It's alive!
For the moment it's powered by my LM317/337 "test" power supply.
I've set bias at 150mA since I'm testing it with power-hungry Fostex T50RP MK3 headphones.
All 4 of my Ebay-sourced uPA parts measured exactly the same, so no matching was necessary.
I measured ~20 x BC560C to find 4 of exactly the same Hfe.
The BF256Bs that I got from Mouser were pretty strong. I used 220R for the two R3s, getting 4.3mA and 4.5mA Id respectively.
I bought 4 x DN2540 from Mouser, and used the 2 of them that measured the closest. The end result was about 10mA of difference in bias between the 2 channels.
My total current consumption is ~330mA for the positive rail and ~320mA for the negative one.
DC offset drift after warmup and adjustments was +/- 3mV without the op-amp installed. Went to 1mV with the op-amp. It might be even less, my meter won't go lower.
It had gotten pretty late so I didn't do any serious listening, but first impressions are very very postive. I'll do more listening and with a better source and power supply in the days to come.
For the moment it's powered by my LM317/337 "test" power supply.
I've set bias at 150mA since I'm testing it with power-hungry Fostex T50RP MK3 headphones.
All 4 of my Ebay-sourced uPA parts measured exactly the same, so no matching was necessary.
I measured ~20 x BC560C to find 4 of exactly the same Hfe.
The BF256Bs that I got from Mouser were pretty strong. I used 220R for the two R3s, getting 4.3mA and 4.5mA Id respectively.
I bought 4 x DN2540 from Mouser, and used the 2 of them that measured the closest. The end result was about 10mA of difference in bias between the 2 channels.
My total current consumption is ~330mA for the positive rail and ~320mA for the negative one.
DC offset drift after warmup and adjustments was +/- 3mV without the op-amp installed. Went to 1mV with the op-amp. It might be even less, my meter won't go lower.
It had gotten pretty late so I didn't do any serious listening, but first impressions are very very postive. I'll do more listening and with a better source and power supply in the days to come.
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if you make the 15Vac tap equal to your zero volts you end up with:15, 6, 3, 0, 3 , 6, 9, 15Vac
or if you make the zero volts at the 18V tap you get:
18, 9, 6, 0, 3, 6, 12Vac. Notice this has only one symetrical pairs.
Whereas the first offers three symetrical pairs.
You also have:
9, 0, 3, 6, 9, 12, 15, 21Vac when the 9Vac is made the zero volts
and:
12, 3, 0, 3, 6, 9, 12, 18Vac when the 12Vac is made to be zero volts.
I can see symetrical options of 3Vac, 6Vac, 9Vac, 12Vac and 15Vac
but these are NOT all available at the same time. You have to choose the option that is most useful and then keep that Zero Volt tap fixed at that tapping.
I got my project playing music for the first time today. Just an iPhone and Spotify as a source for quick test, but everything seemed to be working ok. Infected Mushroom seemed to pound the bass as it should with my LCD-2's. Still need to finish and tidy up the wirings and make a hole in the front plate for 6,3 mm headphone connector. I think I might have to lower the gain, since even with iPhone I had volume only on level 25/50. I have LDR vol. control and it's set to 20 kohms impedance. My current gain is 3x, but I still need to test the DCG3 with my Genelec G3 active speakers before tweaking.
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Tryouts for hand picked best result sample JFET input technology op-amp from your collection. If the 0-1mV wandering seems cyclic then its the normal integration time of servo loop, so no worries.
Cool explanation scenario, makes sense.
BTW I took some loopback shots of my "ancient" interface that runs properly on Win XP only. Two are with a meter long cheapo cable on HiZ and LowZ input config (1MegΩ with jack, 1.5kΩ with RCA to XLR adapter) last one is with short cable sans adapters. You should be able to achieve better than your now base line of interference and residual THD with the modern Focusrite I would suppose and its worth investigating as the DUT included loopback result looks suspiciously like the interface loopback alone times gain and the more exposed area to interference same type of pick up. Its not a measurements thread I know, and we better don't expand in general lab issues talk, but I include them since that thing came along and they might give you a lead.
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I wonder if all this low freq junk I am seeing osndie to the USB powered line. The laptop is unplugged and on battery so not sure where 60Hz is coming from. Yours looks exceptionally clean. It may be that the Solo is baseline model and not as clean? I am using a nice quality RCA cable (1m) with RCA to TRS adapter in one channel and RCA to wire to unbalanced TRS input. Is it because I am using TRS in unbalanced mode? Some more debugging needed.
Spot the cans studio video time
DT-770 Beyers reign the scene but the vocalist will wear open backs (HD595s?) most of the time. For looks I suspect because in the real recording take they could leak to the mic plus the particulars are not a studio cred model. There could be Vgeorge's V6 Sonys also on the drummer's head for a moment. https://www.youtube.com/watch?v=XvZ0Xbyzjw4
All those pics I posted are in unbalanced mode to be relevant. RCA to TRS adapters everywhere there also.
Here's the Focusrite 2i2 on a clean self loop. http://www.diyaudio.com/forums/equipment-tools/266853-behringer-focusrite.html
The REW sweeps seem to curiously peak towards the HF there too, yet another quirky thing you spotted before.
Spot the cans studio video time
https://www.youtube.com/watch?v=XvZ0Xbyzjw4
Not HD595's. They look like HD555's.
Jim
Seems my HD595's are quite odd. Mine look like HD590's. So ignore my "Not HD595" comment.
PS: Thanks for the music links.
Jim
Did you also notice those large gunshot earmuff like phones the drummer wore in the Pidgeon clip? Those have Sony 7506 drivers inside. They are specials for high isolation called UltraPhones. Drummers must protect their hearing the most as the kit is loud and if it leaks in enough they pump up the volume of their foldback mix in the cans too. So they end up with ringing ears after longish sessions or when performing loud live events. In Ear monitors do that job well too.