dsavitsk

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

Looks great, Marc. I am thinking about changing the bias mechanism somewhat drastically. As has been discussed, the WE connection is not my favorite -- I think it sounds a little flat which is why I keep asking everyone about it. Additionally, I think the bias needs to be over ~2.5V in order to prevent high signal from causing grid current, but under 3.1V to keep the plate's voltage reasonable. However, LEDs in that range have a fairly high impedance, which drives up the plate impedance, which is a bad thing. So, on a suggestion from Colin, I am thinking of using a PNP transistor in an emitter follower configuration as a bias element. This is in essence like the pass transistor in a shunt regulator. The idea is that when the base is biased up some amount, Vce (the voltage across the transistor) is the bias + 0.7V. Plus, the impedance is very low -- just a few ohms. Here's what it looks like. Notice that the bias is set by an LED, and the LED gets its biasing current from the resistor string that provides biasing current to the CCS LEDs, so the current is recycled. If you want to implement this on your prototype boards, and I think you should as I think it sound a lot better (and it measures better), here's how: - jumper the transformers to ground (LED connection). - jumper for resistor bias. - remove the bias resistors (R3L and R3R), and replace them with PNP transistors (BC560, etc.) with the emitter connected to the trace that connects to the tube's cathode and the collector grounded. - desolder the ground side of R5L and R5R and stand them straight up. - run a small jumper wire (per side) to connect the unconnected side of R5*, the transistor's base, and the anode of the biasing LED together - For extra credit, connect the positive leg of an electrolytic cap (470u-1000u, 6.3V or higher) to the jumper wire with the negative lead to ground (the base of the transistor, or the cathode of the LED). It seemed to measure a tiny bit better doing this, though this is inconclusive. The overall bias will be the LED's Vf + 0.7V. I used a 2V greed LED for ~2.7V of bias. If you have red LEDs in place, they are fine, too.

Any chance you have a 120:120 isolation transformer around to use before this one? That would allow us to be sure it isn't DC on the power line. At any rate, it sounds like it is likely a bad power transformer -- probably a gap in the lams. If that's what it turns out to be, I have another I can send you. If you can't get that one off the board, I can do that for you, too. And be careful where you put your ear

Looks nice (and looks correct). Any impressions of resistor versus LED?

Are you 100% sure it's the transformer and not the choke? Hammond stuff is notorious for buzzing, but I've never heard an Edcor do it. If you can eliminate the choke as the culprite (remove it and replace it with a resistor), then try the amp without tubes and see if it still buzzes. Also, did you install the jumpers from A to B, and from C to D?

Does anyone have any idea of where to find some of these, or something else that would work for the same purpose, but with threads for screwing them to a bottom plate from the bottom?

And search around for quiet drives -- many hard drives are too noisy.

Look at post 361.

The cable in the picture shows what looks like non-fire related damage -- look at the cut at the base of the burn, and the blue a bit further down. I vote for run over by a chair.

An LED on the cathode is, in theory, similar to a resistor bypassed by a capacitor. At a fixed DC (as from a CCS), it drops a fixed voltage, but it acts as a short circuit to AC. Thus, it biases the tube, but does not increase it's impedance. An unbypassed resistor increases the tubes impedance by ~the resistance X mu. With the LED bias, since there is an AC short to ground, the signal current loop is completed through ground, and thus the transformer primary can be grounded. With the resistor, since there is no capacitor bypass, we need to short circuit the AC somewhere else. Thus, the primary is connected to the cathode which keeps the AC from traversing the resistor, instead being confined to the tube + transformer primary (remember that the plate and cathode are out of phase w/r/t/ each other). This arrangement seems to work better with high current and a high bias -- i.e., with a large resistor, as this is better able to block the AC. It is kind of like a cathodyne with unbalanced loads, and since the plate Z is so high (nearly infinite) you don't lose amplification even as the bias resistor is increased. With the small bias resistors we started with, I thought is was not great sounding. At higher a higher bias point, i.e., a larger bias resistor, it might be more viable -- I have not tried it yet. This does raise the question of why not not connect the primary to the cathode with the blue LED that has a pretty high impedance. And, the answer is that it seems to be not high enough and seems to muck with the phase. Try it. I didn't like it. It also raises the question of why not just use a resistor bypassed by a big cap -- there is some internet lore about how the distortion from electrolytic caps is not measurable, and this turns out to be nonsense. Especially in this spot. The distortion is multiplied by mu, and is clearly higher than the distortion even from a lousy LED. At any rate, I currently have 66.5R CCS resistors (15mA) and crappy blue LEDs, and it seems to sound pretty good at reasonable listening levels. Problem is that B+ is ~205V and plate voltages are 170V and 180V meaning that I don't have a lot of swing room. But, I can probably increase the power transformer by ~30V which should solve that ... at the cost of some more heat.