Bi amping with different amps

IWC Dopplel

Well-known Member
Is there an easy way to match amp levels if you are looking at running a higher power amp to drive the low frequencies on the fronts ?

For example running a higher quality two channel amp and still bi-amp ?
 

motile rod 2

Novice Member
The power of an amp isn't what you should be looking at, it's the gain. Ideally the gain should be matched, any difference will have an effect tonally, but this may work to your advantage.

So it begs the question, which two amps are you looking to match? If its the p7, as far as I know it has the standard THX gain of around 29dB (all THX amps should have this gain, or the option for it). You may have the option to alter the gain to different settings, like my p1000 does. Most stereo amps have a gain of 32.5dB, so that will give a 3dB lift to either the high or low frequencies if used with your p7. But some amps have a much lower gain of 20dB, so not all will work well together.
 

IWC Dopplel

Well-known Member
Thanks, I was considering the following amps in no particular order :

Krell KSA 80, Krell KMA 160's, Usher R-1.5, Bryston 4B ST, even another pair of P1's :smashin:
 

Mark.Yudkin

Distinguished Member
The Arcam P7 has a non-switchable THX gain of 28.3dB. The P1 can be switched between 28.3dB and 31.5dB, and is the obvious match for the P1 or P7.

You will need to check the specs for the other amps you are investigating to ensure you can achieve identical gain. In contradiction to motile rod 2's statement, biamping using mismatched gains will yield a sound that is anything from dreadful to execrable - the level of horror being a function of the size of the mismatch.
 

alexs2

Well-known Member
Thanks, I was considering the following amps in no particular order :

Krell KSA 80, Krell KMA 160's, Usher R-1.5, Bryston 4B ST, even another pair of P1's :smashin:
I've done something along these lines when I had my Linn Keltik active system,and was using Krell KMAs for the bass,KSA 100 for the mid,and a pair of tubed monoblocs for the treble.

With a system like that,gain matching was easy enough,but Mark's point is critical,in that if you don't get the matching correct,you end up with one part of the audio spectrum emphasized by in some cases several dB,which will sound awful.

Done properly,it can work....done badly,it's a recipe for trouble.
 

IWC Dopplel

Well-known Member
I've done something along these lines when I had my Linn Keltik active system,and was using Krell KMAs for the bass,KSA 100 for the mid,and a pair of tubed monoblocs for the treble.

With a system like that,gain matching was easy enough,but Mark's point is critical,in that if you don't get the matching correct,you end up with one part of the audio spectrum emphasized by in some cases several dB,which will sound awful.

Done properly,it can work....done badly,it's a recipe for trouble.
I am looking to get some tonality improvements between the center and the fronts. The older Sonus Fabers are tonally a little richer something like a Krell might add some snap and dynamics over the Arcam but not destroy their midband beauty. The problem is two stereo Krells, Brystons or four mono's adds up !

I could always go back to non bi-amp but like the top end of the Arcam amp so in theory a Krell for the lower/mid registers seems an ideal step forward. If I had another P1 I could experiment but I suspect (don't know) that a Krell will be a bigger upgrade than more P1's :rolleyes:

Maybe my fondness of an old KSA50 is blurring my thinking :cool:
 

alexs2

Well-known Member
I am looking to get some tonality improvements between the center and the fronts. The older Sonus Fabers are tonally a little richer something like a Krell might add some snap and dynamics over the Arcam but not destroy their midband beauty. The problem is two stereo Krells, Brystons or four mono's adds up !

I could always go back to non bi-amp but like the top end of the Arcam amp so in theory a Krell for the lower/mid registers seems an ideal step forward. If I had another P1 I could experiment but I suspect (don't know) that a Krell will be a bigger upgrade than more P1's :rolleyes:

Maybe my fondness of an old KSA50 is blurring my thinking :cool:
FWIW,the KSA80 and KMAs would be an order of grunt beyond the KSA50,but the downside is vast amounts of heat.

Obviously the FPB series are better overall,but substantially more expensive,but I would also avoid the KSA-S series as these didn't sound better than their predecessors.
 

