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Old 10th August 2010, 03:04 AM   #4341
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Well it appears on the surface that we had a succesful several nights. After finding a bad solder joint and a wrongly jumped temporary RIAA cap, the headamp actually amplified a signal. Several in fact.
Several measurements are shown attached.

L/R Channel Frequency response.
Grounded input (actually 50R terminator)
500, 1000, 5000 FFT.

I have alot of noise in the cable voltage divider that I built, however, I don't think it is all of it. It is 1:151 using a 10R:1.5k precision resistors. The divider is shielded inside the RCA housing. Signal fed into the head amp was .3mV. Most of the grass is related to my test gear and the environment I am testing in. Will have to move it out of the area and away from all of the computers and hardware.

What is nice is that the 60,120,etc spikes are almost non-existant. So no HUM!!!!!. Also the Left and Right traces almost fall on top of each other. Blue being right and Red being left.

I also attached the corrected straight through test of the corretion file. A little minor tweeking left to do but it isn't bad. My eyes are crossed at this point so time for bed.
Attached Images
File Type: jpg L and R Response Corrected.jpg (163.1 KB, 173 views)
File Type: jpg Background with 50R term.jpg (196.6 KB, 168 views)
File Type: jpg 500Hz Left.jpg (198.4 KB, 163 views)
File Type: jpg 1000Hz Left.jpg (196.4 KB, 157 views)
File Type: jpg 5000Hz Left.jpg (195.6 KB, 149 views)
File Type: jpg Corrected output into sim bridge.jpg (169.3 KB, 49 views)
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Old 10th August 2010, 03:17 AM   #4342
Salas is online now Salas  Greece
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If that grass isn't inherent to the phono build and its in the set up, then its perfect. Go 48kHz/24bit, 65536 points. Divider should be 1.5k series to 15R shunt. Yes no fundamental hum bands. But we can't be sure what can be masked. For circa your gain with single Jfet input can show like that. The 16k spike is from my neighbor's CRT TV.
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File Type: gif 56dbMC.gif (15.1 KB, 58 views)
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Old 10th August 2010, 03:27 AM   #4343
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Will do, but not tonight. I don't have a 15R on hand. I thought I had a 16R but the bag was empty. Will have to come up with a little larger shield to allow me to combine a few resistors to get 15R.
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Old 10th August 2010, 03:28 AM   #4344
Salas is online now Salas  Greece
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10R is still OK. Are they in the right order?
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Old 10th August 2010, 09:38 AM   #4345
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Quote:
Originally Posted by RCruz View Post
Hum.... So you can compare... let us know the differences

Does the Borberly I/V perform bessel filtering after the dac ?

What dac are you using ?
I bought 3 boxes at Hifi2000: 1 for Salas NJFET RIAA & 2 for DAC so now I have a lot of work, but when I can I will tell the you the subjective differences between both regs.

The Borbely I/V use 3rd order Bessel filter but can be configured of several ways: for example now I'm using passive I/V with resistor instead active with better success.

Buffalo II from Twisted Pear guys.
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Old 10th August 2010, 12:30 PM   #4346
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I will work on my set-up tonight. If you remember I had the same issue when working with my OPUS amp. I have to pull my notes to see what I did to get a clean measurement.

Attached is the schema of my voltage divider. It appears right to me and behaived appropriatley.
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File Type: png V DIvider test lead.png (2.5 KB, 73 views)
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Old 10th August 2010, 12:40 PM   #4347
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Looks OK as a divider. Its how I wire mine too, and I have even grabbed no mains hum off the noise bed in some double box build, so it can't be the divider.
But your 2ndH looks around -90dB which correlates with mine (if I run it -20dB signal), but I don't know the calibration, what mV RMS is your -20dB signal? Can you calculate gain @ 1kHz? That would be another good sign about working properly if near target. Channel tracking I see very good without trimming any resistors, and Riaa flat curve good. But not spanning 40dB on the other, the curvy plot. Are those Riaa caps 47n,15n meausured n' matched?

P.S. Did you write a correction file against textbook Riaa and included the card's kinks, so to produce the flat?
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Old 10th August 2010, 12:41 PM   #4348
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the output from your fixed attenuator is 10/1510 =0.0066 times the input.
500mV input gives 3.31mV output, but only if the receiver impedance is near infinity.

For reasonable accuracy, the receiver Rin>>10 times 10r. Try 1k0 which will give an apparent output reading of 3.28mV.
The error is <1%
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Old 10th August 2010, 12:49 PM   #4349
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He has 150R phono input.
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Old 10th August 2010, 12:58 PM   #4350
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if the receiver has Rin>>10*10r then the error is quite small.
One can calculate the error and make allowance for it if the source resistance and receiver resistance are known.

Note, the schematic shows the output as 300uV, not 3.31mV
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