Marantz CD-63SE manufacturing error (resistors instead of inductors in DAC filter)?

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I have always felt that my Marantz CD-63SE was a bit 'toppy' in the high frequencies, so I decided to look in to it, and perhaps mod it. After inspecting the PCB and its components, it seems I don't have the 220uH inductors at L601 and L602. They are 2.2 Ohm resistors instead! There's no question about it. One measures 2.3 Ohms on my meter (taking tolerance of the resistor and my meter into account, that's okay), and they have the colour coding of: red, red, gold, gold. There is no question about that either - definitely two wide rings of gold. So even if it was an inductor, it would be a 2.2uH one, and not 220uH as it's supposed to be. And they are identical in body colour and shape to the adjacent resistors. All other passive components seem to be the correct value as stated in the service manual circuit diagrams.
Should this be right? Does anybody know of a change of design Marantz performed during the run of this model? Without the gentle curve of audible high frequency cut (made up for by the slight lift of the other aspects of the filtering) leading to a notch at 350kHz, no wonder my machine sounded so toppy and fizzy!!
I suspect the wrong component may have been loaded into the machine that populates the empty PCBs during manufacture....
Anyone know for sure, or would hazard a guess for me?
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A frequency sweep with a test disc and 'scope will confirm if the response is incorrect.

I would doubt very much there is an error, more likely a production change if they really are resistors. Usually full copies of service manuals and their service bulletins detail changes with reference to serial number.
Although I appreciate your reply Mooly, I wish I could share your trust of manufacturing and industry... Many, many experiences of mine and others are to the contrary!
Even if the response measured flat as a pancake to 20kHz on the 'scope, the very presence of the inductors is critical to generating a notch out of the frequency range at about 350 kHz (8* Fs). Without these, the following circuitry is blasted with a much higher level of 350 kHz oversampling noise. Of all the mod'ing articles and contributions that I have searched for from the internet community about mod'ing this particular CD player (both on diyaudio and beyond, and there are a lot!), none mention removing the inductors, and none mention the radical design change of them being removing by Marantz either. In fact the many references to the inductors from other mod'ers out there are about upgrading to better quality inductors, and additionally changing the value of them, in concert with other slight changes in the filter to nudge the roll off curve about, while maintaining the all-important 350 kHz notch. Considering how little a 2.2 Ohm resistor would do in this circuit (and how much cheaper it would have been for Marantz to simply put a 0 Ohm wire link in instead), I'm really beginning to warm to the idea of it being a manufacturing error.

Anyone else?
I also forgot to add Mooly, that I did check the service manual, and the addendums I have for the CD player, and none of them refer to replacing the inductors with a resistor. I also have thought, that considering the extreme rarity of using very low value impedance resistors (sub 10 ohms) in low power solid state audio circuits, and considering how close the colour codes are, it probably is a mistake on the component suppliers side, not Marantz who simply failed to spot it. I have EXTENSIVE experience of being offered the wrong value components when purchasing, especially from a local Maplins (more often than not in fact! I eventually got into the habit of borrowing a multimeter from their own shelves to test components every time I went in to get passives!) but even professional industrial suppliers like RS components have fallen foul of this, for me....
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If you are in doubt the only way is to take one out and test it using either an L meter, bridge, or a sig gen and scope and rig a simple LCR network up. A small 220uH coil would have a DC resistance of around 2 to 4 ohms anyway, so the fact they actually measure around 2.2 ohms doesn't in itself prove much.

You will never be happy unless you prove it to yourself. You have the advantage of having the unit in front of you too. If it were a manufacturing error, it would affect a whole production run, not just yours, so many would be affected. Not saying it's impossible, but it's up to you to prove it now.

Maplins and other component suppliers are a world away from manufacturing... as an electronics engineer I can only recall one instance of an incorrect part being fitted (as opposed to mods that appear in production) and that was a Toshiba TV years ago that had 1N4148 diodes fitted in place of a ZTK33 voltage reference... they all had tuner drift as a result.
I always though it was a bad idea to make small inductors which look like resistors!

You need to check the components, as Mooly suggests, or use an oscilloscope to compare the 'before filter' and 'after filter' signal.

This unit might not have been built by Marantz, but by a factory somewhere else which was contracted to do it. Modern companies are often 'virtual', so their products never actually exist (except as prototypes) in their own premises. Brand 'A' has their products designed by 'B' and built by 'C', then stored in a warehouse by 'D', who responds to orders from distributor 'E' to send to shops 'F', 'G' etc. 'A' might never check that the products delivered to 'G' are actually as they should be, unless a customer complains. 'C' might not be too bothered about getting things right, as it is not his name on the box, so as long as gross errors are avoided (i.e. the thing vaguely works, and doesn't explode) he can be confident that 'A' won't check.

