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Old 5th March 2007, 03:42 PM   #1
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Default Garrard 401 PSU

[edit: new link as old one is dead]

http://members.rennlist.org/lt_texan...owerSupply.pdf

[/edit]

I don’t know if this is the right forum, but here goes:

I’m in the UK and I’ve purchased a Garrard 401 turntable. It is a UK model, so it runs on 240VAC/50Hz.

But it looks like I might need to use this in the US, so I need to convert 115VAC/60 cycles to the UK standard.

I found Dr. Imbabi’s DIY power supply that fits the bill:

http://www.eng.abdn.ac.uk/~eng289/401/401ps.jpg

I figure mains transformers with 115/230 primaries will get me what I want.

Does anyone have experience with this design? I can’t find anything in these archives (except a reference to the above site).

I also don’t understand a couple things, so I’ll toss these out and see if I get a bite:

1. Any ideas on what capacitance should be on each of the “back to back” caps at the output of the LM3886?
2. T1 and T3 rectification looks drawn to be full wave with centre taps to ground, but the voltages calculate as if it is bridge rectification (where CT would not go to ground).

BTW, I know I can convert the 401 to run on 115VAC/60cycles, but I would have to:
1. buy a new motor pulley
2. buy a new strobe lamp
3. buy a new turntable platter (yikes!)
Bet the psu is cheaper, and then I have clean power too.

Thanks much in advance,
Dan

Last edited by lt_texan; 28th September 2012 at 01:15 PM.
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Old 5th March 2007, 05:02 PM   #2
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Build it. The 401 sounds a lot better run off this PS than the wall.

1. Probably around a 1000uF. I never saw much point including these caps - the 3886 has negligible offset and really doesn't mind working into a very low dc load.

2. I don't understand your point. It is centretapped as both opamp and 3886 need a bipolar supply.


I played with this circuit almost 10 years ago so memory is a bit sketchy. The oscillator produced lower distortion with a better opamp; i think i measured about 0.05% with a 5534 after fine tuning. The biggest contributor to distortion was the step-up transformer.

You need a decent heatsink on the 3886 - it gets quite hot, probably due to the inductive load.
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Old 6th March 2007, 07:15 AM   #3
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Dan,

I've build this desig, but deviated a bit.

The parts around the LM3886 are basically a gainclone. If you look in the chip-amp forum you'll find a lot of info. I've build that part it according to
http://dogbreath.de/Chipamps/GainCar...nCardCopy.html

These pages give very clear instructions.

I used an old switchmode power supply which i ripped out of a broken dvd player as the ps for the opamp. As opamp I used the ne5534. (cheap and good).

For R* I used little pots, so I could vary the frequency so that my turntable (Thorens TD160) runs at exactly the right speed (I think the frequency needed for this was 47 Hz).

Be sure to check that the waveform produced is a nice sine. Use an oscillioscoop or the soundcard of your computer (that's what I did). The produced waveform depends on setting of all 3 pots.

The pot which is in the diagram is used to let the thing oscillate right. If you put it to low it won't oscillate, to high and the wave get's distorted.

The other two pots (R*) determine frequency, but if you set them to different values you'll distort the wave form (the setting is not too critical).

As you need only very small adjustments for R* you'll have to find appropriate series and parallel resistors to get a nice set up. You can calculate these from the given formulas.

succes, MArco
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Old 6th March 2007, 07:27 AM   #4
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And obviously a regenerator allows you to run the motor at a voltage, lower than the nominal. There is a fine line between getting a poor torque characteristic and low vibration but it's worth the effort to experiment.
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Old 6th March 2007, 08:35 AM   #5
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Thanks much for the responses and the advice.

On the psu, I think I am confused as to taking a secondary centre tap to ground.

I took a look at my copy of Morgan Jones and saw his example of a ďtypicalĒ transistor amp power supply. This used 8 diodes across 2 bridges.

I attach a picture.

Also I see the one on the dogbreath site. One bridge.

I expect both will work.

Also, looks like Iíve now got the excuse to get an oscilloscope

Dan
Attached Files
File Type: pdf bipolar_psu.pdf (55.0 KB, 164 views)
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Old 6th March 2007, 09:53 AM   #6
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Quote:
Also, looks like Iíve now got the excuse to get an oscilloscope

Or a soundcard It will cope perfectly well with 50Hz. And 60. And let you see lots of harmonics.
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Old 6th March 2007, 10:29 AM   #7
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I'd use a soundcard, because you then also assess the wow and flutter when you digitize sine waves from a test record.

In
New power supply

you'll find how I distilled the wow and flutter signal from a soundcard recording.

In that thread you'll find more info on a PSU for your turntable.

succes, MArco
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Old 6th March 2007, 10:40 AM   #8
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okay, a soundcard

thx again
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Old 6th March 2007, 11:13 AM   #9
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Talk to Martin Bastin and have a 60Hz pulley made; the motor in a 301 or 401 runs better from 60Hz. Build a 60Hz supply if you like, but use a 50Hz strobe light on your 50Hz platter. If you're really keen, replace the neon with rectangular LEDs driven from your 50Hz strobe light.
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Old 7th March 2007, 02:12 PM   #10
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okay, driving the motor with 60Hz makes sense to me.

But to build a second power supply for a 50Hz strobe sounds like a pain.

Would a 5534 provide enough grunt to drive the LED? Would I need a higher power amplifier to drive a setup xformer for the neon lamp.

Sorry, but one more question on Imbabi's design - what rating in necessary on the 12-0-12 xformer for the oscillator? I'm thinking real small. I found a 6 watt in RS. (Maybe that's enought to drive two 5534's - one 50Hz, another 60Hz?)

thanks,
Dan
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