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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 7th November 2017, 08:20 PM   #2241
Salas is online now Salas  Greece
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Salas DCG3 preamp (line & headphone)
Quote:
Originally Posted by JOIMONF View Post
Just received today a custom O-core power tranformer from China.
But manufacturer misread my specifications and sadly wound one sec. instead of two.
I have only one 18v-0-18v available in a 100w. core.
Before complaints, Salas please lets me know best option here:
-Use as it is, wiring parallel to both channels.
-Order another tr. identical to complete double mono, or
-Order new with two sec. as it should.
Thanks in adv.
You can't share a common secondary set between two PSU's without common voltage issues due to non isolation. Its either you use one transformer and one PSU with its DC output shared between channels (compromise) or you use the double PSUs on double sets of independent secondary AC either wound on a shared core or going full double mono utilizing two separate transformers. Shared core option is just satisfactory, double transformers is costlier but its the most advanced option regarding separation.
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Old 7th November 2017, 10:01 PM   #2242
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Got it, I will request another 100w. core. for a double transformer arrangement, as I should have ordered in first.
I hope 100w + 100w not too much oversized or overkill.
Specs. (each) 108mm. diameter / 1,5 kg.
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Old 7th November 2017, 10:32 PM   #2243
Salas is online now Salas  Greece
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Its no doubt overkill but you can't do anything much different now. You can at least hope that the manufacturer's mistake may bring little better sound to your build in the end due to the lower impedance of the oversized double mono final arrangement.
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Old 8th November 2017, 01:53 PM   #2244
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thanks nice to know
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Old 8th November 2017, 03:58 PM   #2245
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I am waiting to receive a fairly unknown high end headphone intended for the internal china market.
It has somewhat unusal parameters for a planar magnetic, with a low 34ohm. impedance and 96dB/mW.
I's reported among the easier to drive in the planar magnetic tech.
What bias and gain settings could I set on DCG3 preamp?
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Old 8th November 2017, 09:42 PM   #2246
Salas is online now Salas  Greece
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96dB/mW at 34Ω translates to 111dB/V and 30mA RMS. So they are voltage sensitive headphones indeed but they demand some appreciable current.

See in post#1 the last two THD graphs with the Grado SR60 used as load for the DCG3 at 100mA vs 150mA bias. Those cans at 98dB/mW 32Ω have close spec to the ones you are expecting. Their level was realistically loud at 105dB SPL in those measurements. The 150mA bias graph showed a THD benefit. So use that bias.

As for gain setting the standard 3X will be more than enough for your cans with reserve for other less sensitive cans or for some quieter digital recordings or a vinyl source.
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Old 9th November 2017, 09:42 PM   #2247
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allright and thanks, no need to say
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Old 16th November 2017, 10:11 PM   #2248
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Salas DCG3 preamp (line & headphone)
Default Fake or mutated NEC ...

Just started the build and came across a fake/mutated NEC while measuring
the idss of them. Can you find it

FWIW, the idss range from 4.2X to 14.4X mA, all are usable except one.
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Old 16th November 2017, 11:08 PM   #2249
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3rd row up from the bottom middle one.
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Old 16th November 2017, 11:16 PM   #2250
pchw is offline pchw  United States
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Yup, I suspect that is a bad one that somehow passed QC.
The casing and prints are identical to the rest except one pin too many.
Wonder what it actual is ....
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