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qusp  
#1 Posted : Wednesday, January 20, 2010 9:19:04 AM(UTC)
qusp

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Joined: 7/22/2009(UTC)
Posts: 11
Location: Brisbane

Hi there, i'm putting together some crazy plans and a BOM to use the COD as a transportable dac with discrete buffers on output Drool (or simple passive I/V art the very least). The dac will be powered by 18-24v of NIMH AAA cells, either with just a few reservoir caps in series or with a modified LCDPS (or SSR01/02 jung type regs) as preregulator for the onboard regs and buffers. The buffers are a desirable component, but not absolutely essential, the best part with them would be the ability to drive my low impedance IEMs balanced with them directly (wish the volumite worked with COD Boo hoo! ) I dont have a balanced portable amp (YET) so I would perhaps use it passively SE temporarily with one of my amps if volume control becomes an issue.

Basically i've become sick of waiting for someone to release what I want, so with your help (thanks guys at TP for the product and whomever might pop in here), mostly parts I already have lying around (the dac chips, batteries and regs) and a few other bits (including the PCBs) I will order, i'm gonna give it my best shot at making it a reality and have some fun, frustration and hopefully joy along the way. this is my first go at putting something together myself and I will probably if prototyping goes well, get a small PCB made for integrating any regs and the buffers. the project is solely for my own enjoyment, probably a bit crazy (read large) for the buying public anyway. i've built things before and done my share of trouble shooting and mods to existing products, but my circuit design and implementation skills are not far advanced. this will be a middle step

Now for the questions as you have some background now,

the areas of concern past what is mentioned above are input and muxing, the options for transports are a few and I would like to have 1 or perhaps 2 of them. the candidates are

1. i2s directly tapped from a modified cowon X5L, this is a definite as its fairly easy, but I must see how well it sounds
2. spdif (toslink) from my iriver H132CF into your toslink module-> spdif or mux board; or i2s from a similar mod as above
3. USB into one of your USB boards, this wont be used that much initially, but I want to have the option if/when I get a decent laptop, plus its bus powered so doesnt complicate things much further than space and perhaps muxing

• now if I used the cowon with i2s I was thinking that I should really use a metronome, the quality of the signal may not be that great to begin with even before the journey from one unit to the other; thats if I dont do something crazy and uncase the cowon and install it in the hammond with the dac, then dremel a hole in the roof for control :d/

• this would negate the need for any spdif receiver and probably result in higher quality playback including upsampling; at least thats my thoughts, please correct me if i'm wrong??

• how to integrate i2s with USB as a second input? can I have both connected and only use one at a time? my thought would be no and I would need a mux or otto which is out of stock? or work on some other relay switching

• if using the metronome with i2s, can I just leave it on the highest output upsampling rate and I can then feed it any input rate without the need for access to the dip switches?

• do I need a pregegulator if using batteries, or will some reservoir caps do? this if not using active output which would obviously need regulation for the analogue stages for best sound and for divying up the voltages

• is there some way of integrating the volumite? Pray is there another solution to the same end (I had thought of some other digital pot, but i'm not really ready for a uC) or do I have to put up with an analogue pot in the signal path in the case of this build when driving headphones directly?

thats about it at the moment, thanks for any help and if there is any way you can suggest to simplify the situation (other than not doing it) it would be appreciated. as mentioned i'm prepared for this to = fail, but that is not the aim of course, regs, dac chips, some good sized hammonds I was sent as a mistake and other bits and pieces are piling up around here due to my bower-bird tendencies, so I want to put them to use

cheers






Edited by user Wednesday, January 20, 2010 9:22:47 AM(UTC)  | Reason: Not specified

glt  
#2 Posted : Wednesday, January 20, 2010 11:29:58 AM(UTC)
glt

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I'll help with some of the questions:

The BB PCM chip in COD does not have volume control, so something like Volumite is out of the question. You will need the sister chip that has a s/w interface (meaning it can be controlled by a uP)

But the PCM chip in COD works with the widest fs range for MCK (we are talking I2S) see: http://hifiduino.blogspo...m/2009/12/blog-post.html

This means you can probably feed I2S from any device without the need for resampling. (For a USB device that can support hires audio try the musiland devices and you can mod it to extract the I2S -see my blog)

You can feed metronome any I2S and it will resample to the specified sample rate. The metro throws away the masterclock of the incoming I2S (you don't connect the mck of the incoming I2S signal). So you can leave it there with fixed output.

