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Salas 15th January 2017 10:25 AM


Originally Posted by Morde (
Now that I changed the R10s to 10 ohm my bias is running at 136/137 mA in L/R channels. The temperatures were after about 45 min with top cover on 46 C for DCG3 and 50 C for DCSTB middle sinks. I'm satisfied. Let's see when I find the time to complete wirings and get to finally listen to this beast. :eguitar:

Good compromise solution for the metal hardware involved. That's not low bias, its plenty. No worries :)

Salas 15th January 2017 10:53 AM

1 Attachment(s)

Originally Posted by ammel68 (
Okay, so I need to have at least 5V more going in or at least 17V for a 12V output?
If so, I would just use a 36V CT transformer.

Because I don't really understand how this PS works, I'm not clear on what you mean by "varying the currents with R1 and R2" if I short out some of the Kingbrights. :confused:
Will raising their value from 33 ohms lower the output voltages or would I need to lower their values to get lower voltage?

Can a 100 ohm trimmer be substituted for R1 and R2 to vary the output voltages?


R1 & R2 govern the Id of the PF5102s by degenerating them. Those Id can differentiate the Vf of the Leds they feed constant current to. So its a place to can potentially trim out small Vref differences between the led bars. Rx Ry can cover easily when needing more V for a weaker rail to match a stronger one. Just additive correction though, can't trim down if you must.

So yes, more degenerative resistor value is less voltage and less is more but don't expect large differences more than a useful matching range. See the Cf/Vf from the datasheet.

Can use trimmers but better replace with steady resistors after finding the values. For better noise & reliability.

24VCT is near enough and it will not give much heat to the pass transistors. 26VCT would be ideal. Not any transfo spec we like is ready made listed though. But its not a make or break goal to have >5V raw. Use Schottky rectifying diodes to save 0.7V of bridge drop.

xrk971 15th January 2017 11:30 AM

That PSU was just what I had lying around to test. Let me give it my real power supply with 100w 20v trafo and cap Mx and 20mF low ESR cap bank (20v rails) and see if slam improves. I have DT880-250's.

Here is what I should try it with (just replace the two amps on the CPU heatsinks):

Salas 15th January 2017 11:43 AM

20V rails will be knocking out the AD823 unless you have an OPA2604 to replace it that has up to +/-24V rails spec. It will be getting hot also because it uses more mA bias than most chips. Sound will change from your now 14V to 20V and the use of OPA to more upfront due to various reasons including the OPS stage behavior. Suitable to the rather sweeter HF kind of headphone like the HD 650 or the Audeze LCD2. But you will see for yourself. Let us know your configs and liking.

xrk971 15th January 2017 11:50 AM

Maybe replace 20v trafo with 15v trafo then?

Salas 15th January 2017 11:56 AM

Should be less dangerous. Still, remove the AD823 and check the rails at the preamp's connectors to know where the PSU settles loaded before inserting the chip. If still more than +/-18V maybe a 5532 as a Sunday solution if having any. It has +/- 22V max spec. I remember it gave more mV offset because BJT input tech but also bit soft sonic subjectively so not too bad for Beyer. Maybe make R14 more aggressive value i.e. lower if you will find the offset control too loose with a 5532.

Salas 15th January 2017 12:41 PM

BTW a recording style that becomes the 770 80s is like this one I am listening on right now:

Your 880s have less artificial bass oomph because semi open but more linear. Try it though.

xrk971 15th January 2017 01:35 PM

Thanks for the song - very nice. I also like this one for testing head phone amps.

eLarson 15th January 2017 01:51 PM


Originally Posted by Salas (
BTW a recording style that becomes the 770 80s is like this one I am listening on right now:

Your 880s have less artificial bass oomph because semi open but more linear. Try it though.

Talk about a small world. They started out in Germantown, Maryland, just north of me.

Salas 15th January 2017 02:20 PM

They had played in Athens GR a couple of times also. Have seen them live in summer 2014. They had great crowd support, a large mass of bearded fans moving like huge sea waves. Especially when they performed The Regulator there was an eerie almost full crowd strong chanting along.

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