On a different note... One of my two ACAs (one per channel) has a dimmer led. It also sometimes goes off completely - I have the impression that warming up tends to solve the problem and then we're back to the one-eyed ACA. Can this be the symptom of trouble? The amps (=channels) seem to generate musical volume symmetrically.
Check the solder joints for the LED and R13. Also check that the R13 value is correct.
If it is still dimmer and cutting out, replace the LED.
If it is still dimmer and cutting out, replace the LED.
Follow Ben Mah’s advice. If that does not solve problem, then measure the voltage at each of the leads of the indicator LEDs. If they are significantly different, you should look at color codes of resistors to verify they are the same value. If they are, then you should measure resistance across the dropping resistor for each LED after unsoldering one of the LED leads. Compare to see if they are the same.
If the resistance is the same, then there is a problem further upstream from the LEDs and dropping resistors.
If the resistance is the same, then there is a problem further upstream from the LEDs and dropping resistors.
I just received a second ACA 1.8 kit having already built one several months back. The resistors R1-R4 supplied this time (see 1st pic) are different than those from the first kit (2nd pic) and also don't seem to match the specs on the board. Since I intend to use the amps as a pair, I am worried that there may be sonic differences. Any thoughts would be greatly appreciated before I start building. (I couldn't find other postings about this issue.)
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There won't be any sonic difference between the two types but if it bothers you then you could fit one of each type per parallel pair. The boards would then be absolutely identical.
When measuring values on a meter remember to account for the meter lead resistance. Low values such as these can easily seem to be 0.1 or 0.2 ohms to high because of that.
When measuring values on a meter remember to account for the meter lead resistance. Low values such as these can easily seem to be 0.1 or 0.2 ohms to high because of that.
Hey everyone, I had a question from those with more experience with the ACA- I built my first one last week and love it. Was considering doing a pair but wanted to know is there any sonic benefit to running these as bridged/parallel monoblocks other than more power? My speakers are highly efficient and don't really need more than a single watt to get things rocking. My current "high power" amp is a 3.5W 2a3 and other guy is a little 2w El84. It looks like the design of the ACA is basically a monoblock in one chassis with a shared power supply so would it even make sense to do a pair and run as bridged or parallel?
On the same note - I'm honestly not really understanding the whole bridged v.s. parallel set up. I poked around on the googles and youtubes as well as some forum posts and to my best ability it sounds like running as bridged gives 2x the power but parallel is more around 4x but you loose some dampening factor. Am I on the right track here? Before this my only experience has been DIY tube gear so slightly out of my element here. Appreciate any input! Thanks 🙂
On the same note - I'm honestly not really understanding the whole bridged v.s. parallel set up. I poked around on the googles and youtubes as well as some forum posts and to my best ability it sounds like running as bridged gives 2x the power but parallel is more around 4x but you loose some dampening factor. Am I on the right track here? Before this my only experience has been DIY tube gear so slightly out of my element here. Appreciate any input! Thanks 🙂
Have a look at this file, may answer some of your questions:
Parallel mode keeps the maxim voltage output the same but allows twice the current delivery if the load demands it. Think of it as putting two small batteries in parallel. The damping factor is lowered by a factor of two.
Bridged mode has the load (speaker) connected between the output terminals of the two amps leaving the ground terminals of the amps not connected. One of the two amps is now fed with an inverted input signal, so as one amps output voltage goes 'up', the other amp goes 'down'. This gives twice or double the voltage across the load and that gives four times the power but that only happens if the amp can deliver the required current to the load. The ACA is very limited in current delivery and so it will not achieve that 'four times power' into say a fixed 8 ohm load but our speakers are not fixed but are a variable impedance.
The inverted signal for the ACA comes simply from feeding the speaker output of one into the input of the other (with correct attenuation) and this works because the ACA inverts as normal.
So with normal speakers and music you will achieve something between a normal and bridged ACA in terms of power.
The ACA has a relatively high output impedance and this is only made worse by bridging meaning the response from a real speaker will be modified considerably by bridging... but that doesn't mean it won't sound great.
https://www.diyaudio.com/community/threads/amp-camp-amp-aca.215392/post-7099071
Bridged mode has the load (speaker) connected between the output terminals of the two amps leaving the ground terminals of the amps not connected. One of the two amps is now fed with an inverted input signal, so as one amps output voltage goes 'up', the other amp goes 'down'. This gives twice or double the voltage across the load and that gives four times the power but that only happens if the amp can deliver the required current to the load. The ACA is very limited in current delivery and so it will not achieve that 'four times power' into say a fixed 8 ohm load but our speakers are not fixed but are a variable impedance.
