Nad 319 Toroidal in Gedden Clone - diyAudio
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Old 12th July 2009, 11:33 PM   #1
moarti is offline moarti  United Kingdom
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Default Nad 319 Toroidal in Gedden Clone

Hi Everyone,

I'm thinking of building a Gedden clone for my newly acquired Linn LP12 and was looking into Toroidal transformers.
I have a busted NAD 319 that wont come out of protection mode and I'm not up for fixing it myself and was quoted silly money buy a local hifi repair shop to fix it. As its just collecting dust I wondered if the massive transformer could be used as part of a Gedden clone? I tried searching on the serial number but to no avail. Can anyone help me here?
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Old 13th July 2009, 06:08 AM   #2
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The geddon requires a 110VAC input Little less or more as you may vary the geddon resistor to get the right voltage output to motor. You could make some measurements and see if it can be used.
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Old 13th July 2009, 11:13 PM   #3
moarti is offline moarti  United Kingdom
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Originally posted by coolmaster
The geddon requires a 110VAC input Little less or more as you may vary the geddon resistor to get the right voltage output to motor. You could make some measurements and see if it can be used.
Thanks for the reply coolmaster
I was going to dive in with my multimeter, but I'm a computer engineer and the only experiance I've had with AC voltage was getting thrown across my room while trying to fix an old PSX! I was a bit worried about getting a shock if I tried to get the voltage from the wrong wires and wondered if any one knew the wiring?

Should have included the serial number; its TI-61244
There is another code on it : 319/1806-2160-1
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Old 14th July 2009, 04:33 AM   #4
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The Geddon does have some AC voltage there and you'd be dealing with it for certain. I reckon anyone attempting the DIY Geddon must be armed with fundamental knowledge and intermediate skill dealing with electrics.
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Old 15th July 2009, 02:03 PM   #5
moarti is offline moarti  United Kingdom
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I think I have enough knowledge to put this very simple circuit together safely if I bought the components new and therefore knew what wires went where! Thats not the problem. I want to keep costs down and thought it advantageous if I could recycle the most expensive component.
I also have an understanding of how the transformer works, I just have no idea what cables are for the primary and what are for the secondary. There are 6 wires coming out of the ring, 3 are of a heavier gauge.
I've build and Alien DAC before, POV systems for my bike, modified just about every console that I've ever had and fixed simple faults on countless devices. All these things work off of DC or have a power pack that I've not had to build from scratch. Thought it best to ask the question on a forum about an unknown component instead of just wiring it up to the mains and seeing what comes out the other end.

If I knew what wires were for each winding I think I'd be happy to build it.
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Old 19th July 2009, 07:38 PM   #6
moarti is offline moarti  United Kingdom
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Well I bit the bullet; got out my multi-meter, plugged in the NAD 319 and got in there.
I managed to get a reading on the primary (which seemed to be on 3 of the six wires, they were also heavier gauge) and got 250 VAC and 124 VAC. So good so far. I couldn't get a probe to the other three wires with the PSU board in situ, so I took it out and got a bit of a surprise! No wonder it wouldn't come out of Protect Mode! It had been butchered! I assume at someone has tried to repair the tracts on the board and made a pigs ear of it! Total mess and probably a hazard.
I didn't want to plug it in again and the board was totally goosed so I just cut the transformer out along with the power switch on the amp, wired the 250 VAC wires to the switch and then to a wall plug and the secondary coil wires to a bit of choc block. Measured the output of the secondaries and got 94 VAC. Ace! With a couple of bits I'll be able to use the transformer.
Well I was on one after that and decided to measure what the motor was getting from the existing supply. I very carefully opened the bottom of my LP12 and got my second surprise! I knew it was an old deck but the parts that made up the power supply looked ancient! There was no board. Just a piece of choc block with a large 0.22 uF cap and three other components that I couldn't read the writing on them, and that was it! I measured the output to the motor and was again surprised to find it was 112 VAC. There was a good bit of noise with just the motor running so thats probably why.
With this info I thought what the heck I'll build a supply up, just to test it out and see what happens; If the motor is getting more than 110 VAC just now it wont harm it if I give it 94 VAC. All I needed was a bit of breadboard and a couple of caps. If I liked it I'll put it in a nice box and make a nice connector, but for the moment I'd just connect it all together with choc block.
A quick cycle to Maplins and an ordeal with a spotty teenager later I had bought (very little) or salvaged (most of it) all the bits that I need.
I put them all together, measured the output again and then connected it to the Linn.
The motor struggled to get going, creaked a bit, then ran much quieter than on the original supply.
I'm listening to it just now and its definitely staying. Im not very good at describing the difference between sounds so I'm not going to try. In my opinion it sounds better so its staying. It would be nice to try and A/B test it but I don't think that there is any need. There is an audible difference in the noise coming from the motor with listening with just my ear and music is very much improved.
Just need to put it in a box The ones in Maplin were rubbish!

