Testing the Active Crossovers for my 10 Channel Amp

These crossover boards are a key component in my 10 channel amp build, and I have to make sure the board layout works properly before I order the professionally made PCBs.
Each board contains an input buffer, a two stage high pass filter, a two stage low pass filter and an output buffer that has some gain and also has a trimpot to adjust the output level.
Credit and thanks to Rod Elliott's excellent website for this design: sound-au.com/project09.htm. His site is a wealth of practical knowledge and projects that I've been using for nearly 20 years. The linked article has a detailed description of how the crossover works if you want more info.
The filter stages combine for a 4th order slope on the high pass and low pass, letting a limited range of frequencies through. In this example, the board is set to drive the woofer of my 4 way speakers from 80Hz to 350Hz. Another board will drive the midwoofer from 350Hz to 900Hz, and so on.
There will be 10 of these, one for each individual amplifier board.
Testing was done first with my scope just to check if it actually works. While the circuit design is proven, the wildcard is the board layout and whether I made any mistakes doing that.
I then set up my computer to run REW to measure the frequency response. This is done in a similar way to measuring a speaker (or room), except instead of using a microphone, the signal is fed directly through the crossover board.
As shown in the video, the measured response very closely matches the simulated.
The next step is to finalize the board layout and order the boards, and then I can start putting the amp together.
Active vs passive: is a topic for another video.
You can watch part 1 in this series here:
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[@IBuildIt]

These crossover boards are a key component in my 10 channel amp build, and I have to make sure the board layout works properly before I order the professionally made PCBs. Each board contains an input buffer, a two stage high pass filter, a two stage low pass filter and an output buffer that has some gain and also has a trimpot to adjust the output level. Credit and thanks to Rod Elliott's excellent website for this design: sound-au.com/project09.htm. His site is a wealth of practical knowledge and projects that I've been using for nearly 20 years. The linked article has a detailed description of how the crossover works if you want more info. The filter stages combine for a 4th order slope on the high pass and low pass, letting a limited range of frequencies through. In this example, the board is set to drive the woofer of my 4 way speakers from 80Hz to 350Hz. Another board will drive the midwoofer from 350Hz to 900Hz, and so on. There will be 10 of these, one for each individual amplifier board. Testing was done first with my scope just to check if it actually works. While the circuit design is proven, the wildcard is the board layout and whether I made any mistakes doing that. I then set up my computer to run REW to measure the frequency response. This is done in a similar way to measuring a speaker (or room), except instead of using a microphone, the signal is fed directly through the crossover board. As shown in the video, the measured response very closely matches the simulated. The next step is to finalize the board layout and order the boards, and then I can start putting the amp together. Active vs passive: is a topic for another video. You can watch part 1 in this series here: kzbin.info/www/bejne/h5aceWNtf9GHbNk

[@gman76utube]

For grins, I repurposed a Parts Xpress amp and designed a 4th order LR 2-way crossover that uses a 4-gang pot to adjust the xover freq. Works great. Freq adjusts from 1500 to 3800 Hz. I could build two of these to realize a 3-way system and have 2 adjustable frequencies (low-mid and mid-high). Haven't gotten there but played around with the 2-way active xover and amp, and it wonders on the classic B652.

[@staLkerhu]

Are these things truly better than passive crossovers? What are the advantages and disadvantages of the 2 solutions in a nutshell?

[@thomasduby728]

I laughed out loud! “As you know, it’s how it looks”. So many things in the world definitely fit that model.

[@garyrobinson7269]

This was a very straightforward explanation, thank you.

[@mfkhometheater7742]

That definitely brings back memories! I use to do a lot of that but I'm just too lazy now days so I just use DSP. At one point I was thinking of doing analog boards for my whole house audio just to use up a bunch of left over old OPA2134 opamps etc but I ended up just getting a bunch of 2x4HD's for the job.

[@billstoner5559]

Super nice, John!! 👏🏻👏🏻😊

[@peterwu831]

The high pass section has equal value capacitors and resistors with unity gain. The cutoff frequency is calculated to be 106Hz instead of 80Hz. And the design yields +3dB overshoot at the cutoff frequency - could be desirable. If replacing R18 with 20k, the cutoff would be at 75Hz, with -3dB “normal” roll-off.