Ian_S

Distinguished Member
Am I right in thinking that volume isn't linear so, if you have two amps with different gain, even if you match the levels at a certain volume, as soon as you change the master volume they move back out of step?
 

IWC Dopplel

Well-known Member
Am I right in thinking that volume isn't linear so, if you have two amps with different gain, even if you match the levels at a certain volume, as soon as you change the master volume they move back out of step?

A potentially interesting point :confused:
 

Mark.Yudkin

Distinguished Member
Am I right in thinking that volume isn't linear
It's logarithmic, not linear.

A correctly functioning power amp has a fixed gain (by definition). Gain defines the multipication factor for the power as 10**gain, where gain is specified in Bels. So a power amp with a 28.3dB gain (your Arcam P7) multiplies the input power by 10**2.83 ~= 676.

The volume control on your preamp alters the level of attenuation: it reduces the power by dividing it by a fixed amount. If the volume control is calibrated in dB, the reduction is by the same formula (-20dB means 10**-2 = 0.01, and the - on the calibration scale means multiply).

so, if you have two amps with different gain, even if you match the levels at a certain volume, as soon as you change the master volume they move back out of step?
The trouble is, since you have one preamp and two power amps, there is no way to match the levels of mismatched power amps at any volume using the preamp, as the volume control is irrelevant at this point (see above).
 
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Ian_S

Distinguished Member
I guess I was thinking of a multi-channel system in the latter point, where you might decide to mix power amps. The levels controls allow you in individually adjust the output volume at the measured level, but I think what we're saying is that because the gain levels remain different, when you increase or decrease the master volume away from the measured value, the different amps increase or decrease at different levels again...

So for stereo use, the two amps on a speaker must have matching gain because as you say there is no way to compensate anyway.

For multi-channel use, whilst you can alter levels between channels, the logarithmic nature of volume anyway means as soon as you listen at anything other than the measured SPL, they go straight out of balance too.

Which strays off of bi-amping a little but illustrates the point of having matching gain throughout any system IMO...
 

Welwynnick

Distinguished Member
A correctly functioning power amp has a fixed gain (by definition). Gain defines the multipication factor for the voltage as 10**gain, where gain is specified in Bels. So a power amp with a 28.3dB gain (your Arcam P7) multiplies the input voltage by 10**2.83 ~= 676.
Care to reconsider that, Mark?

Nick
 

inzaman

Moderator
I have tried bi-amping with non-matching amps, albeit the same brand (Rotel in this case, okay not in the same league as Krell et al but i got strange results).
If i used a different amp to drive either the bass/mid to that of the treble then one of them overpowered the other. If i used a different amp to drive the centre to the left and right then again one would overpower the other (the centre in this case).

Personally i would now only bi-amp if i had exact matching amps, i would rather though put the funds towards one good amp as opposed to two identical amps for multi-channel :)
 

IWC Dopplel

Well-known Member
I have tried bi-amping with non-matching amps, albeit the same brand (Rotel in this case, okay not in the same league as Krell et al but i got strange results).
If i used a different amp to drive either the bass/mid to that of the treble then one of them overpowered the other. If i used a different amp to drive the centre to the left and right then again one would overpower the other (the centre in this case).

Personally i would now only bi-amp if i had exact matching amps, i would rather though put the funds towards one good amp as opposed to two identical amps for multi-channel :)
Thanks :smashin:
 

Mark.Yudkin

Distinguished Member
My post should have said power rather than voltage in the calculation. Corrected.

Bels are a measure of logathmic power ratios (log10 (P1/P2)). We need to substitute P=V**2/Z to figure the actual voltage gain (so if the impedances were the same, we'd get 2*log10(V1/V2) Bels)
 
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IWC Dopplel

Well-known Member
I am not convinced sonically of this route having experimented with naim 250's and 135's.

