maybe a higher impedance on the amp's input?
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Not knowing the speaker, I would guess the 2250 amplifier and speaker setup is running less efficient than the 85/140 biamped setup. With only one amplifier connecting both high and low drivers, the overall power consumption of the speaker to produce sound has to be greater beacause of the crossover inefficiency. Most of the amp power is wasted as heat. Even though the speaker produces so many db per watt, the actual watt that gets through is maybe 20% of the power drawn.
With the biamped setup, each amp feeds the high and low drivers separately. Since the output doesn't split in the crossover and gets converted to heat, more amp output makes it to the drivers. Also, since each amp feeds either an inductor (woofer) or a capacitor (tweeter), the overall impedance is greater at lower tweeter/higher woofer frequencies - so the (bi)amps are operating at lower current outputs which enables them to better maintain their power ratings. So at lower volume levels, more of the power is actually consumed by the drivers, especially if the gain of all three amps are the same.
The 2250 will be louder at higher volume pot settings because the extra power capability will eventually push its way through to the speaker's drivers.
Unlike the posters above I share your concern. All Linn amps have the same gain, or at least they did the last time I inquired. I realize you aren't running these Aktiv. Remember though that when one goes Aktiv the cards are available in mono or stereo and you can mix and match amps without any concern. If the situation were as you described then they couldn't do that. I'd fire off an email to Linn customer support asking about this phenomenon. Better yet, if you have a Linn dealer that you purchased this amp from I'd have them inquire on your behalf.
When you use 2 amps instead of one (as you did,) your TOTAL input impedance has been changed being a factor of the two input impedances in parallel. This presents half the load to the preamp as that of one amp assuming that lugnut is right about the impedances. Some preamps like more load, some less but there is your difference.
Some preamps like more load, some less...No, not really. Lowering the load's impedance always makes things more difficult for the source. The higher the destination impedance and the lower the source impedance, the better.
If all Linn amps have identical input impedance across the FR spectrum, the single 2250 should be a MUCH easier load (twice as high in fact).
Maybe you should follow Lugnut's advice, pronto!
Maybe so, but I haven't always found this to be the case in real life as for actual levels(few other factors envolved.) I don't know about Linn equipment and the type of input configuration it has ( Jfets or whatever) I do know a lot of preamps like a certain load and I based my statement on that ( a generic one at best) and I agree, most preamps like a higher impedance load (especially tubes without a buffer)
I also concur, call the factory.
Here are some gain, impedance and other stats. For those who know about these things, perhaps they help answer the question. Gain looks approximately similar across the board, but input impedance looks different, although I can't interpret the information.
Please let me know what you think.
1. 2250 Amp (which I am using now and which requires me to jack up the volume dial on my preamp):
Balanced 22.3dB [NOTE -- I use unbalanced]
Input Level for Clipping
Unbalanced 1.2V rms
Balanced 2.4V rms
230W rms into 4 ohms
115W rms into 8 ohms
Maximum Input Power
Typical Operating Input Power
2. LK 140
Input signal for maximum output
Maximum input power
3. LK 85
Input signal for maximum output
Maximum input power
I agree, it could be that running the two older amps in passive biamp may have had the effect of summing their input impedances, which is greater than the single new amp, and thus presenting a different load to the preamp.
To test this theory out just run one of your older amps full range and see what kind of gain issues you have then.
Ahhh, too bad.
I'll throw out some hypothetical numbers here just for the sake of illustrating an example.
Say, one of you old amps had an input impedance of 47Kohms and the other old amp you were combining it with had an input impedance of 23Kohms. Your preamp would see them as 70Kohms. But if you reconfigured your set up so you were just using a single amp with 47Kohms or less, this new amp might require more gain to attain the same volume levels as your two older amps being used together.
One other possible solution to the mystery: from looking at the owner's manual I see that there is a small button on the back of the unit that switches from balanced to unbalanced. I have cabled the unit for unbalanced, but never checked to see what position the switch was in (because I doidn't notice it). I am not at home to check, but i wonder if this could explain the problem.
Kdl6769..The little button is your problem for sure. When an amp with balanced inputs is operated single ended the
(-) pin of the input connector must be grounded. That's what the switch does.
Gunbei...When the two amps are both driven by the preamp, the combined input impedance goes down, not up. For example: two amps with 20K would be 10K. Actually, cutting the impedance in half like this might not make much difference if the pream[ is low impedance, and can hold the voltage up dispite the increased current needed.
On my Ayre V5x, it has a switch but it doesn't change the levels any really. The sound quality suffers some if it's in the wrong mode. Of course the Ayre doesn't ground the interconnects to the chassis at all anyway.
I think it could just be, considering the drive levels are double for the bigger amp that the perceived volume just ramps up slower. I mean, there is not going to be much of a volume difference with these amps in absolute terms. Your other amps would hit clipping at a much lower volume setting looking at the drive mv required. It would also depend on your displays calibration(as in, is it a true db indicator.)
Also, it still could have something to do with driving 2 amps instead of one. It doesn't appear input impedance is an issue between them.
I don't think you would notice any real difference in volume level between 115/ch and say 85/ch.
Does the bigger amp go on up to full power with more level? If it does, I wouldn't be too concerned about it.
Check the Dbw scale for exact figures.
The two older amps have completely different input sensitivities (much higher: 685/870mv for full power vs 1,2V for the new one). You need a higher relative source voltage to drive yr new amp to clipping (i.e. turn the volume control higher). That alone could explain the differences you're experiencing.
Also the new amp, alone, is a slightly better load by the looks of it (the old ones together were 5kOhm). Do also use the switch in the back (if you haven't already)!
Yea, I know a lot of manufacturers have different ways of implementing this feature. It sounds like the fellow has solved his problem, so that's good.
It is really hard to say anything on these forums outside of generic information. I used the example of Ayre because I use it and understand how it is implemented.
I also know some equipment is not truly balanced in its circuitry. I think this is why some don't notice any difference from XLR to single ended. It is actually converted back to single ended internally.
Makes it hard not knowing some of this equipments internal workings.