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Old 12th July 2012, 10:35 PM   #1
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Default Using “Almost-right” toroid for Armageddon Clone

Hi All –

I took a chance on an ebay purchase of a NOS Mark Levinson monster low-noise toroid transformer to build an Armageddon Clone for my venerable LP-12 turntable.

I’m trying to determine (1) can I come up with the modifications for it to work as a ‘Geddon clone?; and (2) would it make any sense to build a Valhalla-Armageddon hybrid power supply? More on this below.

The toroid specs are this:

50-60 Hz 693VA
Primary 0-100-120V/0-10-20-120V
Secondary: 72.2-0-72.2 8A

Powertronix No. AA-016633-AU rev C
P/N: 290153-6
LK 0733A

See also jpg attached. (BTW, a few of these toroids should come available from valley_supply on ebay over the next couple of weeks ).

To Q #1:
The info available online for the Armageddon Clone specifies a toroid output at 55V or so per phase. Similarly, the normal Valhalla power supply takes US 120V and takes it down to 100 volts or so (different values are given in various forums). This toroid I bought does the opposite, stepping it up to maybe 140 volts.

So my first issue is how to knock the 72 volt output (per phase) of this toroid down about 30% without causing danger, pain or noise. (Perhaps a pre-toroid step-down transformer? Or does the design of the toroid prevent this from being possible?)

To Q #2:
From what I’ve read from Vinyl Asylum/Pink Fish/DIY audio, several Linnophiles feel that the 50-hz motor option is itself superior to the so-called 60-hz motor option. If I purchase a 60-hz motor, which I don’t have, what I really get is a motor assembly modified by installing a smaller-than-normal pulley. Several have commented that they believe this reduction in pulley size introduces a relative instability to the pulley speed, degrading the sound at least slightly.

So what if I took the 50-hz, 100 V output from the Valhalla circuit, and then ran that through my ‘Gedden toroid? Would I get a workable 50-hz, 90 degree out of phase power, at a voltage low-noise floor that would work well for my turntable?

Crazy idea? Or possible crazy-but-might-be-good-crazy?

Very curious to hear what you think.

-Paul
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File Type: jpg The-madrigal-toroid.jpg (423.0 KB, 348 views)
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Old 13th July 2012, 10:23 PM   #2
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Default Many Voltages Seem OK ... Somewhat confusing.

A post on Vinyl Asylum says the Naim Armegeddon uses a 430VA toroid with an interwinding screen with a 1:93 ratio. Nominally, this gives it 120 Volts in, with a 112 volts out. On various forums I have seen reference to supplying the LP12 motor with:
1- dual 55V secondary ('Geddon build described);
2- dual 64V
3- 80V / 84V on boost circuit (to get turntable started) then drop down to 67V / 62V for low noise steady rotation for TT (DIY supply)
4- 75V / 69V (measured from Valhalla supply)
5- 85V / 90+ V (as goal when measured from Valhalla supply, says that the two legs measured together should be 160V, if less the power supply caps should be replaced);
6- 85V +/- 1V (referred to as voltage specified by Linn tech manual)
7- A "Vss voltage" of 170 to 180V, with resultant "measured" voltage expected to be around 65V.

I think first, this shows that the AC motor is capable of functioning well across a range of voltages (as the frequency of the power, not the voltage, determines the TT speed of rotation). Second, that a lot of experimentation has gone on, with different people finding different sweet spots -- with a fair degree of consistency, varying by Valhalla source or 'Gedden source. And third, I need to understand better what the variables are in all of this -- Vss vs. Volts measured? Volts measured from the power supply, with or without actual TT load? Maybe this is simple, but I don't quite get it yet.

Anyone able to help me out?
Paul
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Old 14th July 2012, 03:18 AM   #3
Zoodle is offline Zoodle  Australia
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Not directly, because you're playing with electricity, and I suspect that you aren't qualified. Because you're a man you'll carry on anyway, in which case you might find some use in the following, or not ;-)


I should preface this by mentioning that for living I restore, repair and generally 'pamper' Linn turntables (www.linnism.com) and now also Rega, plug, plug... :-)

I think that if the 60hz pulley 'disadvantage' was ruining the sound, Linn would have been called on it by now... Theoretically, I suppose a deficit in rotational accuracy is possible, although I'm not aware that anyone has done proper mythbusting on this (IE, multiple, blind A/Bs). Many theories don't survive that kind of testing, and I tend not to believe anything Linn related, unless I know its been tested using Linn's fanatical methods.

