CHanging resistors...... is it me? probably.

[elharvo]

So, I keep hearing that the optimal loading for my Denon 103r is 100ohms.... from my limited understanding, the Eros comes factory set with 47k ohm resistors. I removed 'em, and popped in some 100ohm resistors in their place, eager to hear just how much better my beloved soundsmith modded 103r could sound! First thing I noticed was dead silent , and I mean DEAD silent background.... exciting!
I drop the needle and.... more dead silence! I swapped the 100's for 300's, again, nothing... nothing at all! When I pop the 47k's back in, all is well again!
 For some reason, the thing just won't come out to play with the 100 ohm or 300 ohm resistors in place. When the 47k's are in place it works just fine.
 Am I doing something wrong?
 Btw, I'm using the cap'n bob's cinemag SUT with the Denon.
 Any help would be greatly appreciated, as I am very new to all of this!
This eros is my first ever build.
Thanks, Harv.

[Paul Joppa]

The SUT converts impedance, by the turns ratio squared. If it's a 10:1 step up, then the impedance conversion is 100 times, and 100 ohms on the secondary of the SUT (at the Eros input) is 1 ohm to the cartridge - basically a short circuit.

The best way to do this is to put the 100 ohms at the input to the SUT. This assumes the transformer is designed for a 47K load. Transformers give their best performance with the load for which they are designed. (Of course, the best measured performance is not always the best sound, but it's a good reference starting point.)

If you can identify the specific transformer and its specs, we can be more precise - Cinemag makes many transformers!

[Grainger49]

Look up the specs for your specific cinemag SUT.  Post back the input side impedance and we can tell you what to parallel to achieve 100 ohms.

The cinemag is set up to drive a standard 47k ohm phono stage input resistance.

[elharvo]

Well, I went to the SUT builder's site, and lo and behold, the specs for the cm qee 3440A are:
'Into a standard 47k phono preamp, the effective input impedance of the low gain (1:16 ratio) is  184 ohms.  At 1:30, the effective input impedance is 52 ohms. 

Note:  The 150 Ohm tap and the 37.5 ohm taps are specified by the manufacturer to provide 1:18 and 1:36.5, however 1:16 and 1:30 was measured using a 50 ohm audio signal generator at 1kHz with a 47k output resistance, which approximates the real situation of a moving coil cartridge load using this transformer into a standard RIAA preamplifier.'

It turns out I was fiddling around when I didn't need to!
 Thanks guys, I'll investigate a bit more prior to posting my next silly question.
cheers.

[Grainger49]

If you parallel a [Edit:] 10 300 ohm resistor, a good $4 or even a really good $7 resistor, with the inputs of the SUT you will bring the input impedance down to 100 ohms.  But I think that the 150 ohms is pretty close.

[Paul Joppa]

If you parallel a 10 ohm resistor, a good $4 or even a really good $7 resistor, with the inputs of the SUT you will bring the input impedance down to 100 ohms.  But I think that the 150 ohms is pretty close.

That should be 300, not 10. You knew that.  :^)

[Grainger49]

Nope, my algebra just stinks.  I wrote the formula down wrong!  But should have known better than that value.  I edited to get out the bad info.

[milosz]

I have a Dynavector 10x5 in Rega Planar 3, nice sound.

Also have a Shure V15 MK III in a late 1980's Dual belt-drive 'table.  Doesn't sound great.  However, using a tube phono stage with this older setup makes quite an improvement.