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PostPosted: 27 May 2010, 17:03 
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Location: Australia
mahalaleel wrote:
mwhouston wrote:
There are some small valued caps around the regulator chip, are all these the correct value. Are all electros in the right way?

Around IC2 (L4949) all the caps are 22µF. The PCB marks them as 10µF but the instructional booklet says that 22µF should work as well. They're all inserted correctly.
The non-electrolytic caps are all marked 2A104J, so they should be 0.1µF as needed.

The resistors all have the correct value.

mwhouston wrote:
Can you make the one from the opamp output to the input R smaller (less gain)?

Are these R7 and R8 on this schematic?
Image

Yes R7 & R8. Try piggy backing another 1M. Just tack it on to see the effect. More FB should drop the gain. If this doesn't work try increasing R7 and R8. Sorry to be unsure.

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Projects:"Rosso" - E88CC SRPP preamp | "Pass F5 trubo” - dual mono high-end amp | “MWH” - 1920s UX-171A preamp | ”Image” - Low Profile 100W Class D amp |


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PostPosted: 27 May 2010, 18:48 
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mwhouston wrote:
Yes R7 & R8. Try piggy backing another 1M. Just tack it on to see the effect. More FB should drop the gain. If this doesn't work try increasing R7 and R8. Sorry to be unsure.

Thanks again for all your help!! You are great :up:

I piggybacked an 1M resistor on top of R7 to make it effectively 500 kOhms. The hiss in the left channel is now much quieter. I tried popping on another meg to see if I could get the hiss to stop completely but it didn't give any difference.

By the way, I discovered something else: the hiss is loudest when the 3V (2xAA battery) is not connected. Once the 3V is applied, the hiss noticeably diminishes.


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PostPosted: 28 May 2010, 06:27 
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Location: Utrecht Nederland
Hallo everybody,

Oatley finally did sent me the kit, a little late, but all is good now. Lets say, it was all a series of misunderstandings and a good share of bad luck. Anyway, I am very happy it all turned out alright.

Last night I assembled the kit using stock parts. This one don't hiss, I am using it currently as pre amp for my OddBlock testing. Sounds good. It is bigger than the old kit and, but build nicer somehow, and better shielded as well, maybe the better kit. The LED in series with the two diodes is always lit, is that right? I suppose so. For the rest, pictures will come very soon, need to prepare an enclosure for it.

Thanks Mark for everything and for coming up for me, will not forget that, my Australian friend.

All the best.

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Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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PostPosted: 28 May 2010, 08:14 
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Bennybuis wrote:
Oatley finally did sent me the kit, a little late, but all is good now. Lets say, it was all a series of misunderstandings and a good share of bad luck. Anyway, I am very happy it all turned out alright.

Last night I assembled the kit using stock parts. This one don't hiss, I am using it currently as pre amp for my OddBlock testing. Sounds good. It is bigger than the old kit and, but build nicer somehow, and better shielded as well, maybe the better kit. The LED in series with the two diodes is always lit, is that right? I suppose so. For the rest, pictures will come very soon, need to prepare an enclosure for it.

Thanks Mark for everything and for coming up for me, will not forget that, my Australian friend.

Benny/Forumers

I had a chat with Branko of Oatley tonight and we are working on the next kit idea. Its funny every time I make a suggestion to Branko about a kit, generally tube related, he says he's thought of the same idea. Oatley has more plans for audio kits so stay tuned.

Benny - why do you think this one doesn't hiss? A few others have this problem. I never have???

I have just built this one for a client in Singapore who has bought s tack of my stuff in the past. This is the best I have made - all upgrade parts, silver wire in the signal path, Alps blue velvet pot, 4oz solid brass knob, OPA2134...
Attachment:
DineshJan6418-BBRearSS.jpg
Attachment:
DineshJan6418-BBFrontSS.jpg


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Projects:"Rosso" - E88CC SRPP preamp | "Pass F5 trubo” - dual mono high-end amp | “MWH” - 1920s UX-171A preamp | ”Image” - Low Profile 100W Class D amp |


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PostPosted: 28 May 2010, 08:57 
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Hi Mark and everybody,

yes this one doesn't hiss at all, it behaves perfect as pre amp and as headphone amp (listening to it with headphones right now). Now I am not in possession of my old kit, Alex from Radio Centrum has borrowed it for some time now, will ask for it back next time I am at the store, so I can do some measurements and compare both kits, most of all.

