I have seen a lot of general discussion on measurements, most of which involves lower voltage and a wide variety of different options of complex equipment I do not have available (but not against getting or building from a kit, I just don't know which would be the "right" configuration)
I'm looking for insights for a novice trying to make a foray into doing some measurements of a tube phono stage. The technical issues involved are a bit daunting for me and there doesn't seem to be an introductory overview available. Looking at all the potential gear configurations with widely disparate costs involved has me stumped as to where I should focus my energy.
My goals are fairly basic: RIAA conformance, channel separation, etc.
I realize that most of what I accomplish will be wrong or missing important details- but you've gotta start somewhere.
My understanding was that using a quality sound card and an inverse RIAA I'd at least be able to get some general "beginner" measurements using a sine wave sweep out from the soundcard, through the inverse RIAA, into the Phono preamp, into Aux in preamp and then from tape output in my pre back into the soundcard.
Basically I have:
Is there some method that I could use what is already at my disposal (using a laptop / audio interface to generate a signal and then plot it?) or am I out of my league and require some more precision bench device?
I think others here would also benefit from some recommendations for lower cost and footprint test equipment configurations, with the caveat of course that there will be various limitations if compared to mucho expensive lab test equipment. My understanding was that a computer could also be utilized as a signal generator and scope in many instances.
I was also concerned about the preamp output voltage issue, which is why I came up with the idea of running it through my AUX in line stage and out Tape Monitor.
Or do I need something like this?: Soundcard Interface by Pete Millet / Soundcard Interface
Here are my soundcard specs: E-MU 0204 E-MU 0204 USB
I also have a Behringer UCA202.
I don't want to buy a bunch of stuff if I don't need to..... I'm trying to limit the accumulation of unnecessary "stuff" and keep things on the zen side. Also, utilizing a computer seems to make taking screenshots and sharing information much easier than using a standalone scope. I figure I can always get one of those table top new Tektronics if I decide I'll actually utilize it. Or maybe a picoscope with adequately rated probes?
Priority would be given to devices that are compatible with the widest range of software / operating systems / aren't locked into proprietary environments.
What would you all recommend for someone who just wants to get their feet wet and mostly has tube components?
I understand that my configuration is not ideal and it's error will be exacerbated by the other components in the chain. I'm not looking to publish this in the latest Linear Audio publication.
I managed to get a really basic graph by just recording total silence by using the chain I detailed above with no turntable connected, no inverse RIAA. The noise seems to mimic the RIAA curve, which is promising. That's about all I've got. I'm assuming the spikes are PSU related, but that's another topic entirely and don't want to distract from this threads purpose.
Would also be curious as to what other tests you would attempt and how you would go about them.
I haven't been able to figure out how to get "0db" or a reference level for the preamp.
Keep in mind this is the absolute apex of my diyaudio knowledge so far, and I'm trying here- there just doesn't seem to be a source of info that's digestible for someone just making a beginning.
I feel pretty impressed with myself I got a graph and nothing exploded- so try to keep the flaming to a minimum if possible and limit comments to those that are actually directed toward the goals described above in a way that's digestible to those without an EE background. This is for the benefit of not just myself, but for all those in the community who may want to make a beginning here.
In other words, I would be very grateful if you could imagine you are talking to a child and/or someone who has suffered head trauma... both of which are actually fairly accurate in my case.
I'm looking for insights for a novice trying to make a foray into doing some measurements of a tube phono stage. The technical issues involved are a bit daunting for me and there doesn't seem to be an introductory overview available. Looking at all the potential gear configurations with widely disparate costs involved has me stumped as to where I should focus my energy.
My goals are fairly basic: RIAA conformance, channel separation, etc.
I realize that most of what I accomplish will be wrong or missing important details- but you've gotta start somewhere.
My understanding was that using a quality sound card and an inverse RIAA I'd at least be able to get some general "beginner" measurements using a sine wave sweep out from the soundcard, through the inverse RIAA, into the Phono preamp, into Aux in preamp and then from tape output in my pre back into the soundcard.
