned.
Click to expand...

Hi Kevin

Distortion is not really an issue here - as long as the output signal is an appoximate sine wave with a stable frequency.

I wonder if there is simpler crystal oscillator diagrams somewhere without a complicated PIC and display...

D
 
#6
Distortion is most definitely an issue but this approach delivers reasonably low distortion. A few years ago i did a very similar exercise using a 90S8515 and measured a second and third harmonic within 0.1%, pretty much on par with a good Wien bridge. I used a proper 8-bit dac but accurate resistors are probably fine. Reshaping a square wave is not likely to produce similarly low distortion.

A Wien bridge is certainly a great 5-minute solution, perfect if you don't need fine tuning or two phases.
 
#7
analog_sa said:
Distortion is most definitely an issue but this approach delivers reasonably low distortion. A few years ago i did a very similar exercise using a 90S8515 and measured a second and third harmonic within 0.1%, pretty much on par with a good Wien bridge. I used a proper 8-bit dac but accurate resistors are probably fine. Reshaping a square wave is not likely to produce similarly low distortion.

A Wien bridge is certainly a great 5-minute solution, perfect if you don't need fine tuning or two phases.
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Ja - an issue but not that big an issue... you're not going to pump music throught the thing... he-he!

Man - I am looking for a single phase VFO that enables you to set two seperate freqs for 33.3 and 45 rpm but still allow fine tuning of about +/-20%. Two fine tune pots plus a toggle-sw between the speeds. Thats all - no need for a display... one can check the speed with a strobe on the platter.

Wien-bridge is allright but isnt there a "digital" solution? Will certainly be the only digital in my analogue front-end - he-he!

D
 
#8
GlidingDutchman said:


Ja - an issue but not that big an issue... you're not going to pump music throught the thing... he-he!

Man - I am looking for a single phase VFO that enables you to set two seperate freqs for 33.3 and 45 rpm but still allow fine tuning of about +/-20%. Two fine tune pots plus a toggle-sw between the speeds. Thats all - no need for a display... one can check the speed with a strobe on the platter.

Wien-bridge is allright but isnt there a "digital" solution? Will certainly be the only digital in my analogue front-end - he-he!

D
Click to expand...

The way i see it the main point of aftermarket AC power supplies is the low distortion. At least in synchronous motors it obviously affects the vibration of the motor and the sound. Even with a Garrard induction motor i hear obvious difference in sound depending upon the oscillator quality. But then again i also clearly hear the mains cable to the motor...


A simple digital solution (no micros) won't have easy trimpots. And it will definitely generate a lot of RF noise which will have to be filtered or else will mess with the rest of your system. A micro is the easiest way, especially if you are just repeating an existing design. Even easier is to buy one of Mark Kelly's boards and just solder the parts. I hear they are excellent.

A Wien bridge can do all that you require. Why complicate things?
 
#11
An alternate solution

I am considering the following solution for my Garrard 301 psu.

1. Generate a 30 minute 50Hz wav file using Audacity. (16 bit 44.1kHz, about 2.5MB)

2. Load the wav file into a $20 mp3 player.

3. Use the MP3 player output to drive an old Rotel RB990bx power amp.

4. Take the output from the Rotel into a step up transformer.

The MP3 volume control will adjust the output voltage and it is possible to create other wav files to do a speed change.

This looks like simplicity itself! (Almost too good to be true) My only concern id that the input resistance of the transformer is about .5 ohms and will most likely cause the Rotel to blow it's fuses. I plan on adding a series resistance to the transformer input and will fire this up tonight.

Any comments before I smoke the Rotel?

Else I will report back tomorrow

Wat se jy Mnr Flying Dutchman?
 
#12
An externally hosted image should be here but it was not working when we last tested it.


You'll probably need a linear pot on the output of the MP3 player, the internal digital volume control is a bit crude to get the voltage dialled in.

You will also need to add a Zobel to the output of the amp. Try 10 ohms / 47 uF as a starting point.

If you use a T amp instead of the Rotel you can get away without the Zobel.

Toroidal step-ups appear to have far less problems than EI laminations, probably due to the lower magnetisation currents.
 
#13
Rotel won't do the trick

Thanks for the t-amp tip Mark.

The Rotel amp works for about 20 mins & runs extremely hot before it's protection steps in.

I took a look around and can't find a T-amp that will give me the required 20Watts - whick T-amp are you using?
 
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