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Old 11th January 2013, 12:47 PM   #1571
Telstar is offline Telstar  Italy
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Yes! Elma are my first choice. Used by goldpoint and not hard to find in Europe.
But those i found are with single pcb (per channel) with little spacing, for smd resistors. I'll look further (or get the pre-mounted one)
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Old 11th January 2013, 01:05 PM   #1572
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Yes! Elma are my first choice. Used by goldpoint and not hard to find in Europe.
But those i found are with single pcb (per channel) with little spacing, for smd resistors. I'll look further (or get the pre-mounted one)
Yours are stepped attenuators that have always a chain of resistors in the signal path. Mine only one resistor at each step. A couple of years ago I purchased the last two from a British distributor. They seem to be hard to find meanwhile and if you get some, they are quite expensive.

But have a look at these high grade attenuators from Poland: High Quality Audio & Industrial Attenuators and Passive Preamplifiers
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Old 11th January 2013, 02:20 PM   #1573
Telstar is offline Telstar  Italy
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Originally Posted by permaneder View Post
Yours are stepped attenuators that have always a chain of resistors in the signal path. Mine only one resistor at each step.
Mine? I have got none yet.
You mean a shunt attenuator, i plan something like that.

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But have a look at these high grade attenuators from Poland: High Quality Audio & Industrial Attenuators and Passive Preamplifiers
They had mixed quality issues, so I prefer to go with Elma.
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Old 11th January 2013, 05:30 PM   #1574
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Mine? I have got none yet.



They had mixed quality issues, so I prefer to go with Elma.
What kind of quality issues?
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Old 11th January 2013, 10:47 PM   #1575
Telstar is offline Telstar  Italy
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Search there is a thread in this forum.
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Old 12th January 2013, 08:41 AM   #1576
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Search there is a thread in this forum.
I have read the comments at Khozmo 48 position stepped attenuators.

Sounds good, at least in my comprehension...
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Old 12th January 2013, 09:40 AM   #1577
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Originally Posted by Michael Rothacher View Post
Do you mean a 10k volume pot? The effective input capacitance of the 2SK82 under L'Amp operating conditions was a couple thousand pf as I recall.
can i repeat my "newbie" question ? what is the effect of this input capacitance and how to cure it on the Sit ?
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Old 12th January 2013, 01:02 PM   #1578
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The effective input capacitance and the output impedance of whatever drives it form a low-pass filter with cutoff = 2*Pi*R*C

So, driving the SIT with a 600 Ohm source gives:

6.28 * 600 * 2E-9 = 133 kHz

And, for example, hanging a linear 50k volume pot on the input, set at 50%, gives:

6.28 * (600+12500) * 2E-9 = 6 kHz (which is hi-fi for humpback whales)

Last edited by Michael Rothacher; 12th January 2013 at 01:12 PM.
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Old 12th January 2013, 01:52 PM   #1579
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thanks michael i understand , so the 10K and 47K resistor loading the gate is not in the impedance calcul ? or perhaps for high pass with the coupling capacitor ? i understand but slowly
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Old 12th January 2013, 01:58 PM   #1580
Telstar is offline Telstar  Italy
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From Michael's calculation I get that a 1k pot would be ideal to not have HF rolloff.
My source is very low impedance so I could use a 1k pot, the problem being it unobtainium
Therefore i'll build a stepped attenuator taking advantage of the 10k (which i erroneously called inpout resistance) in it.
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