I noticed my JFET BOZ unit has pretty high gain as designeed in post #2 with 16V supply...any possibility to tweak the circuit to be used as a good phono stage?
Sorry if a lame question...
Sorry if a lame question...
Just finished reading entire thread.
Man! what a thread! From total OT to simple EE... thoroughly enjoyed.
Before I start tinkering with this circuit, I have just one question: Should I order matched JFETs or just bulk order them? These 2sk170s seem everywhere these days.
Man! what a thread! From total OT to simple EE... thoroughly enjoyed.
Before I start tinkering with this circuit, I have just one question: Should I order matched JFETs or just bulk order them? These 2sk170s seem everywhere these days.
Just bought 8 units of SK170 from Ebay and will commence matching and testing them, they are easy to match, whether I can really have enough matched pairs, I have to wait to see.
8 is not a lot, but if you are only searching for one pair I guess you'll find it. The jfet boz doesn't really need to be matched, unless you have a listening-room that is completely symmetrical... 😉
Would it be possible to add a step-down transformer onto to output of the original schematic, to lower output voltage and impedance?
Something like this Edcor XSM 2.5W transformer?
EDCOR - Browse Series
If this would work, which one would reduce the gain to around 6-10dB?
Something like this Edcor XSM 2.5W transformer?
EDCOR - Browse Series
If this would work, which one would reduce the gain to around 6-10dB?
Hi
I would like to build a new preamp. After making good results with a opamp preamp I now want to switch to discrete (and then to tubes 🙂).
Would it be a good idea to build a preamp with JFET-BOZ as 1st stage - pot - and B1 as second stage or bette as buffer?
I would like to build a new preamp. After making good results with a opamp preamp I now want to switch to discrete (and then to tubes 🙂).
Would it be a good idea to build a preamp with JFET-BOZ as 1st stage - pot - and B1 as second stage or bette as buffer?
I find BOZ is better without buffer. Less parts in the signal path! Add local feedback via a trimpot and you can dial in as much gain as you like and match left and right channels perfectly while lowering distortion at the same time.
Jfet BOZ with CCS load
Hi!
Did somebody try a CCS loaded Jfet as one in the attached image?
I'm looking to build a simple preamp with 23db gain (140mV RMS to 2V RMS) and tried in simulator several versions from this thread.
As far as simulation goes I was pretty satisfied with this: 2SK170V preamp but I was told to try it with an active load.
With ideas gathered from spencer's Jfet I/V converter I modified the Jfet BOZ to the one in the image. To the (little) knowledge I have about jfets this could work as Vds > 10V, Id ~10mA with an Idss 15mA device.
What is your opinion? Did it worth trying or I just waste my time?
If it's working what are the pros/cons of such a configuration?
Thanks!
Hi!
Did somebody try a CCS loaded Jfet as one in the attached image?
I'm looking to build a simple preamp with 23db gain (140mV RMS to 2V RMS) and tried in simulator several versions from this thread.
As far as simulation goes I was pretty satisfied with this: 2SK170V preamp but I was told to try it with an active load.
With ideas gathered from spencer's Jfet I/V converter I modified the Jfet BOZ to the one in the image. To the (little) knowledge I have about jfets this could work as Vds > 10V, Id ~10mA with an Idss 15mA device.
What is your opinion? Did it worth trying or I just waste my time?
If it's working what are the pros/cons of such a configuration?
Thanks!
Attachments
It can't be so difficult to build that you cannot answer your
own question. From your sim, I see about .1% thd, which
can't be too awful.
Why do you need so much gain?
😎
own question. From your sim, I see about .1% thd, which
can't be too awful.
Why do you need so much gain?
😎
Sure, but I will have the JFets only next week 🙂
I need that much gain for a passive I/V Dac End2 project, thus the SE jfet preamp to hope to have some tube warm sound 🙄
As my amp needs 1V for full output I might modify it to have 17db gain, but the specs will remain pretty similar.
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How it sounds will depend to a large extent on the quality of your power supply. You might experiment with different transistors in the CCS too. Theoretically all you want is high gain, but in practice, they do have a sound of their own. Try ztx1053's if you can get them.
power supply caps
I want to build the circiut .
Is the value of the power supply capacitors critical ? my spare bin has higher values .
Do I need to match the IDSS of the J310 ?
Thanks for the guidance
kp93300
I want to build the circiut .
Is the value of the power supply capacitors critical ? my spare bin has higher values .
Do I need to match the IDSS of the J310 ?
Thanks for the guidance
kp93300
I would use larger capasitors in the power supply(1000uF+), but the power supply capacitors are not critical.
You'll probably need a larger output capacitor, depending on the power amp you'll be driving and how much you enjoy the lower octaves(normal value is 10uF).
Also add a resistor to ground after the output capacitor (If you look at the initial Nelson Pass schematic, he used 2K2).
You don't need to match the J310's.
You'll probably need a larger output capacitor, depending on the power amp you'll be driving and how much you enjoy the lower octaves(normal value is 10uF).
Also add a resistor to ground after the output capacitor (If you look at the initial Nelson Pass schematic, he used 2K2).
You don't need to match the J310's.
Hi
many thanks for the reply. I hope to start this weekend!
I am using it to drive the F5 with an input resistance of 100K
kp93300
many thanks for the reply. I hope to start this weekend!
I am using it to drive the F5 with an input resistance of 100K
kp93300
That preamp was designed for F5 (Zin=101k) so 1uF is all that is needed in that case. For any other amp, as you say, requirements may be different.
Nelson used that 2k2 to lower the gain. We don't want that in this sch. so something like 1M will be OK if you don't put this preamp in the same case with the poweramp (as it was intended with F5).