1 Topic by acatala (edited by acatala 2023-12-20 07:20:39)

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  • Registered: 2023-12-19
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Topic: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

Hi folks. This is my first post here. I am a new RME user.

I own a ADI-2 FAC FS v2 (AKM 4493) wich is XLR attached to a preamp Rotel RC-1590 and this one to a power amplifier Rotel RB-1582 MKII (XLR too).

The ADI-2 uses USB input from an Allo USBridge. The music stream comes from Roon with DSD256 upsample configured. I used to play HQPlayer Embedded 4 from an Intel NUC with Debian 11, but after the update to Debian 12 I can't use it anymore. I will go back to HQPlayer Embedded as soon as I build a new ad-hoc computer for him.

Anyway, the reason for this post is that I have a doubt on the Line Output Ref Level that I should use. I was using +7 dBu (+13 dBu at XLR output) and volume set automatically to -1 dB (ADI-2 DAC is DSD Direct configured). It sounds nice but lower than the Coax or CD input, as expected.

If I configured Line Output to +13 dBu (+19 dBu at XLR) sounds with similar preasure as Coax 1 or CD, perhaps a bit louder, but the RC-1590 doesn't seem to distort, at least I am not aware of that.

The Rotel RC-1590 has no tone control enabled.

From Rotel specs I am not able to decide if +13 dBu is a right value to configure. These are both specs:

Rotel RC-1590 (Preamp):
Total Harmonic Distortion (20 Hz - 20k Hz) < 0.002%
Input Sensitivity / Impedance
Phono Input (MM) 2.5 mV / 47k ohms
Line Level Inputs (RCA) 150 mV / 100k ohms
Line Level Inputs (XLR) 250 mV / 100k ohms
Output Level
Line Level (RCA) 1 V
Balanced (XLR) 2 V
Frequency Response:
Phono Input 20 Hz - 20k Hz, 0 ± 0.2 dB
Line Level Inputs 10 Hz - 100k Hz, 0 ± 0.1 dB
Signal to Noise Ratio (A weighting)
Phono Input 80 dB
Line Level Inputs 112 dB
Channel Separation
Phono Input > 75 dB
Line Level Inputs > 75 dB

Rotel RB-1582 MKII (Amplifier):
Continuous Power Output 200 watts/channel,
(20 - 20k Hz, < 0.03%, 8 ohms)
Total Harmonic Distortion (20 Hz - 20k Hz, 8 ohms) < 0.03%
Intermodulation Distortion (60Hz : 7kHz, 4:1) < 0.03%
Frequency Response (± 0.5dB) 10 Hz - 100k Hz
Damping Factor (20 - 20,000 Hz, 8 ohms) 800
Speaker Impedance 4 ohms minimum
Signal to Noise Ratio (IHF A network) 116 dB
Input Impedance/Sensitivity
Unbalanced 12k Ohms/1.9 volt
Balanced 100k Ohms/3.0 volt
Gain
Unbalanced 26.5 dB
Balanced 22.5 dB

Thanks!

2 Reply by KaiS (edited by KaiS 2023-12-19 22:33:04)

  • KaiS
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Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

We just had a similar case.

Here’s how to check if your preamp can take the XLR’s +19 dBu without distortions:

Use this online sine wave Generator, set 400 Hz, and volume to 100%:
https://www.szynalski.com/tone-generator/

Bring down pre’s volume dial close to minimum, but not off.
Play the sine wave through ADI-2 DAC and slowly turn volume and Ref Levels up until audible distortion kicks in.
The transition is clearly audible.

This is the max. level the pre can take.
Now use any level not higher than this one.

KaiS's Website

  • From: Spain
  • Registered: 2023-12-19
  • Posts: 15

Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

Thanks @KaIS!!

I will try this afternoon and let you know.

4 Reply by acatala (edited by acatala 2023-12-20 18:21:59)

  • From: Spain
  • Registered: 2023-12-19
  • Posts: 15

Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

Hello KaiS, I have performed your proposed test.

I have set the preamp Rotel RC-1590 to level 30 (lineal level 0 to 96).
A have attached a MacBook Pro with USB cable to ADI-2 DAC FS.
Set audio output to ADI-2 DAC
Set the online generator to 400 Hz and volume 100%

Line Output to +7 dBu (+13 dBu at XLR) and volume to -5.0 dB. Then I have increased the volume. Until +2.5 dB I have only heard the sin tone, but at +3.0 dB the sound changed.

Line Output to +13 dBu (+19 dBu at XLR) and volume to -5.0 dB. Then I have increased th volume. Until -2.0 dB, only the 400 tone is heard, then at -1.5 dB a slight change is perceived, but at -1.0 dB the tone has changed.

So, the conclusion could be this:
With PCM (and DSD no direct) +13 dBu is OK with volume set below -2.0 dB
With Direct DSD (volume fixed at -1.0 dB) +7 dBu should be used. Perhaps +13 dBu could work too, but it is in the limit.

The horizontal meter was configured Pre-FX, so the input signal level is showed. The sinus wave put the meter up to the limit. With an input signal with a headroom of 2 dB or more, +13 dBu could be used with DSD Direct. Right or am I too optimistic?

5 Reply by KaiS (edited by KaiS 2023-12-21 00:23:43)

  • KaiS
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Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

OK, at XLR +17.5 dBu = (nominal Ref Level +13dBu -1.5 dB) is the onset of distortion.

