You may want to contact Jeff directly and inquire if he would install the transformers. You would pull the circuit board out of the MKIl (assumed to be easy) and ship to him.
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Thanks - he will do that but I was hoping to not have to ship and loose the use of the Dac.
Based on Jeffâs experience with the mod(s) it is probably worth the inconvenience.
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@tedsmith would like to know your opinion, for the Vocm mod do you think we would get better sound with electrolytic capacitors or SMD?
Good SMD. Possibly Hybrid/Polymer Electrolytic or Solid Electrolytic (Aluminum or Tantalum.) (SP-Cap, POSCAP, OS-CON, etc) FWIW I used ECASD31C476M040KA0 (47 ”F 16 V Aluminum - Polymer Capacitors sz 7343 SMDs) for a similar purpose in the Mk II, but I could take the room I wanted there.
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I will post here what I recommended you in personal messages.
I thought to mention OS-CON, but theyâre good only new-old-stock (NOS). Currently manufactured are not any close to the NOS ones sound wise.
I didnât want to buy âNOSâ from eBay because there is no guarantee that they were NOS. Thatâs why I didnât mention these as an option.
It is good to use Bi-polar ELECTROLITIC capacitors as broadband as possible with low impedance at audio frequencies. But the leads could act as parasitic inductance. Also, they are sensitive to vibration, causing microphonic effect.
! ! IF ELECTROLYTIC CAPACITORS ARE USED FOR THIS MOD, THEY NEED TO BE SUPPORTED. BUT DONâT LAY THEM FLAT ON OTHER DEVICES ! !
Another ideal option wouldnât be PPS film capacitors, but with their dimensions, it would be difficult to find the right size with the right nominal.
Therefore, good low-impedance electrolytic capacitors designed for audio are the best choices. The higher the quality, the better.
The AD8132s are very fast and operate up to 350 MHz. Accordingly, they can excite or amplify spurious interference over a very wide range. So, for these OpAmps, we need SMD ceramic type C0G/NP0, but I couldnât find any value that could work in a small packaging. Thus, I chose from X7R, which is also very good for this application. And there are already two 1uF X7R already installed there from the factory. Wonât hurt to add more.
Tantalum caps will not fit here according to how they sound like. Tantalum is worse than aluminum oxide capacitors. And (maybe @tedsmith could comment on this?) TANTALUM capacitors have a very low impedance, and PSUs not designed for their use can start generating noise themselves. Most likely, Ted would have already said something if the stock power supply couldnât work with tantalum capacitors on Vocm mode.
So I used a sandwich of ELECTROLYTIC CAP (+) SMD CERAMIC X7R (+) SMD film Polyphenylene Sulfide (PPS).
I have chosen:
- the best available polarized Kaisei 220uF 16V (bi-polar will do, too)
- SMD Panasonic PPS 0.1uF 16V
- SMD Murata ceramic X7R 1.5uF 100V
These electrolytic capacitors have low ESR, and these PPS and ceramic capacitors will suppress interference on HF. So, this sandwich provides noise suppression in a wide frequency range due to the use of three types of capacitors. Itâs just that each type (by dielectric) of a capacitor works ideally only in a certain frequency range.
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In the Vocm position the caps are stabilizing the âgroundâ reference for the output. R5/R6 is a one to one voltage divider setting that reference so any caps used across R6 are well isolated from the power supply. Lower ESR (and ESL) are benefits here. If I wasnât clear I wasnât recommending Tantalum Electrolytic caps, but instead the possibility of Tantalum Polymer caps (as well as possibly Aluminum Polymer or Aluminum Hybrid caps.) The Tantalum Polymer caps donât have the usual Tantalum caveats. Tantalum Polymer caps are one way to get good capacitance but with fairly low ESL and low ESR in this physical space.
Iâm leery of the microphonics of X7R and other class 2 (or II) MLCC capacitors in this position. As well as the microphonics of non hybrid and/or non polymer and/or non surface mount electrolytic caps. (And to a much lesser extent layered film caps here.) But I have no opinion based on personal use about the sound quality of various different styles of capacitor in this position. For me, low ESL and low ESR are what matter here.
Note that the quality of R5 and R6 do make a noticeable sound quality difference here so Iâm not surprised if the type of capacitor will also make a sound quality difference here.
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I agree 100% here.
Yes. We like to use low ESR in this location.
These sound very good in that location.
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And for everyone you installed Tantalum ELECTROLYTIC capacitors that Ted didnât recommend.
Thatâs why Ted installed TWO X7R caps from the factory.
X7R has low inductance. Ceramic works best at this place, but unfortunately, too bulky to use bigger values. Thus, I had to use a sandwich of capacitors.
Ted just gave us some options, other than doing sandwich of capacitors
In my perception JK & Ted clarified very early that this single own experiment was not recommended anymore and then JK also recommended the SMD parts .
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Please take it to PMâs gentlemen.
Thank you.
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Aw Shucks Elk! I just fired up the popcorn!
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Post Deleted.
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My method, maybe, looks silly, maybe overcomplicated. But it works, and covers wider bandwidth to reject more noise (noise from OP amp not the power supply). The AD8132s are very fast and operate up to 350 MHz. Accordingly, they can excite or amplify spurious interference over a very wide band.
The main interference at that point in the circuit is at 22.5792MHz. Thatâs the frequency where the caps need to be effective. My sandwich works for the target frequency and effective way above.
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I think I could 3D print a bracket that holds all them caps similar to what I did for the big Jensenâs.
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I used a cork board, which is well known as a good construction material: light and rigid, with good adhesion. But the main feature is great dampening ability to eliminate microphonics, in this case.
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I believe Ted did recommend the caps I use. I also know firsthand they are one of the best sounding ones.
I tried some other hybrid tantalum that sounded just as good, however after two failures (shorting out) I decided the best most reliable ones are the ones I currently use.
The reason I am posting this is because of all the PMâs I have been receiving lately regarding some statements made recently here in this topic.
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Photo of the Tantalum capacitors I use designed for this 0805 location installed for the Vocm mod.
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Almost forgot. I did manage to get the 8139 opamps working with the stock power supply. I just had to beef up and modify the up stream regulators / filters. I now have a schematic of the analog board. (thanks son)
Sound wise⊠Sweet.
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