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Old 7th July 2008, 10:35 PM   #11
Jaimo is offline Jaimo  Canada
diyAudio Member
Join Date: Oct 2005
Default 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?
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Old 7th July 2008, 10:45 PM   #12
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Join Date: Feb 2006
Location: Willy, VIC
Click the image to open in full size.

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.
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Old 22nd August 2008, 02:31 AM   #13
Jaimo is offline Jaimo  Canada
diyAudio Member
Join Date: Oct 2005
Default 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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Old 23rd August 2008, 12:16 PM   #14
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