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PCM2702 USB DAC Revision B - Page 9

post #121 of 670
10/18/05 at 5:36pm
Quote:
Originally Posted by .: ZMN :.
Just a question on the USB.
Is the design prepared for soldering just the wires of a USB cable to the PCB instead of using a USB B-type plug?
well when I built the USB dac revision A by guzzler I did this. There is no difference at all, but you must be very careful connecting each wire to the correct place. You shouldalso take in consideration some kind of tension relief. I used a gromet in the hole and then glued the cable on the inside to the gromet with hot glue. This way, even if you hold the enclosure by the cable there isn't much tension in the solder joints. I plan to do this as well when I build this new board. You get a much cleaner look and remove a plug/jack from the signal path.

Manuel

ps: I hope it wasn't confusing...
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post #122 of 670
10/18/05 at 5:49pm
I made a mistake sourcing the parts; the plug IS easily available.

Thanks for the advice (I will use to the plug).


/EDIT: Manuel, I was just looking at the Rev A thread. My guess is that portability should be better without the permanent wire, but I'll keep it in mind.
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post #123 of 670
10/18/05 at 6:40pm
Quote:
Originally Posted by .: ZMN :.
I made a mistake sourcing the parts; the plug IS easily available.

Thanks for the advice (I will use to the plug).


/EDIT: Manuel, I was just looking at the Rev A thread. My guess is that portability should be better without the permanent wire, but I'll keep it in mind.

I have cut the wire so that there is only about 5 inches from the enclosure, I couldn't find a USB cable which is 6 inches long!!!!
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post #124 of 670
10/18/05 at 6:45pm
Thread Starter 
Quote:
Originally Posted by MASantos
Alf can the dac be powered by a tread? This way the board gets cleaner power? should there be any audible diference?

Yes, it can be powered by a TREAD. Whether there will be any audible difference, it depends on the quality of your computer power supply. Also consider that the new board benefits from an additional LM317-based circuit which is essentially the same as TREAD. In theory all the changes we have made should make that difference minimal and hopefully inaudible.
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post #125 of 670
10/18/05 at 6:55pm
Quote:
Originally Posted by Alf
Yes, it can be powered by a TREAD. Whether there will be any audible difference, it depends on the quality of your computer power supply. Also consider that the new board benefits from an additional LM317-based circuit which is essentially the same as TREAD. In theory all the changes we have made should make that difference minimal and hopefully inaudible.

I see, already forgot about that!

Just one question, we can use the USB dac board with the new SMD mint which is being developed by cetoole? I think that both boards would fit the smallest hammond. Do you think I should go with tangents mint board?

I am really looking forward to this project!!
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post #126 of 670
10/18/05 at 7:00pm
Quote:
Originally Posted by MASantos
I see, already forgot about that!

Just one question, we can use the USB dac board with the new SMD mint which is being developed by cetoole? I think that both boards would fit the smallest hammond. Do you think I should go with tangents mint board?

I am really looking forward to this project!!
I think that was the intended plan with the new layout for the Mint, i.e., both USB DAC board and the modified Mint will tightly fit into the Hammond 1455C802 case.
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post #127 of 670
10/18/05 at 7:51pm
Thread Starter 
Quote:
Originally Posted by MASantos
Just one question, we can use the USB dac board with the new SMD mint which is being developed by cetoole? I think that both boards would fit the smallest hammond.
It should not be a problem. However if you plan to power both the DAC and the MINT from USB, then you need to take care of the MINT's virtual ground first.

Quote:
Originally Posted by MASantos
Do you think I should go with tangents mint board?
I suggest you go for a bigger Hammond and use a PIMETA board instead.
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post #128 of 670
10/19/05 at 4:14pm
[QUOTE=Alf]It should not be a problem. However if you plan to power both the DAC and the MINT from USB, then you need to take care of the MINT's virtual ground first.[QUOTE=Alf]

Isn't it the same thing as powering the pimeta from USB? From what I understood from the schematics both could be powered by the dac via the buf634. Is this correct?
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post #129 of 670
10/19/05 at 6:25pm
Quote:
Originally Posted by Alf
I suggest you go for a bigger Hammond and use a PIMETA board instead.
I hope it will fit in nicely then...
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post #130 of 670
10/19/05 at 6:31pm

dac plus amp

First of all I apologise for all the posts about powering an amp through the dac, which isn't the threads purpose. I have read the entire thread now and still don't understand one thing:

Can we use the usb to power an amp such as a mint (or pimeta)?

