Look here lucas
click on that tiny down arrow near the thread numbers and go to page 271.
click on that tiny down arrow near the thread numbers and go to page 271.
i have read this and several other threads about the Pacific and some of its derivatives. A long time ago when it first appeared i was going to build it, but that didn't happen. I was about to start again, and realised the Idss of my 2sk170s are all around 12. Is it worthwhile continuing with these, or should i acquire a lower matched quad?
The original schematics did not specify the jfet grade, and that may be why some people really disliked it when they made it with higher Idss jfets?
The original schematics did not specify the jfet grade, and that may be why some people really disliked it when they made it with higher Idss jfets?
It is quite possible to make this with higher Idss JFETs. I have some at 8mA. You can play with supply voltage, load and source resistors. It will also depend on what gain you want for your cartridge and main amp.
Look back a few pages, Salas had some suggestions for higher Idss JFETs. You could also try his simplistic NJFET RIAA - Page 270, post 2706 from ikoflexer has the main pdf with the full design.
Look back a few pages, Salas had some suggestions for higher Idss JFETs. You could also try his simplistic NJFET RIAA - Page 270, post 2706 from ikoflexer has the main pdf with the full design.
i remembered that post, and tried to find it. Was that using 50R timmers on the second stage source to ground to adjust the output? Or did i miss it? I was going to go with 18V, 2k4 for R2 and R5 on your post 192, omir R3, R7 and R9, and slightly different RIAA values.
Will increasing the V (say 27V) increase the gain? my current cart has 0.5mV output, phono is stage is a Dyna Pas (40db) and it lacks gas for this cart running into a B1 buffer.
I have a feeling i will end up with something else in the end, but would like to start here.
Changing the supply V will change the gain and a lot of things. I experimented a lot with the values to get just enough gain and lowest distortion. For your case, the original pacific may work well. Just try some source resistors to add control to an otherwise zero feedback circuit. I would start with 5R. Too much source resistance and the sonic qualities start deteriorating.
If you give me a few hours, I can come up with some sort of circuit for your cart. But I think Salas will beat me to it. He is usually very helpful in these things (and much more knowledgeable than me
).
Also, changing the RIAA values will change the EQ that is needed. Also, the RIAA must have high impedance compared to the first stage.
I would not move very far away from this circuit. It is pretty damn good.
If you give me a few hours, I can come up with some sort of circuit for your cart. But I think Salas will beat me to it. He is usually very helpful in these things (and much more knowledgeable than me
). Also, changing the RIAA values will change the EQ that is needed. Also, the RIAA must have high impedance compared to the first stage.
I would not move very far away from this circuit. It is pretty damn good.
I was thinking of adding the 5R as it seems to be de-rigeur.
The values for the RIAA, i picked up somewhere along the way. They are not that different from what you have. R4 22.6k, R5 3.24k, R6 100k, C2 98n, C3 36n.
Did you ever try moving the coupling cap to after the RIAA?
And Mr. Salas, any advice is welcome.
Salas,
Since you are here, I will not even dare to talk. All yours mastah!!!
Besides, I don't think I can figure out how much gain he needs from the make of his amp. Maybe, I learn something new today.
Studeb,
I have not tried that. But I know that it is supposed to be superior. My pacific pre is still on breadboard. For now, I've settled on one with 16V, 2k2 for first stage and 24V, 3k for second, with 5R source resistors. Gives about .08% distortion, and not just that, it sounds so good that it is telling me to upgrade my cartridge. The input loading resistor is also a great tool for tuning the sound.
I have been trying different power supplies. Right now, I'm on batteries. I tried the lm317 regulator and it completely ruined the sound. Next thing to do is to switch to mains, with simple filtered supply and then the Salas shunt reg.
Oh btw, Salas, I traced the noise (hotness) I was referring to earlier in the pacific to the resistors I was using to drop battery voltage. I think once they got hot, they were generating noise. I tried using several in parallel (and then in series) and the bloody circuit started oscillating. Strange.
Since you are here, I will not even dare to talk. All yours mastah!!!
Besides, I don't think I can figure out how much gain he needs from the make of his amp. Maybe, I learn something new today.
Studeb,
I have not tried that. But I know that it is supposed to be superior. My pacific pre is still on breadboard. For now, I've settled on one with 16V, 2k2 for first stage and 24V, 3k for second, with 5R source resistors. Gives about .08% distortion, and not just that, it sounds so good that it is telling me to upgrade my cartridge. The input loading resistor is also a great tool for tuning the sound.
I have been trying different power supplies. Right now, I'm on batteries. I tried the lm317 regulator and it completely ruined the sound. Next thing to do is to switch to mains, with simple filtered supply and then the Salas shunt reg.
Oh btw, Salas, I traced the noise (hotness) I was referring to earlier in the pacific to the resistors I was using to drop battery voltage. I think once they got hot, they were generating noise. I tried using several in parallel (and then in series) and the bloody circuit started oscillating. Strange.
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Its easy. Say he has a 20W amp with 33dB of gain, B1, and 0.5mV cart. To fully swing his amp in 8 Ohm, he would need sqrt(20*8)=12.65V RMS.
Inverse Log(33dB/20)=44.7 times input. B1 has G=1, count it out. So, 12.65V/44.7=0.283V. Your proposed Phono stage should be able for such an RMS output so to fully drive it. 283mV/0.5mV cart = (log566)*20 = 55dB.
I'm going to give it a go.
Here's what I got from some really preliminary calculations. Gives you about 54dB gain. Pretty low distortion - 0.075% at 1k and not clipping at 20 Hz. Don't lower the source resistors below 5R, coz it will start clipping in the low frequencies.
I used the values you gave me for the RIAA and as you can see, it is within 1dB but not very flat. You may want to tweak those values.
Ideally, I'd say you need to hit the 500mV mark at 1k with respect to gain. I'm using the peak values to calculate gain (salas, correct me if I'm wrong). Guess you preamp/amp will have to do more work.
Here's what I got from some really preliminary calculations. Gives you about 54dB gain. Pretty low distortion - 0.075% at 1k and not clipping at 20 Hz. Don't lower the source resistors below 5R, coz it will start clipping in the low frequencies.
I used the values you gave me for the RIAA and as you can see, it is within 1dB but not very flat. You may want to tweak those values.
Ideally, I'd say you need to hit the 500mV mark at 1k with respect to gain. I'm using the peak values to calculate gain (salas, correct me if I'm wrong). Guess you preamp/amp will have to do more work.
