As with any device removing coupling capacitors depends on the amout of DC offset and the devices downstream. Transformers and amplifiers do not like DC. I am willing to bet your preamp or downstream device utilizes coupling caps. But if you are running this into a Transformer Volume Control this would be unwise.
All the filtering is done via I/V stage in DAC, plus the signal passes through 3 opamps. I doubt there's anything much above 20k, except for some inter-modulation harmonics that are needed for the "air".
I would also recommend changing +15 -15 reg output 10uf C414 C415 caps to something larger (say 100uf silmics or more) and also bypassing C95 C96 with 0.1uf wimas. This would improve power supply to opamps.
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How is changing the capacitors to 100uf supposed upgrade the power supply to the opamps? Add capacitance means drawing current to charge the capacitor. These caps are not doing filtering as that is done the the previous RC filter and the 7815 for a total reduction in ripple by 3203. On there other hand replacing the 15 volt regulators with better ones such as DEXA regulator and chugging the caps to tantalum would help with stray noise. C93, 94, 95, and 96 should all be replaced with tantalums as the make less noise. C414 and 415 I would not go more then 22uf
I didn't say "upgrade" power supply, just upgrade the caps to slightly bigger ones - theoretically it should improve dynamics. The regs are charging those caps, but opamps are also drawing the current from them as well... I would bypass all supply rail smd ceramics with small wimas as the ceramics sound horrible.
I guess you definition of slightly is different then mine 10X is a bit more slightly. Dynamics should improve with caps that have a low ESR and therefore are easier to charge and allow the power supply to respond more quickly. The caps in the unit are chosen more for cost then anything else. I use tantalums because they have lower noise then other capacitor. Yes we are talk a buck more each but given the effort to open the DAC Magic.... For larger caps I use films. At any rate the DAC Magic is not drawing a lot of current.
Try updating to better opamps. I replaced the NE5532s with LME 49720 and the OP275Gs with OPA1612. But this requires that one can surface mount solder.
The 5 volt DAC regulator should be replaced with a DEXA as this is the critical supply for the DAC. It made a huge change. I did my changes one step at a time
Try updating to better opamps. I replaced the NE5532s with LME 49720 and the OP275Gs with OPA1612. But this requires that one can surface mount solder.
The 5 volt DAC regulator should be replaced with a DEXA as this is the critical supply for the DAC. It made a huge change. I did my changes one step at a time
Stuffing it full with dexas, tentlabs, opamps and throwing $250 worth of parts into a $200 dac sure makes little sense. On the other hand adding maybe one regulator and changing some caps will make it sound like a decent $250 dac. For itchy hands there are plenty of good dac kits on online.
Tantalums on anything but digital tend to sound really bad,Id stick with good lytics there.
Tantalums on anything but digital tend to sound really bad,Id stick with good lytics there.
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Up to you. I spent less then $100, and kept the DEXA to the DAC where it made the most sense. Check with Morgan Jones' book on what components are good and bad and why. This research is backed up other places as well. It will also supply proven mathematical formulas for changing out components. You should also use an oscilloscope and current meter to make sure you changes are making improvements. Improvements without measurements are hard to recommend. Understandable that not everything can be measured but power can, unlike cables that have to be heard.
Super reg on DAC makes the most sense, I agree. Changes such as decoupling caps in DAC circuits are somewhat scientific too, easy to see with digital oscilloscope. However, analog stage coupling and power decoupling caps are more ear/taste matter.
78xx, 79xx regs have datasheets too...
Most of the "improvements" in the analog domain are subjective, throwing money on more expensive opamps or "fairy-wings-in-virgin-blood" gold caps might make you feel good...Discerning ear is the ultimate judge.
Dacmagic in stock form is quite excellent given its price/quality ratio. I would add no more than $50 worth of quality parts.
On a separate note I would like to share my dealings with L1 induction coil - it was too noisy and the chirping was really loud with Dacmagic cover off.
Short version: removed it from the board, cut around the base to remove ferrite shield, put some shrink tubing on the coil, packed the housing with epoxy, put it back together. Now it's silent as a church mouse...
78xx, 79xx regs have datasheets too...
Most of the "improvements" in the analog domain are subjective, throwing money on more expensive opamps or "fairy-wings-in-virgin-blood" gold caps might make you feel good...Discerning ear is the ultimate judge.
Dacmagic in stock form is quite excellent given its price/quality ratio. I would add no more than $50 worth of quality parts.
On a separate note I would like to share my dealings with L1 induction coil - it was too noisy and the chirping was really loud with Dacmagic cover off.
Short version: removed it from the board, cut around the base to remove ferrite shield, put some shrink tubing on the coil, packed the housing with epoxy, put it back together. Now it's silent as a church mouse...
