Simplistic NJFET RIAA - Page 986 - diyAudio
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Old 5th June 2013, 09:00 PM   #9851
stajo is offline stajo  Sweden
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Should have known. Well I'm dusting of some old lathes to so whenever ready, bring it on so we can please the lesser gods with some music.
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Old 10th June 2013, 03:18 PM   #9852
AndrewT is offline AndrewT  Scotland
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Quote:
BC560C Fairchild to the left at hfe 630. 2SA970BL
The A970 shows a significantly higher Early voltage.
Does this parameter make any difference, significant or minor, in the performance of the pre?
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Old 10th June 2013, 04:59 PM   #9853
Salas is offline Salas  Greece
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Theoretically it is better to have higher Early for less THD but I don't know if it will be significant in practice at those signal levels. The Fairchild BC560C comes in high Hfe on the other hand which is desirable for less base modulation. So I designed in both options since it is easy so to can compare at a point for FFT when a build will be complete and final or find some subjective clue even.
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Old 11th June 2013, 01:16 AM   #9854
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Because its double mono you can up slightly that channel's PSU until it gets there. Is there same mV drop on all source to ground resistors for both channels input stage Jfets? This small difference should be either you got a bit stronger one there or its PSU is bit lower. Or leds bit higher.
I´ve had a few exams the last weeks, so I (literally) put all the diy gear under the bed for some time. When i fired the riia up again today and patiently fine tuned the psu, the test points were ok on both channels. Then I got sick of measuring and soldered on some connections to see if any sound came through. It sounds amazing! Sadly its night here, so I can only listen at very low levels. Still I can hear a lot of new details, and the bass is really coming through.

I´m also surprised by the lack of hum. Ok, it hums quite a lot when I turn up the volume, but I think its the same I already have from rf pick up due to long unshielded wires from the turntable. When I build a box for this, I need to connect the tone arm earth to the box, right? How about the signal earth?

Thank you Salas! This is really promising. I´ll probably rave some more tomorrow.
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Old 11th June 2013, 01:30 AM   #9855
Salas is offline Salas  Greece
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Up to a good start then. Congrats. Yes you will have to box it up in a way like in this pic I draw and stick the TT ground wire to a post in continuity with the main chassis. For now you can clip it to some earth line on the board.
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Old 13th June 2013, 08:27 PM   #9856
RCruz is offline RCruz  Switzerland
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Once again the importance of cart load strikes.... Searching for a low cost, wirewound pot to replace the expensive vishay metal bulk trimers I am fond of, I found this 534-5,0K - Präzisionspoti. 10 Gänge, 5,0 K-Ohm bei reichelt elektronik

An affordable precision 10k pot multiturn .... orderd two and today I implemented them and guess what... detail... loads of detail... bass precision and attack... outstanding.
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Old 13th June 2013, 08:30 PM   #9857
RCruz is offline RCruz  Switzerland
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Hi Salas... just found this strange schematic of the Sasa Cokic riaa where he loads the input tube with a riaa filter.... Would you please excuse the off topic and comment on the possibilities ?

I guess we have variable gain according to riaa slope.... is it a good idea ?

6moons audio reviews: DIY Sasa Cokic RIAA
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Old 13th June 2013, 08:54 PM   #9858
Salas is offline Salas  Greece
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What material is the resistive element in the precision Vishay pot? Wirewound?

Loading Riaa on upper side you may see in SRPP like with Nikitin solid state phonos. Not that unrelated to an anode Riaa on a pentode. Well, high impedance on one hand adds more noise and EMI susceptibility, also not so good in driving the second stage, but results to smaller capacitors physically on the other. Maybe the noise performance of the pentode as an input element already sets an SNR limit that preserving the head amp gain is preferable in a certain design. For headroom with MM and relying on a high ratio SUT for MC. Only the designer can give the whole story of his choices in reference to a concept he had.
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Old 14th June 2013, 07:42 PM   #9859
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I have to say it still sounds fantastic! I´m really impressed. Have to get it installed inside the turntable one of these days though. It´s too scary looking to have a permanent place in the living room for now. And kind of dangerous with some open mains as well.
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Old 14th June 2013, 08:04 PM   #9860
Salas is offline Salas  Greece
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That's all very well that it honors first impressions still. If to install in the TT see to make nice little shield cans for it. Did you listen at normal to high volume enough? What is the system it plays in? (Sorry if I had asked before and I don't remember).
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