Thanks Calimero! The best person to comment on the sound is moamps, as he designed and built the original circuit. I don't yet have any 2SK389 on hand to comment, but I expect it is quite special.
The wiki "preorder" will go on for about a week and a half more, and then payments for a week after that.
The wiki "preorder" will go on for about a week and a half more, and then payments for a week after that.
tiroth said:
Hi,
IMHO, a discrete OPAMP sounds better than ordinary OPAMPS like TL, NE, OPA .... This opamp (the term itself might be misleading in a way, though) has a small open loop gain, small bandwith and relatively high THD (0.02%). But, it has only two stages and works in class A. I reckon this would suffice for this particular application.
OPAMPS with high bandwith, high open loop gain, minor distortion remind me of many 1970s amps - great specifications and crapy sound.
I haven't tried OPA 627 and AD8065.
(too many zeros in specifications, I don't need an XVGA buffer
)Regards
Well actually.............
"The best person to comment on the sound is moamps, as he designed and built the original circuit."
Nelson Pass actually designed the topology and provided some implementation help for those who want to build such a circuit.
http://www.passdiy.com/pdf/diyopamp.pdf
While a bipolar second stage is great for repeatability for fixed bias resistor values, I wonder if the mosfet second stage might sound better for those willing to adjust the circuit for different values for the gate to source turn on voltage for the mosfet. maybe not practical for a production circuit, but not to hard for DIY small quantiities.
"The best person to comment on the sound is moamps, as he designed and built the original circuit."
Nelson Pass actually designed the topology and provided some implementation help for those who want to build such a circuit.
http://www.passdiy.com/pdf/diyopamp.pdf
While a bipolar second stage is great for repeatability for fixed bias resistor values, I wonder if the mosfet second stage might sound better for those willing to adjust the circuit for different values for the gate to source turn on voltage for the mosfet. maybe not practical for a production circuit, but not to hard for DIY small quantiities.
I wouldn't.............
"good combinations also are:
ZTX450/550"
I think you will find stability a real issue. The Zetex are really more a medium power transistor rather than a small signal amplifier type. I have been burned like this before and am pretty sure the Zetex will require much different high frequency compensation. Mr. Pass uses a
2N4290 in his DIY op amp article. I think the 2SA970 and 2N2240 would be a good bet also and widely used for audio circuits.
http://www.passdiy.com/pdf/diyopamp.pdf
"good combinations also are:
ZTX450/550"
I think you will find stability a real issue. The Zetex are really more a medium power transistor rather than a small signal amplifier type. I have been burned like this before and am pretty sure the Zetex will require much different high frequency compensation. Mr. Pass uses a
2N4290 in his DIY op amp article. I think the 2SA970 and 2N2240 would be a good bet also and widely used for audio circuits.
http://www.passdiy.com/pdf/diyopamp.pdf
Frog licking?
Elso........... I assume you are funning us. With in the limitations of a reasonably low closed loop gain and driving reasonable impedances, >5K or so and reasonable cable capacitance, the circuit will work fine. One could lower the drain load resistor and increase the jfet bias current or even cascode the jfets if one wanted less input capacitance.
The only thing I might add is a small output resistor to isolate cable capacitance a bit.
My wife's Miata can't pull a large trailer and doesn't have cruise control, but it is still fun to drive. You haven't been licking the natural hallucinogenic secretions off that blue frog by any chance?
http://itotd.com/index.alt?ArticleID=34
PS what are you doing in Papua, New Guinea?
Elso........... I assume you are funning us. With in the limitations of a reasonably low closed loop gain and driving reasonable impedances, >5K or so and reasonable cable capacitance, the circuit will work fine. One could lower the drain load resistor and increase the jfet bias current or even cascode the jfets if one wanted less input capacitance.
The only thing I might add is a small output resistor to isolate cable capacitance a bit.
My wife's Miata can't pull a large trailer and doesn't have cruise control, but it is still fun to drive. You haven't been licking the natural hallucinogenic secretions off that blue frog by any chance?
http://itotd.com/index.alt?ArticleID=34
PS what are you doing in Papua, New Guinea?
Re: Frog licking?
Fred, No I am not funning but maybe I am raising the bar too high.....I have built circuits with the 2SK389.....I have an idea how it sounds but not how it measures. Nelsons article is a nice appetizer, but only a start.
I did not lick the blue frog or I would be dead by now. Yes you used the right icon: cannotbe. The blue frog is known for its arrow point poison. What I am doing in Papua New Guinea? Collecting frogs perhaps?
