dsavitsk

Indeed I can. The DAC is pretty simple. It is a CS8416 receiver connected to a SRC4192 upsampling to 96K connected to a Wolfson WM8741 DAC chip. The output is straight off the chip. Generally, people put a buffer, or an opamp, or at least some caps there since the output is biased up ~2.5V and can't drive a difficult load. Here, however, because the amp it was connected to (with short low capacitance cables) has an input transformer, the bias is effectively nullified. The amp thus acts as the output stage for the DAC. The amp is one of my prototypes that Tom has been listening to. It is basically a differential mosfet follower using an input transformer for a little voltage gain, and an output transformer to block offset. The fets are CCS loaded, and there is a servo that measures offset and adjusts one of the current sources to keep them in balance. The arrangement, which is fully differential (not balanced bridged) makes sure that there are no caps in the signal path, no power supply caps in the signal current loops (the "rail" caps are 0.1u per side), and no attempting to match inherently unmatchable P and N channel devices. Here is a simplified schematic: The amp is pretty much designed around, and voiced for Grados. It works OK with a few other phones, but really seems to excel with Grados. There will be a couple of prototypes at CanJam (TomB and I have a table) in nice wood and anodized cases. There will also, I should add, be a new tube amp and maybe a DAC next to it -- more on that in a few days. The long tube amp is one of our prototypes. We had been hoping that prototypers would build them, we'd make changes, and we'd have at least a semblance of the kits at CJ. Alas, the prototype transformers that I thought would take ~3 weeks took two months to get wound. They should be here tomorrow, so more on this very soon. But, we'll have the first version at CJ anyhow with kits sometime later this summer.

Digikey is carrying these now, in case that's interesting: E-Switch - PV6 Series 16mm Anti-Vandal Pushbutton Switch | DigiKey

Guys -- sorry for the long delay. We have the cases. We are just waiting on the transformers which have been promised and delayed a number of times. They are winding them as I type this, so they say, and should ship to me early next week. Also, one person backed out so if anyone wants to jump in for the last one send me a PM. -d

Does anybody (in Chicago?) have a pair of pcb mount octal sockets to share?

What do these (T50rp's) sound like out of the box? Worth playing with for cheap closed phones, or are the mods transforming?

I am going to have to befriend one. But, off the shelf for these would be a lot easier ...

Unfortunately, I haven't found anything like it in the local hardware stores. Sorry, I didn't mean to be that specific. One side will go into aluminum using a small machine screw, the other into wood using a small wood screw. It needs to fit in a space less than 50mm. But, whether those screws are M2.5, 4-40, #4, whatever -- doesn't really matter. I just need something that is overall small. 50, 100? Not sure yet, but more than 3.

Anybody know a good source for angle brackets like the one pictured? Basically, this one would be about perfect if the measurements were in cm, not inches. Overall, I am looking for aluminum or stainless, 20mm to 40mm in length, and holes for 4x 4-40 screws.

Balanced != Bridged. Balanced has no signal ground. The benefits to a balanced topology are many, while the benefit to bridged, at least in headphone use, is that the manufacturer can sell twice as much stuff. http://www.jensen-transformers.com/as/as032.pdf http://www.jensen-transformers.com/an/an004.pdf

Yes No. Sound System Interconnection

More assistance/advice than sourcing ... Anybody tried tapping the mounting holes on the Neutrik PCB mount XLR connectors? Does it work? And, what size tap did you try? The panel mounting holes are very difficult to reach, and when they are packed in on a PCB, the bottom one is, so far as I can tell, completely useless.

With one big difference in that speaker amps are rarely quiet enough.

You got the last one ... I thought you hated output transformers?

Yup, I'll include you on the list. You can probably use whatever you want in terms of size. There can be an issue with a large cap charging across a parafeed transformer and magnetizing the core, but probably not an issue here.

Tom used 3.9u, I used 4u. I think from 3.9u to 4.7u is probably a good spot. Pins are 45mm, so a 41mm long cap is about right. 300V min as unloaded B+ is ~275V or so.

Probably depends on how many people are interested in doing the prototype build. Assuming all goes well, kits should be along before too long Update: Cases will be in the $25 to $30 range.

