More to focus I spoke with Steve Nugent on the purpose of the post analog output filter consisting of a single resistor and cap per channel.
Bill - it is not a brick-wall, just a 2-pole low-pass.
So by lifting a one leg of the brown mica Chiclet cap we are de-activating this simple filter by removing the ground. The positive sonic results where amazing to me. I am looking for further affirmation from the other players who have a Chameleon DAC on hand. I know Pat chimed in already.
Lift one leg from each of he 2 large brown .01uf Chiclet looking caps on the DAC board, take a listen and tell me what you think.
Mine is off as well. As mentioned, it does open up music stage. You may recall I had swapped out those mica caps with Vishay MKPs and noticed a difference, again I first did it with the DAC having less than 50 hours of burn-in time, I now think that once the DAC is fully baked having the two brown mica caps out is the way to go.
I agree that we have discussed enough about those output caps so let me propose something new: NO CAPS!
Is it possible? Yes, it should be possibe.
How? With a DC servo board!
I had to open my modded Benchmark DAC-1 today because one of the opamps of the balanced output stopped service (DC on the output...)
I opened my Benchmark DAC-1 and there I saw that DC-Servo board from which I totally forgot that it was in there when It got modded. I'm not sure if I can just pull out this DC-Servo board and use it for the Chameleon but I will contact the designer tomorrow, which is a friend of mine, to see if I can give it a try.
Now, I can ensure you that this DC-Servo board is the best en most honest solution possible and not expensive either because you don't have to spend a fortune on exotic caps BUT i'm sure that not everybody like it.
Why not? Because it has absolutely NO colouration. All you will hear is 100% pure TDA1543's (and the influence of the I/V resistor).
Could be the ultimate solution to some, but certainly not all of us...
Wood- yea I agree the filter is there just to make the scope shot look good, but just like on the Valab it does bad things for the ears. With the filter out, the instruments & entire soundstage sounds more like "real" living music. The main reason I now live with NOS Dac's. (This Mod falls in the "must try category").
I've got a question to those who modded their old Valab with better dac coupling Caps, did it lower the noise floor?
Edit: I measured the output of my DC-30W today. The way I measured it was to put negative (black lead) on the ground connection, and the red lead on the pins coming out of the DC-30W. This is what I found:
indeed Rhodes, lay it on!
I was looking for a servo schematic but although I understand the principle I'm afraid I do not understand the mechanics of servo's well enough to distinguish the good from the bad....
Better coupling caps are likely to make you aware of more of the noise floor.....but the source for the problem usually is not in them.
I got an answer from Sebastiaan who designed the DC Servo and unfortunately this is not possible with the Chameleon because of its passive output section. It only works in a opamp circuit...
He explained me how a DC-Servo works:
A DC servo circuits is essentially an integrator opamp circuit that integrates offset voltage changes from the opamp amplifier output and feedback the integrated voltage to the opposite input of the same opamp.
For example, if there is a voltage offset of 2VDC on the output, offset will be fed to the inverted input of the opamp, and the opamp will produce a -2VDC correction-signal which essentially leads to zero VDC on the output.
This means we are still stuck with the output caps except when you have input caps on your amplifier, then it is worth testing without the output caps.
On a serious note this thread is a great introduction to understanding what stacked chip NOS DAC's are all about. Coupling caps digs aside, there really is lots of great information and background on why and how the Chameleon DAC came to be. (Think of it as the 101 coarse).
Armed with this knowledge more concise discussion can pursue on this Chameleon thread.
I got more interesting information from Sebastiaan regarding the Chameleon.
One thing he mentions was the that the 74HCU04 (U204 on the schematic) is not needed and can be removed (it's definitely adding jitter while not needed). The TCXO should be able to drive two chips at the same time easily. He will add the changes to the schematic which I will forward to Teradak.
Another thing he mentions is that it's really important to feed the the two clocks their own +5V. I checked the schematic and this is is do-able: It's just a matter of lifting L201 and L301 and feed them an ultra low noise +5V.
Well of course the best output is no cap at all just like you strive for no electrolytic caps in the signal pathways or Zero negative feedback that is servo controlled in the I/V analog stage but all of this costs money and takes up a lot of chassis space .....you guys have to remember that these machines are built with a specific price point in mind which automatically means corners have to be cut. Trade offs, advantage and disadvantage to circuit choice, parts quality all play into the designers list of constraints/restraints etc...I'm sure this is preaching to the choir, so forgive my intrusion if it's already an implicit part of the head fi DIY crowd's lexicon.
For those of you with unlimited funds I question the wisdom of sinking hundreds and hundreds into a DAC when the better option would be the purchase of a much better base unit to work with. I've always contended or stuck with a DIY philosophy that seems to bear fruit and keeps me from racking up huge expense for little gain by examining the relative worth/cost of the mods vs the relative worth of the gains. Moreover is it wiser to spend 1/2 as much in parts on a much better base unit than to spend 2- 3 X the cost of the lower quality base unit in parts and arrive well short of the formers actual performance curve ? Any sane person (DIY types excluded, I count myself as a little bit crazy when it comes to DIY modding) will read this thread and come to the conclusion that these mods can take such a unit as far as your wallet can dole out the money, when in reality you quickly run into the immovable brick wall of the core design itself . The hard part is finding out or knowing where that point lies. Enter this thread much to the credit of dedicated DIY types therein I might add In conclusion there is always a point at which the topology and parts that are holding the unit back end up being the heart of the base unit to begin with. The trick is how does one recognize that mile marker on the upgrade road ? That's a tough call.
I hope that made sense. I don't want to come off as anti DIY I just want to you guys to realize that there has to be hard choices made when it comes to relative worth of a mod vs relative cost. Are you better off spending half as much on upgrade parts on a better base unit ? That's what it really boils down to.
The latest news from Michael at TeraDak is they are changing the AC power transformer in the DC-30 power supply. Now for the really good news ... they will also be using separate windings on the AC transformer for the 5V DC supply and 7.6 DC supply. Nice!
If you are still waiting for your Chameleon DAC to arrive chances are you will be the first to see the new changes to the DC-30. If you are an early adopter like me he informs me the circuit board is different. I will talk to Michael about what our options are.
Pricklely Peete, some very valid and useful points there. But without, I hope, sounding like a fanboy, I would say that with this dac, the low price point is not just about the quality of components/design. The principle of this dac is to minimise the parts in the signal path to the point were there is no badly designed cheap component op amp screwing up the sound, and the multiple 'cheap' nos dac chips increase the resolution to a high level. So it is worth investing in decent coupling/decoupling caps. and messing around with the input signal because the base design is solid.
If I bought instead a very expensive Audionote nos dac, that also uses 'outdated' dac chips they would of already put these expensive components in an also essentialy simple design,(which is their philosopy aslo) and then charge a bomb for it. So for me spending a bit of dosh on this simple dac is far more cost effective then ugrading a more expensive one , with the same components