dsavitsk

I was about to say that I'd trust technical transformer information from Hammond about as far as I could throw one of their power transformers. But, since they undersize the cores, I cold probably throw one pretty far Try these articles -- the bottom two are on PS design audioXpress - Track Listings - Audio Classroom Series

If you are doing a L'es style parafeed amp, those caps are really pretty incidental. The CCSes keep them completely isolated from the signal current loops and can provide up to something like 120dB of ripple rejection meaning that the ripple will be lower than anything you can probably measure. I'd use an electrolytic, and then put a small (0.1u to 1u) film bypass cap right at the CCS. The problem with the Solens is that the big ones are a pain to mount. Oh, and 5ar4 has a slower warm up than the 5u4 as the 5u4 is directly heated. Me, I prefer good sand rectifiers. Tube rectifier impedance is too high. In this amp, again because of the CCS isolation, it makes no difference.

I could be totally wrong, but I'd think a 24V relay would only really need something like 18 to 20V to actually work. That said, could you get away with an 18V relay? Probably easier to find than a 22V transformer

How important are those extra 4 volts? Could you get by with a VPP36-820 at Mouser?

I am certainly happy to help with schematics, ideas, or whatever else you need. The kit is basically a pared down version intended for beginners. But, if you are going to do it P2P, there are a number of things you might do differently -- better CCS, different tubes, a regulator before the CCS, tube rectifier, perhaps a SRPP or a mu follower instead of a solid state CCS (for the record, I don't think this is better, but it is different), etc. Oh, and I happen to know of someone selling some Electra-Print 5K:32 parafeed transformers: FS: Electra-Print 5K:32 2.5W Parafeed Headphone Output Transformer - diyAudio

Proper fuse size is 1.33x the VA rating of the power transformer. Most here use power transformers that are hugely overrated meaning that the fuse is often very large for the circuitry. If that was the case here, you should figure out why the fuse blew as this should not happen under normal operation. This is particularly the case since it happened at a meet so you have no idea what the cause was. Good luck

Just be sure they don't short to the case. And I'll be happy to look at your pre, but probably not till fall or winter.

Take it with a little grain of salt. If you look at the 45 data sheet, renowned as the lowest distortion tube around, at full "undistorted" output it's still up around 5%. Now, it's 5% has basically nothing past the 3rd, but the point is that distortion numbers are nt everything. At least the shape of the distortion is more or less appropriate. My guess is that RMAA is requiring you to run this at a pretty high level, probably higher than you might listen with most common headphones, which results in the 1% THD. If you run it at more like a few mW, the distortion looks a lot better with most upper level stuff buried in the noise. When I switched from using my M-Audio FastTrack Pro as the sound source to instead running it's spdif to my own DAC, a lot of the higher harmonics dropped off quite a bit, so I'd suspect the soundcard is having some influence. All that said, it is what it is -- the tube is not a super low distortion tube, we are running it at the maximum of what it can do, and the OPTs are not super high quality. If you want better tubes/transformers, it will cost a lot more.

There are a whole bunch of tube with different names that may or not be different tubes. I know Tomb likes one of the alternatives better, though I can't remember for the life of me which one it is. Some of them list the acceptabe plate dissipation as being much lower than how we are using them. However, I believe this is the case with Tomb's favorite and to date he hasn't had any issues that I know of. Worst case with this amp if you kill a tube is that the tube dies. Nothing else should be damaged as a consequence, with the possible exception that if the tube shorts internally the CCS transistor could overheat. So, please experiment and let us know what you find out.

"Kiwame" resistors are available from Mouser for $0.16 each. Try this link KOA Speer resistor

Hard to know. Higher might mean a better tube? b/t/w/, looking at the curves again, increasing the cathode bias with a 3 to 3.3V led might be a good thing. It looks like it is a little more linear there.

As the current in the CCSes is increased, the amount of voltage they have to drop decreases both because the plate's voltage increases, and because B+ sags a little. So, the heat will not necessarilly go up too much. I would not use a trimmer, at least not one that is adjusted by hand. These resistors are at high voltage, and the reason we didn't want a trimmer was to keep fingers out. Indeed, there are better CCS designs, but they rely on mosfet Vgs to set current which is a lot less predictable than BJT Vbe and would thus require a trimmer. We decided that it was better to be safe here. Plus, trimmer's can move when they heat up. In the big version of this amp, I use mosfets that are very closely matched. We are going to increase the HS size in the final (boh for BJTs and for the reg). But, I don't think an IC running at 55 or 60C is a big deal.

