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PostPosted: 20 Aug 2012, 13:58 
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Are the modification parts still available for the K272A? I have one I build a few years ago and would like to upgrade it. I am thinking of replacing the caps and op-amps.


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PostPosted: 21 Aug 2012, 03:05 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
prezden wrote:
Are the modification parts still available for the K272A? I have one I build a few years ago and would like to upgrade it. I am thinking of replacing the caps and op-amps.

I can still provide upgrade parts. What I do provide is better signal caps and resistors than come with the basic kit. Also provided is Mil,spec. chip sockets. If required also 1M miniature pots to replace the trimpots on the brd. I have some K272 original kits but no K272A kits except an assembled one I was given for review which I am happy to on-sell.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 21 Aug 2012, 12:06 
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Joined: 26 Jul 2012, 01:48
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Oatley has the K272A kits available, so I would need the upgrade caps and resisters. I noticed that you don't upgrade the op-amps. Is there a reason for this?
How much does a set cost? How much would shipping be to Canada?

Thanks!


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PostPosted: 21 Aug 2012, 17:32 
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prezden wrote:
Oatley has the K272A kits available, so I would need the upgrade caps and resisters. I noticed that you don't upgrade the op-amps. Is there a reason for this?
How much does a set cost? How much would shipping be to Canada?

Thanks!

I do upgrade the Op amp to OPA2134 if the K272A is to be used for a preamp. Otherwise the chip it comes with is a better HP driver. Are to use it as a preamp?

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 21 Aug 2012, 21:25 
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I probably use it as a preamp about 70% of the time and HP the rest of the time.


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PostPosted: 27 Aug 2012, 20:24 
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For those who like the K272 and K272A kit a new version is about to be released. I was talking to the developer last night who has a pure class A headphone amp under development, a MC/MM phono preamp (JFets) complete with power tranni at one end of a long cct. brd. and a new K272 about to be released.

In this release the tube filaments for the K272 will have individual supplies and I am told the brd. is very compact. I'll hazard a guess the kit will be the K272B but I'm not sure. It should be out in the next month or so and sounds like a definite improvement from early versions.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 08 Sep 2012, 19:20 
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Joined: 16 Jun 2010, 11:24
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Location: Texas, USA
I have built 3 of these kits, and they all sound incredible. For the fourth, I ordered the PCB from Oatley and populated it with "upgraded" parts from Mouser. There is no sound coming out of the headphones. Even when I tap the tubes, I still hear nothing from either channel, not even the ringing. I tried an opamp that I know works, and still nothing. It appears to power up fine, so I figure the problem is somewhere in the signal path - both of them. I cannot imagine that both tubes are defective, so I am at a loss. If any of you have any suggestions, I'd really appreciate them.


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PostPosted: 08 Sep 2012, 19:26 
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ewharff wrote:
I have built 3 of these kits, and they all sound incredible. For the fourth, I ordered the PCB from Oatley and populated it with "upgraded" parts from Mouser. There is no sound coming out of the headphones. Even when I tap the tubes, I still hear nothing from either channel, not even the ringing. I tried an opamp that I know works, and still nothing. It appears to power up fine, so I figure the problem is somewhere in the signal path - both of them. I cannot imagine that both tubes are defective, so I am at a loss. If any of you have any suggestions, I'd really appreciate them.

See if the tubes have filament voltage (test at the filament wire), is the tube in backwards and check there is plate voltage. Also check the oamp chip has power on it. Test the chip on the pins where they connect to the chip body.

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Projects:"retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp | ”najah” - Raw 180W Tripath Class D power amp | "Icon" - Shuguang CV-181Z preamp


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PostPosted: 09 Sep 2012, 14:01 
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Location: Texas, USA
[/quote]
See if the tubes have filament voltage (test at the filament wire), is the tube in backwards and check there is plate voltage. Also check the oamp chip has power on it. Test the chip on the pins where they connect to the chip body.[/quote]

Thank you for the help! I'm still pretty new to this hobby.

According to my volt meter, the opamp and the C8050 transistor are both working properly. If I am reading the schematic properly, it appears as though the voltage coming out of the transistor goes through R14 and then goes into pin 5 of V2. Pin 5 also has the proper voltage. However, it appears as though the voltage then comes out pin 3, goes through R15, and then goes into pin 5 of V1. I am getting no voltage on pin 3 of V2, so is my V2 defective?


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PostPosted: 11 Sep 2012, 08:31 
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Location: Texas, USA
mwhouston wrote:
ewharff wrote:
I have built 3 of these kits, and they all sound incredible. For the fourth, I ordered the PCB from Oatley and populated it with "upgraded" parts from Mouser. There is no sound coming out of the headphones. Even when I tap the tubes, I still hear nothing from either channel, not even the ringing. I tried an opamp that I know works, and still nothing. It appears to power up fine, so I figure the problem is somewhere in the signal path - both of them. I cannot imagine that both tubes are defective, so I am at a loss. If any of you have any suggestions, I'd really appreciate them.

See if the tubes have filament voltage (test at the filament wire), is the tube in backwards and check there is plate voltage. Also check the oamp chip has power on it. Test the chip on the pins where they connect to the chip body.


Thank you for the help! I'm still pretty new to this hobby.

According to my volt meter, the opamp and the C8050 transistor are both working properly. If I am reading the schematic properly, it appears as though the current coming out of the transistor goes through R14 and then goes into pin 5 of V2. Pin 5 also has the proper voltage. However, it appears as though the current then comes out pin 3, goes through R15, and then goes into pin 5 of V1. I am getting no voltage on pin 3 of V2, so is my V2 defective?

(Please forgive my previous post. Current flows through the circuit, not voltage.)


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