Simplistic NJFET RIAA - Page 425 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th July 2010, 12:02 PM   #4241
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Quote:
Originally Posted by RCruz View Post
Well, the GND layout is the same as before and I did not have any hum with the v1.

With the v12 fullfilm I hear a slight hum when at full power and no signal in.

I guess the big caps are picking up from the nearby psu lines.

I believe it is a field because the hum is greatly reduced just by closing the riaa case lid
But the very V1 layout on its own board maybe had some tighter ground? But the lid surely is a strong sign you got to shield first.
  Reply With Quote
Old 30th July 2010, 12:03 PM   #4242
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Quote:
Originally Posted by SGregory View Post
Joao, What variant of the sk170 are you using? GR= 3-7 BL = 6-12, and V= 10-?. I was curios, if I could find the V variant it may eliminate the need for a buffer all together and still have a reasoably low impedance.
Don't eliminate the output buffer. Then your Zo will be second stage's load resistor no matter the current in that stage.
  Reply With Quote
Old 30th July 2010, 12:07 PM   #4243
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by RCruz View Post
I believe it is a field because the hum is greatly reduced just by closing the riaa case lid
I wonder if this is telling you that a flow and return of a circuit are separated creating a large loop area. That loop area then picks up the field and generates a voltage that you hear as hum.

LOOP AREA is critical in attenuating interference, both at source and at receiver.
__________________
regards Andrew T.
  Reply With Quote
Old 30th July 2010, 12:20 PM   #4244
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Hi AndrewT

Would you explain this LOOP AREA idea?

(flow and return of a circuit are separated creating a large loop area) ?
  Reply With Quote
Old 30th July 2010, 12:47 PM   #4245
diyAudio Member
 
Join Date: Apr 2003
Location: Southern Tier NY
I was going to eliminate the buffer. Would have to find a V variant first, which is like trying to find a Hens tooth.
__________________
Living Life Doing the Waltz in 4/4 meter.
  Reply With Quote
Old 30th July 2010, 12:47 PM   #4246
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
the circuit supplying power to your active amplifier arrives via two wires (dual polarity requires three wires).
The current from the PSU flows through one wire and returns via the other wire. That is what makes it a circuit, a circular route.

If the flow and return wires are separated then the loop area acts as a transmitting aerial sending interference out for any other circuit to pick up.
Minimise the transmitting loop area by keeping the circuit short helps, but this cannot be made infinitely short.
Twisting the two flow and return wires together has the effect of canceling the transmitted field for all other circuits that are a significant distance away, compared to the gap across the twisted pair.

A similar aerial effect occurs with input circuits. The Flow and Return must be closely coupled and preferably short to minimise the loop area between the wires forming the circuit. A bigger loop area will act as a more effective receiver aerial.

All electronics depends on circuits.They all have a flow and return route. The current must return to it's source, otherwise it is not a circuit. The layout design for all electronics should take account of the flow and return routes for effective interference attenuation and also for parasitic effect attenuation.
It is very possible that your V1.0 and V1.2 layouts (both PCB traces and external wiring) were implemented quite differently. If V1.0 performed well you need to replicate what was good about it's layout when implementing V1.2

LOOP AREA is critical.
__________________
regards Andrew T.

Last edited by AndrewT; 30th July 2010 at 12:55 PM.
  Reply With Quote
Old 30th July 2010, 12:51 PM   #4247
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
Quote:
Originally Posted by SGregory View Post
I was going to eliminate the buffer. Would have to find a V variant first, which is like trying to find a Hens tooth.
The only thing that a V will do is that it can run more current so to make the 2nd stage's drain load resistor smaller for same gain given the same B+. Still it will be kOhm. Without a buffer its too much. Done that, the buffer plays better. That is why there is buffer in Franz's although he used V all over.
  Reply With Quote
Old 30th July 2010, 01:05 PM   #4248
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Thank you Andrew.

V1 and V12 layout are very similar in my case.

I believe the big caps are picking extraneous fields. I will implement the mic wire and report
  Reply With Quote
Old 30th July 2010, 01:09 PM   #4249
Salas is offline Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
And by enormous size they widen the loop area.
  Reply With Quote
Old 30th July 2010, 01:14 PM   #4250
diyAudio Member
 
Join Date: Apr 2003
Location: Southern Tier NY
I need to read my posts better. That was suppose to say "I wasn't going to eliminate the buffer".

I want to build the circuit per your prescription. No modifications. Sorry for the confusion.
__________________
Living Life Doing the Waltz in 4/4 meter.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 02:08 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2