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Old 19th August 2012, 10:24 AM   #11
regal is offline regal  United States
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Quote:
Originally Posted by skyraider View Post
Hi Erin,

I think the bass is there but just too clean... refer to my previous post, I might replace the OPA627 buffer with Jfet discrete buffer. This might introduce some 2nd harmonics back into the music..
I doubt thats the sole issue (lack of 2H.) I like that you are using a passive I/V + active for gain and buffer. You may need a lower I/V resistor. Have you tried a phono preamp-type opamp stage ? But I really think your issue may be powersupply/capacitor choice.

Sometimes you can help the all the 7805's by preceding them with 2 big transformers feeding two sets of big LM317/LM337 regulators stages set to 12V's, then driving the 7xx5's ( so you have a digital +-12V and an analog +-12V.) Keeping the digital supply separate from the analog all the way to the transformer.
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Old 21st December 2012, 03:47 PM   #12
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Thanks Regal, after trying low IV resistor, I agree this is way to go. The bass and details improved marginally, there is no going back!
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Old 21st December 2012, 03:49 PM   #13
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Using higher IV resistor tends to make the subsequent amplifier stage easier to design and build, can achieve good sound with relatively little effort.

But with low IV resistor,it demands tremendous task for the subsequent gain stage. Requiring gain of more than 150... any slight layout mistake can render the sound to be totally UN-listenable. My current implementation uses cascode, with shunt regulated supplies.
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Old 22nd December 2012, 02:02 PM   #14
regal is offline regal  United States
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Quote:
Originally Posted by skyraider View Post
Using higher IV resistor tends to make the subsequent amplifier stage easier to design and build, can achieve good sound with relatively little effort.

But with low IV resistor,it demands tremendous task for the subsequent gain stage. Requiring gain of more than 150... any slight layout mistake can render the sound to be totally UN-listenable. My current implementation uses cascode, with shunt regulated supplies.
Even with the troublesome PCM1704 I've found good results with a 30 ohm IV and + jfet gain (w/nfb) +diamond buffer, 2H right at -96db (there are some tricks to the decoupling caps.)

Basically just a passive I/v with a good phono stage, it works just fine as it did will LPs for years, the trick is finding how much resistance the I-out can handle and not using any feedback to the I-out pin. NFB is fine after the passive I/V just not before. NFB is bad on the I-out pin even when it is in the "current form." I am going to try another NFB free current steering I/V next week but my experience is they just can't keep up with an R2R's I-out sound dry and most just don't measure well. All jmho take it with a grain of salt.
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Old 23rd December 2012, 01:28 AM   #15
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Quote:
Originally Posted by skyraider View Post
Thanks Regal, after trying low IV resistor, I agree this is way to go. The bass and details improved marginally, there is no going back!
In reading this thread, I was going to make that suggestion but I then saw that Regal had already done so. So, while I have not experimented with the PCM56, I have experimented with the AD1865 using this same passive I/V circuit. What I found with AD1865 is that lower I/V resistor values generally improved the sound, and in particular, brought better subjective focus to the bass.
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