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It is currently 30 Mar 2020, 04:50

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PostPosted: 26 Mar 2020, 22:28 
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Joined: 19 Oct 2013, 20:46
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mwhouston wrote:
Cut the track which feeds 5V to the chip which now MUST be an OPA2134 or equivalent. Add a link to the chip V+ (pin 8) from the battery positive rail (now 18V). Ignore all other markings on the image. Only apply the changes which are in the ORANGE circles. No others.

DO NOT APPLY 18V TO THE PT2308 all the smoke WILL come out.


Attachment:
20200326_180630_compress30.jpg

Well, I've got around to doing the 18V cut trace and jumper mod and it's been interesting indeed. From an instant gratification standpoint, I decided to run two 9V in series for now. Also, as per your experience, grounded the top and bottom MuMetal shielding, too. (don't know why I didn't think of that before) I already had the 2134 installed as it was being used for preamp duty previously.

I hooked it up to a phono stage first because at the time my DAC cables were a bit inaccessible. Chose my trusty old AKG K77's rated @ 32 ohms for the maiden voyage. Dropped the needle and... CRAP!! Massive distortion (same as I recalled, anyhow) at about a 1/4 turn. I started to think about it for a bit and thought that it could be a loading issue with my phono stage. After all, running an LOMC cart and all. But It sounds great though my other system so kind of dismissed that for now.

Onward to accessing the DAC. (Schiit Modi 1st gen) Streaming Google Play at highest rate, same distortion. This is where it got interesting. I usually just run the player volume on full and control it at amp. I believe the line output voltage to be on the low side at 1.5V. When I started to mess around with player volume, things got better. Then I wrote it off to the K272 being sensitive to input levels. But when I finally found the sweet spot, it REALLY got better. I asked myself, is this what everyone has been talking about? One of the reasons I started this project was not only being holed up in my place on current lockdown, but also had purchased a new set of cans for a self birthday present last week. A pair of AKG K240 Mk II's that I got open box new for ridiculously cheap. Well, these are 55 ohms. While played through my Yaqin MS30L, they indeed are light in the bass department as reviews had mentioned. I guess that's because they're "studio cans" for mixing. But how wonderfully accurate they are in every other respect. But not clinical by any means. Anyways, I plugged them in and as anticipated, they were about at the extent of loading for the K272. I spent a couple of hours listening, doing A/B comparisons between HP's, Smartphone output, smartphone through DAC, other odd combinations, and re-listening to certain passages of music to test my ears for the "sonics". Things were sounding pretty good until a thought occured...

What about that LM833NG just sitting there in my parts box?

After settling in for another hour or so with the K240's hooked up, I decided to try it out. Would it sound like shite? Would all the smoke come out? After extensively reviewing the datasheet, I felt it was a safe bet nothing would be damaged. Popped it in, flipped the switch, click...

All I can say is holy S***! Everything woke right up. The K240's had bass extension I hadn't heard before, without diminishing all the sparkle and accuracy. Actually, I think it improved all across the frequency range. There was more drive. (headroom?) I was seriously having a hard time turning the music off and going to bed! Yeah, needless to say I'm really impressed. Also, it made the K77's sound a little brighter too. These are a budget set but actually fairly impressive for price point, especially with this kit.

I guess the synergy with this combo really matches.

There are some sonic oddities of note that I ran across while toying around with input/output level matching. While driving the input level close to the distortion threshold (which was also minimized running the LM833) I noticed that when you would pan to either side left up right down, or vice versa, you could hear distorted crosstalk to the other "off channel". But as you equalized right and left level up, output distortion diminished given the same input level. With that said, I'm still stewing on the filaments running in series as a culprit and possibly an alternative. (as others have mentioned earlier here) But for now, the next on the mod agenda is running 6 Li Ion cells for a total of 21V. Another reason that 833 shines, 36V max working supply. Gonna feed those plates the juice!

At any rate, I'm really pleased with the progress and look forward to more extended listening sessions. Getting exited enough to invest in the next upgrade DAC, too. Been looking really closely at the Topping D50s.

Thank you for posting the mod, Mark! I'm having a blast revisiting and messing around with this project, maximizing electronics fun time while on this crazy lockdown. Hope all is well and safe in your realm.

-Phil


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PostPosted: 27 Mar 2020, 00:05 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
We are on lockdown too. I’ve all most finished the two big power Amps and have started a DHT preamp with some 1920s nickel plate tubes.

Why of make your own DAC. You purchase the cct. Brd complete the CNCed enclosures and purchases two trannies (AU$30 in total) and you have a DAC. I built one around the same DAC chip the US$45,000 Esoteric DAC uses for s our AU$600. It has the latest AK4497 chip, six real time selectable filters and three input, USB, COA and OPT and on screen display.

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PostPosted: 27 Mar 2020, 21:58 
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Location: Vancouver Canada
wow


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PostPosted: 27 Mar 2020, 23:45 
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Location: Vancouver Canada
Li-ion eh. Great way to go. Balanced charging 6 with differential pwr sply. Hmmm. Does anyone know of a supplier of trans with multiple low voltage outs. Other than vac tube trans which do usually (2 or 3) but also have the HV which is not needed? Two individual windings are common but 3 or 4 are like hen's teeth unless custom wound.


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PostPosted: 28 Mar 2020, 13:12 
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laurie54 wrote:
Li-ion eh. Great way to go. Balanced charging 6 with differential pwr sply.


Yes, almost all of my other battery powered devices run Li Ion. Haven't purchased alkalines in years until this project. I have some flat 2000mah cells from an abandoned heated jacket project that will do just nicely regarding form factor. The 9V's in series sag about .3-.35V under dynamic load. (with 55 ohm cans) I have a feeling there will be negligible sag with the planned setup.

I've decided to only charge with the balance board so it will be out of the enclosure for space and possible noise issues. Planning to install a 6 pin mini DIN plug for the charge port. I've never seen an issue with unbalanced discharge of quality matched cells so long as charging is balanced, especially at this low current draw. Will be able to externally monitor cells as well.


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PostPosted: 28 Mar 2020, 13:51 
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Ordered some upgrade components for the K272A board that Mark sent with my original purchase. Vishay Dale metal film resistors, Wima film caps, Nichicon UKZ electrolytics for the audio side, and UPW's for PS side. Tracking says Monday for delivery. Mouser really ships out fast!
WooHoo! More electronics fun time.


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PostPosted: 28 Mar 2020, 15:53 
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e_phil_b wrote:
But for now, the next on the mod agenda is running 6 Li Ion cells for a total of 21V.

*edit 25.2V


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PostPosted: 28 Mar 2020, 17:46 
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e_phil_b wrote:
Ordered some upgrade components for the K272A board that Mark sent with my original purchase. Vishay Dale metal film resistors, Wima film caps, Nichicon UKZ electrolytics for the audio side, and UPW's for PS side. Tracking says Monday for delivery. Mouser really ships out fast!
WooHoo! More electronics fun time.

Interesting to see if you can tell a sonic improvement.

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Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


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