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And here's the list of my mods:
DAC Section:
C419 - Panasonic FC 1000uf 16v
C275, C303 Oscon 10uf 25v
The rest are bi-polar Nichicon Muse
Waiting for dexa reg.
All digital section caps changed to Oscons
Removed C17 and C18 from digital inputs 1 and 2 (we absolutely don't need capacitance there)
bypassed C126 and C127
Analog output:
removed C269 and C264, those are HF filtering caps - snip snip.
opamp supply rail caps bypassed with small wimas
The rest is usual cap upgrade to quality Nichicons, Panasonics, and Elnas.
I have a pair of ASC LL/88 transformers, might experiment with output stage a bit since they do fit on the pcb with coupling caps removed...
DAC Section:
C419 - Panasonic FC 1000uf 16v
C275, C303 Oscon 10uf 25v
The rest are bi-polar Nichicon Muse
Waiting for dexa reg.
All digital section caps changed to Oscons
Removed C17 and C18 from digital inputs 1 and 2 (we absolutely don't need capacitance there)
bypassed C126 and C127
Analog output:
removed C269 and C264, those are HF filtering caps - snip snip.
opamp supply rail caps bypassed with small wimas
The rest is usual cap upgrade to quality Nichicons, Panasonics, and Elnas.
I have a pair of ASC LL/88 transformers, might experiment with output stage a bit since they do fit on the pcb with coupling caps removed...
OP275G datasheet shows recommended 0.1uf + 10uf decoupling caps on both power pins, I assume similar recommendations for the rest of opamps. Dacmagic has only 10uf per rail feeding all 6 opamps, not enough I suspect. I would recommend at least 47-100uf for C414 C415, since it would be difficult to put decoupling caps for each opamp separately.
Yesterday replaced AD797 on the +XLR stage with AD823. AD823 run less hot (45-50C), sounds close to the AD797 and sounds less distorting with more detailed than LME49720.
Experimenting with AD797 I infer it runs stable on the XLR topology however due to current draw of 10-12mA per Opamp across 30Vdc I installed them only on the XLR+ stage, they run hot around 65-70C. The sound is the best I've heard across a range of opamps however I am skeptic to go full way on XLR stage with 8 x AD797 on browndogs
Today I tried running ASC LL/88 transformers on Dacmagic output. LL/88 is BBC transformer 1:1 600ohm primary and secondary, with primary centertapped. I believe they were used to convert unbalanced signals to balanced and vice versa, and believed to be made by Sowter.
Primary was connected to to balanced signal running from U55-U56 and U59-U60 and output was fed to right side of the rca coupling cap (removed). The primary centertap is left unused, although I think it could be grounded...
The sound is GORGEOUS.
I think I am going to remove all coupling caps and disable XLR outputs - a pair of RCA will suffice for now. I had previously removed summing opamps that feed RCA outputs and ran one-sided XLR - hardly an optimum setup. The most important thing - those trafos fit within the box and could be mounted on the pcb.
Primary was connected to to balanced signal running from U55-U56 and U59-U60 and output was fed to right side of the rca coupling cap (removed). The primary centertap is left unused, although I think it could be grounded...
The sound is GORGEOUS.
I think I am going to remove all coupling caps and disable XLR outputs - a pair of RCA will suffice for now. I had previously removed summing opamps that feed RCA outputs and ran one-sided XLR - hardly an optimum setup. The most important thing - those trafos fit within the box and could be mounted on the pcb.
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An externally hosted image should be here but it was not working when we last tested it.
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this sounds quite promising...
Mihaylov also mentioned this here, but it was overshadowed by the OpAmp discussions
http://www.diyaudio.com/forums/digital-line-level/142184-opening-new-dacmagic-12.html#post2416747
Could you share a schematic on how the xformers are connected in ?
Mihaylov also mentioned this here, but it was overshadowed by the OpAmp discussions
http://www.diyaudio.com/forums/digital-line-level/142184-opening-new-dacmagic-12.html#post2416747
Could you share a schematic on how the xformers are connected in ?
Mihailov went extreme and bypassed all the opamps, coupling DAC Vout to outputs directly via transformers. I connected my transformers after the first cascade of opamps.
As we all know in audio Less is More. WM Dac chips already have Vout with filtering that are sufficient do drive the output, all the other opamps add distortion and coloring.
I really like tube output stages, and in this case something like Broskie CF would probably work well. Smallish Dacmagic box makes me explore other options and my current transformer mod seems to be OK.
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As I also take the output from XLR+ I am keen to try out the mod.
Led by your mod I found this while looking for xformer parts: Phono Preamplifier with Line Output Transformers
Is the sound improvement because the xformer does the summing up of the XLR+ and XLR- signals ? When you say sound improvement in what way ?