Audio measurements on tube amp. ? look here

Now I have published some more informations about this project.

The my idea was to test the amplifier in a more large frequency range, until 100KHz.

I use the EMU 0404 USB with Lundahl output transformers to ear hi-resolution audio tracks and I consider it like my best source now.
 
Here my solution for audio measurements on vaccum tube amplifiers.

EMU input

Hello,
As always, nice job.
I have a question or request.
Please tell us more about the setup of the EMU mixer software. Are there different settings for 44.1K 48K 96K and 192 K and 16 bit or 24 bit in the mixer software?
I have an EMU 1212, sorting out the mixer software looks to be a long rainy day project.
DT
 
Hello,
As always, nice job.
I have a question or request.
Please tell us more about the setup of the EMU mixer software. Are there different settings for 44.1K 48K 96K and 192 K and 16 bit or 24 bit in the mixer software?
I have an EMU 1212, sorting out the mixer software looks to be a long rainy day project.
DT

On the EMU0404 USB control panel is possible set only the sample rate and it must be set to 192KHz to have the larger frequency response band.
In my webpage there is an image about the EMU0404 USB control panel.
No mixer software is available with EMU0404 USB.

Could you send me an image of your mixer ?
 
On the EMU0404 USB control panel is possible set only the sample rate and it must be set to 192KHz to have the larger frequency response band.
In my webpage there is an image about the EMU0404 USB control panel.
No mixer software is available with EMU0404 USB.

Could you send me an image of your mixer ?

Hello,
Take a look at the attached link. Chapter 4 is the patchmix. It includes control of everything, bit rate, sample rate input to output routing, volume control. There is a preset that works at 16 / 44.1. I will look at the 404 shot at your linked site. Thank You.
http://www.emu.com/support/files/storage/v2_1820-1212-EN.pdf
DT
All just for fun!
 

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If the diodes have a fault these will be open for the signal so does not protect your sound card.

It is necessary a resistance before the diodes to protect these.

The 100K before the sound card introduce with the input capacitor of sound card a filter on high frequency limiting the band.
 
If the diodes have a fault these will be open for the signal so does not protect your sound card.

It is necessary a resistance before the diodes to protect these.

The 100K before the sound card introduce with the input capacitor of sound card a filter on high frequency limiting the band.

Disagree on all counts.

In a small minority of ultra-high pulse current failures, the diode bond wire can fuse open. But far and away the most common diode failure is short. There is a 100k resistor in series, so I can't imagine how much more resistance you'd want.

As far as HF response, the pole is formed by the 100k in parallel with the 20k resistor in parallel with the input resistance of the sound card (usually 10k) and in parallel with R2 (which can be open, 560R, or 51R) interacting with the input capacitance of the line card. If a line card has 50pF of input capacitance (which is more than any sound card in my possession), that f3 is about 300kHz with R2 open. With R2 at 560R, the HF rolloff is in the multimegahertz range.

The voltage ranges given in the schematic aren't exactly correct, but the right order of magnitude.