BX63 replacement?

[dprice]

I have a B460 that will eventually be put to use in a home theater setup. It was found at a junk sale (along with a B380) for $20 several years ago and the BX63 cross-over unit is long gone. So was the finish, grill, and cone... Anyway, what can replace the elusive BX63? I have the schematics but they are meaningless to me at this point. But I can brew beer so maybe I can build one or find someone that can...

Also does anyone have a suggestion for a "cheap" power amp to drive it? Cheap meaning <$400 if possible.

Thanks,

Don

[4313B]

Nice features of the BX63A are that it allows you to place an amp into strapped (or bridged) mode and it has an adjustable low pass filter from ~ 63 Hz to ~ 126 Hz.

If you can't find a BX63A, or don't want to build one, you can use a modified JBL 5234A or a JBL 5235 (preferred since it already has bypass capacitors installed parallel to the electrolytics).

The required modification to make the 5234A or 5235 work with the B380, B460, 4645B, or 4645C is to replace the following 0.27 uF capacitors with 0.22 uF capacitors.

C13, C14, C15, C16, C113, C114, C115, C116

The 5234A schematic can be found in the back of the manual located here:

http://www.jblproservice.com/pdf/Vin...A%20manual.pdf

C7, C8, C9, C10, C107, C108, C109, C110

The 5235 schematic can be found in the back of the manual located here:

http://www.jblproservice.com/pdf/Vin...5%20manual.pdf

In both (modified) models set the first four DIP switches to 1100. This will yield the necessary boost at ~ 25 Hz. You can then use the LFE output of an AVR to feed the 5234A/5235 and something like an Adcom, Citation, or Crown amp purchased off eBay.


Another option might be to build this and apply the necessary boost at ~ 25 Hz:

http://sound.westhost.com/project84.htm


Finally, I think Parts Express has some Plate Amps that might have adjustable high pass bump filters.

[luxmanlover]

If you're looking for cheap gear I would recomend buddying up with your local JBL dealer, preferably one who does PA work. They seem to have no problem ditching "old" (read heavy) amps and such for the newer lighter models. I picked up a used BGW 750G for a $100.00 CND 'cause "I can't drag that old beast around". It had come in on a trade in and they simply had no use for it. One of many deals I've been lucky enough to have stumbled across from the same guy.
Kelly

[Robh3606]

Yes Parts Express does have an amp #300-794 with adjustable boost. From +1db to +5db. The +5 has has ranges with the boost between 20-23 hz and 24-30 hz. There are 2 more with higher frequency ranges. The sheet for the specifics is available on the Parts Express site.

Rob

[GordonW]

Holy cow, first people finding brand new L100s (another thread), now $20 B380s!

With regards to plate amps: I've used some of the same amps as the PE amps, under different names... and I have a reservation as to whether they really have BALLSY enough power supplies, to do a heavy-cone woofer such as a 2235 or 2245 justice. I've thought that the plate amps I've heard, were a little light-weight when the chips were down, on complex, loud low stuff...

There do seem to be some good plate amps out there; for one example, check with Adire Audio, I think they have a heavier amp than the PE, and one model is still less than $400, IIRC...

Regards,
Gordon.

[Mr. Widget]

Originally posted by dprice

Also does anyone have a suggestion for a "cheap" power amp to drive it? Cheap meaning <$400 if possible.

Thanks,

Don

I have found that the most "Bang for the Buck" amps out there are the Soundcraftsmen PM860s and PM840s. There are other models in this 800 series that I have not tried, they all have the same specifications, 205 WPC 8 ohms. They are frequently under $150 on eBay. I have three that I am currently using in my home theater. They are not the best amps ever, and I will be upgrading, but you won't find a better amp at that price point.

You can frequently find one of the crossovers Giskard recommended for under $100, and add in another $100-$150 for a PM 860 and you have something that is significantly better than any plate amp. Well excluding the plate amps Bryston is making, but they are not inexpensive.

I just did a quick eBay search.

Here is one of the other Variants, the PCR 800. This one isn't too pretty, but it could be fine.
BTW you have to look under Soundcraftsman as well as Soundcraftsmen.
http://cgi.ebay.com/ws/eBayISAPI.dll...category=39783

[korgroenewoud]

hello,

you will sell that cabinet of the b380?

kor

[dprice]

Thanks for all of the advice! Is there a simpler solution (than the BX63) for the bass boost "problem" if I am starting from the single channel LFE output (20-120 Hz?) from a DD 5.1 source? I assume there would be since (AFAIK) the BX63 was designed around a full range input...

The plate amps look great but a little weak...any chance a bass amp w/EQ (Ampeg SVT III series or similar?) would be clean enough (and quiet enough) for home theater use?

korgroenewoud - I gave the restored B380 to my little brother as a Christmas gift.

Don

[4313B]

"Is there a simpler solution (than the BX63) for the bass boost "problem" if I am starting from the single channel LFE output (20-120 Hz?) from a DD 5.1 source? I assume there would be since (AFAIK) the BX63 was designed around a full range input..."

Yes there is. Use a suitable high pass boost filter between the LFE output and the sub amp input.

[4313B]

Here is the schematic for the BX63/BX63A bump filter for use with the B380 and B460. It is suitable to place between the LFE output of an AVR and the input of a suitable subwoofer power amplifier that has it's own DC blocking.

[4313B]

Here is a schematic for a nice 25 Hz +6 dB bump filter with Q = 1.93 that is suitable for the B380, B460, 4645B and 4645C.

Again, it should be used with a decent power amp that has it's own DC blocking.

[dprice]

Gaiskard,

Thanks for the schematics! I didn't do well in my circuits class but at least I know what the resistor and capacitor symbols look like. My foggy memory tells me the triangle things are op-amps...correct? If so, is there a particular type or rating (or part #) to look for? I'll read the idiot's guide to elctronics if I can find it...

What is DC blocking? What happens if the amp doesn't have it? I'm almost certain to use a cheap ($50) power amp for testing (at low power and no audible distortion) before getting an inexpensive used pro-audio amp (Crown, Carver, QSC) with some real power.

Thanks again!

Don

[4313B]

"My foggy memory tells me the triangle things are op-amps...correct?"

Yeah, they're symbols for opamps.

"If so, is there a particular type or rating (or part #) to look for?"

A TL072 will do fine here for a VLF bump filter.

"I'll read the idiot's guide to elctronics if I can find it..."

Ok

"What is DC blocking?"

Just an RC filter that blocks DC. Some amps don't have them. If your amp doesn't then pop a 10uF/25V cap into the circuit just before the 180 ohm output resistor.

"What happens if the amp doesn't have it?"

Your woof could go poof if DC get's dumped to the power amp.

[4313B]

DC block in the BX63A.
The BX63 didn't have any... it doesn't take much of an imagination to figure out why JBL added them in the BX63A.

[GordonW]

Originally posted by Giskard
DC block in the BX63A.
The BX63 didn't have any... it doesn't take much of an imagination to figure out why JBL added them in the BX63A.

Gee, you mean people didn't actually WANT hyper-extended 2235s with their voice coils jammed all the way out, cocked and hung up on the top of the gap?? Geesh, what's the world coming to?

Regards,
Gordon.
who had that happen himself once... whoa, that was a bad day...