Help! A RIAA expert wanted!!!!!!

jeepy · 13th December 2011, 04:05 PM

Hi,
I would like to know what the incidence on the curve would be if i use 4.9nf (2 in //) instead of 5 nF in an active RIAA stage. Since I cannot fin the recommended values 5nf and 1.5 nF (polsytyrene 1 or 2.5%).
Many thanks,

kevinkr · 13th December 2011, 04:27 PM

You should trim the values by adding much smaller caps in parallel. Let's say that your 4.9nF actually measured 4.8nF and you need 5nF, then a measured 200 - 220pF cap would be placed in parallel to get as close as possible to the required value.

In fact the closest standard value is likely 4.7nF, so measure its value and chose a small cap (maybe a 300pF to 470pF depending on what you measured) in parallel.
Do the same thing for the 1.5nF, possibly a 1.2nF//270 - 330pF as an example.

100pF is a small, but significant error out of 5nF.

jeepy · 13th December 2011, 05:00 PM

Quote:

Originally Posted by kevinkr

You should trim the values by adding much smaller caps in parallel. Let's say that your 4.9nF actually measured 4.8nF and you need 5nF, then a measured 200 - 220pF cap would be placed in parallel to get as close as possible to the required value.

In fact the closest standard value is likely 4.7nF, so measure its value and chose a small cap (maybe a 300pF to 470pF depending on what you measured) in parallel.
Do the same thing for the 1.5nF, possibly a 1.2nF//270 - 330pF as an example.

100pF is a small, but significant error out of 5nF.

It is time for me buy a capacitance (or LCR meter)! I agree with your comments! But How do I know if the designer of the circuit did not use 'close values himself: 1.5 and 5nF in this case)? Let's imagine the computed value was 4,9 and the guy had 5nF on the shelf. Well the 'guy' is Akihiko Kaneda!
Sorry for my English!

cliffforrest · 13th December 2011, 05:07 PM

Well done so far, and your English is fine!

You need to look up and study how a parallel C and R relates to a "pole" in the frequency response, and a "time-constant" in the time domain. These are two different ways of looking at the same thing.

Google "theory of RIAA response", "time constants" in analog circuits.

A bit of study and it will "click" Eureka!

Keep asking questions! No questions are foolish, but some answers are

jeepy · 13th December 2011, 05:26 PM

Quote:

Originally Posted by cliffforrest

Well done so far, and your English is fine!

You need to look up and study how a parallel C and R relates to a "pole" in the frequency response, and a "time-constant" in the time domain. These are two different ways of looking at the same thing.

Google "theory of RIAA response", "time constants" in analog circuits.

A bit of study and it will "click" Eureka!

Keep asking questions! No questions are foolish, but some answers are

Do you mean that I can' 'easily' calculate or check the values by myself? Do the output stage characteristics has an influence on the values of the RIAA
network?

cliffforrest · 13th December 2011, 05:52 PM

Yes, the feedback network (Series R//C) has a particular impedance at any particular frequency. Long way is to do a 1/(2 Pi f C) for each Cap. Quicker is to learn how to use a simulator :-)

So the network can be modelled as an impedance or "resistor" for that frequency, which, in combination with the 1.2K input resistor gives a certain gain. As the frequency varies, so does the gain. Following a curve which was defined by the RIAA ...

Read, Study ...

jeepy · 13th December 2011, 05:58 PM

Quote:

Originally Posted by cliffforrest

Yes, the feedback network (Series R//C) has a particular impedance at any particular frequency. Long way is to do a 1/(2 Pi f C) for each Cap. Quicker is to learn how to use a simulator :-)

So the network can be modelled as an impedance or "resistor" for that frequency, which, in combination with the 1.2K input resistor gives a certain gain. As the frequency varies, so does the gain. Following a curve which was defined by the RIAA ...

Read, Study ...

Yes dad!

cliffforrest · 13th December 2011, 06:21 PM

That is unnecessarily offensive - so go and wipe your own bottom.

No smiley

jeepy · 13th December 2011, 06:38 PM

Quote:

Originally Posted by cliffforrest

That is unnecessarily offensive - so go and wipe your own bottom.

No smiley

So you can see that my English is bad! Sense of humour is very different depending on countries. Here is Switzerland it is a friendly way to say that we agree but we not happy to do what we have to do! Just kidding you say? Sorry for that.

cliffforrest · 13th December 2011, 07:19 PM

My bad, as they say. Apologies to you for over-reacting.

Now - get on with your studies!!

13th December 2011, 04:27 PM	#2
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	You should trim the values by adding much smaller caps in parallel. Let's say that your 4.9nF actually measured 4.8nF and you need 5nF, then a measured 200 - 220pF cap would be placed in parallel to get as close as possible to the required value. In fact the closest standard value is likely 4.7nF, so measure its value and chose a small cap (maybe a 300pF to 470pF depending on what you measured) in parallel. Do the same thing for the 1.5nF, possibly a 1.2nF//270 - 330pF as an example. 100pF is a small, but significant error out of 5nF. __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

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13th December 2011, 05:07 PM	#4
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	Well done so far, and your English is fine! You need to look up and study how a parallel C and R relates to a "pole" in the frequency response, and a "time-constant" in the time domain. These are two different ways of looking at the same thing. Google "theory of RIAA response", "time constants" in analog circuits. A bit of study and it will "click" Eureka! Keep asking questions! No questions are foolish, but some answers are

13th December 2011, 05:52 PM	#6
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	Yes, the feedback network (Series R//C) has a particular impedance at any particular frequency. Long way is to do a 1/(2 Pi f C) for each Cap. Quicker is to learn how to use a simulator :-) So the network can be modelled as an impedance or "resistor" for that frequency, which, in combination with the 1.2K input resistor gives a certain gain. As the frequency varies, so does the gain. Following a curve which was defined by the RIAA ... Read, Study ...

13th December 2011, 06:21 PM	#8
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	That is unnecessarily offensive - so go and wipe your own bottom. No smiley

13th December 2011, 07:19 PM	#10
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	My bad, as they say. Apologies to you for over-reacting. Now - get on with your studies!!