Hope this helps...
qusp  
#3 Posted : Wednesday, January 20, 2010 10:16:47 PM(UTC)
qusp

Rank: Member

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Joined: 7/22/2009(UTC)
Posts: 11
Location: Brisbane

glt wrote:
I'll help with some of the questions:

thanks, some good news I wasnt expecting and some bad news I was

Quote:
The BB PCM chip in COD does not have volume control, so something like Volumite is out of the question. You will need the sister chip that has a s/w interface (meaning it can be controlled by a uP)

yeah I knew this in my head, but prayed for a miracle, thus the emoticon, I have some PCM1798 (low power) and also PCM1792, the 1792 I suspect would work with volumite or similar as it has software control, but it wouldnt work on the COD PCB for the same reason I suspect because I would lose control via the switches for configuration and would need a full micro to contriol the whole thing I guess d'oh!

regarding uC control like you mention using this external chip, dont these actually resample the data so you are then relying on the 'sound' of the controller chip to be good with much of the good work done by the dac thrown away? or do they sit outside the signal path and just impose the values on the signal? ah just thpouight aboput that some more; it would act on the i2s data before the dac right? I guess it would reduce rthe dynamic range of the signal somewhat when turned down, happy to be wrong there of course

Quote:
But the PCM chip in COD works with the widest fs range for MCK (we are talking I2S) see: http://hifiduino.blogspo...m/2009/12/blog-post.html

cool, sounds good, but I think I like the functionality of the reclocker as far as upsampling the clock independently so a high res output is obtained (mostly) but I will definitely check out your blog, thanks for the link!!

Quote:
This means you can probably feed I2S from any device without the need for resampling. (For a USB device that can support hires audio try the musiland devices and you can mod it to extract the I2S -see my blog)


yeah I actually considered the musiland or similar, but i2s is primary so I need to find a way of integrating the 2, the musiland is bus powered too right? I would probably give the aDum chips by AD and perhaps isolate the power supply to be fed from the batteries and reg if I have enough current, there are a couple of solutions for this already with small PCBs available, but you may have tackled this already in your mod, so i'll definitely check that out.

Quote:
You can feed metronome any I2S and it will resample to the specified sample rate. The metro throws away the masterclock of the incoming I2S (you don't connect the mck of the incoming I2S signal). So you can leave it there with fixed output.
excellent, exactly what I thought and hoped, I think I should use the metronome

Quote:
Hope this helps...

sure did mate, thanks very much for your time, should be fun, i'll buy the COD PCBs and make a donation for Haiti too. It seems the COD is often overlooked, but I actually think it has potential to sound better than the opus and I already have some wolfston dacs, I like the sound, but enjoy the BB chip more. the opus could be used with the volumite so I considered this early on, but since I already have a D10 the main benefit would be balanced output and the ability to fit my discrete buffers, more current for better sound than the D10 as well as the 'I made it myself' upsampler. i'm set on the COD though

thanks again Applause

Edited by user Wednesday, January 20, 2010 10:42:50 PM(UTC)  | Reason: Not specified

qusp  
#4 Posted : Wednesday, January 20, 2010 10:46:16 PM(UTC)
qusp

Rank: Member

Groups: Member
Joined: 7/22/2009(UTC)
Posts: 11
Location: Brisbane

or I could just wait for the new burffalo, since it wont have the integrated I/V stage its probably able to run off 5-7v :D or get a second acko sbre, nah the COD, i'll tackle a portable sabre another day :D
glt  
#5 Posted : Thursday, January 21, 2010 1:03:19 AM(UTC)
glt

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Digital volume in a DAC works by taking away least significant bits, but since internally they work at 24bit resolution, 16 bit material will not be affected until you throw away 8 bits (which is like -48 db). So you loose resolution. The external microprocessor writes values into the DAC registers, so it is outside of the data path. If you suspect noise from the uP, you can isolate the control lines with an adum chip.
qusp  
#6 Posted : Thursday, January 21, 2010 8:27:51 AM(UTC)
qusp

Rank: Member

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Joined: 7/22/2009(UTC)
Posts: 11
Location: Brisbane

thanks again, hmm well unless I can find a higher resolution controller thats not so much of an option its perfectly usable for the portable use (which would be the main use) but since I would also occasionally like to use it downstairs in the workshop with high res content (my own stuff produced in logic at 24/96 and some 24/192) I would need more than 24 bits or downsample anything I wanted to use with it with a playlist or something. ok food for thought. cheers i'm gonna build them up anyway, but will have to think on volume control and output some more Brick wall its not gonna be something that happens overnight anyway with my workload, so some reading is in order. I may just have to live with a pot

Edited by user Thursday, January 21, 2010 8:29:41 AM(UTC)  | Reason: Not specified

Brian Donegan  
#7 Posted : Thursday, January 21, 2010 8:30:56 AM(UTC)
Brian Donegan

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Quote:
Digital volume in a DAC works by taking away least significant bits


This is not a very accurate description. It actually works by gently lowering the binary value, not just chopping off bits.
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