Ah, yes. Thank you for checking. I figured it was the combination of the headphones and the amp, since as I said a moment ago, the Fiio doesn't exhibit this behavior with other gear I've got.
Solution - a little toilet paper in the earcups! 😉😀
So, Greg- are you inferring that the headphone amp has a frequency response problem?
It does not into a 300 ohm headphone- I just checked it, and the Sennheiser has the audible characteristic that one would expect based on wideband sweeps. It also did not on a bench 30 ohm load.
It does not into a 300 ohm headphone- I just checked it, and the Sennheiser has the audible characteristic that one would expect based on wideband sweeps. It also did not on a bench 30 ohm load.
I don't think it rises to a problem, Wyn. Just thinking it would be nice to roll off some highs for some recordings I've got on the Fiio, all of which are high resolution FLAC files. I'm not savvy enough to make any other judgements. I don't detect any high frequency distortions or other artifacts, just the observation that some recordings seem a bit accentuated on the high end. I'm inclined to agree with you that it's the phones, and quite possibly I'm just not getting this frequency response through my other headphone circuits. I don't have any other good headphones to check it with - all cheapies - but I'll try them for kicks.
The issue is that I have no way of testing the amp with a 30 ohm headphone setup and with grounds/supplies/IOs configured by someone else. As a result I'm always anxious to hear of any potential issues, just in case there is an actual problem that needs to be addressed.
In fact I'm trying to come up with a way to apply an additional load to the amps while listening to see if I can duplicate your observation.
In fact I'm trying to come up with a way to apply an additional load to the amps while listening to see if I can duplicate your observation.
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I just tried putting a 1/4" mono jack into the stereo out and using that output to source the left channel power amp while the normal path drives the right channel.
Amazingly enough it works for a while and I cannot hear any difference.
After a time the fault LED comes on and things get a bit squirrely- but as I'm shorting the right headphone channel to ground it's hardly surprising. That did allow me to check the audible frequency response however, and all seems fine.
It also shows that the protection circuitry seems to work well enough, and no failure occurred.
Still not a 30 ohm evaluation though.
Amazingly enough it works for a while and I cannot hear any difference.
After a time the fault LED comes on and things get a bit squirrely- but as I'm shorting the right headphone channel to ground it's hardly surprising. That did allow me to check the audible frequency response however, and all seems fine.
It also shows that the protection circuitry seems to work well enough, and no failure occurred.
Still not a 30 ohm evaluation though.
Well, I have some further observations after more listening and checking my files. First, I must correct an earlier statement, which may provide some explanation.
Not all of the files on the Fiio are hi-res FLAC after all; the ones I was listening to that I felt could have some highs rolled off were actually MP3. I then played them through one of my other sound systems and found them to sound a bit harsher on that system than the FLAC files.
Then I went back and listened to nothing but hi-res FLAC files through the headphone amp, and they sound very neutral, with what I'm thinking is just a higher dynamic range and detail than I am used to hearing through the other headphone amp I'd been primarily using (Fiio Mont Blanc). Bass is really punchy but not boomy, and I'm hearing background voices and instruments more clearly.
It appears your preamp is providing a much higher level of detail, with a lower noise floor, compared to the Mont Blanc, and especially compared to the Audible Illusions I sometimes use, which is quite mid-range heavy. It's a bit like the difference when we moved from cone speakers to our Eminent Technology LFT-8bs; the detail took a bit of time to get used to.
Not all of the files on the Fiio are hi-res FLAC after all; the ones I was listening to that I felt could have some highs rolled off were actually MP3. I then played them through one of my other sound systems and found them to sound a bit harsher on that system than the FLAC files.
Then I went back and listened to nothing but hi-res FLAC files through the headphone amp, and they sound very neutral, with what I'm thinking is just a higher dynamic range and detail than I am used to hearing through the other headphone amp I'd been primarily using (Fiio Mont Blanc). Bass is really punchy but not boomy, and I'm hearing background voices and instruments more clearly.
It appears your preamp is providing a much higher level of detail, with a lower noise floor, compared to the Mont Blanc, and especially compared to the Audible Illusions I sometimes use, which is quite mid-range heavy. It's a bit like the difference when we moved from cone speakers to our Eminent Technology LFT-8bs; the detail took a bit of time to get used to.
I have been using this almost every day to listen to one or two albums a day, and a variety of genres. Just listened to Gregory Porter's new album, sounded fantastic.
Great job, Wyn.
Great job, Wyn.
As of this time there are only three interested parties- not enough to order a new batch.
I'll post again when enough interest exists.
I've had a successful build as well, constructed according to the BOM except for the feedback resistor which I increased to 1K to up the gain a little. I'll be driving 250R DT880s with this amp from an LG VG30 source so I may need to raise the gain a little more.
I had some concern about soldering the DPAKs but it was straightforward in practice. Good cleanliness, a little flux and a large tip in the iron made for a simple job.
I have a chassis coming on the slow boat from China. The headphone amp will live with a Khozmo attenuator and a DRV134 balanced line driver in this chassis to provide a simple but very high quality preamp function.
Thanks again Wyn for making these boards available to a lucky few. It might make your job easier in future if you were willing to share the layout files so interested builders can get their own boards fabricated.
I had some concern about soldering the DPAKs but it was straightforward in practice. Good cleanliness, a little flux and a large tip in the iron made for a simple job.
I have a chassis coming on the slow boat from China. The headphone amp will live with a Khozmo attenuator and a DRV134 balanced line driver in this chassis to provide a simple but very high quality preamp function.
Thanks again Wyn for making these boards available to a lucky few. It might make your job easier in future if you were willing to share the layout files so interested builders can get their own boards fabricated.
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Nice job! I had also considered a Khozmo attenuator, but didn't consider the balanced line driver because I'm building another WP preamp with the headphone amp built in.
It's always a bit of a drag waiting for chassis to arrive!
It's always a bit of a drag waiting for chassis to arrive!
I'd post the Gerbers except that there are almost enough interested parties that a larger build is justified, and I'm still hoping for more conversation on the design itself.
There is, seemingly, sufficient interest for a second run.
Would anyone interested please confirm with a PM?
Would anyone interested please confirm with a PM?