Hi All,
It seems there were only a handful of questions left. I’ll start with the ones that I’d apparently missed the first time round.
Can you make a SMPS with matching low power consumption? I have had both Hypex SMPS1200 and SMPS600 with nc400, and I do not like the heat they produce on idle. If the rationale for going class-d is low power consumption, then I do not get the full picture if the powersupply has high power consumption.
That would certainly be the plan. The design brief for the SMPS is universal mains with PFC, more or less regulated output (to maximise power output from the amp) and low idle losses. It’s quite a job. I should note that Hypex has made clear improvements in the idle losses in their SMPS a few years ago.
Is 1ET400A vs nc400 an audible improvement soundwise? If so, in some certain way, like better high frequencies? Would you think it’d be audible for only driving 15” woofers in closed boxes actively in the range 25-650Hz in my system?
The specs have improved over the whole spectrum so you wouldn’t expect any audible improvements to be restricted only to the top end. That said, I’d be massively skeptical if anyone told me he hears a difference in a subwoofer application. I certainly wouldn’t rush to upgrade amps in a sub.
I thought the low output impedance was the reason why my nc400 gives so nice ”kick” in my woofers compared to class-AB amps I have had before. But now I read that you don’t give low output impedance any credit to sound quality. What is it then giving me the kick I wonder?! Some kind of compression that is lower?
We’d need to see the measurements of those class AB amps if we want to stand any chance of speculating fruitfully.
Is gain variable like on nc400 with r141?
That is the middle resistor of the buffer stage. The 1ET400A has no built in buffer. The structure of the buffer on the I/O board is the same though so you can indeed change the gain there in the same way.
Which is your favourite music record, the one you never get tired of hearing?
Oh goodness, my Desert Islands Discs. Wish Lars were sitting here. He’d rattle off a bunch of classical recordings on the spot. When I was younger I could re-listen a small number of albums forever. More out of economic necessity than artistic sense mind you. Blame streaming for the ADD that I as a music lover have caught since. I’ve become a novelty seeker and don’t often play the same albums over. On the other hand, most of those albums from my youth would cause me a lot of embarrassment if I were to name them.
Things from my old collection I can still listen to:
- Johannes Kerkorrel en die Gereformeerde Bluesband, Eet Kreef (it helps to understand Afrikaans though, and remember what SA looked like in the 80’s)
- The Waterboys, Fisherman’s Blues
- Jean-Michel-Jarre, Equinoxe
A few contemporary albums that spring to mind that I’ve recently played more than 5 times and still like:
- Nils Frahm, All Melody (And the rest. Frahm is one of the few people I’d declare myself a fan of)
- Public Broadcasting Service, Race for Space
The obligatory classical album that’ll be the one saved when the desert island floods (UK readers may have to explain that to the rest):
- Pieter Wispelwey and Dejan Lazic, Complete Sonatas and Variations for Piano and Cello.
And finally a long shot, do you have any comments about choosing dac with AKM or ESS top-shelf chips? Which of these would you prefer if you had to do a dac with any of them? Or maybe we can state it like which one is least bad in your opinion?
I have never toyed with any of the ESS chips, mostly because I felt that if I wanted to have that sort of SNR I might just as well do a discrete circuit and solve distortion and birdies too. But I’ve used a lot of AKM stuff in a variety of products and have yet to be disappointed.
Does the amp emit any on/off thump or noise? The nc400 is not particularly noisy but it does emit a definite noise on power off. I see no trims on the amplifier module: how is DC offset handled and what is its typical value?
A thump is what you get when there is a DC offset that suddenly gets turned off along with the amp. The NC400 had a fully discrete buffer which had the potential for developing DC offsets, especially when driven with a high impedance (e.g. an AC coupled output). That’s why it had trim pots. The 1ET400A has a DC offset of less than 10mV (is on the web site) which doesn’t normally produce a noticeable thump, so it doesn’t need trimming. But of course if you decide to build a discrete buffer, you might need to make the input stage trimmable.
Aside from a DC thump, there is always the potential for a small turn-on and turn-off click because of the sudden start or stop of the PWM signal. We try to minimize that by letting the microcontroller take charge of the output stage the first few microseconds. As it stands you need to put your ear very close to the tweeter before you notice the click. I guess that’s a good enough result.
Will it be possible to install speakon connectors directly on the connector PCB, in place of the binding posts?
I put in four large through hole pads that you can solder wires into so it should be trivially easy to connect a speakon connector with wire terminals. Brownie points for requesting speakon, which I consider the only serious speaker connector around. Sadly the rest of the hi fi market doesn’t seem to care (or prefers to care about other things).
Is it possible to set a different gain for each module of the stereo combo?
Sure, the 2 channels are independent after all. But the place to do so would be in the buffer, the gain of the amp module itself is fixed.
