Active crossover build project

oscroft

Member
Someone suggested I should post a thread on this build project, so here it is. Back in the 80s, I had a three-way active system - pre-amp, 3-way crossover, and three power amps (driving tweeter, mid/bass, and passive sub). It was in a different country, and I still have it all, though it is mostly still out there. But I have the crossover here - it was built to order, with the crossover frequencies I specified. It had failed, and I originally intended to try to repair it. But there are some much better designs, by Siegfried Linkwitz and Russ Riley in particular, with the Linkwitz–Riley filter solving, particularly, the phase errors inherent in other designs.

So never mind fixing the old one, let's build a new one. Rod Elliott (of Elliott Sound Products) has a take on the L-R crossover, and it seemed perfect for me. I can re-use the old case and its power supply, and the new boards are smaller and will fit in easily. After a chat with Rod, I bought two of the PCBs (which came all the way from Australia). When you buy PCBs for one of his projects, you get access to full build instructions, and they're nicely detailed.

So far, I've stripped out the old case, replaced the RCA connectors (the old "gold" ones had rusted), and replaced the power supply capacitors and checked that out. This photo shows it, with one of the old crossover boards and one of Rod's placed inside for size...

D21_003_003a.jpg


I now have a powered subwoofer with its own low-pass filter, so this can give me up to a four-way system - treble, mid, bass and sub. I'm using Audiolab amps - an 8000A (with pre and power sections split), an 8000SX and an 8000P. I'll probably set it up as two-way plus sub to start, as I'll need to build bass speaker units to take it to three-way plus sub system.

Anyway, it might take a while as I have a habit of chopping and changing between projects. But it should be fun, and I hope it will be of interest to others.
 

Helix Hifi

Well-known Member
Someone suggested I should post a thread on this build project, so here it is. Back in the 80s, I had a three-way active system - pre-amp, 3-way crossover, and three power amps (driving tweeter, mid/bass, and passive sub). It was in a different country, and I still have it all, though it is mostly still out there. But I have the crossover here - it was built to order, with the crossover frequencies I specified. It had failed, and I originally intended to try to repair it. But there are some much better designs, by Siegfried Linkwitz and Russ Riley in particular, with the Linkwitz–Riley filter solving, particularly, the phase errors inherent in other designs.

So never mind fixing the old one, let's build a new one. Rod Elliott (of Elliott Sound Products) has a take on the L-R crossover, and it seemed perfect for me. I can re-use the old case and its power supply, and the new boards are smaller and will fit in easily. After a chat with Rod, I bought two of the PCBs (which came all the way from Australia). When you buy PCBs for one of his projects, you get access to full build instructions, and they're nicely detailed.

So far, I've stripped out the old case, replaced the RCA connectors (the old "gold" ones had rusted), and replaced the power supply capacitors and checked that out. This photo shows it, with one of the old crossover boards and one of Rod's placed inside for size...

View attachment 1487190

I now have a powered subwoofer with its own low-pass filter, so this can give me up to a four-way system - treble, mid, bass and sub. I'm using Audiolab amps - an 8000A (with pre and power sections split), an 8000SX and an 8000P. I'll probably set it up as two-way plus sub to start, as I'll need to build bass speaker units to take it to three-way plus sub system.

Anyway, it might take a while as I have a habit of chopping and changing between projects. But it should be fun, and I hope it will be of interest to others.
:clap: Awesome. I envy your ability to do this stuff yourself. Are you perhaps an old electrician of hifi stuff, or something similar? I get that impression when reading threads, that you are. Oh, what kind of amplifier is that?
 

Helix Hifi

Well-known Member
And those big things on the right side of the print boards, are those the caps? Which then works in shift giving the speakers more juice when they need it.
 

Khankat

Well-known Member
Great. Really interesting. Will be following this with interest. I wish I knew how to split the pre and power sections in my 8000A. And I wish I had your talent and expertise. But I don't. To console myself, I bought another cartridge.😁
 

oscroft

Member
I've never done electronics professionally, I've just been a bit of an amateur enthusiast on and off over the years. It all started with an electronics club at school back in the 70s - as I like to say, it's where I first learned to burn myself with a soldering iron, a skill I retain to this day.

