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PostPosted: 09 Jun 2010, 06:23 
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Currently I have four phono preamps. Two tube and two SS (OPAMP) based. The tubes ones are the recently released Oatley Electronics K282 - 6418 Tube RIAA Phono Preamp Kit. Both OPAMP builds run on 3X 9V lithiums batteries (27V). One tube K282 is a dead stock build and runs from a 5V SMPS with a 30V SMPS internally and the other a 30V plug pack SMPS with a lot of DC filtering in the preamp and all upgrade parts, silver wire etc.

I did an A/B/C shoot-out to see which I thought was best. The one preamp not tested was the standard build OPAMP unit.

Let’s get the ugly one out of the way first: The K282 standard build with 5V SMPS was the poorest performer. I used only the parts from the kit: carbon resistors and green caps. It still was very good so far from ugly, maybe just a little unattractive. You know what it’s like, your girl friend’s sister is extremely cute but there is nothing wrong with the one you love. It’s like that. If the K282 was the only one you have you’d be a happy man (or women or whatever).

Three different vinyl selections (1st track from three LPs) were first listened to then the preamp changed and all three tracks were re-visited. At the end of the test the best two preamps were re-compared with just the last track. One 180gm Diana Krall track (When I look into your eyes), a 180gm Leonard Bernstein track (Mozart Symph. #36 – Decca) and Direct Metal Cut David Roth track (Peal River). Three very different types of music/recordings but all audiophile strength.

We are down to two with the dismissal of the standard build K282. What of the other two? The SS preamp presented a better sound stage and more clarity where the upgraded K282 was tonally warmer and fuller and right-on-the-money with instrument and voice presentation but leaning to the darker side Luke Skywalker. Both are very quiet and appeared on pace with maybe the K282 being stricter with its timing. Both had qualities which were very likable and it could almost come to the flip of a coin. The rest of my system is a two stage tube preamp and two stage KT88 SE UL config. The cartridge, the Grado wood bodied reference Sonata (AU$480).

If you held a loaded shotgun to my head and told me to “choose” I would take the upgraded K282 for its fleshier portrayal of tonalities, riper sound stage and more realness of preproduction. Interesting when the Oatley K282 kit is AU$47 and the Jaycar SS kit was $40 (no longer available) and Oatley provides a truly International mains plug pack PS. Both good value for money to me.

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PostPosted: 09 Jun 2010, 18:58 
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Great notes Mark. Thanks for sharing. BTW - which opamp phono pres are you referring to?
Cheers

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PostPosted: 11 Jun 2010, 02:35 
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Gio wrote:
Great notes Mark. Thanks for sharing. BTW - which opamp phono pres are you referring to?

Jaycar kit one with upgraded parts: DIY Phono Preamplifier Kit for moving magnet cartridges

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PostPosted: 11 Jun 2010, 09:24 
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mwhouston wrote:
Oatley K282 kit is AU$47

Hi.

How can one still complain to buy a tube phono preamp for such low low price?

No wonder you found the "upgraded" version sounded better than the stock version as the 30V PS is an outboad plug in type. So RFI will be less as the SMPS is located farther way from the preamp.

My suggestion is: can you replace the 30V SMPS to an anologue AC-DC PS & compare? I think it should sound better as no more RFI emiited from the SMPS to affect the sound.

A question: why SMPS is used to power a phonstage of small current load? For convenience or for cheap cost? It would do not help the sound at all if not screwing it up. I wold never use any SMPS for any phono preamp, tube or SS.

Try more complex & dynamic classical music, like Wagner the Ring, Beethoven Choral Sympony last movement, etc etc. & compare. It will sound better with a properly built analogue PS than a digital PS, IMO.

c-J

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PostPosted: 11 Jun 2010, 17:34 
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The upgraded version started life with an external 24V plug pack tranni, rectified and filtered. So only DC entered the phono stage where further filtering and and some voltage reduction took place. BUT there was always a small hum no matter how much filtering I through at it. When I swapped to the computer grade 30V SMPS the hum vanished.

There was a slight amount of background hash so I swapped the tube phono pre for my battery powered OPAMP unit. Same hash. So I figured it has had nothing to do with the phono stage. But when the phono stage is switched off the hash goes away.

So is the noise coming from my TT? Is it in the cartridge, leads??? The tube phono preamp is quieter with the external SMPS so that's how I tested it. The next comparison maybe between 30VDC supply and 30V SMPS ignoring the slight hum. The Hum can only be heard when you place your ear against the speaker. It is not audible from 1 meter away which I feel is a more realist subjective measurement. Yes some 100hz is mixed at extremely low levels into the final sound but not sure to what level it affects it.

I have felt the upgraded tube phono stage sounded better with the 30VDC supply so I may just go ahead with the comparison. Either way the tube phono preamp is excellent and as has been said here: so cheap and easy to build.

How about the full switch mode version with upgraded parts? The un-upgraded version with full switch mode PS was just a little too edgy compared with the others.

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