Active crossover types

[dennnic]

Hello,

I'm looking for some technical information on active crossover internals. Common belief is that op amps degrade the signal and that puts them out of Hifi application.

So far I was told that signal processing is best done in digital domain. I have managed, using mini dsp Nano Digi, to create a decent two way system. However, it requires two DA converters, inputs potentially more noise from multiple power supplies and then there is an issue of controlling the volume digitally.

Is there a way to do it in analog domain, while avoiding op amps? Are there any disadvantages by doing so?

 

[dennnic]

Maybe to start with a simpler question, since there are no answers.

How does an op amp effect the signal quality and and are there some good op amps?

 

[JRS]

Hello,

I'm looking for some technical information on active crossover internals. Common belief is that op amps degrade the signal and that puts them out of Hifi application.

So far I was told that signal processing is best done in digital domain. I have managed, using mini dsp Nano Digi, to create a decent two way system. However, it requires two DA converters, inputs potentially more noise from multiple power supplies and then there is an issue of controlling the volume digitally.

Is there a way to do it in analog domain, while avoiding op amps? Are there any disadvantages by doing so?

The biggest disadvantages will be 1) finding ADC and DAC that don't have op-amps in the circuit paths of the analog sections, and 2) being able to afford when you do. And if unsuccessful, ask yourself, or better yet, those who blanketly condemn such conveniences, how exactly do they degrade the sound? If you remain undeterred, then ask yourself about the amplifiers and other playback devices--these two will typically include you guessed it, more op-amps. But there are amps and preamps that remain true to the entirely discrete ethic. Sadly, they cost an arm, two legs, and likely half your face. But assuming you are still willing, and OK with their noise and distortion, you will have to find a playback device., say a CD player sans operational amps. There are always records I suppose. Or reel to reel players.

But having come this far, what music will you find that wasn't produced without the help of many, many op-amps. I suspect your best bet would be to hire musicians playing unamplified music. This isn't meant to be sarcastic, but rather a way of considering the philosophical argument that if you are forced to accept that playback will invariably involve their use, what's a handful more? In some ways, it's like wanting a car that contains no plastic, because plastic is inferior to ceramic, metal and rubber. Or there are these:

Now that is in jest. Bear in mind that an op-amp consists of this:

20 transistor count. Be prepared to multiply that by many, many times. What do you expect the cumulative effect of all those discrete devices to be? Then go down to your loca salon, listen to the very best system you can find, and ask the sales person how many op-amps are in the signal chain? Then ask yourself, well it does sound really, really good in spite of it all, and then ask yourself whether such prejudices have any real basis.

 

[dennnic]

Does an active crossover (if not in it's digital variant) always have to use ADC somewhere in it's path?

I wasn't trying specifically to avoid usage of op amps. Let me rephrase:
For what reason are many active crossovers (many that contains aforementioned op amps) thought as not Hi-Fi?

 

[Pluto]

Common belief is that op amps degrade the signal and that puts them out of Hifi application.

As a generalization, that is utter nonsense.

If the process by which a recording is delivered to you is anything other than 100% digital (assuming that the microphones must be analogue, regardless), chances are that your precious audio will have passed through dozens, if not hundreds, of op-amps before it hits any of your kit.

The debate over whether a crossover designed today would be better analogue or digital, is a legitimate one. But don't let your judgement become clouded by some idiotic notion that IC op-amps should be avoided. If you are a home constructor, knock up a test jig consisting of a number of quad op-amps (4 amplifiers in a single package), arranging that each amplifier is followed by an attenuator equal to its gain i.e. 15dB gain followed by a 15dB attenuator. Keep the impedances sensible; high enough to ensure that you are not challenging each amplifier's ability to drive a low Z load, and low enough so that you are not introducing unnecessary thermal noise.

Pass the signal through as many of these as your patience permits and see how many such stages the signal has to pass through before degradation is noticeable.

 

[iMickey503]

Common belief is that op amps degrade the signal and that puts them out of Hifi application.

Who said this?
The IEEE article that notes this is talking about Rectification operational amplifiers

Before going down this path because there is legitimate actual explanations and there are some reasons why op amps can introduce some unwanted effects in the audio signal chain I don't think it's going to be of much practical concern.

here is a link to E.E. Times. they posted a three-part Series going over in depth of operational amplifiers principles of design and a bunch of other stuff that's easy to digest. however it seems that the first two articles have been taken down or behind a pay wall.

Here is a test to see if you can tell the differences with the basic Youtube test.

Thread

The best sounding op amps for audio work.

G'day all, I guess that this sounds suspiciously like the subject of 'op amp rolling, but actually it isn't. As much as I think that op amps do have a 'sound', in recent days I've been revisiting the LM4562 and sonically wise, to my ears it doesn't really have that 'typical' op amp signature, it ...

www.stereonet.com

A genreal of how they work in simple terms and characteristics.

