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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Few questions about a filter/crossover
Few questions about a filter/crossover
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Old 19th October 2019, 05:11 PM   #11
Fergutor is offline Fergutor  Argentina
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Quote:
Originally Posted by sgrossklass View Post
That was JRC's "super 5532" - never got all that popular it seems, even though it did make an appearance in higher-end soundcards from both Creative/EMU and Asus.)
Really? Didn't remember that. But here I never could get any NJM model in my hands...or an OPA or a high end LM, only the old basic opamps/ TL07x/LF35x/NE5532/RC4558/LM833/TL741 probably some other). I can order them but I have to buy tens of them or more in dolar price, wait many days when I just casually need 2 or 4 and just for testing or a small personal project...

Quote:
Originally Posted by sgrossklass View Post
Balanced inputs tend to be a good idea regardless of whether you are living next to an AM flamethrower or not. Some extra attention is likely to be required in your scenario. A common-mode choke between the 47-100p to ground at the input and the T'd larger caps + bias Rs is likely to be a good idea, as well as a few hundred ohms in series in each leg...
I would need a schematic of that. In the other thread I posted this input schematic of the Edifier C200 and it have the commom mode choke in front of the first op amp

c200_61AUX.jpg

I have a small toroidal core form another choke that I could turn into one of those, it's just a bit smaller than the ones in the C200.

Quote:
Originally Posted by sgrossklass View Post
BTW, when you talk about "copying", you are basically talking about coming up with your own layout, are you? As they say, the layout is the circuit, and there still is enough to go wrong there...
Yeah I know, but I still feel like cheating...in my opinion, I know I am!

I'm doing the block diagram of my idea, in some minutes I'll post it here.
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Old 19th October 2019, 05:17 PM   #12
Fergutor is offline Fergutor  Argentina
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Quote:
Originally Posted by Mark Tillotson View Post
The sum of all three (suitably phased/scaled) is exactly the input, that's how the circuit works. Sum high and low and you get a notch filter.
Yes, yes, but my question was more about an anomaly on the expected flat result, like a dip or a peak because of a possible improper design.
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Old 19th October 2019, 06:15 PM   #13
Fergutor is offline Fergutor  Argentina
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Quote:
Originally Posted by sgrossklass View Post
Sounds good.
HA! Took me more than a few minutes...dammit...but here it is:

Block-01.jpg

Should be simpler than that, so probably I will get rid of some parts, some functionalities that probably will never be used...

There are that many aux outputs and not so many switches because here multiple poles switches are almost impossible to get (I know they are hard to get everywhere but here it's worse).

The bluetooth module part is bassically the circuit being prepared for adding one of those and/or something else.

The power supply is one of those multiple voltage, cheap 96 Watts universal notebook chargers (yeah...another problem...but this C200 is powered by an internal switching PS and works perfectly).

Planning to make a subwoofer amp too, in the not so distant future...
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Old 19th October 2019, 07:02 PM   #14
Fergutor is offline Fergutor  Argentina
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Ops! Forgot a switch or at least a 3.5mm with switch at the Headphones output...
And probably an op amp "amp" before it.

Last edited by Fergutor; 19th October 2019 at 07:04 PM.
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Old 20th October 2019, 02:14 AM   #15
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by Fergutor View Post
Really? Didn't remember that. But here I never could get any NJM model in my hands...or an OPA or a high end LM, only the old basic opamps/ TL07x/LF35x/NE5532/RC4558/LM833/TL741 probably some other). I can order them but I have to buy tens of them or more in dolar price, wait many days when I just casually need 2 or 4 and just for testing or a small personal project...
You are most likely to find them in Japanese and other Southeast Asian audio equipment. (NEC opamps may be even more exotic.) I guess the most popular JRC opamps would have to be:
NJM4580 (rather universal, quite low voltage noise, decent output driving, more LM833/MC33078 competition basically but less noisy)
NJM2068 (low voltage noise, good GBW, so-so output driving, Yamaha used those by the bucketload at some point)
NJM4556A (the first dedicated headphone amplifier, and still useful in this function today)

