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Old 8th November 2012, 08:17 PM   #21
nr12 is offline nr12  Germany
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Hello Matthias,

try zhoufang (here in the forum or on ebay), he is selling 2SK170 BL.
Or in germany try kessler-electronic. Ask for BL grade before you order.

Ulf
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Old 8th November 2012, 08:33 PM   #22
juma is offline juma  Serbia
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GentryBa,
you are aware that some of your JFETs are out of specifications (4.7mA and 13.8mA can't belong to BL grade) which makes their other characteristics (gm, transfer curve) highly suspicious.
This preamp works on presumption that JFETs are a complementary pair without big differences in Idss (few mA is OK). Of course, there are ways to balance the input pair (no matter what you choose to use) but soundwise, it won't be worth the effort.

If I were you, I'd choose a preamp made with current production parts - the one with BF862 I like even better, this one too...
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Old 9th November 2012, 09:59 AM   #23
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hi everybody!

@juma:
jepp, I know that they are massive out of the needed specifications.
problem is: I have bought everything I need for building it. (2x r-core transformers, capacitors, etc,etc,etc...)
I don't want to spend more money for new parts like transformer, etc... again.
In the preamp-thread, where you posted your layout, everybody said that it sounds very good- so I will hear it, too...

I think I will have a look at kessler electronic and ebay.
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Old 9th November 2012, 10:14 AM   #24
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by juma View Post
....... the one with BF862 I like......
MOSFET-trioda Mju folover verzija

have to try it
ehh, btw, could it be a single ended to balanced 'converter' ?
sorry if its OT
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Old 9th November 2012, 12:02 PM   #25
Zen Mod is offline Zen Mod  Serbia
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nope
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Old 9th November 2012, 12:10 PM   #26
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by GentryBa View Post
hi everybody!

@juma:
jepp, I know that they are massive out of the needed specifications.
problem is: I have bought everything I need for building it. (2x r-core transformers, capacitors, etc,etc,etc...)
I don't want to spend more money for new parts like transformer, etc... again.
In the preamp-thread, where you posted your layout, everybody said that it sounds very good- so I will hear it, too...

I think I will have a look at kessler electronic and ebay.
G,
are you having a hizzy fit?

Why start again when all you are missing is a couple of jFETs?
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Old 9th November 2012, 12:38 PM   #27
juma is offline juma  Serbia
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Quote:
Originally Posted by tinitus View Post
...could it be a single ended to balanced 'converter' ?...
SE-to-Balanced converter must include some sort of differential amplifier - a building block with inherent feedback (or degenerative) mechanism between elements that can produce signals which are opposite in phase...
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Old 9th November 2012, 01:50 PM   #28
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@andrew:

what does "hizzy fit" mean?

Now I bought some BL-graded matched ones from toshiba.
hope this will solve my problem.

best regards,
matthias
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Old 23rd December 2012, 03:08 PM   #29
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hi everbody!

my BL-graded fets from china aren't arrived yet. it's taking 6 weeks now.
maybe they're hanging in the customs duty?

is there any possibility to use a pair of matched GR-graded types?
which changes would be necessary then?

thank you!

best regards,
matthias
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Old 21st January 2013, 08:29 PM   #30
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hi everybody!

my FETs arrived and Juma gave me all the needful tips to fire up my preamp.
now it was time to build the micro controlled things in it.

I didn't want to have any current through the relais-coils, so I bought some latching types with a single coil.
The latching relais are controlled by normal relais and a atmega 16.

I have 5 inputs and 2 outputs, you can rename them like you want to.
The 2x16 LCD is showing in/output status and some other things.
Selection is done by a alps encoder, if you turn the encoder, then choosing between in/ouput is possible.
Pressing the button of the encoder switches to the next menu.

When I switch to another in/output, then the normal relais get some power (for about 100ms), to switch the latching ones.
After that everything is "dead", only the audio-signal is floating through the wires...

I made a short video, sorry for the music, but the original-audio was much much harder to accept.

https://www.youtube.com/watch?v=Cb7x2WHxk-A

best regards,
Matthias

Last edited by GentryBa; 21st January 2013 at 08:32 PM.
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