dsavitsk

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 ...

I love them -- indeed, they have become the only phones I use anymore. Better than any other Grado, John or Joe, that I've heard.

Here's the layout -- comments and suggestions appreciated http://www.ecpaudio.com/pdf/Les_6J6.pdf

I think I'll switch to a DO-201 package if that's an issue -- 1N5820 layout pic later today.

After much sitting around, I think we are about ready to move this project to the next stage. We have implemented several changes to the PCB, but if anyone has any thoughts on additional changes that should be made, please let us know. The changes so far are as follows: - implemented the BJT biasing scheme - added larger CCS heatsinks - moved the heater regulator sink further from the side - added various venting holes - switched to a fixed, LDO, regulator to reduce heat (we'll lower the heater winding voltage, too) - increased board length (!) to 14" to move the OPTs further from the PT to further reduce hum - also increased board width slightly to utilize split construction cases (Context, Heeger, etc.) - switched package for low voltage PS cap to eliminate chance of putting the wrong part in the wrong spot - all jumpers are gone, save for the 120-220 option ... though, we are thinking of making the first batch 120 only due to RoHS issues. We''ll see. - power jack and input jacks have a little more space between them - all panel parts should be spaced correctly for panel mounting - changed part names so no more L/R designation. - added spots for "box" type parafeed caps

B&W is notorious for using really cheap caps in the crossovers, and there is a lot of room for improvement. Likely that even some solens, or something like them, will make a big difference. You have to remove a driver and pull the crossover out that way. Then, desolder and replace. Mine were a pain, but then mine had smaller diameter drivers which gave less room for reaching into the cabinets. Not sure whether the matrix construction will block access, though. Also, when my B&W's got old, some rubber o-rings started decomposing. I emailed a B&W rep who sent me a whole new set.

Sounds like a loose lam. Easiest fix might be to find what is rattling, press it into place, and put some epoxy on it. Or, I can swap you for another one.

I would -- if you don't risk it, you don't have a working hub. If you do, you might. But, I wouldn't risk it if you are not in the room in case is burns up