Class A SS: Journey for a budget champion for LCD-X

I have been thrown for a loop - in a way that was so unexpected, that I am still struggling to figure out how this could be.

Warning: this is a long post - apologies!

Quick background: about 2 years ago, I was in the market for a budget solution to drive my LCD-X (2021), so I ended up picking the Schiit Lyr 3, opting for the ES9028 dac card version. Features, flexibility, aesthetics (thing is friggin' gorgeous), and sonics-wise for a complete package, it was a no-brainer. That said, even after demo'ing a small handful of different standalone dacs to pair with it over the past year (and ultimately landing on a Bifrost 2/64), the Lyr 3 has proven to come up just a bit short in a couple key areas for me personally, namely: macrodynamics, speed, and snap/PRaT/etc.

Personal fact: I'm greedy, in that I have a champagne palate on a (premium) beer budget. I also listen to primarily prog / metal, but dabble into a large variety of genres. However, my ears always gravitate towards complex, layered, driving music that lays out a feast of little nuggets. Most audio gear that I've heard over the past 2 decades left me unsatisfied, and I walk away feeling meh. The general sense I end up having is based on a perception of a flat, lifeless, minimally engaging sum of the parts. I think I've been searching for a total audio experience that I couldn't put my finger on, and especially in my price bracket (~$2000 all in), I have come to believe was unattainable...until, so it appears, now.

A few months ago, I attended a Head-Fi Schiit Meet locally here in NC. While I had so much fun getting to listen to a myriad of products (and some great Schiit), I was most surprised by one amplifier in particular that an attendee personally brought with them: a DIY Nelson Pass-designed Amp Camp Pre/Headphone Amp (aka ACP+). He had this paired with his Soekris dac, and when I plugged in my LCD-X, I was a bit floored. An important note: I plugged into the ACP+ very shortly after listening to his Pass Labs HPA-1. To my surprise, there was very little difference when "stepping down" to the very modestly priced ACP+ (which goes for $200 as a DIY kit). Obviously this was in meet conditions, so I'm sure there are more considerable differences/improvements with the HPA-1, but in these conditions, the delta was not as big as I was expecting. While I didn't spend a huge amount of time with it, the experience (and shock) stuck with me long after that meet. Going back home to my Lyr 3, I fell out of love with it. There was something, really multiple things, that I just felt was missing.

Fast forward to a week ago, and I decided to reach out to that attendee (who fortunately lives very locally), to see if I could borrow his ACP+ to have a more dedicated and extended demo period with it, especially since I've recently added the BF2/64 to my chain. To my benefit, he agreed, and for the past several days I have been going through a mental tailspin over this ACP+.

For anyone unfamiliar, or interested, here is a link to the complete kit (which seems to always be out of stock): https://diyaudiostore.com/products/acp-amp-camp-pre-amp?variant=40205532397641

Enter the baby Pass HPA-1 (ACP+)

Recalling from audio memory is always a toss-up for me. So I went into the comparison between the ACP+ and my Lyr 3 with very little expectations or preconceived notions. I have long felt that the Lyr 3 was about as good as you can do for a ~$500 headphone amp, and it has served me well - even with nice improvements when inserting the BF2/64 into the chain. I started with my round of reference tracks, covering a range with some Opeth, Tool, Anathema, Zac Brown Band, Adele, Chris Botti, Daft Punk, and others. I started with the Lyr 3 to get my baseline reference point with several songs and keeping key time points for things to look out for.

Important note: I don't have an A/B switcher, nor did I volume match, and switching between the amps is not a quick process, as the RCA inputs on the ACP+ are every so slightly loose (but safely and securely in place), so I need to use caution and go slow.

So I switch to the ACP+...WTF?!?

Within seconds of starting up Tool's 46 & 2, I was floored - as in, noise-floored. The first thing I noticed was the pitch black background (here I thought the Lyr 3 already had that!). Notes were absolutely popping out of nowhere, and then decaying into nothingness, with no lingering or smearing. First up in that track is the leading guitar work supported by a subtle array of cymbal taps and tings, which right off the bat offer a nice spatial presentation of the depth in the soundstage, and the decay structure of the cymbal strikes. Tasty. The ACP+ rendered all of this with an immediately engaging and fluid manner and highlighted the technical ability of this amp's detail retrieval.

Then the bass drum and bass guitar came in...WTflubberingF?!? My jaw dropped and I LOL'd out of sheer dumbfoundedness. The bass drum kick wasn't just full and with impact, it was precise, tight, snapped, and...was that texture? Every subsequent bass drum kick was as clean and accurate as the one prior. I was sucked in. Note: On the Lyr 3, this initial bass entry comes off with more of a bwub bwub effect, whereas with the ACP+ is was more of a dun dun.

