Jump to content

Rob's Amp tests


peniku8
 Share

Recommended Posts

Pmillett Sound Card Interface loopback measurements:

Measurement chain is Fireface UC → SCI (Generator input) → Internal loopback → Fireface UC
The SCI converts the balanced signal of the Fireface internally and outputs either balanaced or unbalanced, which can be switched. It doubles the output voltage, so if I input 2V balanced, it outputs 4V balanced or 4V unbalanced. Voltages seen are after conversion (means the Fireface outputs half the voltage displayed).

Measurements are sorted by voltage ascending.

91wVcNH.jpg

 

8pv5qIL.jpg

 

Nn3n8JF.jpg

 

2YsvVSP.jpg

The 1V measurement looks similar to the Fireface loopback, so I guess the pmillett isn't adding too much distortion.
The pmillett started distorting at about 8.6V output (unbalanced). When I switched it to balanced, the distortion increased a bit, but there was more headroom (presumably twice the voltage).
Here is a measurement of the Fireface at 0dbFS, which produced 13,25V at the Pmillett's generator output, which is about 24,6dbU:

XEKh1SO.jpg

Link to comment
Share on other sites

The level seems quite low.  I would expect the noise to be constant with level so SNR should improve if a larger signal is used.  The Fireface UC is spec: THD+N AD: < -98 dB (< 0.0012 %), THD+N DA: -96 dB (0.0015 %) so you're getting pretty close.*

 

*didn't see your last post I think optimal level for the Fireface will be around 4V from your results.

Link to comment
Share on other sites

11 minutes ago, kipman725 said:

The level seems quite low.  I would expect the noise to be constant with level so SNR should improve if a larger signal is used.  The Fireface UC is spec: THD+N AD: < -98 dB (< 0.0012 %), THD+N DA: -96 dB (0.0015 %) so you're getting pretty close.

What do you mean by low level? The last measurement was taken at 0dbFS, which produced 6,6V at the Fireface's output.

Here is a direct measurement of the FF without the pmillett in the loop (max output 6,6V as before):

iBiOQEj.jpg

Best THD is achieved at 0.5V output, best noise floor at maximum.

Here is the THD/Noise vs output plot:

gAlahVs.jpg

  • Like 1
Link to comment
Share on other sites

  • 4 weeks later...

And the loadbank causes another casualty.. this time it's a Yamaha CR-600. Fuses are done for, but I hope everything else is still good. Measurements of my Hypex FA123 coming soon. Also ordered dedicated measurement equipment, since I already had trouble measuring the true performance of the Hypex amps... Fireface not clean enough. Getting the Cosmos ADC to use with a Topping D10b. Probably also going to get the Cosmos APU once it releases, which includes a 1khz notch and a preamp capable to delivering phantom power with lots of gain.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...