M553 need help

[macaroonie]

I have just taken delivery of an M553 crossover and wish to use it in my L300 ish project. For this to work the mid - hi crossover point has to be changed to give a x/o at 8.5 khz. Stock x/o is at 5khz maximum.
Has anyone been down this road before. It should only be a couple of small caps to make the change. I have downloaded the service doc but am having difficulty locating the appropriate components.
Strange that JBL would have restricted the HF range given the extensive use of 24xx tweets over the years.
I have e mailed JBL tech help but I,ll wager this forum is quicker.
Thanks all

[Robh3606]

The other alternative is to set it up as a 4 way. Then you can go up to 9k as is.

Rob:)

[macaroonie]

4 way mono then you need 2 and the 4 way split is a bit useless for an L 300 ish project. Thanks anyway

[macaroonie]

The project is not for the 4315 system in my avatar but is for a 3 way---- 2235 - 2380 + (driver ) - 2405 system ie more or less an L300.
800hz low to mid and 8.5 to 10 kHz mid to hi.
I am certain that the m553 can be modified by changing the caps that determine the resonant frequency of the filter.

[Robh3606]

You can set the first crossover point up as a subsonic filter and still use it as a 3 way. But yes will need 2 unless you do some surgery.

Rob:)

http://www.jblproservice.com/pdf/M-Series%20Electronics/M553.pdf

[macaroonie]

I had those files. Its the surgery I'm interested in , is anyone up to speed on the intricacies of LW/R filters. Basically I need to double the turnover frequency Mid to Hi.
:(

[Robh3606]

What does the Mono switch do?? You can't find it of the schematic??

Rob:)

[macaroonie]

Was that you being a sly dog and steering me in the right direction ever so gently ?
The mono switch changes the value of the filter capacitor from 0,0032 to 0.0018. Not quite half which i suppose accounts for the f max becoming 9kHz rather than 10kHz.
The solution would seem to be to make the 0.0018 permanent in ch 2 and to replace the 0.0032 x 4 in ch 1.
I missed that point completly my excuse is that scanning about in adobe it is sometimes difficult to spot differences. Thats my excuse anyway.
Assuming that you have more know how than you are letting on would you agree with my solution ?
:o:

[Robh3606]

Well I would love to say yes but I was just thinking it through and figured that if you traced the schematic from the Mono switch you would find the change where the one filter bank changes values to go up to 9Khz. I didn't know before hand what the actual change was although I did assume it was probably part value changes. I glad the sugestion helped you.

Rob:)

[macaroonie]

Its right there clear as day. See the attatchments. All it does is extend the range on ch2 for the HF /UHF x/over. I missed it because of the way it is layed out on the pdf. Ch2 is pages away from Ch1. I have the rascal in bits now and the components are c60 62 64 66 They need to replace the standard setting components c61 63 65 67. A further 4 x 0.0018 are required for Ch1 to replace c24 25 26 27.
In other words for clarity remove C 24 25 26 27 61 63 65 67 and replace ALL with 0.0018.
I,ve added a further diagram so y'all can find these on the board.

End result should be a variable 3way stereo 1 unit suitable for use with 077 2405 3 way projects ---- L65s on up.

[macaroonie]

Its right there clear as day. See the attatchments. All it does is extend the range on ch2 for the HF /UHF x/over. I missed it because of the way it is layed out on the pdf. Ch2 is pages away from Ch1. I have the rascal in bits now and the components are c60 62 64 66 They need to replace the standard setting components c61 63 65 67. A further 4 x 0.0018 are required for Ch1 to replace c24 25 26 27.
In other words for clarity remove C 24 25 26 27 61 63 65 67 and replace ALL with 0.0018.
I,ve added a further diagram so y'all can find these on the board.

End result should be a variable 3way stereo 1 unit suitable for use with 077 2405 3 way projects ---- L65s on up.

Are the 0.0018 caps needed for 9kHz operation/COLOR]
These replace[/COLOR="Blue"]the 0.0032 capsand the caps in Ch1 will need new ones at 0.0018

[macaroonie]

The term mono in the context of this x/o is slightly confusing in the sense that it refers to single channel use with a four way split. In stereo terms mono usually refers to a commoning of left and right channels or in this case Ch1 and Ch2. I confess to having been thrown by this term and spent some time hunting for the connection link between channels. It was of course not there.:banghead: