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Aml ez1073 pre calibration
Old 30th November 2017
  #1
Here for the gear
 

Aml ez1073 pre calibration

Hi guys and gals,

Quick question. I have just built my first diy project, an AML ez1073 pre.

I'm at the calibration stage and need to follow these steps.

-apply a signal of -40dBu to the input then turn front panel gain up to +60

Measure output signal, and adjust the gain trimmer until output reads +20dBu.

I'm using pro tools and my apollo to generate and return the signal.

My issue is that I can't find anything that measures in dBu so I can be sure of the levels.

Any advice?
Old 30th November 2017
  #2
Gear Maniac
You can use the linked website to convert to volts and measure your DAW outputs with a True RMS DMM. You will probably want to measure the voltage while it is hooked up to the input of the ez1073, since the voltage will probably drop a bit due to the input impedance of the pre.

dB dBu dBFS dBV to volts audio conversion digital - calculator volt to dBu and dBV dB mW SPL dB decibels 0 dBFS - convert dB volt normal decibels relatioship relation explanation analog audio absolute level true rms convertor converter decibel to dbfs

Hope that helps!
Old 30th November 2017
  #3
Here for the gear
 

Hi Scott,

Did I mention I'm new to this? Lol. Thank you so much for reply but is there a way you could explain in a more simple way?
Old 30th November 2017
  #4
Gear Maniac
Well, I'm certainly no expert either, compared to many others on this forum.

dBu is an analog voltage level referenced to 0.775 volts RMS (AC). So 0dBu = 0.775 Vrms. This does not have an absolute correlation to the signal level (dBFS) in your DAW. The D/A converters are calibrated to match a specific digital level (anywhere from -14dBFS to -20dBFS) to a specific analog level (usually +4dBu, or 1.228Vrms, for line level balanced outputs).

If you use the website I linked to above to convert -40dBu to Vrms, you get about 0.00775 Vrms. Come to think of it, this may be pretty hard to measure on even a decent multimeter that only give you resolution in millivolts, or 0.001V, but it might get you in the ballpark.

Connect the signal to the input of the pre, and measure across pins 2 & 3 of the XLR input jack, but on the inside of the chassis where the pins go into the PCB. Try to get the reading to just below where it turns over to 0.008, and you'll be in the ballpark. Also, a lot of DMMs don't read accurately at 1kHz (definitely check yours to see what the specs are), so you may want to test at a lower frequency, like 400Hz.

Once you measure the input signal, you will probably need to move the DMM to the output XLR to measure the voltage there as you adjust the trimmer. (20dBu = 7.75Vrms).

Hope this helps. Like I said, I'm no expert, just a hobbyist. So if anybody here has better suggestions for the OP, or if I got something wrong, please let us know.
Old 17th December 2017
  #5
Lives for gear
Did you manage to get your build up to spec? I need some help. I was struggling to get the molex connector to fit into the pins on the circuit board. There was something wrong with it so I hard to force it down into position. I use molex connectors all the time when building PCs.

Now when I connect a power source I’m getting 26.8 mV when I put probes on the TP1 and TP2 test points. Turning the bias adjuster has no effect on this. So I am unable to get it up to 90 mV as required in the build doc. What’s the next trouble shooting step
Old 4th January 2018
  #6
Gear Maniac
 

Quote:
Originally Posted by miscend View Post
Did you manage to get your build up to spec? I need some help. I was struggling to get the molex connector to fit into the pins on the circuit board. There was something wrong with it so I hard to force it down into position. I use molex connectors all the time when building PCs.

Now when I connect a power source I’m getting 26.8 mV when I put probes on the TP1 and TP2 test points. Turning the bias adjuster has no effect on this. So I am unable to get it up to 90 mV as required in the build doc. What’s the next trouble shooting step
Read Colin's Colourbook calibration steps, it's pretty straight-forward.
1) Power unit up, put your digital multimeter probes on J6 and J5 spade terminals.
Your multimeter (set to Volts) should read +24V. If not, check your your work
and solder joints.
2) Next, put your multimeter probes on J3 and J5 spade terminals and turn
48V Phantom Regulate (R10) trim screw with a fine screwdriver until you read
48V on multimeter.
3) Attach multimeter probes (with alligator clips, if you prefer) to left and right
sides of R26 resistor (one below 24V Regulate heatsink). Adjust trim screw
of Output Bias Trim (R20) until you get 130mV (this is millivolts, so you may
need to set multimeter from volts to millivolts).

