Thanks ZM. OPA1612 is unity stable, but for some reason doesn't like me messing with those resistors. However, Wayne's notes about the resistors next to the pot seem to not introduce hiss when I changed those.
I bumped the 2.2k up to 6.8k, and using a 10k pot. Seems to have helped allow for more use of the pot level, but not as much as I would've thought by jumping up to 6.8k. Hmm. I wonder if it's because I'm using a 10k pot..?
I bumped the 2.2k up to 6.8k, and using a 10k pot. Seems to have helped allow for more use of the pot level, but not as much as I would've thought by jumping up to 6.8k. Hmm. I wonder if it's because I'm using a 10k pot..?
pot value is having nothing with attenuation (in -db) per se, but combined with series resistor it forms another L attenuating cell
personally, I don't like doing that - wasting signal energy, and I would stay even without series resistor in front of pot, doing everything with OP gain
if you have too much gain, make 1:2 ratio of these resistors (feedback loop of OP, mentioned before) and then if still high, make them 1:1
personally, I don't like doing that - wasting signal energy, and I would stay even without series resistor in front of pot, doing everything with OP gain
if you have too much gain, make 1:2 ratio of these resistors (feedback loop of OP, mentioned before) and then if still high, make them 1:1
I seem to remember having similar experience. Not that noticeable at normal listening levels with my HD6XX but very distracting with sensitive (32 ohm) IEMS
See pics. I made a reusable part. You are talking about the cap mod? The details for this were in a guide on Burson's site if I recall. I don't hear a difference with or without it, and the V5i seems to run at the same temp with or with out it—my rails are the same as Jim's build guide ~17+/-. I have one set of cans that are around 100 ohm, I also happen to have a stack of IEMs, some very high end, here that were given to me—I will try with them to see about this noise floor.
@JermNZ: Your builds are superb—just thought I'd mention that.
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@JermNZ, Based on your pic there -- did you use 22uF Elna Silmic II instead of the Nichicon bipolar ecaps?
I have some noise floor! Haha. Tried the IEMs, 32 ohm. Definite background shhhhhh, seems to get a little more present when the music plays which is interesting—it attenuates a tad with the volume control. It's really very soft—but I can't unhear it either. I can also get the IEMs to crackle when I mess with the 1/4" adapter. Plug in the LCD-3 and the amp is perfectly silent, they're around 100 ohm. They also sound way way better to me than the IEMs... so this isn't really an issue for me... I have plenty of headphones around, I don't find IEMs particularly comfortable.
So what phones are you using A Jedi?
So what phones are you using A Jedi?
Yeah I think I did.
These ones for the 22uF/25V are Elna Simlic II
But the ones adjacent to the Opamp are Panasonic FC 220uF/25V
Thanks for the pics above - that's sort of what I assumed you were doing but wasn't sure.
My headphones are HD600 and ...... 35 Ohm Focals lol. Shhhhhhhh say the Focals.
I was planning on going the exact same route.. tho with 100uF Panasonic FR instead of 220uF FC.
I'm using the Elegia (105db sensitivity). They're my daily driver while I work. If I could just get the noise down...
Perhaps lowering the gain would help? How would I go about doing that?
Was busy for more than a year after soldering the boards and never really got to fitting it to the chassis. Finally did it today and I must say the sound is clear and crisp and dead silent. Thanks Wayne and everyone who helped make this possible!
Some photos of my build.
Some photos of my build.
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Out of curiosity, I noticed the filter resistors (R20, R21, etc) are recommended at metal film 2W, yet dicussions of CRCRC or CRC filters outside this thread seem to prefer wirewound, then MOX, but recommend against metal film due to handling of surges and peaks, etc.
So why is metal film recommended here? What is appreciated about the technical or sonic attributes to prefer that on the BOM? I do see that they are low noise and have a good temp coefficient.
So why is metal film recommended here? What is appreciated about the technical or sonic attributes to prefer that on the BOM? I do see that they are low noise and have a good temp coefficient.