Bi-amping with two different amps, same manufacturer

[Roborobo]

I have a B&K PT3 pre-amp, a B&K ST 1400 series II amp (125 watts @ 8 ohm) and I just picked up a B&K ST3030 (200 watts @ 8 ohm). I'd like to bi-amp my JBL L7, but neither amp has a level or gain control. Also the pre-amp does seem to support bi-amping in the manual, so I assume I need to run a splitter from the speaker-out outputs (correct?). I know bi-amping usually means at least one amp has a gain control or both amps are the same model, but Is there a way I could crunch some numbers to see if these two amps would be compatible by looking at their watts or some other spec? I know I could just try it, but I would need to order more speaker cable, more banana plugs, etc., so I first would like to know your thoughts before I spend the time and energy possibly for naught... Thanks!

 

[knotscott]

It should work fine in a passive horizontal configuration with one amp on the woofers, and another up top. Their input sensitivity is very close (1.2v ST1400, 1.4v ST3030), input impedance are both 33.2k ohms, and voltage gain is the same. I'd start by trying the ST3030 on the woofers. You can always try swapping them to see which way you like best.

Yes, you'll need an RCA splitter if the preamp doesn't have dual outputs, and two sets of speaker wires.

 

[swechsler]

I would use the high pass outputs for the upper portion of the JBLs and the full range for the subwoofers. No Y cables required. If it turns out that the balance is off, you can add a passive level control to whichever part (either top or bottom) is louder, and adjust as needed. Here's a nicer looking version (although reviews aren't as good).

 

[Roborobo]

Thanks @knotscott! That's the kind of info I was looking for. Definitely horizontal- not sure why anyone would want to do vertical? Just ordered a make to two male y-splitter two pack.

@swechsler I thought about that but it seemed like the high pass would send out... what, just some signal above XX hz? Wasn't sure if that cutoff frequency would be above or below the crossover frequency of the JBL's internal crossover and I wanted the internal JBL's crossovers to do all the thinking. Does that make sense? Still, it's worth a shot while eI wait for the splitter to arrive (can easily return it if the high-pass suggestion works) Thx!

 

[knotscott]

Thanks @knotscott! That's the kind of info I was looking for. Definitely horizontal- not sure why anyone would want to do vertical? Just ordered a make to two male y-splitter two pack.

@swechsler I thought about that but it seemed like the high pass would send out... what, just some signal above XX hz? Wasn't sure if that cutoff frequency would be above or below the crossover frequency of the JBL's internal crossover and I wanted the internal JBL's crossovers to do all the thinking. Does that make sense? Still, it's worth a shot while eI wait for the splitter to arrive (can easily return it if the high-pass suggestion works) Thx!

Vertical bi-amping is well suited for two identical amps. The advantage is that each side has a separate power supply, and is completely isolated from the other channel...so no crosstalk. There are pros and cons to both configurations, but every situation is unique so there aren't many absolutes.

 

[swechsler]

I thought about that but it seemed like the high pass would send out... what, just some signal above XX hz? Wasn't sure if that cutoff frequency would be above or below the crossover frequency of the JBL's internal crossover and I wanted the internal JBL's crossovers to do all the thinking. Does that make sense? Still, it's worth a shot while eI wait for the splitter to arrive (can easily return it if the high-pass suggestion works) Thx!

The high pass frequency in the L7's crossover is 180hz, so the 80hz HP of the preamp is fine. Since you won't be defeating the built-in crossover, soundwise, there probably will be little if any difference. Which does raise the question of: is there is any benefit in passive biamping (which is what you're doing since you're keeping the internal crossovers), which has been a subject of debate here over the years. I believe the majority of AK'ers who have tried it say "no", but since you already have the equipment, it won't cost you much to try.

 

[knotscott]

The high pass frequency in the L7's crossover is 180hz, so the 80hz HP of the preamp is fine. Since you won't be defeating the built-in crossover, soundwise, there probably will be little if any difference. Which does raise the question of: is there is any benefit in passive biamping (which is what you're doing since you're keeping the internal crossovers), which has been a subject of debate here over the years. I believe the majority of AK'ers who have tried it say "no", but since you already have the equipment, it won't cost you much to try.

What can be heard is unique to each setup, but it's definitely worth a try since he has the amps. The amps up top will have the benefit of not having to drive the larger woofers. If he had volume control on each amp there'd be the option to vary the output of the low woofers relative to the upper drivers. Only time will tell how audible it is. There likely won't be much if any change to the original tonal balance, but any improved clarity could impact the soundstage too. Ya just never know....

 

[swechsler]

If he had volume control on each amp there'd be the option to vary the output of the low woofers relative to the upper drivers.

I provided a solution to that in my first reply.

 

[Powertech]

A couple of points.
First a bit of context - I run a fully active 3 way system using a 6 channel power amp (Rotel RB976Mk2 - modified).
With this amp you have 6 identical power amps set up as 3 stereo pairs. Each pair shares a single PSU. So 3 in total c.oming from a single 700VA rated mains transformer with 3 separate output windings. And each pair has a separate input level control.