The inverted signal for the ACA comes simply from feeding the speaker output of one into the input of the other (with correct attenuation) and this works because the ACA inverts as normal.
So with normal speakers and music you will achieve something between a normal and bridged ACA in terms of power.
The ACA has a relatively high output impedance and this is only made worse by bridging meaning the response from a real speaker will be modified considerably by bridging... but that doesn't mean it won't sound great.
https://www.diyaudio.com/community/threads/amp-camp-amp-aca.215392/post-7099071
I just finished a pair of 1.8 versions today. I have been comparing the three modes of operation all day. To my surprise, so far I like the sound of the two amps in paralleled mode best. At least when using my small, inefficient SP-BR22 speakers. Fairly noticeable improvement paralleled vs. other modes to my ears listening nearfield with preamp out from Korg DSD DAC 10R with Foobar on Win 11.
I did not expect it would be so much fun to have the different modes available with a simple switch mounted on the back panel (and connecting the inputs/ outputs differently). I also listened to my FIIO M11 Plus streamer outputting balanced. But with the SP-BR22 speakers it sounds to me that paralleled is the way to go.
I have yet to try the amps with my much more sensitive Ref3A DeCapo I speakers. I may end up preferring a different mode using those speakers...
You do a pay a price having two amps, twice the cost, and twice the heat 🙂 But for me, twice the fun also...
I did not expect it would be so much fun to have the different modes available with a simple switch mounted on the back panel (and connecting the inputs/ outputs differently). I also listened to my FIIO M11 Plus streamer outputting balanced. But with the SP-BR22 speakers it sounds to me that paralleled is the way to go.
I have yet to try the amps with my much more sensitive Ref3A DeCapo I speakers. I may end up preferring a different mode using those speakers...
You do a pay a price having two amps, twice the cost, and twice the heat 🙂 But for me, twice the fun also...
With Gilles we built an amp (his main amp now) that encloses 2 ACA Mini and that enables various combinations to drive his LS (these have 2 terminals, HF and LF). Modes such as one amp only, 2 amps vertical biamping, 2 amps horizontal biamping, 2 amps in parallel with bridged LS terminals for max power acros all frequencies were possible (the ones we retained still are in fact) on a switch, for direct comparisons..
His LS, the same I have in my second system, are VERY easy to drive: minimal impedance is 5,6R but mostly at or over 8R, phase shifts are mild and whatever the music we listen to we never needed more than measured 2W (they are quite efficient). Needless to say damping factor and max power aren't a problem and even a single Mini can drive them easily. Or my VFET.
While an ACA Mini sounded absolutely great so that we thought more would be overkill for such an easy load, we found that 2 Mini in bi-amping mode sounded even better. And only at silly sound pressure levels, 2 Mini in parallel, driving a bridged LS terminal, sounded then (and only then) even better / less distorted... at insane levels LOL. So quite in line with your post, and that despite in our case using efficient LS.
It can't be due to DF or max power, it might perhaps (?) have something to do with the harmonic level raising with the power output... or whatever else. One amp would have been more than enough from an electrical POV and also from a sonic POV, but 2 in that case sounded better...
Yes, these little amps thanks to their nearly double mono configuration and output caps enable a lot of things to play with!
Have fun
Claude
His LS, the same I have in my second system, are VERY easy to drive: minimal impedance is 5,6R but mostly at or over 8R, phase shifts are mild and whatever the music we listen to we never needed more than measured 2W (they are quite efficient). Needless to say damping factor and max power aren't a problem and even a single Mini can drive them easily. Or my VFET.
While an ACA Mini sounded absolutely great so that we thought more would be overkill for such an easy load, we found that 2 Mini in bi-amping mode sounded even better. And only at silly sound pressure levels, 2 Mini in parallel, driving a bridged LS terminal, sounded then (and only then) even better / less distorted... at insane levels LOL. So quite in line with your post, and that despite in our case using efficient LS.
It can't be due to DF or max power, it might perhaps (?) have something to do with the harmonic level raising with the power output... or whatever else. One amp would have been more than enough from an electrical POV and also from a sonic POV, but 2 in that case sounded better...
Yes, these little amps thanks to their nearly double mono configuration and output caps enable a lot of things to play with!
