Entre' ET-100 SUT

It is confusing, I learned from others here first, then subsequent research.

I also have a TT with 3 Tonearms, multiple cartridges

 

I often see the ET-100 listed for sale, and have not crossed path with detailed info. You might ask seller’s if they have a spec sheet they could take a photo of.

I chose a Fidelity Research FRT-4, very similar to the ET-100, usually costs a bit more. It is totally quiet.

It has 3 front selectable inputs, PASS for MM, and 4 settings for MC Low Outputs needing signal boost:

3/10/30/100 ohms. Respective X Factors: 35.84/20.68/18.27/10.55

others are listed, this one looks darn good

 

FRT-4 has a captive phono cable out, sounds great, sometimes I think about having Steve or Ray at VAS change it to RCA out, to use a ’better’ or shorter cable, but that’s just because I’ve run out of things to change, no need.

...............................................

My notes from original research list, a few I never investigated

Andros, Allasso: 4 low x factors: 4/6/8/12: (multiple arm inputs?)

EAR MC4: 4 x factors 10/18/24/30 (multiple arm inputs?)

EAR MC3: 3 x factors 10/20/30 (multiple arm inputs?)

a scribble ’cinemac 36,18,12,9 ????

Thanks, Elliot (I assume),

 

I saw the FR4, but was hoping to spend less.  A possibility, though.

 

So just to confirm, by "X factor" you the number times which the cartridge voltage output is multiplied through that setting?

 

Richard

"you mean", I mean.

Elliott is correct, and yes, x factor x cartridge signal strength = resultant signal strength out of the SUT into the MM phono stage (allow for a bit of loss).

use X factor squared to calculate what ’resultant’ impedance that will be shown to the phono stage:

say x factor 20 i.e. xfsq 400.

typical phono input 47k (not all).

47,000 divided by xfsq 400: impedance ’shown’ out of the SUT to the phono stage will be 117.5 ohms

guidance for ’shown’ impedance is cartridge impedance x 10.

my at33ptg?II is .3mv and 10 ohms impedance. So, I’m looking for enough/not too much signal strength and resultant ’shown’ impedance of around 100 or higher.

FRT-4’s 10 ohm input is x factor 20.68. that gives me signal strength of 6.3mv (remember to deduct some loss) and ’shown’ impedance of 110. Nice combo!

Some cartridges signal strength and impedance are difficult, a phono stage with individual gain settings and individual impedance settings may be needed.

 

My approach is: (below #s using typical phono stage 47k, verify yours)

a. find 'shown' impedance' goal ____?

b. use 'shown' goal ____ to select x factor range ______

i.e. 47,000/___ goal = xf sq. (square root of xf sq = ____ x factor)

c. that x factor: ____? enough/not too much signal strength?

(your phono stage has 'sensitivity': minimum/maximum .if you can find it.

......................................

Nothing works? SUT with Individual Gain and Individual Impedance Needed!!!

....................................................

1. formula: impedance 'shown' to MM Phono input = 47,000 divided by xfsq

(your phono stage 50k, then 50,000 divided by xfsq)

(i.e. x factor 24 xfsq = 576. 47,000 / 576 = 'shown' impedance 82)

2. formula/guidance: cartridge impedance ____ x 10 = ____ 'shown' GOAL. a bit below, above is ok, just a goal.

3. knowing that, what range of x factors is close to the desired answer?

 

.................................................

found examples for SUT X Factors (assumes MM input 47k)

(MM Phono Stage has subsequent additional signal boost and RIAA EQ)

ROUND NUMBERS

+32db = xf 40 = 1600 xfsq = 29  'shown' impedance 

+30db = xf 30 = 900 xfsq = 52 'shown'

+28db  = xf 24 = 576 xfsq = 82 'shown'

+26db = xf 20 = 400 xfsq = 118 'shown'

+25db = xf 18 = 324 xfsq = 145 'shown'

+24db

+22db = xf 12 = 144 xfsq = 326 'shown'

+20db = xf 10 = 100 xfsq  = 470 'shown

+18db = xf 8  = 64 xfsq = 734 shown

+16db = xf 6

+14db

+12db = xf 4