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Old 29th November 2012, 01:46 PM   #911
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Finished stuffing the boards and currently checking dc op points. As usual i jump into these GBs at the frenzy of the moment and only get to do some reading afterwards

Does anyone have an idea if converting this to a FET input is at all possible? Even at the expense of major surgery? The idea of an even small offset does not fill my heart with joy. Whilst it may not kill the cart, it will very likely cause some permanent magnetisation. What's even worse is that the trimming pot makes a mockery of my Shinkoh loading resistors, being effectively in parallel.

Sorry if this has already been discussed in the monumental MPP thread.
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Old 29th November 2012, 02:36 PM   #912
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Trimming has being discussed. You need a dummy resistor in the value of the DC resistance of your cartridge parallel to the loading resistor. Then trim the DC, take out the dummy resistor and connect the cartridge.
Yes, it can be transferred to Fet with major surgery but i would not recommend to do this with the Paradise boards.
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Old 29th November 2012, 02:50 PM   #913
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Thanks for the answer Joachim. Yes, i am aware of the trimming procedure. A major pain with multiple carts.

If at some stage you decide to publish an alternative take of the front end with K389/J109 per example i will be very grateful. And no doubt, so will be others.
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Old 29th November 2012, 03:20 PM   #914
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I have published MC input stages with J-Fets on the MPP thread.
One of the more successful ones was build by Sampler, our friend from Litunia.
When i find the time i will search for the schematic.
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Old 29th November 2012, 06:29 PM   #915
Ryssen is offline Ryssen  Sweden
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Package arrived today.Transisitors are not the same though,-25 vs -40
does it matter?
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Regards Åke
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Old 29th November 2012, 06:35 PM   #916
MiiB is offline MiiB  Denmark
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The 25-40 is HFe groups.
The work here has shown that the groups are not that well defined.. So if you can find good matches the groups are meaningless.
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Old 29th November 2012, 06:39 PM   #917
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And you can pack the lower Hfe ones in the mirrors without a problem.
They even work in the input stage although input DC offset will be a bit higher in proportion to the loss of Hfe. Can be dealt with just fine with the offset trim.
The only problem that remains is when you swap cartridges quite often that have a big difference in DC impedance. To fry a cartridge is unlikely though.
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Old 4th December 2012, 03:26 PM   #918
Max1410 is offline Max1410  Germany
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Unforunatly I bought for the R2 and R21-R28 (33 Ohm) and for the R107, R108 (47 Ohm) Vishay RN55C 1/10W is it enoght?
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Old 4th December 2012, 04:34 PM   #919
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The RN are military rated so in fact they can stand more wattage. I think they will do the job just fine.
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Old 4th December 2012, 04:48 PM   #920
studeb is offline studeb  United States
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RN55 are usually thought of as 1/4W in the DIY world
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