Have fun
Claude
Thank you all for the info! The PDF is a handy reference! Looks like a 2nd ACA build may be in order just to play around. Would be cool to be able to A/B some upgrades along the way too . . . its a dangerous hobby 😉
Claude- I've been reading all your posts about the B1 upgrades you did - really cool stuff! I actually included a few caps to try out soon in my next parts order. Got some Wima MKS2s in .33, 1.0 and 3.3uf. Also discovered my Solens (fabriqué en France, oh là là) I had from an old tube project fit the board holes perfectly without filing the leads thinner. I think the Solens are 0.8mm - Had a few good values to play with in those and can mount like you did the Cornells vertically with shrink on the long lead.
Thanks again everyone, much appreciated!
Claude- I've been reading all your posts about the B1 upgrades you did - really cool stuff! I actually included a few caps to try out soon in my next parts order. Got some Wima MKS2s in .33, 1.0 and 3.3uf. Also discovered my Solens (fabriqué en France, oh là là) I had from an old tube project fit the board holes perfectly without filing the leads thinner. I think the Solens are 0.8mm - Had a few good values to play with in those and can mount like you did the Cornells vertically with shrink on the long lead.
Thanks again everyone, much appreciated!
[[ Would be cool to be able to A/B some upgrades along the way too]]
That is one of the reasons I made the unconventional - dare I say unheard of - choice to use inline lever connectors in all the wiring between the boards and front and back panel components of the ACA 1.8 chassis.
So now I can R&R boards, switches, jacks, etc. and even perhaps add features without repeated soldering/de-soldering.
Already I want to upgrade the jacks on the back panel; I never liked the RCA jacks that have the loose ground tabs. They can come loose. And I will upgrade the 3-position mode switches, and probably eventually experiment with some upgrades to the board components. Even perhaps adding a clipping detector (I already encountered some clipping with my low sensitivity Pioneer speakers) or perhaps some hi-pass filters.
To facilitate any potential troubleshooting, I first assembled one ACA without any connectors, just straight point to point wiring and did some listening. Then inserted lever connectors to wires one at a time to the various jacks and switches, and did listening tests after each added connector. I never heard any increase in noise, hum, hiss, distortion. The amps are still dead silent background.
That is one of the reasons I made the unconventional - dare I say unheard of - choice to use inline lever connectors in all the wiring between the boards and front and back panel components of the ACA 1.8 chassis.
So now I can R&R boards, switches, jacks, etc. and even perhaps add features without repeated soldering/de-soldering.
Already I want to upgrade the jacks on the back panel; I never liked the RCA jacks that have the loose ground tabs. They can come loose. And I will upgrade the 3-position mode switches, and probably eventually experiment with some upgrades to the board components. Even perhaps adding a clipping detector (I already encountered some clipping with my low sensitivity Pioneer speakers) or perhaps some hi-pass filters.
To facilitate any potential troubleshooting, I first assembled one ACA without any connectors, just straight point to point wiring and did some listening. Then inserted lever connectors to wires one at a time to the various jacks and switches, and did listening tests after each added connector. I never heard any increase in noise, hum, hiss, distortion. The amps are still dead silent background.
@kenzo3:
I support the idea of easy connection and disconnection, either using on/board terminal blocks or 1/4” spades, but the overall sentiment is that people rather solder. Your lever lol spproach is interesting; I had not seen those types of connectors before. They do take up a lot of room though and I think barrier blocks would be better (although their unprotected state for power would probably not be accepted, but for DC I think it is OK. I tried looking for chassis mount Euroblocks but my search skills are poor and have not found them on Digikey or Mouser. Euro-style are much safer as the connection is fully protected.
As far as RCA, I support your feeling about those that have loose tabs. The Neutrik RCA with cup that fits in standard D-size hole has “fixed” ground tab but will require special bore to enlargen the 3/8” hole in the ACA chassis. As long as I am at it, I might as well also say that for DIY, it is way easier to use outside nut RCA, because one can solder the RCA and connecting cable/twisted pair directly to PCB before mounting in the chassis! However, the outside nut style requires 1/2” home to fit the i dilating shoulder washers. I have a punch that will enlargen a 3/8” hole to 1/2”, but ACA panel is too thick. I am going to look at using a step drill. But that also represents a problem with my drill press as the step drill will cut into the platen or platform on which the piece sits.
