February 18, 201016 yr A cheap OPT headphone amp is a really cool idea. Are the tubes NOS or in production ? NOS, but plentiful.
February 18, 201016 yr We use a custom made transformer with 300 and 32 ohm taps on the secondary. Without accounting for copper losses, etc, this gives an overall gain of just under 2 into 32 ohms, and just under 6 into 300 ohm loads. In reality, this probably turns into 1.5x and 4x, or something like that. But, I've been using an old TDA1545 DAC with very low output, and there is plenty of gain for that, but with a dac with normal output, there is still enough play in the pot. Sounds perfect. Desperately straining my eyes to see if I can make out the tube markings in the photos...... Oh, and I assume the front selector switch is to select the transformer tap?
February 18, 201016 yr Once they anodize them, that'll probably add back the 0.5mm. ;) Good point -- for now, I think we are going to have to add a tiny shim inside the front bezel.
February 18, 201016 yr Good point -- for now, I think we are going to have to add a tiny shim inside the front bezel. No chance that you're forgetting the fact that the Hammond end panels already essentially have a shim built into the plastic bezel?
February 18, 201016 yr Oh, and I assume the front selector switch is to select the transformer tap? I guess On / Off switch since the power supply is included on the PCB.
February 18, 201016 yr I guess On / Off switch since the power supply is included on the PCB. It's the impedance selector. The on-off switch is built in to the IEC, as is the fuse. This is for safety reasons so that the fuse can't be easily defeated, and when the switch is turned off, there is nothing past the IEC that is live. Also, the yellow caps block the high voltages, so the the front 4" of the amp is entirely low voltage.
February 18, 201016 yr No chance that you're forgetting the fact that the Hammond end panels already essentially have a shim built into the plastic bezel? <IMG]http://www.hammondmfg.com/1455v1B.jpg[/img>I think Doug means that the PCB sticks out by 0.5mm. If I'm not mistaken, the shim in the bezel is going to cover the slots, meaning it will stick out, too. Still, trivial in the scheme of things and Hammond just supplied us a couple of one-offs straight from the production line. We'll get them custom-machined and have them in good shape, eventually, I hope.
February 18, 201016 yr I think Doug means that the PCB sticks out by 0.5mm. If I'm not mistaken, the shim in the bezel is going to cover the slots, meaning it will stick out, too. Still, trivial in the scheme of things and Hammond just supplied us a couple of one-offs straight from the production line. We'll get them custom-machined and have them in good shape, eventually, I hope. It doesn't take much to cut the plastic bezel to allow the board to protrude into the cavit it creates behind the back panel. Not that I've had to do anything like that before...
February 18, 201016 yr It doesn't take much to cut the plastic bezel to allow the board to protrude into the cavit it creates behind the back panel. Not that I've had to do anything like that before...Yep - good point. That will certainly work.
February 18, 201016 yr It's actually not Hammond's doing, as much as I'd like to blame them. The board fits in the case just fine, but the person who did the layout had the pot extend a tiny bit too far. Now, the intention was that the board would be just shorter than the case to allow for some wiggle, in which case things would be fine, but since the board and case are matched, a couple of washers will be needed. As Tom says, this will be fixed in the final.
February 18, 201016 yr That's the idea -- the parts cost is remarkably low -- $1 tube, which is still a secret for now , $9 OPT. The most expensive things there are the IEC and the Alps pot (unless you use Auricaps, I suppose). well, not to mention the case so, surely you have a ballpark full kit number you could throw out in strictest confidences of the hallows of Head Case
February 21, 201016 yr Had a chance to check it out last night, as Doug stopped by with the amp, as well as his balanced solid state. I was really impressed, we spun disks all night and everything sounded killer. Considering what the parts count and what the total kit may cost, this is one sick of a deal for the sound that I was hearing.
March 5, 201016 yr looking for some beta volunteers? 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.
March 20, 201016 yr Finally cased it up - Note: Hammond supplied us with these special length cases "unofficially." Hence, the black endplates and unanodized extrusion.
March 21, 201016 yr Congratulations, that turned out to be a very good looking amp. Would love to listen to it one day.
March 22, 201016 yr Very cool. I like that form factor, it has a look about it. I think mine ( ) will have to have a mesh top to see all the goodies inside.
May 7, 201313 yr The availability of inexpensive circuit boards has been a blessing, and a curse. This is just the crap I don't know what to do with. Note the original Millett Hybrid on the far left Edited May 7, 201313 yr by dsavitsk
May 18, 201313 yr The availability of inexpensive circuit boards has been a blessing, and a curse. This is just the crap I don't know what to do with. Note the original Millett Hybrid on the far left IMG_0157.JPG IMG_0158.JPG Damn! I bet more than half that stuff is still better than the DIY designs available today. Yes, I recognize the original Millett Hybrid PCB - just as it looked in the Audio Xpress magazine.
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