Maybe it would be useful to reframe this and make it clearer what Im after and why.
A while back I came to realize that I didn't know how to make anything. Nothing. I didn't like that. I remember my grandfather always seemed able to weigh the option of buying something or making it. That really appeals to me. I got into diy audio because I was tired of being seduced by convenience so often that it became my only choice.
With that in mind, maybe I should refer to this project as something like:
MrKramers somewhat inconvenient active crossover.
A project for experimenters, learners and makers.
Myself included.
Budget: 150$usd
Goals:
Make something. Understand as much as I can about why it works.
3 way active crossover to drive a variety of amps, ranging from generic receivers found on craigslist to chip-amps to , well, whatever I hook up to it.
Capable of at least 2nd order slopes.
Some way of altering gain/volume levels per out without de-soldering something.
Some way of altering crossover points without de-soldering something.
Boundaries:
Discreet parts only.
Jfets preferred.
Parts I can get just about anywhere in bulk.
Bonus:
Sounds good due to clever thinking.
MrKramer
A while back I came to realize that I didn't know how to make anything. Nothing. I didn't like that. I remember my grandfather always seemed able to weigh the option of buying something or making it. That really appeals to me. I got into diy audio because I was tired of being seduced by convenience so often that it became my only choice.
With that in mind, maybe I should refer to this project as something like:
MrKramers somewhat inconvenient active crossover.
A project for experimenters, learners and makers.
Myself included.
Budget: 150$usd
Goals:
Make something. Understand as much as I can about why it works.
3 way active crossover to drive a variety of amps, ranging from generic receivers found on craigslist to chip-amps to , well, whatever I hook up to it.
Capable of at least 2nd order slopes.
Some way of altering gain/volume levels per out without de-soldering something.
Some way of altering crossover points without de-soldering something.
Boundaries:
Discreet parts only.
Jfets preferred.
Parts I can get just about anywhere in bulk.
Bonus:
Sounds good due to clever thinking.
MrKramer
"...it encourages you to continue, as opposed to not working which is frustrating" I can't fault your logic there. Seems like a big advantage.
Seems they are also cheaper. Thats good.
They are made up of lots of little components. I don't really like that as much.
Any other advantages/disadvantages compared to jfets?
MrKramer
Seems they are also cheaper. Thats good.
They are made up of lots of little components. I don't really like that as much.
Any other advantages/disadvantages compared to jfets?
MrKramer
Hi,
"A TL071 op-amp costs about the same as a JFET, and you need two JFETs for a decent design."
That tells just half of the truth! It needs only 2 JFETs for a decent design, that´s right. But, wether You use one or one million TLs You will hardly ever achieve a decent sounding design
Of course it is easier to treat the active elements as black boxes and just have to think about the filter components, but I´d like to hear the OPamp based filter that outperforms a decent JFET based.
When You concentrate on unity gain SallenKey structures all You need is a buffer as active element. That´s an easy task for a single or a pair of JFETs. In Mr. Borbely´s articles on JFETs such buffers have been measured with very low distortions, high bandwidth, and low noise.
Such buffers are as easy to use as OPamps, are no greater effort in parts number count or budgetwise and seriously outperform OPamps sonically.
If You look at the way such a buffer works it seems logical to me that it should be better than an OPamp.
Oh one good reason is still missing: The threadhost asked for discretes on purpose.
jauu
Calvin
"A TL071 op-amp costs about the same as a JFET, and you need two JFETs for a decent design."
That tells just half of the truth! It needs only 2 JFETs for a decent design, that´s right. But, wether You use one or one million TLs You will hardly ever achieve a decent sounding design
Of course it is easier to treat the active elements as black boxes and just have to think about the filter components, but I´d like to hear the OPamp based filter that outperforms a decent JFET based.
When You concentrate on unity gain SallenKey structures all You need is a buffer as active element. That´s an easy task for a single or a pair of JFETs. In Mr. Borbely´s articles on JFETs such buffers have been measured with very low distortions, high bandwidth, and low noise.
Such buffers are as easy to use as OPamps, are no greater effort in parts number count or budgetwise and seriously outperform OPamps sonically.
