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Lack of bass with DAC+

Siegmund Schekel

January 17, 2022 20:48

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Hello

Since 2 weeks I hear music over a PI2B and a Hifiberry DAC+ with Volumio as Software. The most seems to be fine, the sound is quite good. But compared to my CD-player and the HDMI-sources it has much fewer deep bass then them. So I build a little line driver with an OPA 2134. Gain is 1. Now the bass is as expected.

Is it possible that the DAC+ can't drive the input impedance of 10k from my Amplifier? The cables are from Sommer and short as possible. The Amp is an old (but well working) Myryad MI-120. Even my cheap HDMI-Dac from China has no problem to serve the Amp.

Regards

Siegmund

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8 comments

• 0
  
  HiFiBerry team January 18, 2022 12:13

  Output impedance of our DACs is about 500 Ohm and the frequency response of the DAC+ is flat to frequencies will below 20Hz. I can't say what's causing this in your setup. Unfortunately, without measurement of the specific setup, it's impossible to say what's going on in your setup.

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  Siegmund Schekel January 18, 2022 13:16

  OK. I now tested it by myself. I replaced the line driver with R's between the DAC-out and the Amp-in in series with the signal. At first I use 5k, makes 15k total for the input impedance. The volume increased and I noticed a little more bass. Next R was 10k, makes 20k input impedance. Half the volume and a lot more bass. At last I used 15k, makes 25k total. Distinct lower volume but the same bass response as from my CD-player. After that experiment my conclusion is, that the DAC+ can't drive inputs below 25k ohms with the full frequency response. Because I don't own any measure equipment I use a Denon CD: J.S.Bach, Die Orgelmeisterwerke, Helmut Rilling. It contains the deepest frequencies I ever heard on a record. The player is an Onkyo C-7030.

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  HiFiBerry team January 18, 2022 13:48

  The DAC can't easily drive very low impedances. The coupling capacitor of your amplifier limits the frequency response. As the DAC is DC coupled, there is no element that limits frequency response depending on impedance.
  But as I said, without measurements, everything is just pure speculation.

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  Siegmund Schekel January 18, 2022 14:13

  Ok, I see. Imho 10k ohms isn't a very low input impedance. It's usual for many audio devices. In this case it results from the resistance of the volume poti. The first active stage in the Amp was coupled by a 1uF capacitor at 100k beyond it. No other of my devices have a (bass)problem with that. No matter. Currently I have to live with the buffer-solution and to build a new case to get both parts together. I would wish that you measure the output impedance of your DAC's. For some people (like me) it's not unimportant. Oh and, yes, can you tell me, if the DAC2 HD was buffered?

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  HiFiBerry team January 18, 2022 14:14

  I wrote above: output impedance is about 500 Ohm.

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  Siegmund Schekel January 18, 2022 14:31

  Thank you. But can you tell me, if the DAC2 HD was buffered?

• 0
  
  HiFiBerry team January 18, 2022 20:23

  There is no specific definition of  "buffered". What you think is a buffer might not be what others think. The important fact is the output impedance. In this regard the output is "buffered". 

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  Siegmund Schekel January 19, 2022 15:20

  Hello and thank you for the answer. Yes, "buffered" isn't an accurate definition. But in current language it means, that the device is able to drive a line out or cables. No matter. I studied the data sheet of the 1522 and find there, that it can load 5k ohms. So it's a mistery for me, why it doesn't work with my combination of DAC and Amp. The 1796 can serve 4 mA. Thats enough to drive ~600 ohms at 2.1 Volt output. So I hope that the DAC2 HD is able to reproduce deep bass with my Amp without the need for a buffer stage. I'll try it.

  Many thanks for your patience with me and friendly regards.

  Siegmund