Upgrading the Tentlabs DAC (split from- Anyone use this clock upgrade?)

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Joseph K

Member
Joined 2004
Pinkmouse, moderators,

Excuse me very much! It was really a cruel intrusion!
And thanks for the efforts of the cleanup & opening this thread.
Though may I ask one more favore? So as not to be misleading, instead of the Xo2 could you put the TubeDac?

Otherways shame on me.
Thanks,
George
 
G

Guido Tent

Member
Joined 2001
TentLabs.com
pinkmouse said:
Make your mind up guys! :) [/QUOTE

The initial thread started based on a new clock module. Following the discussion a request was made for jitter measured results. Then, as example, I posted a measured result of my XO2.

Secondary effect was discussing powersupplies, thirdly the performance of PLL opamps and VCXO supplies

Whatever splitoff is proposed, XO2 isn't the right subject. Our DAC design as linked by me is also known as Heijligers DAC or sometimes known as tubeDAC.

best
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C

carlosfm

Banned
Joined 2003
Joseph K said:
Carlos, welcome!

I hate it, but I have to point out that I was looking for cmos opamps..
With low input bias & offset currents and unity gain stability.
This BB one, though is not applicable in the special application discussed here, is a "meraviglia' in itself. A new arrival in that wonderful family of stratosferic amplifiers, which started with comlinear.
Click to expand...

Sorry if I was not clear, George.
I didn't mean to say the OPA847 is good for your application.
My post was only an example at how things evoluted, as you pointed out too.
Voltage noise is very low, but other parameters are not as good as you need.
 
C

carlosfm

Banned
Joined 2003
Joseph K said:
Carlos,

by the way, as I have it at hand, I just can't stand & not show this pic about the way how these things should be applied:

[This is what I would call good low impedance power supply decoupling, up into the hundreds MHz region, ai it is absolutely necessary with such a chip]

Ciao, George
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Yes, George, the bypasses ON the chip's PSU pins.
Not always you see things done that way on commercial gear, isn't it?
That circuit looks good.

Btw have you ever opened an Arcam CD7 SE? :bawling:
 
J

Joseph K

Member
Joined 2004
Carlos,

It's Ok. By the way, that AD8009 worths it's money, too. And I like that realization, too. [this is why I have shown] A talented russian group has done it. It should pass a mV range pulse with ~7nsec FWHM, without ringing, so as the following discriminator would trigger on the real edges only..

Else. As you see, not only You, but me too, being an old client of Guido.. :)

Now, I would like to explain why I had been thinking of such a thread.
First of all, hat's off to Guido and clan for this project. Then, I've been always following with great interest the wonderful job of Algar_emi; Pedro; ALP & others developed in those other threads.
Actually, it would be nice to hear their present opinions / experiences on this Dac. Then, as I have seen, almost all of them had started some kind of modifications - it could be interesting to collect some results.

So, as I had already mentioned, I would have some questions on my mind. Some of them are upgrades, that is, trying to apply new ideas of the old authors.. ;) The others are problems that I have encountered, maybe only me, maybe also the others.

One of the most burning one is that maledetto U4. I have followed faithfully the assembly directives, and had put that AC74 in there.
I understand that for shynronicity the chip should be fast, but still..
It was causing soo much noise.. The unit worked, sounded well, even, very well, but still, ideologically I was just not relaxed.
Here I have to notice, that I was making local EMI test's, sniffing around with a little jig in the circuit, and the amongst the most noisy points was exactly this chip & neighbourhood.
After some hesitations, I have put in there an F74. The noise is decreased by some orders.. not joking. The sound? Now, it's a problem. I have made the big error of applying too much things at a strike, and now I can't really tell. I did not change back, it works, and sounds well also now, though different.
So my question to Guido: did You consider to exchange this part?
Any technical problems with my choice? I know, the more appropriate part here would be a VHC74, in fact, it's under order..

Ciao, George
 
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