[SteveRB]

Hello,

i'm starting my Bugle project soon and have done some research for the modifications i need to match it to my Denon 103 with AU-250 Step up transformer. I will be using the stock gain of 40dB and the step up transformer which has 10:1 gain ratio to boost the signal to 3.0 mV.

However, i cannot figure out what the resistor values for R16 and R34 need to be.

The step-up has an amplification ratio of 10; therefore, has a natural impedance and load impedance of 470 ohms with the Bugle. How does this all relate, and how do i match up the system.

A little clarification would be awesome, thanks...

[SteveRB]

just working through some numbers -- i hope this makes sense:

the load resistance of the bugle is 47000 ohms, so with the natural impedance and the load impedance the result is a load of 470 ohm.

if the load was 10000 ohms than with the natural impedance factored in the result is 100 ohm. Which is the value recommended by Denon.

so if i add a 12000 ohm resistor in parallel to the existing 47000 ohm load of the bugle the result is 9559.3 (close enough to the 10000 ohm goal). Right?!

does any of this make sense -- i'm really trying on this but i'm a little out of my element.

[poty]

Hi,
I don't know what you mean about "natural impedance" (inductive impedance of the fist coil of the transformer? Then it should be very high to not taking into consideration in calculations), but I think your calculations are inaccurate. If you have ratio of 1:10 you have impedance change 1:10 too. It means, you have 47000/10=4700 Ohm in stock Bugle version (not 470 as you stated).
For Denon 103 there is only bottom limit of impedance:
(from the datasheet) Load Impedance: 100 ohms min. (40 ohms when using a transformer)
so it should be OK. But if you want to be close to the presented in the datasheet value you shold use something like 100*10=1000 Ohm loading resistor on the input of the Bugle.

[SteveRB]

thanks for the reply,

i got the terminology from here:
http://www.vinylengine.com/step-ups-and-mc-cartridges.shtml

 the calculation for impedance change vinyl engine uses is 47000/10^2 = 470

here is the paragraph from the website:
A step-up modifies the impedance of the output by a factor equal to the square of the amplification ratio. This is known as ‘natural impedance’. A word of caution: by itself, a step-up doesn’t have any impedance. The natural impedance is directly linked to the impedance of your MM entry and to the amplification ratio.
So, a step-up with an amplification ratio of 10 has a natural impedance and load impedance of 470 ohms (if your MM input impedance is 47 kohms: 470=47000/10²).

[poty]

Yes, it makes sense - it was my hasty and therefore wrong opinion.
But what question do you have? According to the article to obtain good SUT you should match internal impedance of the cartridge with the first (primary) coil of the SUT, get the right amplification (gain) for voltage and correct load impedance (counted from the gain and load resistor of Bugle). That's all.

[SteveRB]

the cartridge and SUT match; i have the correct amplification gain; it is the load impedance for the for the bugle that i need -- specifically, what resistors to add to match the cartridge SUT pair.

[poty]

The article answers the question too:
"If the load impedance (for active devices) is said to be > or equal to 20 ohms, the internal impedance is 3 ohms, you should try to load your cartridge at load impedances between:

1.the load impedance given by the manufacturer (20 ohms)
2.the load impedance given by the manufacturer + 10*internal impedance (50 ohms)"

You can also use the http://www.hagtech.com/loading.html or several topics like http://www.audiocircle.com/index.php?topic=70309.0.

But in my opinion, it is very subjective to be a science. You should try several values to find the right just for you.
If you mean how to calculate the values - your reasonings are right. You should get the right value from the 47k and the parallel resistor.

[SteveRB]

thanks for the links -- i missed the worksheets on the Hagerman website.  But i feel like i really learned something coming at it from the long-way round.