Silicon Chip Mag DAC project

[caddisgeek]

Any one looking at building the DIY DAC in this months silicon chip mag?

I might give it a go

http://www.siliconchip.com.au/cms/A_111597/article.html

cheers

Steve

[Poita]

I bought the mag because of it, but then realized it didn't have any USB input

[Monkeyboi]

No USB, can't do 176.4 and 192kHz sampling rates. No DSD support.

Hardly worth the effort. Anyone know what they estimate the cost of the kit will be? There's bound to be a DAC kit out of HK for a fraction of the price.

Just before you ask, no I didn't buy the mag.

Cheers,

Alan R.

[kye]

like all things from silicone chip, I would anticipate this would be a very well engineered piece of equipment, designed to minimise THD... the design will not pay attention to any other measurements and will not have taken any subjective impressions into account whatsoever.

all the SC amp kits i've built have been the worst sounding "low distortion" amps.

it may, however, form a good base for which to upgrade from (i'd be looking at the PSUs and the output stage circuitry first up) so might be good to get working and then upgrade as the whim takes you.

[caddisgeek]

Hmmm, maybe I'll hold off a bit then

[Bosk]

Out of interest I notice they're using a toroidal transformer. Isn't this something of a no-no for digital gear?

I've been under the impression that EI & R core transformers are better for this role.

[kye]

hi caddis,

after making the above post and thinking about it while in the chair getting my hair cut I realise I may have been a little unfair.. the DAC is likely to be good, it's just not likely to be brilliant.

I have very high standards and regularly hear world class gear that costs world class prices, whereas depending on how much the kit goes for, it may offer good value for money.

the nature of DACs is that they're modular and the weakpoints are likely to be something that's fairly easy to do something about if you're inclined to DIY. I am in the middle of a rebuild of my DAC (which I also use as a pre-amp) and the things you need to do to get good sound aren't that hard at all - it's just about using quality parts in the right way, which many here can assist you with (circuits and advice etc).

I started my journey in DIY building speakers and have slowly been working back up the audio chain over the years, and found that starting with a kit and then tweaking it before going independant and building my own designs was a good way to ease myself into the deep end of DIY. the above DAC may provide a basis for you to do the same if you're keen.

it's all about what level of performance and cost you're currently at... a $200 CD player is a step up from a hello kitty boom box

[caddisgeek]

it's all about what level of performance and cost you're currently at... a $200 CD player is a step up from a hello kitty boom box

Thanks for the post Kye

To give some perpective, my current set up (for digital, won't go into analouge here) is NAD 502 CDP, Nikko STA-8080 reciever, and I switch between JBL Apollos, and Infinity RSb's depending on my mood, what I am listening to and how I am listening to it.

Not a super high end set up by any means, but it sure beats the **** out of my daughters hello kitty boom box

So I was hoping (if it's not too expensive this might be a good intro into DIY and DAC's at the same time

Cheers

Steve

[Zaphod Beeblebrox]

Thanks for the post Kye

To give some perpective, my current set up (for digital, won't go into analouge here) is NAD 502 CDP, Nikko STA-8080 reciever, and I switch between JBL Apollos, and Infinity RSb's depending on my mood, what I am listening to and how I am listening to it.

Not a super high end set up by any means, but it sure beats the **** out of my daughters hello kitty boom box

So I was hoping (if it's not too expensive this might be a good intro into DIY and DAC's at the same time

Cheers

Steve

You'll get a MUCH bigger bang for your Buck, by buying/building some new speakers. VAF sell some excellent kits, well worth considering. Next on the list would be a new amp. If you want to DIY, then I dissagree with Kye. Silicon Chip have described two, very fine, amplifiers. The Class A amp:

http://www.altronics.com.au/index.asp?area=item&id=K5125

and the ULD amp (mark I, NOT mark II).

http://www.altronics.com.au/index.asp?area=item&id=K5155

Most of the other kit amps described by Silicon Chip are, indeed, average. For my money, the old ULD amp was a stunner.

Warning:

Do not THINK about the MOSFET amp kits. They are shockers.

[caddisgeek]

Thanks for the input Zaphod, I should also point out that I'm on a budget, and 900 bucks for an amplifier kit (which I may or may not balls up) isn't really a consideration at the moment

[Zaphod Beeblebrox]

Thanks for the input Zaphod, I should also point out that I'm on a budget, and 900 bucks for an amplifier kit (which I may or may not balls up) isn't really a consideration at the moment

Easy. Save your money. Wait 'till you can afford a better pair of speakers. Changing CD players (or DACs) will make a miniscule (if any) difference.