Now I have much better tools, a oscilloscope and a signal generator, so I can really try to find out, why the old kit hisses.
Attachment:
Oscilloscope.jpg

It will be also interesting to compare, because this kit now I build with stock parts, as supplied from Oatley, while the old kit is built with somewhat better parts, 0,22 uF interstage caps and better output caps, but it hisses. My other old kit, the one that Nikola has now, also hisses on every amp I have, so it is not a ground loop thing from my other equipment, I am sure. Anyway, I am very very happy this one don't hiss. I wanna listen to it some for some time longer in stock condition and then maybe replace the 100 nF caps with 220 nF caps. Maybe not, depending on what the oscilloscope has to says.


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_________________
Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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PostPosted: 28 May 2010, 20:55 
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Joined: 28 May 2010, 20:42
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mwhouston wrote:
I had a chat with Branko of Oatley tonight and we are working on the next kit idea. Its funny every time I make a suggestion to Branko about a kit, generally tube related, he says he's thought of the same idea. Oatley has more plans for audio kits so stay tuned.

I just purchased 2 sets of this K272A kit. How much different as compare to the current one. Hope the "next kit idea" has not too much changes that make the current one obsolete. :(


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PostPosted: 28 May 2010, 22:43 
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AnA wrote:
I just purchased 2 sets of this K272A kit. How much different as compare to the current one. Hope the "next kit idea" has not too much changes that make the current one obsolete. :(

The big change in the K272A was the inclusion of seperate filament cct. The idea was to use higher capacity batteries to provide regulated filament current. I think it was a great move though the K272 only drew 20mA anyhow.

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Projects:"Rosso" - E88CC SRPP preamp | "Pass F5 trubo” - dual mono high-end amp | “MWH” - 1920s UX-171A preamp | ”Image” - Low Profile 100W Class D amp |


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PostPosted: 29 May 2010, 01:26 
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mwhouston wrote:
The big change in the K272A was the inclusion of seperate filament cct. The idea was to use higher capacity batteries to provide regulated filament current. I think it was a great move though the K272 only drew 20mA anyhow.

Thanks mwhouston, that inclusion of the separate of filament cct we already know. However, when you mentioned about the "next kit idea"; I am sure you are not referring to the "separate of filament cct" which we already know? Or maybe you are referring to something else? Please advise and correct me if I am wrong. Thanks.


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PostPosted: 29 May 2010, 01:44 
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Thanks mwhouston, that inclusion of the seperate of filament cct we already know. However, when you mentioned about the "next kit idea"; I am sure you are not refering to the "seperate of filament cct" which we already know? I think you are refering to something else? Please advise and correct me if I am wrong. Thanks.[/quote]

Well yes, something far away from the K272 or K272A. I'm not sure how much I should say here but as long as you keep it strictly between you and me and utter none of this to any body else.

Remember this is only in the first discussion phase so there is a strong chance it may never eventuate. You are no doubt aware of the S5 K-12M bread board 8W PP amp.

http://diyaudioprojects.com/Tubes/

Wouldn't it be nice if there was a kit that pick-up where this left off. So if you built a K-12M and now looking for something with bigger tubes, there was a bread board amp which used bigger tubes. And you could plug and play six or so other large tubes e.g. EL34, 6L6, 6V6, KT88 etc. And you could switch between triode and UL mode. I think it is would be a great kit. If it existed.

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Projects:"Rosso" - E88CC SRPP preamp | "Pass F5 trubo” - dual mono high-end amp | “MWH” - 1920s UX-171A preamp | ”Image” - Low Profile 100W Class D amp |


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PostPosted: 29 May 2010, 03:26 
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Hi guys,

listening to the new K272A most of the night with headphones, I am impresed, it sounds very sweet. Just scoped it, it goes flat down to about 17 HZ, then the output level drops a bit, but is still strong at 10 HZ, maybe 3 db down, though. It also rolls off at 17 khz, which may be due to my home brew signal generator, but hey, at least I got one, haha. This kit don't hiss, not as pre amp, not as headphone amp, will give it a nice enclosure and operate it on batteries. What I liked about the old kit better is it's smaller size an the fact, that it only uses one battery, makes building a psu cheaper and easier. While I type these lines, I get some ideas, maybe build a psu only for 9 volt and put in lithium batteries for the filament? Those go for a long time. Maybe just keep it battery operated, don't know yet. That was really the only advantge, the smaller sice and one voltage. But the new kit is much better shielded, somewhat better spaced out, probably just better. Guys, one of the LED's always stays lit, is that right? Must be, probably. Its the one in series with the two diodes. Thanks.

_________________
Greetings from Holland, Ben

My DIY Audio Projects:
- Single-Ended 12B4A tube amp with ECC802S driver
- DIY Push-Pull KT88 tube amp (OddWatt amp from scratch)
- 832 / GU32 tube push-pull amplifier project


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