DIY Audio Analyzer with AK5397/AK5394A and AK4490

[B&W_arthur]

Got my boards to day.

They are much smaller than I expected.

Unfortunately, I dumped my magnifier & lamp a few days ago~

 

[nyt]

Hi sonnya,

Yes, the commercial version will have the fix on board.

Cost is actually a bit unknown at the moment. The current price for the RTX6001 is USD 2495, but there could be some changes in the design and setup. I will return with more details, hopefully fairly soon. (This actually belongs in the GB section).

As far as I can see, you are included in the GB list, we just haven't come around to delivering your unit yet.

any thoughts on offering a different da?

 

[JensH]

The idea has crossed my mind.
I don't like to introduce too many uncertainties though, so let's see

 

[sonnya]

Why should you want another dac with this performance?

What I think could be nice. If rtx would supply optional low pass filter for measuring class D amplifiers.

 

[anatech]

Hi nyt,
That would make it an entirely new product if I'm not mistaken.

-Chris

 

[nyt]

Hi nyt,
That would make it an entirely new product if I'm not mistaken.

-Chris

The dac is on a daughter board

 

[nyt]

Why should you want another dac with this performance?

What I think could be nice. If rtx would supply optional low pass filter for measuring class D amplifiers.

If you use software like REW, you can specify a frequency range for calculating thd+n measurements. I bugged john to add that for this very reason.

 

[nyt]

The idea has crossed my mind.
I don't like to introduce too many uncertainties though, so let's see

If it happens, let me know if you need any testing

 

[DualTriode]

I have switchable 1X/10X probes, 1X and 10X non switchable probes. I actually need the sensitivity for a lot of the stuff I do (phono stages in particular). I break probes on a regular basis so I generally avoid the expensive ones. Many probes basically suck so you have to be careful about which cheap ones you buy. Tektronix makes decent cheap probes now, and there are a few others.

This morning I used a Agilent 10073C 10:1 probe at the input of a APx analyzer with the expectation of seeing -20dB attenuation.

10:1 is -20dB.

I do not recall the exact number; it was more like -40dB attenuation that was on the FFT.

I did not do the math.

The input impedance to the typical oscilloscope is 1M ohms the input impedance to the analyzer is 100K ohms.

It is not a straight up swap for the 10:1 oscilloscope probe for the BNC test lead.

An Introduction to Oscilloscope Probes

see figure 5 in the above link.

DT

 

[JensH]

Since the probe expects a 1 Mohm load, 40 dB sounds just about right. With 9 Mohm and 100 kohm you should end up at -39.18 dB.
The RTX6001 also has a single ended input impedance of 100 kohm.

 

[DualTriode]

I woke up thinking about this measurement stuff this morning.

If you are going to be poking around inside vacuum tube voltage equipment that is what digital voltmeters and oscilloscopes are for. Down and dirty with your near state of the art one part per-million audio analyzer is not a good idea. 1uV, or -120dBV, is 0.000001 Volts.

You can buy a pretty nice scope with onboard volt meter, function generator and FFT for not too much.

Now I am going to play outside.

DT

 

[anatech]

That was an excellent point. I can't imagine why anyone would be probing around with this instrument.

-Chris

 

[kevinkr]

That was my point as well a few pages back.

 

[mbrennwa]

That was an excellent point. I can't imagine why anyone would be probing around with this instrument.

Because I can? And because I don't have a nice scope with a spectrum analyser and 120 dB dynamic range?

But you are right, the RTX is not the right tool for probing around in high-voltage gear. Next time I shall use my old garden type USB audio interface with a DC blocking cap to keep the dangerous stuff away from the RTX.

 

[soongsc]

The tube amps we probed around were some 500 volts....

 

[anatech]

Hi mbrennwa,

Because I can? And because I don't have a nice scope with a spectrum analyser and 120 dB dynamic range?

I'm at a complete loss as to why you would like to do that. A scope or meter are the appropriate tools for the job. I don't use the spectrum analyser function of the 'scope to examine the signals inside circuits. On reason is that the waveform is distorted anyway, we already know this. The feedback creates a signal that is distorted in a complimentary way to partially cancel distortion created in the output stages.

-Chris

 

[soongsc]

Some times you might want to look at where you can improve internally, and how much margin from saturation you have.
This little gadget seems useful:
Oscilloscope, Multimeter & Logger that Fits in Your Pocket! by Pokit Innovations —Kickstarter

 

[1audio]

I wouldbevery cautious work I aground potentially lethal voltages. A Fluke DVM today represents.years of experience making stuff safe. Its more than getting past the tests.

The wireless dvm is a cute item but not quite the same.

A coupling cap is NOT enough to safely test High Voltage. The charging current maybe enough to damage a sound card.

 

[PaulBC]

I used REW to measure the frequency response of my unit with loopback connection. The FR result is extremely flat, but the phase is 180 degree. I've checked my cable to make sure that I didn't do the polarity wrong. Did I do something wrong? or the polarities are different between the input and output?

Paul

It is quite easy to forget about polarity in circuit design, I wonder...

 

[jan.didden]

I wouldbevery cautious work I aground potentially lethal voltages. A Fluke DVM today represents.years of experience making stuff safe. Its more than getting past the tests.

The wireless dvm is a cute item but not quite the same.

A coupling cap is NOT enough to safely test High Voltage. The charging current maybe enough to damage a sound card.

A few days ago I got one of these: Intona – Products .

I connect it between the PC running the measurement software and my USB scope TiePie HS3 Handyscope HS3 key specifications.

I can now connect the scope probe ground lead anywhere in the circuit I want and do measurements wherever I want. Works really beautiful, and should work with any USB instruments. The adapter is guaranteed to deliver 300mA at the isolated USB side, but the designer told me in practise it should be close to 500mA. Enough for most USB instruments.

This should also work well to isolate DACs.

Jan