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Measurements and comparison of isolation transformers and DI boxes

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dominikz

dominikz

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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

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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

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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.
 

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nagster

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Countryman type 85 (Active type. 9V battery or 48V phantom power.)
type85_01.jpg
 

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nagster

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Radial J48 (Active type. 48V phantom power only.)
j48_01.jpg
 

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nagster

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Tritech DB-LL1 (passive type. lundahl LL1530 1:7 connection)
tritech_01.jpg
 

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nagster

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@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.
 
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dominikz

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morillon

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maybe he would be welcome, if not already done (?), to measure some active or passive options from aes to spdif or vice versa?
;-)
 

AnalogSteph

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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

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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

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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.
 
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