Simplistic NJFET RIAA

[merlin el mago]

please read few posts back

what are your impressions with obbligato gold

I have several builds with obbligato gold... I like those a lot, sweet extended trebble, no harshness at all.

Same impressions, for me taste lacks a little bit of bass & mid-bass.

 

[RCruz]

For a more bass biased sound you can try 4.7uF 630V Ampohm Metallized Polypropylene Audio Capacitor Polypropylene Capacitors

Not as good as the obbligato (that are even better than the Mundorf supreme) but quite inexpensive

 

[Bksabath]

Sends me to #4945 alright.

4945 got it tanks

 

[RCruz]

Almost finished the second V12R for my new 57db cascoded "Wallis" build.... smooth

 

[Salas]

Wallis?

 

[RCruz]

I live in the Wallis Canton (More commonly known as "le canton du Valais")

 

[Salas]

Oh, didn't know, that was Ioannis Kapodistrias area of expertise.

 

[RCruz]

You never fail to amaze me.... Now I know a little bit more about swiss history

 

[RCruz]

I was doing some phono related stuff too. Was checking the bias for the experimental ones. I put the two stages together with the Riaa in between. Not too bad the sim models, they only showed 1V more load drop in the second stage. Gain was spot on. So I trimmed the values around it a bit to center the buffer best. It gave ~20 Volt peak to peak before compression started kicking in. I have noted the practical values in red, should be the same for all such example schematics discussed, they share the same second stage and B+. If choosing 7.5mA Idss Q5 & Q6, R11 can be 1.5K. Q3 can be a bit slack for exact Idss choice due to enough degeneration from R8 that takes it near 3.5mA. Looking for ~23V drop across R10 should be that stage's channel matching criterion.

After finishing the shunts I am now preparing myself to build this new toy.

For second stage cascode I have severall options:
R10 = 6200r with Vdrop=23V => Idq= 0.0037 so if Vgsq=0.141 => Rs = 38r
R10 = 6800r with Vdrop=23V => Idq= 0.0033 so Rs = 43r

Why not to use:
R10 = 5600r and Rs = 34r ?

 

[merlin el mago]

I live in the Wallis Canton (More commonly known as "le canton du Valais")

Parlez vous français?

 

[Rush]

DCB1 added to output

I found a drawing buried in this thread that showed a B1 cap coupled out, so I modified it.
See if this would work.
Question is where to break the ground as the supply for the B1 will also be used for my crossover or it could be from my Mesmerize which ever you think best. Now that I am thinking about it the Mesmerize is closer to the phono and may provide less chance of grounding issue.

Thanks Salas, maybe others will appreciate this exercise as well.

Rush

OK, received the caps, Mundorf 0.1 uF Silver and oil.
Took out the direct coupled JFET, added a 0.1 uF cap with 1 meg to ground on the RIAA board. Then ran to an out board DCB1 sub board and pulled power and ground from the Mezmerize B1 Buffer. I am not fretting about large caps anymore and no hum issues, sounds fantastic.
This is a must do, actually the Mezmerize B1 Buffer board could have double set of DCB1s before and after the volume as I have essentially done and it wouldn't hurt. Four JFETs are a lot cheaper than high quality, large value, coupling caps.

Thank you Salas,

Wonderful stuff!

Rush

 

[Salas]

Cool.

 

[Salas]

After finishing the shunts I am now preparing myself to build this new toy.

For second stage cascode I have severall options:
R10 = 6200r with Vdrop=23V => Idq= 0.0037 so if Vgsq=0.141 => Rs = 38r
R10 = 6800r with Vdrop=23V => Idq= 0.0033 so Rs = 43r

Why not to use:
R10 = 5600r and Rs = 34r ?

6800 & 43 worked precisely on my breadboard. 43 gives less THD than 34 is enough reason.

 

[RCruz]

Parlez vous français?

Oui... tout le monde le fait par ici

 

[RCruz]

6800 & 43 worked precisely on my breadboard. 43 gives less THD than 34 is enough reason.

Do we get more gain with 6800 ohm ?

 

[Salas]

Than 6200, 38? More or less the same.

 

[merlin el mago]

Oui... tout le monde le fait par ici

 

[RCruz]

I only trying to learn in the process of building.... In the breadboard with a 8mA K170, I get only 10.7V on the BF245C Drain... is that enough ? You posted we should get 12v there.

I am using a 6800 Rd and a 43 Rs

 

[Salas]

Yes its enough. The most it may do is you are bit better for gain. With my parts I got 12V. Maybe your BF245C opens your K170 a bit more than mine for Vds. Or our DMMs show IDSS little different for our K170.

 

[RCruz]

Nice.... It is a very good practice to experiment in the breadboard before actual implant

I am improving my methods with time.