Does this current board layout allow this?

do we have to make any changes in any of the designs?

Where in the board do we connect the wire which will take the power to the amp?

I am sorry for this but I haven't figured it out yet!!

manuel
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post #131 of 670
10/20/05 at 4:44pm
Quote:
Originally Posted by Alf
Manuel,

I'll bite on my view of the power supply.

The BUF634 has been added by Alf so that the DAC can be powered from a MINT/PIMETA (the other way round from what you want). Look at the first post from Alf at the start of the thread and you see it in his notes. Looking at the schematic above, it's used as a result of the +ve, -ve & gnd rails of the amp.

So onto the question of using the USB to supply an amp. Lets look at the schematic.
- USB is 5Vdc max 500mA.
- The TPS6734 is a DC-DC converter that outputs 12V @ ~150mA max. How quiet is this supply as it uses a 170kHz current mode PWM controller? Look at the datasheet and there should be something. I'm lazy.
- There is a 12V pad but you have to think about noise and the amount of current available.
- after the LM317A its going to be cleaner at the 9V pad. Still no magic extra current here and we have to think about what the DAC needs.

Now you need to think about:
What sort of amp are you thinking of using?
Will it have a single voltage rail or dual +ve & -ve rails? How are you going to isolate the signal output gnd if you split the supply for dual rails?
How much current are you going to need?

Personally I like the way the DAC design is going under Alf's direction and can not really see any need to modify the supply circuit.

Botch...
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post #132 of 670
10/20/05 at 5:31pm
Another few cents on the headamp+dac idea...

I've tried/seen a few diy-ish usb-powered dac+amp solutions, and in most cases the amp does not have sufficient current so it distorts heavily or the amp drawing too much power shuts down the dac and causes it to malfunction.

The only acceptable combination I've come across is the Edirol UA-25 which apparently has a highly optimized and clean power supply unit that utilizes the full 500mA of USB power and has a very very efficient and optimized headphone amplification section. While I like the headphone amp section on the UA-25 (it's not high-end but it's frankly quite good) in order to get pimeta-quality traditional analog headphone amp then a separate power source should be considered.

Someone here has suggested before to use two more more USB ports to pool in the power and raise current capabilities. I can't remember if there was ever a solution to that but if one builds a small USB power supply unit that can be paralleled, then maybe with using two USB ports on a laptop a decent headamp + dac solution can be created.

Any ideas? Sorry, I'm not an EE so I really don't know all that much but hopefully what I've scrapped over the past few months can help.
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post #133 of 670
10/22/05 at 9:29am
I thought I could post that here since it's of direct interest :

ASIO4ALL version 2.6 didn't work with the PCM2702 on my laptop. Version 1.8 works perfectly though.
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post #134 of 670
10/22/05 at 12:14pm
Quote:
Originally Posted by doobooloo
the full 500mA of USB power
The 500mA limit of the usb port isnt really something you have to stick that close to, there is no current limiting on it and the only limits you have that are of any effect are the psu at the computer end and the interconnects on the way to the device under power

MWP posted up on these forums a usb dac and headphone amp in one circuit that ran entirely off usb power and drew over 600mA from memory and he said it ran fine off his laptop. I've also read a app note/newsletter thing from Maxim who said they have had no problems drawing upto 2A off a range of PC's even, not that I'm suggesing to go that far just that you do have a little headroom in the 500mA spec

I would be designing this to use the curren usb dac that has been done here and after that a tpa6810 headphone driver chip for the amp section and the only problem is finding a switchmode regulator to go from 5V to +/- 5 to 15V that does it cleanly enough, if I had the time I would look into the idea myself
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post #135 of 670
10/22/05 at 6:56pm
Quote:
Originally Posted by 00940
I thought I could post that here since it's of direct interest :

ASIO4ALL version 2.6 didn't work with the PCM2702 on my laptop. Version 1.8 works perfectly though.
Is this the "bit perfect" windows driver that was spoken about in the beginning of the thread?
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