Hello CWelsh52 and everyone, I'm glad that active crossover works well for you, but it doesn't make things any easier for me. I still don't know which type of amplifier is best for direct connections to a horn speaker with a recommended 800 Hz crossover frequency and a 15 inch woofer? Thanks
Well it kind a depends on what sound you like. At the moment, i am driving a 15" bass woofer with an F6 and a Fulltone driver with the ACA Mini, with a crossover point (-6 dB) at 160-170 Hz. All driven by a ZM iron Pre and a NP FR EQ before the BiAm6-24. The ACA Mini is to be exchanged by a ZM LuDEF amp very soon.
Some of the questions you can consider, for choosing an amp:
What is the sensitivity of the driver?
What is the resistance (8/4/??)?
What kind of sound do you like? Consider harmonics, both the content (neg 2nd dominating, 3rd dominating etc.) and the amount - to my ears, too much harmonics content, can make some simpler music sound out of this world, while take the life out of more complex music
Some might use a class D for bass and choose a glorious sounding, low efficiency class A amplifier for mid and tweeter.
There is no correct answer, the fun is in the journey
By the way for the right music i highly recommend the ACA Mini, it really sounds good - instruments and voices are magical with it.
On one of yours the lead spacing looks to be 15mm. I think you want 5mm for that figure. I can't see that data on your second cap variant. For what it's worth I used these:
https://www.digikey.com/en/products/detail/wima/MKS2D021001A00MSSD/9370565
https://www.digikey.com/en/products/detail/wima/FKP2D014701G00HSSD/9370190
These for my first variant and recall the crossover point is as you calculated. I've since changed those caps to cross ~ 100hZ.
Paid the princely sum of $3 for a wood +mdf chassis. These crossovers are so quiet at least in my experience require no shielding, I had it sitting naked on top of my Iron Pre no problems.
Thanks, @JKiriakis. With help from others, I did get it all figured out.
Pretty cool chassis you've got there!
Pretty cool chassis you've got there!
I was involved in evaluating these crossovers early on in the piece.
Just be aware the slope refers to the acoustic slope. Given no driver is ever ideal you will need to tweak the crossover voltage drive.
I recommendation is to make a voltage drive measurement in REW and Save these curves.
Then use these curves as objecti
Just be aware the slope refers to the acoustic slope. Given no driver is ever ideal you will need to tweak the crossover voltage drive.
I recommendation is to make a voltage drive measurement in REW and Save these curves.
Then use these curves as objecti
The other thing to bear in mind is the LR24 low and high pass filters have non symmetrical group delay. What this means is that you will need to take this into consideration when looking at the driver offset. The effect is that the on axis lobe will be tilted.
You can incorporate analogue 3rd order Bessel all pass filter to compensate for the difference in the group delay.
The alternative is to introduce phase compensation by shifting one of the crossover points slightly. This will move the on axis axial response to produce a flat response in the crossover region. Vance Dickason covers this in the Loudspeaker Cookbook.
It’s more of an issue for tweeter crossover points than say a horn @ 800 hertz.
Above all measure your native driver frequency response on the loudspeaker baffle before commencing the active filter design process.
Also use DATS3 to check the impedance for driver resonances.
Try and also measure the 30 degree off axis response as well. This will help you realise the optimum crossover point in a two way design.
Tip. Do not attempt a nearfield indoor measurement with the mic right on the dust cap. This will cause errors in both the low and high frequency response. Your measurements should be at 3 x the diameter of the driver. Use 1/12 octave smoothing. Better still do it outside a a chair if it’s not raining to avoid loosing resolution lost with Gating.
You can incorporate analogue 3rd order Bessel all pass filter to compensate for the difference in the group delay.
The alternative is to introduce phase compensation by shifting one of the crossover points slightly. This will move the on axis axial response to produce a flat response in the crossover region. Vance Dickason covers this in the Loudspeaker Cookbook.
It’s more of an issue for tweeter crossover points than say a horn @ 800 hertz.
Above all measure your native driver frequency response on the loudspeaker baffle before commencing the active filter design process.
Also use DATS3 to check the impedance for driver resonances.
Try and also measure the 30 degree off axis response as well. This will help you realise the optimum crossover point in a two way design.
Tip. Do not attempt a nearfield indoor measurement with the mic right on the dust cap. This will cause errors in both the low and high frequency response. Your measurements should be at 3 x the diameter of the driver. Use 1/12 octave smoothing. Better still do it outside a a chair if it’s not raining to avoid loosing resolution lost with Gating.
I've taken the plunge and ordered two boards for a 3-way speaker project. I've read the entire thread, and strayed into a couple of side quests like balanced operation and JFET buffers.