Pulley size:
With a Majik, Basik, Geddon, Geddon clone, or the thing I mention below, one MUST use the pulley size appropriate to the local mains frequency.

A 50hz pulley is an option for owners in 60hz areas provided they fit a Lingo, Valhalla, the 50hz version Hercules, or other supply that is synthing a 50hz signal. If the option is available, then I suppose I would prefer to use the larger 50hz pulley, but it's not a black and white issue. If a US customer loves what the Geddon does, then of course they should keep using it and not worry about the possible, slight disadvantage of the 60hz pulley. At the end of the day, it's the net result that counts.

At the moment, I'm using a Geddon style PS (I won't claim it's a clone). It outputs approx 55 and 59 volts ("110" volt secondary, with phase splitter). It sounds excellent to me, although the voltage is too low for most situations (IE most old motors need a bit more horse power). An older motor can have too much friction due the earlier style, spring loaded, thrust bearing. Below about 75 volts the vibration damping effect of the thrust bearing become marginal, but its friction side product can be a problem. So, removing this part can help. This friction reducing tweak is 'blessed' by Linn when, for example, fitting a "Lingo" -- which is a lower voltage PS. In fact, their first recommendation is a brand new motor because the new ones simply sound better -- although the actual outcome will vary according to how well installation is done (plenty of bent flanges out there...).

Geddon
The Naim PS outputs 85 volts per phase (approx), which is similar (slightly less) than the average Valhalla (the Linn spec quoted above is interesting because most of the Vals I've measured are 90volts or higher. Perhaps Linn changed the spec over time, perhaps after the Geddon came out :-) or perhaps there is a rise over time. Vals do seem to 'go off song' after ten or fifteen years, so perhaps the voltage does shift... Not sure what's going on there.

Back to the Geddon. 85volts is in the practical butter zone, providing low vibration, but still enough oomph to be compatible with an older, crappier motor, so that installers won't need to start fooling with it (sometimes, removing the thrust bearing leads to other problems, but I don't have time to get into that). BTW, I believe there is at least one other reason why the Geddon sounds good, aside from the voltage.

Meanwhile, Linn's "Lingo" starts the platter at high voltage then drops to a well filtered/monitored 65 volts (don't quote me on my numbers as they are only quick measurements that I took for my own amusement. The proper specs are available elsewhere). Based on the sound quality outcome, I think Linn must have turned over a lot of leaves and rocks in their search for maximum excellence(!) and although I won't comment on the price, I do think those Scotts know what they're doing -- both scientifically and musically.

That said, I've installed several Hercules PSUs (external option), and I think this is brilliant value. It's a high quality knockoff of the Linn PSUs. The fact that Edmund has accepted that Linn know their craft is reflected in the quality of his own version (which is a bit different to the Valhalla, but uses similar principles). IMO it does sound better than an average age/condition Val, and is impressively close to a Lingo.

I'm not keen on the internal fitting version of the Herc, but won't go into that here.

Last edited by Zoodle; 14th July 2012 at 03:31 AM.
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Old 14th July 2012, 02:06 PM   #4
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Default Thanks !

Zoodle, yes, very useful, thank you for your informed reply ! I now see why different voltages are being reported in different contexts – older motors vs newer, etc. This gives me a better base to work from.

And yes, I'm new to DIY, and power supply circuits are a beast I don't understand well. (I plan on being *very* cautious! )

So I take it you would recommend that I get a Linn 60-Hz motor installed as an upgrade if I move to the ‘Gedden power supply? And this itself is likely to be an improvement, compared to my stock "crappy" motor?

OK. this is good.

Can anyone comment on whether it would it be difficult to build a decent power supply around this toroid I've purchased?
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Old 17th July 2012, 08:29 PM   #5
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Not to go overboard with multiple posts if this is really not interesting, but I think the the core idea here could be very exciting !!

Here's the IDEA -- modified with more thinking plus the post I've received (and read from other forums):

1- FIRST, MODIFY an existing Valhalla circuit to produce a simple, clean 50-Hz waveform (without motor-to-PSU feedback loops and the 90 degree out-of-phase component).

2- SECOND, take this output power through the large toroid transformer to further reduce any noise in the circuit.

3- THIRD, Apply the simple 'Gedden cap + resistor circuit to generate the 90 degree phase power.