One interesting thing is that these mistakes almost always involve a cheap component replacing an expensive one. Must be coincidence!

Indeed, my first question would be have you measured the inductance? If you don't have an LCR meter/bridge maybe you can borrow one.

Secondly, it's been pointed out by some who have measured and/or simulated it that the DAC filtering on the CD63 doesn't generate a flat response, but one that peaks in the treble about 1dB IIRC. This is partly why some people have changed one of the capacitor values to reign it in. I would like to say that, personally, I don't feel a small alteration here will fix the sound of this cd player. You need to spend time reducing the psu noise and jitter and, crucially, regulate the servo driver op-amps in order to remove the harsh, thin and woolly sound and lack of detail.

Thirdly, the CD63 will always have a slightly bright and upper-mid-forward sound, it can't be completely tweaked out. I assume it's the nature of the chipset.

Hey! Thanks for the input, people. Of course I've definitely got some testing to do. But first:

Mooley - I agree about the low impedance of inductors, and that it is not conclusive that it's a resistor from that. But considering the colour code definitely is red, red, gold, gold, it is therefore 2.2 something (ohms, or microhenries) , unless there is a colour coding error on the correct component. Still an error there though! I did check many of the inductors on Farnell's website (including those suggested by some other mod'ers lists of components to upgrade to), and the DC resistance hovered between 5 and 9 ohms... If it is an inductor, it's a bit of a coincidence that its DC resistance matches almost perfectly with the colour code on its body, (and even then it would be out by a hundred fold from the 220uH inductor that's supposed to be there)... But testing it is the DEFINITIVE way, I agree. Now I have an oscilloscope, a multimeter, and stacks of passive components around my workshop (but no signal generator, except for a CD test disc with audio frequencies on it which I play through another CD player, if necessary). Could I go about setting up a rudimentary rig to test if it is an inductor (and hopefully its value too, although at this stage that's not so important) with the above ingredients, and if so how? I assume it could be basic enough to be described in writing, and as we're on the very edge of my relatively modest knowledge of electronics, I'd be most grateful! I did think that I could lift R607 from the circuit so as to form an RLC network after the first opamp based filter, and could raise C605 to 1uF from 1pF. That would cause the response to fall away rapidly at from as little as 10Hz and go on to cause a -90dB notch to form at a few kHz instead of 350kHz (which would rise back up 20 dBs or more above that) - if it was an inductor. However if it wasn't an inductor, and was effectively just an RC network, then the response would just gradually roll off from 10kHz or so a few dBs. I could use my test disc and 'scope to measure for that. Have I got all this right?

DF96 - Yes.... This is my experience of things... It used to amaze me that life is as error free as much as it is, with all those areas for mistakes to creep in.
I used to have a strange desire years ago for reading up on aircraft disasters and their causes, and you wouldn't believe how many aircraft have been downed due to the communication breakdown along the chain of engineers in construction and maintenance, and how tiny and trivial some of those errors are, with such devastating consequences sometimes many years later. And that's in something as serious as aviation. God knows how many errors actually occur in consumer electronics! It will be interesting to see if my current issue is another one though...

SimontY - Thanks for the input. Definitely some testing coming up. I've since also been looking into the various improvements this CD player can garner. I'll take your advice into consideration for some of the more up market tweaks, but first things first!
Hi Mooly,
Yes, there are sweeps. It's the Sound Check CD by Alan Parsons and Stephen Court mastered at Abbey Road. I actually got it from RS - stock number 245-376. There may be more on it at RSs website, but it has:
a variety of pink noise bands and phase test combinations,
22 separate 1/3 octave band tests from 20 Hz to 20 kHz, and sweeps from 20 Hz to 8kHz,
spot sine freqs from 60 Hz to 15 kHz in 11 steps,
sine sweep from 20 hz to 20 kHz

Plus other stuff, but the above is what I think is what we're interested in. Which one(s) should be used?
DF96 - sorry, I meant: change to 1uF from 1nF, (the stock 1000pF fitted, obviously) not 1pF as I first wrote. Doh!

Mooly - I have to check if I've got those different components. I did have the others you first suggested. I've got to deal with a couple of other things just now as well, so I'll be back in half an hour!!... Hang on.
Mooly - Great thanks for that link. Got the equation, the circuit layout, and the components are here. I'm going to extract a suspect inductor after doing DF96's quick test with a couple of the recommended passives to form the high-pass filter with the 'scope.

