• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Measurements and comparison of isolation transformers and DI boxes

OP
dominikz

dominikz

Addicted to Fun and Learning
Forum Donor
Joined
Oct 10, 2020
Messages
580
Likes
1,995
Was it mentioned anywhere in the article what DI stands for?
There are a few interpretations of the acronym "DI", but often it is said to stand for "direct injection".

It is a device used to connect high impedance, high level unbalanced sources (like e.g. passive guitar pickups) into low impedance, low level balanced inputs (e.g. microphone preamplifiers). Very common (and useful) device in recording studios as well as on stages (live sound).
 

pseudoid

Major Contributor
Forum Donor
Joined
Mar 23, 2021
Messages
2,786
Likes
1,666
Location
33.6, -117.9
I hate ground loops.
Not even 'gremlins' can publicly admit that they "love" ground-loops.;)
202204_XLRisolatorFloater.jpg

This arrangement of grounding flexibility seems to be about the most useful.
 

nagster

Active Member
Joined
Jan 24, 2021
Messages
250
Likes
410
DI was measured.
There are two DIs each, but since there was no difference at the time of the FR and THD ratios, we are measuring one each after that.
DI_j48_type85_tritech_02.jpg

The DI output is connected to the analyzer via apx1701. For phantom power. Input impedance is fixed at 20kohm. I didn't use a 9V battery.
Bypassed apx1701 only when measuring FR with a load of 600 ohms.

The voltage applied to DI in HF IMD and 32tone measurement is half the voltage when 1kHz THD ratio is -60dB.
However, tritech stopped at -100dB, so I applied the maximum voltage of the AP generator.
 

Attachments

  • DI_Relative Level (1kHz).png
    DI_Relative Level (1kHz).png
    66.6 KB · Views: 43
  • DI_THD Ratio vs Measured Level02.png
    DI_THD Ratio vs Measured Level02.png
    47.4 KB · Views: 43
  • DI_SMPTEsweep.png
    DI_SMPTEsweep.png
    93.5 KB · Views: 36
Last edited:

nagster

Active Member
Joined
Jan 24, 2021
Messages
250
Likes
410
Countryman type 85 (Active type. 9V battery or 48V phantom power.)
type85_01.jpg
 

Attachments

  • type85_DB_100mV.png
    type85_DB_100mV.png
    144.6 KB · Views: 35
  • type85_DB_nosignal.png
    type85_DB_nosignal.png
    153.4 KB · Views: 32
  • type85_thdvsG.png
    type85_thdvsG.png
    95.7 KB · Views: 34
  • type85_thdvsM.png
    type85_thdvsM.png
    95.6 KB · Views: 32
  • type85_H2.png
    type85_H2.png
    102.9 KB · Views: 33
  • type85_H3.png
    type85_H3.png
    100.8 KB · Views: 32
  • type85_7+13.png
    type85_7+13.png
    112.7 KB · Views: 32
  • type85_19+20.png
    type85_19+20.png
    112.7 KB · Views: 34
  • type85_32tone.png
    type85_32tone.png
    105 KB · Views: 33
Last edited:

nagster

Active Member
Joined
Jan 24, 2021
Messages
250
Likes
410
Radial J48 (Active type. 48V phantom power only.)
j48_01.jpg
 

Attachments

  • j48_Relative Level (8kHz).png
    j48_Relative Level (8kHz).png
    58.6 KB · Views: 39
  • j48_DB_100mV.png
    j48_DB_100mV.png
    146.6 KB · Views: 40
  • j48_DB_nosignal.png
    j48_DB_nosignal.png
    156.2 KB · Views: 38
  • j48_thdvsG.png
    j48_thdvsG.png
    99.1 KB · Views: 31
  • j48_thdvsM.png
    j48_thdvsM.png
    99.2 KB · Views: 39
  • j48_H2.png
    j48_H2.png
    106.3 KB · Views: 30
  • j48_H3.png
    j48_H3.png
    110.1 KB · Views: 34
  • j48_7+13.png
    j48_7+13.png
    109.3 KB · Views: 33
  • j48_19+20.png
    j48_19+20.png
    109.5 KB · Views: 32
  • j48_32tone.png
    j48_32tone.png
    102.7 KB · Views: 38
Last edited:

nagster

Active Member
Joined
Jan 24, 2021
Messages
250
Likes
410
Tritech DB-LL1 (passive type. lundahl LL1530 1:7 connection)
tritech_01.jpg
 