And a General on why people change and upgrade them.
https://www.psaudio.com/askpaulvideo/what-are-op-amps/ (No Comercials)
Youtube

Now about your conundrum:
" it requires two DA converters, inputs potentially more noise from multiple power supplies and then there is an issue of controlling the volume digitally. "


Okay. So, to make sure I understand your question:

-You are running an Active 2 way speaker.
-You are using a NanoDigi with 4 digital outputs.
-You are also using a MiniDsp with 4 analog outputs.
-You are also using two of some kind of digital to analog converter.

And what you want to do is eliminate the operational amplifiers? and somehow go directly digital into your speakers that you are running active?

So This for Digital sources. With this being where the Dual DAC's are since they are 2 channel dacs.
____________________________________________________________________________________

And this for analog sources:
___________________________________________________________________________________________

So if you could just post a photo on how you have your system set up this would absolutely help.

The reason why I ask, and pardon me if I have your objective incorrect is simply this.

Without out an OpAmp? How are you going to couple to your Amplifiers?

The Op Amp is right before the RCA.

Glossary of Electronic and Engineering Terms 'Op Amp Mono Amplifier'

Electrical Engineering Dictionary, Operational Amplifier Mono Amp circuit schematic, component values and operating description. Single channel speaker amplifier using an LM386 operational amplifier

www.interfacebus.com

You kind of need them a they are the Basics for amplification.

https://www.robots.ox.ac.uk/~gari/teaching/b18/background_lectures/1P2-Op-Amp-Circuits-L3-Notes-Collins.pdf

So as far as I know? You kind of need them. All of these from my understanding have some kind of implemenation of an Operational amplifier chip or circuit.

Types of Digital to Analog Converter (DAC) (Links to video explanations bellow)

• Binary Weighted Resistor D/A Converter Circuit.
• Binary ladder or R–2R ladder D/A Converter Circuit.
• Segmented DAC.
• Delta-Sigma DAC.

So you kind of need an Op Amp someplace.


Seems to me you just need a 4 channel DAC. But you already have good ones. So? To remove noise?
Build this if Power supply noise is the primary concern. This is ZERO NOISE. You can't get better then this.

And you got to get this! The Best 12v AC Barrel plug ever made.

 

[sergeauckland]

Does an active crossover (if not in it's digital variant) always have to use ADC somewhere in it's path?

I wasn't trying specifically to avoid usage of op amps. Let me rephrase:
For what reason are many active crossovers (many that contains aforementioned op amps) thought as not Hi-Fi?

By whom? Certainly not by anyone who understands about these things. Op-amps have been totally transparent pretty much since the 741!
S.

 

[DVDdoug]

The advantage of digital is that once you have digital processing it's "easy" and free to make a filter with sharp cut-off or to combine EQ with a crossover.... A more complex crossover/EQ just requires more software which doesn't add to the production cost. With analog it requires more hardware and of course that adds to the cost. (But a simple crossover is cheaper in analog and with some speakers/monitors it may be perfectly adequate.)

Does an active crossover (if not in it's digital variant) always have to use ADC somewhere in it's path?

No. If there is no digital there is not ADC or DAC. Passive speakers don't have op-amps or anything digital...

For what reason are many active crossovers (many that contains aforementioned op amps) thought as not Hi-Fi?

Maybe an "audiophile" myth? Some audiophiles don't like anything "modern" but those guys don't like digital either...

I can't imagine making a lo-fi active crossover. If you're going through the trouble of making an active crossover there's no reason to make a bad one, and you wouldn't save any money making a low-fi one. If you want something cheap you're going to use a passive crossover. Some cheap speakers just have a (passive) capacitor for the tweeter and no filtering for the woofer.

 

[Pluto]

Who said this?
The IEEE article that notes this is talking about Rectification operational amplifiers

We need to consider the distinction between signal degradation and audible degradation. Suitable measurements will detect signs of the former well before anyone will hear the latter.

 

[Jim Matthews]

So far I was told that signal processing is best done in digital domain. I have managed, using mini dsp Nano Digi, to create a decent two way system. However, it requires two DA converters, inputs potentially more noise from multiple power supplies and then there is an issue of controlling the volume digitally.

I've had both types of active crossover and much prefer the digital version. Forgive my ignorance, but can the DAC be placed before the MiniDSP?

 

[levimax]

I have managed, using mini dsp Nano Digi, to create a decent two way system. However, it requires two DA converters, inputs potentially more noise from multiple power supplies and then there is an issue of controlling the volume digitally.

Is there a way to do it in analog domain

Despite audiophile myths both op-amps and DA and AD conversion can be transparent for audio applications. I very much doubt you will gain anything by changing your current digital crossovers to analog but experimenting can be a fun and learning experience . Since you know what crossover points are working you might look at this project if you want to try analog crossovers. The crossover points are "hard wired" which saves money and eliminates the use of potentially dodgy potentiometers and makes it easy to keep noise and distortion very low... but it is hard to change the crossover points. https://sound-au.com/project09.htm

 

[Pluto]

can the DAC be placed before the MiniDSP?

