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Old 1st February 2008, 07:26 AM   #1
irishbk is offline irishbk  United States
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Default Question about system design with the K-12

Hi all. Forgive the possibly elementary nature of this post. I'm embarking on my first foray into the world of DIY tubes. I've spent my entire week reading these forums and have learned a lot. Of course, I still have many many questions.

I was looking at purchasing a K-12/K-502 amplifier kit. It seems like a good beginner project, and one of the few within my meager budget. But I also need a pre-amp, specifically for a turntable. I'd love to do the Bottlehead Seduction, but I'm trying to keep my costs down. I know that's a "budget kit" relatively, but my lack of funds just require me to go cheap as possible for now.

S-5 also sells the 12AX7 pre-amp tube kits. But I don't think this is designed specifically as a phono pre-amp. Would this be a poor choice? Another option I was considering was the Hagerman Bugle . I know, I know... it's SS (gasp) and I'll be bastardizing the tube sound. But as a temporary solution, until funds allow me to replace it, will that be a decent/workable pairing?

I would also, ideally, be able to incorporate some sort of stand-alone, multiple-input switching block into the system between pre-amp and amp. So I can plug in CD, Tuner, etc.

Any thoughts/insights you might have would be most appreciated.
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Old 1st February 2008, 02:23 PM   #2
Sherman is offline Sherman  United States
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About source switching- why not build it in to the K-12? Put the K-12 in a chassis with your RCA inputs on it and add a rotary switch to select the input. That's what I did with my K-12.

The phono-pre is a more difficult matter. You need to have a phono preamp that was designed as a phono stage. A regular preamp won't have sufficient gain and won't have RIAA correction. If your budget is tight going solid-state and then building a tube pre when funds permit is a good idea. Take a look at the Art DJ preamp. It has adjustable gain, selectable input capacitance and actually sounds quite good. They are usually available for about $50 US.
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Old 1st February 2008, 06:27 PM   #3
Jeb-D. is offline Jeb-D.  United States
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Quote:
About source switching- why not build it in to the K-12? Put the K-12 in a chassis with your RCA inputs on it and add a rotary switch to select the input. That's what I did with my K-12.
That's what I did too. + added a phono stage of my own design in with it.

Click the image to open in full size.

The Phono stage out of the enclosure.
Click the image to open in full size.
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Old 1st February 2008, 06:52 PM   #4
irishbk is offline irishbk  United States
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Sherman,

Thanks very much for the response and recommendations. The Art DJ Pre is an interesting option. I was hoping to build my own, but for cost and ease... maybe I should be happy with just building the K-12 for now.

Question on building the switch into the K-12. This would be great. Did you find wiring schematics somewhere to do so, or do you have any tips on achieving this? I'm not comfortable designing something myself yet. Thanks again!

-bk
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Old 1st February 2008, 07:55 PM   #5
Sherman is offline Sherman  United States
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Originally posted by irishbk
Sherman,

...

Question on building the switch into the K-12. This would be great. Did you find wiring schematics somewhere to do so, or do you have any tips on achieving this? I'm not comfortable designing something myself yet. Thanks again!

-bk
I've attached a quick diagram on the basics. I've only drawn 2 inputs but you should get the idea. The round thingy is the back of the rotary switch.

One thing to note is you need to make sure which pairs of contacts on your rotary switch are switched together for the left and right channels.

If you go this route don't solder the RCA jacks that come with the kit to the PCB. Instead solder the leads from the rotary switch and the grounds from the new jacks to those holes in the PCB where the original jacks would have mounted.

HTH,
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File Type: jpg input_selector.jpg (32.7 KB, 202 views)
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Old 1st February 2008, 07:58 PM   #6
Sherman is offline Sherman  United States
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Originally posted by Jeb-D.

That's what I did too. + added a phono stage of my own design in with it.

I like that enclosure!
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Old 2nd February 2008, 10:49 AM   #7
irishbk is offline irishbk  United States
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Thanks a lot, Sherman. That drawing is very helpful. Seems like something even a noob like myself can manage.
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Old 2nd February 2008, 10:49 AM   #8
irishbk is offline irishbk  United States
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Quote:
Originally posted by Jeb-D.

That's what I did too. + added a phono stage of my own design in with it.

Click the image to open in full size.

The Phono stage out of the enclosure.
Click the image to open in full size.

Very nice, Jeb. Thanks for the pics.
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Old 2nd February 2008, 02:49 PM   #9
Sherman is offline Sherman  United States
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Originally posted by irishbk
Thanks a lot, Sherman. That drawing is very helpful. Seems like something even a noob like myself can manage.

If you look at Jeb's amp in the photo you'll see he has simply used a DPDT toggle switch as a source selector. A very good solution if you only need two sources.
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Old 3rd February 2008, 04:10 AM   #10
Jeb-D. is offline Jeb-D.  United States
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Thanks for the compliments. I got the chassis for $18 from surplus sales of Nebraska, it's half way down the page.
http://www.surplussales.com/Cab-Rack...re/encl_2.html

The walnut veneer is really nice, the pics don't do it justice. The panels were machined from www.frontpanelexpress.com
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