oscillation fixed
i went back to using source resistors, since it seemed like a good idea. i kept the original 22 ohm values, but i put an additional 25 ohm resistor in parallel for a net value of around 12 ohms (to compensate for the lower Idss of the GR devices i'm using - too bad i can't get V's!). however, i still saw the oscillation when hooked up to my power amp (i'm assumming it has an RC input filter or something, my cable capacitance is probably a couple hundred pF at most)... so i put some 25 ohm resistors in series with the output, just before the coupling caps, and voila, no more oscillations... i guess decoupling resistors are a good idea in any circuit with feedback. ok, time to do some listening tests now...
p.s. mirlo, i already have 1k gate resistors, so i don't think that should be an issue. i may still play w/some compensation techiques though, although it isn't strictly necessary w/the coupling resistors.
i went back to using source resistors, since it seemed like a good idea. i kept the original 22 ohm values, but i put an additional 25 ohm resistor in parallel for a net value of around 12 ohms (to compensate for the lower Idss of the GR devices i'm using - too bad i can't get V's!). however, i still saw the oscillation when hooked up to my power amp (i'm assumming it has an RC input filter or something, my cable capacitance is probably a couple hundred pF at most)... so i put some 25 ohm resistors in series with the output, just before the coupling caps, and voila, no more oscillations... i guess decoupling resistors are a good idea in any circuit with feedback. ok, time to do some listening tests now...
p.s. mirlo, i already have 1k gate resistors, so i don't think that should be an issue. i may still play w/some compensation techiques though, although it isn't strictly necessary w/the coupling resistors.
Hi dorkus,
Sorry if everyone has been asking you this, but any word on the website for this project?
Cheers,
Mark
Sorry if everyone has been asking you this, but any word on the website for this project?
Cheers,
Mark
hi mark,
yeah... website... right... i was supposed to work on that. 😛
i have space set up for it and all but have been too lazy as of yet to put anything up... i'm a programmer/web dev by day so the last thing i want to do when i get home is more HTML... but hopefully when i get to the next stage of the project i will have an abundance of material and a little motivation to put somethign up. stay tuned...
yeah... website... right... i was supposed to work on that. 😛
i have space set up for it and all but have been too lazy as of yet to put anything up... i'm a programmer/web dev by day so the last thing i want to do when i get home is more HTML... but hopefully when i get to the next stage of the project i will have an abundance of material and a little motivation to put somethign up. stay tuned...
sounds better w/o oscillation...
with the output coupling resistors, it is sounding very good again. i don't think it was oscillating too much when i first rigged it up with 22 ohm source resistors, but the resistors are definitely necessary with the 12 ohm values i have now. the sound is even better i think, cleaner and less forward, and still DEAD quiet... if i stick my ear on top of my tweeter i think i can hear a tiny bit of noise but i can barely tell. it is still a little flat for my tastes, soundstaging could be deeper and the overall presentation could be more "organic" and rounded (still sounds like active circuitry), but maybe with better parts and layout i could alleviate these things.
so, what now? maybe work a little gain in with the Borbely SE line stage design? i'm also curious to compare to try this JFET follower as a buffer after an IC opamp (AD825, AD8610), and see how that compares to a discrete design. let's see some votes on what i should work on next.
with the output coupling resistors, it is sounding very good again. i don't think it was oscillating too much when i first rigged it up with 22 ohm source resistors, but the resistors are definitely necessary with the 12 ohm values i have now. the sound is even better i think, cleaner and less forward, and still DEAD quiet... if i stick my ear on top of my tweeter i think i can hear a tiny bit of noise but i can barely tell. it is still a little flat for my tastes, soundstaging could be deeper and the overall presentation could be more "organic" and rounded (still sounds like active circuitry), but maybe with better parts and layout i could alleviate these things.
so, what now? maybe work a little gain in with the Borbely SE line stage design? i'm also curious to compare to try this JFET follower as a buffer after an IC opamp (AD825, AD8610), and see how that compares to a discrete design. let's see some votes on what i should work on next.
How about this for an active circuit? http://www.psyber.com/~dibsed/CIRCATS/je-990.pdf
Boulder gain stage?😉
Boulder gain stage?😉
cool
ah, the Jensen opamp... i wonder how it compares to the Forsell and Borbely designs. of course, the big difference is that the Jensen is bipolar... so we may end up with the JFET vs. bipolar camps going head-to-head. i'm acutally ambivalent, i'll take whatever sounds best w/o being too much of a pain to implement properly.
my JFET buffer is doing ok, but the lowest bass is a tad flabby possibly due to the black gate cap. it also still has a little bit of that electronic sound signature that most any active circuitry tends to have (that's why we like passive preamps so much), but it is not bad at all. maybe with better parts it'll be more transparent.
ah, the Jensen opamp... i wonder how it compares to the Forsell and Borbely designs. of course, the big difference is that the Jensen is bipolar... so we may end up with the JFET vs. bipolar camps going head-to-head. i'm acutally ambivalent, i'll take whatever sounds best w/o being too much of a pain to implement properly.
my JFET buffer is doing ok, but the lowest bass is a tad flabby possibly due to the black gate cap. it also still has a little bit of that electronic sound signature that most any active circuitry tends to have (that's why we like passive preamps so much), but it is not bad at all. maybe with better parts it'll be more transparent.
lowest bass is a tad flabby possibly due to the black gate cap
Probably not...... What kind of power supply are you using? From what I have heard the Jensen discrete op amp is not that special.
I have seen the schematic and I was not that impressed with the design.
Probably not...... What kind of power supply are you using? From what I have heard the Jensen discrete op amp is not that special.
I have seen the schematic and I was not that impressed with the design.
harry, it's the simple pass-MOSFET regulated supply in my power supply thread. i think it is ok, but you mayhave a point about a PS problem... the cable connection between the ps and the circuit is too long and skimpy (3-wire 18 gauge braid, about 3 feet long) so that could be screwing up the bass. i had it that way for prototyping purposes but i should probably replace it with shorter heavier cable. i suspect that may help.
attenuator + active stage
since it's related, check out my latest comment in the Attenuator thread:
http://www.diyaudio.com/forums/showthread.php?postid=115489#post115489
the MSB preamp i'm using sounds very very good and could be a good active stage/attenuator solution to investigate.
since it's related, check out my latest comment in the Attenuator thread:
http://www.diyaudio.com/forums/showthread.php?postid=115489#post115489
the MSB preamp i'm using sounds very very good and could be a good active stage/attenuator solution to investigate.
- Status
- Not open for further replies.