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Alien DAC v1.1 Construction Thread - Page 13

post #181 of 1560
8/9/06 at 1:34am
Seaside,

If you are using USB power, you either want to use unregulated 5V or use the adjustable regulator. A regulator works by REDUCING the input voltage to a constant level. it cannot increase it and it will not do any regulating unless it drops the input voltage a certain amount, in this case at least 100mV I think (check the datasheet-I'm going by memory here) but dropping more than the minimum increases the performance of the regulator, which is why it is recommended to drop it to 4.6V to 4.8V.

If you use the 5V regulator (or the adjustable reg set to output 5V) , you will get 5V in, about 4.9V out (because the reg will drop the voltage just like it was a diode) and the 4.9V out will be no cleaner than the 5V in from the USB port. An expensive part basically doing nothing.

I used R31 = 31.2K and R32 = 11.5K to get 4.7V out.

The discussion of overclocking at 5.4V assumed you had external power coming in somewhere north of 6V or so, from a Tread for instance or a simple wall wart. The external power MUST NEVER exceed 10V or the regulator will go poof.
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post #182 of 1560
8/9/06 at 1:49am

Thanks Neir

Thanks, You really helped me a lot.
It is very hard to understand all these electonic thingy for person like me, who has no backround at electronics. I can replace those bulbs tho...

I guess my best bet is making Vout of 4.6~4.8V using adjustable reg. Your R31,32 value looks alright to me. Do you mind if i use the same value?

Thanks again.
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post #183 of 1560
8/9/06 at 2:51am
Quote:
Originally Posted by Seaside
Thanks, You really helped me a lot.
It is very hard to understand all these electonic thingy for person like me, who has no backround at electronics. I can replace those bulbs tho...

I guess my best bet is making Vout of 4.6~4.8V using adjustable reg. Your R31,32 value looks alright to me. Do you mind if i use the same value?

Thanks again.
No, you may not use those values. I filed for a patent on those values last night.

Just kidding... those will work well, but if you have trouble sourcing the precise parts, anywhere in the 4.6-4.8V range should work just as well.

Good luck!
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post #184 of 1560
8/9/06 at 4:44am
why i'm confused here?!

the regulators for the specific job, do as follows

they accept for minimum a few mV over the voltage we want
to regulate and maximum less than 10V (if i remember correctly)
and in that range they regulate to the specified voltage e.g. 3.3V-5V
in any other conditions either they pass away or they don't regulate!

the adjustable regulator, regulates according to the input voltage the input resistors specify the region in which the regulator starts to regulate! in fact they shift the working range.

correct me if i am wrong!


P.S i think the basic reason we use them here is for their low noice... (filtering the input voltage)
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post #185 of 1560
8/9/06 at 5:33am
Quote:
Originally Posted by Seaside
(Alf's support site states this value as 1.1267, so is it 1.267 or 1.1267?)

Here's some question regarding this option.

A. Does input voltage from USB port(Vusb) has to do anything with the regulated voltage(Vout)?

B. If the answer above is "Yes", Am i need to aim at Vout 0.4V less than Vusb?

C. Assume the answer above is "No. It doesn't matter as long as it is close to 5V" then, Can I choose values of R31 and R32 to make Vout approx 5.3V in order to over-drive the DAC?
For example, R31=33K, R32=10.5K, then Vout will be approx 5.3V. Is this possible?

Thank you very much.
You can confirm Vref in REG101-A datasheet Its 1.267V.

Vout will always be less or equal Vin.
So no - you can't overdrive with REG101-A.

Alf said that Vin should be at least Vdrop (60-100mv) more than Vout.

Though REG101 datasheet guarantees listed regulation accuracy only if you provide Vin = Vout + 0.4V (up to 10V) and do not draw more than 100mA (top of the pg3 in REG101UA pdf)
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post #186 of 1560
8/9/06 at 1:52pm
I have a couple questions about the DAC

First of all, is there anything wrong with this BOM?

Attachment 8037

My next question is, can this DAC power a set of earbuds / headphones fine without connecting an amp to it?

Would CL and CR not be necessary if the DAC was used only for headphones?
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post #187 of 1560
8/9/06 at 2:02pm
Quote:
Originally Posted by abcheng
I have a couple questions about the DAC

First of all, is there anything wrong with this BOM?

Attachment 8037

My next question is, can this DAC power a set of earbuds / headphones fine without connecting an amp to it?

Would CL and CR not be necessary if the DAC was used only for headphones?
I connected my prototipe board to my etymotic er4p and hd650. the sound achieved reasonable levels(not even loud) but there was no bass or impact in the music.. the highs were very detailed but overall the sound was "strange" this was some time ago and I don't remember very well. When I connected an amp(PA2V2) the sound became much better. With a PIMETA it became even better.

