Recommandation for 1:6 1:8 SUT under $5K?

@billstevenson 

I encourage watching the video

I did... doesn't really explain what is actually going on.  It seems the "transimpedance" term is used to indicate the input impedance is tied to and  inversely related to gain.  This is a non-traditional use of the term and doesn't help identify what the stage is actually doing while at the same time attaches an accepted term of art for a different 'trending' topology type.

Lew is correct that the one important factor in the choice of a SUT is the turns ratio and without that number, only a guess can be made about the rest based on unkown assumptions. In the case of the FRT-4 the waters are murky at best.

In the below numbers there are a few issues. 

-What is the 'X-factor'?  A clear definition is required. (assuming it is turns ratio the 2 digit precision seems odd)

-How can a 100Ω input have a 423Ω 'resultant' load?

-Why does the X factor not mathematically equate to the dB gain?  It is close with a bit of rounding but the actual dB gain will be lower than the turns ratio and this is based on the ratio of source to load impedance.

-Why do the 3Ω and 10Ω inputs see a load of ~10X the labelled impedance and the 30Ω and 100Ω only present a 4X load?

-for all practical purposes from the X and dB numbers the 10Ω and 30Ω settings are the same.  This is where the load goes from 4X to 10X but there is no clear reasoning as to why.

It's an inverse relationship, as x factor goes up, the 'resultant' impedance goes down. my SUT's 4  options

100 ohm input = 10.55 x factor (+20db) = 423 ohms 'resultant' load

30 ohm input = 18.27 x factor (+25db) = 141 ohms 'resultant' load

10 ohm input = 20.68 x factor (+26db) = 110 ohms 'resultant' load

3 ohm input = 35.84 x factor (+31db) = 37 ohms 'resultant' load

I understand the traditional Japanese approach to specifying SUTs is to label the impedances for the actual cartridge impedance and design so the load is some multiple of that.  This makes things easy from the 'basic consumer POV' but leads to confusing number salads when people try to interpret what is going on. 

The one specifications that remain fixed and should always be given in a SUT is the turns ratio (for gain and loading calculation).  The rest of the typically given numbers all rely on assumptions which are not always clearly stated or known.

dave

input designations: 3, 10, 30, 100 are for the simple minded, 

it took me quite a while until I found the actual specifics of gain that occurred at those designated positions for my FRT-4 SUT.

We want to increase a too-low signal strength

You cannot multiply a +db number

What can we multiply the signal strength by to know?

X is the symbol for Multiply

Multiply by What ____ ? How Much? what term do you use?

turns ratio is not clear to my brain

a specific number is an answer,

a FACTOR in my brain

so X Factor, the factor that you multiply by

the factor that you square

before you divide

to ascertain a result

Of Course.

Perfectly Clear

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

"and 4 optional X Factors (4 different windings thru the passive transformers)"

i.e. 4 different 'turns ratio'

4 different GAIN options

I forgot I made this 'SUT INFO' on this site

https://www.audiogon.com/systems/11318

I just used the term X Factor I found on this chart

then I made my own chart

@elliottbnewcombjr 

it took me quite a while until I found the actual specifics of gain that occurred at those designated positions for my FRT-4 SUT.

Turns ratio and gain (X??) are not the same thing and the two only match when the load impedance is infinite and the source impedance 0.  The chart you present seems to use gain, X and turns ratio as the same number which can lead to confusion.   The turns ratio is used for impedance calculations and the gain is the result of applying the related impedances to the turns ratio.

Consider the Altec Peerless 4722.  This transformer has 1:18 and 1:36 turns ratios.  If you feed it with a Denon 103 (40Ω) into a typical 47kΩ,  both turns ratios will give about the same gain (X) of around 23-24dB and not the expected 25dB (1:18) and 31dB (1:36).

The above case is extreme and using the X factor for calculating impedances will not assure accurate results.  Of further interest, in the case of the 103-4722 combo, many (including Mitch Cotter) find the 1:36 position to be better sounding than the 1:18 even though the 103 is being loaded at a value below its internal impedance.  

dave

Given the specs, how/who came up with 3/10/30/100 for the designations?

I'm sure they moved over to Sony's camera division, and continued their mission