If anyone reading this has built a Geddon clone also; Is it worth putting a pot in to drop the voltage a bit more? The motor is struggling to get going just now - I've been told that very early LP12's had an heavier platter and that mine has one.
I cant hear the motor anymore really - is there much more to get out of this mod?

Finally, Thank you to all that have posted info on the Gedden clone, there is some great pages for this fantastic mod that's really easy after you get over the fear of getting shocked by VAC
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Old 20th July 2009, 10:02 AM   #7
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I'm guessing the LP12 creaked at startup as your transformer is supplying less than the 112VAC it was getting originally. The reduced voltage now would affect the torque and a slower startup. It'll all be ok when it revs up to 33rpm.
You see, you're already in principle using another transformer to step down and supply AV voltage to the LP12 motor. In effect its also a isolating transformer which will be a lot cleaner than direct from the mains. I reckon thats the secret to a better sounding LP12. I think I've the same LP12 as yours with the simple board with 4 capacitors. The 2 bigger caps are for phase and the other to drop the voltage to the motor winding. The smaller caps are 0.01uF across the switch terminals to suppress switching noise.
I've replaced the lot to modern ones. (I'd replace any cap thats 30 years old anyhow). Cheers mate!
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Old 30th June 2012, 11:22 AM   #8
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Which characteristic resp. feature of the toroidal core is important for a good sound quality?
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Old 30th June 2012, 04:46 PM   #9
Nanook is offline Nanook  Canada
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Default good going moarti...

...ah, the joys of DIY.

AFAIK, the "secret" to the DIY geddon is twofold:
  • isolation from the mains
  • dropping voltage to the motor.

The Thompson/ Airpax/... /Premotec motors are not what I might consider a great motor. Most of these types sound best at much lower voltage than the voltage supplied (usually 115 VAC). Someplace I read that 72VAC was the "best" but each motor varies from the norm. So perhaps dropping the voltage to say 150-175 VAC prior to the transformer would get you the quietest running motor.

For start-up you might consider feeding it 110VAC if you have access to another transformer (even a "traveler's transformer" for appliances to go from 220VAC to 110VAC , such as those sold to North Americans traveling to the UK). This can then be switched on for start-up, providing the most torque available. You should be able to use the same circuit, just switch between the 'geddon and the plug in transformer. The pug-in transformer can be noisey, but this is only used for start-up. A simple single throw, double pole switch operating from the AC can be used as long as properly spec'd (perhaps something like 220 VAC 3A, just to be safe) and mounted on the enclosure. Alternately you could make a simple voltage divider (with suitable components) and use that to go from 220 VAC (or whatever the UK is) to 110 VAC prior to the transformer in the 'geddon, rather than a traveler's transformer.

I highly suggest the inclusion of a fuse or circuit breaker for safety's sake.
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Old 1st July 2012, 08:04 AM   #10
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I've been through the whole, geddon, valhalla, hercules/mose selection process with all of them available to me at the same time and being able to measure them all electrically and the output speed from the turntable via an interesting FM speed demodulation.

The issue as best i can simply explain is that both of the electronic supplies are spoilt by back emf from the motor. Though they may have a nice stable 50hz, there is no method for trimming the phase for you exact motor and no way to trim the output voltage- and to compensate for the lack of phase trimming they both drop one phase to around 90 volts for lower noise.

While this does lower motor noise it also means that one phase is constantly having to compensate for the other, so you get underspeed/overspeed at multiples of the motor poles every single revolution. You can clearly see this on the FM speed demodulation.

In contrast the big-*** transformer isn't affected by this, so while there may be relatively trivial mains voltage fluctuation, in the UK at least, the frequency is rock solid and there's no deleterious effects from back emf.

Your motor will not require a 0.22uf capacitor, it will be slightly less or more, mine trims at 90 degrees with a 0.2uf capacitor. if you get the trimming exactly right you can use the same voltage on each leg and still have an incredibly smooth running motor. (It's not the motor at fault- it's the poor matching in use by the likes of Linn et al that creates the noise).

I run mine at 110volts on both phases and the phase offset is exactly in line with the motor. Run your motor from another motor and measure the output into a scope to find out what the phase offset should be. ;-)

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