bi-amp...

[Schu]

For those that have bi-amped... with success, how do you reconcile the output differences between the amp (solid state) running the LF section and the tubes running the HF section?

How is the signal split from the pre amp?

Edited April 21, 2016 by Schu

[Arash]

if you have a measurement mic just measure the frequency response once in single amp mode. than bi-amp and try to set both amps volumes to get to the relatively same levels as the first frequency response you just got.

if you are using an active XOver there might be a gain option you can compensate the output of each channel.

 

you also can put a dummy load at each amp output and measure the voltage and set the volume for a same RMS output. you should use P=V^2/R

[Schu]

I can control channels with gain... but its the same channel.

[pzannucci]

If you are just unhooking the straps from your speakers and passively biamping, you will need to have something to adjust the volume on each of the amps or gain controls built into the amps themselves.  You could also be using a crossover in front of the amps but that wouldn't be a very good idea in the passive case as then you have conflicting roll offs and crossover manipulation.

 

Individual volume controls or gains are the only good way if you want to fine tune it cheaply.   More expensive way is to buy a bunch of line attenuators.but you can't fine tune unless you buy a bunch.  http://www.parts-express.com/harrison-labs-12-db-rca-line-level-audio-attenuator-pair--266-244

[NBPK402]

We used REW software and looked at the graphs, and raised/lowered the gain of each driver until we got a graph that gave us the best crossover point.

[The Dude]

http://sound.westhost.com/bi-amp.htm

[Arash]

If you are just unhooking the straps from your speakers and passively biamping, you will need to have something to adjust the volume on each of the amps or gain controls built into the amps themselves.  You could also be using a crossover in front of the amps but that wouldn't be a very good idea in the passive case as then you have conflicting roll offs and crossover manipulation.

 

Individual volume controls or gains are the only good way if you want to fine tune it cheaply.   More expensive way is to buy a bunch of line attenuators.but you can't fine tune unless you buy a bunch.  http://www.parts-express.com/harrison-labs-12-db-rca-line-level-audio-attenuator-pair--266-244

 

 

in this case if you know the exact dB of attenuation you need the best way is to build an autotransformer. it's like an inductor with a center tap. I can calculate it for you if you can wind it

[Coytee]

I don't know enough technical stuff to know if this is what you're asking or not...

 

You can use the formula 20*Log(V1/V2) where V1 and V2 are the input sensitivities of each respective amp (say 1V and 2.5V)

 

20*Log((1)/(2.5)) = -7.95 (disregard the negative sign)

 

This tells you that inside the active crossover (presuming you are using one), you can attenuate the MORE sensitive amp (1V) by 8 db's and now, the two will be matched for their output.....relative to the output of the smaller amp.

 

So, if you put a 5 watt SET amp on the HF and a 400 watt amp on the woofer, your SET amp will dictate the ultimate loudness of the system and the SS amp will be coasting along irrespective of how hard you are pushing it (as long as you don't clip the tube amp)

 

If you flip the V1/V2 numbers you will get the same number, you will just have a positive result instead of negative which is why I say disregard the sign and just attenuate the higher sensitive amp.

 

Think of it as a rev-limiter on an engine.  You can "floor it" as much as you want but you can never go past "X" RPM's.  Here, you CAN exceed the limits but as long as you are respectful of the lower amp, everything will stay in place.

[Coytee]

Oops, you asked how's it split.

 

In the case of using an active, you simply take the preamp out to for example, 'channel 1' input of the active for your right channel.  You'll then have output 1 and output 2 that would become your HF and LF signals.  Signals out of there into your amps, to speakers & you're done.

[Schu]

I don't know enough technical stuff to know if this is what you're asking or not...

 

You can use the formula 20*Log(V1/V2) where V1 and V2 are the input sensitivities of each respective amp (say 1V and 2.5V)

 

20*Log((1)/(2.5)) = -7.95 (disregard the negative sign)

 

This tells you that inside the active crossover (presuming you are using one), you can attenuate the MORE sensitive amp (1V) by 8 db's and now, the two will be matched for their output.....relative to the output of the smaller amp.

 

So, if you put a 5 watt SET amp on the HF and a 400 watt amp on the woofer, your SET amp will dictate the ultimate loudness of the system and the SS amp will be coasting along irrespective of how hard you are pushing it (as long as you don't clip the tube amp)

 

If you flip the V1/V2 numbers you will get the same number, you will just have a positive result instead of negative which is why I say disregard the sign and just attenuate the higher sensitive amp.

 

Think of it as a rev-limiter on an engine.  You can "floor it" as much as you want but you can never go past "X" RPM's.  Here, you CAN exceed the limits but as long as you are respectful of the lower amp, everything will stay in place.

Interesting... thanks.

[pzannucci]

I don't know enough technical stuff to know if this is what you're asking or not...

 

You can use the formula 20*Log(V1/V2) where V1 and V2 are the input sensitivities of each respective amp (say 1V and 2.5V)

 

20*Log((1)/(2.5)) = -7.95 (disregard the negative sign)

 

This tells you that inside the active crossover (presuming you are using one), you can attenuate the MORE sensitive amp (1V) by 8 db's and now, the two will be matched for their output.....relative to the output of the smaller amp.

 

So, if you put a 5 watt SET amp on the HF and a 400 watt amp on the woofer, your SET amp will dictate the ultimate loudness of the system and the SS amp will be coasting along irrespective of how hard you are pushing it (as long as you don't clip the tube amp)

 

If you flip the V1/V2 numbers you will get the same number, you will just have a positive result instead of negative which is why I say disregard the sign and just attenuate the higher sensitive amp.

 

Think of it as a rev-limiter on an engine.  You can "floor it" as much as you want but you can never go past "X" RPM's.  Here, you CAN exceed the limits but as long as you are respectful of the lower amp, everything will stay in place.

Coytee, provided you have the same gain structure or sensitivity in the amplifiers.  If you are dealing with an Older IcePower amp with no input module and it takes 3.6 volts (balanced probably half for unbalanced) to get to rated output.  Something like Rogue Audio 90 has an input sensitivity of 1 volt.  Now in theory if you know the input sensitivities you can apply some of the math you are talking about but you may not be close in the end.  

 

Give me a pair of knobs to vary the sensitivity and output of each amp :-)

 

Active, removing the crossovers, a whole different story dictated typically by the active crossover arrangement.

 

Arash,

I believe the Auto-former idea, as PWK stated in one of his patents, is a good idea as long as you are not thinking of using it on the woofer.  If you do you will have to recalculate it's impact on the damping, enclosure, and other things (at least what I have read, I haven't tried it).  Probably why I have not seen auto-formers on woofers to raise efficiency though it sounds like an interesting idea.

[Ol_mcdonald]

I think he meant how do you split the signal from the preamp to the two amps. DBX DriveRack PA2, Auto room EQ, driver phase alignment, 3 in 6 out all balanced; Sub, LF, MF/HF work? Using the AK2 (high end portion) for the MF/HF split. That's what I am considering.

Edited January 13, 2017 by Ol_mcdonald