4- AND Power the TT !!

I'm thinking of the result as a very clean "fixed" power source, around 65 - 70 V. As the motor may need higher voltage to start up, add an inexpensive (if noisy) switched PSU to use just for start up, which is subsequently turned off before music is played.

The result should be a very steady, clean power source, created without the need to install a new (60-Hz) motor & pulley to the LP12.

Thoughts ??
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Old 19th July 2012, 12:48 AM   #6
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If you want an easy option, buy the Hercules. But note he uses the .22uf phase cap value which may not be the correct value for your particular motor, the one on my deck runs much more quietly with exactly 0.2uf. It is worth trying a few values.

Regarding the 50/60hz pulley. Assuming all other things to be equal, the smaller 60hz pulley will have a slightly higher run out error than the larger pulley. This is simply due to the difference in size of the pulleys and how they are shaped on a lathe which will have a constant angular runout error. I'd be very surprised if this difference was audible though.
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Old 19th July 2012, 04:55 PM   #7
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Default Actually, I'd like to build a 'Geddon

Thanks for the reply. BTW, on another thread, didn't you say that while the Hercules tested out as the best of the Ac regenerators, it still isn't as good as the 'Geddon?

I've been considering the Hercules / Mose power supply, and I've read from other posts that many or most who have tried it see it as a worthy upgrade to the stock Valhalla (though some argue refurbishing one's Valhalla first is the only way to make it a fair test).

I've also been talking with a Linn tech about installing a new motor for me, as that may be a good route to go in itself. My TT hasn't seen a tech practically since I bought it in '86. So --- I'm no longer concerned about 50 Hz vs 60 Hz on the motor ... sounds like that was a false lead.

But i do want to upgrade power supplies. I'd like to be able to compare the Valhalla to a DIY Armageddon ... but with different motors, not so easy.

In any case, I'm hoping to get some advice on building a DIY Armageddon. If this "almost right" toroid I bought is a can of worms, what's a better choice? Should I look for a toroid that's specifically built or audio, or is that overkill? Are there electrical parameters for "low noise" that I should look for? Without going for a custom built toroid, are there certain manufacturers that anyone would care to recommend ???
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Old 20th July 2012, 12:42 AM   #8
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A power supply is a power supply, any good toroid will do, a larger one will give a little more regulation/rejection but there's no need to worry about an 'audio spec' one. I do think the Geddon sounds better than the other alternatives, I'm not sure how that might translate in the US though, UK mains is rock solid for frequency. More importantly for my specific usage is that I require more torque because of the higher drag in my bearing and a big transformer does that better that all the psu's I tried.

If you are using a Premotec motor you really should run it with a little drag, it has a huge effect on linearising the rotational speed. It might be worth looking at Turntable speed analysis - pink fish media there's a lot of info there, particularly in the post from 2012 towards the end.
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Old 2nd August 2012, 10:49 PM   #9
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Thumbs up Off to the tech bench ...

Thanks to all who commented in this thread !!

I've purchased a 60 Hz motor-pulley assembly with a modded/upgraded bearing kit from a Linn aficionado I met online. When time permits, I will build a 'Geddon motor control/PSU with this toroid of mine. Then, Test it and see -- in the DIY spirit. My toroid puts out 72V so that's the voltage I'll feed to the phase circuit (which I assume doesn't change the voltage greatly). I'll build a separate circuit to supply the motor with start-up "phase adjusted" power at about 90V, then switch that over to the 'Geddon to play music.

I'll report back when it's done... I'd say, "stay tuned" but I know this is going to be months from now...

Best,

Paul B.
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Old 4th August 2012, 06:15 AM   #10
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Quote:
Originally Posted by sq225917 View Post
If you want an easy option, buy the Hercules. But note he uses the .22uf phase cap value which may not be the correct value for your particular motor, the one on my deck runs much more quietly with exactly 0.2uf. It is worth trying a few values.

Regarding the 50/60hz pulley. Assuming all other things to be equal, the smaller 60hz pulley will have a slightly higher run out error than the larger pulley. This is simply due to the difference in size of the pulleys and how they are shaped on a lathe which will have a constant angular runout error. I'd be very surprised if this difference was audible though.
I'll second the opinion that the phase capactor can be lessened compared to the default value with a decrease in motor vibration. I tuned mine by holding the motor by hand and switching cap valued to obtain the lowest vibration. Quite a noticable changes as cap values change.
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