leo
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Post by leo on May 17, 2008 12:50:11 GMT
Leo For the life of me, I still can't see what is so special about that 5V power supply. I must be missing something somewhere. I think Rick may have posted something about it in another thread ? Alex Well thought I'd post it seeing as though its on the thread and easy to do I use something else with mine but its more complex
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leo
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Post by leo on May 17, 2008 12:53:42 GMT
You know this dacs not bad at all for a cheapo, sounds better once modded than quite a few commercial offerings thats much more expensive I'm not mentioning any names
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Post by jeffc on May 24, 2008 1:02:42 GMT
First post here as I've been tweaking this cheapo DAC with just enough electronics knowledge to get me into trouble. Before the mishap, all caps in the digital section had been replaced with Oscons and all power pins on the CS4397 bypassed with 1000pf silver micas, signal coupling caps from the DAC removed and jumpered. Sound even with the stock JRC5532 opamp feeding a Charlize Tamp into OB Visaton B200s was really getting me excited about just how good this DAC could be with improvements to the output stage. Now what a think I've done is accidentally (fumble fingers) shorted the opamp Vcc and out2 pins. No sound right channel. Replaced the opamp, still no sound right channel. Multimeter across R+ and R- and the L outputs of the DAC gives similar AC, so hopefully I haven't fried the DAC chip but have no idea. Any advice on what I am likely to have stuffed and whether it might be fixable would be most welcome. Thanks, jeff
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leo
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Post by leo on May 24, 2008 1:18:42 GMT
Have you tried bypassing that chip on the bottom of the board? it may have been damaged, the dac sounds better without it anyway IMO
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Post by jeffc on May 24, 2008 3:22:55 GMT
Leo, Yep, right on the mark Thanks ever so much, disaster averted and lucky that chip can be bypassed. cheers, Jeff
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leo
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Post by leo on May 24, 2008 18:49:26 GMT
Leo, Yep, right on the mark Thanks ever so much, disaster averted and lucky that chip can be bypassed. cheers, Jeff Nice one Jeff, have fun!
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leo
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Post by leo on May 24, 2008 20:47:40 GMT
On another thread Minivan gave me an idea I've tried it in both dacs supplies from the JLH, it sounds much better in the modified Elcheapo
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Post by Deleted on May 24, 2008 21:21:45 GMT
Leo Why not ? The X-DAC V3 was further markedly improved when a JLH was fitted in the outboard dual regulated supply. Alex
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leo
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Post by leo on May 24, 2008 22:45:16 GMT
I've been using the JLH with both the Elcheapo's even when using the op-amps, it sounded much better to me than using standard regs on their own As you can imagine these Burson discrete work a lot better with something like the JLH anyway, they are more dependent on the supply quality
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Post by jeffc on May 29, 2008 3:57:02 GMT
Leo,
I’ve just come across this tweak from Marc Legare posted at the Lukasz Fikus site. It was done using the larger CS4397 through-hole board but I guess it will be applicable to the Cheapo DAC board too.
It’s based on the using an LM4562 (which I have on the way) directly coupled to the dac as you’ve recommended. Quote
“There's 0.85 V at the output of the op amp with 2.5V at IN- and IN+. To get rid of this 0.85V at the output of the opamp, there's a 1k in series (in place of the output caps) with the output that goes to the RCA plugs. After this 1K resistor, connect a 14.7K that goes to the -12V that feeds the opamp. This will cancel the 0.85 V at the opamp output and the opamp will be more in class A operation. The DAC will be directly coupled without any cap. The LM4562 needs at least 100 hours of breaking time to play correctly.”
Any thought’s on this?
In addition, might this be worth a try with the stock JRC5532 or the LM833 I have whilst I wait for the LM4562 to arrive? And another noob question, would the 14.7K resistors needed for each channel both go to the -12V. I suspect not but need reassurance.
