My understanding is that there is a secondary PLL somewhere in there.
I haven't really looked too hard however.. So that may or may not be the case. My focus has been primarily on the analog board which I hope to replace with a discrete version.
Whatever they are doing it is extremely enjoyable to listen to.
I haven't really looked too hard however.. So that may or may not be the case. My focus has been primarily on the analog board which I hope to replace with a discrete version.
Whatever they are doing it is extremely enjoyable to listen to.
I agree the LM4562's in my Zhaolu 2.5C is incredibly good! Have you guys tried disconnecting the power to the front LED's and disconnecting the headphone amp? How about shorting the signal degrading DC blocking caps on the analog board? All very nice improvements.
kevinkr - Interesting your comments on the 2.5's power supply. Zhaolu has said the new power supply in the 2.5 was an impvroement over the IC dominated supply of the 2.0. I'm no expert here and am out of my league but it was interesting you mentioned the "Jung Super Reg" approach to the 2.5's supply design. There is a guy over at Head-Fi who's disputing the 2.5's supply and saying the 2.0 is better. To my ears I find the 2.5 to be much superior in sound quality than the 2.0 and I currently own both. I'd be interested to hear any ellaboration you might have about the 2.5's power supply design.
kevinkr - Interesting your comments on the 2.5's power supply. Zhaolu has said the new power supply in the 2.5 was an impvroement over the IC dominated supply of the 2.0. I'm no expert here and am out of my league but it was interesting you mentioned the "Jung Super Reg" approach to the 2.5's supply design. There is a guy over at Head-Fi who's disputing the 2.5's supply and saying the 2.0 is better. To my ears I find the 2.5 to be much superior in sound quality than the 2.0 and I currently own both. I'd be interested to hear any ellaboration you might have about the 2.5's power supply design.
Hello Hamburger Boy,
Thank you for your comments. It's nice to hear
from someone who knows both the 2.0 and the 2.5.
Do you have any experience with the D2.0's balanced
vs single-ended output?
Hi Kevin,
I was looking at some info.
Did I read things correctly that it's actually possible
to put a full balanced analogue output stage on
the D2.5?
Cheers,
Dennis
Thank you for your comments. It's nice to hear
from someone who knows both the 2.0 and the 2.5.
Do you have any experience with the D2.0's balanced
vs single-ended output?
Hi Kevin,
I was looking at some info.
Did I read things correctly that it's actually possible
to put a full balanced analogue output stage on
the D2.5?
Cheers,
Dennis
Hi Dennis,
Yes it is possible, the output of the dac is balanced.. The current analog stage converts it to an unbalanced output - which is what I also plan to do in my discrete implementation. (Saves a bunch of transistors and most people don't use the balanced output anyway.)
Hi Hamburger.
The analog voltage regulator is a mix of discrete devices and op-amps. I have not tried sticking an LM4562 in that location yet, nor I have I tried any op-amp upgrades of the headphone amp.
I would expect disconnecting the headphone amplifier might result in small, possibly significant improvements if the reduced loading improves some aspect of the performance of the analog supplies. Possibly there might be a small reduction in cross-talk with all the removal of that unneeded signal wiring.. Then again the basic design is quite good, and it could be that the changes will be inaudible. As always YMMV..
I can't see any harm in unplugging the headphone amplifier connections. I find the LED indicators useful so I will leave them connected regardless.
Note you should be careful about ESD injection into the dac. I would use a wrist strap and proper ground connection. If these are not available a warmer, rainy day will be "tweak" safer than a dry, cold day, and keep a hand on the chassis at all times to minimize potential difference buildups between you and the internal circuitry of the dac. It's winter afterall in the northern hemisphere a.k.a "The ESD witching season"..
Yes it is possible, the output of the dac is balanced.. The current analog stage converts it to an unbalanced output - which is what I also plan to do in my discrete implementation. (Saves a bunch of transistors and most people don't use the balanced output anyway.)
Hi Hamburger.
The analog voltage regulator is a mix of discrete devices and op-amps. I have not tried sticking an LM4562 in that location yet, nor I have I tried any op-amp upgrades of the headphone amp.
I would expect disconnecting the headphone amplifier might result in small, possibly significant improvements if the reduced loading improves some aspect of the performance of the analog supplies. Possibly there might be a small reduction in cross-talk with all the removal of that unneeded signal wiring.. Then again the basic design is quite good, and it could be that the changes will be inaudible. As always YMMV..
I can't see any harm in unplugging the headphone amplifier connections. I find the LED indicators useful so I will leave them connected regardless.
Note you should be careful about ESD injection into the dac. I would use a wrist strap and proper ground connection. If these are not available a warmer, rainy day will be "tweak" safer than a dry, cold day, and keep a hand on the chassis at all times to minimize potential difference buildups between you and the internal circuitry of the dac. It's winter afterall in the northern hemisphere a.k.a "The ESD witching season"..