Last question regarding the future directions you might want to explore with purifi: are you going to tackle the task of bringing transconductance/current drive amplification to the DIY and OEM market? I know your new woofer uses special trick to avoid voltage drive distortion, but having a good offering for a current drive amplifier would still be very nice for reducing distortion in "legacy" cone drivers (and maybe even for your woofer, to a lesser degree) in active filtering scenarios
I think you are referring to the current drive used in the Kii and Grimm speakers to reduce the hysteresis distortion in the legacy drivers that are used there.
The Purifi woofer doesn’t rely on anything on the amplifier end for its performance, because we don’t want to force people to buy both drivers and electronics from us (or give the impression that we do). But neither would it make sense to give people instructions how to improve the performance of their non-Purifi drivers. Or give the impression that doing so brings them anywhere close to what our driver does. Current drive cleans up the mid-band like a treat but low frequency performance does not improve.
Besides, we sell amplifiers and drivers. If we were to start selling complete solutions, what value is there to be added by the manufacturer that buys our stuff and puts it in a box? It’s bad enough as it is with amplifier companies fearing the inevitable question “so what justifies the price of your amp compared to a DIY build”.
Oh, almost forgot: When? How much? (for the DIY market)
I mentioned it already but for completeness: webshop to open somewhere in the autumn. Prices competitive (i.e. low enough for other parties to start re-thinking their DIY price settings).
still a lot of people said:
Folks, CMRR is spec’ed as 60dB or better, and the resistor tolerances are chosen accordingly (working this out is left as an exercise for the reader). It is a matter of statistics that if you have a grab bag of x% resistors and you take two at random, they are quite likely to be matched within a fraction of x%. So there’s nothing unusual about a module that suddenly has a CMRR of 20dB better than spec. In fact, it would take a lot of effort not to have the occasional “way better than spec” exemplar.
As I read Maty’s first remark after my post, he said that if people are going to charge a mint for an input buffer to go with the 1ET400A, the least they could do is provide measurable evidence that it actually adds value. I wouldn’t necessarily pick CMRR specifically as the item they have to improve but I sympathise massively with the sentiment.
Sadly that is not how the free market works. It’s very much buyer beware: if the buyer doesn’t request evidence of added value before handing over money, the seller has no reason to provide such evidence. What’s great about a forum like this one is that it’s basically about collecting that evidence whether the seller wants to or not. But it’s only people who realise they need consumer protection that’ll seek it.
Especially the high end audio market has successfully bamboozled customers into thinking value lies in esoteric materials and parts (which after all is easy to do, easy to communicate and easy to make a margin on) rather than in improving actual performance by engineering (which is hard to do, hard to get across and only turns a profit if enough people see the point). Starting a company like Purifi is a way bigger gamble than starting an “accessories” company. It relies on enough people questioning the status quo.
[Am I] completely wrong in my conception that I'd need an amp capable to rock short duration signal space something something?
If you replay two identical musical signals over two identical speakers in a good room, it sounds like it’s coming from a point exactly in the middle between the speakers. If you delay the right hand signal by 2us, that will sound like the image has now moved left by a few millimetres. Under ideal circumstances you might be able to train yourself to detect that.
When people claim that the human ear is sensitive to time scales in the low microseconds, this is the experiment they are referring to. The important thing is that you do not need “fast” signals to do that. It works fine with Red Book CD audio. It might even work with lower bandwidths. So, your ear’s ability to hear tiny time shifts does not require a high bandwidth, not in the signal and not in the electronics.
But now consider this: do you think anyone can hear the difference between
1: A 10V, 1us long impulse
2: Two 5V, 1us long impulses 20us apart (slightly EQ’d for the pedants among us)
Clearly not. The two would sound exactly the same. Human listeners do not need equipment with with the sort of time resolution (=bandwidth) that could resolve the second case as two separate pulses.
The ability to discern short delays between left and right channels have nothing to do with time resolution.
I would like to stress the shyster epithet was not aimed at you. I reserve the term for people who follow and understand this completely and still claim that you need to invent a new (preferably proprietary and specifically their) digital audio format based on the minimum audible interchannel delay, knowing full well that the argument is flawed.
I’m not sure whether I should read your questions regarding employment as half-serious or not, so for the sake of completeness: you can always send a CV.
Any more details on the drivers? What else comes with them? Do I need to lego my own cross overs? Will they fit my old wife-dissapproval speaker cabinets? (I dont have a wife, I meant the cabinets) And speaking of, since they're addressing some particular issues, would it make sense to have a post amp adjuster circuit thingy that kind of tells the amp how to drive the speakers?
You get the driver. For the rest you’ll have to, well, DIY. Should you feel unsure of your speaker design skills, it’s probably best until some of the more seasoned folk in the community have tried their hand and put their designs online. The driver is designed to be easy to work with for designers of normal passive speakers, so no specific adaptations on the amplifier side are required.
Right, I’ll be off on holidays for the whole of August. Should any pertinent questions turn up, maybe someone can drop me a pm. That would save me a fair bit of scrolling in September.
Cheers!
Bruno