Basically I have:
- Inverse RIAA
- Audio Interface (E-MU 0204 & Behringer UCA202)
- Phono Preamp (output ~150V)
- Line Preamp with Tape Out
- Computer (Mac OS & Linux)
- Audacity (Would be willing to boot into windows if Rightmark was preferable)
Is there some method that I could use what is already at my disposal (using a laptop / audio interface to generate a signal and then plot it?) or am I out of my league and require some more precision bench device?
I think others here would also benefit from some recommendations for lower cost and footprint test equipment configurations, with the caveat of course that there will be various limitations if compared to mucho expensive lab test equipment. My understanding was that a computer could also be utilized as a signal generator and scope in many instances.
I was also concerned about the preamp output voltage issue, which is why I came up with the idea of running it through my AUX in line stage and out Tape Monitor.
Or do I need something like this?: Soundcard Interface by Pete Millet / Soundcard Interface
Here are my soundcard specs: E-MU 0204 E-MU 0204 USB
I also have a Behringer UCA202.
I don't want to buy a bunch of stuff if I don't need to..... I'm trying to limit the accumulation of unnecessary "stuff" and keep things on the zen side. Also, utilizing a computer seems to make taking screenshots and sharing information much easier than using a standalone scope. I figure I can always get one of those table top new Tektronics if I decide I'll actually utilize it. Or maybe a picoscope with adequately rated probes?
Priority would be given to devices that are compatible with the widest range of software / operating systems / aren't locked into proprietary environments.
What would you all recommend for someone who just wants to get their feet wet and mostly has tube components?
I understand that my configuration is not ideal and it's error will be exacerbated by the other components in the chain. I'm not looking to publish this in the latest Linear Audio publication.
I managed to get a really basic graph by just recording total silence by using the chain I detailed above with no turntable connected, no inverse RIAA. The noise seems to mimic the RIAA curve, which is promising. That's about all I've got. I'm assuming the spikes are PSU related, but that's another topic entirely and don't want to distract from this threads purpose.
Would also be curious as to what other tests you would attempt and how you would go about them.
I haven't been able to figure out how to get "0db" or a reference level for the preamp.
Keep in mind this is the absolute apex of my diyaudio knowledge so far, and I'm trying here- there just doesn't seem to be a source of info that's digestible for someone just making a beginning.
I feel pretty impressed with myself I got a graph and nothing exploded- so try to keep the flaming to a minimum if possible and limit comments to those that are actually directed toward the goals described above in a way that's digestible to those without an EE background. This is for the benefit of not just myself, but for all those in the community who may want to make a beginning here.
In other words, I would be very grateful if you could imagine you are talking to a child and/or someone who has suffered head trauma... both of which are actually fairly accurate in my case.
> I haven't been able to figure out how to get "0db" or a reference level
You *need* a reliable audio volt-meter.
I would not know how to "calibrate" a sound-card absolutely without a meter.
Since you can believe the sound-card is flat 50Hz-10KHz, you "can" use a common DMM to make 1.00V at <400Hz (some DMMs fall-off above), then figure if the soundcard shows the same at say 5KHz then it "is" 1.0V for practical purpose. But a good flat audio volt meter is IMHO better.
OTOH, you can run-up the output level until the PC shows rising THD. Hold that setting, unplug the output cable, and put it on your tongue. Under 1V is hard to feel. 9V unexpectedly will curl your tongue. You can calibrate off 1.5V and 9V batteries.
You *need* a reliable audio volt-meter.
I would not know how to "calibrate" a sound-card absolutely without a meter.
Since you can believe the sound-card is flat 50Hz-10KHz, you "can" use a common DMM to make 1.00V at <400Hz (some DMMs fall-off above), then figure if the soundcard shows the same at say 5KHz then it "is" 1.0V for practical purpose. But a good flat audio volt meter is IMHO better.
OTOH, you can run-up the output level until the PC shows rising THD. Hold that setting, unplug the output cable, and put it on your tongue. Under 1V is hard to feel. 9V unexpectedly will curl your tongue. You can calibrate off 1.5V and 9V batteries.
From my point of view you are already well equipped with hardware.
EMU-0204 is a good choice, I use EMU-0202 and EMU tracker with good results.
What you need now is a plan how to configure your test setup.