Fred Dieckmann said:Elso........... I assume you are funning us. With in the limitations of a reasonably low closed loop gain and driving reasonable impedances, >5K or so and reasonable cable capacitance, the circuit will work fine. One could lower the drain load resistor and increase the jfet bias current or even cascode the jfets if one wanted less input capacitance.
The only thing I might add is a small output resistor to isolate cable capacitance a bit.
My wife's Miata can't pull a large trailer and doesn't have cruise control, but it is still fun to drive. You haven't been licking the natural hallucinogenic secretions off that blue frog by any chance?
http://itotd.com/index.alt?ArticleID=34
PS what are you doing in Papua, New Guinea?
Fred, No I am not funning but maybe I am raising the bar too high.....I have built circuits with the 2SK389.....I have an idea how it sounds but not how it measures. Nelsons article is a nice appetizer, but only a start.
I did not lick the blue frog or I would be dead by now. Yes you used the right icon: cannotbe. The blue frog is known for its arrow point poison. What I am doing in Papua New Guinea? Collecting frogs perhaps?
Moamps, Fred,
thanks for the input. I usually substitute parts wildly (and widely) but on this one I'd like it to work w/o too much fiddling , that's why I asked. For instance I also have a lot of J309 lying around that could potentially work for the input stage but here I prefer to just buy the 2SK389 and be over with it. Too many questionable compromises in my circuits already (and they always look like spaghetti).
thanks for the input. I usually substitute parts wildly (and widely) but on this one I'd like it to work w/o too much fiddling
, that's why I asked. For instance I also have a lot of J309 lying around that could potentially work for the input stage but here I prefer to just buy the 2SK389 and be over with it. Too many questionable compromises in my circuits already (and they always look like spaghetti).Re: Too simple
I have been wondering about the quality of the discrete opamp circuit since it was posted here, and that has kind of made me pause.
There are quite a few of these in the signal path so it's likely that the whole system will sound as good as the opamps do.
Elso Kwak said:Hi, the circuit is really too simple!
You cannot expect quality from that.
The 2SK389 is a large geometry FET with big capacitances. Now what are you going to do about it?
Lay it on the line!
I have been wondering about the quality of the discrete opamp circuit since it was posted here, and that has kind of made me pause.
There are quite a few of these in the signal path so it's likely that the whole system will sound as good as the opamps do.
Re: Re: Too simple
I haven't built the moamp yet. But I have built more rudimentory versions of it (using bjts and mosfets, with just resistor loading). I used small signal bjts and small / medium and power mosfets as input. the cgs ranges from <100pf to about 2000pf for the mosfets.
I could not detect any difference in sound quality.
I would suggest that you try it out this thing on breadboard first.
grataku said:
I haven't built the moamp yet. But I have built more rudimentory versions of it (using bjts and mosfets, with just resistor loading). I used small signal bjts and small / medium and power mosfets as input. the cgs ranges from <100pf to about 2000pf for the mosfets.
I could not detect any difference in sound quality.
I would suggest that you try it out this thing on breadboard first.
Hi,
I realize that what I'm about to say here may be off-topic but I feel that certain things regarding the active crossover design I've published on the forum should be cleared up:
1) I've published the MOX for the sole purpose of helping out those DIY members that expressed the need for such a project. This means that I have no financial interest whatsoever in publishing the design here and that I do not expect to be financially (or otherwise) compensated/rewarded for my efforts regarding the matter.
2) I measured basic characteristics of the active crossover using the equipment I happen to have at hand, which (I admit) may not be the best or the fanciest equipment in the world (nor the worst for that matter). As I was quite satisfied with the results I got, I decided to publish the crossover for those who might be interested.
3) My discrete opamp is just a basic circuit, which may be replaced with any standard IC opamp. I personally prefer the discrete opamp I've published. Certainly, its measurements are not as good as those of a standard IC opamp (something I've already pointed out quite clearly) but this is acceptable having in mind the simplicity of my design (whose characteristics I've also discussed on several occasions earlier). With certain modifications made to the design, it is possible to use the opamp as an amplifier for high-impedance headphones (for example, AKG 240) and get good results.
4) As I'm apparently the only person who has implemented this discrete opamp design on DIYAudio so far, I recommend to all of you who are really interested in how the thing works to test it first on a breadboard and see for yourself. I do not think anyone should mass-produce or purchase the board (or anything else) without having tested it first. For this reason, I do not feel responsible at all if anyone should spend a whole lot of money on parts only to find out it's not what he/she expected. This is all common sense really and I advise you to use it.