I run the system as horizontal pairs. Although I take the point about absolute stereo separation with vertical alignment, there is also the issue that if any amp is going to pull sufficient current to cause PSU line voltage droop, it will be the bass amplifier. With horizontal alignment, if this should happen (highly unlikely in my case) the midrange and treble amps will not be affected as they have different power supplies. Also, if the bass system does clip, this will be less audible than any clipping in the midrange or treble frequencies.

The second point is that in a hi-fi context you should never be running an amp anywhere near clipping anyway as we are into quality not quantity. Any amplifier used in a hi-fi context should be operated with plenty of headroom. Mine are actually turned down to about 50% input level. One advantage of active (frequency split prior to amplification) systems is that each power amp is only carrying part of the audio spectrum so you don't have high frequency signals superimposed on top of low frequency signals as you would in a full range amplifier. This naturally increases power (current drive) headroom. This increase can be up to a factor of 4 for bass section amplifiers.

 

[twiiii]

Well you use an electronic crossover and Bi amp horizontally with the big amp on the LF where it should be and the smaller amp handling the high frequencies. If you are keeping the passive crossovers then you remove the straps combining the HF and LF sections on the speakers. I don't like the idea of doing it that way, but thats up to you. Using an electronic crossover allows you to balance your amps. But then you should remove the woofers passive crossover components and the HF crossover components, but leaving the shaping components of the crossover for the HF drivers. Its not easy. Then you also have to decide which type of electronic crossover you want to use. Constant arrival time, constant phase, flat frequency response and at what rate. 6. 12. 18. or 24 db per octave. Its not a simple process to do it correctly. Digital crossovers are the most flexible Allowing you the most flexibility. Some folks want analog and I don't blame them. Ashly and Rane are middle priced and perform well. I use the very famous Urei crossovers. But they are getting long in the tooth.

 

[Akustic]

A Schitt SYS ($50 passive preamp) can be an easy, inexpensive way to put a level control on one of the amps ... and even the levels of the two amps up..
I use mine on the bass amp (an Aragon) to minimize the audibility of the extra set of interconnects and level pot ..

My L7's are more dynamic when they're bi-amped ..

 

[Roborobo]

I would use the high pass outputs for the upper portion of the JBLs and the full range for the subwoofers. No Y cables required. If it turns out that the balance is off, you can add a passive level control to whichever part (either top or bottom) is louder, and adjust as needed. Here's a nicer looking version (although reviews aren't as good).

Triumph! Order the y-splitters but don’t need them- did what @swechsler suggested.
Had no idea I could use those outputs like that but I just set it up and I love it. The balance of low to high sounds perfect as is thankfully. There’s clarity in the midrange that wasn’t there before. I love it. The highs are a bit higher and need to be tamed a bit, too. Interesting.

It all started because I heard Fleetwood Mac’s song Landslide and it sounded better than the other tracks and I figured maybe because it had seemingly zero low frequencies (no male vox or bass or drum). That made me consider this bi amp biz is legit. Plus the JBL L7 manual had a whole supplemental section of bi-amping and seemed to really push it with the L7’s.

Anyways time to listen to all my old favorites on my new-again speakers. Thanks all!

(Bonus- I have an old silver faced JVC EQ that’s a 4 channel controller and I can assign two channels to one side and the other two channels to the other. I only used half of it but once I get some more RCAs I can use one side for low and high of each channel. Necessary because my listening room is a little asymmetrical and one speaker is inevitably a bit more in the corner. Anyway, stoked!)

 

[Akustic]

Triumph! Order the y-splitters but don’t need them- did what @swechsler suggested.
Had no idea I could use those outputs like that but I just set it up and I love it. The balance of low to high sounds perfect as is thankfully. There’s clarity in the midrange that wasn’t there before. I love it. The highs are a bit higher and need to be tamed a bit, too. Interesting.

It all started because I heard Fleetwood Mac’s song Landslide and it sounded better than the other tracks and I figured maybe because it had seemingly zero low frequencies (no male vox or bass or drum). That made me consider this bi amp biz is legit. Plus the JBL L7 manual had a whole supplemental section of bi-amping and seemed to really push it with the L7’s.

Anyways time to listen to all my old favorites on my new-again speakers. Thanks all!

(Bonus- I have an old silver faced JVC EQ that’s a 4 channel controller and I can assign two channels to one side and the other two channels to the other. I only used half of it but once I get some more RCAs I can use one side for low and high of each channel. Necessary because my listening room is a little asymmetrical and one speaker is inevitably a bit more in the corner. Anyway, stoked!)

To my ear the tweeters in the L7 can drill your ear ears with the wrong amp ... they will let you know ..
Mine are best with EL-34 tube amps on top, and okay, but sharply defined with the with the MOSFET B&K St-140 or the John Curl Parrasound HCA 1500a amps ..
Definitely too edgy with the Aragon amp on top ..