And I recommend ARTA software for analysis - for instance STEPS offfers an easy way for frequency response measurements.
EMU-0204 is a good choice, I use EMU-0202 and EMU tracker with good results.
What you need now is a plan how to configure your test setup.
And I recommend ARTA software for analysis - for instance STEPS offfers an easy way for frequency response measurements.
What I want to say is that your attempts do not look totally wrong.
As a general rule, before measuring something, it is a good idea to have an expectation result in mind and then compare this to your measurement. The questions arise from the difference between both.
I mentioned ARTA because this software is widely accepted here and many folks can help you.
If you want more specific help, you must put more specific questions.
My measurements are focused on class-d-amps actually, optimizing THD and noise.
The procedure is a mix of understanding and of trial and error, to be honest.
To explore the features of your software I recommend some loopback-measurements, i.e. feed soundcard output to soundcard input and then check the measurement options, playing with sample rate, FFT-size, FFT-windowing, avering and all these switches, looking for the best results in frequency response, noise, THD and so on.
The loopback measurements show the limits of what can be measured with your soundcard.
ARTA provides a guided calibration procedure, not really intuitive for my taste, but it works.
As a general rule, before measuring something, it is a good idea to have an expectation result in mind and then compare this to your measurement. The questions arise from the difference between both.
I mentioned ARTA because this software is widely accepted here and many folks can help you.
If you want more specific help, you must put more specific questions.
My measurements are focused on class-d-amps actually, optimizing THD and noise.
The procedure is a mix of understanding and of trial and error, to be honest.
To explore the features of your software I recommend some loopback-measurements, i.e. feed soundcard output to soundcard input and then check the measurement options, playing with sample rate, FFT-size, FFT-windowing, avering and all these switches, looking for the best results in frequency response, noise, THD and so on.
The loopback measurements show the limits of what can be measured with your soundcard.
ARTA provides a guided calibration procedure, not really intuitive for my taste, but it works.
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Hi,
This question could have many answers depending on budget. ARTA and something like the Scarlett 2i2 can go a long way. In general swept frequencies are a poor choice as the the FFT plots become a mess. Multi-tones or single frequency measurements are the best with or without inverse-RIAA. It is important to carefully consider the levels at each point in the signal chain to keep everything in the linear region. This might mean attenuation before a phono preamp to prevent overload.
This question could have many answers depending on budget. ARTA and something like the Scarlett 2i2 can go a long way. In general swept frequencies are a poor choice as the the FFT plots become a mess. Multi-tones or single frequency measurements are the best with or without inverse-RIAA. It is important to carefully consider the levels at each point in the signal chain to keep everything in the linear region. This might mean attenuation before a phono preamp to prevent overload.
Scott thanks for chiming in.
Are you suggesting the Scarlet interface in lieu of what I already have?
http://www.creative.com/emu/products/product.aspx?pid=15186
The inverse RIAA from hagtech has -40db and -60db levels.
My primary concerns were output voltage and volume levels of the Phono pre, matching the ideal input levels of the interface / computer.
I have not found time to play with the ARTA software but I will take a crack at it this week and post my trials here.
Are you suggesting the Scarlet interface in lieu of what I already have?
http://www.creative.com/emu/products/product.aspx?pid=15186
The inverse RIAA from hagtech has -40db and -60db levels.
My primary concerns were output voltage and volume levels of the Phono pre, matching the ideal input levels of the interface / computer.
I have not found time to play with the ARTA software but I will take a crack at it this week and post my trials here.
Since you have a meter of more than adequate accuracy you can start by getting a sense for the output level from your EMU. Its more than good enough for these tasks. You want to keep the input to no more than 2-3V RMS. You can make a simple attenuator with two resistors that can reduce the input level. You don't need a soundcard interface but I can recommend Jan's Autoranger if you do go that way. I don't see much use for 90V from a phono preamp but you do need to protect the input to the soundcard if the source will go that far. There are methods using diodes that work fine.
ARTA is your best starting point. I think it even has a pre-equalized test for checking phono sections. RMAA is also nice because it generated good plots that are easily shared. Both are Windows and just about everything in software for this stuff is as well. There are apps that will turn the soundcard into a scope of sorts. Try a free one before spending $500-$1000 on a scope.
