ACA amp with premium parts

Jump to Latest
#1,561
razvanbrates said:
Hi all! Thank you so much for the advice, it really helps.

First off, even a bit of burn-in seems to have helped: I left them on for about 24h and the bass warmed up a bit on XLR too. Which is why I posted in this thread - as I feel at least a recap and burn-in will help tremendously.

@myleftear - switching to parallel RCA did the trick (sort of): the bass and mid-bass is back to where I expected it for these speakers, but now I'm missing some of the detail in the highs, and imaging is less vivid. But the overall "listenability" is far superior (now I can listen to opera, whereas on XLR there was no way). I also have a loss of volume, but I'm not throwing raves, so all good here.

My two reasons for wanting to use XLR are noise floor and cable length (I want them near the speakers, on the floor - but at the same time they're dead silent on RCA as well) and laziness (my DAC outputs on both RCA and XLR, so I wanted to keep both the ACAs and my tube amp connected and just switch speaker cables). So at the end of the day nothing blocking.

But is there a way to get "the both of both worlds"? Could I rewire the back panel to use XLR in parallel mode? (I'm thinking not, w/o some extra components, because of the inverted phases?)

Oh, and at volumes over about 50% on XLR, I can hear some distortion in the highs as well (none on RCA).

@Loudthud - I've yet to hook it up to the scope (I first need to figure out how to even use it), so I'll keep investigating that as well.

@Skylar88 - this is a stock build ATM, I was asking if upgrading would bring my bass back. So now I know it wasn't this, and I'll go on to the upgrade anyway. Which brings back this question: what's your workflow for the upgrade? Take everything apart, or is there a better way to go about it? (you may notice laziness is a theme here)

@Ericc1 - at your recommendation, I triple checked everything with all the build pics, and all seems fine. Plus it's now much better on RCA parallel, so I'm guessing they're connected right.

@Skylar88 (again) - I couldn't find a lot of specs for the output of my specific DAC, but I could also try running it through my other solid-state amp (Yamaha A-S500). It does have a "pure direct" mode, but I feel that would add unnecessary complication to my signal path. Worth a test, though.
I'll also be building an EAR834 soon, so we'll see how it pairs with that one as well.

@Zamjazz27 - well, why not? I'll add one to my project list 🙂

I'll run some more tests over the weekend, and re-calibrate the room on Dirac for the ACAs as well and will follow up.

Thanks again, great being here 🙂
Click to expand...
Hmmm. I suppose parallel mono does help, but it shouldn't be needed; not in the way described. If anything, the ACA gained a lot of popularity due to it's ability to produce a bass response un parallelled from single ended, low watt amps.....wherein bass reproduction unfortunately gets abandoned in favor of biamping of some sort-typically via the pedestrian route of just adding a subwoofer and/or preamp that cuts everything below 80Hz (sometimes higher). IOW, most people, upon hooking up the ACA will report issues with the high frequencies or usually explained as the compression of the entire signal, as the ACA runs outta steam when turning up the ol volume knob. Verbage description aside, most know what sound I'm referring to, and ya will easily discern it as well......as a result of the ACA's inherent "soft" clipping a la 2nd harmonic overload, like tube amps, etc.

I say all that, as I just noticed you are going to recalibrate with DIRAC. Now I can't comment on it and the ACA from personal experience. If not because, for me anyway, the ACA doesn't require room correction in my setups that I've used it in for 5 years. However, one universal issue I always seem to have with room correction software, especially any involved in a surround setup, especially; Is that more often than not = totally crushes the bass no matter the shape and size of the room. But hey, buyinf an extra ACA for parallel monoblocks is great for the store!!!! It's just that going that route to obtain the correct sound signature doesn't sit right with me. Granted, as mentioned, my preamps have gain in spades......but for the record, I've had the cops called using one ACA to drive 90Db/watt Boston A150 speakers. I'd hate for ya to eventually sell your amps or put em on a shelf, only to find out that your amps are only putting out 1/3 or so of their normal output. The great and sometimes frustrating thing about the aca is that one thing can be reversed, etc. and yet the music will still be output. I had a friend solder the switch on the pad across from the correct location and it seemigly played perfect, he didn't notice till he tried to reg bridge the amp and it output the same as if it were in stereo mode but with half the volume coming out of a singular speaker (or basically 25% output compared to normal bridged)
 
#1,567
Hello builders..I've finally decided to try my hand at building the ACA and I've decided to do it with premium parts. I have a good number of the components on hand so I only bought the boards and the chassis. I have two questions concerning part #s Q4 & Q1-2:

1) Which matched set of 2SK170s should I buy from the store..the quad 6-8 or 8-11 mA?
2) my understanding is that IRFP240s should be matched as well but one can use either IRFP140s or 150s (without matching?) or altering sound characteristics of the ACA much?

Many thanks,

Pete
 
#1,568
Hi Turion64

you need 1 pcs for 1 channel of 2SK170- normally it is in the store example (aca mini) they are GR rating - means 2-6mA. sould be okay for quad 6-8mA.

MOSFET.
IRFP140 and IRF150 are bit "stronger" - less rdson and more transcundactance -so a little bit more bias current is allowed 😉 .
matching is not needed. i prefer IRFP044N - but i see its sold out.
IRFP150NPBF is a good choice (ZEN mod uses this very often) - is a double IRF240.

power supply:
if you use SMPS then please use Amyalice SMPS filter by marc.

kr
chris
 
Last edited:
  • Like
Reactions: turion64
#1,572
Loudthud said:
The nearly double input capacitance of the IRFP150 will show up as increased THD above 1KHz.
Click to expand...


1736540210462.png



yes...nearly
 
  • Like
Reactions: Halauhula and turion64
#1,579
Folks, just want your opinions on my potential build for my ACA.

The typical TungstenAudio mods and :

R3&4 - 0.56R
Q1 - IXTQ75N10P
Q2 - IRFP140
C3 - Silmic II 10uF 50V (had them in my stash)
24VDC via a Meanwell PS for now but will eventually assemble a linear power supply (regulated or straight?)
12-12.5V bias ok?
R5&6 will stay at 100R
R9 - will stay at 1K unless go higher than 24V in
C1 - Nichicon KG 4700uF 35V (LKG1V472MESZBK)
Q4 - 2SK170 from the diyaudio store
R16 - 200R (unless I want to use higher voltage in)
Will incorporate an ACA Supply Filter by rhthatcher but will also build the MJ AmyAlice DC filter board to try

I think I got all of the particulars right

Many thanks, Pete
 
  • Like
Reactions: chermann
You must log in or register to reply here.
Top Bottom