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PostPosted: 05 Aug 2013, 21:32 
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I used some rca cable for my turntable/preamp/amp.

But I just used single strand hookup wire to wire in the female connectors to the phono stage.

So from the 3 prong put the earth ground to the chassis, from the PS board drop a ground, and from the "sound" section of the PCB, drop a ground with the 150 ohm resister/ two caps in parallel?


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PostPosted: 06 Aug 2013, 09:34 
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NuttyLemur wrote:
I used some rca cable for my turntable/preamp/amp.

But I just used single strand hookup wire to wire in the female connectors to the phono stage.

So from the 3 prong put the earth ground to the chassis, from the PS board drop a ground, and from the "sound" section of the PCB, drop a ground with the 150 ohm resister/ two caps in parallel?


The ground of the amp PCB and PS pcb are common. Make connection from only one PCB using the resistor/capacitor.

If the wires from the jacks to the PCB are short you may be OK, however, if they are long meandering wires that's another issue. I recommend using shielded wire from the jacks to the PCB or even tightly twisted pair. But connect the shield/ground at only the PCB end to avoid ground loop.

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The key to a successful build is to keep the smoke IN the circuit.
-Les

We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
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LM380 Bridged Guitar Amp, Oatley K301 Phono Pre-amp, Oatley K272 Headphone Amp, Tube proto-board


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PostPosted: 08 Feb 2014, 17:27 
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Joined: 09 Jan 2014, 16:34
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Hello there,

I'm reearthing a slightly aged thread because i am in the process of building the k301. I have a few questions though if anybody can help out. I have a plastic project enclosure (lousy one from ratshack) that has an optional metal lid/bottom piece. In other words you can enclose the whole thing in plastic by using the plastic lid or use the metal lid. I notice quite a bit of talk about grounding to the metal chassis so I am wondering if I should use the metal lid and if so, would that be enough to provide chassis ground? Would i just install a chassis ground screw through the metal?

Second question... I have a lighted SPST AC switch (http://www.mouser.com/Search/ProductDet ... 2B2-02R-EV) that i was hoping to use as the power switch and in lieu of a led power light. I was thinking I could just put it in between the main coming off of the AC block and the power supply board AC in point. Would this be doable or would it be likely to disruptive?

I've attached a pic of the enclosure with the two PCB's in roughly the manner in which I plan to install them. I haven't soldered the tubes in because i was considering matching them if i have time.

Any thoughts on either of the questions? Thanks guys. Awesome and very helpful thread.


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PostPosted: 08 Feb 2014, 17:29 
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Joined: 09 Jan 2014, 16:34
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Unfortunately I wasn't able to get the picture to upload. But I figure you guys know what your standard ratshack plastic enclosure looks like =)


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PostPosted: 09 Feb 2014, 09:48 
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Hi Ryugreen, welcome to the forum. The photo must be less than 500kB. After you select the photo from your computer, you have to push the "Add the file" button (one row down to the right) to upload the image to the forum.

Cheers

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PostPosted: 09 Feb 2014, 16:30 
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I have two things associated with phono preamps and sub-mini tubes. Firstly when I built my first Oatley phono kit in a metal enclosure I could not get the tubes to stop ringing. Therefore a plastic enclosure works better with the tubes. But when I built a phono stage in a plastic enclosure I had problems with hum etc.

Maybe a combo of the two may work. I would run a thin earth wire to the metal parts. It should help with hum etc.

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Projects: "Grace" - Psvane 6SN7-SE Globe preamp | | "VoXUno" - Single driver MarkAudio 12P speaker | | "Lagoon Take 2" - Single stage tube preamp | Website: retro-thermionic


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PostPosted: 01 Mar 2014, 11:04 
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Les wrote:
NuttyLemur wrote:
I used some rca cable for my turntable/preamp/amp.

But I just used single strand hookup wire to wire in the female connectors to the phono stage.

So from the 3 prong put the earth ground to the chassis, from the PS board drop a ground, and from the "sound" section of the PCB, drop a ground with the 150 ohm resister/ two caps in parallel?


The ground of the amp PCB and PS pcb are common. Make connection from only one PCB using the resistor/capacitor.

If the wires from the jacks to the PCB are short you may be OK, however, if they are long meandering wires that's another issue. I recommend using shielded wire from the jacks to the PCB or even tightly twisted pair. But connect the shield/ground at only the PCB end to avoid ground loop.



Hey guys. Continuing my build of the k301. I have Musicman Turntable with a MM cartridge specified for a 47k resistor. Is it correct that i need to change R1 from 100k to 47k? Wouldn't I also need to change r101 from 100k to 47k if that is the case since they appear to be two channels with the same schematic?

Thanks


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PostPosted: 01 Mar 2014, 16:57 
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Yes you need to change both of these resistors as they sit across each channel.

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Projects: "Grace" - Psvane 6SN7-SE Globe preamp | | "VoXUno" - Single driver MarkAudio 12P speaker | | "Lagoon Take 2" - Single stage tube preamp | Website: retro-thermionic


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PostPosted: 01 Mar 2014, 22:25 
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Joined: 09 Jan 2014, 16:34
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Hey there guys. Trying to get a little help with some troubleshooting.

I finished up my k301 build and everything seemed to be okay but then I realized I needed to go back and change out r101 due to my MM cartridge. I did so, but somehow afterwards, I have lost audio on channel 2. I've confirmed that the resistor is correctly installed. Checked the value. Double checked make sure i have continuity with all my input/output jacks.

I'm starting to think I may have inadvertently fried a component while reinstalled or removing... I have some foil shielding around the edges of my case. Could have shorted something i guess.

My question is what components are likely to cause this? I'm looking at the MOSFETS in particular. I noticed one has continuity between all leads while the other three don't. Also wondering if tube damage was likely?

I have checked voltage throughout and nothing seems totally amiss although I'm not really sure where the best points to compare are. I'm still an amateur when it comes to reading schematics.

Any guidance from those of you with more experience with this build or schematics in general would be great.

Thanks
Ryan


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PostPosted: 20 Jul 2016, 04:33 
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Joined: 20 Jul 2016, 04:05
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I noticed that this preamp has a low cut filter, cause the speakers woofers stop moving like crazy, unlike happens with my others phono preamps. So, I feel a lack of bass extension due to this low cut in K301. Someone knows what should I do in the circuit to cancel or decrease this low cut filter?

Schematics: http://oatleyelectronics.com/files/k301notes.pdf

Attachment:
6418-Tube-Stereo-RIAA-Preamp-Kit-Schematic.jpg


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