Armageddon clone for LP12 - why such a large transformer? - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th December 2012, 10:18 AM   #1
diyAudio Member
 
Join Date: Oct 2005
Default Armageddon clone for LP12 - why such a large transformer?

Very probably missing something basic, so please put me right.

The Armageddon is basically a big transformer with 110v secondary (or dual 55v) with large series R (3.3k) between one motor connection and the transformer secondary. There is also a 0.2uf phase shift cap connected to the motor side of the 3.3k resistor and third motor connection.

It seems to be taken for granted that the transformer needs to be 400VA or so. When I do the sums I can't see how more than 33mA could ever be pulled, which would suggest that the transformer could be 3.6VA and do th job.

It's often stated that the low impedance of the 400VA transformer is the reason it is required, but I can't see how this matters given the large series R.

Ultimately, I have a 65VA transformer with suitable secondaries and want to know if this could be used without significantly compromising the result.

Many thanks in advance.

Armageddon Clone
  Reply With Quote
Old 15th December 2012, 10:24 AM   #2
freax is offline freax  Australia
diyAudio Member
 
freax's Avatar
 
Join Date: Sep 2007
Location: NSW
I can think of only one good reason, voltage regulation.

Aside from that, prevention of theft.

I cannot imagine a huge transformer like that being too good on the motor, especially if its hooked up as the schematic is designed, I bet that 3.3k ohm 3 watt resistor limits that.

Quote:
the red letters refer to the photos of my circuit below. This is basically the same as the other circuit, but with a switch to drop the resistance for initial start up of the turntable, and a variable resistor to allow me to increase the resistance to drop the voltage down as much as possible to minimise motor vibration. X and Y are the where the red and blue wires attach - Z is the connection for the two grey wires.
Wow

Be careful or that could actually create hum/vibration by reducing the voltage going to the motor.
__________________
"It seems that perfection is reached not when there is nothing left to add, but when there is nothing left to take away" - Antoine de Saint Exupéry

Last edited by freax; 15th December 2012 at 10:40 AM.
  Reply With Quote
Old 15th December 2012, 02:35 PM   #3
diyAudio Member
 
Join Date: Jun 2004
Location: sheffield
Send a message via MSN to sq225917
Regulation, regulation, regulation.
__________________
hoping to pick up some things.
  Reply With Quote
Old 15th December 2012, 02:43 PM   #4
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
Here is an idea - build (breadboard, do a case for it later) the circuit with your transformer. If the basic sonic signature appeals to you then pursue it with the bigger trafo. TT PSU do make a diference and you might find that you don't like it vs. what you have.

I have never regretted breadboarding a project. Even if it works perfectly from the start. I have regretted completing projects whole-hog in the beginning that needed a bunch of modifications and tweaks later to get it working properly.


Quote:
Originally Posted by freax
Be careful or that could actually create hum/vibration by reducing the voltage going to the motor.
One of the design points of the Armageddon is that the motor worked on a reduced voltage, in theory to reduce the strength of the synchronous pulses. That said, your point is very valid.

Last edited by 6L6; 15th December 2012 at 02:45 PM.
  Reply With Quote
Old 15th December 2012, 03:23 PM   #5
diyAudio Member
 
Join Date: Jun 2004
Location: sheffield
Send a message via MSN to sq225917
The Geddon works on quite a high voltage compared to most other LP12 psu's, the lowered voltage on the 2nd rail is to reduce the effects of cogging. But all is does in reality is alter the frequency of the inherent speed instability.The best way to reduce the noise from cogging is to increase the load on the motor so that the magnetic field in the motor collapses, damping the cogging effects to next to nothing.

Try it for youself, hold the motor in your hand and let it free spin, now lay a finger tip on the top of the pulley to add some drag and feel how much smoother it runs....

Now figure out how to do that in your deck.
__________________
hoping to pick up some things.
  Reply With Quote
Old 15th December 2012, 04:15 PM   #6
diyAudio Member
 
Join Date: Oct 2005
Thanks all.

As 6L6 recommends I'll use the tx I've got and see whether I like the results.

I appreciate that a bigger tx will have better voltage regulation, but must admit that given the very small loads involved I don't understand why this would be so critical. I probably just don't fully understand :-)

I should have mentioned that I'll be using an EI type rather than toroidal. I thought EI types offered better isolation from HF noise, although I could also see bandwidth limitation skewing the sign wave, so not sure how much of a compromise this will be.

Time for an experiment!
  Reply With Quote
Old 16th December 2012, 05:05 AM   #7
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
Any (fantastically minute) waveform skewing due to bandwith limits of an EI will be practically unmeasurable after the series resistor. And this is going to be operating at mains frequency, which is exactly what the transformer is made for.

I would actually prefer the EI in this case as it will not couple all the HF crap that lay on the mains these days.

  Reply With Quote
Old 16th December 2012, 10:53 PM   #8
diyAudio Member
 
Join Date: Jun 2004
Location: sheffield
Send a message via MSN to sq225917
Click the image to open in full size.

There's no substitute for having built a few of the damn things.
__________________
hoping to pick up some things.
  Reply With Quote
Old 18th December 2012, 05:31 PM   #9
argibbo is offline argibbo  United Kingdom
diyAudio Member
 
Join Date: Aug 2010
To my mind it's not critical, it's just a way of selling you an un-necessarily large transformer. A while back my Valhalla board packed up and I found the original mains frequency locked circuit, dead simple, on a forum. As a temporary measure I built the circuit and the motor ran beautifully. Several years on, my Sondek is still running on the original circuit. The Valhalla board is still awaiting repair, when I get round to it. There's no damn difference at all! If they sell you £400 worth of upgrade, when you've paid £400 then by the simple power of suggestion you'll hear £400's worth of difference. Peter Belt made a living out of this sort of 'psychoacoustics'

Meanwhile, there's a whole shed load of tricks, based on simple engineering logic, you can do to the Sondek to improve it without spending anything more than DIY money.

Best of luck. Andy
  Reply With Quote
Old 18th December 2012, 06:52 PM   #10
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

Its that big just to make sure the box you buy seems heavy
enough to be worth the silly price your paying for what is inside.

rgds, sreten.

The transformer is simply the same size as one of Naims Flatcaps.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Using “Almost-right” toroid for Armageddon Clone truepaul Analogue Source 14 15th August 2012 01:34 AM
Using a large 60hz toroid transformer as an SMPS transformer EWorkshop1708 Power Supplies 20 22nd June 2011 08:05 PM
Large one to one transformer available tjencks Swap Meet 0 7th April 2011 09:45 AM
Kove Armageddon 15" 1050rms gadgeteer123 Swap Meet 1 25th December 2009 04:09 PM
Transformer: How large? sangram Solid State 22 15th January 2003 04:58 PM


New To Site? Need Help?

All times are GMT. The time now is 02:16 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2