TomB and I are ready to start gathering people to prototype our new amp. For those who do not know, this is a CCS loaded, transformer coupled parafeed headphone amplifier. The transformers are custom designed 10K:300 ohm with a 32 ohm tap so they should work well with just about any dynamic phones. We would prefer people who have some experience with high voltages and or building with tubes. Also, people who can take a few measurements would be nice, though none of that is, strictly speaking, necessary. All you really need is a soldering iron. Here's how it will work -- we will supply a circuit board, a pair of output transformers, a power transformer, a pair of tubes, and a pair of tube sockets. This will cost about $80 shipped. We will also supply a case, but we don't know the cost yet -- we are still working this out with Hammond, so factor in a bit more than the $80. Everything else (except for the parafeed caps) is available from Digikey or Mouser and should cost in the $40-$60 neighborhood -- the difference being that there are some optional parts, some places to use slightly more expensive parts, etc. For parafeed caps, there are some options for caps with free shipping, or we may see if we can't get a bulk discount somewhere. But, they will cost as low as $6/pair for Solens, about $16 for Clarity Caps which would be our recommendation, or more for Auricaps or whatnot. At any rate, expect between $150 and $200 in the end. For now, we need 6 to 7 people. Both of the prototypes that have been built went together without any issues so the board is a known working board. TomB's comment to me upon firing it up the first time: "The presence is incredible. The blackest background I've ever heard. Bass is spectacular." So, we are not anticipating any real problems, but are looking for feedback on the build process, etc. Once we have people in place, we'll order the transformers and cases which can take a couple of weeks, so this will be late March, early April. PM me directly if you are interested. Thanks!

We will be, but we need to figure out the details of how that will work ... probably take a few days/weeks to get that organized.

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Still probably best to measure it wide open as our interest here is what level the source can output. Nate -- can you set up a spread sheet at the forum level to enter numbers into?

I'd assume that meters will do fine with either 50 or 60Hz as I think they are pretty universal.

What is the source?

I am looking for measurements of the voltage out level of various sources, commercial and otherwise. Nominally, sources are "line level", but this turns out to be a term without a lot of real adherence. Consumer gear is said to be at -10dBV, which equates with ~0.316V RMS, but most sources seem to run hotter than that. Pro gear has a US standard (+4dBu or ~1.228V RMS which is 1.78dBV) and a German one (+6dBu, 1.55V RMS or 3.78dBV). Notice that V RMS, dBV, dBu, and dB are all different things -- you can convert between some of them at dB dBu dBFS dBV to volts conversion - calculator volt volts to dBu and dBV dB mW - convert dB volt convertor converter calculation online attenuation loss gain ratio reference audio engineering dBFS dBVU 0 dB audio logarithm level converter peak to p So, in order to determine what level stuff actually outputs, it is pretty simple to just measure. To do that, you will need a 60Hz 0dB test tone, and a $5 multimeter. A test tone can be downloaded from Free download of bass test tones -- there are several available, but it is probably a good idea to standardize on one. Basically, all you do is play the tone and measure the AC voltage on the meter. For balanced outputs, measure from pin 2 to 3. For single ended, from the pin to ground. You use a 60Hz tone because multimeters are designed to measure AC at the wall, which is 60Hz, so they tend to be reasonably accurate here. Some will work fine at other frequencies, but some probably won't. To get the ball rolling, my WM8741 dac (http://www.head-case.org/forums/do-yourself/476-diy-amp-such-build-gallery-153.html#post331335) that takes the output directly from the chip is ~1.96V (balanced signal) or a little over 8dBu. My other DACs run a little cooler -- for instance, my AD1865N-K based dac which uses a passive IV into C3g's that are parafeeded (parafed?) into Magnequest 15K:500 OPTs runs at ~1.32V, or ~4.6dBu. Measurements of commercial cd players and dac's would be appreciated. For extra credit, it would be interesting to measure the voltage out of listening level across headphones, but that might be another thread. It is best to do this with the phones attached. Thanks!

I think I disagree -- the CCS load is good as it is a high impedance load that keeps the signal current away from ground. An LED is a low impedance load that shunts AC to ground, exactly the opposite of what you want. I'd just stick with a resistor. A negative supply to tie it to would be helpful. If you are feeling really ambitious, use the choke in the cathode. Otherwise, use a CCS in the cathode and a shunting element as a voltage regulator (with a cap from B+ to the cathodes). And, I am not sure I'd run a 6c45 as high as 30mA. 20mA has worked better for me.

I think that's right -- IIRC, the Neko uses dual mono 1794's and a Wolfson receiver.