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Old 22nd May 2013, 06:58 PM   #3301
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Originally Posted by availlyrics View Post
Don't want to discourage your DIY skills but if you are new to electronics stick with the original RS design as 5V from USB involves SMPS ckts using SMD components.
I'd use it as a learning opportunity to get more familiar with SMD soldering--I'm more of a software guy though (do fpga's count?).
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Old 22nd May 2013, 07:47 PM   #3302
6L6 is offline 6L6  United States
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65dB gain with your HOMC cartridge is severe overkill...
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Old 22nd May 2013, 08:00 PM   #3303
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65dB gain with your HOMC cartridge is severe overkill...
But it works so well with the DCB1 and the F5! No overloading or distortion with that rig.
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Old 22nd May 2013, 10:24 PM   #3304
billyk is offline billyk  United States
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Originally Posted by McQuaide View Post
But it works so well with the DCB1 and the F5! No overloading or distortion with that rig.
But that's just it. The DCB1 has no gain and the F5 under normal conditions could use a bit, so that combination would work nicely. The O2 that already has a good bit shows how much the phono pre is putting out. (too much!)
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Old 22nd May 2013, 10:35 PM   #3305
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But that's just it. The DCB1 has no gain and the F5 under normal conditions could use a bit, so that combination would work nicely. The O2 that already has a good bit shows how much the phono pre is putting out. (too much!)
So is there a good way to attenuate it so I can have the best of both worlds?
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Old 22nd May 2013, 10:58 PM   #3306
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Idea: Put the DCB1 in line between the Pearl and the O2?

I don't have the amp wired with a pre-out, but that could be done. Unfortunately it would mean a complete tear-down to drill for more jacks, but it may be worth it.
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Old 22nd May 2013, 11:04 PM   #3307
6L6 is offline 6L6  United States
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Nah. Put the B1-F5 in your second system...

The solution is simple -- It's time to build a new amp!!

BA-2 or-3, complimentary output.
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Old 23rd May 2013, 01:01 AM   #3308
billyk is offline billyk  United States
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Originally Posted by McQuaide View Post
So is there a good way to attenuate it so I can have the best of both worlds?

I am fuzzy on the details, but the O2 has a gain switch, I would think that you may be able to mod it in such a way that one of the positions would be suitable for the phone pre and the other for CD, etc.
I use my O2 every day, but would need to look it up regarding just what values to use to set the gain.

Edit: From NavGuys' blog:
Quote:
THE GAIN RESISTORS: Before you solder in the four gain resistors by the gain switch, you might want to consider different gains than the approximately 2.5X and 6.5X default values. You want just enough gain so typical music plays loudly enough with your headphones and source and not much more. Extra gain means using less of the volume control’s range, more noise, more distortion, and makes accidental headphone damage more likely. Here’s what you need to know about calculating gain:

Lower Is Safer - Lower gain settings make the amp less likely to damage headphones by limiting the maximum output voltage to only approximately what’s needed.
Lower is Cleaner – As shown in the first article, there’s a slight increase in distortion, especially at high frequencies at higher gain settings. Lower gains also result in lower noise.
Resistor Values – The O2’s gain (for one channel) is:
Low Gain Ratio = 1 + R16/R17
High Gain Ratio = 1 + R16/R19
Voltage Gain in dB = 20 * Log(Gain Ratio)
Example – The standard amp has R16=1500 and R17= 1K so 1 + 1500/1000 = 2.5X. And 20*Log(2.5) = ~ 8 dB.
Feedback Impedance – For many reasons it’s generally best to leave R16 and R22 at 1500 ohms unless U1 is replaced with a weak op amp that can’t handle a 1.5K load.
See The BOM - Gain resistors are pre-calculated in the BOM parts list for gains of 2X – 12X. For 1X gain just leave out the gain resistors (or clip one end if they’re already installed).
Hopefully a setting of 0 gain can get you close, looks easy enough to try...

Last edited by billyk; 23rd May 2013 at 01:10 AM.
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Old 23rd May 2013, 07:58 PM   #3309
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That worked! I snipped all four gain resistors, and the distortion is gone. I'm still running it on the low gain setting with the knob around 10-11 o'clock. Thanks for the tip.
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Old 23rd May 2013, 08:56 PM   #3310
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Originally Posted by McQuaide View Post
That worked! I snipped all four gain resistors, and the distortion is gone. I'm still running it on the low gain setting with the knob around 10-11 o'clock. Thanks for the tip.
That's good news!! 10-11 on the volume may not be ideal but no distortion is great!! Glad to hear it worked for you.
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