There are spare pins, if you don't want the use of the mic in line for its intended purpose. It would be quite simple to route the sub signal out of this cable using a minijack to RCA adapter.

However, if you also want a center output as well, you will run into trouble I think. There is only one mic in line after all.

Stu

It would be quite simple to route the sub signal out of this cable using a minijack to RCA adapter.

Could you ellaborate on this, or point me to something that will explain how to do it. I'm looking to add a sub before the Cinncinnati meet, but most of this thread is beyond my level of tech speak.

Well, find the wire(s) (inside the empeg) going to the mic connector. Disconnect it/them from what it/they're currently connected to, and connect it/them to the sub out board instead. Then get an 3.5mm mono (?) jack to RCA adapter. Plug adapter into mic connector, RCA wire into the resulting RCA jack. Other end of RCA wire to sub amp.

Couldn't be easier

Of course, getting a sub out board before the meet (forgot when it's planned) might not be realistic....

/Michael

Thanks...

Okay. Open the player. In the rear left corner of the MK2s are two rectangular connectors. One is labeled "Analogue" and the other "Digital."

Pull the one labeled analogue from the board. Use a very fine flat bladed screw driver and remove the gray/black striped wire from the connector located on the far left of this connector. This wire will carry the sub signal across the mic in cable. I don't remember what color the ground half of the cable is, but you can get ground from almost anywhere. Connect the sub board output cable to that pulled wire by some means such as soldering or some sort of connector (what I will be doing). Connect the ground half of the output from the sub board to the cable ground. Put everything back together and connect your cables using an appropriate adapter. Enjoy.

DISCLAIMER. This ia all from memory and I've never actually done this, so this post could be riddled with errors.

Stu

Of course, getting a sub out board before the meet (forgot when it's planned) might not be realistic....

Not likely to happen by 9-21, unless he learns how to design and build one himself. Digital out boards yes . They will be ready before then.

Stu

I'm looking to add a sub before the Cinncinnati meet, but most of this thread is beyond my level of tech speak.

Keep in mind that you probably won't be getting your hands on a working sub-out board by the time of the Cincinnati meet, so you will need to wire up a sub the regular way. Please click here to see details on the regular way.

OK, according to page 108, the centre channel is simply the sum of the Front Left and Front Right channels divided by 2 after the fader coefficients have been applied (i.e. fading to the back will decrease the volume of the centre channel.

The mono subwoofer channel is calculated similarly and is (FL + FR + RL + RR)/4 but taken from before the fader coefficients so they don't affect the subwoofer level. After that a 4th order low pass crossover is applied.

If using left and right subwoofer modes (no centre channel available) the left subwoofer channel is (FL + RL)/2 and the right channel (FR + RR)/2. The low pass filter is only 2 order though for each channel if you use stereo subwoofers.

So they are simply averages according to the doco which I dont see being much problem on the subwoofer channel but I can see being an issue with the centre channel - constructive and destructive interference will be happening I think.

I tried both sides actually, in an effort to avoid using a buffer, but I got the same results from either side

Well the side you used is the OSC_OUT pin which is what you should be using so it's all good...

I can see being an issue with the centre channel - constructive and destructive interference will be happening I think.

Only one way to find out. . . Who needs stereo subs anyway?

Stu

I'm not worried about stereo subs.

Where did you take +5v from? I almost have my DAC wired up so I can find out now.

There is a small jumper under the 2nd drive bay labeled "+5." That's where it's coming from. Would you like another picture (uncropped this time)? Good job on the DAC.

Stu

Cool. I was looking for a place to solder though so I soldered to the inductor connected to that jumper.

It works fine. Sound quality is good considering I'm not using anything other than the DAC to drive the auxiliary of my home stereo. I need to hook it up to a decent system to test it for sure. I will probably connect it to my PC sound card and do a spectral analysis of some pink noise to see the subwoofer roll off.

My kernel stuff all seems to work OK too - only prob is a slight thump when changing the crossover frequency to a lower value (i.e. 100 to 80 Hz but 80 to 100Hz is fine)

There is however some noise getting in somewhere when I turn the gain of my amp right up (at normal levels you can't hear it), but I would guess that it is getting in on my breadboard (or the power supply lines) more than anything. Sounds kinda 50Hz-ish so I think that will go. I will do some PCBs next week some time.

