The ask dsavitsk thread

[dsavitsk]

A cheap OPT headphone amp is a really cool idea. Are the tubes NOS or in production ?

NOS, but plentiful.

[Beefy]

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?

[dsavitsk]

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.

[n_maher]

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?

[Bidoux]

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.

[dsavitsk]

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.

[TomB]

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.

[n_maher]

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...

[TomB]

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.

[dsavitsk]

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.

[luvdunhill]

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

[Smeggy]

ooh, gonna build this one, and it might even work afterwards

[recstar24]

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.

[TomB]

:D:D

[Beefy]

Brilliant. How long until we get some more details?

[luvdunhill]

looking for some beta volunteers?

[dsavitsk]

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.

[TomB]

Finally cased it up -

Note: Hammond supplied us with these special length cases "unofficially." Hence, the black endplates and unanodized extrusion.

[mrarroyo]

Congratulations, that turned out to be a very good looking amp. Would love to listen to it one day.

[fierce_freak]

That's awesome

[Smeggy]

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.

[dsavitsk]

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

[Tari]

There are lots of cool things you can do with extra circuit boards.

[spritzer]

They are a bloody curse... 

[TomB]

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.