The O2 (DIY) headphone amplifier designed by one NwAvGuy used the latter two parts to make a point - that it doesn't take fancy expensive parts to make something that performs very well for the vast majority of people (well, except for the owners of certain planar headphones or vintage 600 ohm AKGs perhaps). He measured performance of a few opamps, too.
Quote:
Originally Posted by Fergutor View Post
I would need a schematic of that. In the other thread I posted this input schematic of the Edifier C200 and it have the commom mode choke in front of the first op amp

Attachment 788832

I have a small toroidal core form another choke that I could turn into one of those, it's just a bit smaller than the ones in the C200.
Just one? Well, I suppose since the inductance of a common-mode choke cancels out for differential-mode signals, so should any coupling between the two. So you could probably wind 2 pairs of wires on there, or even more, space permitting.

Here's what I had in mind:
Click the image to open in full size.

I used two types of ground symbols (COM and GND) to differentiate between chassis ground and circuit ground. A balanced (e.g. +/-15 V) power supply is assumed. Hand-matching of critical resistors R1-4 strongly advised, and it's not a bad idea for any other components that occur in pairs in both legs. Maximum input amplitude is determined by U1/U2 input common-mode range at given supply voltages. A standard balanced input with shield connection is shown, you will need IN+ and IN- only.

Take it as a starting point. More components may be required for RF proofing, and R1-4 can be optimized according to the abilities of U1-U3.

The layout should not look like the circuit is drawn, but rather both legs should be kept closely together. Not a bad idea for e.g. supplies V+/V- either.

Quote:
Originally Posted by Fergutor View Post
I'm doing the block diagram of my idea, in some minutes I'll post it here.
Quote:
Originally Posted by Fergutor View Post
HA! Took me more than a few minutes...dammit...but here it is:

Attachment 788844
So what you want is not that exotic, really.

Just one major change that I would suggest:
I would move the tone control between source selection and crossover input.
a) This makes its noise essentially irrelevant, and any old Baxandall with 50k or 100k pots and NE5532 would work perfectly fine. OK, you do want film capacitors rather than ceramics in the Baxandall.
b) It also means that the tone control's absolute phase is irrelevant and can't mess up sub/main XO.

Speaking of absolute phase, it would be really nice to have at least a choice of normal and inverting on the sub output. Subs of the better kind tend to include an analog phase shift control. Not sure how that works, possibly some sort of variable allpass.

I would leave crossover frequency variable for better flexibility, though you would probably get along fine with a reduced range (up to about 150 Hz is likely to do just fine).

The input level control in the crossover could serve as a main volume control.

If you want to use an off-the-shelf headphone amp, best tap off after input selector.

You can have a lot of fun with the grounding if you want to supply both the crossover and the tone control and maybe something else from the same power supply... at AF and RF.

I would suggest studying some of Bruno Putzeys whitepapers... especially "The G Word" and the one on legacy pun 1 problems.
Hypex Electronics B.V.

Quote:
Originally Posted by Fergutor View Post
There are that many aux outputs and not so many switches because here multiple poles switches are almost impossible to get (I know they are hard to get everywhere but here it's worse).
You could always make a binary tree of switches, just like a relay-based input selector. (So the last one selects between groups A and B, and then 2 more between A1/A2 and B1/B2, etc.) I hope you can get some DPDTs at least? What about 4PDT?

The crux of switching balanced inputs is needing twice as many switch contacts. On the plus side, you do not have to connect the grounds of all your sources then, avoiding potential ground loops between them. Having one balanced receiver circuit per input isn't a particularly enticing prospect either.

