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ACP+ (Amp Camp Pre-Amp + Headphone Amp)

  • 2500


This is the ACP+ (Amp Camp Pre-Amp + Headphone Amp) PCB, as built at Burning Amp Festival in 2019.

PCBs ($25)

The pre-amp PCB along with the ground plane are available for purchase (gold traces, 2oz copper). Previously we offered the ability to purchase these separately, but since 99% of customers bought both anyway we have bundled them together allowing for a modest price reduction.

The ground plane allows you to build it naked just like they did at BAF.

Both boards are 8" (W) x 6.5” (L) or 203.2mm (W) x 165.1mm (L).

Parts Kit ($179)

This kit of 122 parts across 48 line items includes everything you need to build a "naked" ACP+ ("naked" meaning there is no chassis).

Notably it includes the matched quad of Toshiba 2SJ74-GR JFETs as well as an alps "Blue Velvet" potentiometer.

Nelson's recommended Triad "wall wart" style power supply is included, which accepts input voltages of 90-264V and has US-style power prongs (if your country uses a different style of prong you will need an adapter).

Please see note below about the parts used in the photographs on this page.

Full Naked Kit Bundle ($199)

A full kit bundle includes the pre-amp PCB, ground plane PCB, parts kit, and JFETs.


Photos of Poet's DIY ACP+

The photos you see here on this page with the gold knob of a built-up ACP+ (taken by Thuss and Farrell) are shown to demonstrate what a completely do-it-yourself ACP+ with a colorful parts selection can look at. 

The parts shown in that photo were all chosen, stuffed, and soldered by Patrick Farrell's 10-year-old daughter, Poet. 

It did not use the parts kit sold on this page. Please refer to the parts kit photo to see what's included in the parts kit. Notably, the knob shown is a silver anodized aluminum knob from Patrick's spare-parts drawer, which was then spray painted gold by hand. This is do-it-yourself audio, let your imagination run wild.

Customer Reviews

Based on 17 reviews
Andreas W.
Exellent Preamp

Since one week I'm listening with the ACP to my favorite playlists of music and I am really fascinated of the musical flow of this Amp. I've build it with a Wolfson DAC together in one enclosure and a separate linear unregulated power supply 2x18V/50VA with main power filter, DC-Blocker and several smoothing capacitors in series. It's the best Preamp I've ever listen to, so thanks to Mr.
Pass and the DIY-store!

Great all round

It’s a Pass design so it sounds great. No need to say more really. But the ‘go naked in the world’ concept is also brilliant. Not only does it keep the cost in the ‘no-brainer of a purchase’ category but, as someone else commented - this thing belongs in the MOMA.

Had some glitches with delivery - first time I’ve ever had any issue with the Store’s brilliant Delivered Duty Paid arrangement for non-US delivery. The Store was very responsive and helpful with putting this right. Thanks Jason.

There were two caps missing but luckily I had near-identical substitutes in the spares bin and, after all, this is DIY so two caps shouldn’t stop the build. Again the Store was prompt with sending the missing caps.

Another superb addition to the Store’s arsenal of great-sounding pieces at what amounts to a steal of a price for what you get.

I built two. Awesome kit

No prior experience with electronics or soldering. First I built the kit. I wasn’t careful. I burnt myself along the way, made a hash of it, but it worked and sounded awesome. Loved it so much I wanted to try and build one with upgraded parts.

I got a second kit but replaced all the resistors and capacitors in the signal path based on some reading and experimentation. Takman metal film resistors, a couple of expensive “audiophile” resistors at the headphone output, Elna Silmic II capacitors, and Audio Note KAISEI 2200uf capacitors to replace the gold 1000uf caps in the kit. The new caps were too big, so I had to MacGruber them in. Designed a custom chassis for it with space for a raspberry pi and an OLED display.

Does it sound better? Maybe, maybe a bit sharper up top and more robust down low; the kit sounds awesome as it is, though. It runs all my headphones from 20 Ohms to 150 Ohms fantastically. The preamp out sounds great on a Mytek Brooklyn Amp+. I don’t have much experience with audiophile amps, but the ACP+ sounds amazing even with headphones I thought were lifeless (HD 660s). Planar or dynamic drivers, different DACs and phono stages, everything sounds great. There’s hiss at the far end of the volume pot, way beyond any volume I would dare listen. Normal to loud listening levels are dead quiet in the background.

I got suckered into buying a couple HPAs that were highly recommended by YouTubers, and this amp is better. If all you need is a single ended HPA with a couple inputs and a preamp out, I think you might be hard pressed to find anything that sounds better even at 3-4 times the price of the kit. Plus you get the satisfaction of knowing you built it.

Highly, highly recommend you get a soldering iron and the kit and build one yourself.

Peter B.
ACP Plus

Just finished it. No issues, all went to together well, and tested well. I followed Nelson's guide and also looked at 6L6's guide and I am still going through the blog to see what adventures others are having building this. I am not an electronic engineer but I will give advice if I can, but most members beat me to it...

Ended up using a Meanwell 24v 2.2A internal smps for the power supply, and as I intend leaving it on most of the time, this is probably best best choice from a power bill point of view these days.
Although I may try a linear supply later to see if it makes any difference in the sound. My B1K uses a linear supply as does an AMB M3 I built as a headphone amp, both are truly great sounding devices. The ACP+ sounds good too, just different, not sure which I like more at this point . Still to try the ACP+ as a preamp yet into my DIY Akatika power amp, that's in a another room, just enjoying it as a headphone amp at the moment. Oh, and I should mention I'm not normally a classical music fan, but I accidentally came across a bit on DAB radio and it sounded very good, so I would suggest classical fans should defiantly check this amp out.

Next up, I will have to build a box for it... that gold knob has got me imagination think'in...

Two weeks later: Box is built as per photos, no gold knob yet, can't get the paint due to lock down, hoping to soon though, but I think it looks good as a piece of serious hi fi just for the moment.

Georg S.
ACP preamp done

Perfect sales good that i bayed this unit great Sound
topp on my Rotel Amp RB 1090 and together with my Titan Quadral speakers

compliments to the DIY staff :))) kind regards Georg Pass fan....

Andre v.d.A.
recommended wholeheartedly

This is a very nice headphone amplifier indeed. It sounds terrific. Many thanks to Nelson Pass and the diyaudio community!

I built mine with the recommended components, except for the decoupling capacitor at the entry, which consists of two 4u7 capacitors in parallel. The heatsinks are hovering above the MOSFETs on a piece of alumininiun u-profile The case is made from scrap aluminium sheet welded together with Durafix.
The power source source is from an 2 * 12V Amplimo toroid transformer and a series of 1500uF smoothing capacitors. It's then followed by a super-regulator for which I built my own PCB.

Dirk H.
ACP+ very good preamp - excellent headphoneamp

I built the ACP+ and was very curious if it will beat Waynes LineStage and the B1 Korg NUTUBE-pre?
There is no winner! Built them all! The ACP+ is a very good sounding preamp. I like it especially as a headphoneamp.
The pcb is well made and big size. Add to buy a matched set of P-channel-JFets (LinearSystems) from
the DIYaudiostore and you have a very good basis for an excellent sounding preamp.
Thanks to Nelson Pass to offer this design to the community!
Thanks to the DIYaudiostore -team for the perfect service! Super fast delivery!!!

Cody T.

Great design, layout and board. I’ve been spending more time with ACP than any of my other pre’s - it sounds fantastic. Probably the best HPA I’ve heard too.

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