I support the idea of easy connection and disconnection, either using on/board terminal blocks or 1/4” spades, but the overall sentiment is that people rather solder. Your lever lol spproach is interesting; I had not seen those types of connectors before. They do take up a lot of room though and I think barrier blocks would be better (although their unprotected state for power would probably not be accepted, but for DC I think it is OK. I tried looking for chassis mount Euroblocks but my search skills are poor and have not found them on Digikey or Mouser. Euro-style are much safer as the connection is fully protected.
As far as RCA, I support your feeling about those that have loose tabs. The Neutrik RCA with cup that fits in standard D-size hole has “fixed” ground tab but will require special bore to enlargen the 3/8” hole in the ACA chassis. As long as I am at it, I might as well also say that for DIY, it is way easier to use outside nut RCA, because one can solder the RCA and connecting cable/twisted pair directly to PCB before mounting in the chassis! However, the outside nut style requires 1/2” home to fit the i dilating shoulder washers. I have a punch that will enlargen a 3/8” hole to 1/2”, but ACA panel is too thick. I am going to look at using a step drill. But that also represents a problem with my drill press as the step drill will cut into the platen or platform on which the piece sits.
[[ I think barrier blocks would be better]]
yep, I might agree. I expect blocks would at least result in much cleaner/better organized internal environment, and save space... I may give them a try since it should be easy to replace the levers...
yep, I might agree. I expect blocks would at least result in much cleaner/better organized internal environment, and save space... I may give them a try since it should be easy to replace the levers...
Went ahead a put the upgraded caps in my ACA today - Kept C1 alone for now but will order and try out one of the 4700uf KG gold tunes based on other posts. So far did the 1000uf Nichicon RNL for C2, 10uf Elna ROA in C3 and 100uf Nichicon RL8 in C4. Will see how they sound after a bit of break in but so far they're really nice out of the box.
Any other C1 caps that I should consider over the KG?
I read on another post about changing some resistors (R11 to 20 kOhm metal film and R12 to 90.9 kOhm metal film) What will this do to the sound / circuit?
This and the B1 have been a fun project so far!
Any other C1 caps that I should consider over the KG?
I read on another post about changing some resistors (R11 to 20 kOhm metal film and R12 to 90.9 kOhm metal film) What will this do to the sound / circuit?
This and the B1 have been a fun project so far!
Have you noticed improvement, or do you think it is too soon to tell?
Edit: Sorry, I missed your comment about break in.
Edit: Sorry, I missed your comment about break in.
At the risk of sounding too audiophile, compared to the original caps (I think were panasonic? no labels and not elnas) it sounds more present and "there" - the original caps were good for sure, a touch warm I'd say which being a tube guy I liked. It's a bit more "solid sate" sounding, very accurate and clear but still nice and musical for sure. I'll give them some time to warm up. I was skeptical about the whole break in thing for a while but after my last tube build I'm a believer. My 2A3 sounded horrible and had absolutely no bass for the first few days to a week. One day it just woke up. The other factor is I left the main C1 cap but will probably leave it alone instead of changing too much all at once. One of the fun things with part swapping is you really can tune the amp to your personal preferences. My speakers (see profile pic) are Altec 604s with custom Xovers and they're insanely transparent and clinical. I love them but they are a very very unforgiving mistress lol - makes lousy / mediocre recordings sound like trash but man, when you have a well recorded/mixed album its something of beauty! Huge fan of the vintage Altecs!
that all being said - I'm probably going to pull the kit wiring and put my go-to silver plated 20g solid core teflon coated stuff in its place. I also went with shielded twisted pair 8450 Belden for power supply in this and my B1. Might re-do the signal wires in both with shielded while I'm at it too- either the belden, my Mogami mic cable I use for interconnects or just the Cat6 but leave it in the jacket and cut off the extras.
that all being said - I'm probably going to pull the kit wiring and put my go-to silver plated 20g solid core teflon coated stuff in its place. I also went with shielded twisted pair 8450 Belden for power supply in this and my B1. Might re-do the signal wires in both with shielded while I'm at it too- either the belden, my Mogami mic cable I use for interconnects or just the Cat6 but leave it in the jacket and cut off the extras.
It will raise the input impedance from 10k to 20k while the gain remains essentially the same at less than 1dB more (no load). The damping factor will be increased slightly making the amp even more susceptible to real world loading with a variable impedance (a speaker). I suppose the noise must increase slightly to with higher R values.
How does it sound... try it and let us know.