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NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=1799
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Author:  Gio [ 21 Sep 2010, 22:51 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

kallisti5 wrote:
Bah, I've got the Amp built, however I am having strange issues.

The output is really low, if I turn the source up too much the volume gets better however it starts to distort.

Heaters are on and glowing red.

I think there's a problem with the IRF510 or the LM317... adjusting the 10k pots gives me the exact same voltage output on the LM317's (1.27v)

I do notice changes in volume while making the adjustments however... ideas?

FYI... I am using replacement parts which might be causing the issue:

IRF510 -- NTE2382
LM317 -- NTE956

I have some *real* LM317's coming... It might be the NTE956 however that are giving me the problems... thoughts?

Are you able to Set the Bias for the output stage? Are voltages elsewhere ok? Check that the trim pot is working.
Sorry, no experience with those parts.

Let us know how you make out.

Cheers

Author:  TDMalcolm [ 22 Sep 2010, 05:11 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Well Guy's I've started to build my headphone amp based on this one, but, using a novel case design i'll keep things updated as i proceed, but, (another but :? ) it wouldn't be quick :sleep: :mrgreen: cheers for now..
TDMalcolm

Author:  kallisti5 [ 23 Sep 2010, 17:51 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Gio wrote:
Are you able to Set the Bias for the output stage? Are voltages elsewhere ok? Check that the trim pot is working.
Sorry, no experience with those parts.

Yeah, the Bias won't adjust.. it just stays steady at 1.2v even with adjustments. 10k pots on the IRF

Voltages are fine everywhere except on the outward side of the clone LM317

I definitely think the crappy NTE IRF510 clones are the culprit... they are at the heart of whats not working. I'll swap them for some *real* IRF510's and see.

Thanks for the great project!

Author:  solo [ 25 Sep 2010, 09:38 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Hello All
When I finished the PCB, then turn the power on,the R4 10ohm is very hot and after that it's burned ! I don't know why ,something shorted ? someone help

Author:  bennjammin [ 25 Sep 2010, 17:01 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Hey,
Awesome looking project, I'll be starting my build as soon as the parts come in but I have a few questions before I have a few questions. I'm building this in an aluminum chassis and am wondering if I can mount the IRF510 and LM317 on a heat sink attached to the chassis without isolating it. If this can't be done what is the best way to do isolation? I want to basically do what homik did here with the heat sinks...

Image

I'm planning to go without a board and just use ceramic terminal strips. Also, I'm not sure if I have the 10k pots aligned properly. I have a rough layout for reference below...

Image

Thanks,
Ben

Author:  solo [ 27 Sep 2010, 09:52 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Hello
Can any body help? I am using R4 10ohm 1/2 w but it too hot after few second voltage supplied . Then it's smoky and burned! please help

Author:  Gio [ 27 Sep 2010, 11:14 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

solo wrote:
When I finished the PCB, then turn the power on,the R4 10ohm is very hot and after that it's burned ! I don't know why ,something shorted

1/2 W is plenty for that resistor so you do have a problem somewhere which may well be a short. Look for thin stands of wire causing the short. Also, check the pinout of the mosfet and regulators. Any chance you can post a couple of photos?
Cheers

Author:  Gio [ 27 Sep 2010, 11:21 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

bennjammin wrote:
I have a rough layout for reference below...

Hi Ben, note that R4 (on the LM317) is 10 ohm, not 10k as you have shown. Pot layout looks ok.
Cheers

Author:  kallisti5 [ 27 Sep 2010, 21:11 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Here is a picture of my tube amp. (thanks batchpcb for some great PCBs!)

Having issues still.. replaced IRF510 and LM317 to be sure... same issue.

I was measuring the wrong pins before.. Turning the 10k pots will adjust the bias from 8.39 - ~8.69v on the left and right audio sides on the IRF510 source

Source voltage is from a known good 12v 5a power supply... tested drain and the voltage matched the input.

Thoughts? (FYI, yes the wiring of the volume pot is dumb, yes I will replace it at a later date as soon as everything is working :) ) For now the audio pot stays at 0 ohm and i very the volume of the source audio.
Attachment:
tubeamp.jpg

Thanks!

Author:  KrammeAcoustics [ 28 Sep 2010, 09:15 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Hi kallisti5

The build of yours looks great :thumbsup: ...nice PCB.

It's not easy to see why some 12AU7 tubes, acts like this, but they do. It seems this problem with adjustment of bias happens again and again to "some people". I've tried the same thing with a noname 12AU7 tube, which also was acting more like a 12AX7 ...i couldn't adjust lower than 7,5 VDC bias. Problem was the border of 10Kohm. Easy troubleshooting for me, were to add serial 10K resistors, to the 10K trimpots, then it was possible to trim between 10Kohm - 20Kohm ( at ca. 13 Kohm, measurements was 6,3 VDC = half of supply voltage 12,6 VDC ). Problem solved. :wizard: An even better "looking" solution could be a change, from 10Kohm trimpots to 22Kohm trimpots ( then adjustable between 0 - 22Kohm ).

I hope this will help to future "adjust bias problems". Happy DIY to all. ;)

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