DIY 3-way analogue crossover with Gainclone amps

Tony_J

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Some while ago I bought a pair of bare boards from KMTech - 3-way analogue crossovers with on-board LM3886 "gainclone" chip amps - intending to populate them at some point. Some projects need to "mature" for a few years before they are ready for prime time, so they gather the right thickness of dust. I came across the boards shortly after the last show and decided that they were ripe for development - having played with miniDSP tech in my recent builds I was interested to see how an analogue setup would fare driving my 3-way Tannoy-based speaks that I took to stoke. So I decided to start accumulating and salvaging the necessary bits. The biggest issue was sourcing the LM3886 chips - these have become a particularly rare form of unobtanium in recent years, and as a result, genuine chips (there are lots of nasty clones around) are at a premium, so being a cheapskate, it took a while to accumulate the 8 chips required (the bass channel uses 2 in parallel) at prices that didn't cause too much grief.

I've been slowly building these up, plus the necessary power supplies - the boards have their own rectification/smoothing, and need separate twin rail AC supplies for the power amps and the crossover sections, so the PSUs are just a couple of metal boxes with BFO torroids in each.

Finally finished building up both boards and PSU boxes yesterday, so I've been testing the first board one a channel at a time with a nasty 2" driver to make sure there are no surprises when I connect up the real deal. So far, all has gone smoothly. It will now take a few more hours to arrange proper connection to the speakers and to start adjusting the levels on the 3 channels, but so far, so good.

The component side of the board:
IMG_20230318_105953.jpg

The LM3886 chips are mounted on the back of the board:

IMG_20230318_110043.jpg

One of the PSU boxes:

IMG_20230318_110017.jpg
 

Tony_J

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One thing yet to be determined is how I will mount the boards - the KMTech writeup suggests mounting them in the speaker cab with just the heatsinks protruding outside, but I am a bit dubious anout this for various reasons, so the end game will prolly involve a couple of project boxes of some kind with a cutout to allow the heatsink to protrude. We'll see - first step is to get them singing properly.
 

Tony_J

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If you're going to do any op-amp rolling try the LM6172. It replaced a NE5532 in my DAC and sounded a lot cleaner.
Thanks - I may well give them a go once it is all properly up & running.
 

Tony_J

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So far, so good ... Wired up with a picoreplayer front end, not attempted any channel balancing yet, but initial sound test with a spot of Dvorak followed by a spot of Yello shows promise - amps are gratifyingly quiet on switch on with minimal background noise, slight hum if you stick your ear hole next to a driver but inaudible at listening position. Sound obvs needs balancing between the 3drivers, but listenable to "out of the box". The boards and PSU boxes are sitting atop the speaks till I figure out something more sensible!
IMG_20230319_121519.jpg
 

greybeard

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Looking good Tony, I have recently swapped my dcx for a cx3400, and also added the power filter board to the Pi4. The results have been very satisfying musically. A smoother dare I say more analogue sound, and I am using no room correction.
 
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bencat

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Colin would you like to try a 5 V LPSU for the Pi ? I can say that this does make a real difference on all my various Pi players . If you are interested I have a spare one currently and could post it off to you for a long term loan and listen .
 
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Tony_J

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Looking good Tony, I have recently swapped my dcx for a cx3400, and also added the power filter board to the Pi4. The results have been very satisfying musically. A smoother dare I say more analogue sound, and I am using no room correction.
Sounds good Colin.

I'm going to spend a bit of time getting the channels properly balanced before doing anything else, then see what difference adding Dirac to the mix makes - it will be interesting!
 
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Tony_J

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Did a spot of measurement using REW and the response curve is surprisingly flat with all 3 channels set to max, so not a lot of point in making adjustments there. So I did a quick-and-dirty Dirac calibration, with a single measurement at the centre position to see what difference it makes, using my customary Harmann target curve. As I have found in the past, with the levels balanced before doing the Dirac sweep the addition of the Dirac filters doesn't have a great effect on the overall balance, but brings the imaging into focus.

Surprisingly, the impression I get is that these little chipamps have more "headroom" than the Icepower amps I was using in Stoke. I haven't had a chance to crank the volume up to 11 yet though..:unsure:

All in all, seems to have been a worthwhile project as it signigicantly reduces the number of boxes and cables and performs (at first impressions) very well.
 

Tony_J

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A proper set of Dirac measurements this morning - sounding pretty good to my ears. I can't say with any certainty that it sounds significantly different from the previous setup (miniDSP Flex 8, 4x Icepower amps) because the last time I heard that setup was in the room at Stoke, but it is certainly working well! Yello Touch sounding as good as I have ever heard it.
 
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Tony_J

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I've found a pair of suitably sized diecast ally boxes that will house the crossover/amp boards very nicely, and they also fit perfectly in the available space on the back of the speaker cabs, so it will end up as a very tidy solution.
 

Tony_J

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Further work on hold as I managed to bust a metacarpal in my right hand...but the silver lining, more time to listen. All in all, sounding very well at the moment. The DDRC-24 is now just doing Dirac processing and I have replaced a bunch of Icepower amps and the digital crossover with the new analogue setup, but it is hard to say either whether anything has really changed in terms of SQ, or if it has, which of the changes is responsible. A-B comparisons are out of the question of course!
 

greybeard

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Colin would you like to try a 5 V LPSU for the Pi ? I can say that this does make a real difference on all my various Pi players . If you are interested I have a spare one currently and could post it off to you for a long term loan and listen .
Andrew, sorry I missed this post somehow, if you still have a spare PSU, I would like to try it, thank you. PM me if it is available.
 

Tony_J

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Finally amassed the necessary round tuits to finish the job by embedding these boards in suitable diecast ally boxes. The flying leads are the AC feeds for the crossover and power amp sections of the boards. The boxes were bare diecast ally but a coat of spray paint makes them a bit neater. Next job - fix them to the backs of the cabs and make up 3 pairs of short speaker cables. IMG_20230429_152449.jpg IMG_20230429_152413.jpg
 
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