Topic: Best impedance matching

I have a question about the best impedance matching of the RME ADI2 pro FS BE. This is about the analog input.

My turntable goes to a Croft RIAA. There isn’t an official output impedance available, but somewhere on the internet it is stated as 500 Ohm. It is a tube amp.
The sound through the analog input of the RME is excellent. The only thing is that the input signal on the analyzer isn’t higher than say -40 db. Volume isn’t a problem btw.

A second set up is to install a Croft preamp between the RIAA and the RME. Output of this preamp is stated at 800 Ohm. The input on the analyzer is way better and can be optimized though the volume potmeter of the preamp. To my ears the sound is comparable. Ofcourse the Croft pre is coloring the sound. Both Crofts are tube amps.
I use for input and output on the RME the Auto Ref feature.

Which of both setups would you recommend?

2

Re: Best impedance matching

Which ref level did you choose for the Analog Input? -40 dB on the analyzer sounds like something is wrong, as any RIAA device also amplifies by around 40 dB. The impedance is completely irrelevant here.

Regards
Matthias Carstens
RME

Re: Best impedance matching

I choose auto ref is on. The ref level says +24 dBu. Should I try lower settings and Auto Ref off?

Re: Best impedance matching

Better try it straight instead of asking you☺️
I did auto ref on off and switched back to +4 db.
The analyzer gives much higher figures now.
This is great, however I don’t understand why autoref doesn’t pick this up?

5 (edited by KaiS 2022-07-28 18:15:48)

Re: Best impedance matching

johanj wrote:

I did auto ref on off and switched back to +4 db.
... I don’t understand why autoref doesn’t pick this up?

I think Auto Reference Level in the analog input works in one direction only, protecting from overload:

Manual page 50:
The analog inputs also feature automatic overload protection. Activating the option Auto Ref Lev(el) changes to the next higher reference level when overloads are detected.

Auto Reference Level for the input is quite different than for the output, it really changes the level, which is not desirable all the time.

On the output you hardly notice it working, as it combines analog AND digital switching for continuous volume changes.

Re: Best impedance matching

autoref for input does not work the way you expected.
It raises the level whenever the input signal closes to clipping.
If it’s already 24dbu when turned on, it won’t go lower.
You need to put it into 4dbu before turning on this feature.
For your case if 4 dbu is sufficient better to just leave it off.

Re: Best impedance matching

Oh KaiS is faster…

Re: Best impedance matching

Thank you Ning and Kaïs. It is working like a charm now.
I did read the passage in the manual, but I think I now understand it.
This all saves me to use the extra pre-amp with extra power and cables.
I could sell it....

9 (edited by KaiS 2022-07-28 18:20:04)

Re: Best impedance matching

johanj wrote:

This all saves me to use the extra pre-amp with extra power and cables.
I could sell it....

Yes wink

And there’s 6 dB of digital extra gain in the Analog Input settings, in case you still need a bit more level for convenient handling.

Re: Best impedance matching

Ah yes, I saw that option. Will try it out, but for now it all sounds great. Thanks

Re: Best impedance matching

johanj wrote:

Ah yes, I saw that option. Will try it out, but for now it all sounds great. Thanks

The 6 dB Digital Gain doesn’t change the sound, it’s just an adaption AFTER the AD-Converter to better fit the level to other sources.

Re: Best impedance matching

Thanks, but the level is nicely even with my digital source. Good to know that it can be used to finetune the level.
I also noticed that after switching the level back to +4db, I can just turn the Autoref ON again. That is also a nice safeguard.

Re: Best impedance matching

johanj wrote:

I also noticed that after switching the level back to +4db, I can just turn the Autoref ON again. That is also a nice safeguard.

Sooner or later the Analog Input’s Auto Reference Level will unintentionally switch back to a higher reference level.

With vinyl turntables lowering the needle or occasional clicks can produce high levels that trigger the mechanism.

Probably better to leave Auto Ref Level OFF in this case.

At least, when this happens, you’ll know why wink

Re: Best impedance matching

Thank you Kaïs, your tips are very valuable. I think I put the autoref off, because the input level is always from the same turntable. The pops can indeed be loud. Or what to think of cleaning the needle while forget to turn down the volume a bit.
Thanks again. This forum is the most efficient I ever met.

Re: Best impedance matching

And you had a provisional thought… the autoref did switch to +13 allready.