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ORTOFON ST-7 STEP-UP TRANSFORMER REVIEW

dougi

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I just got this stepup this week and thought I would post some comparative measurements with it in use/not-in use.

It is a mid-level one in Ortofon's offerings. Still expensive! Weird pricing, Euro 899 via Ortofon or I could get it locally for A$700-800.

Stock pics:
1690074240135.png


I wanted to use it for my "cheap" MCs, (AT OC9XEN and Denon DL103R) into either my NAD C3050LE directly or to get lower noise with my Dynavox TPR-2 phono stage which is quieter in mm mode.

Specs are as follows:

1690074580646.png


With the turns ratio it should be well suited to the two carts, having impedances of 12 and 14 ohms respectively.

There was a bit of hum in my test setup, audible with ear near speaker but OK at the listening position. It was better with the Dynavox than the QUAD Artera PRE used for testing. (Say -60dBu hum vs -55dBu hum going by the ADI-2 peak meters).
I grounded from the turntable to the stepup only. Continuing grounding to the preamp did not improve hum.

I didn't measure the gain, my interest was how the transformers were affecting the frequency response and distortion.

To measure I used @Balle Clorin 's wonderful measurement script and a test record in twosetups:
  1. Denon DL-103R cart into QUAD Artera PRE MC setting, no stepup, into RME ADI-2 PRO.
  2. Denon DL-103R cart into QUAD Artera PRE mm setting, with the stetup, into RME ADI-2 PRO.
  3. Note capacitance incorrect in the plot headers, total capacitance seen by the mm stage would be around 300pF (200pF cable, 100pF loading)

NO STEPUP
Denon DL103R plot 6_2_2.5g_RIAA mc_100 ohms_80pF incl cables_CA-STR-1007.png


WITH STEPUP
Denon DL103R steupup2_2.5g_RIAA mc_100 ohms_80pF incl cables_CA-STR-1007.png


A COMPARISON PLOT OF LEFT CHANNELS, NORMALISED
Denon DL103R steupup comparison l_2.5g_RIAA mm_47k ohms_CA-STR-1007.png


CONCLUSIONS
  • As hinted at by the specs, a bit of lower bass roll-off, probably ~3dB @20Hz in my setup. It actually flattens the response a bit above that.
  • Slight high treble rolloff, ~1dB at 20 kHz.
  • No significant noticable distortion added to the cart, but some at 18kHz+
  • In-use, hum is fine and plenty of gain for my carts. Bass is fine with my speakers (Heritage Linton's).
 
Last edited:

Balle Clorin

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IMG_9323.jpeg
@dougi ,
I do not deserve any honour for the script, i think it is @scott wurcer @JP who made it.
I did use the script to plot the effect of my Ortofon T-5 step up.

Post in thread 'Fun with vinyl measurements'
https://audiosciencereview.com/foru...un-with-vinyl-measurements.20278/post-1644372

Post in thread 'Fun with vinyl measurements'
https://audiosciencereview.com/foru...un-with-vinyl-measurements.20278/post-1641539

PS , strange that the bigger Ortofon step up has much worse low end response than the small cheap T-5 that I paid 80USD for this year.Are you sure you did not inadvertently activate a rumble filter?
 
Last edited:
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dougi

dougi

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Location
ACT, Australia
View attachment 300931@dougi ,
I do not deserve any honour for the script, i think it is @scott wurcer @JP who made it.
I did use the script to plot the effect of my Ortofon T-5 step up.

Post in thread 'Fun with vinyl measurements'
https://audiosciencereview.com/foru...un-with-vinyl-measurements.20278/post-1644372

Post in thread 'Fun with vinyl measurements'
https://audiosciencereview.com/foru...un-with-vinyl-measurements.20278/post-1641539

PS , strange that the bigger Ortofon step up has much worse low end response than the small cheap T-5 that I paid 80USD for this year.Are you sure you did not inadvertently activate a rumble filter?
Yep, no rumble filter. I will remeasure at some point with the OC9X at some point.
 
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