In all an easy job - I only spent about 5 or 6 hours from whoa to go. I can put up some quick pics of the hack on Monday...

Glad it worked. I went with a jumper because I like to minimize permanent modifications to the player as much as possible. Even if I unsoldered the connection it would still show, hence the jumper.

I will be doing my own design although not for a few weeks. Emphasis will be on small size and sound quality. Did you test the center output? You put no circuitry of any kind between the output pins and the stereo?

Stu

Glad it worked. I went with a jumper because I like to minimize permanent modifications to the player as much as possible. Even if I unsoldered the connection it would still show, hence the jumper.

Yeah but you soldered to other parts of the board that will show so what's the difference. I also didn't have a suitable jumper to use.

Did you test the center output?

Yes it works fine - easy to test since it's simply the other channel of the DAC. A little hard to tell how "centred" it is though.

You put no circuitry of any kind between the output pins and the stereo?

The only circuitry I have after the DAC is the RC network on page 10 of the CS4334 datasheet. They are after all line level outputs. I believe this CS4334 is designed to be used like this without any further major circuitry after the DAC. The eval board even has outputs like this although it does have another circuit with an active output stage

Stu,

are you doing a center channel output also??? If you do, you're going to end up making me gouge apart my dash to install a center!!

Calvin

Well given that the centre channel out is simply the right channel of the digital I2S output and the DAC will probably be stereo, it's simply a question of having the output circuitry and the connector.

However I think Stu is planning on using the mic connector so it can be used in car on the sled which would rule out having two channels. You could however forgo the sub out for a centre out.

For the sake of size, I think it would be most sensible to make it sub out only. An ultra high quality output stage would be less important at these frequencies and having only one channel of analog circuitry would allow the board to be significantly smaller, but we'll see what turns up this week.

Stu

We built a DAC board for sub/center out. Something's not right with the digital signals. It almost acts like it needs another stage of buffering. When connecting it to the I2S output on my Rio it outputs terribly distorted sound unless I bridge the MCK input to ground with my finger. Then it sounds pretty good. There's nothing wrong with the I2S outputs. Those were tested and provide pristine sound through a P-3A DAC.

It turned out pretty small at only 11/16" x 1 1/16". The output is selectable as sub or center via a jumper. No time to work out the bugs at the moment. Hopefully soon. Here's a poor quality pic.



Stu

What? You mean your finger won't come with the kit?

Do you have any bypass capacitors for the DAC? I've had a few that kept going nuts from the interference from the switched mode PS until I put some bypass caps in close to the chip.

You could always fudge it by putting in a resistor + capacitor to simulate the loading on the clock line due to your finger

- Trevor

The bypass caps are there. I thought about loading the line down too. That's next. Right now I have another little project that needs my attention . Thanks for the suggestions though.

Stu

Whatever was bothering the board seems to have corrected itself. It works reliably and admirably now. The only change is that I rewired the digital out board (necessary to buffer the I2S signals) to digital supply and ground from analog supply and ground. Not sure why that would help.

What do people think would be a good voltage output level for this thing? I can go pretty close to five volts, but no higher. I will be ordering parts for an improved version pretty soon, so I need to figure out what value resistor I need for the gain to achieve the desired output level. So far one vote for 4 volts. RMS or P-P? The caps in the analog path will be poly, rather than ceramic and resistor will be precision .1% instead of 1% so so resistors. I may need to experiment with layout too in order to get the best sound.

So far highs are not real extended and the noise floor could be better, although it's better than many stereo components already. More updates to follow.

Stu

wouldn't it be safe to set it the same voltage output as the other line outs? isn't that the way most head units with sub out work?

Okay, then I guess the output will be 4 Vpp. That is what the Empeg hardware outputs right?

Stu

I finally ordered the parts (nice metal film .1% 10 ppm SMD resistors and PPS SMD caps) to improve the sound quality of the sub board and to increase output to 4 volts P-P. I might change the layout or circuit a bit too if that doesn't help enough.

Stu