Thoughts on Oatley K282 Valve Preamp?

[Maxwell Smart]

I was looking around trying to find a nice preamp for my turntable to pair it with my newly completed S5 K-12 kit, when I came across this recent article on the Oatley K282:

6418 Tube RIAA Phono Preamplifier Kit (Oatley Electronics K282)

This seems ideal as its reasonably priced (~$41ish USD), compact, and completely tube based. I was just posting here to find out if anyone has completed one of these kits and if so, their thoughts on the preamp. If anyone has built a project with these tubes and has any information on them, that'd be appreciated too, thanks!

[Eli Duttman]

I glanced at the link. The mention of switched mode PSU sent me running away. Can you say noise?

I repeat, obtaining a decent phono preamp requires that you part with some cash. A $41 POS will not get the job done.

[tinitus]

yeah, had me worried too
ecpecially when I read they wrote them tubes ring like a bell without rubbers
maybe its microfonic, and related to smps

But I wouldnt want to ruin a possibly good cheap project, so I didnt post

But I also thought that playing vinyl, a phono pre is the most important part of a setup
and it should match the pickup
and many other gain matching through the setup should be considered

Broskies new Tetra with onboard supply looks good, and cost more
But the higher voltage is more dangerous, and so a lot more problematic

[Eli Duttman]

I looked quickly at the 6418 spec's and there's more bad news. It's a multi-grid power type. There's no way on earth that a satisfactory S/N ratio can be obtained. Also, R_P is in excess of 400 KOhms, which suggests ZERO load driving capability.

The more I read, the more turned off I get.

[Maxwell Smart]

Hmm, well it's difficult to find a decently priced tube preamp, and I really would like to be able to build one or purchase one for a reasonable price, considering all the time, effort, and money I just spent on getting my K-12 kit setup.

[Maxwell Smart]

I wonder about preamps like this:

HIFI Buffer Audio preamplifier 6N3 Tube PRE-AMP NEW-B1 - eBay (item 120595904218 end time Sep-12-10 03:58:45 PDT)

Of course, you can never find out any information about them online, which is why I don't think I'd ever spend any money on something that others haven't at least mentioned online in forums, reviews, or otherwise.

[ThyDntWntMusic]

its tubes! they sound like you're listing with cotton wool shoved in your ears anyway! who cares about distortion and everything else!

the oatley electronics kit is cheap enough just to give it a try, if it fails, who cares.

[arensattic]

Hallo guys,

The Oatley kit schematics raised the same doubts in my mind as in yours. However, one of your comments is not quite correct. It is true that the 6418 has virtually zero drive capability, but in the K282 kit, each tube is followed by a MOSFET source follower. Gain is provided by the tube and output impedance matching by the MOSFET.

I gave Oatley the benefit of the doubt and have bought both the K272A and K282 kits. My K272A (portable headphone amplifier) is finished and it sounds surprisingly good. VERY good when driving Grado SR125 headphones. For 30 AUS$, I consider the K272A a real winner. The K282 (RIAA phono preamplifier) is not yet finished. By the end of September, I'll (hopefully) know what it sounds like. Will keep you informed. Rumor has it that it sounds much better than one would expect. Keep your fingers crossed...

If you have doubts about the (dual!) switched-mode power supply of the K282 you may consider replacing this by a good quality series or shunt regulator providing 30V output. Or even by 20 AA cells wired in series....

Greetings,

Aren van Waarde
aka arensattic

[richwalters]

Originally Posted by Eli Duttman

I glanced at the link. The mention of switched mode PSU sent me running away.

Ah ! not that bad....

richy

[chlorofille]

I think the K272 preamp/headphone amp is excellent. It is the primary pre-amp in my system and sounds great when run off batteries. (12V car battery in my case). The tiny tubes may turn people off. They add no warmth, but instead expand the soundstage of the music.

If I had a turntable, I'd not think twice about the K282A.

To overcome tube ringing - use rubber grommets and damp your enclosure well with bitumen pads etc. My tubes only ring when I whack the enclosure very hard.