How to measure the frequency response of a phono preamplifier.

[Aero]

How to measure the frequency response of a phono preamplifier.

I don't know much about this and I'm interested in the condition of my rather old phono preamplifier?

Can I connect the output from the preamplifier to the computer (sound card)

 

[staticV3]

Can I connect the output from the preamplifier to the computer (sound card)

If your sound card has a Line input then yes.

Do not connect the Preamplifier output to your soundcard's Mic input.

 

[mfalcon]

I’m interested in doing this as well. If I wanted to measure the FR, and noise of a phono pteampmhow would I input the test signal in the phono stage? The signal is at a different level than what would be needed to test a Dac as an example I would think.

 

[Aero]

If your sound card has a Line input then yes.

I plugged it in. What's next...?

 

[MaxwellsEq]

I plugged it in. What's next...?

Play a test LP with a frequency sweep and use REW to analyse it in real time.

 

[MaxwellsEq]

I’m interested in doing this as well. If I wanted to measure the FR, and noise of a phono pteampmhow would I input the test signal in the phono stage? The signal is at a different level than what would be needed to test a Dac as an example I would think.

You can only use a signal generator if it has a reverse RIAA capability. You can use a normal signal generator and set it to a low level and run a scan, but you won't get a flat response. Also, signal generators don't behave like cartridges in terms of impedance etc. The most "life-like" approach is a test LP with frequency sweeps.

 

[restorer-john]

@Aero

You need to firstly, ensure you have a signal suitable for driving the phono stage. If it's a moving magnet input, you are looking at 2.5mV to 5mV. If it's a moving coil input, the level is 20dB less (0.1mV). At those low levels, using a DAC is problematic as noise is a serious issue. The best option is an attenuating network to take your DAC level down, not just turn down the DAC digitally.

Also, you need to account for the RIAA curve. That can be done with an inverse RIAA network with attenuation- plenty out there to build.

If you are looking a frequency response and ultimate deviation, you need a very accurate RIAA compensation in your software or your external inverse network.

 

[restorer-john]

Play a test LP with a frequency sweep and use REW to analyse it in real time.

Yep, and throw in the record and the cartridge as well into the mix...

 

[MaxwellsEq]

Yep, and throw in the record and the cartridge as well into the mix...

Indeed. Still, at least it gets someone started and avoids all the issues with inverse RIAA, attenuation etc.

We used to measure professional phono stages all the time, so had suitable generators and test rigs, but I'm not sure I could be bothered to start out doing this as a hobby now...

 

[Balle Clorin]

Where are you taking the input signal from ?
The input signal would likely be way too high.. 5mV is what you want in . With my Tascam 144mk2 Audio interface and REW I am able to do it in combination with REW. You may need a attentiator voltagedivider … and a USB ADC/DAC saoundcard and a PC . Dlock has a cheap one but it is not flat , make sure to calibrate it, see below

1. You need to calibrate the sound/card by running a Loop Out to In and run a sweep, that allows you to make a calibration file so the out to in response is flat See REW manual
2. Run a test loop with Out-in and make sure it is flat when using the calibration file.
3. Insert the RIAA in the loop: Pc-sound card out- RIAA-Soundcard IN. Set level out and in to avoid clipping.
4. Run a REW sweep 10-24 000, apply the sound card calibration file , then you will see a sloping RIAA curve as a result.
But the plot will have a -10db/decade slope in addition due to the nature of the sweep, so you need a calibration file to convert that too. I make that by generating a sweep file in REW Generator,
5. Then you need to have a reverse RIAA file… to make the RIAA result flat, can be done manually, create a text file with tabulated RIAA valued and” add “to calibration file
6.this becomes a total of 3 calibration files and REW can only handle 2 individually. So then I have to apply 2 calibration files, and use a digital sweep file that I subtract from the compensated file…


It is a mess.. It would be easier for you to run a white noise signal from REW through the RIAA, and manually edit a reverse RIAA file as mic calibration, and use the sound card calibration file too. I will add som calibration files here,,

 

[Aero]

I thought about measuring the preamplifier without using a test cartridge and a test disc. On this forum, measurements of phono preamplifiers are made, there are many of them.
How is it measured?
My knowledge in this topic is very small, I expect a simple solution, not specialist tips, because they are useless to me, I simply do not understand these specialist tips.