Maybe you can get the good ol' CD4052B multiplexer IC? I mean, it's only good to 20 V tops (so e.g. +/-9 V) but might make this whole ordeal a bit easier or at least more feasible. I might put it between the input filtering and the bias resistors. (Knowing CMOS circuits and their propensity to being fried, the 330R resistors may also be worth resizing to 1k or even 2k2, matched.)
You will have to keep distortion due to r_ON nonlinearity at bay (see datasheet) - this basically means making (source + load) impedance as high as possible to keep r_ON negligible. I'll suggest upsizing R6/R7 to 100k and just adding another 22k across IN+ and IN- at the input filter... going capacitor-coupled at the input and connecting bias R5 to a low-noise ca. +1.25 Vdc also seems worth a shot. (10k to -9V, 7k5 to +9V, 10F to ground, sounds good to me.)
Maybe even better, keep the circuit up to and including U1/U2 as originally suggested and ahead of the 4053 (alas, replicated for each input - so you basically need a cheap dual opamp with rather good common-mode linearity and decent slew rate but without major driving abilities; maybe this is the MC33078's or LM833's time to shine? Or even the LM837 quad, though that is notorious for its low phase margin and hence lack of stability near unity gain). This will protect the 4053 from being zapped quite effectively. After the 4053 you put in another set of unity-gain buffers with standard 100k-220k to ground (or rather +1.25 V) buffering before following that up with U3/R1-4 again. I would even be tempted to bootstrap the input bias to get super high input impedance. (I'll have to draw that for you, don't I?)
Silly me, you don't even explicitly have to generate +1.25 V and AC-couple the input, you might as well use e.g. a +7.5 V / -10 V supply. (If a 79M10 regulator is too exotic for your tastes, there's always the old trick of using 1-2 diodes in series with the ground connection to bring up the voltage on a more common 9 V part.) +8V/-12 V would be on the limits of this part but quite common types. If in doubt one could always use an adjustable regulator circuit e.g. with LM317/337. Or maybe you wanted some RC filtering after the regs anyway...
Quote:
Originally Posted by Fergutor View Post
The power supply is one of those multiple voltage, cheap 96 Watts universal notebook chargers (yeah...another problem...but this C200 is powered by an internal switching PS and works perfectly).
How much does this thing normally cost? The one off-brand charger I've come across that actually seemed half-decent was such a multivoltage job.

Being 96 W, it pretty much has to have a 3-prong power receptacle, like an IEC of some sort. How does it connect protective earth and secondary-side ground? Directly, or any R and/or C?

Generic knockoff (counterfeit "original") chargers can be outright terrible... nonexistant mains power filtering ... nonexistant cable strain relief.... bad parts quality... heat not transferred to outside case efficiently... the list goes on.

SMPS definitely are not all made alike! I'd prefer one of these metal case jobs for internal use, ideally one that gives you a way to control how to hook up the mains filter - so you should have L, N, PE terminals as well as OUT+ and OUT-. Compliance with common safety regulations is not something I would consider optional.

Do you have your eyes set on a matching case for the whole stuff already?
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Old 20th October 2019, 06:56 PM   #16
Fergutor is offline Fergutor  Argentina
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Quote:
Originally Posted by sgrossklass View Post
You are most likely to find them in Japanese and other Southeast Asian audio equipment. (NEC opamps may be even more exotic.) I guess the most popular JRC opamps would have to be:
NJM4580 (rather universal, quite low voltage noise, decent output driving, more LM833/MC33078 competition basically but less noisy)
NJM2068 (low voltage noise, good GBW, so-so output driving, Yamaha used those by the bucketload at some point)
NJM4556A (the first dedicated headphone amplifier, and still useful in this function today)
I will have to go and see what I can find. I think the RC4558 and NE5532 will be enough, no need to go high end on this thing.
Ha! My now broken X-Fi Xtreme Music had the JRC4556:

X-fi amps.jpg

Quote:
Originally Posted by sgrossklass View Post
The O2 (DIY) headphone amplifier designed by one NwAvGuy used the latter two parts to make a point - that it doesn't take fancy expensive parts to make something that performs very well for the vast majority of people (well, except for the owners of certain planar headphones or vintage 600 ohm AKGs perhaps). He measured performance of a few opamps, too.
Oh see? No need for super high end, especially given It will take time to find good enough speakers (I stupidly lost the chance to buy an used 3 way speaker with a planar ribbon tweeter and dome mids for almost nothing, I will never stop kicking myself over that!)

Quote:
Originally Posted by sgrossklass View Post
Just one? Well, I suppose since the inductance of a common-mode choke cancels out for differential-mode signals, so should any coupling between the two. So you could probably wind 2 pairs of wires on there, or even more, space permitting.
I had only one lying around but I knew there were more, I just found 2 more, 2 alike and one slighty different, all very small.

