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resonance at 500 Hz using headphones - maybe need a different DAC?

I'm primarily a headphone listener (Audeze LCD 2 pre-fazor) and I've been troubled by a resonance around 500 Hz that seems curiously dependent on my digital source. I'm looking to troubleshoot this resonance.

Note that all my equipment has modifications by a technician in the N.J. Audio Society. He adds bypass caps, damping, and ERS fabric.

I was using a modified iFi Nano for a while and liked it (with linear 5V power supply). Then I purchased a Gustard x20pro DAC, had the guy tweak it out. I noticed at first that the sound was much improved compared to my iFi Nano, in terms of an immediacy, transient power, dynamics (micro- and macro-), and so forth, but I was getting something undesirable, which was a resonance in my headphones on certain notes.

I have a musical keyboard and piano synthesis software on my MacBook, so I played different piano notes along with a spectrum analyzer plugin and a parametric EQ, and determined that the main resonance was happening at approx 500 Hz. (C above middle C). There was another resonance an octave above that.

This resonance is particularly noticeable on choral music.

Furthermore, I've made several improvements to my digital sound, like adding a better power cable to the Gustard, experimenting with an Aurender N100 music server, and experimenting with an iFi Zen Stream with different power supplies.

Whenever I tried something that improved the USB source (like adding a better power supply on the Zen Steam, putting a better power cord on the Aurender, etc.) the sound from the Gustard became even more immediate, involving, dynamic etc. But the more of this I was getting from the Gustard, the worse the resonance became. 

I tried two other DACs I had lying around. I went back to the iFi Nano. I also tried a Beringer 24/96 DAC from a long time ago (it's modified, runs off battery supply and is actually pretty good). Both of these DACs had much less resonance or maybe none. But they were less dynamic, transient speed, involving, etc. than the Gustard. Very dynamically tame compared to the Gustard and that's a bit disappointing were I to go with these DACs long term.

So I may want a new DAC if this is the fault of the Gustard, But that's what I'm trying to determine... could a resonance be related to some general good quality of a DAC, like transient speed? Or is a fault in the Gustard?

Before I decide that I want a new DAC, I just want to debug this resonance. If anyone has encountered something like it or has a theory where it comes from, I'd like to know.

magon

Showing 3 responses by magon

magon OP
28 posts
 

It only happens with the Gustard. Did you think the other equipment I mentioned like the Aurender or Zen Stream were DACs? Those were servers/streamers driving the USB input of the Gustard.

I've tried two different headphones, two different headphone amps, and when listening closely to speakers there seems to be some of the peakiness, too.

I did another experiment which helps to convince me that it's the Gustard. I set up my modified iFi iDSD Nano, which is using a very hq linear power supply, and I put my best power cord on the supply, using the Aurender as USB source. The sound had a lot of the qualities of the Gustard, in terms of transient speed, dynamics (micro and macro) etc. But almost no resonance. I then played piano notes through the DAC, and almost no resonance. 

What the Gustard is doing technically... frequency response, etc. ... I don't know, but somehow it makes this resonance worse.

magon OP
28 posts
 

By resonance I mean a sharp peak in the frequency response curve. If I play increasing tones on the piano they sound normal until I get around C above middle C. Suddenly the tones will get much louder and sound distorted for a few notes around middle C. They it will calm down as I keep going up. There's another, less prominent, resonance around an octave above, that is, two octaves above middle C.

The resonances are more obvious with some USB sources than others. They are much more obvious on an Aurender N100, and less obvious on a Windows 11 NUC. Generally the more transient power I'm getting from source/DAC combined, the worse the resonance.

Maybe the DAC is broken. I don't know any other way to explain it. 

magon OP
28 posts
 

To address some of your comments:

Re: LCD-2: I don't think it's the headphone because it only happens on the Gustard. It doesn't happen on the modified iFi iDSD or the Beringer. Also it happens with another headphone, the AKG K712. And furthermore it's a very high-Q resonance. Very sharp, spans only about 3 half steps.

Re open strings: it is true that the 500 Hz resonance is triggered by notes with a lot of fundamental, because it's when the fundamental is at 500 hz (i.e. C above middle C) that it's loudest. It's much more noticeable on close-miked instruments. So for example an album by Maria Scheider, Walking By Moonlight, has a lot of close-miked instruments like piano and saxophone that move up and down scales and keep hitting the resonance. Whereas a chamber music album by Sheffield lab that has more of a perspective miking doesn't trigger the resonance much.

Bondmanp: so obviously you know were talking about Igor Kuznetsoff. He is still doing things from time to time and I'm in touch. I'm having him do one of his Dynamo power cords right now. I'll ask him if he can look at the Gustard. I was thinking I might solve this resonance by tweaking something, but at this point it's obvious I need the original expert to look at it.

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