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XLR Isolation Transformer with Amp DI

#21
Wasnex said:
I read through the thread and didn't pick up on why you are using the isolation transformer. It should generally be unnecessary, unless something in the signal chain has a malfunction.

I would trouble shoot in the following order: Confirm your XLR cables are good and properly wired (use a multi-meter or cable tester), try the isolation transformer on another amp, try another isolation transformer on your amp, try a different mic pre. It appears you have done most but not all of these steps.

Beyond that, I don't find the GK DI to be particularly good sounding to begin with. Perhaps you would be better off using a quality DI.
Click to expand...

I use it live to proactively avoid ground loops and damage from phantom power. I realize most amps have built-in phantom power protection measures, but I have read about some 1001RBs having issues related to phantom (though this could have been an older revision of the amp that was affected since they've been around for decades; mine was purchased new last year).

I do also have a passive Radial ProDI I could patch in after my pedal board, and I do have a Tone Hammer DI on my pedal board. That said, I have been using the Tone Hammer as an overdrive pedal with the GK so it's only on for a few songs. I like that the "woofer high cut" is passed through to the GK's DI in post-EQ mode as I am a tweeter-less flatwound user, and I like the independent level control.

Old Garage-Bander said:
I would expect a 1:1 (aka isolation) to measure the same on both sides.
You may have an impedance matching transformer rather than an isolation.

Can you post a pic or give any info (model # and such) that is printed on the device?
Click to expand...

It's a Radial IC-1 Ice Cube. [Invalid or Expired Link Removed]
 
#22
voided3 said:
I use it live to proactively avoid ground loops and damage from phantom power. I realize most amps have built-in phantom power protection measures, but I have read about some 1001RBs having issues related to phantom (though this could have been an older revision of the amp that was affected since they've been around for decades; mine was purchased new last year).

I do also have a passive Radial ProDI I could patch in after my pedal board, and I do have a Tone Hammer DI on my pedal board. That said, I have been using the Tone Hammer as an overdrive pedal with the GK so it's only on for a few songs. I like that the "woofer high cut" is passed through to the GK's DI in post-EQ mode as I am a tweeter-less flatwound user, and I like the independent level control.
Click to expand...

FYI: My series I 700RB works fine with phantom and it is almost 20 years old. If yours was purchased new last year it should be a series II. Are there reports of DI issues with the series II amps?

Regarding pre vs post DI. Just be mindful with Post DI that any changes you make to your amp settings in a live situation will be translated to everyone's mix. You seem pretty on top of this, so my guess is you understand the potential problems this may cause. As an audio tech I generally prefer to use pre DI or to mic a speaker if the player's amp contributes significantly to the sound. Better yet, use both.
 
#23
voided3 said:
I use it live to proactively avoid ground loops and damage from phantom power. I realize most amps have built-in phantom power protection measures, but I have read about some 1001RBs having issues related to phantom (though this could have been an older revision of the amp that was affected since they've been around for decades; mine was purchased new last year).

I do also have a passive Radial ProDI I could patch in after my pedal board, and I do have a Tone Hammer DI on my pedal board. That said, I have been using the Tone Hammer as an overdrive pedal with the GK so it's only on for a few songs. I like that the "woofer high cut" is passed through to the GK's DI in post-EQ mode as I am a tweeter-less flatwound user, and I like the independent level control.



It's a Radial IC-1 Ice Cube. [Invalid or Expired Link Removed]
Click to expand...
Looking at input and output impedance, they are 8.66 K and 600 ohms respectively.
Instructions (right page, center-ish) discusses a 6 db loss if going from balanced to unbalanced.

If the thing works OK for you and you feel more secure in having the isolation then I see no reason to worry about it.
 
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#24
Wasnex said:
FYI: My series I 700RB works fine with phantom and it is almost 20 years old. If yours was purchased new last year it should be a series II. Are there reports of DI issues with the series II amps?

Regarding pre vs post DI. Just be mindful with Post DI that any changes you make to your amp settings in a live situation will be translated to everyone's mix. You seem pretty on top of this, so my guess is you understand the potential problems this may cause. As an audio tech I generally prefer to use pre DI or to mic a speaker if the player's amp contributes significantly to the sound. Better yet, use both.
Click to expand...

Glad to hear you haven't had any phantom-related issues!

Correct, and I only use the EQ for minor corrections; I typically "set it and forget it" after setting up.

Of course, the ultimate ground isolation: mic the cab! I have very strongly debated buying a good kick drum mic and a Cab Grabber XL so I still only need an XLR from the board, but our band is a 10-piece with monitors everywhere and I fear I'd cause feedback issues using a mic.
 
