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Measured output impedance in reamp box 20% of impedance specified in data sheet
Old 1 week ago
  #1
Here for the gear
Measured output impedance in reamp box 20% of impedance specified in data sheet

EDIT: This is interesting. Anyone with the means to do it, try and measure the output impedance of the X-Amp and get back to me with results!

I need professional help. Audio engineering student.

User guide with specs for the X-AMP here.

I'm measuring the input/output impedance of a Radial Engineering X-Amp device.

I'm using a tone generator to send 1 kHz, 1 V into it.

Specified input impedance is 600 ohm, and i did measure it to 587 ohm which i believe is good enough.

I went on to measure the two outputs of it. The first main output I measured to 1 kohm, the second to 2700 Ohm. Specified impedance is 5 kohms. Whichever way I tried to measure, and changed cables, and changed the input voltage, I got the main output to 1 kohm.

Scenario A: I've measured it wrongly, meaning I might just have to redo it again later and try with a different multimeter, tone generator, cables, and check all connections.

Scenario B: I've measured it correctly and 1 kohm is the impedance under these circumstances.
If so, I really need help understanding what factors may play into the circuit and affect the output impedance. I was thinking it might be the input voltage and the frequency.

Just tell me if there's any more info you need to understand the problem.

Thanks in advance for any help.

Last edited by willcon; 6 days ago at 01:06 AM.. Reason: Want others to try the same measurement.
Old 1 week ago
  #2
Lives for gear
 
🎧 15 years
Quote:
Originally Posted by willcon ➡️
I need professional help. Audio engineering student.

User guide with specs for the X-AMP here.

I'm measuring the input/output impedance of a Radial Engineering X-Amp device.

I'm using a tone generator to send 1 kHz, 1 V into it.

Specified input impedance is 600 ohm, and i did measure it to 587 ohm which i believe is good enough.

I went on to measure the two outputs of it. The first main output I measured to 1 kohm, the second to 2700 Ohm. Specified impedance is 5 kohms. Whichever way I tried to measure, and changed cables, and changed the input voltage, I got the main output to 1 kohm.

Scenario A: I've measured it wrongly, meaning I might just have to redo it again later and try with a different multimeter, tone generator, cables, and check all connections.

Scenario B: I've measured it correctly and 1 kohm is the impedance under these circumstances.
If so, I really need help understanding what factors may play into the circuit and affect the output impedance. I was thinking it might be the input voltage and the frequency.

Just tell me if there's any more info you need to understand the problem.

Thanks in advance for any help.
Good of you to post these results, Will.

be aware of the radial fan club that frequents this site.
no doubt their members will question your methodology.

they are super loyal to the brand though perhaps not all that smart with electronic design.
Old 1 week ago
  #3
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brianroth's Avatar
 
🎧 15 years
Describe the exact method used to measure the impedance. Perhaps something wrong with the test setup?

Bri
Old 1 week ago
  #4
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Radardoug's Avatar
 
🎧 10 years
If it is a transformer, the load impedance you measure will depend on the driving impedance.
By the way, you need to exactly specify your test setup, otherwise we have no idea what you are doing.
Old 1 week ago | Show parent
  #5
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Quote:
Originally Posted by Radardoug ➡️
If it is a transformer, the load impedance you measure will depend on the driving impedance.
By the way, you need to exactly specify your test setup, otherwise we have no idea what you are doing.
Tone generator (GAG-810 Audio Generator) with 600 Ohms output, putting out 1 kHz at 1 V.

The output of the tone generator connected to the X-AMP's input with an XLR that divides into 3 experiment cords; whereas the cords for pin 2 and 3 are connected into the tone generator. Ground is left out.

Gain set to highest on X-AMP.

Telecable that divides into two cables goes from main output (1) of X-AMP.

I measure the open circuit voltage between the two cables from the tele-cable. Simply letting the ends be free and connect them to the multimeter.

I measure the loaded circuit voltage with a resistor between them.

This website is used for guidance, and the circuit is constructed exactly as shown in the picture under the title "Output Impedance Measurement and Calculator".

Maybe the 600 ohms from the tone generator has to be accounted for?

See if this helps to clear it up.

EDIT: The X-Amp unit that is automatically linked in my post is NOT the same that i'm measuring on. I'm using the one in the user guide i linked to in my main post — might be the same specs but i can't guarantee that.
Old 1 week ago | Show parent
  #6
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Quote:
Originally Posted by Radardoug ➡️
If it is a transformer, the load impedance you measure will depend on the driving impedance.
By the way, you need to exactly specify your test setup, otherwise we have no idea what you are doing.
See my reply to brianroth.
Old 1 week ago
  #7
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Radardoug's Avatar
 