Start with loopback tests to get a feel for how the software works with your hardware. Use the meter to gauge what level/sensitivities the soundcard has. From there getting meaningful measurements of a phono preamp should be pretty straightforward. You will have ground loop issues to sort out. If you can connect the meter across the input to the soundcard while taking measurements you are less likely to get in trouble.
Its important to understand the tests and how to inperpret them as well as whether the results suggest doing anything. For example RIAA correction of +/- .5 dB is really good and distortion below .1% may not be audible but both can be improved by orders of magnitude for no discernible effect. Learn the hardware and software and what you want to accomplish before buying expensive test instruments that won't show anything new.
ARTA is your best starting point. I think it even has a pre-equalized test for checking phono sections. RMAA is also nice because it generated good plots that are easily shared. Both are Windows and just about everything in software for this stuff is as well. There are apps that will turn the soundcard into a scope of sorts. Try a free one before spending $500-$1000 on a scope.
Start with loopback tests to get a feel for how the software works with your hardware. Use the meter to gauge what level/sensitivities the soundcard has. From there getting meaningful measurements of a phono preamp should be pretty straightforward. You will have ground loop issues to sort out. If you can connect the meter across the input to the soundcard while taking measurements you are less likely to get in trouble.
Its important to understand the tests and how to inperpret them as well as whether the results suggest doing anything. For example RIAA correction of +/- .5 dB is really good and distortion below .1% may not be audible but both can be improved by orders of magnitude for no discernible effect. Learn the hardware and software and what you want to accomplish before buying expensive test instruments that won't show anything new.
I thought you were thinking of buying the EMU, it is a fine card I have one also but had some trouble on WIN10 and true 24bit performance. This does not matter as a test instrument.
For serious analysis I record files and use Python and SoX. You might find SoX useful as a do everything tool (free) for sound file manipulation.
ARTA has built-in multi-tone so that into a hardware inverse RIAA into a preamp and back into ARTA should go a long way in getting you what you want. This could be set up in demo mode IIRC, but you can't save results. ARTA is decently priced for hobby users. BTW a comment in case you are not aware of all the math pitfalls, a tool like ARTA has a multi-tone locked to exact bins and using the same card (clock) for both input and output assures accurate magnitudes across the entire frequency space. At the .5dB level you can easily get errors due to any number of math details if you don't do this.
If you saw my thread .1dB was easily resolved.
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Well I can be of limited help, I have nothing to do with Apple products anymore.
I had a thread about inverse RIAA and RTA's. I was looking for a native solution for inverse RIAA. The solution I think I found is ARTA. They have a calibration function for microphones, you can make/find a calibration curve for your microphone and use it to get a compensation for its errors. They have a RIAA compensation file on their site. I think, if you take the file (in notepad) and changed the sign, + db to - db and - db to +db, you can get an inverse RIAA calibration curve for phono preamp measurements. This would eliminate the component errors from a discreet inverse RIAA network, then all you need is a good sound card. Follow the requirements for how the file is formatted. I intend to try this soon.
I have bought the ARTA license after using it for some time on my linux machine with wine - there is no need for a windows VM.
I've also just confirmed I'm able to run ARTA on OS X Sierra using Wine/ Homebrew.
The appearance with x-quartz is a bit dodgy, but nothing I can't make friends with.
You did not have any driver or calibration issues with various interfaces / sound cards?
One more piece of the puzzle down... slowly but surely.
Also, going to take a stab at assembling Pete Millett's Sound Card Interface.
Are you referring to the phono stage you designed? I did not see that part, but will look.
On that subject- do you think they will organize a group buy for pcbs?
Also, did I hear you are doing pretty well with a Grado and a U-Turn Orbit over there? After a long time with various MC's I'm thinking of going back to a Shure... maybe the S35C (The closest to a V15 still in manufacture).
I think I'm starting to figure out at least the chapter 1 dummies guide of how to pull this all together.... I'd rather struggle and learn the nuts and bolts than invest my psychic energy in perusing magical audio charms. Plus, it's nice for humility to get pummeled a little bit on something that is effortless for others.
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