dsavitsk

Does anyone have a 1uF, 250V or higher electrolytic cap (on 2.5mm pins)?

I don't get the appeal -- I don't listen to headphones because I can't afford speakers, I listen to them because I like them better. Why would I want to ruin that experience?

There is this weird belief at HF that a 10W amp is really different from a 1W amp when putting out 1/10W. I heard a pair of these at the NYC meet, and they sounded like PA speakers in a gym. All resonance and awful. Maybe the felt had fallen out, or maybe the amp was a bad match, or maybe I was just not in the mood, but it was not good. Very odd. I am itching to hear another pair now that are known good on a system I am familiar with as something definitely felt wrong.

The auditory neuroscience community uses Etymotic, if that means anything.

The Wolfson WM8741 DAC chips have a voltage output of 2Vrms with a full scale digital signal. 2Vrms is about 5.7Vp-p. The DAC chips can only handle a PS of up to 5.5V, and are really recommended to run at 5V (actually, they can take 7V, but Wolfson will tell you never to actually run them over 5.5V). Anyhow, suffice it to say that the chips clip. They have an option to cut the signal by 2dB which results in 4.5Vp-p (~1.59Vrms) which they do just fine with. Different headphones perform differently with different amplifiers. Full stop. The notion that one perfect amp can perfectly drive everything is simply nonsense. For instance, with a traditional voltage amplifier, I think Grados do best with 10-15 ohms of Zout, balanced or SE. With an amp with near 0 Zout, they sound terrible. And this is a large part of the reason for the "Grados work well with tubes" myth in that tube amps tend to have a non-0 Zout. However, I also think they really shine with a Gm amp with a Zout in the hundreds, if not thousands, of ohms. Those same amps may not do well on other brands/designs. So, finding just the right synergistic combo would be a lot easier if we started matching gear in reasonable ways, rather than treating every headphone as a black box to be driven the same as every other one. Nobody expects a 45 amp to drive their B&W 801's, and nobody expects their Krell monstrosity to drive Loethers, so why do we expect this in the headphone world? Anyhow, this is a great thread so far

I could use one of his his XO's @ 24.576

Basically, the only step left is telling the case manufacturer to go ahead and start. That should happen this week ... I think.

Good to hear you solved this. And, good to know that we need to check each of these transformers individually before sending them out.

Too many hand matched parts/different configurations to make that work. Also, I am concerned that stencils and/or ovens will leave filled through holes. So, the directional hot air seems like a decent solution. Pace is definitely too expensive, but I think I'll give one of the less expensive ones a try and see what happens. I took rework to suggest that nobody would solder a whole PCB full of SMD parts with one, but that it was the best way to do a few. I guess I'll find out.

Happy Birthday!

Does anybody here have any experience with hot air rework station soldering? Anything to look for or avoid? And, how does this compare to flood and suck or toaster oven soldering? I was looking at this one as being in my price range and having generally good Amazon reviews.

Assuming there is no DC across the primaries, you probably just want some standard 600 ohm line level transformers. There are lots of these available for not too much money. My favorites are probably the Cinemag CMOQ-4H which are quad filar on 80% Ni cores. Only issue is that ordering from Cinemag takes some time (I have a couple dozen around, though made to my specs -- send me an email). The Lundahl LL1527 is a good reasonably inexpensive option (it dispenses with some of the features that make Lundahls expensive and which you don't need here), though if the output level is high the cores might be too small. Jensen has a dizzying array of choices, but the Cinemags are probably better and cost less. Probably not a bad idea to pick up some Edcors which can be had for $10 each. Hammond also makes some like the 145E (available at Mouser) which look pretty crappy, but might be OK to play around with. Oh, and eBay is a good source for vintage stuff, something like an Altec 15356, though frankly I don't get the obsession with vintage transformers -- I think new is good here due to improvements in core material.

Transformers vibrate, so anything loose that could rattle due to that vibration could be causing your noise.

Happy Birthday!

Just to keep everyone in the loop, we are waiting on a vendor. But, I think we are getting close ...

One other note -- fwiw, the 80dB down distortion peak in those graphs is ~0.01%, Adding in -95dB brings it to 0.01016%

Yes, yes, but you can consider everything up to the DAC chip the "transport". That is, comparing the effect of two different jitter reducers is one way to decide if you think jitter matters. Plugging in two different transports is another -- I just happened to have these graphs on my HDD and thought they might be interesting.

I built these two DACs. Both use a CS8416 receiver, a WM8741 DAC, and the same output stage. One uses a Wolfson receiver between the 8416 and the 8741 to reduce jitter, the other an ASRC. The ASRC is upsampling which may be a bigger difference than the jitter, so the test is not quite fair. I'll need to retest with a different clock speed to equal that out. But, the jitter is one of two main variables, so take it as you will. THD and frequency response differences shown below. Note that there is 0 feedback in these designs (not even source follower local fedback), so THD is higher than for an opamp output stage, but still very good and the sort of distortion that generally does not sound bad. 8804 has (very slightly) higher 2nd harmonics, ASRC has higher everything else. 8804 has higher noise floor which I can't explain. (The 60Hz/120Hz/180Hz/... bumps are an artifact of the soundcard.) The frequency response for the 8804 looks slightly better, too. I think the ASRC sounds better. Colin has heard both so he may be able to comment further. 8804 THD ASRC THD 8804 FR ASRC FR

This is true, but it is only part of the problem. More important than the length of the sentences is that we prosecute and lock people up at all for minor stuff. And, more important than that is that while incarceration is costly, the process of getting someone from arrest to prison via plea bargains is hyper efficient and cheap. Require a trial for the 95% of convictions obtained through plea bargains and the prison population would drop dramatically.

The mounting hole has depth, so unless you are cutting a gouge in the PCB to accommodate it, then the board can't be any higher. Also there are some little feet on the other side that are at the same level as the edge of the mounting hole.

It looks like 12.5mm to me ...

If you do this, make sure you can put it back. I think it will be noisy. Yes. It was the interaction of the choke + the regulator that sounded like a police siren. When I put in a new regulator (LR8 + a pass transistor), all was well. And with mine (a SHA-1 so maybe different), basically all noise was from B+ and the tubes. The tubes I just had to dig around to find a reasonably quiet pair, but replacing that horrid B+ regulator they used made a big difference.

As far as gain goes, you are probably better off replacing the 6dj8 with a lower mu tube if that's an issue. It does not need to drive anything very difficult, so increasing the rp is fine. Biggest issue in doing this is the heater which may mean some creative trace cutting. Compared to what was available at the time, it was a nice amp. But, there are lots of much better amps out there today.

Just swap them from channel to channel, if the problem moves, you've found the issue.

It doesn't really matter. The PS has a bleeder resistor that you could tie an LED to the end of, but either is fine. But, the amp does already have 6 LEDs and two tubes, all of which glow when it is on ...