Gyrator loaded Son of ZV9/F3

If i want to put a coupling capacitor between input volume pot and R3...
No, you put it before the pot, with minus pin towards the gate. If you expect the DC voltage at the input you got to protect the pot too. Also, the JFET's gate must have a firm DC reference to GND so you shouldn't interrupt it with a cap. Or, you can add another 100k - 1M resistor between the JFET's gate and the GND so you can put put the cap wherever you like (as long as gate has a firm DC reference to GND).



Regarding the 470ohm gate stopper resistor,should i ommit it ithis case? i have already made space for the resistor in my small pcb.
As you wish - it doesn't make a difference in this case, as I already wrote.
 
Also, the JFET's gate must have a firm DC reference to GND so you shouldn't interrupt it with a cap......

I thought the gate was DC referenced to GND through resistors R1-R4 series combination so i wouldnt need 100k - 1M resistor between the JFET's gate and the GND to put the cap wherever i like.Do i still need that 100k - 1M resistor you suggest? My plan was to not use a pot at all but include an input 10u cap bypassed with 100n wima.
 

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While I wait to BF862 to arrive I was impatient and first redraw the schematic to me understanding way and then make minor changes to can work with BS170 instead of BF862.
I need voltage swing of ~12Vpp for SEWA preamplifier. I make this for rail supply of 48V, but when I finished the building realized that I have only 37.5V and changed the schematic again. I was intended get 13mA on source of BS170.
Now it works, on left channel have 13mA on right only 10mA. Looks like that I must put trimmer pot instead R5 to fine adjust.
I share this because I am very pleased how it sounds. I get little warming and softly sound. This is my best sounding preamplifier yet built. I was build Bridge of Zen and Apex Fet preamplifier which sounds very precise and clear but they have no softness what I hear with this preamplifier .
I do not have much knowledge about electronics, maybe I put some wrong values somewhere, so if somebody has better suggestions I will accept that.
I only wish to get warm, wide and soft sounding preamp.
Soon I'm intend going to do this same preamplifier with the j310 to see what's changing in the sound image.
Thanks Juma.
 
Gyrator Son of ZV9 for M2x IPS

Hi Juma,
I have a different application in mind for this circuit. I would like to have an input stage (IPS) with a small amount of gain for the M2x amplifier. I started working with the Bride of Zen circuit, then realized there was not practical way for this to drive the Edcor WSM 600:15k transformer that the M2 uses for its main voltage amplification. The gyrator loaded circuit that you have described in post #24 of this thread seems much better suited for this application.

I have attached a modified version of the gyrator loaded Son of ZV9 that I would like to try as an IPS module for my M2x. I have made transistor substitutions based on what I have available, and what might handle the higher power supply voltage in this application. This circuit just barely fits in the space that is available for the IPS boards. The main board has a 1k input resistor followed by a 100k shunt to signal ground, so I omitted that in the IPS circuit. I also omitted the output load resistor, as the Edcor transformer already represents a heavy load. I figured the ZVN3310A would be more capable of driving the transformer, but I have a small number of BS170 Mosfets if necessary. I have also substituted a trimmer resistor in place of the 68k to allow adjustment as necessary. I am hoping for a gain of about 6 dB, which will be added to the 14dB of the autoformer configuration.

Does this look like a reasonable adaptation?
Thank you,
James
 

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Perhaps my wording was not clear. I was hoping that my schematic would indicate what I was planning to do.
In place of the BF862, I would like to substitute a 2SK170 JFet. I have some genuine Toshiba parts in the 10mA range for Idss. The BF862 is very difficult to build with, so I am hoping that the K170 will be a reasonable replacement. I also have some Linear Systems PN4416 and J309 devices available if those would be a better match for this circuit. I can probably sort a few parts to get some in the 10mA range.
I wanted to use the ZVN3310 in place of the BS170. The Zetex part has similar Gate-Source threshold, similar Transconductance, with higher current and power dissipation. I was hoping it would provide better drive into the Edcor transformer.
 
Hi Juma,
I played a bit with LtSpice trying remove 3k3 and 47uf, (I thinks this is some feedback, or voltage divider for signal) and came to idea put serial resistor in signal path to a gate of first upper BS170 as is on picture. I got in FFT view most second harmonics, half of 3.harmonic and so on. In original schematic all harmonica are mostly same.
Please can me tell is it good or bad idea, and why ?
 

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I finally built the gyrator with lat fets post #164 after making pcbs and sitting on them for over a year. The pcb is the same size as an F5. I mounted them on 300mm U4 heatsinks for testing. The preamp is the one from post #1. The single supply was about 37 VDC, about 15 W, at 1 A bias, going into 8 ohm speakers. I used Profusion lat fets, and I had a bunch of BF862s left over. The sound is similar to my cubie 3, which says a lot. It is clean and nice; I have no complaints. I listened to my whole music collection again, if that means anything. I would be very happy using these. Seriously, this amp is so simple and sounds so good, I am surprised more people do not build it. Thank you juma for another wonderful design. Of course, I see now that juma has come out with a couple more amp designs that are simple...and beg to be built...will it ever end? :D
 

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You want J310 with occasional BJT to deliver clean and high voltage swing to drive the unity gain power amp - it's a no go here; J310 can not easily replace neither BF862 nor BS170 in this circuit, it's too different.

It would have to be a whole new circuit and I would have to build a prototype to test it. I could do it on commission but it would cost you much more than few pennies for appropriate parts. :D
Actually, for your needs, this (see attachment) is safest bet, stick to it ; #24 is too specific, no fooling around with it.
In attached circuit, you can use J310 instead BF862, but R14 should be 220R or so (for Id of 10mA or so), R20 should be 22k or so, and R27 should change to 56k. It will sound different, try it to find out if you like it
4 years later...
I built this preamp. It is still in test phase, I have just assembled it. A few remarks/differences:
I used J310 jfet, Source resistor : 204 ohm (3x68 ohm in series)
R20 changed to 22k
R27 chanhed to 56 k
Power supply: Old printer smps 32v, with a cap multiplier, like in post nr. 1
I added some 27 ohm resistors in series with the posititive supply, and some caps after. Can't hurt. I measure voltage drop across these. One channel has a voltage drop of 230 mV, while the other one around 300mV.
Is it normal for two J310 jfets to have such a different Id?
I will write more when I finish/test it...
 
Thanks Juma.
Now I am wondering whether I should match the two Jfets, or I may leave them just as they are...
But I have to test it first, I assume ot will work :)
Another possibility is to replace the J310 with K170, I have some of them, but... Grrr, they are GR type (maybe put 3 of them in parallel).
Anyway, I will see how it goes, and will post about the progress here...