Simplistic NJFET RIAA

[Salas]

Originally posted by nicoch46
I use a mad_k with ska optvol ,good sound for me

I will try at first stage 170bl with 33r to ground for lower the second armonic dist.....
I will order more exotic part and report
this circuit are not so good for mm because have higth input capacitance near 300pf and no more 3-4mv at input ,Iuse denon dl-160 mc 1,8 mv

In my design to experiment with I included Rs trimmers and switchable cap bypasses so to listen for best sonic balance and gain, looks it will be practical since you mention degeneration.

Hmmm no feedback circuits can cost a fortune if looking for best parts to cook. I would do that in best tube RIAA, I don't know if the ''Pacific'' class is the ultimate circuit to throw big bucks in. Have to listen to a rather generic one with Wima caps first, to gauge its potential.

I looked for margins in my simulator, I gave it a bit better headroom for input, less current, big drain resistors and B+. But the 300pF + input cabling is really a problem except Grado MM. Miller bites there, it can be BJT cascoded though if destined for typical mm. I have in mind the Denon DL-160 too, just on a Technics 1200MKII and 1K input resistance.

[kevinkr]

Originally posted by salas



Now that's a decent one. SRPP to drive the properly impedance sized RIAA, BJT follower for output. Kevin you dropped in here to remind me of glass...
How does it compare to decent vacuum?

Not really sure as I have not heard it in an A/B situation. Given the designer's orientation to detail and serious listening tests I suspect it would be about on par with a middle of the road tube set up. (His tube stuff is very, very good.) Certainly better than most SS designs I've heard and more open sounding than the typical cookbook op-amp based implementation which it was intended to better. Results are very dependent on the amount of effort put into building it. (Jfet choice and matching, passives, layout, etc.)

[Salas]

Did some simulations, calculated some Zo, modified the RIAA for that, added an output buffer. Gives a lot of gain for 12mA IDSS. I have some strong BL ones. See where it gets in real life though.
One of my DIY friends has a very low 0.25mV Ortofon MC on a Walker turntable. We have modded a Steve Bench double 12AY7 cascoded by ECC88 schematic. It is input driven by Lundahl X20 step up. Sounds best so far after 4 other tube RIAA circuits. One was a Thorsten Loesch. I guess I will have to make the attached configuration and listen in that system VS the glass so to know where it stands.

[h_a]

@Bonsai: please post/mail me a link to the Dennis Collins schematic!! I would be very interested! Thank you!

Have fun, HAnnes

[nicoch58]

Hi Salas

I play with Rload , 3k close to much the sound , usally I like 23k , but in my system i think 8-15k range are optimal
(a switch // r for two setting, soft or racing )


Pacific+ dl160+P3 compete with last Pedja dac.....not so bad!!!

for me is exceptional result, this dac are nos , trafo have 7 separate seconday, psu all discrete regulator ,1541 are S2 ,no feedback,no output caps ,all quality component.....

[Salas]

Which resistor you refer as Rload? The drain resistor?

[Zoran]

This is good concept...
and it will be working better then any OP amp riaa
expetialu ones with feedback riaa circuit...
try to move the C1 and R9 from input of
Q2 to outout of Q1
in my tube riaa that was the move to linearise totaly db curve...
try to calculate propper passive netvork
You can use morgan jones example
(the very few are right...)
I am not shure for this one...
Use passive inverse riaa network for simulation
not only straght signal...
try haggerman inverse riaa
cheers
You will be amazed

[Salas]

I calculated (AES Lipshitz) the RIAA by subtracting the given input stage's Zout from R10//R5. That is why it looks a bit odd for values given it's displayed 36k input. I will have to check real life accuracy of course.
Had C1 where you suggest initially, and it was a 4.7uF. Then I saw some mods in the Pacific links that they moved it before Q2. Why is that exchange? They claim its for better.

*Can it be that in your tube RIAA the shunt was miscalculated and was changing the curve?

[nicoch58]

cartridge load

[Salas]

For Denon DL-160 some say 1k is good. Have you used 1k?