Updated april 2018

 

In this section I am noting down some ideas I have for future projects.

As you can see on the photo's I have other interests too and plan to spend more time on them.

During the build of the Pre amplifier it became clear that my old Audio Tester using the FireWire interface box has its limits.
Especially digital inputs and outputs are missing if I want to do a proper analysis of the performance of the whole Pre-amplifier.

My next scheduled project is therefore an audio interface box, that connects to my ESI Juli@XTe PC card.
The card has fairly good analog inputs and outputs (-110DB SNR in loopback mode) but I will be using the non isolated Coax SPDIF I/O's that are capable of sample rates up to 192KHz. to hook up to my new DIY audio box.
In loopback mode these Coax SPDIF I/O's have a clean -130dB Frequency Analysis sweep on the audio analysis program Arta.

I am using on my PC a combination of two audio analysis tools being Arta and AudioTester.
Arta is in my mind easier to use and gives more information on the Spectrum Analyser like TDH and TDH+Noise in percentages besides the frequency plot showing harmonics in dB's.
Also the Frequency Response analyser works better to my taste than that of Audiotester, something that already came in handy with testing the acoustic behaviour of DiCoSS.
Audiotester however has a feature called "frequency sweep" to measure for instance a phono preamp RIAA curve that I could not find in Arta.
In my mind should a frequency sweep be an easy addition to Arta. A adding an inverted RIAA sweep would make life realy easy.
I found that swapping between Arta and AudioTester is easy, as long as you close down one program before using the other.

The inputs and outputs of my audio box will have to be switchable between analog, SPDIF optical and SPDIF coax.
The analog inputs must be able to handle a maximum input voltage of 100Vrms. to allow measurement of high power amplifier outputs and must be able to attenuate by a factor of 10 and 100 to also cope with 1Vrms. signals full scale.  Signals below the 1Vrms. range can be dealt with by the PC audio card.

The analog output should have a 50Ohm output impedance and able to drive a maximum of 10Vrms. into 50Ohm loads.
It also must have a continuous attenuator of 40dB range and a switchable output attenuator of 1/10, 1/100 and 1/000 to be able to generate low voltages in the range of 0.1mV-10mV-RMS for testing of Moving Magnet and Moving coil Phono stages. SNR should be in the -120dB range.

The digital audio inputs should be able to accept sample frequencies from 44.1KHz. up to 192KHz. and the digital output should be able to work a-synchronously from the input at sample rates from 44.1KHz. to 192KHz, (Optical to 96KHz.)

Routing must be possible between audio -inputs and -outputs at different sample rates and routing of any input to the PC card and any output from the PC card should also be possible at any standard sample rate.
The digital audio links to and from the PC ESI Juli@XTe card will run at sample rates determined by the card settings but can be a-synchronously from the audio I/O sample rates.
This allows for maximum flexibility and testing options. This flexibility therefore requires several Sample Rate Conveters.

One additional feature I want to implement is that the audio tester is both battery (battery pack) and mains powered.
This will allow for very low noise and hum output signals to safely drive very sensitive analog inputs like Moving Coil Phono inputs.

With so many possible settings and controls the front of the audio tester quickly becomes cluttered with switches, pushbuttons, potmeters and LED indicators.
I therefore decided to re-use the touch screen display that I used for my Pre amplifier to control all settings.
Most of the firmware I wrote for the Pre amplifier touch screen is re-usable so that will cut down the programming efforts a lot.

I have my hobby cut out for the coming time.