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Old 4th November 2009, 06:21 PM   #151
Zigis is offline Zigis  Latvia
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Toshiba 2SK170BL for sales
see post 284
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Old 4th November 2009, 09:07 PM   #152
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Thanks Zigis, but I think they're all BL and I need GR.

Lucas
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Old 4th November 2009, 10:47 PM   #153
Zigis is offline Zigis  Latvia
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Hi Lucas,
you can try to ask him to find matched quad at 4-6mA, letters itself is not so important.

I am thinking about this too, my RIAA is with unmached jfets from ebay, audiable difference in channels volume, need to rebuild.

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Old 5th November 2009, 08:31 AM   #154
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Spencer says he has matched 6.8mA idss 2SK170-BL. What effect could I expect with those jfets? More gain overall, or would other anomalies be introduced?

Many thanks
Lucas
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Old 5th November 2009, 09:17 AM   #155
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Try bdent.com for 2sk170gr they don' t select for Idss so you'll have to buy extras - not cheap but that's the way it is.......

I have 2sk147GR (and 2sj72gr) but you don't want know what those would sell for .......

Last edited by ticknpop; 5th November 2009 at 09:23 AM.
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Old 5th November 2009, 09:20 AM   #156
Salas is offline Salas  Greece
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Quote:
Originally Posted by LucasAdamson View Post
Spencer says he has matched 6.8mA idss 2SK170-BL. What effect could I expect with those jfets? More gain overall, or would other anomalies be introduced?

Many thanks
Lucas
You can expect 7.6V at the drains, 51dB gain, and the curve in the attachment. The 6.8mA matched look pretty OK in this circuit. I used 30m beta in the sim for them. 51dB is good for 1mV cartridge.
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Old 5th November 2009, 01:05 PM   #157
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Quote:
Originally Posted by Salas View Post
You can expect 7.6V at the drains, 51dB gain, and the curve in the attachment. The 6.8mA matched look pretty OK in this circuit. I used 30m beta in the sim for them. 51dB is good for 1mV cartridge.

So Salas, are you saying I can go ahead and get the 6.8mA idss chips and not have to adjust other components values? Have you built this design, by the way? How do you get on with it? The schematic you have drawn shown here is a simplified version of what I am putting together:

(copyrighted image removed by moderators)

Many thanks
Lucas
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Old 5th November 2009, 01:47 PM   #158
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I haven't made the MadK but I am pretty sure that the simulator goes OK for what it shows. The other one you show its first time I see. Its a fully bjt cascoded and bjt cascode followed 2 stage jfet base cct with passive Riaa. Seeing the B+ and RLcollector values I should expect it to have the space for 0.8mA Idss more than the author gives as top ballpark value of 6mA. Again expect some more gain than stated if with 6.8mA which is obviously more than the 5mA average recommended on that cct. In case the collector voltages drop too much, you can always control the current and a bit of gain by rising R15 & R18 degeneration resistors. I would use 50R trimmers there instead of fixed resistors if in your boots, so to control it and match it easily for voltages between channels when with the stronger jfets.
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Old 10th November 2009, 11:23 PM   #159
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I had some problems with channel matching, even though the 4 JFETs were "matched" for Idss of 8mA. I solved it by putting a 100k trimmer pot at the output and matching the levels between the channels. Simple as that.

I don't know what impact it has on the sound, but I can't discern anything in listening.
Also, I'd like to say that this circuit is a beaut. Its pretty close a nice-sounding tube phono.

Salas, would you recommend 25 V supply with an Idss of 8ma?
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Old 11th November 2009, 12:46 AM   #160
Salas is offline Salas  Greece
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Tell me your cart, pre amp gain, main amp gain, speakers spl/2.83V 1m. Then I will tell you in detail. As you have it with 24V B+ and 8mA Idss, your Vds must be too low, your gain high, enough 2ndH, no means to match leveles between channels without Rs.
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