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Old 18th December 2010, 07:59 PM   #21
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Quote:
Originally Posted by opc View Post
Hi Guys:

A group buy for the LME parts would indeed be wise. Digikey has the worst pricing for these parts, and they can be had for half as much at other sites.

Either way, I've got 25 boards and that's 150 LME49990 and 50 LME49600.

For 100pcs of LME49990 you've got:

Avnet = 2.57 each
Newark = 3.00 each
Digikey = 4.15 each
Arrow = 2.95 each
Future = 3.12 each

Digikey's single part price is $5.70.

For 50pcs of LME49600 you've got:

Newark = 6.98 each
Digikey = 9.47 each
Arrow = 6.53 each
Future = 6.90 each

Digikey's single part price is $11.56.

I would consider doing a group buy kit for the boards and parts, but I'm not prepared to do it at cost. I just got through that process with 40 DAC boards, and it took easily 50 hours of my time and I ended up more than $200 in the hole.

If there's enough interest though, I'll look into it. The price would end up being less than buying all the parts on your own, but it wouldn't be at cost.

Cheers,
Owen
Hello,

GB := yes I am in
Cost plus := yes i am in

Let us know
DT
All just for fun!
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Old 18th December 2010, 11:07 PM   #22
johnm is offline johnm  United Kingdom
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Originally Posted by qusp View Post
john?? there is no john here but you
Haha yes not quite sure what I did there - I meant Owen. I mean.... Owen sounds like John.... erm.... after a few Christmas drinks it does at any rate



At any rate, if a group buy goes ahead I'm definitely down for a amp/PSU board. Using a Little Dot III for a pair of Audio Technica ATH-AD700s but feel I'm missing out on a punchier sound, particularly in the bass.

Cheers,

- John
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Old 19th December 2010, 06:51 AM   #23
qusp is offline qusp  Australia
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oh absolutely, I see what you did there...

what are you using for source? you do realize you really kinda need balanced input and you'll have to look after source, because this thing is gonna be pretty transparent. or is it the LD dac and has HP out? sorry i've seen the LD gear at meets and such, but to be honest i've never paid much attention, only thing I remember is that they run insanely hot, as in heating the room hot

Last edited by qusp; 19th December 2010 at 06:57 AM.
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Old 19th December 2010, 11:10 AM   #24
Bonsai is offline Bonsai  Taiwan
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I am also using s similar set-up to OPC on me new pre-amp (look at 'Line Pre-amps' on my web page - right at the bottom are some pics). I am using an LM4562 driving an LME49600 buffer inside the feedback loop and confirm the awsome sound on this combo. There's no doubt that h/phones sound very much better when driven from a very low source impedance. I have quite a bit of experience with op-amps, and have built a few pre-amps and power amps, my first about 25 years ago. The Natsemi signal chain is really good - ultra smooth with great highs. My pre-amp (including the h/phone stage) is fully DC coupled. I am using a TI PGA2320 for th evolume control function. Despite what the detractors say, if you follow a few simple rules, also a very fine sounding device.

Very nice looking/phone amp btw way opc!
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Old 19th December 2010, 01:31 PM   #25
Jen-B is offline Jen-B  United Kingdom
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opc,

This looks like a lovely neat project. I hope it is OK to ask a couple of questions...

Is the output short-circuit proof against momentary shorts?
Is there any measured DC offset at the output?
If I wanted to change the gain to x2 which resistor do I change?

Thank you,
J.
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Old 19th December 2010, 03:14 PM   #26
qusp is offline qusp  Australia
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yeah sorry but you wont catch me running anything with a PGA chip in it, especially considering my set up is similar to OPC in that my headphone amps hang directly off, or ARE the IV stage of a high end dac. I think adding another process in the form of the PGA and limiting the entire chain to this quality (no matter how good) kinda undoes all the good work done before and you are listening to your volume control.

just one opinion

other than that I have seen your projects and think they are very well done and the above is just a matter of taste. the sabre the dac this is designed to tack onto has its own volume control so is not needed.

speaking of that Owen, do you use the volumite?

Last edited by qusp; 19th December 2010 at 03:30 PM.
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Old 19th December 2010, 03:52 PM   #27
opc is offline opc  Canada
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Hi Guys,

Thanks for the positive comments! I'm still taking a look around to see what pricing can be had on these parts, and then I'll figure out a total cost that will probably include the boards, the IC's, and all the SMD C's and R's and flat rate shipping.

I should have this done by the end of the day.

qusp:

As I mentioned above, if I do a kit, it will probably be for the IC's, the SMD caps, and the SMD resistors. All the other parts would be left to the individual since people have different tastes and preferences.

I will be sending you two boards, but I have yet to make the trip to the post office. I'll try to get you a BOM as well, so you can work the parts into your order if you want to get a head start.

Johnm:

I've got two more days of work to go, then I'll be joining you in a druken Christmas stupor. On that note, I completely understand.

I'll start up a list and add your name. I'll let you know when I nail down pricing.

DualTriode:

Thanks for the early interest! As with John, I'll add your name to the list and let you know when I sort out the details.

Bonsai:

I definitely agree with you that the low output impedance has a huge impact on LF performance. I've seen headphone amps with upwards of 100 ohms of output impedance! Between the DC coupling and the low output impedance, you really do get great performance in the bottom few octaves. Better than I've ever heard with any other setup.

You should try out the LME49990 for fun. They're my new favorite op-amps! Extremely well behaved, and they sounds superb. I never thought I'd let go of the AD797 as a favorite, but I do think the 49990 is a better part.

Jen-B:

Questions are always welcome, especially when they're good ones!

1. Yes, the output is fully short circuit limited. The LME49600 starts to current limit at around 350-400mA. You can see in the 4 ohm distortion plot that the current limiting starts to kick in at a little over 1VRMS output.

There's more about this in the datasheet for the LME49600.

2. Very good question, and one I completely forgot to mention in the original post. The DC offset is less than 1mV at the output with the input floating, or connected to ground. I was initially worried about this since the reference board for the LME49600 has a full servo to minimize DC, but to my surprise, the DC offset was actually lower on the reference board with the servo removed from the circuit. Of course, if you have DC from the previous stage, the servo would help to null it out, but I'm assuming nobody here would be foolish enough to feed a DC coupled circuit from something with a DC offset. Obviously it will make it through with a gain of 1.

3. For a gain of two, you'll want to change R3, R6, R9 and R12 to 2k. Using 0.1% resistors in this circuit is critical to get good CMRR and low DC offset. The better the matching of these parts, the better the performance.


Here is an informal list of those who have shown interest in a board. Once I post pricing and kit info, I will ask that everyone confirm their interest, and then I'll start a formal list.

? Nikon1975
? Frex
1-2 dggs
1 DualTriode
1 Johnm

Cheers,
Owen
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Old 19th December 2010, 04:52 PM   #28
pidesd is offline pidesd  Canada
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Quote:
Originally Posted by opc View Post

The circuit provides differential input, or the option to ground one phase and drive the circuit with an SE input.
how well do you expect the the single end input setup to perform? have you done any measurements, by any chance?
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Old 19th December 2010, 04:57 PM   #29
L-Train is offline L-Train  Canada
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Hi Owen,

I'm also interested in 2 amp PCBs.
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Old 19th December 2010, 05:36 PM   #30
Jen-B is offline Jen-B  United Kingdom
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Thanks for the quick answer opc. I'll take a closer look at these chips over the Xmas break. Good luck with it.
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