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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Budget active 3 way crossover - buy, eval, mod
Budget active 3 way crossover - buy, eval, mod
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Old 4th February 2018, 09:50 PM   #21
Soldermizer is offline Soldermizer  United States
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Default The solder-averse budget method...

If you can bring yourself to consider a PC based DSP, these could be done as cheaply as a PC that will run DSP software (such as J River Media Center); you can get PCs well < $200 that have HDMI out (such as Pipo X9), feed HDMI to a cheap 5.1 or better HTR and you have, effectively, a multi-channel DSP to use as you like.
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Old 4th February 2018, 10:19 PM   #22
DonVK is offline DonVK  Canada
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Nothing against DSP approaches, its often the only way to do certain things. I have used my PC with APO equalizer's convolution engine and Rephase to generate filters for both the room and the speaker. I also have another thread trying to do a similar thing on an RPI which is where I would prefer it. After I get basic EQ and a convolution engine working on the RPI, I plan on trying a s/w crossover as well. Maybe both will be used, a hardwired filter is safety from rogue s/w.

Last edited by DonVK; 4th February 2018 at 10:21 PM. Reason: left out
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Old 5th February 2018, 07:24 AM   #23
zdr is offline zdr  Belgium
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I have been using FreeDSP and never looked back.
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Old 5th February 2018, 09:14 AM   #24
AndrewT is offline AndrewT  Scotland
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thanks for the name. Didn't know anything like that existed. Do you have any recommendations?
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Old 5th February 2018, 05:07 PM   #25
DonVK is offline DonVK  Canada
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Default Distortion

The following are measured with REW and a PC soundcard (24b). The graphs are scaled so that the max line in = 0db. So I adjusted the output such that the max signal into the soundcard is -3db to avoid clipping. It also means that the soundcard output can't be maxed because of the gain at the active XO input.

In all cases the TH is -80db which I'm good with. Its hard to determine if its the XO or the PC sound card that's the limiting factor here but I suspect the PC. I also need to clean up some switching noise from the SMPS. Then I might try a different setup that would allow me to figure out the actual noise floor on the XO and if I can push the TH a little lower.
Attached Images
File Type: jpg LowBand Distortion.jpg (100.2 KB, 281 views)
File Type: jpg MidBand Distortion.jpg (102.8 KB, 279 views)
File Type: jpg HighBand Distortion.jpg (97.9 KB, 271 views)

Last edited by DonVK; 5th February 2018 at 05:09 PM. Reason: typo
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Old 10th February 2018, 03:22 AM   #26
DonVK is offline DonVK  Canada
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Default Noise

I don't have equipment or a method of proper noise measurement other than time waveform and an oscilloscope. There is some SMPS HF noise present, and the XO board lacks HF decoupling. This test was with the inputs shorted to ground and a 10K load on the outputs.

The on board regulators attenuate some of the lower freq SMPS variation. Pic#1 show the ac component of the +15vdc rail with the mid outputs (M) as a wide view. Pic#2 shows the zoom in of the ac components of the +15VDC and the low (L) outputs. Pic#3 is a zoom in of the ac components of the +15VDC and the high (H) outputs. Pic#2 and #3 show the onboard regulator helps for some variations, but the HF goes through everything. A power filter will be added after I test a few other related pieces of equipment.
Attached Images
File Type: jpg 15VDC and mid out wide view.jpg (104.8 KB, 245 views)
File Type: jpg 15VDC and LF out.jpg (87.5 KB, 240 views)
File Type: jpg 15VDC and HF out.jpg (83.6 KB, 22 views)
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Old 3rd June 2018, 07:23 PM   #27
DonVK is offline DonVK  Canada
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Default packaging

Finally got around to putting it in a box. The fan will eventually something like a LM317 based speed control to make it quieter. There is enough room left for additional boards. The current FR is shown with the mod'd sub bandpass.

I'm getting closer to deciding on the final 3way XO points that I want. Each driver would handle 2.5 octaves and behave well in the XO overlaps.

sub : 20-100Hz
woofer : 100Hz-600Hz
mid : 600-3.6Khz
tweeter : 3.6Khz-20Khz
Attached Images
File Type: jpg DSCN5233 reduced.jpg (640.4 KB, 74 views)
File Type: jpg DSCN5234 reduced.jpg (560.0 KB, 71 views)
File Type: jpg DSCN5240 reduced.jpg (587.4 KB, 58 views)
File Type: jpg Sub bandpass mod + stock 3way.jpg (95.9 KB, 66 views)
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Old 7th June 2018, 03:25 AM   #28
keilau is offline keilau  United States
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How do you roll off the woofer below 100Hz? The woofer and the subwoofer seem to have the same SPL from 30 to 100Hz. Will this arrangement make the sub-100Hz range 3dB louder the rest of the sound spectrum?
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Old 7th June 2018, 04:23 AM   #29
DonVK is offline DonVK  Canada
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The woofer will have a sealed chamber, so it will have a -12db/octave acoustic rolloff at 100Hz. Still, the slopes are different (sub -24db, woofer -12db) so a small bump could occur. The sub's volume (gain) and XO point are adjustable for this reason.
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Old 29th June 2018, 09:46 AM   #30
keilau is offline keilau  United States
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How do you tailor the individual pass band's output level to adjust for different driver sensitivity? The crossover board has no provision for output volume.

I am building a crossover trying to use this board.
Preamplifier Crossover 2-Way Electronic Frequency Divider board Free adjustable 831230323184 | eBay
But I cannot get the seller to provide a schematic or to send instruction on how to set the jumpers and trimmers after I got all the other parts and a case sized for this board. I may need to look at this.
Linkwitz-Riley 2-way electronic crossover at 2.2KHz stereo (changeable by user ) | eBay
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