If You look at the way such a buffer works it seems logical to me that it should be better than an OPamp.
Oh one good reason is still missing: The threadhost asked for discretes on purpose.
jauu
Calvin
Uniform heat dissipation.
Don't know if it's cheaper in the short term but a PC with an outboard soundcard with 8 ins and outs and some free software would perform the functions you are looking for and most likely out benchmark both Opamps and Jfets .
"most definitely not! How should they with all those OPamps around? ;-)"
What, those 17 opamps and 15 electrolytic coupling caps in a DCX 2496 signal path degrade the signal?
http://www.diyaudio.com/forums/attachments/pass-labs/148919d1259843055-b1-active-crossover-lr2.pdf
http://www.borbelyaudio.com/adobe/ae699bor.pdf
What, those 17 opamps and 15 electrolytic coupling caps in a DCX 2496 signal path degrade the signal?
http://www.diyaudio.com/forums/attachments/pass-labs/148919d1259843055-b1-active-crossover-lr2.pdf
http://www.borbelyaudio.com/adobe/ae699bor.pdf
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Yes. Better power supply rejection ratio, and no need for additional capacitors in the signal path to get around the problem of a couple of volts DC offset.
Hi,
Ouch! And don´t forget the startup- and shutdown-offset when the beloved OP is not fully operational. And last not least don´t forget the little cap You need in the feedback path of the OP without which the OP wouldn´t work as a DC-servo.
jauu
Calvin
ps. sorry...simply couldn´t resist it
You may use a decent power supply right from the start
Yeah, You just need another OPamp and associated circuitry insted. Just think of how much better a couple dozen transistors resistors and caps on a common substrate of this OPamp must be compared to a single highquality device
Ouch! And don´t forget the startup- and shutdown-offset when the beloved OP is not fully operational. And last not least don´t forget the little cap You need in the feedback path of the OP without which the OP wouldn´t work as a DC-servo. jauu
Calvin
ps. sorry...simply couldn´t resist it
I am pretty new to building these kind of circuits and I have a lot to learn. I really appreciate the replies.
Having said that, I think this thread has gone off the rails a little bit.
I spent a little time reading up on opamps. Quite interesting but not what I'm looking for right now. I want to make this crossover with simple discreet parts.
It seems there is quite a disagreement regarding the merits of opamps vs fets vs... I'll reserve judgement until after I've made and/or heard a few good examples of each.
So...
I think I'll go the PLLXO route i.e. RC filters followed by a unity gain buffer. A Source Follower with a CCS looks pretty easy to both understand and make. Other than the limitations that have already been pointed out, am I giving up anything vs a Salen Key filter?
Also, I said before I have a decent +/- 18V power supply. Is there a jfet that would work reasonably well with this voltage?
Thanks
MrKramer
Having said that, I think this thread has gone off the rails a little bit.
I spent a little time reading up on opamps. Quite interesting but not what I'm looking for right now. I want to make this crossover with simple discreet parts.
It seems there is quite a disagreement regarding the merits of opamps vs fets vs... I'll reserve judgement until after I've made and/or heard a few good examples of each.
So...
I think I'll go the PLLXO route i.e. RC filters followed by a unity gain buffer. A Source Follower with a CCS looks pretty easy to both understand and make. Other than the limitations that have already been pointed out, am I giving up anything vs a Salen Key filter?
Also, I said before I have a decent +/- 18V power supply. Is there a jfet that would work reasonably well with this voltage?
Thanks
MrKramer
RC filter + buffer gives you Butterworth single pole.
Cascade a pair of these with buffer and you get 2pole L-R.
That's your choices.
S&K or MFB allow a far wider choices of poles and filter characteristics.
When you come to notches and EQ, to make the drivers sound right, you cannot get away from opamps whether discrete or integrated.
Cascade a pair of these with buffer and you get 2pole L-R.
That's your choices.
S&K or MFB allow a far wider choices of poles and filter characteristics.
When you come to notches and EQ, to make the drivers sound right, you cannot get away from opamps whether discrete or integrated.
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