P1210460.JPG

The C200 have 1 per input running the 3 poles in parallel: left, right, ground.

InputCoils02.jpg
InputCoils01.jpg


It will be great to do mine with the coils, and if I have to sell one to somebody, use the differential balanced instead, right?

Quote:
Originally Posted by sgrossklass View Post
Here's what I had in mind:
Click the image to open in full size.
Aaahh the link doesn't work!


Quote:
Originally Posted by sgrossklass View Post
So what you want is not that exotic, really.
It shouldn't be, but actually I never see something like this, and it's not so complicated either. Seriously, things like this should be common but DIYers and companies insist on make either super cheap, super simple or super premium stuff and none with common or useful functionalities.

Quote:
Originally Posted by sgrossklass View Post
Just one major change that I would suggest:
I would move the tone control between source selection and crossover input.
a) This makes its noise essentially irrelevant, and any old Baxandall with 50k or 100k pots and NE5532 would work perfectly fine. OK, you do want film capacitors rather than ceramics in the Baxandall.
b) It also means that the tone control's absolute phase is irrelevant and can't mess up sub/main XO.
Yeah you told me that before, but where I put it made more sense as sub outputs aren't equalized (except with especial subwoofer controls that I originally wanted for my separated version of the crossover, a 1 to 3 bands parametric one) like that, and that the baxandall itself can make the headphones amp (I did this before with gain in the first opamp). But then one could simply return the baxandall to 0 and the gain would mess up the balance on outputs...although it wouldn't matter as they would go to different amps...Also will make the switching to amp easier as they are 2 (4) instead of 3 (6) poles to switch...Bleh!

The film capacitors I use to find here (I didn't buy any in about 2 years!) are the red and green ones, only once I got the grey box shaped ones. So, if those are ok, no problem.

About "b", not sure what you're saying. You mean the phase changes because of the tone control and crossover or the inverting? If the former, well, it's important.

Quote:
Originally Posted by sgrossklass View Post
Speaking of absolute phase, it would be really nice to have at least a choice of normal and inverting on the sub output. Subs of the better kind tend to include an analog phase shift control. Not sure how that works, possibly some sort of variable allpass.
Yes, good idea, didn't thought of that here because the crossover here it's just a way to further improve the functionality. But in my main crosoover project for my C200 yes it will have. I don't know how the phase shifting in subs work but knowing that "phase" is used in two different ways, "direction of waves" and "delay of a signal", given that it's usually a 0 to 180 knob rather than a 0 or 180 switch most of the times, and reading this

"The phase control operates over a range of 0 to 180 degrees. Adding delay to the subwoofer signal can sometimes help the subwoofer to integrate better with the loudspeakers in the room."

Then it says:

"All SVS subwoofers feature a continuously variable 0-180 phase control which allows the most complete range of adjustment in small increments to achieve the best sound possible. Other brands of subwoofers may only offer a simple 0/180 phase switch (also referred to as a polarity switch), which not as useful as a true variable phase control."

...then it's usually just delay, and I refuse such a thing! (and people in sound complain about real features that they call gimmicks! Amazing...). Now, this ones are real phase switching/inverting from old subwoofer schematics I have:

Infinity-BU2-sub-SchPre.jpg
jbl1500tone.jpg

Quote:
Originally Posted by sgrossklass View Post
I would leave crossover frequency variable for better flexibility, though you would probably get along fine with a reduced range (up to about 150 Hz is likely to do just fine).
I would love to, but pots are F expensive here, and as I said limited functionality is fine. But given there will be only 2 dual gang pot (forget about finding a 4 gang one) probably will be variable...

Ok, that's it!! You pushed me enough! I'm going to make it more complete and possible to use it alone!

...but now makes even more sense to put the tone control out of the crossover path (especially becasue of the HPF/FLAT line out)...

Quote:
Originally Posted by sgrossklass View Post
The input level control in the crossover could serve as a main volume control.
Yes, I kept forgetting about this important part.
And before I forget, I think a gain/sensitivity switch will be good because of all the different sources with different power, some too weak, some too strong.