If all your soldering and assembly work is good, you should have no problem going through these steps. 2-3 minutes max and the EZ1073 is good to go.
Make sure you've got a fuse in your IEC receptacle. For 240 volts, I am using 1/2 amp Slo Blo.
Old 4th January 2018
  #7
Gear Maniac
 

Sorry, I was referring to the AML EZ1073 19" mic pre/EQ rackmount.
Were you talking about the new AML 500 series single-slot EZ1073?
I haven't tried those, but they should be much simpler to build (no 3rd stage, EQ, extra transformers, inductors, power supply, grounding the case, etc...).
Old 20th May 2018
  #8
Here for the gear
 

Hi! I had trouble adjusting the bias of my ez1073-500. I checked R24 not to be correct resistor, (2.2 Ohm instead of 1 Ohm). Luckily, Collin sent me correct 1 Ohm resistors, and I could replace them.
Now I have to adjust the signal gain and ready!
Old 30th November 2018
  #9
So did anyone know how to calibrate the preamp properly, what do I need to do it. As far as I know you need to send a signal to the preamp then at the same time read the output of the preamp, so basically you need two tools to do it at once not? like a Nti Minirator to send the signal and a Nti minilyzer to read the output. Wow that mean like $800 to do the calibration... is there a cheaper way to do it. I mean yes you can use a Multimeter to read but what would you use to send the proper signal?
Old 26th December 2018
  #10
Lives for gear
Quote:
Originally Posted by blacky123 View Post
So did anyone know how to calibrate the preamp properly, what do I need to do it. As far as I know you need to send a signal to the preamp then at the same time read the output of the preamp, so basically you need two tools to do it at once not? like a Nti Minirator to send the signal and a Nti minilyzer to read the output. Wow that mean like $800 to do the calibration... is there a cheaper way to do it. I mean yes you can use a Multimeter to read but what would you use to send the proper signal?
You can use anything that can produce a sine wave to produce the test signal. Even an iPhone with a test oscillator app. Just make sure the signal level is measuring at exactly -40.
Old 26th December 2018
  #11
Lives for gear
I’m getting noise on my ex1073-500 build. At lowest gain setting the mouse is barely noticeable. But at +60 gain the noise is peaking at -38 dB. I could upload a sample if anyone is interested.

I’ve tried reflowing the whole circuit board but no success. Could it be a defective transformer?
Old 26th December 2018
  #12
Lives for gear
 
Radardoug's Avatar
 

Have you terminated the input?
Old 5th February 2019
  #13
Quote:
Originally Posted by miscend View Post
You can use anything that can produce a sine wave to produce the test signal. Even an iPhone with a test oscillator app. Just make sure the signal level is measuring at exactly -40.
All good easy! I also had to calibrate the JLM LA500A and the new AML ez1073eq, pretty much all the same once you figure it out and made a few cables to go with it.
Old 5th February 2019
  #14
Quote:
Originally Posted by miscend View Post
I’m getting noise on my ex1073-500 build. At lowest gain setting the mouse is barely noticeable. But at +60 gain the noise is peaking at -38 dB. I could upload a sample if anyone is interested.

I’ve tried reflowing the whole circuit board but no success. Could it be a defective transformer?
Did you figure it out, here I build one of the two new AML ez1073eq that I just got and I have a problem with the first one, so I will start the second one and compare the two, hopefully the second one will work ok. I was able to calibrate the first but when I try it, bypass work but not the actually eq, it sound very distorted and far. So I will build the second one and try each module (PCB) seperatly to see where is the problem, Colin told me it is perhaps a power problem, but then I would have had problem with calibration I think.
Old 30th April 2020
  #15
Gear Addict
 
greyskull's Avatar
Quote:
Originally Posted by blacky123 View Post
Did you figure it out, here I build one of the two new AML ez1073eq that I just got and I have a problem with the first one, so I will start the second one and compare the two, hopefully the second one will work ok. I was able to calibrate the first but when I try it, bypass work but not the actually eq, it sound very distorted and far. So I will build the second one and try each module (PCB) seperatly to see where is the problem, Colin told me it is perhaps a power problem, but then I would have had problem with calibration I think.
Sorry to drag this one up from the depths, But I too am having a bit of a head scratchy moment trying to figure how to calibrate the AML 73 500 with only an Apollo and a cheapish Rapid Electronics DMM.

I've tried the suggested above, but the readings I get are wildly different to what one would expect, and there's no way I can goose the output up to as high as that. That being said, pre works great, and in the meantime I've just lined it up to match my Apollos pres gain wise.

Cheers!
g
Old 25th May 2020
  #16
Here for the gear
 

I am having a bit of difficulty here as well. I have the ez1073 19" rack mount version, and am on the last step of calibration, and I am getting nowhere...I dont see anywhere in the build manual requiring the use of an input signal. In measuring R26, I get the initial 70-80 mV reading, but it escalates up to 24V rapidly. I turned R20 ccw, and now am at 0V. With, and without, the 1K signal input. Any suggestions?
Old 25th May 2020
  #17
Here for the gear
 

Oops...I had a major dufus moment...all is well, and calibrated..
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