I will confirm my findings when my other pair of 135's arrive next week :cool:
 

lbstyling

Novice Member
in theory, if its going to work, you would want 4th order or higher crossovers -i have never managed to get it to work right with different power amps myself, it may be that having a active xo with a digital stage filter may be the answer here- ive certainly heard of many people on the HES side of things trying this and finding the results good.-and it does make sense that it would with a vertual 100db/oct filter as the different amps dont play the same region.

i would also be inclined to say that the crossover freq's will make a significant difference-
if your mid covers the critical range, without the tweeter being at a significant level- its more likely you will get away with it.
along the same lines -im sure for much the same reason a 3 way has a better chance of working well.

if you are using a 3 way, my recommendation would be for the same type of amplifier for the mid and tweet and the alternative for the bass, unless your mid runs particularly high (ie crossover of 4k or so) (this would likely be a HES design)
 

IWC Dopplel

Well-known Member
It does sound a little bit of a double edged sword as high order crossovers usually sound poor IMO. I am not a fan or 3rd order let alone 4th ;)
 

lbstyling

Novice Member
3rd order has its own dissadvantages to 4th as 3rd isnt phase coherent. (odd order)

the sq result isnt depentant on the order imo anyway, as the drivers chosen will dictate the order needed-regardless of what the designer would prefer. enforcing a lower order is a bad idea for many reasons.

and the style of sound is dictated by the drivers used combined with the restraints imposed by the designer on the enclosure volume.

with a high order crossover, the LCR quality becomes very important. manufacturers dont use quality crossover parts much if ever -regardless of the retail price of the speaker.

the crossover design itself and the size constraints vs optimum qts are more important.

its good to remember that low order crossovers can only be used propperly with a wide band driver- wide band drivers are usualy higher efficiency.
HES drivers are usualy faster to stop (better self dampling)and have potential for higher dynamics along with more head-room.

so when you hear a low order crossover (1st order)-what are you realy identifying that you like?

-its all a compromise.
 

IWC Dopplel

Well-known Member
I agree with the crossover point. The simpler the better as Caps in crossovers can make or break the sound of the speakers (Certainly with Horns)

The Extremas use first order with no capacitors ;) The good news is seamless integration across the drivers and incredible body and weight to the sound plus resolution that makes most speakers sound muffled. The bad news is they are one of the most challenging box speakers to drive (Not quite an apogee but an amplifier crusher all the same)

Hence the reason for looking for four of these to drive 'em
 

Attachments

lbstyling

Novice Member
I agree with the crossover point. The simpler the better as Caps in crossovers can make or break the sound of the speakers (Certainly with Horns)

The Extremas use first order with no capacitors ;) The good news is seamless integration across the drivers and incredible body and weight to the sound plus resolution that makes most speakers sound muffled. The bad news is they are one of the most challenging box speakers to drive (Not quite an apogee but an amplifier crusher all the same)

Hence the reason for looking for four of these to drive 'em
very interesting!!!
it sounds like they are a design progression from the early jbl concepts (ie-L100 century)- thats some advanced engineering.
its very hard to get a flat response for that method, id be interested to see a FR chart for those.:smashin:

if it is flat, i would almost certainly say that the drivers are designed specifically for this speaker (not a series) and that the designer came up with the drivers himself as opposed to specifying the perameters.(not normal these days)

if the FR is good and the speaker is 1st order (natural roll off) this is no ordinary speaker.

id love to try a pair.

have a look at the emotiva pre amp- very good quality (shocking for the price actually) and a sallen key line level crossover for a sub, sounds perfect for those.
 

IWC Dopplel

Well-known Member

lbstyling

Novice Member
im quite surprised in all as i didnt get on with the faber cremonas, so i kinda mentally wrote off faber as a company for further investigation, but looking at the detailed writeup, perhaps i should investigate a little further into this specific speaker.:smashin:
 
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IWC Dopplel

Well-known Member
im quite surprised in all as i didnt get on with the faber cremonas, so i kinda mentally wrote off faber as a company for further investigation, but looking at the detailed writeup, perhaps i should investigate a little further into this specific speaker.:smashin:
Were they Cremona M's ? I personally don't like the later Fabers (M's are later) as much, The original designer moved on and complex crossovers and a more lean/analytical approach ensued.......
 

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