'noodle' dac (ebay special)
Sep 7, 2008 at 6:09 PM Post #65 of 180

gurusan

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Quote:

Originally Posted by adamus /img/forum/go_quote.gif
that should be fine.

I only say fo for 1uf, some amps etc have 10k input impedance.



I have a 10k pot on my cmoy...this explains the lack of deep bass I have been noticing. I thought it was just the sound signature of the amp but now I know better because I know that equation!

I had .1uF input caps which gave me a 159Hz bass rolloff! :/

I now have a mix of different caps on their way to me. Some Philips 2.2uF, 3.3uF and Wima MKP10 .33uF

According to you and some research I've done the Wimas are very good, but I can't find much info on the Philips. I hope they will be ok as the Wimas are only .33uF which will make F about 48Hz....not bad but obviously still within the audible spectrum! :/



However I am confused on 1 thing. Do you really need output caps on the DAC if there are already input caps on the headphone amp? Sorry for all these noobish questions but I have to learn some how!
smily_headphones1.gif


Also 1 addition question, if I have the space can I wire up two .33uF Wima caps in parallel for each channel to get a net of .66uF? I mean I know you can do it but are there other factors such as distortion that will also double by putting in another cap alongside the original?
 
Sep 7, 2008 at 10:30 PM Post #67 of 180

guzzler

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It's worth putting the caps on the DAC if you intend to use it for anything else. If you're certain it will only be with an amplifier with AC coupling, then fine, but it's a bit of a risk...

Also - regards the rolloff frequency, what you've quoted is the -3dB point but there will be attenuation and phase shift at much higher frequencies. As you're still dealing with relatively small capacitances, try and get your -3dB point below 10Hz.
 
Sep 8, 2008 at 6:19 AM Post #69 of 180

adamus

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Amen to that.

Last night i changed the interstage caps on my soa + jisbos. The caps had the 3db point at 27 hz and everything sounded a bit hollow.

Put some 1 uf obbligatos in and what a difference. deep bass, much stronger mid bass. Its a different amp. the obbligatos need some time though, they sound ever so slightly 'plastic' a bit too smooth. almost like i need slightly more extension up top.
 
Sep 9, 2008 at 9:40 PM Post #70 of 180

gurusan

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got my Chinese DAC up and running and installed in a case under my CMOY just for testing.

img3594nq8.jpg


Currently have it from my P5Q ADI200B optical out and it sounds pretty good.
Next I'm going to swap in a LME49860NA opamp I have here, going to add a power LED, remove some caps and bypass the output stage to go straight to my CMOY.

I crammed the transformer in there (superglued it to the roof as far away from the DAC board as possible) along with the other audio components and can't detect any humming or EFI symptoms...but I will buy some copper tape and make some kind of shield just for peace of mind.

and 1 question, does this need any ventilation as the Vregs got warm after just a few min. I'm thinking of just drilling a ventilation hole up top and on the bottom to let out warm air?
 
Sep 10, 2008 at 11:17 AM Post #71 of 180

keiths

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^^^ Looking good, Gurusan.

FWIW, I drilled a quite a few vent holes in my DAC's case (top and back, close to the VRegs). As you say, the regs' heatsinks get pretty toasty.

I got some larger value MCaps (1.5uF) and am going to install those tonight to get the -3dB point below 10Hz when the DAC is used with my Arcam speaker amp.
 
Sep 10, 2008 at 2:04 PM Post #72 of 180

gurusan

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yeah i think it definitely needs some ventilation.

After about 10 min the large heatsink was 58C...and a few minutes later evened out to about 60C...and this is outside the case!

.....does anyone know the temp specs for these VRMs?

img3599xg1.jpg


On another note, this DAC sounds seriously good! Going from Winamp playing FLAC rips -> ASIO -> Optical out -> DAC -> CMOY -> HD-580

I have swapped a LME49860 in (LM4562) and it sounds MUCH better...but I would like to bypass the outstage completely and for the signal to go straight to my CMOY.

How can I do this?


and another sidenote, I changed out the .1uF output caps on my CMOY to 2.2uF caps and OMG I didn't realize how much my bass was lacking before. Now my -3dB point is at 7.23Hz instead of 159! lol!
 
Sep 11, 2008 at 7:14 AM Post #74 of 180

error401

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Quote:

Originally Posted by adamus /img/forum/go_quote.gif
the 7812's etc go up to 105, some 150.
60 is fine.



The temperature in the datasheet is the maximum junction temperature, not the case or ambient temperature. The junction will be much, much hotter than the outside of the case, and you need to do some math to figure out exactly how much hotter.

Read ESP - Heatsink design and transistor mounting if you're interested.

Though I agree that 60 is probably 'fine', but it's still quite hot.
 

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