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| K301 RIAA amp from Oatley http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3157 |
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| Author: | mwhouston [ 20 Jul 2016, 16:46 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
You may be able to remove the input cap but make sure you do not see any voltage on the input. |
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| Author: | strobo [ 20 Jul 2016, 23:57 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
Thanks. Do you mean the C1 (100nF) cap? Which value should I try to just release the bass and keep blocking any voltage at the input? PS: Curious about being this cap, I'll would never suspect about it. I thought that could be the 4.7uF or some components at the inner stage. |
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| Author: | mwhouston [ 21 Jul 2016, 18:04 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
Never make the caps too big. You could try slightly larger in both spots but it may do nothing. Generally as long as your previous stage has an out out cap you can remove the input cap. |
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| Author: | divali [ 16 Feb 2018, 07:59 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
Here's my Oatlety pe-amp working nicely. (No sandbed needed, thank you). https://www.youtube.com/watch?v=1cAJjpmlZrU |
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| Author: | divali [ 19 Feb 2018, 10:23 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
Attachment: 20171201_155245.jpg Here it is. There was a bit of harmonic distortion from the valves whistling but it soon settled down and was then very quiet. Lovely sound sweet and clear. Attachment: 20171201_155227.jpg
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| Author: | mwhouston [ 19 Feb 2018, 18:28 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
Good one. |
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| Author: | dleh [ 03 Apr 2018, 14:46 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
Apologies for adding to an old thread, but I've recently obtained an (unbuilt) second hand K301 Oatley kit to experiment with. Having soldered up the power supply I find I am measuring ~56V at the output not 30V, so I must have done something wrong! What's the most likely cause? David. |
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| Author: | dleh [ 04 Apr 2018, 03:53 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
It must be one or both zeners that have gone open circuit, right? And hence I'm seeing the unregulated voltage. I think I may get a couple more just to try. Anyone know what part number I should replace them with? The markings on these damn things is way too small for my ageing eyes! |
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| Author: | dleh [ 04 Apr 2018, 13:04 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
I've removed what I thought were the zeners and under a magnifying glass can see they are marked 4148. A quick search on the net indicates that these are not zeners at all, but normal signal diodes!? So unless I am mistaken, Oatley must have accidentally put the wrong ones in the kit. I've ordered a pack of BZX85C15 zeners - hopefully these are going to be ok. I've also been wondering whether it's safe to test the output voltage of the power supply without having a load attached? I.e. Is turning it on with no load going to put too much current through the zeners? |
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| Author: | dleh [ 10 Apr 2018, 00:38 ] |
| Post subject: | Re: K301 RIAA amp from Oatley |
Success! With actual zeners in the voltage is now stable at a shade under 30V. So I've completed the kit and it am pleased to report that it actually works! Inside an alu case I am getting some microphonic feedback from the tubes, plus a small amount of mains hum. I guess the case needs dampening and a strip of metal to separate the power supply, so not quite finished yet. |
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