Regards
I realize that what I'm about to say here may be off-topic but I feel that certain things regarding the active crossover design I've published on the forum should be cleared up:
1) I've published the MOX for the sole purpose of helping out those DIY members that expressed the need for such a project. This means that I have no financial interest whatsoever in publishing the design here and that I do not expect to be financially (or otherwise) compensated/rewarded for my efforts regarding the matter.
2) I measured basic characteristics of the active crossover using the equipment I happen to have at hand, which (I admit) may not be the best or the fanciest equipment in the world (nor the worst for that matter). As I was quite satisfied with the results I got, I decided to publish the crossover for those who might be interested.
3) My discrete opamp is just a basic circuit, which may be replaced with any standard IC opamp. I personally prefer the discrete opamp I've published. Certainly, its measurements are not as good as those of a standard IC opamp (something I've already pointed out quite clearly) but this is acceptable having in mind the simplicity of my design (whose characteristics I've also discussed on several occasions earlier). With certain modifications made to the design, it is possible to use the opamp as an amplifier for high-impedance headphones (for example, AKG 240) and get good results.
4) As I'm apparently the only person who has implemented this discrete opamp design on DIYAudio so far, I recommend to all of you who are really interested in how the thing works to test it first on a breadboard and see for yourself. I do not think anyone should mass-produce or purchase the board (or anything else) without having tested it first. For this reason, I do not feel responsible at all if anyone should spend a whole lot of money on parts only to find out it's not what he/she expected. This is all common sense really and I advise you to use it.
Regards
Prudent advice, as usual. I think people often are of the mind that opamps can be substituted at will, and that certainly isn't true. I'm confident though that the design is a reasonable candidate for many audio tasks, which often don't require extremely high bandwidth, open loop gain, etc. (Especially since it is FET input.) In fact, these statistics often lead to negative results (parasitic oscillation, high NF). It isn't a magic bullet though.
My "production" active crossover is simply single FETs with a current source. I was attracted to moamps' design because it retained that simplicity.
I'd be interested to hear what kind of subjective measurements people are interested in. It takes some time to do a thorough battery of tests, but I'd be happy to start on some when I get my 2SK389 in a few days.
The first that come to mind are slew rate + square wave, CMRR, PSRR, THD. And of course with regard to MOX, some indication of its behavior in that circuit versus a monolithic FET-input opamp.
My "production" active crossover is simply single FETs with a current source. I was attracted to moamps' design because it retained that simplicity.
I'd be interested to hear what kind of subjective measurements people are interested in. It takes some time to do a thorough battery of tests, but I'd be happy to start on some when I get my 2SK389 in a few days.
The first that come to mind are slew rate + square wave, CMRR, PSRR, THD. And of course with regard to MOX, some indication of its behavior in that circuit versus a monolithic FET-input opamp.
Discrete Opamp
Not true. See for example Sonnya's design:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=1794&highlight=
Hi moaps,moamps said:
Not true. See for example Sonnya's design:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=1794&highlight=
Ahhhh...... hard at work at R and D I see!
"Is it good to have a high impedance output in this opamp appplication? This will create a very sensitive amp against load variations. The gain will variate with load." --- P-A *
You are absolutely right. It is totally unsuited to be one your projects to design a PCB for, to cash in on someone else's design work. Bad, bad, bad design for your purpose. Don't try to add a follower output stage. It won't work right, honest! You need to look else where, honest. Nothing to see here folks..... move along, move along. I hear Brian GT has something new that you might want to copy.......... check it out.
*Pay -in- Advance
"Is it good to have a high impedance output in this opamp appplication? This will create a very sensitive amp against load variations. The gain will variate with load." --- P-A *
You are absolutely right. It is totally unsuited to be one your projects to design a PCB for, to cash in on someone else's design work. Bad, bad, bad design for your purpose. Don't try to add a follower output stage. It won't work right, honest! You need to look else where, honest. Nothing to see here folks..... move along, move along. I hear Brian GT has something new that you might want to copy.......... check it out.
*Pay -in- Advance
Follower added or Not
The question brought up if an output follower of some sort should be appropiate is interesting. James Bongiorno had a similar circuit for the Thaedra phono amp, that is without followers. Later in version II he added followers. I will try to find the schematics.
I doubt the output impedance is high because of feedback in moamps and James' circuit.
The question brought up if an output follower of some sort should be appropiate is interesting. James Bongiorno had a similar circuit for the Thaedra phono amp, that is without followers. Later in version II he added followers. I will try to find the schematics.
I doubt the output impedance is high because of feedback in moamps and James' circuit.
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