#25
voided3 said:
Glad to hear you haven't had any phantom-related issues!

Correct, and I only use the EQ for minor corrections; I typically "set it and forget it" after setting up.

Of course, the ultimate ground isolation: mic the cab! I have very strongly debated buying a good kick drum mic and a Cab Grabber XL so I still only need an XLR from the board, but our band is a 10-piece with monitors everywhere and I fear I'd cause feedback issues using a mic.
Click to expand...

Most kick drum mics have a lot of baked in EQ. Personally I would rather use a relatively neutral mic on a cabinet. An Audix D4 would be a decent choice at a relatively low price. See attached and notice the difference between older and current models. I have two of each.

A more high-end choice would be an Electro Voice RE20, a Beyer M88, or a Sennheiser MD421. The RE20 has no proximity effect and will sound very true to your amp, but allow a bit of bleed. The M88 has a tight polar pattern and also a really strong proximity effect. It will provide greater isolation but may be more sensitive to placement and may require a High Pass filter or a bit of EQ on the low end. The 421 performance will be somewhere in the middle.

Before spending you money on a mic, I suggest trying the technique out with whatever you have. An SM57 will work fine.
 

Attachments

#27
voided3 said:
Pins 2 and 3 on the input side read 239 ohms and pins 2 and 3 out the output side also read 43.4 ohms.
Click to expand...
Almost certainly there's your problem. You do not have a 1:1 transformer installed in your unit. Contact Radial, they are good folks and are sure to get this sorted out for you!

Good, systematic troubleshooting by the way. Appreciated very much the lack of attitude that we sometimes see here.
 
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#28
agedhorse said:
Almost certainly there's your problem. You do not have a 1:1 transformer installed in your unit. Contact Radial, they are good folks and are sure to get this sorted out for you!

Good, systematic troubleshooting by the way. Appreciated very much the lack of attitude that we sometimes see here.
Click to expand...

Thank you for all of the advice! I see they have a three year warranty so I’ll reach out to them.
 
#29
This product appears to be the same as the Jensen IsoMax GLX, and the published reflected impedance specs indicate that it's a 1:1 ratio transformer (or very close to that), and the published insertion loss going from a 10k source to a 600 ohm load reinforce this.

Hunch is that they are based on the JT-11 series transformers which are great parts.

Mistakes sometimes get made, I'm sure it will be taken care of.
 
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#30
agedhorse said:
This product appears to be the same as the Jensen IsoMax GLX, and the published reflected impedance specs indicate that it's a 1:1 ratio transformer (or very close to that), and the published insertion loss going from a 10k source to a 600 ohm load reinforce this.

Hunch is that they are based on the JT-11 series transformers which are great parts.

Mistakes sometimes get made, I'm sure it will be taken care of.
Click to expand...

I hope so! Just sent them an email and found my old receipt, too.
 
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#31
voided3 said:
Thank you for all of the advice! I see they have a three year warranty so I’ll reach out to them.
Click to expand...

If it has a Jensen transformer, they are warrantied by the manufacturer longer than what Radial offers, 20 years. Not all their products use Jensen’s products. It may not be the transformer though, it could be something in the box.


Warranty | Jensen Transformers
 
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#32
agedhorse said:
This product appears to be the same as the Jensen IsoMax GLX, and the published reflected impedance specs indicate that it's a 1:1 ratio transformer (or very close to that), and the published insertion loss going from a 10k source to a 600 ohm load reinforce this.

Hunch is that they are based on the JT-11 series transformers which are great parts.

Mistakes sometimes get made, I'm sure it will be taken care of.
Click to expand...

Out of curiosity, would this be the Jensen IsoMax you are referring to? Invalid Link Removed
 
#33
voided3 said:
Out of curiosity, would this be the Jensen IsoMax you are referring to? Invalid Link Removed
Click to expand...

I was referring to the raw transformer family. There are many possible options, I am not that familiar with their finished products.
 
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#35
agedhorse said:
I was referring to the raw transformer family. There are many possible options, I am not that familiar with their finished products.
Click to expand...

Pretty sure Radial specs an Eclipse transformer in this device. As you probably know, Radial acquired Jensen awhile back and specs Jensen transformers in other Radial products.
 
#36
voided3 said:
True, though I was surprised that it attenuates that much with an active source (my amp's DI). It still gives off a "mic level" signal that any mixing board's channel strip can work with and it's worth having the piece of mind that it prevents ground loops and phantom power damage. If I ever need to run a preamp into a power amp, though, I definitely won't be using one!
Click to expand...
attenuation is relative.
 
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