Hi everyone,

Well I steped up to dual power amps and bi-amping my custom made (self built) speaker system that I have finally finished- Cerwin Vega 15 inch subs, Vifa 8" bass and 6.5 Mid bass, dual Vifa 3 inch SoftDome mids, with a Morel 30's for the tweeter. The subs are @ 80Hz (via the B&K), the speakers are crossed @ 300Hz, 500Hz, 700Hz, and 3200Hz- 2nd order for the lows and 3rd order for the highs. One amp runs the subs and the other the speakers.

I am using two (2) Proton D-1200's, a B&K PT5 preamp, with an Audio refinement CD player. I am running Monster MCX 2s wire (4- 15' foot runs), Audio Quest power cables, and Monster M850i Interconnects, this is connected to a dedicated 20A wall outlet.

My room size is 28x14, shot gun style, painted dry wall, and half carpeted/harwood flooring, 8' room height.

My question is: I was expecting a more powerful sound then what I have presently. While everything did open up, it seems the DB output did not increase substantially, as a matter of fact, it seems I must now nearly max the volume control on the B&K to achive similar output when I was using a single amplifer. All be it, the sound is more refined and much tighter, the DB output did not increase. And I am concerned that the B&K is having trouble outputing enough voltage to run two amplifiers.

Is this the norm? Am I not suppling enough "juice" to the amplifiers via the wall outlet? Or, do I have to large a "hole" between the subs and the Speakers?

While this does sound very impressive, I am not as "jazzed" as I thought I would be.

Any ideas, comments, help?
Are the crossovers active???
Nah. You just discovered the truth about bi-amping without using an active line level crossover: Improvements are modest at best.

It's going pretty much as it should.

I think those amps are 100 w/ch each, yes?

Even if both amps were fully additive in the bi-amped configuration and equal to 200 w/ch, it would be only a 3dB increase in volume. 3dB is generally the point at which people just start to notice a difference in the loudness. This is the best case scenario.

If much louder is what you want, you'll have to come up with much more powerful amps. It will take roughly 10 times the power you have now to make the system sound twice as loud.
Could your room dimensions be sucking the volume or impact out of your system? You have the classic no-no 1:2 proportion in width to length.

I was discussing this with an architect in connection with my current listening room, where the room width is double the ceiling ht, and the music sounds incurably recessive. He's not an acoustic specialist, but said that the 1:2 proportion is a well known problem for any room with an auditory function. Architects try to avoid it when designing such facilities.
I echo the advice about an active crossover. The difference between passive biamping, which you are doing, and active biamping is large.

Good luck
That's a lotta crossing over from disc to ears. Two-ways rule when done right. Active xovers are probably the way to go. I laugh at $1K spkr cables feeding inductors with turns and turns of tin wire. Love the Protons. Good luck.
Even with active x-overs etc. going from 100 watts to 200 watts is at best only 3dB increase. This is just past the verge of an audible increase in SPL.
Well the B&K PT-5 pre-amp has an active Low pass section @80Hz, while the rest is thru the typical crossover network with in my speakers. Mind you it sounds very very good, I am mainly concerned with the matter of the B&K's output via a maxed volume control, the amps are not hitting peak power is my thought.

As for the Proton's - they are 110wpc, however, they are able to deliver 1500wpc transients for 200ms into 2ohm loads, or more, depending on the source material. They are very very powerful amplifiers. And with a S/N ratio of 120dB, they are very quite as well.

By way of example, I have an AB international 1100A which is rated to 550wpc, the Proton side by side (single amp) Is everybit as poweful, and, more refined. I also have an Adcom GFA-555 and the Protons beats it as well.

Again, it is my belief that the B&K hasnt the output to run two amps, but then I could be wrong, hence my question.

Thanks for the comments.
Nobody is questioning the Proton amps - I'm sure they are very nice.

Pretty much the bottom line is that the very best case only provides 3dB more volume doing what you are doing and the average case, less than 3dB. So, it is no surprise to some and no indication of a problem that you hear little difference; it is what it is and the principles of physics/acoustics/electronics are what they are.

