dsavitsk Posted February 18, 2010 Report Share Posted February 18, 2010 A cheap OPT headphone amp is a really cool idea. Are the tubes NOS or in production ? NOS, but plentiful. Quote Link to comment Share on other sites More sharing options...
Beefy Posted February 18, 2010 Report Share Posted February 18, 2010 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? Quote Link to comment Share on other sites More sharing options...
dsavitsk Posted February 18, 2010 Report Share Posted February 18, 2010 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. Quote Link to comment Share on other sites More sharing options...
n_maher Posted February 18, 2010 Report Share Posted February 18, 2010 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? Quote Link to comment Share on other sites More sharing options...
Bidoux Posted February 18, 2010 Report Share Posted February 18, 2010 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. Quote Link to comment Share on other sites More sharing options...
dsavitsk Posted February 18, 2010 Report Share Posted February 18, 2010 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. Quote Link to comment Share on other sites More sharing options...
TomB Posted February 18, 2010 Report Share Posted February 18, 2010 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. Quote Link to comment Share on other sites More sharing options...
n_maher Posted February 18, 2010 Report Share Posted February 18, 2010 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... Quote Link to comment Share on other sites More sharing options...
TomB Posted February 18, 2010 Report Share Posted February 18, 2010 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. Quote Link to comment Share on other sites More sharing options...
dsavitsk Posted February 18, 2010 Report Share Posted February 18, 2010 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. Quote Link to comment Share on other sites More sharing options...
luvdunhill Posted February 18, 2010 Report Share Posted February 18, 2010 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 Quote Link to comment Share on other sites More sharing options...
Smeggy Posted February 18, 2010 Report Share Posted February 18, 2010 ooh, gonna build this one, and it might even work afterwards Quote Link to comment Share on other sites More sharing options...
recstar24 Posted February 21, 2010 Report Share Posted February 21, 2010 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. Quote Link to comment Share on other sites More sharing options...
TomB Posted March 5, 2010 Report Share Posted March 5, 2010 :D:D Quote Link to comment Share on other sites More sharing options...
Beefy Posted March 5, 2010 Report Share Posted March 5, 2010 Brilliant. How long until we get some more details? Quote Link to comment Share on other sites More sharing options...
luvdunhill Posted March 5, 2010 Report Share Posted March 5, 2010 looking for some beta volunteers? Quote Link to comment Share on other sites More sharing options...
dsavitsk Posted March 5, 2010 Report Share Posted March 5, 2010 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. Quote Link to comment Share on other sites More sharing options...
TomB Posted March 20, 2010 Report Share Posted March 20, 2010 Finally cased it up - Note: Hammond supplied us with these special length cases "unofficially." Hence, the black endplates and unanodized extrusion. Quote Link to comment Share on other sites More sharing options...
mrarroyo Posted March 21, 2010 Report Share Posted March 21, 2010 Congratulations, that turned out to be a very good looking amp. Would love to listen to it one day. Quote Link to comment Share on other sites More sharing options...
fierce_freak Posted March 21, 2010 Report Share Posted March 21, 2010 That's awesome Quote Link to comment Share on other sites More sharing options...
Smeggy Posted March 22, 2010 Report Share Posted March 22, 2010 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. Quote Link to comment Share on other sites More sharing options...
dsavitsk Posted May 7, 2013 Report Share Posted May 7, 2013 (edited) 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, 2013 by dsavitsk Quote Link to comment Share on other sites More sharing options...
Tari Posted May 7, 2013 Report Share Posted May 7, 2013 There are lots of cool things you can do with extra circuit boards. Quote Link to comment Share on other sites More sharing options...
spritzer Posted May 7, 2013 Report Share Posted May 7, 2013 They are a bloody curse... Quote Link to comment Share on other sites More sharing options...
TomB Posted May 18, 2013 Report Share Posted May 18, 2013 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. Quote Link to comment Share on other sites More sharing options...
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