[@KipdoesStuff]

I like learning new things, even if I will never apply that knowledge. Knowing is half the battle, YO JOE!

[@rickharms1]

I have a question. Please understand, this is curiosity, not judgmental. Why cut off at 80Hz? I like going down to at least 20Hz. I am fully capable of admitting that I am full of crap. I greatly admire what you do.

[@IBuildIt]

I have 5 subwoofers in my listening room handling everything from 80Hz and below.

[@AquaPeet]

No sponsorship from PCBWay? ;) So awesome that you were able to do the whole process of prototyping. Does the length of copper tracks on your board matter?

[@IBuildIt]

I had an email from JLC to do a sponsored video, but I haven't taken them up on it, even though I ordered the amp boards from them. Board layout for audio frequency analog circuits is not very demanding. You just need to pay attention to the grounds and how they are routed.

[@mfkhometheater7742]

@@IBuildIt I always just did a ground plane on the top layer, that worked pretty well.

[@summerforever6736]

VERY TALENTED !!

[@jeffbeck6501]

Why did you not include pots so that you adjust the frequency cut-offs, like a commercial active crossover? I want to build what you are building, and that is an active crossover with 3 pairs of stereo amps for a tri-amp'd speaker system. But I want to be able to control the frequency of the 2 cut off points, between low and mid, and between mid and high, and I want a volume for each of those outputs.

[@peterwu831]

Why not just use an eight channel DSP, or two of four-channel Mini DSP for this build, as you have used previously for your 4-way open baffle project? Do you like analog crossover better than the digital?

[@FixthisCD]

Is there any pros/ cons to putting the gain at the end versus the beginning of the circuit?

[@diegovigano6322]

usually you should put gain as soon as you can. this allows you to suffer less from electromagnetic interferences or thermal noise from big resistors

[@hazembata]

Looking to build my own speakers soon. I am no expert. DSP is new to me. Can one design a speaker with no passive crossover and just use DSP. If so, can you explain that process? Thanks.

[@sudd3660]

where in the chain does the Active Crossovers fit in? maybe between the dac and a amplification is my guess. and my second question: is it easy to make a Active Crossovers that fits on before the dac?

[@IBuildIt]

For my system, the crossover comes after the computer - the output from the sound card. A USB DAC is basically a sound card, so exactly the same. To be before the DAC, it would have to be a digital crossover, whereas this is analog.

[@bbfoto7248]

​@IBuildIt What will the be the variable range of output voltage from these active analog crossover boards? They obviously need to be within spec of the input sensitivity of your amplifier boards, so maybe I should watch your 10-channel amplifier design/build video first. 😊

[@bradstone2603]

Rpi, paxoverrack, 5 dacs, likely cheaper too...

[@valdimirputin1335]

At what stage Active Crossovers are connected? Between pre-amp and power-amp or between power-amp and subwoofer?

[@Humbulla93]

Between pre amp and power amp

[@analoghardwaretops3976]

..so these active xovers are slightly over 2 octaves wide....hence 5 per stereo channel?? How difficult would it be to have a one octave wide... design .... (a 10+10 active) in terms of acoustic performance only...??

[@bbfoto7248]

@IBuildIt Maybe it's been asked, but what will your Final Total Cost be for all prototyping + the finished versions of these 10 active analog crossover boards?

[@IBuildIt]

Impossible to say. But I do this because I enjoy it and therefore it qualifies as entertainment, so the actual cost (in time and money and materials) in inconsequential.

[@danielh12345]

​@IBuildIt this is what people often forget when the argument is made against DIY; "DIY is not cheaper, look at all the time and money you spend". Yeah someone spends their free time doing something they enjoy, instead of going to the movies or something like that. Besides, it doesn't even have to be cheaper as long as you have fun and like what you're making :)

[@bbfoto7248]

@danielh12345 @IBuildIt 🙄 Ummm...I get it. I've been doing DIY for over 30 years as well in speaker design/building, electronics, and woodworking, as I was inspired by my father who was a carpenter/cabinet maker, musician, HiFi/Stereo enthusiast, and an Advanced/Extra Class Amateur "HAM" radio operator who built most of his RF electronics and antennas, etc. And, I also realize that these many DIY projects also provide your several KZbin channels with HEAPS of content, which is your main livelihood, is it not? So this could potentially allow you to "write-off" these expenses on your income taxes, so the costs are not as impactful to you as they would be to others...which also means that if you are submitting them as tax write-offs, you probably do, in fact, know what these projects cost you, and are not "impossible to say". However, I'd still like to know (and maybe others do as well) a rough estimate of what this project will cost, as I don't believe you can say that costs are never a factor for a DIY enthusiast who is interested in tackling any given project.

