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Graeme
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Joined: 28 Oct 2008
Posts: 1040
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 Posted: Mon Jul 26, 2010 6:36 pm Post subject: phono SUT loading |
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I know this has been covered before, but just wanted to check.
Loading SUT, this can be done on the primaries or the secondaries right?
I have to take the SUT ratio into acount yes?
Does that mean putting 10 on the primary is the same as putting 100 on the secondary? (1:10 Tx)?
Also, what about the 47k resistor in the phono stage? (wd phonoIII clone)
Do we ignore that or does that mean im already loading at 4.7k?
Im using a dl103 through dennon SUT's into the mentioned WD III clone.
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Graeme
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Joined: 28 Oct 2008
Posts: 1040
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| Posted: Mon Jul 26, 2010 8:27 pm Post subject: |
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Just found out its the square of the turns ratio.
So at the moment, with the 47k in the phono, im loading the cart at 470.
If i wanted to try primary loading at the same value then i guess i can just remove the 47k from the phono and ad 470 across the primary instead?
Just out of curiosity, what if i have no load on the primary and then take out the 47k secondary load in the phono? Will it all be fine, but probably sound bad? Just so i know how far i can mess around with things.
Can i load both sides?
If i wanted to load at say 500, can i add 30 to the primary and leave the 47k in the phono?
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Mike H
No idea why I do this anymore
Joined: 04 Oct 2008
Posts: 6596
Location: East Anglia, or Darn Sarf and then left a bit
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| Posted: Tue Jul 27, 2010 4:31 pm Post subject: |
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| Graeme wrote: | Does that mean putting 10 on the primary is the same as putting 100 on the secondary? (1:10 Tx)?
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Repeat after me .... 
| Graeme wrote: | Just found out its the square of the turns ratio.
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Oh well there you go 
I might suggest, take out the 47k's, have the secondaries act as grid bias for the first stages, and put your load resistor at the cartridge end. So it's whatever it should be for that cartridge. Seems the simplest option to me unless anyone else knows different
If they're 1:10 step-up then the impedance ratio will be 1:100. Note that will mean Miller capacitance impedance is whatever / 100 for the cartridge.
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Graeme
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Joined: 28 Oct 2008
Posts: 1040
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| Posted: Tue Jul 27, 2010 5:01 pm Post subject: |
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Thanks.
Capacitance is something im not looking at right now, but will do eventualy.
What is miller capacitance anyway?
I know i need to run the cart into a certain capacitance.
I know cables and the phono stage input has capacitance.
Ill work it out, and play with it another day.
But Miller capacitance, thats valve specific isnt it?
Is it just the capacitance of the input into the valve?
Whatever the figure is, i divide it by 100 to get the capacitance the cart is now seeing right? |
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Nick
Site Admin
Joined: 06 May 2007
Posts: 5676
Location: West Yorkshire
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| Posted: Tue Jul 27, 2010 6:41 pm Post subject: |
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http://en.wikipedia.org/wiki/Miller_effect
Its the multiplication of the capacitance seen looking into a inverting amplifier by the gain of the amplifier. The wiki article says (correctly)
Cm = Cin ( 1 - A )
Where A is the gain of the amplifier, but as its a inverting amplifier, A is negative. So if you regard the gain as a simple multiplication or the µ of a valve (say 100 for a ECC83), then
Cmiller = Cin ( 1 + µ )
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