Thanks, there's a lot of interesting information in that thread. Most of the power-on burp seems to come from the SMPS trying to deal with the initial current surge.
I like the idea of the capacitance multiplier in #82 although (a) there will be a ~2V drop across it and (b) it will probably not do anything for the power-off thump. So it is not a good solution for the SMPS.
I like the idea of the capacitance multiplier in #82 although (a) there will be a ~2V drop across it and (b) it will probably not do anything for the power-off thump. So it is not a good solution for the SMPS.
The setup is the standard ACA 1.8 from the diyAudio store with the Meanwell SMPS.
When used in single-ended stereo config, there is a power-up sound when flipping the front switch to on. It is not just a "thump", but a ~1 sec long modulated sound. At power-off there is just a small "thump". Neither of this is a real problem, I was just wondering why it happens. After going through the thread that Mooly kindly linked, I have come to the conclusion that the SMPS must be modulating the rail during power-up, probably because of current limitation.
When used in bridged config with XLR input, there is not power-up noise. This also points to the SMPS as the source of the signal - otherwise I would expect small differences between the channels to produce some remnant signal. The rail of the two channels is exactly the same, so cancels out exactly in bridged mode.
When I find the time, I will try to put a scope on the rail to confirm.
When used in single-ended stereo config, there is a power-up sound when flipping the front switch to on. It is not just a "thump", but a ~1 sec long modulated sound. At power-off there is just a small "thump". Neither of this is a real problem, I was just wondering why it happens. After going through the thread that Mooly kindly linked, I have come to the conclusion that the SMPS must be modulating the rail during power-up, probably because of current limitation.
When used in bridged config with XLR input, there is not power-up noise. This also points to the SMPS as the source of the signal - otherwise I would expect small differences between the channels to produce some remnant signal. The rail of the two channels is exactly the same, so cancels out exactly in bridged mode.
When I find the time, I will try to put a scope on the rail to confirm.
It is the input caps charging and the Meanwell trying to push through them, but tripping its overload protection, so it will keep trying after pausing for a second or so (each SMPS has its own timing). The sound you hear should not be a thump but more like a soft warble for a few seconds which I have found varies slightly depending on the caps in question. Look back a few posts where 6L6 explained why Bridged mode doesn't do this.
--Tom
This is normal behaviour and does not require 'fixing'. Call it a feature as is the start up 'burp' in stereo mode. Accept it as it is and start listening to the music...
Wrong.
(a) with a mosfet as the pass element in a CapMx there will be around 4V drop.
(b) it suppresses very well the power-off thump
(c) it's an excellent solution for an SMPS, provided you have 4 extra volts to spare.
(d) the proof is in the pudding, all you have to do is try it.
There are cap multiplier designs in the Juma's Easy-Peasy Capacitance Multiplier thread that drops less than 4V. You just have to look for it. I think the Gtose, M Johnson design has an adjustable V drop.
But I concur with Stanislav's other points; Using a Cap Mx with the ACA is a very workable solution to the bumps and farts of the SMPS. The added bonus is that you also get about 100dB channel separation.
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But I concur with Stanislav's other points; Using a Cap Mx with the ACA is a very workable solution to the bumps and farts of the SMPS. The added bonus is that you also get about 100dB channel separation.
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FWIW, i turned to smps when i could not get the hum issue to go away when building ACA's.....
these are the smps that i used, https://shopee.ph/Superparis-AC-DC-...MIh-PWgKvf7wIVs8EWBR179AZvEAQYECABEgJH1fD_BwE
i never had issues when using these, a unit of this psu can power two channels of ACA's, and you can even mount them close to the boards and still have quiet operation, this is my experience....
i did not hear NP mention anything about farting noise, i suspect it is about the psu brick you used....i never had such issues...
NP did not design the psu for use on his ACA, afaik...
btw, i have a friend who purchased the kit from diyaudio and mentioned the same farting incident....replacing the psu solved that issue...
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a mere annoyance......when we started building amps with 2n3055 in the 70's burps or thuds were common, then the speaker delay relay was invented and became standard practice...then came the 80's when the caps were investigated by Jung, Marsh and others, and then soft starting came about...