I‘d stay with nominal Ref Level +7 dBu and Vol 0 dB (= XLR +13dBu).
This works with all sources and formats and gives max. SNR - Signal to Noise Ratio, and resolution.

It even leaves a little headroom, which is better for a clean sound, like for ISPs - Inter Sample Peaks.
Electronics even doesn‘t like to be pushed to the limit under all circumstances, specifically at higher frequencies.

KaiS's Website

  • From: Spain
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Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

Thank KaiS!!.

After the test, I have configured the Ref Level to +7 dBu.

Many thanks for your advice and many thanks to RME for the ADI-2 DAC (and the other devices). It's awesome!

  • From: Spain
  • Registered: 2023-12-19
  • Posts: 15

Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

KaiS wrote:

OK, at XLR +17.5 dBu = (nominal Ref Level +13dBu -1.5 dB) is the onset of distortion.

I‘d stay with nominal Ref Level +7 dBu and Vol 0 dB (= XLR +13dBu).
This works with all sources and formats and gives max. SNR - Signal to Noise Ratio, and resolution.

It even leaves a little headroom, which is better for a clean sound, like for ISPs - Inter Sample Peaks.
Electronics even doesn‘t like to be pushed to the limit under all circumstances, specifically at higher frequencies.

Your recommendation is +7 dBu (+13 dBu at XLR) because it "works with all sources and formats". In my specific case, I use the ADI-2 as DAC in DSD Direct configuration, so the volume is fixed to -1.0 dB. The upsampling software (Roon and/or HQPlayer) set -3.0 dB of headroom for the upsampling process and an extra headroom could be configured.

I wonder if this math is correct:

Ref Level set to +13 dBu (+19 dBu at XLR):
+19 dBu (Ref Level) -1.0 dB (DSD Direct fixed volume) -3.0 dB (upsample headroom) = +15 dBu

+15 dBu < +17 dBu (non-distortion limit)

Should it work? There is a +2 dB headroom and even additional headroom could be applied at the upsampling process.

I am not an audio pro, so my math could be pure fantasy :-)

8 Reply by KaiS (edited by KaiS 2023-12-21 17:16:44)

  • KaiS
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Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

Both Roon’s 3.0 dB headrooms and ADI-2 DAC’s 1.0 dB are there for a reason:

Reconstruction Filter related peaks and ISPs (Inter Sample Peaks) that are created by the upsampling and DA-conversion process.
They only exist with complex signals like music, not with stationary sine waves.

The peaks are short, when they run into clipping/distortions they most likely are almost inaudible.
So if, for any reason, you need as high as possible analog level, your math can be used.


Set:
SETUP / Options / Display /  Hor. Meter: Post-FX dBu

Now you can check if ADI-2 DAC‘s output exceeds +11,5 dBu (= +17.5 dBu at the XLR, which is 6 dB higher by design).

ADI-2‘s meter, as any non-oversamping digital meter, can not show all ISPs, (ISPs only exist in the analog domain), but is a good hint to check your idea in reality.
The meter will at least catch the upsampling related peaks.

KaiS's Website

  • From: Spain
  • Registered: 2023-12-19
  • Posts: 15

Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

Thanks for your wise advice, KaiS. I appreciate it very much.

I will keep the +7 dBu Ref. Level. Actually, it is not a big issue for me. I can compensate with preamp volume. Even, I guess I can set the remote to toggle between +7 dBu and +13 dBu.

10 Reply by KaiS (edited by KaiS 2023-12-21 18:09:30)

  • KaiS
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Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

acatala wrote:

…Even, I guess I can set the remote to toggle between +7 dBu and +13 dBu.

You can store and use a “Setup” for each configuration - that includes Ref Level settings.
If you enable “ Load Volume with Setup” you get what you want.

Read manual page 29 (DAC), 30 (Pro) or 29 (2/4 Pro SE).

Loading certain “Setups” can be assigned to a button push on the device or remote.
Read manual page 26 (DAC), 28 (Pro) or 30 (2/4 Pro SE).
Watch out:
The  “Remap key” configuration is part of each individual “Setup” and needs to be set for each individual “Setup”.
This can be used to toggle through 2 or more Setups with one single button.

Works like this:
As the button assignment isn’t global, but part of each “Setup”, you can even have different assignments to the same button in each Setup - a nice feature that we can use for the following:
Choose ONE single button that you usually don’t need.
In Setup 1 assign: “load Setup 2”
In Setup 2 assign: “load Setup 1”
Now this single button toggles between both Setups.

This method can be extended to load even more Setups if needed, like:
In Setup 1 assign: “load Setup 2”
In Setup 2 assign: “load Setup 3”
In Setup 3 assign: “load Setup 4”
In Setup 4 assign: “load Setup 1”
Now the single button circles through Setup 1-4, clever, isn’t it?!

As for loading Setups ADI-2 asks for confirmation, a double-push is needed to execute the load.
Holding the button more than 1s, the button‘s original function is available.
Therefore I typically assign the SETUP button to load Setups – sic!

KaiS's Website

  • From: Spain
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  • Posts: 15

Re: ADI-2 DAC FS and Rotel RB-1590 preamp (XLR)

You are the man, KaiS!!

Hehe, clever indeed. I take note.