Bridging a PL 700B

[Peter Stoffregen]

Hello Everyone;
I have just finished my new (sub)woofer cabinets, (two for stereo because I need to cross over at 100 or 120 Hz), basically copying the JBL 4645c.
I am using RCF LF18X401 drivers. They have a 50 mm max cone excursion but are about 3 db less efficient than the JBL woofers.
I have 3 Phase Linear Amps (I must be a masochist) Two 700B's and an old 700. I am running out of power at 350 W/chan, driving the subs.
QUESTION; Can I use the balanced (+ & -) output of my Rane Crossover to drive two series resistors, centre grounded, to produce opposite polarity signals for L and R inputs of the 700B's.
I have some pro audio back-ground but would like some reassurance before I start experimenting.

 

[Northwinds]

Bridging means a spectacular explosion usually for PL amps

 

[P.L.F.]

More info here: http://forums.phxaudiotape.com/show...ear-700-Series-II-White-Oak-Conversion/page13 - post #126... In many P.A. applications the 700B's were running bridged. And with heavy duty fans...

 

[Peter Stoffregen]

Down sides to Bridging

Thanks for the comments so far. I'm guessing that bridging might be safer with the output transistors changed to ON MJ21196's. I have changed one channel of one amp. (That was the end of a $400 JBL driver) Specs suggest a great improvement over the plx909's.
Is damping factor halved by bridging? Can anyone suggest another power amp in the 1000 wpc range that is "HiFi" but not priced out of this world.
I was considering a QSC RMX 5050, but with a three tier power supply, it seems like there would be whole lot of 'gear shifting' ever time you hit it with a large signal. Any advice/ideas?
Thanks, Peter

 

[orange]

Bridging means a spectacular explosion usually for PL amps

Might as well have a concert and write it off as pyrotechnics.

 

[Northwinds]

More info here: http://forums.phxaudiotape.com/show...ear-700-Series-II-White-Oak-Conversion/page13 - post #126... In many P.A. applications the 700B's were running bridged. And with heavy duty fans...

8 ohms and higher though right. A lot of Brothers here run Vega's and those are around 6ohms and that's already pushing it. Other dudes run 4ohms with fans already. Bridging just seems like asking for early failure. 350w to two subs seems like more then enough bass for most applications LMAO. If I am wrong, please explain since knowledge is power and I might be tempted to try hehehe

 

[Northwinds]

Pete, I have a Peavey CS800 3 rack space amp that I think will spark your speaks pretty easily, already fan cooled and a pretty quiet fan at that. I think you can get it to 1200 or 1600w somehow? It sounds pretty damn good with the NAD 1020 hooked up driving it. I could easily melt the Bose 501's with it, I see why these are PA legends LOL. Look into them

EDIT: Just get your amps WOPL'd, you'll get your 1000w each then

 

[premiumplus]

I heard a rumor that the original CS-800 was very similar to the PL-700. That would account for it's quality sound. I've been impressed by those old Peaveys...they made some nice equipment.
I recently got an old early '80s Peavey Encore 65 guitar amp in trade for some guitar pedals, and it sounds surprisingly great. I'm more into my vintage Fenders and the new DSL40C I play, but that old Peavey is cool. Very gig-able.

 

[Peter Stoffregen]

Hi Northwinds;
I have a large listening room. I built my house around my sound system. The room is approx. 24 by 35 feet, 17 ft ceiling. I was using 2 Cerwin-Vega M horns in the corners,(sensurround style). Very efficient above 40 Hz, mostly noise below that. I did not want to spend $5k on two JBL 4546c subs, (Pink Floyd needs stereo sub woofers). I enjoy brief sessions at 115 db and found that my PL 700 was working fairly hard to drive my new RCF LF18X401 drivers. With a P to P max cone ex. of 50 mm, it looks like MORE POWER is called for.
My goal is to build a HIFI system that can produce PA system levels.
I will attach photos of my self designed Line Arrays. I have what I think is a unique design feature and will post photos when I a chance.
I have rebuilt one of my 700B's with the nice White Oaks main pcb and ON MJ21196's outputs but this still only produced about 400 (maybe 420) WPC before clipping.