Dennis - I have not used the balanced outputs on the 2.0, I don't have any other balanced equipment.
Kevin - Thanks for the comments on the power supply, very interesting. Disconnecting the headphone amp results in a minor improvement, you are right. It's not huge but noticeable. I have the upgraded discrete headphone amp module - which is excellent by the way. Disconnecting the front LED panel/digital switching results in similar improvements. The biggest difference I have noticed in these small tweaks is shorting those four red Elna's on the analog board which resulted in a very nice improvement. The U.S.A. Zhaolu dealer over at ifiaudio.com noticed the DC offset remained very low after doing this. Thanks for the tip on ESD! I agree. Funny thing is the chassis is not grounded though!
Kevin - Thanks for the comments on the power supply, very interesting. Disconnecting the headphone amp results in a minor improvement, you are right. It's not huge but noticeable. I have the upgraded discrete headphone amp module - which is excellent by the way. Disconnecting the front LED panel/digital switching results in similar improvements. The biggest difference I have noticed in these small tweaks is shorting those four red Elna's on the analog board which resulted in a very nice improvement. The U.S.A. Zhaolu dealer over at ifiaudio.com noticed the DC offset remained very low after doing this. Thanks for the tip on ESD! I agree. Funny thing is the chassis is not grounded though!
Member
Joined 2003
You are talking about the coupling caps? Mine are Nichicon Muse bipolar Electrolytics (green) that are bypassed with some small poly cap of 100nF I think. First thing I did when I got my Zhaolu was to bypass the coupling caps, so I can't compare to how much better it sounds, but no cap in signal path is always better. DC offset is at 50mV which is a little high for line level signals, but as long as theres a coupling cap somewhere in the signal path you'll be good. I have coupling caps at the input to my power amplifier, and no where else are they to be found.Hamburger Boy said:
I've closed up my D2.5 so I'm not sure what coupling caps
it uses. However, I remember seeing green caps, so they're
probably muse as well.
I think Ashok mentioned seeing 80 mV offset with the caps
bypassed.
What value/voltage are the coupling caps? Maybe it's time
for me to save up for some Blackgates.
What I really need though is a second D2.5 to use
as a control and one to hack around with.
Cheers,
Dennis
it uses. However, I remember seeing green caps, so they're
probably muse as well.
I think Ashok mentioned seeing 80 mV offset with the caps
bypassed.
What value/voltage are the coupling caps? Maybe it's time
for me to save up for some Blackgates.
What I really need though is a second D2.5 to use
as a control and one to hack around with.
Cheers,
Dennis
Hi Guys - Hmm, I don't recall units with Nichicon's. My 2.0 and 2.5 has Cerafine's, four of them in a row right near the opamps.
DcibeL - Are the small caps that bypass the Muse caps on the underside of the board? Did you get this from Eddie Wu? If so that's a mod that Eddie does to brighten up the sonics as he found those coupling caps to lack a bit in the highs. Both my units are from iFiAudio.com here in the states and it doesn't have them. If you guys measure higher DC offset and don't have coupling caps on down the line then putting in some Black Gates or the like would be the best call as these caps do degrade the signal some. Having shorted them I hear cleaner highs, more extension at the extremes, better bass and a bit more resolution.
DcibeL - Are the small caps that bypass the Muse caps on the underside of the board? Did you get this from Eddie Wu? If so that's a mod that Eddie does to brighten up the sonics as he found those coupling caps to lack a bit in the highs. Both my units are from iFiAudio.com here in the states and it doesn't have them. If you guys measure higher DC offset and don't have coupling caps on down the line then putting in some Black Gates or the like would be the best call as these caps do degrade the signal some. Having shorted them I hear cleaner highs, more extension at the extremes, better bass and a bit more resolution.
Mine definitely has non polar nichicon muse (or clones of same) in it, four in a row right near the audio connector from the dac board. In addition there are 4 green through hole 1uF (box caps) in parallel with these.
I need to check the value of those non polar caps, but IIRC I have heard that they are 33uF from other sources. Verify first before ordering NX blackgates. They actually aren't all that expensive from Michael Percy, but the closest value he stocks in the NX type is 47uF at $2.50 each..
I think it is possible to sub a polar type as well as the dac has about 2.7Vdc sitting on its outputs and the analog circuitry has 0V. You would orient the cap + towards the connections to the dac board.
I need to check the value of those non polar caps, but IIRC I have heard that they are 33uF from other sources. Verify first before ordering NX blackgates. They actually aren't all that expensive from Michael Percy, but the closest value he stocks in the NX type is 47uF at $2.50 each..
I think it is possible to sub a polar type as well as the dac has about 2.7Vdc sitting on its outputs and the analog circuitry has 0V. You would orient the cap + towards the connections to the dac board.
