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Old 22nd December 2003, 12:38 PM   #1
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Default ono mc section

I have built the ono but the 2sk170s have Idss of 4mA each, sometime ago in this forum it had been stated that is too high and it should be about 2mA for proper working-.
One possibly solution is to increase Rs from 22R to 100R but this will increase the noise too and I have heard this change the high frequency response too.
Has someone affronted this aspect or not?
Giorgio
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Old 22nd December 2003, 02:20 PM   #2
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Default Re: ono mc section

Quote:
Originally posted by giolight
I have built the ono but the 2sk170s have Idss of 4mA each, sometime ago in this forum it had been stated that is too high and it should be about 2mA for proper working-.
One possibly solution is to increase Rs from 22R to 100R but this will increase the noise too and I have heard this change the high frequency response too.
Has someone affronted this aspect or not?
Giorgio
I do not see where the increased current through the 2K170 is a problem. But if it is, buy a sack of 2SK170's and match up some that have higher internal impedance from source to drain. The 2SK170GR may be what you need. I assume the parts you used are 2K170BL.
What is the measured DC drop across each 2SK170? For best performance somewhere around 10v is a good starting point.
I assume you need two pairs for the balanced input. I think have some spare GR's if you want to try some.

George
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Old 22nd December 2003, 03:36 PM   #3
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the problem is with the cascode that drives the four sk170. Maybe the GR could be good
I have 11v across the fet.
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Old 22nd December 2003, 05:38 PM   #4
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Giorgio,

I´ve got the same problem. There are two sollutions for this.

1. Try finding 2sk170 gr with lower Idss

2. Put the jumper over one of the 499R resistors. This will reduce gain by 4dB (6dB?) and the cascode will function as planned even with 4mA per fet.

Upping the source resistors really isn´t an option cause this also lowers the gain of this stage and raises noise at the same time.....

Another not very practical option would be to raise the voltage from 26 to above 30V.

At the moment I´m also using the second jumper (-10dB) and still have more than enough gain for my Benz L04 (balanced output used)

william
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Old 23rd December 2003, 12:27 AM   #5
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At least for some of you this might help, as they stock 2SK170GR.
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Old 23rd December 2003, 10:21 AM   #6
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I will keep the jumper because I cecked n.40 sk170 and I couldn't find anyone with lower idss.
I couln't open the link's HBarsche
Giorgio
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Old 23rd December 2003, 10:49 AM   #7
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It's a German parts supplier, you might try from the start: http://www.heho-elektronik.de/.
Go for ->"Katalog-Übersicht"->"Halbleiter"->"Japan-Transistoren".
I have no idea if they ship to Italy.
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Old 23rd December 2003, 11:14 AM   #8
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Quote:
Originally posted by giolight
I will keep the jumper because I cecked n.40 sk170 and I couldn't find anyone with lower idss.
I couln't open the link's HBarsche
Giorgio

If you are having trouble finding 2SK170GR let me know. I have a few spares.
They should run at lower current when subbed for the BL series.

George
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