 

[Northwinds]

I have rebuilt one of my 700B's with the nice White Oaks main pcb and ON MJ21196's outputs but this still only produced about 400 (maybe 420) WPC before clipping.

Is this the Quasi comp build? You should be pulling 490+ if it's FC

Sounds like a fun and expensive project. The echoes in your listening space must play a huge factor also

 

[Northwinds]

I heard a rumor that the original CS-800 was very similar to the PL-700. That would account for it's quality sound. I've been impressed by those old Peaveys...they made some nice equipment.
I recently got an old early '80s Peavey Encore 65 guitar amp in trade for some guitar pedals, and it sounds surprisingly great. I'm more into my vintage Fenders and the new DSL40C I play, but that old Peavey is cool. Very gig-able.

Lee was saying that also. It does sound good. Are these direct coupled also?

I guess I should read about them because with a good quiet preamp, this amp pretty much kicks serious ass, it sounds easily as good as the Carver M1.5T that Jer has now. Really kicks the lowend but I can't take it all the way up, I run out of speakers. It still looks like a PA amp though LOL

 

[P.L.F.]

Hi Northwinds;
My goal is to build a HIFI system that can produce PA system levels.

That's exactly my goal too!!!!!

For that I'd need second PL700 and separate (sub)woofers setup, currently on Lee's bench waiting for WOPL conversion (http://forums.phxaudiotape.com/show...ase-Linear-700-Series-II-White-Oak-Conversion). By the way Guys, anyone knows when Lee is going to be back?

Peter, please share your approach in details as much as you can, with some pics of course... many thx!

 

[Peter Stoffregen]

Hi P.L.F.;
I will send pics asap. I used 16 drivers, 5-1/4" each. Slightly overlapped to allow use up to 2kHz. Drivers had to be 5-1/4" to allow use down to 100 Hz. I have raised the crossover point 120 Hz to safely produce 120 db at a 4 or 5 meter distance.
Pictures coming soon.

 

[Peter Stoffregen]

My Line Array

This is my line array design. The cabinet is 84" tall so it will fit in a listening room with 8 foot ceilings. The cone drivers are over lapped to keep centre to centre distances of the drivers to less than 5" to allow true "line radiation" (minimal interference pattern) up to 2 kHz. Above that, the plannar tweeter line takes over.
Still doing some tweaking, and I would welcome any comments and be happy supply more details.
I have done considerable research on line array principles before starting this project.

 

[Northwinds]

Nice speakers Bro!

 

[orange]

Who is YOUR avatar? At first I wondered if it was Tanya Tagaq, whom I heard about on CBC's Q but I don't think so.

 

[Peter Stoffregen]

That's my wife, and she cooks too! (Well, a little)

 

[orange]

Maybe not food, but you married her, so she cooks in a sense. 'Nuff said.

 

[kevin]

View attachment 16427 This is my line array design. The cabinet is 84" tall so it will fit in a listening room with 8 foot ceilings. The cone drivers are over lapped to keep centre to centre distances of the drivers to less than 5" to allow true "line radiation" (minimal interference pattern) up to 2 kHz. Above that, the plannar tweeter line takes over.
Still doing some tweaking, and I would welcome any comments and be happy supply more details.
I have done considerable research on line array principles before starting this project.

WOW !!!!!! Nice job man !! REAL nice work ! I bet those sound good !!! I have the same design... Just not that big !

 

[wattsabundant]

I heard a rumor that the original CS-800 was very similar to the PL-700....

Depending on who you talk to the CS800 is a BGW750 with frills. It has no resemblance to PL 700B. The 750 was used as a sub amp in pro apps. It will drive anything you put on it, reliably. see the link. http://en.wikipedia.org/wiki/BGW_Systems

Although quite old, I really like the BGW 20 crossover for use with a sub. I used them in clubs in the 80's. Speaking of crossovers, the JBLBX63 is intended for home systems.