[caddisgeek]

And here's me thinking I had some decent speakers

[Zaphod Beeblebrox]

And here's me thinking I had some decent speakers

I did not suggest that your speakers were not decent. However, with speakers, the options are limitless. There is far more scope for improvement in any system, by using better speakers, than any other change. Changing CD players/DACs will almost always represent the leat significant change you can make.

[kye]

And here's me thinking I had some decent speakers

you've got to remember that hifi is relative - just because your speakers aren't the best in the world doesn't mean they're not good, and the law of diminishing returns kicks in pretty early in the pricing scale!

I would disagree with ZB on the importance of source as I believe that it's just as important as speakers, however as i'm not that familiar with the commercial offerings I can't comment on your setup in particular.

if you're considering upgrades then listening to things in your own setup and making your own mind up is just as important as getting good advice.

if you're wondering about what might give the best bang for your buck, see what you can borrow for your system and see what improvemenst you can make. buying without trying can be hit and miss unless the advice you get takes into account all your existing equipment, your room and also your listening preferences etc..

[Hugh Dean]

I'm with you, Kye, on your very sharp observations about SC generally and the obsessive drive to keep down THD. Did you ever read Leo Simpson's withering editorial about tube amps a year back when he reviewed a rather expensive Chinese tube amp? He offered just two sentences in five full pages of THD analysis for'listening impressions'. He absolutely abhors tube amplifiers....

Low THD very seldom makes for a good subjective presentation, but there you go, opinions differ....

Xaphod, I would (humbly!) suggest none of the SC amp designs offer any great refinement. By ignoring the subjective listening experience, this outcome is almost guaranteed. With an improved power supply and a significant mod to the input stage current mirror, the latest ULD200 is not too bad, but with real music and particularly with ES speakers the design does not cope well with high frequency detail or midrange layering. Bass is excellent, however.

Hugh

[kye]

I'm with you, Kye, on your very sharp observations about SC generally and the obsessive drive to keep down THD. Did you ever read Leo Simpson's withering editorial about tube amps a year back when he reviewed a rather expensive Chinese tube amp? He offered just two sentences in five full pages of THD analysis for'listening impressions'. He absolutely abhors tube amplifiers....

Hi Hugh!

No I haven't read that - I generally don't bother with SC except the occasional issue when it's caught my eye, and that I have used their kits (through jaycar and altronics) to ease my way into DIY electronics over the years.

I was quite suprised when they did the valve preamp kit and built it with good results (except the stepup transformer I wound was really noisy, but that might have just been my windings!).

Interestingly though, when I replaced their high feedback circuit with an SRPP stage using the exact same PSU, valves and grade of parts, there was a large step up in sound quality. obviously the SRPP wasn't as flat at the frequency extremes, but a quick adjustment to my passive crossovers in the speakers and I was back to a level response and have not looked back since - as you say, far more refinement.

I have been mulling over a number of possibilities around why high feedback designs tend to sound less promising than their measurements suggest and have come apon a number of theories but nothing that resolves all the evidence I have gathered.

I am working on something though (which actually corellates to a previous conversation we had around the issue in SS amps being the VAS) and will report on this once I have done some tests. I have the equipment and components, just have to get my butt in gear and do them

[Zaphod Beeblebrox]

Xaphod, I would (humbly!) suggest none of the SC amp designs offer any great refinement.

Which is why I was VERY specific in suggesting that the original ULD amp was the one to look at. The latest version is certainly nothing special. Downright ordinary, in fact. The original ULD amp, OTOH, is very special. With some minor modifications, the amp sounds excellent - for a high Global NFB design, that is. It still has that considerable limitation.

By ignoring the subjective listening experience, this outcome is almost guaranteed.

I sort of dissagree with you here. IF the designer knows what to look for in a design, sound-wise, then he/she can work out which measurements are important. Even better, instrumentation takes the vagueries out of the design process. The human ear, whilst remarkable, is subject to all manner of unreliabilities. The problem with most Silicon Chip designs, is not the abscence of listening tests, but the refusal to accept that there are other, possibly more important, design goals than just low THD.

With an improved power supply and a significant mod to the input stage current mirror, the latest ULD200 is not too bad, but with real music and particularly with ES speakers the design does not cope well with high frequency detail or midrange layering. Bass is excellent, however.

Hugh

The big problems lie in the way the output devices are configured. Emitters should never be connected to loads. Never ever. This is one of the fundamental differences between most BJT amps and valve amps. As you know, the Emitter is analogous to the Cathode and the Collector analogous to the Plate. When connecting the Plate to the load (like the vast majority of valve amps do) considerable isolation exists between Grid and load. Same deal with BJTs. Using the Collector provides considerable isolation between Base and load.