Quote:
Originally Posted by sgrossklass View Post
If you want to use an off-the-shelf headphone amp, best tap off after input selector.
Nah, the idea is either a simple opamp or not even that, and as I will need the baxandall tone, after this will be enough. It's just for normal headphones, not high impedance ones. And remember that the NE5532 can drive big loads...supposedly...
I made this thing years ago and drives normal headphones strongly:

ampcd-1sch.JPG

Quote:
Originally Posted by sgrossklass View Post
You can have a lot of fun with the grounding if you want to supply both the crossover and the tone control and maybe something else from the same power supply... at AF and RF.
My fears. That and any other kind of noise and distortions due to PS (or bad desing).
And something I forgot to add to the black diagram. But yeah the original idea was to use the one PS filtering after it and use a single supply for the opamps to simplify (as I don't have to create a negative voltage from the single supply notebook charger). I know it works fine and the C200 has that. As it says in the other thread, the C200 has the switching PS +15v with it's filtering, goes to the board feeding the 7379 directly and the with the opamps, there's an SMD inducor or similar before a 7809 that feeds them in single ps mode.
But on the other hand all the shcematics have to be changed, a lot...So if there's a good proper way to turn a single PS into a dual ps (the 7379 will be fed from 16v to 18v).



Quote:
Originally Posted by sgrossklass View Post
I would suggest studying some of Bruno Putzeys whitepapers... especially "The G Word" and the one on legacy pun 1 problems.
Hypex Electronics B.V.
Thanks, will look.


Quote:
Originally Posted by sgrossklass View Post
You could always make a binary tree of switches, just like a relay-based input selector. (So the last one selects between groups A and B, and then 2 more between A1/A2 and B1/B2, etc.) I hope you can get some DPDTs at least? What about 4PDT?
Yes, I had that idea, but of course, don't wanted such a thing. Yes, DPDTs are no problem and I already have some. 4pdt no, impossible to get, but I will ask again.

Quote:
Originally Posted by sgrossklass View Post
The crux of switching balanced inputs is needing twice as many switch contacts. On the plus side, you do not have to connect the grounds of all your sources then, avoiding potential ground loops between them. Having one balanced receiver circuit per input isn't a particularly enticing prospect either.
Why? Aren't these kinds of "balanced" just as normal inputs, you know, with 2 poles, signal and ground?

Quote:
Originally Posted by sgrossklass View Post
Maybe you can get the good ol' CD4052B multiplexer IC?
I always wanted to do something with those, but don't wan't to complicate this that much. I need to keep this simpler.

Quote:
Originally Posted by sgrossklass View Post
(I'll have to draw that for you, don't I?)


But again, maybe I should not do it. It's cheaper and nicer than switches and mnultiple jacks but I prefer less compications, less board size, etc (also I would love to replace dual pots with digital solutions...oh yeah!!).

Quote:
Originally Posted by sgrossklass View Post
How much does this thing normally cost? The one off-brand charger I've come across that actually seemed half-decent was such a multivoltage job.
About 10 to 20 Us$. And they have good reviews. Now for audio...uncharted territory...
I bought it used and super cheap, that's why I already have it

Quote:
Originally Posted by sgrossklass View Post
Being 96 W, it pretty much has to have a 3-prong power receptacle,
Yes, 3 legs.

P1210464.JPG

Quote:
Originally Posted by sgrossklass View Post
like an IEC of some sort. How does it connect protective earth and secondary-side ground? Directly, or any R and/or C?
No idea.

Quote:
Originally Posted by sgrossklass View Post
Generic knockoff (counterfeit "original") chargers can be outright terrible... nonexistant mains power filtering ... nonexistant cable strain relief.... bad parts quality... heat not transferred to outside case efficiently... the list goes on.
Yes, and I expect nothing better! But it's the only PS I can afford for the moment so I have to make it work. Through heavy filtering I guess...a thing that needs coils...things hard to find here! So I have to use simple stuff.
Of course I could obtain a normal transformer, but they are absurdly expensive and the quality...

Quote:
Originally Posted by sgrossklass View Post
SMPS definitely are not all made alike! I'd prefer one of these metal case jobs for internal use, ideally one that gives you a way to control how to hook up the mains filter - so you should have L, N, PE terminals as well as OUT+ and OUT-. Compliance with common safety regulations is not something I would consider optional.
They sell those, but they are too expensive here.

