CS4397 DAC - Output Stage layout. Advice sought and comments welcome
Oct 12, 2008 at 12:03 PM Post #16 of 31

fordgtlover

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Well here is what I have ended up with. How does this look? It is now 80mm x 50mm.
os30tj6.jpg


On a side note, I only want to get a few of these boards made, but the best value offer I can find on PCB manufacturing give me 650CM sq for $99. Even if I get 5 of these boards made I am still well short of the available space.

I was thinking that since I need a dual 12V PS for this board anyway, perhaps I could get some made at the same time. Adding an extra design costs $30 to the order.

Does anyone have an eagle layout for a relatively small, decent quality dual PS that I could add to this order. In return, I'd happily provide you with a couple of boards. Preferably, the layout should be tried and tested.

I would also probably ask for some assistance to panelize the layout if there are any takers.

Any thoughts on either the board above or the PS idea?

Please note that I would be looking to sell some of these boards to other DIYers to recoup some of the costs.

Regards
 
Oct 12, 2008 at 9:27 PM Post #17 of 31

error401

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You might look at PCBCart for fab, they're a bit cheaper than Gold Phoenix for small runs. BatchPCB is good too, but for larger boards it gets a bit pricey. Still cheaper to run off a couple boards from them than a dozen you can't use at gold phoenix.

If you're okay with surface mount, I did this power supply design. I don't use Eagle, but the gerbers are there for you.
 
Oct 20, 2008 at 11:48 AM Post #21 of 31

Ciu

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Hello !

That's what I 've done :
http://img206.imageshack.us/img206/3...cfecc86rt8.png
I redrawn an original schematic published by JR Broskie in Tubecad.com
This is a buffer with no gain, and filtered input, with low voltage tube ECC86/6GM8
The B+ is 24v, simple LM317, with a slow turn-on , about 30s
The heater,6.3v, 600mA, is also a simple lm317, with a slow turn-on , about 10s
Works perfectly for a symetrical voltage DAC...
R.C.
 
Oct 20, 2008 at 2:07 PM Post #22 of 31

mwofsi

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Hello fordgtlover, hadn't read this thread before, and I too have become interested in the noodle/lampucera dac. Also, I know nothing (and what little I learn I forget).

In the circuit diagram in your first post you have Q2 as a darlington? This isn't the case in Leo's diagram in the first post link. I seem to recall reading on some forum that packedged darlingtons weren't favorable for audio, and that a two transistor solution might be better. Also if it's just a stand-in, wouldn't it be handy if you could give yourself alternate solderpads to use a TO220 package? That way you'd have more choice in output transistors?

EDIT: Also the inclusion of C2/C9/C10 is a bit strange in this setup. It's there I believe because of the DC offset introduced by Q2's vbe(?) drop, unless Leo meant it as one of his original output caps.Clearly it will have a direct effect on sound quality. An external cap, assuming you need one might be more handy. Perhaps an opamp offset servo would remove the need for an output cap altogether? EDIT:
frown.gif
(got myself confused about the offset servo and can't see how to make it work)

(The last time I tried to create something like this in Tina it went all wrong and PRR told me I needed to learn more!)
 
Oct 21, 2008 at 9:56 AM Post #23 of 31

majkel

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Guys, has anybody compared signal coming out of this discrete buffer to the direct coupling of L/R+ DAC outputs (caps required to cut off DC)? I'm just curious if this is really an advantage, as you divide the complementary outputs by two to amplify it later. The current efficiency of the output is depending on the transistor chosen, and I expect there the BC550 or something like that, while the DAC might be loaded down to 1k with no harm to the specs.
 
Oct 21, 2008 at 11:32 AM Post #24 of 31

mwofsi

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Quote:

Guys, has anybody compared signal coming out of this discrete buffer to the direct coupling of L/R+ DAC outputs


Interesting point majkel. Wouldn't that require a balanced amp and headphones? If the join was before that wouldn't the dacs outputs be shorted? One could of course take the signal from just one side of the dacs balanced outs and amplify that.
 
Oct 21, 2008 at 11:44 AM Post #25 of 31

majkel

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Quote:

Originally Posted by mwofsi /img/forum/go_quote.gif
Wouldn't that require a balanced amp and headphones?


No, for unbalanced you need to connect the analog ground to your amp's and the + analog output of the DAC coupled via the capacitor to the amp's input. For balanced you use both + and - outputs, in some cases even without capacitors (if common mode voltage of 2.5V doesn't matter).
 
Oct 21, 2008 at 11:47 AM Post #27 of 31

mwofsi

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Quote:

Originally Posted by majkel /img/forum/go_quote.gif
No, for unbalanced you need to connect the analog ground to your amp's and the + analog output of the DAC coupled via the capacitor to the amp's input. For balanced you use both + and - outputs, in some cases even without capacitors (if common mode voltage of 2.5V doesn't matter).


majkel, we seem to be saying the same thing!
 
Oct 22, 2008 at 10:03 AM Post #28 of 31

00940

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Quote:

Originally Posted by majkel /img/forum/go_quote.gif
No, for unbalanced you need to connect the analog ground to your amp's and the + analog output of the DAC coupled via the capacitor to the amp's input. For balanced you use both + and - outputs, in some cases even without capacitors (if common mode voltage of 2.5V doesn't matter).


You can do that... but then the advantages of the balanced out DAC are lost.

If you insist on direct coupling, you could configure your amp as balanced to unbalanced converter. This works only if your amp has inverting and non inverting inputs.
 
Oct 22, 2008 at 10:35 AM Post #29 of 31

majkel

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Quote:

Originally Posted by 00940 /img/forum/go_quote.gif
You can do that... but then the advantages of the balanced out DAC are lost.

If you insist on direct coupling, you could configure your amp as balanced to unbalanced converter. This works only if your amp has inverting and non inverting inputs.



I completely agree with you but it's not the matter I posted my thoughts. I'm just trying to understand the purpose of building the circuit dscussed in this thread. I could imagine why people build tube buffers (SRPP, cathode or anode follower) and want to know what I'll get building a BJT circuit.
 
Oct 22, 2008 at 10:43 AM Post #30 of 31

00940

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The low pass filter is isolated from possible variations in the following stage, to start with.

Btw: I would add a 600R resistor in serie at the output, to protect it from shorts.
 

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