But you knew all that (I included the above explanation for other readers). The important thing to note is that the original ULD amp uses the Collectors to drive the load. THAT makes it a vastly superior amp to both the later ULD amp and most BJT amps on the market today.

In MY Opinion.

Edited September 11, 2009 by Zaphod Beeblebrox
Brain fart

[Hugh Dean]

Zaphod,

It is not my place to educate, takes too bloody long, or put myself above others. You have been very emphatic about CFP (complementary feedback pair) output stages, as used in the ME, so I should contribute meaningfully here.

In the mid-nineties I built two SC amps, one with CFP output stage, and one with double emitter follower (DEF = conventional) output stage. Standard LTP input stages, with common emitter voltage amplifiers. Both Class AB, no other differences.

On audition I was stunned - for I had believed as you do that CFP was superior - the CFP version sounded flat, lacking in vitality, dull even, compared to the conventional DEF version.

I repeated the trial numerous times over the next week, and even called over my 80 year old neighbour to confirm, as well as my wife and two daughters. No doubt at all, we all heard the same things.

Drivers and output devices were identical, just connected in different ways.

When you do simulations in LTSpice you begin to see some of the problems. Transitions at the switching points create undamped oscillations, and at large signal throughput phase shift is far higher than a typical emitter follower.

Oddly, the CFP measures better, giving lower odd order harmonic distortion. This is, of course, most appealing, but it's a false dawn. The reason is that there is less signal compression (steadily diminishing output at increased input), since the increasing Vbe of the slave devices does not affect the transfer function, and the Vbe increase of the drivers is very small.

The oscillations can be damped with CB caps across the slave devices. But this flattens the sound quality even more.

My conclusion was that CFPs can be used effectively only in Class A, where they never switch off. In this class of operation, and with phase shift taken into account, they are just fine.

But NOT for Class AB.

So, for Class AB, best is the double emitter follower (Self Type II) output stage, but for Class A, where there is no switch-off at any point in the waveform, CFP is best, with some reservations concerning phase shift.

In my view, there is nothing wrong with the DEF output stage on the ULD200, rather, it is the input stage and the voltage stage which need attention. The problem is that an audio amp is a minefield of compromises, and the ear is very good at picking them up. Most of the problems are not discernible from the THD, although knowing the spectral distribution of the various artefacts can be helpful. The other problem is that some audiophiles like tubes, some like SS, and you ain't gonna change that any time soon.......

Cheers,

Hugh

[nvinen]

I bought the mag because of it, but then realized it didn't have any USB input

Keep an eye out over the next few months, there will likely be a USB add-on.

[nvinen]

Here is the Jaycar kit, now available

Still waiting for Altronics, they are designing and manufacturing a custom case so no surprise that it's taking a little longer.

[DanFi]

Warning:

Do not THINK about the MOSFET amp kits. They are shockers.

Why? They hard to make or dont sound good?

[Poita]

Just checked up on this the other day to see if the USB option had been added yet and it doesn't seem like it had.

BUT I did notice that the 2x100W amp kit mentioned earlier is now on a very good special. Normally $749.00 but marked down to $549.00

http://www.altronics.com.au/index.asp?area=item&id=K5155

Did anyone end up getting one? I am struggling to find any reviews on it...

[Greg Erskine]

Hi Poita,

I have a few friends that build mainly Silicon Chip projects and after a bit of tweaking they end up with very good sounding systems for very little money. I heard one of their modded DACs last weekend and was quite impressed. It was quite a bit better than a Benchmark DAC and a little better than their modded XDAC. It also improved the performance of a reasonably good Marantz CD player. Sorry I don't know the models. Anyway I was happy enough that I bit the bullet and ordered one today.

I know they have added JLH regulators to the voltage supplies and modded the output circuitry from the DAC chip a little, mainly component values and metal can opamps. I can't really comment what it sounds like standard, out of the box.

regards

[LogicprObe]

Did you ever read Leo Simpson's withering editorial about tube amps a year back when he reviewed a rather expensive Chinese tube amp? He offered just two sentences in five full pages of THD analysis for'listening impressions'. He absolutely abhors tube amplifiers....

I have a lot of time for Leo...........but you're right.

He loves silicon more than vacuum!

[Poita]

Hi Greg, well let us know what you think when yours arrives unmodded

Right now the Maverick Tube Magic D1 is the main one I am looking at, but I get a discount from Altronics, so this kit is looking quite favourable...

Would your friends be prepared to go into a little more detail about what mods they had done?

Cheers

Pete