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6418 Tube / Opamp Headphone Amp (Oatley Electronics K272A)
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Author:  Amperex [ 26 Jul 2013, 21:49 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

mwhouston wrote:
You can put in a pot where the trimmers are. Remove the trimmers. I leave the trimmers in to balance the channels and use the vol. control on my player (Cowon) to control volume level. If you can avoid a pot do.


Aren't the trimmers for adjusting voltage to the tubes?

Author:  mwhouston [ 27 Jul 2013, 08:58 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

Amperex wrote:
mwhouston wrote:
You can put in a pot where the trimmers are. Remove the trimmers. I leave the trimmers in to balance the channels and use the vol. control on my player (Cowon) to control volume level. If you can avoid a pot do.


Aren't the trimmers for adjusting voltage to the tubes?

No for signal level in.

Author:  Les [ 27 Jul 2013, 13:03 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

mwhouston wrote:
I leave the trimmers in to balance the channels and use the vol. control on my player (Cowon) to control volume level. If you can avoid a pot do.


Mark has hit on an important note. Those trimmers, of course, are the volume adjustment for the amplifier. HOWEVER, the amplifier is not balanced due to variations in tube gain from tube to tube. I would recommend, if you want to have external volume control of the amplifier, that you replace the trimmers with equal value, but separate, pots. In other words, don't use a stacked control. This way, you will be able to individually adjust the channel level. Otherwise, is better to set the trimmers so the amplifier is balanced and use the source's volume control to vary audio level outright, as Mark has indicated.

Author:  mwhouston [ 27 Jul 2013, 19:49 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

Les: I agree with the two separate pots. I have used this solution in the past. The last two K272Cs I built I used pink noise and spoken word to balance the amps using the trimmers.

Lately I'm I only use my player volume control to set listening level.

Author:  nicinico [ 16 Sep 2013, 00:06 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

I'm back to show you the redesigned circuit for my K272A.

Using 555 IC for voltage doubler, the tube plates now has 17 to 18 volts from a single 9v battery.
Metal caps for output and Polystyrene caps for inputs.

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The diagram.

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Added another deck for Modified Linkwitz Crossfeed Filter with "Op Amp keeper".

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Author:  mwhouston [ 16 Sep 2013, 02:57 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

Nicinico: you are going off big time. Love it. Don't stop. What's next?

Author:  nicinico [ 16 Sep 2013, 03:53 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

Thanks Sir,

I have another project in mind...

Author:  mwhouston [ 16 Sep 2013, 05:27 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

nicinico wrote:
I have another project in mind...

What country are from?

Author:  nicinico [ 16 Sep 2013, 07:08 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

Philippines Sir.

Here's my next project.

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Author:  mwhouston [ 16 Sep 2013, 07:17 ]
Post subject:  Re: 6418 Tube / Opamp Headphone Amp (Oatley Electronics K272

nicinico wrote:
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Do you always shoot-up when doing electronics? Or what is the hypodermic for?

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