For anyone who might be interested: Nelson Pass-designed ACA amplifier kit "back in stock" :)

EndersShadow

stretchl wrote: »

Anyone reckon the Pass amp would work well with a pair of 705’s? Or perhaps as monoblocks, which apparently is a build option? Thanks.

Ehhh.... I'd pass...... the 705's need a decent amount of wattage and current, and the pass aren't built to do either of those to the scale you'd need.

ZLTFUL

The ACAs need some decently high sensitivity speakers. Otherwise, you are going to miss a LOT on the low end and things are going to sound sloppy.

mhardy6647

Performance-wise, the original morph of the ACA isn't all that dissimilar to a single-ended 2A3 amplifier -- albeit a bit more powerful and probably wider flat response compared to any even marginally affordable 2A3 stereo amp.

So... think SET/fleapower friendly loudspeakers.

Vintage Altec, JBL or (shudder) Klipsch fills the bill nicely (e.g.).

mpitogo

Pre-order for batch 2 is available!

Amp Camp Amp - Complete Kit (PRE-ORDER, SHIPS SEP 15TH) – diyAudio Store

Post fromJason @diyaudio.com

leftwinger57

So 'Doc' I can't believe no one has asked you about this after all these years. Why didn't you paint or ,stain those speakers. They stand out like very sor thumbs and need some beautification. Being an old Yankee you must have some Marine varnish up there so throw some coats on. and counter sink those screws. Chemistry and radionics are your strong suit but not to much on the the aesthetic. Look who's the critic now ....lol

EndersShadow

He's a "form" over function kinda guy DUH!

Also with as much as he's tweaked them over the years at times (adding in super tweeters, other horns, etc) at the top of them it wouldnt make sense IMHO to finish them.

mhardy6647

The answer is supremely simple. I could only make them look worse if I tried to finish them.

mpitogo

The kits came in yesterday, spent Sunday building. The monoblocks are now breaking in... er heating the room. Measured 126F at the heatsinks. The entire chassis is hot.

msg

Looking good!
Can't wait to hear the listening impressions.
What will be the rest of the setup?

mhardy6647

They look excellent. Nice work.

126 ain't bad (assuming that's Fahrenheit kind of degrees, and not those Commie Celsius degrees ). "Hot" is about 150 (relative to my sense of touch)!

mpitogo

So I've played them for a little bit but two things.

1) Polk T15 are not the best speakers. I also have a pair of ML Motion 40's sitting around but these are 4ohms and the bridged mono's look to only be rated for 8 ohms or higher.

2) I need to redo the bias. I had followed the v1.5 build guide, these kits came with 19v supplies and bias is set at 10v. The new v1.6 kits come with 24v 5a supplies and should be biased at 12v per diyaudio.com members.

mhardy6647

Time for high sensitivity, baby!

DSC_9976 (3) by Mark Hardy, on Flickr

Clipdat

Does it run hotter with no load connected to it because of it's class A topology? Or will it run at that same temp when it's in use?

heiney9

I really wanted to pick one of these up, but I have 3 other projects and I have no current use for this little wonder amp.

vcwatkins

Have regrettably been away for quite a while but thought I'd check in re: the ACA.
This thing sounds FANTASTIC!

Meridian Exporer II Test
The day after it was finished I brought it in and hooked it up to a simple little computer rig to get some hours on it. The rig was:

PC (Roon Remote) > Jitterbug > Wireworld Starlight Red A/MiniB > Meridian Explorer II dac > AQ headphone-RCA adapter > MIT S3 interconnects > Amp Camp Amp > MIT S3 speaker cables > Hartley Reference Mini-Towers

I believe the speakers are 95db but am not certain. The room is about 12'x12' with an 8ft opening centered on the back wall. Using Roon's software volume control, I needed to set it 80ish% for most music; but, at 90% it provided plenty of gain for any music I played.

Amazing clarity and detail, excellent soundstage with instruments spread evenly from ~5 degrees outside the speakers. Fantastic, detailed bass. Not sure how to describe this, but it has an addictive purity of tone; detailed but not brittle; lush but not overly sweet - it just sounded right and true. The best sound I've ever had in this location. Instantly fell in love with it. I was ecstatic, especially given this is not, what I assume to be, an optimal rig.

Audio Research LS-3
I ordered a Schiit Saga to try out. While waiting for it to arrive, I tried the ACA with my usual sources in the study and an AR solid state pre:

Roon > ethernet > Bryston BDP-1 > Bryston BNC > Bryston BDA-1 > MIT S3 > ARC LS-3 > MIT S3 > Amp Camp Amp > Hartley Ref MiniTower

Way more gain - too much in both passive and active - and the sound suffered and was no longer magical. Reverted to the Meridian-direct source while waiting a little longer for the Saga.

Schiit Saga
Saga arrived a few days ago, so I slotted into the Bryston source rig. Sounds noticeably better than the Meridian-direct (or is it the Bryston's?, likely a combo of both). But, a bit surprising to me, the Saga does not add any gain - in fact, it seems to be less. In passive, I have to turn it to 3:00 to listen to most things at a realistic volume. Still fantastically detailed, but I do worry about distortion at that level (or higher when I'm feeling my oats). Switching to the tube adds the slightest amount of gain (I think) but is barely perceptible. I like the little Schiit enough to keep and try with other gear. I'll also try to slot in the Joule pre for fun, even though they won't likely be paired for any length of time.

I have yet to build Frugel-horn cabinets or similar (hope to do that this month), and am considering used Zu Omens or new Tekton Double Impacts. But for now, I'm happy as a clam listening to this lovely little amp with stuff that I have on hand.

I HIGHLY recommend this amp if you get the opportunity to buy a kit or an assembled one. Many thanks to @mhardy6647 for the heads-up on availability.

Craig

heiney9

Dang it! After your review, I think I want one again

SOLD out again..............I'm on the waiting list, AGAIN...lol

H9

mhardy6647

The only "problem" with the ACA relative to SE DHT(2A3) amplifier (in my hands, that is) is that it doesn't quite have the midrange realness of the 2A3 amp. It is just a bit drier sounding (but there's probably a certain amount of expectation bias goin' on, too!). You all probably recall the one that is on a long-term visit (maybe it's a hostage?!) here; it's a little tricked up relative to the stock (first generation, I think) ACA configuration.

Otherwise, it is at least in the running with a decent quality SE 2A3 amplifier. Bass may be a little better (not necessarily easy to tell with my loudspeakers). Certainly cheaper than SE 2A3 and its hottest parts don't run as hot as a pair of 2A3 output tubes in Class A I suspect (but haven't checked) that power consumption of the ACA (the one here, it may be recalled, is physically configured as a stereo amp with a "Bottlehead" like footprint) and the 2A3 amp are comparable.

mpitogo

@Clipdat same temp load or no load.

leftwinger57

Another question for the DOC here. You went fairly in depth in soldering and how to get the right heat and flow. What you did not specify is the type of instrument you personally use. Is it a tried and true Weller, the portable butane type, old school pencil type w/ holder, and a very old and large enough to weld a Liberty ship called the Cummings.
Lew.....

]

mhardy6647

I am seriously not an expert on modering soldering stations.
I (still) like the Weller controlled heat stations... but there may well be better; I dunno.

lightman1

Sketchy Craig is back!

vcwatkins

Dayum right.