I've also ordered a bunch of LSK170's because clearly I like the deep end. Mostly the conversation around FETs in here is about biasing, so have that well understood. Where I'm still missing context is around matching. It's been mentioned in passing a few times, but there seems to be contradictions. I've also learned that when smart people seem to spout contradictions, there's something interesting to learn. It was never contradictory, but lacking context.
There looks to be some fuss around matching among builders here, then N.P. drops this nugget in post #932:
Everyone is scrambling to "match" their JFETs, when Mr. Pass is casually hand-waiving it away and blasting Idss values into the stratosphere, well beyond the J Fringe. And to my layman, tiny brain it seems logical that pairing a J113 (Q2, CCS) with an LSK170 (Q1, Follower) would be quite impossible to match, they are quite different parts. For instance, J113 has an Idss of 2-? (I've seen 40mA+ in other's measurements?), whereas the LSK170 is 6-12mA.
Quote below is not about matching per se, but builders seem to want to match for the purposes of staying within Idss "limits". From this article elsewhere on the Internet:
Huh? No wonder there's confusion around this topic. There's a devil lurking in the details, I suspect. On to the questions:
1. In what context is matching FETs important for this particular circuit? Vp? Minimum Idss? Between Q1 and Q2? Horizontally across channels? Vertically along one signal/filter path?
2. I see Beyond the J Fringe has LS parts in a push-pull circuit, and Toshiba parts in another. Can drain current overdrive work safely in the context of this crossover?
3. If the answer to the above question is no, what are the considerations/pros/cons for dropping drain currents from the stock 8-10ma to my lowest common denominator ~6.5mA?
Wow long post. Thank you Nelson Pass for this fantastic design, and thanks to all the folks in here for sharing your knowledge and builds!
I've also ordered a bunch of LSK170's because clearly I like the deep end. Mostly the conversation around FETs in here is about biasing, so have that well understood. Where I'm still missing context is around matching. It's been mentioned in passing a few times, but there seems to be contradictions. I've also learned that when smart people seem to spout contradictions, there's something interesting to learn. It was never contradictory, but lacking context.
There looks to be some fuss around matching among builders here, then N.P. drops this nugget in post #932:
Everyone is scrambling to "match" their JFETs, when Mr. Pass is casually hand-waiving it away and blasting Idss values into the stratosphere, well beyond the J Fringe. And to my layman, tiny brain it seems logical that pairing a J113 (Q2, CCS) with an LSK170 (Q1, Follower) would be quite impossible to match, they are quite different parts. For instance, J113 has an Idss of 2-? (I've seen 40mA+ in other's measurements?), whereas the LSK170 is 6-12mA.
Quote below is not about matching per se, but builders seem to want to match for the purposes of staying within Idss "limits". From this article elsewhere on the Internet:
Huh? No wonder there's confusion around this topic. There's a devil lurking in the details, I suspect. On to the questions:
1. In what context is matching FETs important for this particular circuit? Vp? Minimum Idss? Between Q1 and Q2? Horizontally across channels? Vertically along one signal/filter path?
2. I see Beyond the J Fringe has LS parts in a push-pull circuit, and Toshiba parts in another. Can drain current overdrive work safely in the context of this crossover?
3. If the answer to the above question is no, what are the considerations/pros/cons for dropping drain currents from the stock 8-10ma to my lowest common denominator ~6.5mA?
Wow long post. Thank you Nelson Pass for this fantastic design, and thanks to all the folks in here for sharing your knowledge and builds!
Attachments
determine which part of buffer cell is signal, which is CCS
logically - precioussssss JFet is signal one, cheap drek JFet is CCS
measure all your precious JFets for Idss, make pairs and use pairs in same position of both channels; say HP both channels one pair, LP both channels second pair
measure all your drek JFets for idss,, derive source resistance for target Iq to pair them with preciousssss JFets
say that you have 10mA precioussss Idss Jfet in HP cell; say that you want to push it to 90% of Idss, that's 9ma; find source resistor value to bias drek JFet to 9mA; when you pair these two - preciousssssssss JFet biased with drek JFet 9mA CCS ......... that's it
work cell by cell , and you'll have it
edit: in case that you post exact schmtc, I can be very specific, regarding nomenclature
that's only way to avoid broken telephones effect
logically - precioussssss JFet is signal one, cheap drek JFet is CCS
measure all your precious JFets for Idss, make pairs and use pairs in same position of both channels; say HP both channels one pair, LP both channels second pair
measure all your drek JFets for idss,, derive source resistance for target Iq to pair them with preciousssss JFets
say that you have 10mA precioussss Idss Jfet in HP cell; say that you want to push it to 90% of Idss, that's 9ma; find source resistor value to bias drek JFet to 9mA; when you pair these two - preciousssssssss JFet biased with drek JFet 9mA CCS ......... that's it
work cell by cell , and you'll have it
edit: in case that you post exact schmtc, I can be very specific, regarding nomenclature
that's only way to avoid broken telephones effect