After another minute or so of nuanced drum and guitar work, mixed with Maynard's suppressed vocals, the real business rolls in just before the 2 minute mark. A full detail of drum, guitar, and vocal attack and slam drills into the mix. Holy balls, we're off! This was already the most fun I've had with this track that I can recall in a really long time - not since listening to a Vandersteen Treo CT with Mark Levinson gear combo have I gotten this immediately engaged and enthralled with this track. I won't go into a full song play by play here, but everything that came before only continued all the way through.....but that drum solo, hrrrrrnnnnngggg.

Track after track, I could not get over the overwhelming engagement factor of this amp. In the past year with the Lyr 3 (even with the BF2/64), I found myself feeling a sense of "Ok, moving on" when listening to music...and even a bit disengaged with my prog and metal. I could easily get distracted by my surroundings or flittering through music libraries. It just didn't grab and hold my attention, especially due to the dynamics that were on the softer side. Particularly with bass drum kicks, they tended to hit like a pillow and decay and blend with other notes, a tad slowly. With the ACP+, the PRaT factor is off the charts, and I've found myself being fully engaged with tracks from start to finish. This isn't just new toy syndrome...it's a stark contrast to what I'd been experiencing with the Lyr 3.


To sum up the immediate (and ongoing) comparison between the ACP+ and the Lyr 3, the ACP+ offers the following advantages over the Lyr 3:

• Dynamics (both macro and micro), impact, slam, speed and PRaT
• Noise floor / blackgound - this thing is the definition of inky blacks
• Image precision, definition, and location
• Soundstage depth (width is the same, but likely due to the blackgound, the stage goes much deeper)
• Midrange sweetness and naturalness (and that Class A tube-like "ness")
• Treble clarity, timbral and tonal accuracy
• Detail (both macro and micro)

Comparatively, the Lyr 3 sounds more grey, and while all the information is still there, it requires significantly more focus to hear that detail amid the more smeared and grey stage. Lyr 3 does have a slight advantage in treble smoothness, which I might prefer at times, whereas the ACP+ definitely has the harder solid state attack and slight brightness, but it's just done so well. There is also an ever-so-slight tipping up to some part of the treble frequency response within the ACP+, and while it is definitely present and noticeable, it doesn't really bother me. And for sure, the sum of all other parts far overshadows any slight awareness of the tipped up-ness. I can certainly live with it.

So where does this leave me? Well, for one, it has made me realize that I won't be able to live with the Lyr 3 for much longer. Once I heard this ACP+ sound, I can't unhear that, and I would constantly wish for that sound back upon returning to the Lyr 3. But herein lies the problem: the ACP+, while only costing $200 for the complete kit, is rarely in stock with no known ETA for a new batch to be in stock. Furthermore, I'm not a DIYer and don't know the first thing about putting a kit of electronics together like this. Yes, I know how to solder (yay car audio!), but I'm still a novice with it.

This sparked the question: are there any production-grade, comparable, Class A (or similar) headphone amps on the market that could offer this performance - at a similar price? Uhhh, not really? My rabbit hole search led me to the Headamp Gilmore Lite mk2. So I asked my (very patient) wife if I could purchase one, with the intent to return within 30 days (which I HATE doing, as I respect companies - especially small ones - and don't want to take advantage of them by using/returning products). But Headamp has a very generous return policy, and I needed to know first-hand how it could (or would) compare to this DIY headphone amp, and whether it would similarly outperform my Lyr 3.

Next up will be Phase 2 of demo'ing the Gilmore Lite mk2 against the ACP+.

 

I’m not sure if the GL will get you same results as the Pass, but please update us. I do think that to get the most out of a GL you should consider the optional linear power supply. Supposedly the combo brings it closer to GSX-mini level, but with a warmer tilt.

I would probably go for the DIY anyway. It’s a fun project for beginners (my own experience with the ACA) even if you end up keeping the GL.

 

@HeyWaj10 the circuit boards are in stock, the other components required are listed here, and there's a build guide so you could make up your own kit. The DIYA discussion thread doubtless has valuable info about the build process & components too.

I'm a DIY noob but found putting together the Pass/DIY WHAMMY pretty straightforward. But if you're not comfortable, maybe the friend who loaned you his unit could be persuaded for certain favours.

I see his example also has Mark Johnson's power supply filter attached. Budget an extra few $ and time for that too.