Attachments

  • tritech_02.jpg
    tritech_02.jpg
    72.5 KB · Views: 37
  • tritech_DB_100mV.png
    tritech_DB_100mV.png
    144.6 KB · Views: 36
  • tritech_DB_nosignal.png
    tritech_DB_nosignal.png
    148.7 KB · Views: 38
  • tritech_thdvsG.png
    tritech_thdvsG.png
    118.4 KB · Views: 36
  • tritech_thdvsM.png
    tritech_thdvsM.png
    119 KB · Views: 36
  • tritech_H2.png
    tritech_H2.png
    145.1 KB · Views: 33
  • tritech_H3.png
    tritech_H3.png
    127 KB · Views: 35
  • tritech_7+13.png
    tritech_7+13.png
    111 KB · Views: 33
  • tritech_19+20.png
    tritech_19+20.png
    108.9 KB · Views: 33
  • tritech_32tone_10V.png
    tritech_32tone_10V.png
    104.8 KB · Views: 36
Last edited:

nagster

Active Member
Joined
Jan 24, 2021
Messages
250
Likes
410
@nagster That's really amazing work, thanks a lot for contributing!
If you don't mind I'll add links to these posts at the end of post #1, so people can find them more easily.
Is it a link? No problem at all. I'll leave it to you.
Thank you for posting an interesting review.
 
OP
dominikz

dominikz

Addicted to Fun and Learning
Forum Donor
Joined
Oct 10, 2020
Messages
580
Likes
1,995

morillon

Addicted to Fun and Learning
Joined
Apr 19, 2022
Messages
579
Likes
93
maybe he would be welcome, if not already done (?), to measure some active or passive options from aes to spdif or vice versa?
;-)
 

AnalogSteph

Major Contributor
Joined
Nov 6, 2018
Messages
2,503
Likes
2,385
Location
.de
Excellent thread that I somehow missed. @dominikz, if you ever run across a Behringer HD400, that would be high on my list of isolation transformers to be measured given that it's so common... (I don't remember where you were located... I wouldn't mind ordering one from Thomann if need be, it's not like it makes one go bankrupt immediately.)

Transformer performance is known to vary with source impedance, so looking at the influence of that may be interesting. One might be plugging such a transformer into a soundcard output with 22 ohms, onboard audio of 75 or 200 ohms, or an audio interface with 400 ohms.
 
OP
dominikz

dominikz

Addicted to Fun and Learning
Forum Donor
Joined
Oct 10, 2020
Messages
580
Likes
1,995
Excellent thread that I somehow missed. @dominikz, if you ever run across a Behringer HD400, that would be high on my list of isolation transformers to be measured given that it's so common... (I don't remember where you were located... I wouldn't mind ordering one from Thomann if need be, it's not like it makes one go bankrupt immediately.)

Transformer performance is known to vary with source impedance, so looking at the influence of that may be interesting. One might be plugging such a transformer into a soundcard output with 22 ohms, onboard audio of 75 or 200 ohms, or an audio interface with 400 ohms.
Thanks a lot for the kind words! :)

I was indeed looking at buying the HD400 at some point, but went for the Palmer PLI instead at the time.

Regarding sensitivity to source impedance - I should be able to test this, but it might take me some time as I have other miscellaneous projects in the backlog :D
 

Rja4000

Major Contributor
Forum Donor
Joined
May 31, 2019
Messages
1,953
Likes
2,488
Location
Liège, Belgium
Hi

Thanks for this.

Just one comment:
You'd probably have egough with
- THD vs level (when does it starts saturating ?)
- Multitone (which gives you FR, IMD and THD in one plot) for max level -20dB or for a fixed input level.
 
Top Bottom