 

[Balle Clorin]

Wlll you need to be kind of a nerd and specialist to do it properly, and you need as a minimum to have and understand REW. I add a calibration file for REW that you may try, is a combined file to make a RIAA sweep flat, if it is not flat it is a deviation from RIAA, but it really only applies to my sound card--

A REW sweep with RIAA and soundcard in loop looks like this. Here I am measuring my Cambridge CP2 with low filter engaged-

Then "choose change calibration"I apply the RIAA and soundcard corrcation combined in RIAA.TXT could be named RIAA.CAL too

An then I get this, pretty flat

If you are doing the same, you will probably se deviations from your soundcard and RIAA compared to mine



UPDATE here is a file where soundcard calibration and RIAA correction is separate. USBloop.cal and RIAAcal.cal attached as "usbloop 48k.txt" and "riaacal 48k.txt"
Make your own soundcard calibration file by looping soundcard out-in and make a sweep, and use theresulting calibration file instead of USBloop.cal

Rename .txt to .cal

 

[Thomas_A]

I thought about measuring the preamplifier without using a test cartridge and a test disc. On this forum, measurements of phono preamplifiers are made, there are many of them.
How is it measured?
My knowledge in this topic is very small, I expect a simple solution, not specialist tips, because they are useless to me, I simply do not understand these specialist tips.

It's a bit more complicated with phono pre. I made one here:

Muffsy phono preamplifier minireview (update)

This review was updated September 21, 2023. Main change was the use of the E1DA Scaler to fix the impedance issues that is evident when using the E1DA ADC alone. This is an attempt to make a small review with measurements of the Muffsy MM phono preamplifier. It is a DIY kit so it is far from...

www.audiosciencereview.com

 

[MaxwellsEq]

I thought about measuring the preamplifier without using a test cartridge and a test disc. On this forum, measurements of phono preamplifiers are made, there are many of them.
How is it measured?
My knowledge in this topic is very small, I expect a simple solution, not specialist tips, because they are useless to me, I simply do not understand these specialist tips.

There's no simple way to do this. You have had THE BASICS explained to you, not "specialist tips". If you don't read and study the background you won't know how to do this, nor know how to interpret the results.

How do others do this? Amir uses a test set worth thousands of dollars to do his reviews of phono preamplifiers. You can now buy slightly lesser, dedicated test gear for a few hundred dollars https://quantasylum.com/products/qa403-audio-analyzer. Or use an ADC or soundcard. You can also build an inverse RIAA network and attenuator network to work with the soundcard / ADC. Or you can use calibration files with REW.

 

[morillon]

multitones can do to...

 

[MaxwellsEq]

BTW I just found a thread about using the Quantasylum to measure phono preamplifiers:

Phono preamp measurement setup

For creating the new higher-resolution RIAA curves, I compared two curves: One with 100 points per octave (reference), and another curve (candidate) with many fewer points per octave. Then I went through the reference curve and checked the interpolation at each point in the candidate curve and...

forum.quantasylum.com

 

[restorer-john]

https://quantasylum.com/products/qa403-audio-analyzer.

This is my QA403 doing a high resolution RIAA MM phono sweep (@5mV) into one of my best phono stages. +/-1dB vertical scale. We are within 0.05dB from 20Hz-20kHz.

 

[MaxwellsEq]

This is my QA403 doing a high resolution RIAA MM phono sweep (@5mV) into one of my best phono stages. +/-1dB vertical scale. We are within 0.05dB from 20Hz-20kHz.

View attachment 403150

That's impressive!

 

[morillon]

the precautions are really on the level side..(even if we can of course play a little on the overload capacities of the phono stage)
(MT not use cal-text but mathematical fonction for riaa)

 

[restorer-john]

That's impressive!

I can't take credit for it, Denon built it in 1983. It puts every phono stage Amir has measured to shame in most areas including a 320mV 1kHz overload...

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