Quote:
Originally Posted by sgrossklass View Post
Do you have your eyes set on a matching case for the whole stuff already?
Nah, I don't care about aesthetics. After I make the internals I will build one from some 1mm (or 1,5mm, don't remember) aluminum sheets I have, and/or wood. Or maybe I will get some metal case for racks...

------------------

If I put the baxandall before the crossover I could just go with this Elliot design, modify the input for RF filtering (balanced or the coil), remove the balance, add a gain switch maybe, etc.
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Old 21st October 2019, 01:52 AM   #17
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by Fergutor View Post
Aaahh the link doesn't work!
Oh no. Fixed:

Few questions about a filter/crossover-bal-input-generic-png

The forum software has a habit of deleting what it thinks are "unused" attached images if you keep editing for a while after uploading them without posting yet. You don't immediately notice because you have done a preview and the browser has cached the image.
Attached Images
File Type: png bal-input-generic.png (11.3 KB, 95 views)
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Old 21st October 2019, 02:07 AM   #18
Fergutor is offline Fergutor  Argentina
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Quote:
Originally Posted by sgrossklass View Post
Oh no. Fixed:

Few questions about a filter/crossover-bal-input-generic-png

The forum software has a habit of deleting what it thinks are "unused" attached images if you keep editing for a while after uploading them without posting yet. You don't immediately notice because you have done a preview and the browser has cached the image.
Yeah I found out precisely when doing this thread...or was the other...? Well, one of them.

Your circuit confuses me too much! I'm really not sure what I'm seeing! Haha!
I mean it's very similar to the Edifier C200 near the input, but apparently balanced. Remember I don't need that.

Last edited by Fergutor; 21st October 2019 at 02:12 AM.
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Old 21st October 2019, 03:47 AM   #19
Fergutor is offline Fergutor  Argentina
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Quote:
Originally Posted by Fergutor View Post
but apparently balanced. Remember I don't need that.
I mean, XLR type balanced. It's a mistery to me.
(Surely there's something here I'm not understanding, but I'm saying just in case )
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Old 23rd October 2019, 03:30 AM   #20
Fergutor is offline Fergutor  Argentina
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Default Ufff!

Quote:
Originally Posted by sgrossklass View Post
.
Hey Sgrossklass, I made 4 schematics of most of the circuit.
I tried to make all the changes you proposed in earlier comments, but also did the baxandall in parallel version that you don't like, just to see if it's valid anyway.
Most sections were actually made separately for different reasons at different times, so I modified what I could register. The opamps models for example are mostly 4558 because that's what was at the original, you tell me which to change (I want to simply use 5532 and 4558).
Power supply is of course mostly missing as I still don't know how to solve that, you know: all from the charger, dual or single for opamps (prefer dual now so I don't have to modify everything)... (and the 7805 ad USB is for cellphone charging and to feed a cheap bluetooth audio dongle).
And well, it's very rudimentary and faulty etc. So if you can, tell me what's wrong.
Pr01-aCortado.JPG
Pr01-bCortado.JPG
Pr01-cCortado.JPG
Pr01-dCortado.JPG

The crossover section is from the PX600.2 and forgot to check it so it's as I originally drew it back then.
Some pots are pots and the volume are connectors, but you will realize that easily.
The baxandall is on from Elliot.
Inputs from Edifier C200 (as it's similar to your last drawing) and the car amplifiers
Amplifier section from C200 with some modifications from others (unused pins).
The Common mode choke are connectors too.
There's one 3.5mm at the end, near the TDA7379, and the rest are connectors, but that particulary should be the headphones output, I simply didn't "connected" yet.
And well, many other stuff that you will see weren't on purpose, etc.
Also there are some confusing stuff at the input, I added some "High level inputs/outputs" to use the crossover (you know if I'm going to make it variable, then I will make it useable...). I copy them from different subwoofers schematics...no idea what I'm doing there...as with the rest of the circuit ... well, tried to use some common sense and the very very little limited knowledge.
Awaiting your response!

Last edited by Fergutor; 23rd October 2019 at 03:32 AM.
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