Nelson Pass ACP + V1R2 Headphone Amp

Just finished my ACP + headphone amp.
Class A.

Setup for 300 Ohm HD 650’s
Added a SMPS filter.

Amazing value for $199.

Typical Nelson Pass discrete class A minimial parts.

Works absolutely

10/10 with Senn 650’s.

The filter added another $10 to the cost of the overall build.

ACP+ (Amp Camp Pre-Amp + Headphone Amp) – diyAudio Store

Highly recommended for folks that want to start building stuff.
This one is simple and hard to get wrong and performs very well.

The design is optimized for 32 ohm headphones, ie Grados etc…but can easily be modified for any impedance. Has 2 inputs and a line out as well.

I am using it only for the HD 650’s.

Its as good as any other amp I have used.


art_acp.pdf (



how warm does it get? i might build one, but i would put it in a case. grandkids and cats =)

want to know how much breathing room it may need.

The heat sinks do get very warm, class A etc…but nothing really super hot.
Just leave some ventilation holes on the top and bottom of the enclosure for some allowance for hot air to escape…

you can see several ACP+'s in cases in the ACP+ discussion at the

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This looks pretty cool, so to speak! I have to ask the dumb question… Where are you getting your ground from? The power cord/supply? I’m just curious.

The Volume Control is grounded to the RCA inputs through the PCB.
The amp is on top of a ground plane pcb.

If your going to use metal case, keep the grounds to it at a minimum.
You need to read the diy audio thread…lots of discussions there…

I am not using a case so only have one ground…its that pcb board.

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Switching supply…only the +/- coming in.

I might add if you want to put it in a case try to have a single ground to the case. To minimize any chances of ground loops. Star ground etc…The “naked” design has the “audio” ground floating in regards to other stuff…and the bottom PCB is to allow it to safely sit on top of stuff and have it out in the open.

That said you still want to be careful with the exposed amp even though there are no really high voltages etc…its still “on” and the heatsinks do get pretty warm.


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Well we have had the ACP + now for over a month now and its setup to match 250-300 ohm headphones in impedance. I use it mainly for my Senn 650’s. I had the 600’s for a few years as a good low cost entry level gold standard. After trying the 660s and 650s my ears liked the 650 sound just a tad better so we sold the 600’s and kept the 650…

Along comes this new low cost, EXCELLENT Class A amp from Nelson Pass and when it became available at DIY Audio I jumped on it. It has been an excellent DIY project. No casework. Hard to really screw this one up…if u can solder.

I have never heard the senns sound as good as the 650 sound with this amp. Feeding with a Schiit Bifrost 2 (now sold) and now with a iFO Pro DSD multibit dac…its a 10/10…Solid. Bass like never thought possible with the Senn 650’s…

I had the Whammy as well, great amp, sold it as well…I love the ACP+ even more.

There are a lot of magic pairings and this is one of them. You can set it up for 32 ohms (the original design and kit setup) or set up with some resistors for almost any impedance. Or pick and intermediate impedance that works well with a wide range of headphones. Not liking compromises, I choose to set it up for senn 6xx’s.

This little amp can stand up to most any other amp well above its $200 price of admission.

You should run. not walk to:

Its one of those really great amps and a really great price

HIGHLY RECOMMENDED…and No I dont get any kickback here…just sharing the love!