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Old 19th December 2007, 04:24 AM   #2011
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Quote:
Originally posted by mikelm
How long do we think it will be to reach full potential ?
Based on a customer feedback, it seems like the break in point is achieved after a month or so.

You can furhter adjust the highs by installing Caddocks TF020 in place of Rikens and switching to different coupling caps.

In order to use small value V-Caps (0.1uF or so, to save on cost) a simple Borbery buffer can be installed at the output with very good results (fig 15C): http://www.borbelyaudio.com/adobe/ae699bor.pdf
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Old 19th December 2007, 04:56 AM   #2012
okapi is offline okapi  United States
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Default buffer

Hi peter,

are you recommending the borbely buffer over the one you offer?
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Old 19th December 2007, 06:03 AM   #2013
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I don't, as I never tried Borberly buffer myself.

A forum member, whose judgement I trust, compared both buffers and preferred Borberly. However, he used all Vishays for Borberly and IIRC ALW regulators.
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Old 19th December 2007, 01:43 PM   #2014
Bobken is offline Bobken  United Kingdom
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Hi,

I am sure Peter is referring to me here, but I must say that his buffer is excellent sonically, and it outperformed a commercial (Burson) buffer which I compared it with.

However, in the pursuit of perfection I did try other designs and the best I have come up with so far is based on the quite simple Borbely circuit mentioned.

This was constructed with the finest components available anywhere, like 2SK389 dual J-Fets, all Vishay bulk-foils & non-polar BGs etc., and complex discrete regs (actually of my own design, not ALW's).

This was a 'cost no object' exercise, and the advantage of this J-Fet circuit is that there are so few parts needed (apart from PS) so it it is not quite so frightening in parts costs as some more-complex alternatives.

In some respects it is preferable to my ears than Peter's Buffer, but if the same quality of parts were to be used for Peter's buffer circuit as I used in the J-Fet version, I wouldn't like to predict the outcome.
At this level of perfection, VHQ parts do make a worthwhile difference, but at a collossal additional cost of course, and it is possible that Peter's Buffer might equal (or even exceed) the J-Fet buffer's performance if the same parts were used throughout.

In my opinion, you will find it very hard to better Peter's design without spending considerably more than he charges for his kits, and there is (almost) always scope for improvements with any circuit if you are prepared to throw unlimited funds at the project.

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Old 19th December 2007, 02:28 PM   #2015
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Default DAC output impedance

Peter,

I read a thread somewhere that your DAC has output impedance of around 3K ohm.

How actually do you calculate to get this value?

Thanks,

Joshua
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Old 19th December 2007, 02:40 PM   #2016
Bobken is offline Bobken  United Kingdom
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To save Peter the trouble, as I was looking at this thread anyway, it is based on the output (shunt) resistors to ground.

In Peter's design these are R8 & R9, which I believe are usually 2k7.
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Old 19th December 2007, 03:04 PM   #2017
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Quote:
Originally posted by Bobken
To save Peter the trouble, as I was looking at this thread anyway, it is based on the output (shunt) resistors to ground.

In Peter's design these are R8 & R9, which I believe are usually 2k7.
Ok, that's most likely the answer...

Thanks,

Joshua
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Old 19th December 2007, 03:27 PM   #2018
Bobken is offline Bobken  United Kingdom
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Hi Joshua,

With the greatest respect, it *is* the answer, or at least it is these resistors which determine the output impedance in this particular circuit.

No doubt Peter will confirm the values of resistors he uses here, but in the circuit which I am aware of he uses 2k7 for R8 & R9., and therefore the output impedance will be (approx) 2k7, allowing for any component variations.

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Old 19th December 2007, 03:59 PM   #2019
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Quote:
Originally posted by Bobken
Hi Joshua,

With the greatest respect, it *is* the answer, or at least it is these resistors which determine the output impedance in this particular circuit.

No doubt Peter will confirm the values of resistors he uses here, but in the circuit which I am aware of he uses 2k7 for R8 & R9., and therefore the output impedance will be (approx) 2k7, allowing for any component variations.

Regards,
Hi Bob,

I'm not arguing, I'm just trying to understand what output impedance is in that DAC.

As we are talking about amp, in my understanding the output impedance (in series with the output) will determine the regulation of that amp.
The higher the output impedance, the less output voltage under the load.

As for the DAC (output I/V), I don't know much...

And yes, I looked to the schematic before post this thread and notice 2K7 ohm at the output for both left and right channel.
Just want to fulfill my curiosity and learn something...

Joshua,
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Old 19th December 2007, 04:07 PM   #2020
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Thanks Bob for clearing that up.

The DAC output section of my DAC is very similar to 47Labs DAC, which was measured by Stereophile: http://stereophile.com/digitalproces...00/index5.html
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