The black and gold coloured can things are indeed the power supply capacitors (they're Nichicon Fine Gold grade, hence the colour). They provide the smoothing for the rectified power (you can just see the four rectifier diodes in line in between them), which would otherwise be a sine wave with the bottom half flipped upwards - like a rounded mountain range, and no good at all for audio power. The crossover doesn't actually provide gain, it just splits the frequency ranges - which then feed into the power amps for the speaker-driving gain.

Splitting the pre and power stages of the 8000A is a straightforward mod, designed to be easy. You just need to be able to move two resistors - I'll dig out the details.

And finally... Ooh, what's the new cartridge? :)
 

Khankat

Well-known Member
I've never done electronics professionally, I've just been a bit of an amateur enthusiast on and off over the years. It all started with an electronics club at school back in the 70s - as I like to say, it's where I first learned to burn myself with a soldering iron, a skill I retain to this day.

The black and gold coloured can things are indeed the power supply capacitors (they're Nichicon Fine Gold grade, hence the colour). They provide the smoothing for the rectified power (you can just see the four rectifier diodes in line in between them), which would otherwise be a sine wave with the bottom half flipped upwards - like a rounded mountain range, and no good at all for audio power. The crossover doesn't actually provide gain, it just splits the frequency ranges - which then feed into the power amps for the speaker-driving gain.

Splitting the pre and power stages of the 8000A is a straightforward mod, designed to be easy. You just need to be able to move two resistors - I'll dig out the details.

And finally... Ooh, what's the new cartridge? :)

Thanks for another interesting thread. Thanks also, for seeking out the details for pre-power mod. I believe, but am no way sure, that different incarnations of the 8000A have different boards and layout, if that makes a difference. As far as I can tell, without opening the beast, it was one of the later models, one with gold-plated RCA's. All I know is, I won't ever part with it. And upgraded, it sounds very good indeed.

I am fortunate in that I have a nearby independent phone shop, one that offers mods and repairs. They also buy and sell some new but mostly pre-owned video games machines, TV's and laptops. Occasionally, they have the odd bit of Hi-Fi. One such, was a Rotel power amp, which was of interest, and for £50 fully checked over, was a bargain. The only minus point, was that the model in question does not have speaker protection of any sort- I read something somewhere about this being desirable. So I did not buy it.

Cartridge is a rare-as-hens-teeth, pre-owned Audio Note (UK) IQ3 . I have yet to fit it. But as I like the Goldring 1xxx series, one of which the IQ3 is based on, it'll do me.
 

oscroft

Member
I believe, but am no way sure, that different incarnations of the 8000A have different boards and layout, if that makes a difference.
There are variations in the boards, but the pre/power mod is essentially the same with them all. Does yours have "video" as one of the inputs? If so, it's the last generation and the same as mine.

Cartridge is a rare-as-hens-teeth, pre-owned Audio Note (UK) IQ3 . I have yet to fit it. But as I like the Goldring 1xxx series, one of which the IQ3 is based on, it'll do me.
Oh wow, that * is * exciting :)

(Oh, and yes, speaker protection is very much a good thing :smashin:)
 

Ugg10

Distinguished Member

Khankat

Well-known Member
There are variations in the boards, but the pre/power mod is essentially the same with them all. Does yours have "video" as one of the inputs? If so, it's the last generation and the same as mine.


Oh wow, that * is * exciting :)

(Oh, and yes, speaker protection is very much a good thing :smashin:)
Yup, mine has the 'video' and until replaced, had gold plated RCA's.

I do not know what form speaker protection takes. But as the previously mentioned Rotel was on offer, I did some swift but brief research, whereupon I learned of speaker protection. So disappointment on the one hand and relief on the other.

I have wanted an Audio Note IQ3 for some considerable time, so was happy to snag one. Audio Note do not publish their prices but they gave me them on request. They make very fine and very expensive equipment. Plenty to lust after, that's for sure.
 

oscroft

Member
Yup, mine has the 'video' and until replaced, had gold plated RCA's.