[@IBuildIt]

@@bbfoto7248 What makes it impossible to say is that I'm using stuff that I either got for free, or bought nearly 20 years ago, along with some new parts that are pretty much pocket change if you are earning a decent living. A ballpark figure would be less than $1000 but more than $300. BUT, that's for ME, using the stuff I'm using. For someone else it might be double or triple that. Or more, depending upon how many mistakes were made. And for most the cost would be zero, because they wouldn't / couldn't do it.

[@danielh12345]

@bbfoto7248 sorry, I never meant to say / make you think I believed you don't get it. I just like his attitude is all. And I agree, cost definately is a factor to consider for DIY for me. Its keeping me from doing stuff I would otherwise do most likely. But thats life. Im still young and needs and wants are 2 different things haha. E.g. I would love to make a 3 way speaker but finding a design thats worth building + I have the tools and space to do has proven difficult. My only DIY audio so far has been a set (2 actually, one for my twin brothers birthday) Overnight Sensations Bookshelf kits which I glued, assembled / soldered veneered and made some minor modifications to the bottom to mount to speaker stands in same style and veneer that I made for them. Added some leds underneath the stands to provide extra lighting on my desk. Controlable by philips hue. Its fun and I enjoyed the process and what I have. Curious how much better DIY audio gets but my wallet / conscious won't allow it for now haha. Edit, I'm also limited to (ported) boxes/ towers since I have a pet bird that could otherwise hurt himself or damage stuff on open baffle designs

[@Aswaguespack]

Very cool John!

[@fredthompson1279]

Any plans to sell blank boards?

[@IBuildIt]

That's not something I want to get into. And besides, it's not 100% my design - I just did the board layout.

[@lohikarhu734]

I was wondering if you have any "funny things" in phases among the crossovers...24dB makes a lot of phase changes... You could probably, or did, simulate the crossovers, but, then, speaker phases, et al...

[@IBuildIt]

Phase "funny things" show up in the frequency response, as in one driver playing out of phase with another will cause peaks and dips in the response. There's nothing inherently bad about a higher order crossover, if it gives you what you need for the best response. Sometimes a phase change is needed to produce the best response. But even in a "phase perfect" speaker (as if one could exist...), it's playing in a room that introduces a swarm of reflections from the walls, floor, ceiling and any furniture that's in the room to cause such an unholy mess of what actually reaches your ear. That makes worrying about phase shift from a higher order crossover a drop in a very big bucket.

[@TriAmpHiFi]

Why not variable x-over points?....................... You'll be stuck if new drivers are chosen, like a horn mid-range. 🔈🔉🔊

[@IBuildIt]

Making it variable is very complex and certainly a lot more work than just changing out a board to get a different crossover frequency.

[@TriAmpHiFi]

@@IBuildIt Hhmmmmm............. wouldn't that be 2 boards for each side? 4 boards.

[@IBuildIt]

Still easier. It's still easier to replace ALL of the boards completely (and probably cheaper) than to design and build variable ones.

[@TriAmpHiFi]

@@IBuildIt Thank-you. Good luck. 🔈🔉🔊

[@johncnorris]

"It's not how you sound, it's how you look. And you look..."

[@gcarson19]

MARVELOUS!

[@ballsrawls]

........ Like you know what you're doing.

[@KravchenkoAudioPerth]

I love it. Overly anal. You are making a ten channel amp and going to make fully active Loudspeakers. But not overly anal :) Awesome presentation John. Seriously you are spot on a tiny difference like you measured will never be audible. Mark

[@IBuildIt]

Thanks Mark. It's the lost art of balancing macro and micro, sorting the important from the trivial, the wheat from the chaff, it's all grist for the mill where you don't lose the plot after falling into a rabbit hole and chasing a mad hatter. Sorry, I've been sniffing too many lacquer thinner fumes.

[@KravchenkoAudioPerth]

@IBuildIt Been there. Keep it up John.

[@FOH3663]

Limitless Flow