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PostPosted: 05 Sep 2011, 17:59 
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I was lucky enough to be sent a couple of the Oatley Electronics K303 RIAA phono preamplifier kits. An earlier phono preamp from Oatley used a couple of JAN 6418s and jFets. That phono preamp kit was very good. I built and sold two of them and thought them excellent. So did some hard core audiophiles.
Attachment:
k303notes.pdf

The new K303 jFET phono kit comes with a mains powered PS for 110 and 240 mains. The parts are truly pedestrian with carbon Rs and X2 MKP and MKT caps (green caps). I'm told some like the sound of carbon Rs. I decided to build straight out of the pack and change nothing so as to judge the kit at face value. Problem was the kit came with two pairs of 2SK246s where there should have been one pair of 2SK170. When assembled with the wrong jFETs at the front end there is no gain. Therefore just a whisper from the speakers.
Attachment:
K303ss.jpg

I had some 2SK170s spare so I swapped them over. First problem solved. Secondly I build in a timber box. I get a 50hz hum through everything. Today I will upgrade the enclosure to a cheap Al case and see if the hum goes. I thought it may have been due to the fact the AC tranni is near the amp section but this is not the case.
Attachment:
K303finSS.jpg

Also the preamp has too much gain. I cut away the bypass cap on the first jFET (2SK170). This reduced the gain and dropped some of the hum. Sibilance is not well controlled in this preamp. This could be due to cheap parts or some high frequency distortion. By increasing the NFB of the first stage the sibilance control improved.

Is there any good news: Sound stage is big and detailed but I do require further listening. The kit is easy to assemble and with a mains driven universal voltage PS a good starter kit for the novice.

More to come.
Attachment:
K303inboxSS.jpg

Attachment:
BoxSS.jpg


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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 05 Sep 2011, 22:24 
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When you have a device with gain in the 100s of times any AC hum or radio transmission noise is going to get a free ride right to speakers. That was certainly was the case when I housed the K303 jFET phono preamp kit in a timber box. What didn't help was the excessive gain this preamp started with. I would thoroughly recommend you do not bypass either of the source resistors on the jFETS unless you have a low very low output cartridge or MC. If MC change the load resistor to something like 100ohms. 47K is good for most MMs.

As you can see from the images I chose the cheapest crappiest metal instrument case I had on hand. This flimsy bread box may be a good shield against air born electrical noise but for resonance and vibration issues its a failure. As a note it is interesting how quickly you can build in anger. I go this case drilled and filled in but a few hours.

How does it sound. I'm a little embarrassed, it sounds excellent. Why embarrassed. I have done all wrong things in construction. Cheap solder, stayed with the kits cheap parts, flimsy case no shielding of the PS. I tried to make it bad it sounds better (on initial listening) than the BHL jFET phono kit which I think is phenomenal!! With care in construction and a much better enclosure this phono preamp my be the best I have every heard. It runs straight from mains, is dead quiet (a capacitor multiplier is part of the PS) and cheap. The PCBs are solder masked and silk screened. Most of the PCB is earth plate. In this build I did keep the signal earth and case earth separate.

How does it sound? This is a non-comparative description. I am yet to compare it with the BHL preamp. Bass is very deep and very, very punchy, mids and treble are crisp and bright. Treble extended and controlled. Sibilance is good. But where this phono preamp (K303) exceeds is in sound stage detail. Though a little hemmed in it is very deep and extremely detailed. I expect the overall sound to improve over the next few weeks. So far: - very impressed. In fact I found myself smiling out loud when I first listened to it. The kit (Oatley Electronics K303) is to be recommended.
Attachment:
K303preampSS.jpg
Attachment:
K303PSss.jpg
Attachment:
K303RearSS.jpg
Attachment:
K303Assembled_IIss.jpg
Attachment:
K303CanSS.jpg


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PostPosted: 07 Sep 2011, 12:27 
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Great report Mark - thanks for sharing. Will definitely be interested in hearing about your detailed comparison between the two kits. For $30 this is another Oatley kit that looks like it will be a lot of fun and great for the beginner.

Cheers

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PostPosted: 07 Sep 2011, 17:10 
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Gio:It is dead easy to make. One afternoon you could have it up ang going. I have already assembled a second set of brds. but this time I am going to put them in a much better enclosure.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 07 Sep 2011, 21:31 
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The film caps provided with the kit don't look terrible. I would swap out those electrolytic types and go with decent metal film resistors before replacing the film caps.

Cheers

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PostPosted: 08 Sep 2011, 07:49 
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Well I did investigate the caps used and yes they are better than I thought. Polypropelene and Mylar.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 16 Sep 2011, 22:07 
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I had the chance for a second listener to help me compare the Boozhound Labs jFET phono preamp to the Oatley K303 yesterday. The Oatley should have performed much worse than the BHL preamp. But swapping them in and out and comparing a few different LPs didn't really see any big difference. When you think the K303 comes with MKP caps and the BHL Russian PIOs you would think a difference would be obvious. Though I feel a bigger comparitive test is required the K303 for $30 with PS is looking both a good performer and excellent value.

I am building the same K303 PCBs up to go in a better enclosure. If the ensclosure benifit the sound the K303 may rule over the BHL. More comaprison is required.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 24 Sep 2011, 09:22 
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I have two K303 kits. The first I used in a light weight "bread tin". I liked what I heard from the kit so now a better enclosure for the second Kit. I use ferrit beads on the input leads from the TT. The sticky stand-offs have rubber dampeners. These are split rubber gromets.

The paint is Epoxy Enamel. The PS and the phono preamp are seperate. I had a short listen. Sounds very good.
Attachment:
Satndoffss.jpg
Attachment:
FerritBeadss.jpg
Attachment:
K303Casedss.jpg


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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 24 Sep 2011, 23:50 
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All finished and sounding very, very neutral and natural the K303 Red Case. I'm currently listening to the the K303 with dead stock parts and enclosed in a cast Al heavy weight case. I can't say any more than I think this is the best phono preamp to date. Now Cheap-jack said the single stage tube pre I have seen on the 'net is the best. Well I'm going to take the challange. Using the PSs I have developed with the four single tube preamps I have made of late it's a no brainer to make build the phono pre. based on that PS. I may just throw in another 100uf cap to ensure this baby is extra quiet.

Take a look at the snaps. If you could only hear this $30 kit. Excellent. Yet to be A/Bed with the BHL unit.

Bruce I'm going to send you the first I built in the bread tin. Send me your address mate. I'll strap it for 120V.
Attachment:
K303RedCaseRearss.jpg
Attachment:
K303Redcasess.jpg
Attachment:
Gearss.jpg


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PostPosted: 29 Sep 2011, 13:39 
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Hi Mark, I understand one is on the way. I'll give it a thorough test and listen. I have several to compare it to (my current all valve one, a Simaudio Moon LP3, the IC one from Jaycar as I upgraded it, another SS one, a Hafler and a Marantz). Pickups will be a Denon Dl110, Dynavector 10X5 and a Grado Reference Platinum I. A good sampling to test with/against. Without actually hearing it yet, my bet is that it will sound like the Moon LP3. Good company for a $30 kit as the Moon originally went for as much as $500.

BTW I use the same type of cast boxes as you do. For all you diyers out there you can get these things from both electronics suppliers and many hardware stores in several sizes. Cost is quite reasonable. They machine well and take paint well. Some even come in powder coated colors.

Good listening
Bruce

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