🎧 10 years
Have you actually measured the output impedance of the generator?
And the question has to be asked. Why are you worried about the output impedance of the radial? Have you talked to the manufacturer?
Old 1 week ago | Show parent
  #8
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Quote:
Originally Posted by Radardoug ➡️
Have you actually measured the output impedance of the generator?
And the question has to be asked. Why are you worried about the output impedance of the radial? Have you talked to the manufacturer?
I'm not worried or concerned about it at all... I'm just concerned about getting my degree in audio engineering, and understanding the bigger picture, this is one of my school tasks.
Old 1 week ago
  #9
Gear Addict
 
samwinston123's Avatar
 
🎧 10 years
What size load resistor are you using to test? The impedance of the generator shouldn’t have any effect on the output of the x-amp. Also what is a “Telecable”? I’m not familiar with that.
Old 1 week ago | Show parent
  #10
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Quote:
Originally Posted by samwinston123 ➡️
What size load resistor are you using to test? The impedance of the generator shouldn’t have any effect on the output of the x-amp. Also what is a “Telecable”? I’m not familiar with that.
Different load resistors between 50 Ohm to 70k Ohm they all lead to Z = 1000 Ohm ±30

Tele cable = 6.3 mm / 1/4 inch jack plug cable. Interesting that you don't know what i mean by tele cable. I'm thinking it might be a European/Swedish thing to call 6.3 cables tele cables.
Old 6 days ago | Show parent
  #11
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by willcon ➡️
Different load resistors between 50 Ohm to 70k Ohm they all lead to Z = 1000 Ohm ±30

Tele cable = 6.3 mm / 1/4 inch jack plug cable. Interesting that you don't know what i mean by tele cable. I'm thinking it might be a European/Swedish thing to call 6.3 cables tele cables.
I had no idea either, but now it's obvious that it's the kind of cable you would plug into a TELEcaster guitar!

Seriously though, it sounds like you have done the measurements correctly. It's not generally a problem to have the output impedance lower than spec, although that principle might not hold for guitars and guitar amps, which is what this box will be used with.

The output impedance will not vary with level (as long as you don't overload the box), but you might see some variation, particularly on the transformer isolated output, with frequency. You might earn some extra points on the assignment by repeating the measurements at 100 Hz and 10 kHz, just to be extra thorough.

Geoff
Old 6 days ago | Show parent
  #12
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Quote:
Originally Posted by cbc6403 ➡️
I had no idea either, but now it's obvious that it's the kind of cable you would plug into a TELEcaster guitar!

Seriously though, it sounds like you have done the measurements correctly. It's not generally a problem to have the output impedance lower than spec, although that principle might not hold for guitars and guitar amps, which is what this box will be used with.

The output impedance will not vary with level (as long as you don't overload the box), but you might see some variation, particularly on the transformer isolated output, with frequency. You might earn some extra points on the assignment by repeating the measurements at 100 Hz and 10 kHz, just to be extra thorough.

Geoff
Yeah i can't see the fault in my chain. I might try and measure at different frequencies too but the deadline is in 24 hours so im probably not going to have time to do it. I've noted the data when trying with different resistors though.

But look. Hear me out, i might be onto something here.

The X-AMP exists in basically two versions. The old version that was blue, exactly the same color as the J48 DI because it seems they would sometimes be sold together. The new version is yellow, and apparently it's the exact same unit except for the aesthetics, tech-wise.

The old manual says 5kOhm: https://manualzz.com/doc/7076964/rad...box-owner-s-ma...

The new manual says nothing about out impedance, it only says "Hi-Z Output": https://www.radialeng.com/wp-content...eb-05-2021.pdf

Now, consider my measurement of 1000 Ohms (although not 100% accurate) and consider the fact that a guitar has an output impedance of, what, 10kOhms?

Is it bold for me to explore the idea that Radial realised the unit was maybe a bit imperfect spec-wise? I mean it's a popular product but they seemingly backed off on specifying the output impedance for the newer version. What's even more interesting; it says 10kOhms on the output on the unit itself.

This particular unit is borrowed from my school and according to the staff it's simply uncommon for anyone to borrow and use it. So i'm thinking it's probably not a faulty unit.
Old 6 days ago | Show parent
  #13
Gear Addict
 
🎧 5 years
Quote:
Originally Posted by willcon ➡️


Now, consider my measurement of 1000 Ohms (although not 100% accurate) and consider the fact that a guitar has an output impedance of, what, 10kOhms?
The actual output impedance of a guitar could be 10 kΩ, or if it has active electronics inside, it could be a lot less than that, maybe only 150Ω.

My guess is that Radial was a little bit sloppy with the specs, and instead of specifying what the output impedance was, gave the recommended minimum load impedance for the outputs. Contrary to popular belief, we don't usually match input and output impedances these days (there are exceptions for vintage tube and broadcast equipment), but good practice is to have the input impedance at least 5 or 10 times the output impedance. If you read the spec that way, it makes more sense with what you measured.

For instance a lot of line level equipment is specified as delivering rated voltage (perhaps +20 dBu) into 600Ω. The actual output impedance is likely anywhere from 50 to 150Ω.

Manufacturers usually have a disclaimer somewhere on the spec page that they reserve the right to make changes to the specs without notice, to incorporate improvements or accommodate other production requirements (like a certain part is no longer available).

Geoff
Old 6 days ago
  #14
Gear Addict
I have to agree with Geoff.

Matching impedance exactly results in maximum *power* transfer. This typically is used for RF work; in fact it essential to protect against reflected power from damaging the driving output (such as a broadcast transmitter).

When matching to drive a *voltage* input, a lower impedance on the output, feeding a much higher impedance input (such as the 5k0 ohm input of a guitar amp) delivers maximum voltage to that input.
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