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Simplistic NJFET RIAA
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Old 18th April 2018, 10:51 PM   #17091
Salas is offline Salas  Greece
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Quote:
Originally Posted by Pars View Post
I took some measurements:
They compute. Can you remind what is your Q5 and Q6 IDSS?
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Old 18th April 2018, 10:56 PM   #17092
Salas is offline Salas  Greece
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Quote:
Originally Posted by Pars View Post
One other thing I didn’t mention, but my workbench is 3 feet or so from my house electrical panel. It always has seemed noisy; scope probes go crazy when not connected to a ground, etc. I should try this somewhere away from this area...
A very possible hum culprit that electrical field nearby source or there is some oscillation with the third party supply and this load so check the rail is thin, steady & flat, free of riding AC patterns.
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Old 19th April 2018, 02:09 AM   #17093
Pars is offline Pars  United States
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Quote:
Originally Posted by Salas View Post
They compute. Can you remind what is your Q5 and Q6 IDSS?
Code:
ref des	type	1	2
Q1	2SK369BL	12.41	12.41
Q2	2SK369BL		
Q3Z	2SA970BL	657.1	655.6
Q4	2SK170BL	8.37	8.34
Q5	2SK170BL	7.77	7.78
Q6	2SK170BL	8.37	8.56
Q7	2SK117GR	5.69 	5.71
When I posted them initially, you agreed

this is a 5mV MM configuration with 90.9R R2, 5.6K 1W R13, 1.82K R4, and using the PRP 6.754K R5.

I'll try to bring the board and the Fluke up to the kitchen on Saturday and see what the mV AC reads there.
Best,
Chris

Last edited by Pars; 19th April 2018 at 02:32 AM.
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Old 19th April 2018, 11:46 PM   #17094
joztom is offline joztom  Slovenia
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It is impossible to measure AC with any digital instrument like my Fluke 17b. You need old fashioned analog instrument for this purpose or finding any oscillation.
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Old 20th April 2018, 12:04 AM   #17095
joztom is offline joztom  Slovenia
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I am just finishing my own construction RIAA with MC/MM pincode switch, all discreet transistors 2SC2244/2SA970, with servo nulling, two stages passive RIAA filtering. I will inform you about final measurements.
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Old 20th April 2018, 12:28 AM   #17096
Salas is offline Salas  Greece
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This is out of topic here. Open a thread for it.
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Old 20th April 2018, 01:31 AM   #17097
anatech is offline anatech  Canada
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Hi Joztom,
Quote:
It is impossible to measure AC with any digital instrument like my Fluke 17b. You need old fashioned analog instrument for this purpose or finding any oscillation.
Buy a new bench meter from Kiethley, Fluke or Keysight. Fluke really does their best work with hand held meters.

Analogue meters generally do not have the frequency response needed to do much over 400 Hz. The wideband meters use a "true RMS converter chip", same as the digital meters do (HP 3400 - excellent meter). For even higher frequencies I'll go to my HP 437B witch is good to GHz and is digital, or my 436B - same response. If you're talking about a VTVM, you have to check them. Newer digital bench meters are better though.

You can't make general comments like you did. They are often not true.

About your last post ...

This is out of topic here. Open a thread for it.


-Chris
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Old 20th April 2018, 01:30 PM   #17098
joztom is offline joztom  Slovenia
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Excuse me for disturbing. In any case analog meters are much better for measuring oscillations, last 40 years I always use digital meter for exact DC and analog for possible AC oscillations together by any start of new project.
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Old 20th April 2018, 02:07 PM   #17099
anatech is offline anatech  Canada
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Hi Joztom,
Quote:
In any case analog meters are much better for measuring oscillations,
We'll agree to disagree then. I normally use a spectrum analyser for that job. About the only thing an analogue meter does better than a digital one is to show trends. However, if you look at the current Keysight meters (and a few others), they have addressed that in their DVMs. I like using analogue meters for some things. However, they are no longer better than a digital meter at all. About the only meter I don't have right now is an HP 3400. I would like one for sane money, just because.

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Old 20th April 2018, 10:12 PM   #17100
joztom is offline joztom  Slovenia
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Spectrum analyser cost a lot, it is not for DIY scene. I have Fluke 17 DVM, Phywe analog instrument for fast detecting oscillations at first start, HP1701B oscilloscope (old battery type for Boeing servicing). For calibration and measuring 3-way analog filters is analog instrument the law.
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