audio-talk

SteveTheShadow · Posted: Fri Jul 17, 2009 10:01 pm Post subject: All DHT Phono Stage

Now that the school summer holidays are upon us and I've finally got a "proper" teaching job to go back to in September at a school 5 minutes walk from our house Very Happy

I can think about spending a few bob to build a phono stage.

I stumbled across this one on Dmitri Nizhegorodov's website that uses miniature battery DHTs.

I was partly inspired by this quote by t'other Andrew in my old 46 monkey amp thread

Andrew · Shed dweller Joined: 24 May 2007 Posts: 2301

Ohh err

Now, that I can look forward to Smile

-- Andrew

andrew Ivimey · Posted: Sat Jul 18, 2009 8:15 am Post subject:

errr-oooooo!

'''''''success or failure will depend on how good a PSU I can build. ''''''

and how!

good luck

simon · Posted: Sat Jul 18, 2009 9:17 am Post subject:

Phwwwwwwooooooaaaaaaarrrrrrrrrrrr!!!!!!!!!

Copyright DTB.

A DHT phono, fabulous, can't wait to hear it. Good luck with the filament supplies. Cool

Andrew · Shed dweller Joined: 24 May 2007 Posts: 2301

I notice he has a Spice model for this little valve too, a nice piece of work.

My only concern is the poor output impedance, might need a pre?

Edit, yes I think it will need a pre as its a bit short on gain too.

-- Andrew

SteveTheShadow · Posted: Sat Jul 18, 2009 10:55 am Post subject:

Andrew · Shed dweller Joined: 24 May 2007 Posts: 2301

I would consider building it as stock and then seeing what we can do with the last two stages to increase drive and add a bit more gain. I'd be tempted to try a different last stage rather than add a pre etc.

cheers,

-- Andrew

SteveTheShadow · Posted: Sun Jul 19, 2009 3:43 pm Post subject:

SteveTheShadow · Posted: Sun Jul 19, 2009 4:45 pm Post subject:

Right,

Here are some voltages and currents. The data was taken from the small gif on Dmitri's page so the calcs can only be approximate due to the smallness of the chart I had to work with. It'll do to start with though, so at least I'll know what to expect in terms of voltages, when I come to test the thing.

Not a lot of drive without at least a cathode follower on the end by the looks of it, although he does acknowledge that fact. Nevertheless, it is far too intriguing for me not to build it.

Will · Posted: Sun Jul 19, 2009 7:27 pm Post subject:

Steve I had a look at this as a possible project and it seems nobody has built it, power to your elbow.
I did look on AA and the 3a5 is a wee bit bright, other than that is very good.
Those STC valves could be usefull as a pre to counter any brightness.
I'll be behind you all the way Smile

great stuff.

SteveTheShadow · Posted: Mon Jul 20, 2009 6:25 am Post subject:

Thanks for the vote of confidence Will Very Happy

In terms of PSUs, the choices are clear; either it is to be three power supplies full of iron and valve rectified with EZ81s and gas tube regulated, or three rectified/regulated supplies, full of very big caps and things with legs.

Methinks I need to put Windows 2000 back on the Macbook Pro and break out PSUD. That is unless somebody else could give me a start from their end with some simple supplies: creep creep Smile

Steve

al newall · Old Hand Joined: 06 Aug 2007 Posts: 910 Location: Chester

Andrew · Shed dweller Joined: 24 May 2007 Posts: 2301

Regulated will be cheaper than lots of iron. Question is do you want solid state or valve?

-- Andrew

SteveTheShadow · Posted: Mon Jul 20, 2009 8:34 am Post subject:

Will · Posted: Mon Jul 20, 2009 9:12 am Post subject:

Steve I would build a cLCLC small C before the the first L and a dropper resistor to ground to pull some current through the chokes, before going with regs. Also I would use one supply and decouple the stages before building separate supplies.