 

The ACP+ looks like it has a whole boatload of filtering intended to be fed by a switcher. Using a Gilmore with a linear supply would really be a different league.

This makes a nice complement to the Whammy. Same class of MOSFET output devices, FET input vs OPAMPs. But hey, if I was looking in this class, I'd go years back to a CKKIII.

 

This is the part I'm struggling a bit with, but not against the idea in the meantime. The GLmk2 + GR-PS is an $800 total, which is a really big difference from the ACP+. (Spoiler) The GLmk2, from what I can tell, is sounding like it's doing 90-95% of what the ACP+ is capable of, wherein the ACP+ absolutely still wins in blackness and spatial content. So the question becomes: would the extra $300 investment into the GR-PS bridge that gap?

This is what gets me - for such a "simple" design and minimal cost, how is this thing performing at this level, when full production-value, market-ready amplifiers don't compete with its SQ capability?

All great points. Having two very young kids and a very demanding job leaves me with little time to dedicate to the learning and building process (at this stage). I'm extremely interested in building something like this in the future, but it's really not feasible at this time. That said, the local friend who loaned this to me did offer to help me build it, so it's not completely out of the realm of possibility. I would just need to individually source any components not currently available in the current in-stock offerings. And yes, he did add his own SMPS circuit, which is not in the standard build guide. Not sure how much that addition is attributing to the overall sound this is putting out, hopefully someone can explain that to me .

From what I've read around on the Headamp GR-PS, it's actually a high grade SMPS, not linear PS. Maybe I've misread that, and not sure whether that would make it more an apples to apples situation? And the local friend said many do prefer the ACP+ to the Whammy (Nelson Pass included, apparently) for headphone duties. I haven't heard the Whammy myself, but supposedly it's better suited for a wider range of impedance headphones.

 

Yes, you've misread that on the HeadAmp GR. It uses two switchers as pre-regs (instead of a transformer and bridge rectifier in previous designs), then feeds them through the Golden Reference. It's an extremely low noise, high bandwidth, high current linear PSU design.

 

Thank you for clarifying that, makes a lot more sense now!

 

you might balk at calling it a switcher, but I think that is a more apt description than calling it a linear supply. it has switchers in it, just cause it has more regulation after them its linear now? I think if thats the case a lot of designs that are using switchers would be considered linear

 

Well, yes. In the Headamp, the switchers supply ±24V that is filtered and fed into a linear regulator to supply ±15V (I think?) to the amp. Quite distinct from many amps with switching supplies that only have filters (or a noise nuke), without following that by a linear regulator.

I mean, maybe we can get nitpicky about the quality of the regulator. Feeding a switcher into a LM7815/7915 combo is linear, but probably not a great idea, as you'll pass a lot of HF noise from the switching. But the Golden Reference is MUCH more capable than that.

 

I'm not sure how good is the HF noise rejection of the GR circuit. I've used it in 3 builds and always with a transformer. DUnno if you can regulate away HF hash, might be best to just filter it.

 

I recall it cuts down to microvolt noise into the Mhz range.

 

It can be a smps and still be good. You seem to have some issue with it being good but it being called a smps

 

It does look pretty decent. Even some LC filtering after the Meanwells.

Might consider this approach for my CFA2 build.

 

I have an issue with it being called a SMPS, because it isn't an SMPS. The SMPS is providing rectification and pre-reg to DC, and the power supply itself as seen by the amp is absolutely a linear regulator.

And yes, SMPS can be good. With good filtering, it can cut a lot of the noise, and be perfectly cromulent. The ACP+ looks middle ground here. Nice little C-L-C offboard and then a C-R-C-R-C filter onboard, but I'd wager it's not as effective as something hefty like atomicbob's Noise Nuke.

 

Yep, it's absolutely a great approach with a very good regulator.

As I said, I wouldn't do it with a monolithic linear regulator, or maybe even a Sigma 11/22, but the Golden Reference is a tier above.

 

There used to be this compact SuSy Dynalo project with everything on the same board. It took LM7815/7915 after the SMPSU and seemed to work okay. It was a bitch to cool tho.

My own build was about 30% bigger but I managed to fit a GR and a trafo there.

 

Very nice! Output protection board and everything.

I'm never creative enough to jam things into a tight space. My casework for the same build would have been huuuuuuuuuge.

 

I'm no stranger to huge builds, my man! Just hate seeing space going to waste.



That Dynalo ended up driving a client's Susvara. The amp boards were stacked and everything was stretched to the thermal limit.

 

ACP+ doesn't have casework or 4X materials markup. So it's cheap. That's how DIY works.