If you want significantly louder you will need to drive the speakers with much more powerful amplification.
But I do not understand why the pre-amp needs to be cranked all the way up just to get nearly the same sound (dB) I had previously, using a single amplifier in bi-wire mode and yet the pre-amp would allow the amp to clip if I drove it to hard- (around +2 on the display) this would would be at ear spliting levels. Now, with the present set up, I can not clip the amps, even with the volume turn up as far as it will go. Mind you the B&K uses a digital volume control, and I have it set to it's maxium output of +8dB.

This is what I believe to be my problem. The specs for the B&K state 8volts max output, I wonder if this is indeed the problem?
Good grief.......

I missed this first time out.........

You have an 8" bass, 6.5" midbass, and a 3" dome midrange?

There is the clue why you don't like the sound. I won't even touch on the mish-mash of crossover points and slopes.

Go ahead......hate me.

After you get over hating me, seriously consider going active. I suspect that you will enjoy twidling with an active crossover. Much easier, and therefore more gratifying, than twiddling with caps and coils.

Cheaper in the long run, also.

I have built custom made crossovers, but they were all "twiddle-proof". It is too tempting to twiddle with them, and one can waste a lot of time twiddling and making things worse. Lots of fun, but not always a step in the right direction.
LOL, well I am not one to hate anyone, I appreciate your.....comments. However, you can, and may, snub your nose at my set up- but I would challenge you to a listen before you condem what I have built. With that aside, I enjoy the sound, as do every friend I have, some have better systems and say mine sounds better. But again, as previously stated, I believe the power output is limited due to the B&K's 8volt output. One listen to Rush's Red Barchetta, or Tchaikovsky's 1812 Overture, or Yanni Live at the Accropolis will instuct you as to the performance of a multi driver, extreamly low bass, done right system that can only be recreated using many drivers, not your typical 2 or 3 way system, but then the experts over at Wilson Audio have no clue why they use multi driver systems do they?

I have verified the problem - finally - I borrowed a Luxman pre from a friend that has a pre level sub out @75Hz- I believe, and I can now cause the amps to reach full power and clip, while the B&K sounds better, the Luxman gets much louder.

While I am no fan of bleeding ears, I am going to call B&K and see what can be done, if anything. Maybe I have a defective pre amp, who knows? (as of yet)

Again thanks for your comments.
You can hate won't hurt my feelings! Some of my ex-coworkers will tell you that I made a career of getting people (mainly bosses) to hate me. Ah......the good ol' days.


Seriously, if you are going to try that many drivers, with that combo of crossovers, you MUST use some fancy measuring stuff to know that it is done right. In which case, you would know for certain what the problem is.

I'm not saying that multiple drivers, etc. won't work. I am saying that you can't guess what works and what doesn't. I think it is a safe guess that you do not presently have the gear to do such. Ergo, you don't know why you have a gain problem.

OK, back to your problem.

8 V out of a preamp is enough to melt any amp. Most amps have 26 dB of gain. A few dB either side, maybe.

As for drive, it should be able to drive 2 amps. Most amps are at least 10K input Z. That is not likely to be the problem. 5k is not that hard of a load to drive, which is probably a safe guess for worst case. A mismatch in gain more likely is.

As for your may want to try 4th order Linkwitz-Riley. That many drivers, with crossover points so close together, can be a nightmare. Not only do you have to take into account the phase of the crossover, but also that of the drivers. Heh, heh.....

One of my famous audio designer buddies had a very expensive multiple driver systen, made by a very well-known designer. I showed him how it had a nasty comb filter effect, depending on whether you were a short guy like me sitting down, or a really tall guy like him standing up. And everything in between.

He very quietly put them up for sale 2 weeks later.
8 volts should be enough to drive any amp or pair of amps into clipping. Take a look at the amp's sensitivity rating; it's usually around 2V for full output.

