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Old 7th July 2011, 05:20 AM   #591
opc is offline opc  Canada
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Hi sek,

That's essentially just an active balanced preamp stage added onto the existing BAL-BAL circuit isn't it?

A big bonus of "The Wire" as a concept is that it's scaled down to the most basic level of simplicity, and does only what it's supposed to do very very well as a result.

I personally use the output of a Buffalo II DAC to drive the discrete I/V stage I designed a while back, and feed that directly into "The Wire". In that setup there is no need for a volume control since the one implemented in the digital domain on the Buffalo is more of less perfect and requires nothing at all in the signal path.

What you have there would require me to add an extra gain stage and 12 components into the mix. Even if you didn't have the luxury of the volume control on the DAC, wouldn't you rather just use a good stepped attenuator with 0.1% resistors? That's only two parts in the signal chain, and no active devices at all.

Don't get me wrong... I do like the idea you've come up with, and it looks like it works perfectly, it's just not really a good fit with what I'm trying to do here.

Overall, there's no substitute for simplicity. If you want a volume control that matches well with "The Wire", then either get yourself a Buffalo II DAC, or a good quality balanced stepped attenuator! You can build a decent stepped attenuator yourself for less than $100, and you'll have it for the rest of your life. Trust me... it's money and time well spent.

Cheers,
Owen
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Old 7th July 2011, 09:57 AM   #592
sek is offline sek  Germany
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Hi Owen,

Quote:
Originally Posted by opc View Post
That's essentially just an active balanced preamp stage added onto the existing BAL-BAL circuit isn't it?
The output stage resembles that of the BAL-BAL circuit (although I prefer the BUF634 over the LME49600) and is basically a mixture of fig.2, p.3 as well as fig.22, p.14 in TI's Differential Op-Amp Circuit Collection and fig.4, p.7 in the INA163 datasheet (which in turn is basically your BAL-SE).

But as both gain and interstage impedances change, the calculation is entirely different from the BAL-BAL: adjustable input stage gain (to account for headphone sensitivity), varying attenuator impedance (in case of a pot), output stage with gain (to make up for attenuator loss).

I've refrained from using the TPA6210A2/THS6012 and changed focus to the BUF634/LME49600 after reading up on issues with the former in the FiiO E9 and QRV09 into low impedance headphones. My current feature set is represented by Violectric's HPA-V181. I'd like to improve on that one by going all balanced throughout.

Quote:
I personally use the output of a Buffalo II DAC to drive the discrete I/V stage I designed a while back, and feed that directly into "The Wire". In that setup there is no need for a volume control
I understand you went all digital, as far as source material is concerned. But even when doing so, others might use different I/V and filter stages.

Let's not forget that the BAL-BAL circuit has the OPA1632 directly on the input (unlike your BAL-SE, where you also employ an instrumentation amplifier). For people using a different setup, would it sound and behave the same on high impedance sources as well as low impedance sources?

Quote:
What you have there would require me to add an extra gain stage and 12 components into the mix.
How come?

It's basically like merging SE-BAL with BAL-BAL. Plus an attenuator (which is the whole culprit). Assuming it works this way, of course (still not fully tested).

If you account for power supply bypassing, there's of course some increase in parts count, but I assume you were referring to signal circuitry.

Quote:
Even if you didn't have the luxury of the volume control on the DAC, wouldn't you rather just use a good stepped attenuator with 0.1% resistors? That's only two parts in the signal chain, and no active devices at all.
A differential buffer consisting of something like OPA1612/OPA2211/LME49990 in a gain-of-one configuration doesn't bother me, especially if it solves problems. Add to that the proper use of high precision resistor networks (+/-0.05% tolerance, +/-7.5ppm drift) in a tight, good PCB layout and the amount of error introduced quickly becomes a matter of belief.

And to answer your question: no, I rather wouldn't like to use two balanced attenuators (stereo) if I can substitute it with one unbalanced stereo attenuator and a high quality buffer stage.

Quote:
Don't get me wrong... I do like the idea you've come up with, and it looks like it works perfectly, it's just not really a good fit with what I'm trying to do here.
Totally. That's why this project of yours should be carried on the way you like. I was basically just wondering why volume control wasn't taken into consideration at all, seeing that a couple of people asked for it. But as it's a dedicated stage in an existing setup (and not a headphone amplifier, as the thread title would suggest), then there's no reason to compromise on your simplistic approach.

Quote:
Overall, there's no substitute for simplicity.
Don't get me started on the "there's always a simple solution" discussion.

Otherwise we would have to discuss why the balanced stepped attenuator you propose shouldn't be replaced with, say, an MPC507...

Quote:
If you want a volume control that matches well with "The Wire", then either get yourself a Buffalo II DAC, or a good quality balanced stepped attenuator!
The Sabre DACs (and what Brian and Russ do with them in the Buffalo II and soon to be released Buffalo III) is certainly a kind of a milestone. But not everyone solely listens to digital content.
Which leaves us with the balanced stepped attenuator. Well, my idea is to reduce the requirement from a balanced to an unbalanced attenuator (stepped or pot, if possible) while still preserving all the benefits.

But I'm getting carried away.

Cheers,
Sebastian.

Last edited by sek; 7th July 2011 at 10:04 AM.
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Old 10th July 2011, 07:09 PM   #593
enantra is offline enantra  Spain
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HI Owen i need

1BAL-BAL and 1SE-SE kit, (2 kit) WITH updated PSU
thanks
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Old 15th July 2011, 09:32 AM   #594
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Is it only me or other experience the same?

I could not properly open Owen's "THE WIRE - THREE BOARD - 4.pdf" file.

The text is always missing, with the message that Verdana font is not available, which is not true since my PC has Verdana installed.
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Old 15th July 2011, 10:39 AM   #595
JBdV is offline JBdV  Netherlands
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where is that file located ?
(I may need to update my desired quantity as well)
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Old 15th July 2011, 11:14 AM   #596
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Quote:
Originally Posted by JBdV View Post
where is that file located ?
(I may need to update my desired quantity as well)
http://www.diyaudio.com/forums/headp...ml#post2613496
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Old 15th July 2011, 01:04 PM   #597
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Quote:
Originally Posted by dw1narso View Post
Is it only me or other experience the same?

I could not properly open Owen's "THE WIRE - THREE BOARD - 4.pdf" file.

The text is always missing, with the message that Verdana font is not available, which is not true since my PC has Verdana installed.
Try to update or re-install your Acrobat Reader app
I've tried right now and it's Ok.
Cheers
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Old 18th July 2011, 11:09 AM   #598
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Any updates on the amp Owen?
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Old 18th July 2011, 09:16 PM   #599
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Default Any more kits available?

Any more kits available?
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Old 19th July 2011, 10:56 AM   #600
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Quote:
Originally Posted by korben69 View Post
Try to update or re-install your Acrobat Reader app
I've tried right now and it's Ok.
Cheers
I see... thanks...
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