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Old 24th August 2012, 07:53 PM   #1161
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I bought few BF862 to match IDSS and tried to measure it. At 9 Volts it appeared to be around 29-31 mA, which is obviously out of specs. Gate and source were connected to one plane of copper board, and drain connected to nearby plane, separated with blade cut. Marking seems to be OK, 2AW... Where might be a problem?

Also I am going to try this output with PCM63. KT602 is small signal Soviet BJT.
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Old 26th August 2012, 05:03 AM   #1162
EUVL is offline EUVL  Europe
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BF862 has a quoted Yfs of 45mS.
Measured values are mostly lower at say 35~40mS.

That will give you a Zin of 25~30 ohn for s single device.
If I were you I would use 2x in parallel.

And 4.2V Vds is too low if you want to swing 2Vrms Vout.


Patrick
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Old 26th August 2012, 07:45 AM   #1163
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I am going to make a PCB that will accept 2 pairs as well as 1. PCM63 is known to tolerate quite high voltages at its input, contrary to AD R-2Rs for example.

With Riv 792 Ohm and 2 mA current there will be around 1.1 Vrms at the output, which seems acceptable. 2 8.4-Volt batteries will lead to almost absolute maximum rating dissipation at BF862.
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Old 4th September 2012, 05:43 AM   #1164
ENSen is offline ENSen  Sweden
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Started the soldering yesterday and realized I had forgotten the bypass caps (C3 and C4) when ordering parts for this and another project from Mouser. The only alternatives I can source locally are;
Evox Rifa PHE426
Icel MPL 125 (Axial)
Scr PB0 (Axial)

Does anyone now if these are any good?
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Old 4th September 2012, 05:58 PM   #1165
orelli is offline orelli  Italy
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My favourite of the trio is Evox Rifa PHE426
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Old 4th September 2012, 07:17 PM   #1166
EUVL is offline EUVL  Europe
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I have not tried any of those, as I have easy access to WIMA MKP2.


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Patrick
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Old 4th September 2012, 07:34 PM   #1167
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The Rifas are very good. There is an even lower loss Rifa with double metallization but most prefer the single metallization.
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Old 4th September 2012, 07:47 PM   #1168
ENSen is offline ENSen  Sweden
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Ok, Rifa it is. Thanks for helping me out!
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Old 7th September 2012, 04:33 PM   #1169
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Smile simple questions

I have read both the article and most of this thread, but still a little confused about some things. Not being an electronics type, but wanting to try the circuit on an old Adcom with PCM1702s. Reading the Bill of Material list indicated that each channel or "per single ended IV converter" needs a battery PS. Does this mean each channel? One other question. I will input this into a power amp with an input impedance of 250k ohms. Normally, I use a .22-.47uf signal coupling cap. Is there some special need to use the large caps, that is 220uf with a by pass? Thanks for the clarification!
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Old 7th September 2012, 05:25 PM   #1170
bcarso is offline bcarso  United States
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Quote:
Originally Posted by optimationman View Post
I have read both the article and most of this thread, but still a little confused about some things. Not being an electronics type, but wanting to try the circuit on an old Adcom with PCM1702s. Reading the Bill of Material list indicated that each channel or "per single ended IV converter" needs a battery PS. Does this mean each channel? One other question. I will input this into a power amp with an input impedance of 250k ohms. Normally, I use a .22-.47uf signal coupling cap. Is there some special need to use the large caps, that is 220uf with a by pass? Thanks for the clarification!
If the DAC has balanced outputs, one I-V is needed for each output. And each I-V needs a floating supply, completely separate from everything else.

For that high of a power amp input impedance the smaller caps should be fine IMO (470nF will be -3dBr at 1.35Hz).

[EDIT] And the 1702 is single-ended, thus requiring only one Sen per channel and a total of two floating supplies for stereo.

Last edited by bcarso; 7th September 2012 at 05:31 PM. Reason: PS
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