But I do not understand why the pre-amp needs to be cranked all the way up just to get nearly the same sound (dB) I had previously
Your ears are fine, and yr setup seems correctly done. What's happening is you're losing energy in the pre->2amp connection. That's because you have halved the input impedance of the amps by putting them in parallel -- i.e. the "combined" load the pre sees is now very difficult and it is struggling to provide the appropriate amount of energy (and isn't making it). The two amps together are sucking up the pre. Remember, when you halve the voltage, the wattage drops to 1/4th.
The rest (room, you need a shrink, 3way xover, etc) don't apply;^) Cheers!
Heh, thanks Gregm, yout thoughts (final ones are noted) :)

I agree, the pre is my problem and I have confirmed this by using another preamp. I have sent an email to B&K but I havent recieved any return responce as of yet. Possibly a phone call on mMonday would be a better idea.

The only options I believe I have are to either use a different pre, or, an electronic cross-over.

As for my cross over points, each driver has it's own independent crossover network which is terminated to it's appropriate power input. With exception given to the subs, they use the internal 80hz low pass x-over via the B&K.

Since I do not have the working knowledge of how the output from the B&K is provided (independently, or summed), I can not say what amount of voltage is present under a given load (the amplifiers draw at various output levels).

I appreciate your help guys, I really do, while I do not agree with all that has been written it is food for thought.

Thank you
Oh and BTW, (sorry I missed this comment) here are the specs according to the Proton manual:

Rated power output 20Hz to 20khz 110 wpc

Dynamic Power at 8 Ohms/4 Ohms/2 Ohms

20ms - 540/1000/1500 wpc

Dynamic Headroom @ 8 Ohms/4 Ohms/2 Ohms: 7.3dB

I.M.D @ rated power: 0.02%

Damping Factor: 150

Freq. Responce 20-20kHz: +/-.02dB

Power Bandwidth @T.H.D 0.1%: 10 - 40kHz

Input resistance / capacitance: 1V

Channel Crosstalk: 85dB

S/N ratio 120dB

Hope this helps (I guess)
This one makes no sense:

"Input resistance / capacitance: 1V"

Check that one, and let us know...........

The one about "dynamic power" is just marketing nonsense, written to impress you. The idea is that the peak power, at the top of the waveform, is calculated to be such-and-such watts. In the real world, it is a useless figure.

The one about head room is more revealing. That tells me it probably has a smallish power supply, and that the rail voltage will sag a great deal under a constant load. Problem is, they give one figure for all 3 impedance levels, and that can't be right. I bet it is a lot less than 7 dB @ 8 ohms. At least I would hope so.

So much for believing specs.
No offence Ar t, but you obviously have no experience with Proton gear. And yes those specs I posted are correct, as taken directly from the Proton manual. In their day the Protons were among the most powerful amplifiers money could buy, and even today they still make one of the best tube televisions on the planet. And no it is not a marketing play, ploy or other. They use twin transformers and are of a dual mono design, with over 60,000mfd of capacitence.

However, FYI, I have at my disposal several amplifiers, ranging from Rotel, AB International, Crown, Carver, Sumo, and Adcom. One single Proton is more powerful then all of them, some which are rated to 500 wpc, real world power.

Perhaps it is your belief that I am some how stupid, uninformed, or ignorant as to the workings of electronics, and specs as they go? I surely hope you do not think this to be the case, for if you do, you would be very mistaken.

BTW, since when is 7.3dB of headroom indicitive of a "smallish" PSU? These amps weigh 36.5 lbs each, as per my digital scale, not light, but certainly not Krell's either.

If you get the chance, audition one, you'll be impressed, when one considers their design, age, asthtics and cost. Even today - on ebay they bring $300.00- to $500.00, those who know what they are snatch them up as fast as they are posted for sale.

BTW, ever heard of Onix? Legacy Audio of Ohio? NAD?
opps, I left out your initial question, I did actually miss a line, the above question you asked:

It should read:

Input sensitivity: 1V

Input resistance / capacitance: 15k OHM / 220pF

sorry for the mistake
That sounds better. Any preamp should be able to drive 2 of those (or most anything) in parallel.

As for specs.........

Most are not to be taken seriously. Does not matter who wrote them, or for what gear. I'm sure you told us what they claim the specs are. Doesn't mean they are correct.

Back to headroom..........

If that figure is for 8 ohms, then the supply is too small. If it is for 2 ohms, then probably not. But they don't really say, do they? In which case, it is a meaningless number.