The dac isn't supposed to drive headphones. Use an amp. You can build a Cmoy cheaply but it will not use all the capabilities of the Alien DAC.
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post #188 of 1560
8/9/06 at 2:17pm
Quote:
Originally Posted by MASantos
I connected my prototipe board to my etymotic er4p and hd650. the sound achieved reasonable levels(not even loud) but there was no bass or impact in the music.. the highs were very detailed but overall the sound was "strange" this was some time ago and I don't remember very well. When I connected an amp(PA2V2) the sound became much better. With a PIMETA it became even better.

The dac isn't supposed to drive headphones. Use an amp. You can build a Cmoy cheaply but it will not use all the capabilities of the Alien DAC.
I have a couple CMoy amps already, but that means I would have to add a BUF634 since the CMoy has a virtual ground circuit correct? I'm trying to keep this as portable as possible since I would plan to use one of the four I'm building with my laptop, since my laptop's sound card is literally a piece of crap.
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post #189 of 1560
8/9/06 at 2:23pm
Quote:
Originally Posted by whiz
why i'm confused here?!

the regulators for the specific job, do as follows

they accept for minimum a few mV over the voltage we want
to regulate and maximum less than 10V (if i remember correctly)
and in that range they regulate to the specified voltage e.g. 3.3V-5V
in any other conditions either they pass away or they don't regulate!

the adjustable regulator, regulates according to the input voltage the input resistors specify the region in which the regulator starts to regulate! in fact they shift the working range.

correct me if i am wrong!


P.S i think the basic reason we use them here is for their low noice... (filtering the input voltage)

??
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post #190 of 1560
8/9/06 at 2:28pm
Quote:
Originally Posted by abcheng
I have a couple CMoy amps already, but that means I would have to add a BUF634 since the CMoy has a virtual ground circuit correct? I'm trying to keep this as portable as possible since I would plan to use one of the four I'm building with my laptop, since my laptop's sound card is literally a piece of crap.
I believe IC4 (BUF634) is only required to POWER the DAC from the virtual ground rails. If you use USB power for the DAC, you can just hook DAC output pads to Cmoy input pads. If independently powered, it's no different than if you were hooking it to any other external amp via interconnects. You're just eliminating a set of jacks and interconnects.
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post #191 of 1560
8/9/06 at 3:14pm
Quote:
Originally Posted by NeilR
I believe IC4 (BUF634) is only required to POWER the DAC from the virual ground. If you use USB power for the DAC, you can just hook DAC output pads to Cmoy input pads. If independently powered, it's no different than if you were hooking it to any other external amp via interconnects. You're just eliminating a set of jacks and interconnects.

ahhh.. ok. I guess I'll give the DAC a try with and without an amp and see how much of a difference there is.

As for CL/CR, it isn't necessary if an amp isn't used correct?
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post #192 of 1560
8/9/06 at 4:09pm
Quote:
Originally Posted by abcheng
ahhh.. ok. I guess I'll give the DAC a try with and without an amp and see how much of a difference there is.

As for CL/CR, it isn't necessary if an amp isn't used correct?
You always need CL/CR. The audio stage is powered by the +5V from the IC3 regulator, or directly from the USB bus. The architecture of the chip is such that the audio output has a DC offset of almost exactly 1/2 of the supply, or about 2.5V. You need the output caps unless you want to power your hedaphones with 2.5V DC.
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post #193 of 1560
8/9/06 at 4:18pm
Quote:
Originally Posted by NeilR
You always need CL/CR. The audio stage is powered by the +5V from the IC3 regulator, or directly from the USB bus. The architecture of the chip is such that the audio output has a DC offset of almost exactly 1/2 of the supply, or about 2.5V. You need the output caps unless you want to power your hedaphones with 2.5V DC.

ahh ok, I understand now. Thanks for answering my questions.
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post #194 of 1560
8/9/06 at 5:23pm
Quote:
Originally Posted by MASantos
I connected my prototipe board to my etymotic er4p and hd650. the sound achieved reasonable levels(not even loud) but there was no bass or impact in the music.. the highs were very detailed but overall the sound was "strange" this was some time ago and I don't remember very well.
Well, the output caps are forming a high pass filter here, and my guess is that the 3db point is up in the midrange. So, not only will there be no bass, but from the mids down the sound will be out of phase which would account for the strangeness. If you want to power your earbuds (in response to the other poster), increase the output caps to at least 100uF, and more like 470uF for low impedence phones. Obviously this is not optimal, but it will work in a pinch.

-d
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post #195 of 1560
8/9/06 at 5:38pm
Sorry for the mess with Vref on my site. I updated the page with proper values. If you notice any typos or errors, please do bring it up.
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