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Simplistic NJFET RIAA
Simplistic NJFET RIAA
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Old 11th August 2009, 12:55 PM   #2151
Salas is offline Salas  Greece
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Simplistic NJFET RIAA
Quote:
Originally posted by RCruz
Looking very good already.

Ricardo
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Old 11th August 2009, 08:13 PM   #2152
RCruz is offline RCruz  Switzerland
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Simplistic NJFET RIAA
Finalizing the new shunt layout to acomodate the big heatsinks.

Are the mosfets tracks too large... any RS issues ?

Ricardo
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File Type: pdf shunt evo 10.pdf (19.1 KB, 110 views)
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Old 12th August 2009, 12:50 AM   #2153
Salas is offline Salas  Greece
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Simplistic NJFET RIAA
Move the gate stopper resistors next to the gates, you have space. Better use star grounding.
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Old 12th August 2009, 04:21 PM   #2154
RCruz is offline RCruz  Switzerland
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Simplistic NJFET RIAA
Hi Salas

After several hours designing.... I hope you agree with this layout.
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Old 12th August 2009, 04:30 PM   #2155
AndrewT is offline AndrewT  Scotland
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no.
go to the shunt thread and look at the latest schematics.
They are laid out that way to help PCB designers.
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Old 12th August 2009, 06:07 PM   #2156
Salas is offline Salas  Greece
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Simplistic NJFET RIAA
Quote:
Originally posted by RCruz
Hi Salas

After several hours designing.... I hope you agree with this layout.
It will surely work. Its better than the previous one. With very short and twisted cables to the load. But what Andrew says is that if you are going to make a PCB, you can make it with nodes ready for ''remote sensing''. The benefits are, that the reference and driving circuit can ''sense'' and correct for the cable to the load impedance. That becomes more critical if you put the shunt in another box with a transformer, or even for vaporizing the short length if near. There is some benefit in perfection, if near the load just incremental, but you are to decide. Here is the remote sensing with 4 wires for the V1 shunt.
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Old 12th August 2009, 06:19 PM   #2157
RCruz is offline RCruz  Switzerland
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In this case I should connect four wires to the riaa ?
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Old 12th August 2009, 06:20 PM   #2158
Salas is offline Salas  Greece
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Yes, W1,2,3,4. They go to the same places on the riaa really, they just help the shunt to ''see'' the length and compensate, by returning to different points on it. If you gonna have it just next to the riaa board, the benefit is going to be small I remind you.
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Old 20th August 2009, 03:39 PM   #2159
RCruz is offline RCruz  Switzerland
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Just testing to verify if I can post here.
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Old 20th August 2009, 09:08 PM   #2160
urbano63 is offline urbano63  Italy
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Default newbie need help

Hello to all,
I built one channel of these 2 circuits:
Click the image to open in full size.
By net_urbano

Click the image to open in full size.
By net_urbano

the rectifiers diodes, the bulk C 10000uF, the shunt and the RIAA are together all on a single perforated board.
Before to build the second channell, for try, i connect the output of the riaa to a stax srm-313 headphone amplifier. What I hear in headphones is a very thiny music and a big hum. Reading the thread I saw that Thomo had a similar problem to mine and Salas suggested to measure some voltages because it is possible that last Q (buffer NJFET) has higher than calculated Idss and drops its Vd too much, Vg under its Vs, so it won’t work.
First of all I checked all the wiring, and all the parts are correctly oriented.
Than i measured some voltages:

Q5: VD = 17,7V; VS = 6,83V (OK?); VG = 6,80V (BAD);
Q3 BASE = 7,62V (OK?); Q3 COLLECTOR = 15,07V (OK; PSU = 24,6V)
Q1: VD = 6,96V (OK)

The Idss of Q5 is 9,7mA so i changed it with another one with Idss = 8mA but the problem remains the same. Big hum, no music. Q5 Vs is now = Q5 VG: 6,72V.

Can someone help me ?

Luca
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