Gain matching for biamp

[Tiver]

Hi folks,

I have acquired an ADS C2000 and will be looking to bi-amp some ADS L1230. I don't have a lot of knowledge on the demands I will be putting on the amplifiers. What I think is, as different program content puts demands on the amplifiers, they will respond accordingly and the output (watts) will be in response to that. Therefore the rated output of the amps can be different as the low end generally will be more demanding (watts) than the mid/hi and a bigger amp on the bottom can be advantageous.

I have a Rotel RB-1080 (200wpc) that will handle the bottom end and will experiment with several different amps on the top. None of the amps I currently possess have any gain controls. Do I understand that I would attempt to match the lo and hi gains with a full frequency tone (white noise) so as to get a similar spl at a fixed volume? If the output of the amp is determined by its sensitivity, I want to try and compensate for that by adjusting the input of a standardized signal? Accordingly, two of the same amps wouldn't require any adjustment.

So the C2000 picks up the full frequency output from my preamp Rotel RC-1070 and splits it into hi and lo output. I have a little one in/one out Dilvpoetry FX Tube 03 tube preamp. Could I put that on either the hi or lo out from the crossover prior to amplification for the purpose of balancing the gain? If not, is there another way to gain match (another component to place between the xo and amp) that would allow me to experiment with different amps for the hi pass signal?

My apologies if I have misused terms like gain and sensitivity.....I know what i am trying to ask, just not sure if I am wording it correctly.

In the long run I could end up with totally different amplification, but I would like to be able to try what I have.

 

[whoaru99]

Looking at the C2000, it appears crossover is in the 300 - 500 Hz range.

If that is correct then the power distribution for low and mid/high is around the equal split point for average power. So, you would not want amps of very different power else the smaller one will reach limits/clip materially before the other. That said, if the smaller of the two amps provides all the oomph you need then different power of the amps is of little concern.

FWIW, the C2000 manual I found online gives suggestions for gain/level matching.

Far as gain and input sensitivity, yeah, they are different but related.

Input sensitivity tells you how much signal voltage you have to put into the amp for it to produce X power. Usually, X is the full rated power of the amp.

For example, an amplifier rating may be 100 watts per channel and have 1.5 volt input sensitivity. That means the signal needs to be 1.5V into the amp to get the 100 wpc rated power output. If the 100W was @ 8 ohms then the gain of the amp would be 25.5dB.

Gain tells you the voltage multiplication of the amp. If an amp has 26dB gain that means the amp will (within its limits) multiply the input signal by roughly 20x. 1V input would be 20V output and if the load was 8 ohms the amp would be delivering 50 watts.

 

[sqlsavior]

I would think that your active crossover would have the capability of level adjustment? You can get the manual here:

https://www.hifiengine.com/manual_library/ads/c2000.shtml

 

[sqlsavior]

The wiring diagram for using a preamp with two amplifiers has the amps used as left channel and right channel, not treble and bass.

The diagram for use with a receiver and one additional amp looks to use the additional amp for the bass, and the receiver for the treble, so I assume either way is possible. This C2000 crossover is not as flexible as a general-purpose active electronic crossover, but it looks like it could work for the frequency it was designed for.

 

[Tiver]

.....

FWIW, the C2000 manual I found online gives suggestions for gain/level matching.

........
.

I have looked at the manual. But it presupposes that gain is adjustable on the amplifier. Then it goes on to suggest a way to balance the two amplifiers using a listening test. I am fine with that approach except I can't attenuate the hi and lo independently with the amplifiers I have currently. I just wondered if putting the other pre in one of the signal paths would be a reasonable approach. The only bad thing I can think would happen would be the second pre would be over driven at it's input. The challenge there is I can't find the input sensitivity spec for it. It's one of the $31 wonders for which there is a mega thread on elsewhere on AK.....I suppose I could dig a little deeper and maybe find that spec....or I could just wing it. I guess .

I guess if I just wing it, the second pre would go on the lo end. If the pre isn't overloaded at the input, I could bring up the volume knob until I feel it sounds right.

I would think that your active crossover would have the capability of level adjustment? You can get the manual here:

https://www.hifiengine.com/manual_library/ads/c2000.shtml

The bass level has a small adjustment to about 3db, but the manual suggests this only as a fine tune, not a level match.

 

[Akustic]

Here's a simple solution .. to add a level control to an amp.. but depending on the resolution of the amps,
the quality of the interconnects, and the volume pot in the SYS will be factors. (meaning that I wouldn't use it with multi-thousand dollar amps )
It sounds fine on my B&K amps ..

https://www.schiit.com/products/sys

 

[Tiver]

Here's a simple solution .. to add a level control to an amp.. but depending on the resolution of the amps,
the quality of the interconnects, and the volume pot in the SYS will be factors. (meaning that I wouldn't use it with multi-thousand dollar amps )
It sounds fine on my B&K amps ..

https://www.schiit.com/products/sys

I thought something like that would do what I want. Not much to it. I guess most of the cost is for the case.

Thanks for the heads up.

 

[whoaru99]

If you don't want to pay for the case/someone else's work then I'd imagine a couple potentiometers however you see fit to house and connect them would work. I've never been much a fan of stacking pre amps but, on occasion, I have. Despite the typical high input sensitivity (low number), they usually don't overload until a much higher input. YMMV, of course.

If you can't find the gain specs for the amps then you'd need to measure (or I suppose do the ADS listening test) so you could put the attenuator on the amp with higher gain, presuming they are not the same/similar.