The best game plan is to remain in the digital domain as long as possible. The MiniDSP (or indeed any DSP) operates in the digital domain (by definition) so the optimal approach is to convert the DSP outputs to analog at the last possible point in the chain.

Implementing a digital crossover for a pair of three way speakers will require six channels of conversion i.e. three stereo converters.

 

[iMickey503]

can the DAC be placed before the MiniDSP?

Yes. That would be a ADC. analog to digital converter. you would do this for example if you wanted to not use the built-in ADC of the MiniDSP.

The reason why anyone would do this would be a situation where you wanted to not use the built-in analog to digital converter inside the MiniDSP, and prefer to use something that may provide higher Fidelity for the conversion to digital via the MiniDSP's Digital input.

some people say that this would be a waste however, the point to life is to experiment and to try out new things.
The MiniDSP is a workhorse. It does so much right at a great price, it would be wrong not to experiment and see what works and sounds best.

a classic example of this would be a tube input stage. not because you like the sound of the tubes but because you're at a live environment and tubes have a softer and warmer style clipping then a solid state device or solid state preamp. in a situation like this it would be an absolute godsend.

the other application for something like this as you are describing would be mastering or doing a actual transfer from a reel to reel tape or another analog media Source where the output is varied and not constant and often so you will see reel-to-reel tapes clip a digital input stage to the point it just shuts off like some Panasonic DAT decks.

something like this would help you get a higher signal-to-noise ratio in a specific situation like this for most of the recording if not using a compressor limiter for example... Etc.

more common would be something like interfacing with Pro gear with Balanced XLR --->ADC to RCA to MiniDSP.

 

[dennnic]

Maybe I should put the whole situation up to explain the problem:
I build a pair of open baffle speakers, two way (two woofers and a full range), which differ in efficiency between drivers and require a lot of eq boosting towards the low end (low Qts woofers). I was suggested to use digital crossover and bought Mini dsp Nano Digi.

Current system: Source (PC/raspberry) -> digital crossover -> two DA converters (one borrowed) -> two amps (one SS and one tube) -> speakers (no passive components).

Option 1 - retain my digital crossover, buy a power supply for it and a second DAC (hopefully identical to the other one). Total expense 1300 euros.

The Naim dac V1 that I currently use is an USB converter in the first place, has a preamp, a nice headphone amp and a remote (or knob for setting the volume). All of those stuff would be redundant.
On the plus side - I do get parametric EQ and ability to add a subwoofer later on.

Option 2 - Apply the EQ on the PC (somehow) and feed the full signal to the V1 (via USB), use it's preamp (and a remote!) and put the electronic crossover between the preamp and amps.
Total expense - well, the crossover and perhaps it's PSU.

The question is - what do I get, or lose, in the option 2 in terms of audible sound quality?
By the way, I heard about the negative impact of op amps and AD conversion from a high end tube amp designer, and hence, this thread.

Since I already know the crossover frequency, slopes and driver efficiencies, the simple fixed frequency electronic crossover would still do the job done.

 

[dennnic]

Naim makes a fixed frequency electronic crossover, the Snaxo. This seems to be a three way design. Unfortunately, they offer it as an upgrade just for a handful of speakers and won't do custom order. If only I could figure out the parts and make something similar...

 

[phoenixdogfan]

Alternatively you could use a software based crossover, provided you have a multichannel dac and a way to control volume. Three software alternatives are Ekio which is around $150, JRiver for around $65, and Dephonica which is freeware. If you need eq you could use Equalizer APO which is also freeware and very popular around here.

 

[dennnic]

Alternatively you could use a software based crossover, provided you have a multichannel dac and a way to control volume. Three software alternatives are Ekio which is around $150, JRiver for around $65, and Dephonica which is freeware. If you need eq you could use Equalizer APO which is also freeware and very popular around here.

That would be a good solution to implement parametric equalisation, if nothing else

 

[levimax]

Apply the EQ on the PC (somehow) and feed the full signal to the V1 (via USB).

I have a tri-amp system using analog active crossovers similar to your option 2. For EQ and filtering and phase correction I use REW and Rephase to create FIR filters and apply them with foobar2000 convolution. It is not as flexable as all processing in the digital domain but it works and I havent felt like spending the time and money requred to go all digital. Rephase is an amazing free tool that does much of what digital crossover can do.

 

[levimax]

If only I could figure out the parts and make something similar...

Linkwitz-Riley Electronic Crossover

ESP Project Pages - Linkwitz-Riley Electronic Crossover. Suitable for bi-amping or triamping, subwoofers, hi-fi or pro-audio use.

sound-au.com

 

[dennnic]

They even sell the PCBs, great. Just what I was looking for. Thanks everyone for help!

One more thing for the end, since I started with op amps... Is it worth investing a lot into discrete op amps and what are good ones to look for?