Member
Joined 2003
Yes, I did get my board from Eddie, and no there are no caps on the underside of the filter board. See this image, the small red caps beside the large EL caps are the bypass caps, though on my board all the red caps shown in that pic are green, just like Kevinkr.Hamburger Boy said:
Since the op-amps are combining a balanced signal to generate an unbalanced signal, the 2.7V DC offset out of the DAC is cancelled, and what you are left with is the difference between the DC offset at each of the DAC ouputs. The Error differs from chip to chip, evidently. If you wanted to save a few dollars when purchasing new coupling caps, you could just buy two and place them at the RCA output terminals.
Given the existing topology I would not recommend the use of a trimmer as depending on implementation this could seriously degrade cmrr which for good common mode noise and distortion cancellation needs to be as high as possible. You could probably trim on the second stage, but I have not reverse engineered the existing topology to see how to properly do that.
Being duals these devices of course do not have offset trims brought outside the package, but on singles that do you should never use this feature to trim external offsets as all sorts of parameters degrade when used this way. (Input offset drift being a major one)
Frankly 2.7vdc is not that a trivial common mode offset either, op-amps generally suffer significant degradation of key parameters in the presence of large common mode offsets at the input, and it does reduce the input stage dynamic range as well. Some op-amps are degraded more than others, you have to look at the specs of each op-amp considered to determine whether the issue is significant or not. Given the 15V rails used here you can certainly get away with it.
I am designing what is essentially a discrete op-amp which will be unity gain and which is designed to operated properly in the presence of dc offsets from the dac. Given the slight differences in both phases of the dac output I am either going to servo to ground or use a coupling cap at the output to handle the small and unpredictable output offset resulting from the imbalance. It's going pretty slowly - no progress to report at the moment. Simulations look good though.. I have yet to start a board layout.
Being duals these devices of course do not have offset trims brought outside the package, but on singles that do you should never use this feature to trim external offsets as all sorts of parameters degrade when used this way. (Input offset drift being a major one)
Frankly 2.7vdc is not that a trivial common mode offset either, op-amps generally suffer significant degradation of key parameters in the presence of large common mode offsets at the input, and it does reduce the input stage dynamic range as well. Some op-amps are degraded more than others, you have to look at the specs of each op-amp considered to determine whether the issue is significant or not. Given the 15V rails used here you can certainly get away with it.
I am designing what is essentially a discrete op-amp which will be unity gain and which is designed to operated properly in the presence of dc offsets from the dac. Given the slight differences in both phases of the dac output I am either going to servo to ground or use a coupling cap at the output to handle the small and unpredictable output offset resulting from the imbalance. It's going pretty slowly - no progress to report at the moment. Simulations look good though.. I have yet to start a board layout.
kevinkr said:
Sadly. no trace of a secondary PLL or any particular attention paid to jitter. Still, sounds very nice after just a bit of tinkering.
I bought mine mostly because it's a buzz item and was also curious about the sound of the 1852. Its is amazing how nice it sounds with so little inside the box
So far i've replaced the opamps with 4562s, shorted the caps, replaced the dreadful rca block with decent connectors, removed the follower from the output (recalculated the o/p RC filter with a 200ohm o/p resistor), switched off the headphone amp and bypassed the o/p muting relay (i am not using it as a preamp). The muting relay's contacts are annoyingly in line with the signal instead of shunting it. The output now feeds an AD815 line stage.
The 50mV output offset seems to be a feature of the 1852. It is impossible to deal with this in the differential amp/ filter stage but entirely possible in the subsequent (useless) follower stage.
An even simpler compromise is to short circuit the four input caps and include two new dc blocking caps at output - these can be of much smaller size -4.7uF BG N seem fine.
If i decide i really like to keep the case i would leave just half of the dual opamp to do summing and filtering (they maybe great opamps but one sounds much better than two) and replace the headphone board with an AD815 line stage. A separate PS would be appropriate. This is exactly what i'm listening to now, only the line stage is separate.
So, how does it sound? Pretty good after the minor surgery. It's quite neutral, good soundstage, reasonable detail and dynamics, very good rhythm and separation, average bass.
If my memories of the Citypulse 7.2 are correct, the difference between the two is no longer huge, but the Citypulse still has obvious advantages.
What the Zhaolu certainly achieved was to raise my enthusiasm to build a better dac. First iteration will probably resemble it. It looks so simple, it should take no more than a couple of days to build.
Btw, i've had a pretty good look at the boards and could draw a reasonably accurate diagram if there is sufficient interest and i don't feel too lazy. It is straightforward datasheet/appnote stuff.
I am also curious about Kevin's solution. A zapfilter clone is probably another, more flexible, option.
cotdt said:
How so? The D1 is an I/V stage and the Zhaolu has voltage outputs. Some of Pass differential preamps seem much more viable with some simple passive filtering at the input.
Of course if you have cap-phobia the Pass solutions will only aggravate it.
A Zapfilter clone will be completely diy
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