DF96 - Good call with that high-pass filter wheeze for the scope... I'm going to quickly prod some 'scope probes into the CD player while in 'high-pass filter mode'! I'm not sure how easy it might be to see the HF noise component though, and if the inductor isn't an inductor I may get thrown off a bit. But it's a good wheeze to observe the HF noise when I get it all working in a known way...

I'll deal with this over the weekend, and post the results when I get to the bottom of this.

Thanks again for the help...
These days production machines can measure components during placement to prevent these sort of problems.
Back when the CD63SE was made far less likely, but I suspect a cost down as inductors are far more expensive components and usually have long purchasing lead times.
I had one of these machines, labelled "Made in Singapore" with a Johore Bahru (which is actually in Malaysia) address
I'm beginning to suspect it was a cost down davidsrsb, especially as it looks like they are resistors to me. Here are the results of the measurements I took on one with Mooly's circuit suggestion (and link - thanks!) of an inductor, a capacitor and a 1K resistor all in parallel and being fed by a 470 ohm resistor: (all voltages measured are peak-peak)

20 Hz to 20kHz sine wave sweep (low to high) across common/ground and 470 ohm resistor

test 1: above circuit with 'our 220uH inductor', a 0.47uF capacitor
result: 800mV at signal generation side of 470 ohm resistor. 5mV at sweep start, dropping to 2mV at about 5kHz and 1 mV at 15kHz, at network side of 470 resistor.

So not a 220uH inductor then? I though it could be a 2.2uH inductor, so I added a 47uF cap (polarised electrolytic - but if polarity reversed was same result) that should according to the equation should bring the resonance peak back down to 15.6kHz from 156kHz if it was 2.2uH

test 2: above circuit with 'our 220uH inductor', a 47uF capacitor
result: 800mV at signal generation side of 470 ohm resistor. 5mV at sweep start, dropping to 3mV at sweep end from about 5kHz and on, at network side of 470 resistor.

Still no resonance peak. So removed 47uF cap and 'our 220uH inductor' and left 0.47uF in place. (Different filter now, but just to test set-up).

test 3: above circuit with 'our 220uH inductor' removed, a 0.47uF capacitor
result: 900mV at signal generation side of 470 ohm resistor. 650mV at sweep start, dropping to 30mV at sweep end evenly dropping throughout range, at network side of 470 resistor.

It's a resistor isn't it? And the chances that it's a mistake in BOTH value AND type is remote. So it's pretty obvious that it has been selected to replace the inductor because it's the one that MOST LOOKS LIKE IT AT FIRST GLANCE. It looks physically like an inductor, and the gold bands could be mistaken for brown, taking it from 2.2 in someones mind to 220.

Now, I could think - how smoke and mirrors is that? How cloak and dagger? But I'm a forgiving person, so I'm going to suggest maybe it's for internal manufacturing reasons, so eagle eyed people down the construction line don't cause unnecessary down time by halting the manufacturing process thinking they've spotted a mistake (a wire link instead of a component).

But someone has definitely gone about selecting a cheaper component and surreptitiously sneaking it in hoping the change isn't noticed!!! The fact that the circuit is now behaving in a far less efficient way, further away from what the designers intended, and the negative effects on sound quality to boot is what REALLY irritates me. And I'm sure many modifiers and tweakers out there who may have upgraded other parts of the CD player thinking they're improving it, when there is this glaring error still present, would probably be peeved too. I can only hope that the 'inductors' are one of the first things they upgrade...
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Interesting :)

So do you think you will fit an inductor in place of what is there. Can you be sure there are no other changes that have been implemented to compensate for resistors instead of the inductors being fitted... an extra cap or a different value of R and C somewhere.
All passives in the filter section from the output of the DAC onwards, are as stated in the service manual, except the resistors feeding +/- 12v to the supply pins of the ICs are now 27 ohm from the stated 10 ohm. Haven't checked the HDAM section though, but the CD player's output citcuitry following it checks fine. What could they change that would emulate what the inductor is supposed to do so well? What could have the same effect of creating a tight 350kHz notch?

The HDAM sections are hidden under the copper shield covers, which I'm not going to tangle with just yet. I'm going to decide whether to order a couple of the 220uH inductors first, and see how it sounds with them, and what the output frequency response measures. If it sounds good and the response reads as what is expected from the stock machine, then I may go no further with this detective work, except to upgrade it as planned with better quality components here and there...
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