I do not know what form speaker protection takes. But as the previously mentioned Rotel was on offer, I did some swift but brief research, whereupon I learned of speaker protection. So disappointment on the one hand and relief on the other.

I have wanted an Audio Note IQ3 for some considerable time, so was happy to snag one. Audio Note do not publish their prices but they gave me them on request. They make very fine and very expensive equipment. Plenty to lust after, that's for sure.
The 8000A service manual I have is for an older version than ours - the pre/power mod is identical, but the component numbers changed between versions. So, I'll have to take a look inside mine to get the correct numbers - I'll let you know as soon as I do that.

And yes, Audio Note don't do cheap ;)
 

oscroft

Member
You know the way sometimes things come together unexpectedly? I just watched Paul McGowan on YT talking about volume controls where he said that PS Audio doesn't use potentiometers, and that's something I've had in mind for a while. Can I modify my Audiolab 8000A to use a stepped attenuator instead of a potentiometer? I don't know if it would make any difference, but, well, I like to try these things. The problem is, there isn't enough space in the amp case to fit one, so I'd pretty much dismissed it as impractical.

But it just struck me, in a "Duh!" moment. Why don't I put a stepped attenuator volume control in the crossover? Set volume on the pre-amp to max so it's not using any of the pot's resistor film, and use the crossover volume control instead. There's plenty of space in the crossover case to fit one. I might do that :smashin:

Oh, and for those who don't know what I'm talking about, there's an explanation here. (They're trying to plug something a lot fancier there, so they talk down the stepped attenuator approach, but the gist is there.)
 
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Khankat

Well-known Member
Thank you for this. Your idea of moving volume control from one place in the chain to another is interesting.
 

oscroft

Member
I've made some progress, getting over a major hurdle - being unable to decide how to configure the crossover. It's designed to be configured in a number of ways - two way, three way, mono, stereo. I had intended to put the left and right high-pass on one board, then put the low-pass crossovers on the other board - that would be more efficient in components, and would let me try it as a two-way crossover as a first step.

But I couldn't help thinking dual mono would be better, with a full single-channel crossover on each board. That got me thinking about the power supply too, and I'd been in two minds about reusing the old one anyway. It has an old square transformer, and the PS board itself is not particularly low noise.

So, the old power supply is being ditched (but I can reuse the Nichicon caps). I've got myself a suitable Talema torroidal transformer, and I'm ordering some better PS boards from Rod Elliott - I'll have to wait for them to arrive from Australia. I'll use two PS boards to make it dual mono past the transformer.

I also made another decision that's been plaguing me. I have a set of NE5532 op-amps, but I kept thinking I should maybe use better ones - Rod recommends three different ones that work well. I checked the specs and various tests, and the LM4562 op-amp measures better. Would I hear any difference? Probably not, but I'd always be wondering... So I got a set of LM4562 chips (and I now have some NE5532s spare for other projects).

And, after all that waffle, I've built up the two boards. Here they are built as three-way mono crossovers...

D21_003_014a.jpg
 

Khankat

Well-known Member
No, no, I said I needed a cr... Charlie. Romeo. Oscar...

I have a thing for populated boards. Don't know why, but they really appeal to me aesthetically, PC mobo's in particular. I don't understand them but they are good to look at. I recall BBC TV using populated boards in those little clips they show between programmes. Initially, and with only a cursory glance, they looked like City streets. Clever.
 

Ugg10

Distinguished Member
Just for you @Khankat, Silicon Valley at sunset!

 

oscroft

Member
After ditching the old power supply, the only thing left from the original was the case - and it's a bit tatty and bigger than I need. So that's out too, and I have a new case. I'm also leaving out the stepped attenuator for now - I probably will try one in due course, but I'll put it in its own small case, as it would go straight on the crossover input anyway. The new power supply PCBs arrived from Australia and I've built them up, so the parts now all look like this (they won't necessarily be oriented this way, I haven't decided yet)...

D21_003_018a.jpg
 

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