Just choose the amp for the top end carefully ..
They do like power though, and bi-amping is the way to get there.
They're amazingly dynamic with big power in a big room ..

 

[Roborobo]

Thanks for the info @Akustic Yeah there is a little shrillness with the highs. The only downside and I’m trying to tame it a little with the EQ. I’d love to try these with a tube amp for the highs but any tube amps I’ve seen new are just out of my price range. But as I keep looking, what would be a minimum WPC for a tube amp for the highs?

 

[Akustic]

Thanks for the info @Akustic Yeah there is a little shrillness with the highs. The only downside and I’m trying to tame it a little with the EQ. I’d love to try these with a tube amp for the highs but any tube amps I’ve seen new are just out of my price range. But as I keep looking, what would be a minimum WPC for a tube amp for the highs?

ChiFi can get you there for about $500-$600 for a new, excellent quality tube amp .. I really like this Yaqin MC13s .. It's a very well built piece ..
EL-34's pushing about 35 watts per channel .. Basically a well executed copy of the old Marantz as modified by Wadia ..

As for power, more is definitely better .. these are not speakers for a flea watt amp, especially if you're using the existing crossover points .. which I am.
As they sit they're a sealed 8" 3-way and a big 12' ported bass box attached in one package .. so there's significant mid-bass above the crossover from those 8's ..
The inefficient 8's need big power to sound good ..
Given big, big power, the JBL's have a dynamic slap and power that will make you jump around the room .. They push on your chest and flap your pants like Rock & Roll should.

The tubes sound sweet and wonderful in the mids and treble with a beautiful wide open soundstage, but tube amps have a wooly roundness in the mid-bass that irks me ..
They simply lack the mid-bass slap and definition of big SS and MOSFET amps.
That's how I ended up with the John Curl on the top end and the Aragon 4004, which is a definitive bass amp, on the bottom ..

The tube amp ended up attached to an old pair of 1957 EV Tri-axial's that were designed for the amp .. Sounds beautiful with jazz and acoustic music but the bass sucks ..
One system at one end of the room, another at the other end of the room ..

 

[izeek11]

my two cents.
im running vertical biamp with identical amps at 150wpc. i used some quality splitters from mediabridge and custom biamp cables.
my pre is a jbl pre/pro. the subs are using the same splitters and sub cables, also from mediabridge.
simplicity.
and, imo, synergy.
with two amps of different power, maybe listen for awhile and see what needs balance. and there is dsp. i haven't got around to that yet, myself.
have fun. those jbls are schweeet.
#jbl4life!
ed.1 use the pre for gain control. my amplifiers have gain controls but are set at wide-open. the pre is set for auto-gain. sure your pre will handle it.
i don't think you'll have a major problem as the high amp isn't going to be driven as hard as the low amp.
ed.2-i have a set of bluejeanscable.com biamp cables also, 4s11. really nice, decent price. the custom cables use the same wire.
ed.3-may i suggest you start your crossover at ~50hz and blend the rolloff to your tastes. iont know jack, but that and minimal sub gain will really make your mains shine.
i have L890s that are close in specs with your L7s.

 

[Akustic]

my two cents.
im running vertical biamp with identical amps at 150wpc. i used some quality splitters from mediabridge and custom biamp cables.
my pre is a jbl pre/pro. the subs are using the same splitters and sub cables, also from mediabridge.
simplicity.
and, imo, synergy.
with two amps of different power, maybe listen for awhile and see what needs balance. and there is dsp. i haven't got around to that yet, myself.
have fun. those jbls are schweeet.
#jbl4life!
ed.1 use the pre for gain control. my amplifiers have gain controls but are set at wide-open. the pre is set for auto-gain. sure your pre will handle it.
i don't think you'll have a major problem as the high amp isn't going to be driven as hard as the low amp.
ed.2-i have a set of bluejeanscable.com biamp cables also, 4s11. really nice, decent price. the custom cables use the same wire.
ed.3-may i suggest you start your crossover at ~50hz and blend the rolloff to your tastes. iont know jack, but that and minimal sub gain will really make your mains shine.
i have L890s that are close in specs with your L7s.

Ditto with the Canare S-11 cables .. a nice cable with excellent definition and a truly deep extended bass .. blows the doors off the Canare S8 that has also been and some still is, in and out of here when it comes to warmth and bottom end.. I have multiple systems that are wired with the S11 .. (a great bi-wiring cable as well) ..

.

 

[Bill Ferris]

I`ve been successfully tri- amplifying using (4) mono configured Mc. MC-275LE tube amps for the Mc. XRT-30 speaker system for their L/R line array tweeters and midrange drivers, and (2) Mc. MC-1201 SS mono block amplifiers for the speaker system`s 2 bass cabinets for nearly 14 yrs. now.

Neither of those model Mc. amps have any level controls installed on them, as their input differences in sensitivity needs are easily dealt with the balanced in/out time align-able, very HP digital 3 way crossover`s output level controls.