Jeff
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Post by Deleted on May 29, 2008 5:10:51 GMT
jeffc You would need to connect a 14.7Kohm 1% metal film resistor from the output side of each 1Kohm resistor to the -12V supply rail. i.e, the other side of both 14.7Kohm resistors connects to -12V. I will leave it to Leo to comment on whether it is worthwhile getting rid of the output capacitors, then introducing a 1Kohm resistor in each output path. SandyK
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leo
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Post by leo on May 29, 2008 19:47:35 GMT
It should work, as Sandyk hinted though would having 1k resistor on the output be better than a biased coupling cap? you may as well try it and let us know what you think I use a coupling cap mainly because I have more than one amp, a couple of those uses no coupling caps on the input so I keep one on the dac mainly as a precaution when used with the amps that have no protection
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leo
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Post by leo on May 29, 2008 19:49:17 GMT
BTW you could easily add the 14k7 on the bottom of the board, it should be easy to do, if your struggling I could probably edit a pic and draw it on if it helps
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Post by jeffc on May 29, 2008 22:03:39 GMT
SandyK/leo, OK, thanks for the advice. Wet weekend on the way so I'll see what I can do. The T-amp has input coupling caps so I should be safe there. Already had the thought to place the 14k7s under the board from the DIP socket to the OUT pins, might be starting to get the hang of this. BTW, with the T-amp DC blocking caps in place, could I simply remove and jumper over the DAC output caps, minus resistors? Jeff
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Post by leo on May 29, 2008 22:35:56 GMT
Hi Jeff,
I wouldn't just link the caps out without the resistor mod tbh, although your amp has input coupling caps, your vol pot won't have any blocking, DC across a carbon/plastic pot can damage the track over a period of time, you'll probably also get unpleasant scraping sounds through the speakers when adjusting the volume
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Post by jeffc on May 30, 2008 0:12:58 GMT
Hi leo,
Once more thanks for words of caution. I am using a 10K stepped ladder-type pot, but advice headed as I’d prefer to avoid scratches/pops when adjusting.
BTW, I might be easily pleased, but once warmed up I am really enjoying the additional detail, texture and focus that the LM833 seems to provide over the JRC5532. If a $2 opamp can sound this nice in this DAC, I’m really looking forward what gains can be wrought by use of an LM4562 or burson audio module, which I contacted them about a few weeks back. You’re several steps ahead of me though. I received word yesterday that they’ve just received new stock. At $75AUS for a single ‘dual’, and you having tried one, are they worth the expense over a good opamp IYO.
Jeff
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Post by leo on May 30, 2008 2:00:34 GMT
I just tried that resistor mod, instead of giving out 800mv DC offset it now gives 1.5v I'll look at it later, its way past my bedtime
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leo
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Post by leo on May 30, 2008 2:03:38 GMT
Can the burson module be used in an X-Can V2 or V3? I don't know the X-can circuit so not sure tbh Miguel
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Post by dotnet on May 30, 2008 6:50:57 GMT
Once more thanks for words of caution. I am using a 10K stepped ladder-type pot, but advice headed as I’d prefer to avoid scratches/pops when adjusting. This reminds me of something I've been meaning to ask for a while, sorry for the off-topic drift: How do stepped attenuators transition between positions? Will they short the two adjacent positions for a moment, or will they open the circuit? If the latter is the case they would be totally unsuited for designs where the volume pot is the negative feedback loop, because they'd spice up every turn of the knob with a series of maximum volume bursts. Cheers Steffen.
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Post by Deleted on May 30, 2008 7:39:40 GMT
Steffen The majority of Stereo Audio Attenuators appear to be make before break types, although there are some break before make types. SandyK
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Post by dotnet on May 30, 2008 10:14:59 GMT
Steffen The majority of Stereo Audio Attenuators appear to be make before break types, although there are some break before make types. SandyK Thanks, good to know. I'm still toying with the idea of replacing the pot in my amp with a stepper, but I don't want to make a $200 mistake Cheers Steffen. EDIT: so when it says "switching function: shorting" like here, then that presumably means it is the make before break type?
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Post by Deleted on May 30, 2008 11:54:05 GMT
Steffen Yes , that is what they mean. I am not so sure I would use any kind of attenuator , or potentiometer in the NFB circuit though. BTW, I use a DACT2 in my Class A Preamplifier. You can turn the volume down a bit, and still hear stuff you never noticed previously. Soundlabs ? BTW, a friend of mine bought a DACT2 also, after he heard how it further improved my preamp. SandyK
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Post by dotnet on May 30, 2008 12:08:43 GMT
Yes, Soundlabs. The volume pot in the feedback loop is a weird MF design flaw (IMHO). It's what is causing the "scratchy" pot after a couple of years. The pot (an Alps Blue Velvet) isn't actually scratchy, but sliding over tiny deposits on the track will make the pot go high-ohm momentarily. This you wouldn't hear with a pot in regular position, but here it means short max volume bursts that sound like a terribly scratchy pot. Mark Hennessy has a schematic here. One of the things I'm pondering (as per Mark's suggestion) is eliminating the pre-amp altogether and wiring the pot to the inputs as you'd normally do... Cheers Steffen.
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Post by Deleted on May 30, 2008 12:19:43 GMT
Steffen The website told me I didn't have permission to access that jpeg. If you are getting that problem with the Alps, I wouldn't use a DACT2 at that location either.
Regards Alex
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Post by kittenyberk on May 30, 2008 12:24:08 GMT
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