DIY Audio Projects Forum

NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread
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Author:  john55 [ 28 Jun 2017, 05:00 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

What are you using for your power supply? What is your audio source? Put up some photos?

Author:  hbekel [ 08 Aug 2017, 06:40 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Hi everybody,

I have a PSU that delivers both 16V and 33V, So i figured I can build this amp using two lm317s to bring the 16V down to 12.6V for the heaters, and maybe use about 30V for B+.

Is this feasible at all? Or is it a bad idea? My reckoning is that the sound will be more "tuby" at 30V B+.

I know I'll definitely have to use heatsinks for the 317 and 510, and I plan to use 100k pots for the bias voltage. As far as I can tell from the datasheets, the lm317 and irf510 can operate at 30V.

However, I'm not sure about the other components. Should I use 2W resistors instead of 1/4W? And will I need to adjust the grid bias resistor? I tried to figure out how to calculate the grid bias resistor, but I don't really understand how to do it.

Do any other resistor or capacitors need to be changed?

Author:  Gio [ 10 Aug 2017, 20:33 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Hi hbekel, yes, you can do that and it works well, I've tried it out with 24V B+. The LM317 can put out 37V regulated. The limits are noted in the datasheet.

Author:  hbekel [ 12 Aug 2017, 15:20 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Hi Gio,

Thanks, that sounds reassuring. I will just try it and report back :)

Author:  hbekel [ 27 Aug 2017, 11:35 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

I have now build my amp, running at 30V B+. This works and sounds great so far, but there is one major problem: it only works well with input from my mp3 player, which only features a headphone output.

But once I connect a line-out signal from my computers sound card, only the left channel is as loud as with the mp3 player, the right channel is very low in volume. The same happens with a line-out signal from a CD player.

My idea was that maybe the overall input impedance is somehow lower when running on a higher B+(?) and that the line level signal is too weak in terms of power to drive low input impedances. Looking at some introductionary pages about tube amps I found statements that the amps input impedance (for a common-cathode triode amp) is about as high as the input resistor after the input coupling capacitor, Rg or R1 in this circuit. Also these pages noted that a 1M resistor is usually used for Rg as a rule of thumb. So I have tried to use 1M resistors instead of the 100k, but that hasn't changed a bit, neither in volume nor sound quality. The mp3 player still sounds fine while line level inputs won't work properly.

So why is the Rg in this circuit "only" 100k, and might boosting B+ to 30V have anything to do with the behavior I see? Are my assumptions about the input impedance correct? What else could I look for or try? Any help will be greatly appreciated.

Best Regards,

PS: I have already build a version of this circuit using 20V B+, and that one can handle the same line level signals without problems.

Author:  jollyrogr [ 28 Aug 2017, 14:50 ]
Post subject:  Re: 12AU7 / IRF510 HeadAmp Support Thread

KrammeAcoustics wrote:
Hi Forum

To the Head-fi DIY people, build this one, you'll be very pleased. :headphones: I've got ver. NP-100v12 runing ( tested ) for a while and must say i'm really satisfied with the sound. One of the important things in this amp. is the CCS. :lightbuilb:

Applaus to Mr. Gomez've done it again, thanks. :thumbsup:

Thanks to both Mr. Gomez and Gio, for a very detailed presentation, good work. :up:

Instead of 12AU7, i've used 6J5GT tubes, simply because iv'e got a dusin of these. :sleep:

So I could build this with a 6SN7 or 12SN7 then? Any other changes necessary beside the heater voltage?

Author:  Geek [ 29 Aug 2017, 15:11 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

You would have to change some values. *SN7 and 12AU7 are different animals ;)

Author:  hbekel [ 30 Aug 2017, 05:37 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Ok, I found the problem with my build myself, it was a really stupid mistake in the PCB design.

I created the footprints for the input and output jacks myself and failed to note that the datasheet said "pin assignment as seen from the solder side". I blindly assumed they were shown from the component side, so my footprints turned out mirrored.

This caused the right channel and GND to be swapped on both the input and output jacks. My mp3 player is battery powered, so it still kind of worked with this source.

So now my jacks are mounted on the solder side, which promptly fixed all the oddities.

The amp sounds really nice now. Running the tube at about 29.7V has definitely added some more warmth to the sound. Apart from that, I've used 2SK 216 instead of the IRF510, which has also increased the output volume (as was recommended somewhere in this thread). All other components were left at their original values.

Author:  jollyrogr [ 08 Sep 2017, 17:16 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

I want to PTP one of these babies. See attached pdf for my planned layout. Added features are using a 20VDC power supply, regulated to 18v for the plates, regulated to 12.6v for the heaters and e12 delay circuit. The power supply was based on MKEM's design (attached) and the delay is the e12 from the Millet max (also attached).

Does anyone see any mistakes or reason this wouldn't work? Can the e12 use 12.6v dc, or must it have 12v exactly? In MKEM's design, he used a 7812 regulator to put out 12v. My plan was to use a second LM317 to make 12.6 but maybe that's overcomplicating things.


Author:  Matt911 [ 02 Oct 2017, 15:16 ]
Post subject:  Re: NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread

Looks like a fantastic amp! Perfect!
I will be looking to use this in my hifi setup, from my turntable, so the signal goes from my turntable to phono preamp, through this valve amp, then into my power amp.
Will I have any problems with this? Will the sound still have the valve colouring?
Also, how can I increase the colouring of the sound ("the valve sound")?
Thanks in advance!

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