Behringer CX2300 replace caps (values change) - diyAudio
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Old 7th April 2015, 08:26 PM   #1
Trileru is offline Trileru  Romania
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Default Behringer CX2300 replace caps (values change)

Hello,
I just got a Behringer cx2300 crossover and I was thinking of replacing the electrolytic capacitors.
The unit looks decent. I see no apparent repairs, although the blown fuse has been bypassed with a wire :/
The regulators seem stock, encased in plastic. No metal tabs on them.
My issue is that there are many 22uF capacitors in the circuit, in the signal path.
I could replace them with Wima caps, the MKS2 series has 10uF values (with 5mm pin distance), and I'd have to parallel them but this will quickly get very expensive as there are about 32 x 22uF caps in this crossover. 64 Wima caps would be too expensive and I don't think they would fit anyway.
Is there a way to redesign the circuit using 10uF caps (instead of the 22uF ones) and different values resistors?
I would appreciate any detail on this as I would like to remove as more electrolytic capacitors as possible from the signal path.
I could also bypass the output ones as I have input caps in my amplifier.
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File Type: png p3.png (105.9 KB, 96 views)
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File Type: png p5.png (100.5 KB, 95 views)
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Old 7th April 2015, 08:40 PM   #2
Trileru is offline Trileru  Romania
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The unit uses a simple regulated supply with 7815/7915 devices.
The positive rail is at +15VDC but the negative sits at about -14.6VDC. The regulators are incased in plastic, no metal tabs.
Lots of quad op-amps, 12 of them. And a dual JRC 4580.
I don't know exactly what kind of op amps the BE037 are but I might replace them for TL074. They might have been replaced at some point (the existing TL074) as I've seen some other pictures of this unit with more Behringer branded opamps (and fewer tl074). Or they might be from the factory and they installed them at random.
I might replace the small white film caps with some Wima caps. There are some crazy values like 1.8nF and 5.6nF that I might have some problems with.
But the most important thing would be to get rid of as many electrolytic capacitors as possible, and up the ps ones a bit (or maybe more if recommended).
I might use some Panasonic FM/FR as I have easy access to those and are cheap.
Also I'm thinking of getting a DI4000 unit as it has 4 transformers that fit on my board. I have the footprint and it is shunted by 0R resistors.
Click the image to open in full size.
They run pretty cheap for what they offer.
But at the moment I need to focus on replacing the electrolytic caps.
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Old 7th April 2015, 11:35 PM   #3
Trileru is offline Trileru  Romania
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I made the circuit in LTSpice as an exercise and I seem to have got it right

It's a bit of a mess but feel free to play with it.
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Old 8th April 2015, 12:33 AM   #4
Trileru is offline Trileru  Romania
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I added some comments on the crossover frequency setting.
To switch the range you have to brake some traces and make others but should be simple looking in the schematics.

Also I plotted the frequency response with both 22uF original values and 10uF values (I replaced all 22uF in the schematic).
Seems like a small increase in the lower part, sub 10Hz. I don't mind that at all.
If there aren't any obvious reasons that I don't understand then it seems I can replace them with 10uF value.
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File Type: png 22uF.png (366.9 KB, 31 views)
File Type: png 10uF.png (361.0 KB, 12 views)
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Last edited by Trileru; 8th April 2015 at 01:02 AM.
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Old 8th April 2015, 10:08 AM   #5
DF96 is offline DF96  England
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Most of the 22uF are feeding resistances around 10k. One feeds only 2k, but even then the LF rolloff will be 3.6Hz so quite low. As there will be very little signal voltage across the 22uF caps they cannot do any harm.

By all means replace them if it makes you feel better. If the replacements are physically larger then there will be an increased risk of stray capacitive coupling.
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Old 8th April 2015, 10:44 AM   #6
Trileru is offline Trileru  Romania
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That's what I saw as well and it looks ok.

I see that in this design there's a 1dB rolloff from 7KHz to 20KHz. With the xover point at 2KHz or so.
Is there something that I could do to address this issue? This is with stock values by the way. But it doesn't make any difference for the high end if I use 10uF values.

What exactly creates that in the circuit?
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Old 8th April 2015, 11:01 AM   #7
DF96 is offline DF96  England
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Several of the opamps have a low pass function due to a cap across the feedback network.
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Old 8th April 2015, 11:38 AM   #8
Trileru is offline Trileru  Romania
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Yes I have played a bit and decided to remove the limiter circuit. I just need to remove the N channel fet and a diode and the frequency response is way better.
First picture is with the circuit the second is without.
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Old 8th April 2015, 11:54 AM   #9
Trileru is offline Trileru  Romania
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There's also the last thing that bothers me, the 220uF/6V electrolytic capacitor. What is it's purpose in that spot?
I can leave the feedback network values stock by removing the limiting circuit. I don't need this function at all.
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Old 8th April 2015, 12:11 PM   #10
DF96 is offline DF96  England
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It is a coupling capacitor. When the FET imposes a low resistance on the signal (high attenuation) then the 220uF works with the 68R to maintain LF response. With the FET missing the cap does not do very much, but it does no harm either.

Why do you have such a dislike of electrolytics? I'm guessing that your questions imply that this does not arise from a careful consideration of their exact use in the various circuit positions. Wait, don't tell me - you read on a website that electrolytics kill good sound?
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