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6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=1528
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Author:  mwhouston [ 17 May 2010, 03:15 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

Bennybuis wrote:
beware from Oatley, you may buy something from them and never receive it, they will not answer your e-mails and laugh at you at the telephone. This kit I never got turned out expensive now, counting all the phone calls to Australia. Even my very dear friend Mark, having a good relationship with Oatley, couldn't help to solve the situation, Oatley lied to him as well. I ordered 3 kits from them, one of it I just never got.

I believe Oatley has sent the kits but for some reason Benny does not receive them. I am hoping to talk with the owner of Oatley shortly to see what is happening. I and a number of others have all bought kits from Oatley which have all arrived.

Author:  metzb1 [ 18 May 2010, 07:07 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

I just received my two K272A kits in the US less than two weeks after ordering FWIW.

Author:  Bennybuis [ 18 May 2010, 07:39 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

Hi everybody,

now at least Oatley admitted to Mark that they screwed up and never sent the kit to me. Supposedly it is all fixed now. Well, we will see.

Author:  mwhouston [ 18 May 2010, 07:42 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

Bennybuis wrote:
now at least Oatley admitted to Mark that they screwed up and never sent the kit to me. Supposedly it is all fixed now. Well, we will see.

Benny it may take a couple of week for the kits to show.

Author:  mahalaleel [ 25 May 2010, 16:36 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

Hey all, I'm new to the forum :)

I just built the kit! I added the option to switch between TRS and RCA-connectors.
Attachment:
CLOSED.jpg

Attachment:
OPEN.jpg

However, there's always a low-volume background hiss, regardless the headphones I use. I tried Sennheiser HD485 (32 Ohms), Westone UM1's (25 Ohms) and some cheap earbuds.

Also, when using the UM1's, the basses are really boomy and sound distorted (clipped). Does anyone know what may cause this and how to fix it?

Author:  mwhouston [ 25 May 2010, 19:35 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

Strange with these preamps/headphone amps, some people get hiss other don't. I only finished one for a repeat customer in Singapore the other night and it is perfect.

Try turning the gain down. And try a totally different battery. I only use lithium batteries.

Author:  mahalaleel [ 26 May 2010, 04:40 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

mwhouston wrote:
Try turning the gain down. And try a totally different battery. I only use lithium batteries.

The gain doesn't seem to have any effect on the hiss at all. Changing the batteries does not help either. I even tried hooking up an external power supply, but the hiss does not diminish.

Also, as you can see in the pictures, I lined the inside of the box with alu-foil to provide some shielding & reduce hum. It doesn't really seem to have any effect at all... when I touch the foil you can hear a loud buzz as well.

Any other ideas?

Author:  mwhouston [ 26 May 2010, 05:10 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

Electrically connect all the foil areas. Connect all the foil areas to the RCA ground and battery ground. Try that.

Author:  mahalaleel [ 26 May 2010, 06:06 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

mwhouston wrote:
Electrically connect all the foil areas. Connect all the foil areas to the RCA ground and battery ground. Try that.

Did that, does not do much either.

I tried rewiring my circuit so that the switches are bypassed and I just have TRS-to-TRS connection, but the soft hiss is still there :bawling:

Author:  mwhouston [ 26 May 2010, 06:12 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)

Hiss will ocure in most tubes at various levels. It can also be controlled by reducing the filament voltage/current. See if you can reduce the filament volatge by 0.1V. A series resistor with the filament should work.

What voltage is across your filaments at the momment?
Is the hiss the same in both channels?

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