I am, and I am quite impressed by the sound. But a big part of DIY instead of buying off-the-shelf is to try and understand how things work (a professional deformation for me
), and to see what you can do about it.I played with simulations a bit. There are some ups and downs in Vout at power-up as Q2 becomes conducting well before Q1. The value of C2 has an effect on that: Increasing C2 reduces the amplitude of the bumps, but it also slows down the start-up even more. A soft-start, ramping up the supply from 0 to 24V over 10sec, does very little to reduce the bump. The bumps are quite slow anyways (sub 10Hz) so not audible. So no real reason to "fix" here.
The audible burp is almost certainly from the SMPS. That's a bit of a surprise (for me at least) as the current draw of the amp rises pretty smoothly near the end of the startup, when Q1 starts to conduct - at least according to LTspice.
Again, all of these are first-world problems and not worth losing any sleep over. So far the only "issue" I fixed are the little stick-on rubber feet that come with the chassis. I replaced them with Al feet that are a bit taller and keep the hot heat sinks a bit further away from the shelf, allowing better air flow.
As my first DIY project a few months ago, I built two ACA’s.
I finished one and hooked it up, nice amp. Clear, detailed and OMG the bass....lots of bass. More than I thought 8 watts would put out. Well maybe a bit fat....for bass.
So then I added the second one, I had to wait a bit as I ordered some balanced interconnects, a few days anyway of living with the single stereo ACA.
The sound of two ACA’s in balanced mono mode was astounding compared to a single ACA in stereo. The sound just blossoms into a completely immersive experience. I still, after three months of listening, find myself captivated by the listening experience. Relaxing in my chair foot tapping, all of the instruments clearly there, percussion is there and believable, bass is less than in stereo mode, but tighter and the low notes are defined, and identifiable. Top end is perfect.
I have thought of trying the other two modes on the amps, parallel mono and bridged mono, but I don’t have RCA cables that are long enough to do that.....I will try to figure that out in the future and report on those configurations.
KMF
MiniDSP preamp
Pass ACA class A amps
Blue sound 2i streamer DAC
Sonos Connect streamer
Paramount DAC, headphone amp
Denon Super Audio DVD player.
Zu Audio “Soul” speakers, 96db
Streaming sources, Tidal, CD’s, CD’s stored on a hard drive, Radio Paradise in Flac
I finished one and hooked it up, nice amp. Clear, detailed and OMG the bass....lots of bass. More than I thought 8 watts would put out. Well maybe a bit fat....for bass.
So then I added the second one, I had to wait a bit as I ordered some balanced interconnects, a few days anyway of living with the single stereo ACA.
The sound of two ACA’s in balanced mono mode was astounding compared to a single ACA in stereo. The sound just blossoms into a completely immersive experience. I still, after three months of listening, find myself captivated by the listening experience. Relaxing in my chair foot tapping, all of the instruments clearly there, percussion is there and believable, bass is less than in stereo mode, but tighter and the low notes are defined, and identifiable. Top end is perfect.
I have thought of trying the other two modes on the amps, parallel mono and bridged mono, but I don’t have RCA cables that are long enough to do that.....I will try to figure that out in the future and report on those configurations.
KMF
MiniDSP preamp
Pass ACA class A amps
Blue sound 2i streamer DAC
Sonos Connect streamer
Paramount DAC, headphone amp
Denon Super Audio DVD player.
Zu Audio “Soul” speakers, 96db
Streaming sources, Tidal, CD’s, CD’s stored on a hard drive, Radio Paradise in Flac
I joined the club, have an ACA on order. I'll wait and see when I get the kit to decide if I'm going to build it myself, as my vision, dexterity and soldering skills are not what they used to be. I have a friend (current service tech and former ModWright guy) willing to build it if I don't. Looking forward to hearing it with Wharfedale Linton's.
Thanks for all the interesting reading here!
Thanks for all the interesting reading here!
Question - my ACA is is a 1.8 with the 3 position toggle on the back, currently running this in stereo mode, sounds great. If I change the position of the toggle on the back it makes no difference in the output, is this expected? Just curious.
My second ACA will be here this week, will be bridging them off my Nutube B1 through Triangle BR03s.
My second ACA will be here this week, will be bridging them off my Nutube B1 through Triangle BR03s.