When you are dealing with tubes that might be +/- 20% and transistors that could be worse, matching resistors hardly matters. If you do want to match anything, tubes would be first followed by Q1L and Q1R, and really matching Q's is not important at all. However, we are recommending that R4L and R4R be closer to 56 ohms instead of 75 which will boost the current through the tubes quite a bit -- up to around 18mA. It measures better, and Tom says it sounds a lot better, particularly on high Z phones for some reason. If you don't want to pry the 75R resistors out, just bypass (parallel) them with something around 200R. To determine more specifically what resistor to use, just divide 1 by the current you want. 1 is approximate here, and depends on how close Vbe is to 0.7, and how close the drop across the CCS's biasing LED is to 1.7 (notice that 1.7-0.7 = 1). As for measurements, these transformers are not likely to be inductive enough that they will give very much bass when run into a high Z load like a sound card. Though, I don't have any idea with the primary inductance is. But, assuming it is not sure high, the high load will likely give you better than expected results at mid to high frequencies, and worse than expected results at low ones. @Colin - THD was definitely better with the LED. I didn't save any of the measurements I did, and it was a while ago, so I'll have to redo them at some point. Overall sound was flat and bass was really flabby and weak. Ryan listened to it for about 8 seconds before declaring the WE option inferior -- it was not a subtle difference. I can't say, though, if this is just this amp, or if this is a generalizable result. I have a DAC that runs an AD1865 into the grid of WE connected, trafo coupled, C3g's and it works fine there. Maybe it would work better with LED bias, though?

For this amp, unless someone has a wildly different take on it than me, I think we are going to do away with the WE option. I think it sounds (and measures) worse. But, as for the larger comment, I was leaving biasing out of the article as it was only meant to deal with parafeed specific issues. Maybe I'll do a separate short article on biasing issues, though there seems to be plenty out there on the topic.

up is 300, down is 32. Article updated

This is just symantecs -- I consider the flow of electrons to be -= to the flow of current. In solid state world, it is, as you say, the opposite. Bah -- this is what proofreaders are for -- I said it exactly backwards You can indeed think of it as an inherent resistance in the tube. In phono stages where you need a certain rp for filter purposes, it is common to augment the rp with an additional resistor. That, I'm afraid, it way too big of a topic for here, and something I can't help much with -- you''ll need to read up on transformer theory.

A couple of the questions here suggested that a more thorough explanation of this amp might be in order. So, to that end I wrote up a little primer on parafeed amps for headphones. This is still a bit of a rough draft, but I posted it in case it is helpful to anyone. Comments on where I might clarify things are appreciated. http://www.ecpaudio.com/pdf/parafeed_basics.pdf

Hard to know whether the imbalance will matter. Yours do seem a little more off than most I have used. Ideally, you can find a pair of tubes that are matched for both mu and gm. But, the way to do this is to put them in the circuit, run a test tone through it, and measure the output. A 60Hz tone and a basic multimeter measuring AC is the easiest way to do this.

Regardless of the difficulty of sourcing the transformers, building that amp is difficult. There are lots of "real" obstacles to having it in one's living room. There's a reason there is only one Frank around ...

Simple in terms of parts count, perhaps, but, getting that thing quiet and stable is real work.

Guys -- there is a fair amount of play front to back in the IEC -- the holes in the board are round, but the pins are wider than they are deep. If you are having issues lining things up, you might try desoldering the IEC, then use the cutout back to line things up, then resolder it. As a general rule, if you have multiple board mounted parts to line up on a panel, it is always easier to mount them to the panel first, then solder.

Not surprising, though if they were matched then you might want to check the CCSes or the bias. Jumpers set the bias -- CCS is always on. Gain is what it is. It is slightly adjustable depending on the impedance of the bias and the amount of current, but not enough here that you'd ever notice. I have my doubts that this is appropriate for orthos, though there is no reason to not turn the dial up to 70 or 100%. [ATTACH=CONFIG]3386[/ATTACH]

15 * 24 = 360 You have 110 hours to spare.

Sure. If there is a big signal swing on the grid and a lot of the current is being delivered to the load, the LEDs current should change with signal. I'd think it would need to be really low frequency to see.

Yes, when you put the legs through the holes in the circuit board, melt a little solder on the juncture to hold them in place.