Simplistic NJFET RIAA

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#5,902
An additional way to avoid some nasties would have been to wrap the input cascode so it will be referencing to earth than to PSU, surely good for EMI/RFI, don't know how far it would go for the off transient though, since its the 2nd stage & coupling caps also contributing.
 
#5,903
hello

just wondering...what is the output phase of the riaa pre?
is it shifted to 180 degrees?(if i guess right the signal colected from the drain of the second stage jfet is phase inverted to 180 degrees )
what consequence does this have? should i change the polarity of my speakers?
 
#5,904
As it's also mentioned in the PDF instructions, it does not invert. Its two gain stages and a follower. 2 inversions means back to 0, follower does not further invert. No issue. Just look to use the proper output capacitors value for your pre amp's input impedance.
 
#5,905
i found an article from nelson pass about matching mosfet and there are presented three ways to use if i can say so a mosfet(common source, common drain and common gate)
here is the article http://www.passdiy.com/pdf/mos.pdf check page two

common gate looks like first stage of the riaa, common source looks like the second and the last is common drain.he shows there which configuration inverts or not the signal

my knowledge about this is minimal if i can say so...but i`m trying to understand them not just to solder electronic parts.

i`ve read the pdf(your pdf about riaa) but the things you said the are a little bit in contradiction with what i found on that pdf(nelson one).is it right or i`m confused?

thank you
 
#5,907
We have 3 parts in this Riaa preamp. First is input stage. It is common source Q1 and has a transistor on top of it Q4 connected like common base to help it be less capacitive as it amplifies. That is called a cascode (telescopic type) and we take signal out of it. It still inverts phase as a whole because Q1 has done that and Q4 does not object. Second stage Q2 is again common source. It inverts again. Last Q3 is source follower (S pin goes to R7, the one called common drain in your link). We take signal from S pin. That does not invert, it just utilizes its might to lower the output impedance by magnifying current and not voltage. Mosfets can be loosely described as 'big jfets' if they are of the 'depletion' type. Meaning always on like jfets. The other much more common types 'enhanced' are off until a DC voltage is used to open them gates.
 
#5,908
a little bit more clear.i`ll do some more reading so i could better understand the ''problem''.

the configuration of the first stage got me into questions.looks very similar with common gate configuration from nelson`s pdf

thanks again for your quick and subjective response
 
#5,909
What is probably making you wonder, is that you see the signal source in common gate of Nelson's PDF where Q1 is in phono, and Q4 is the ''Mosfet'' in phono. Imagine Q1 as that ''signal source'' but it has already inverted what it got from the cartridge before, and Q4 follows for voltage phase as common gate in Pass's pdf.
 
#5,915
Salas said:
As it's also mentioned in the PDF instructions, it does not invert. Its two gain stages and a follower. 2 inversions means back to 0, follower does not further invert. No issue. Just look to use the proper output capacitors value for your pre amp's input impedance.
Click to expand...
I'm with Salas here. Most two stage or even stage active devices with leave no phase inversion. When using my BoZ I flick the speaker leads over (pos for neg) because BoZ has only one active stage.

But with most active devices there is generally a difference between current and voltage phasing (coming out of the device). This can 'tend to make the device look capacitive (current leads voltage) or inductive (current lags voltage). From my CD player to my speakers I have only three active devices and two inline capacitors and one OPT. And no negative feed back. The chance for phase differences with a simple system like this is generally lower than if you have many active devices in the signal path. What a friend once did was put more active devices in the path to correct for the phase slurring. He has since "chopped" his whole system down. Less IS more.
 
#5,918
yes this is right.the most important thing in all of this i think is the corect implementation of the parts(transistors, tubes, ic`s ).if you do it right i think then you will get good results. if not...probably you`ll get a big oscilator circuit or blow something up :d
 
#5,919
a friend of mine bought today a pair of 32 ohm headphones rated at 1.5w input power.i would like to make s surprise with building him a simple portable headphone amp.
saw somewhere one powered from 3.6v 1200mah lithium accumulator but was with bjt.
do you think 2sk170 will work at such a low voltage(3-3.7v)?
 
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