Two stereo amps

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Charles Calkins

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Two stereo amps
« on: 7 Nov 2018, 07:23 pm »

      Hi Guys:
                   I've been listening to talk about using two stereo amps in a system.
                    Suggestion is have a solid state amp to drive the bass and mid range.
                     Have a stereo tube amp to drive the tweeter. I can do that. My pre has
                     two pair of inputs. They run parallel.
                     Has anybody tried this? If so what were the results. Good. Bad. No difference?

                                                          Cheers
                                                          Charlie

Speedskater

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Re: Two stereo amps
« Reply #1 on: 7 Nov 2018, 07:39 pm »
Sure lot's of audiophiles do that. Only if each loudspeaker has four terminals. The two problems are matching woofer & tweeter levels and polarity.

Charles Calkins

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Re: Two stereo amps
« Reply #2 on: 7 Nov 2018, 08:10 pm »
Sure lot's of audiophiles do that. Only if each loudspeaker has four terminals. The two problems are matching woofer & tweeter levels and polarity.
  By four terminals on each loudspeaker do you mean L+R for the bass and L+R for the tweeter.
   
                                                        Cheers
                                                        Charlie

avahifi

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Re: Two stereo amps
« Reply #3 on: 7 Nov 2018, 09:02 pm »
whoops, double post

avahifi

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Re: Two stereo amps
« Reply #4 on: 7 Nov 2018, 09:04 pm »
We often use our DVA 4/2 amplifier for this purpose.  It can do either four independent channels or two very high power channels.

We simply use all four channels to bi-amp speakers with separate top and bottom speaker terminals.  Two channels of the amplifier per speaker.

Make sure you remove the links between the top and bottom speaker terminals before trying this!

It does make an obvious difference in overall system performance and since the four channels are identical, no gain matching is required.

Frank

toocool4

Re: Two stereo amps
« Reply #5 on: 7 Nov 2018, 09:12 pm »
This is possible as long as the speakers have separate terminals for the tweeter and the bass / mid range.
I have done this in the past but only using 2 identical stereo power amps. I did this years ago when I had Roksan L2.5 pre and 2 x S1.5 stereo power amps, it worked nicely I got cleaner more refined sound.
What you are proposing doing is completely different type of amps, sounds you like you may have problems first you will need to find different amps with the same gain. Also if one amp is slow and the other fast, I don’t know how that will play out. Example my Spectral is very fast if that is what is called for, I can’t imagine how the sound would be if I pair it up was say a slow amp driving the tweeters.
I guess only one way to find out, give it a try.

Charles Calkins

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Re: Two stereo amps
« Reply #6 on: 7 Nov 2018, 09:39 pm »
This is possible as long as the speakers have separate terminals for the tweeter and the bass / mid range.
I have done this in the past but only using 2 identical stereo power amps. I did this years ago when I had Roksan L2.5 pre and 2 x S1.5 stereo power amps, it worked nicely I got cleaner more refined sound.
What you are proposing doing is completely different type of amps, sounds you like you may have problems first you will need to find different amps with the same gain. Also if one amp is slow and the other fast, I don’t know how that will play out. Example my Spectral is very fast if that is what is called for, I can’t imagine how the sound would be if I pair it up was say a slow amp driving the tweeters.
I guess only one way to find out, give it a try.

   Well it was just something I've heard about doing. I don't think I will. I have a mac 352 amp. Van Alstine hybrid pre
   And a pair of Von Schwikert loudspeakers. Sounds pretty good to me. I'll just keep things like they are.
   If I got into this it would be like opening a big can of worms.

                                                    Cheers
                                                   Charlie

Speedskater

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Re: Two stereo amps
« Reply #7 on: 7 Nov 2018, 09:50 pm »
By four terminals on each loudspeaker do you mean L+R for the bass and L+R for the tweeter.
Make that Plus & Minus for the bass and Plus & Minus for the tweeter.

* * * * * *
first you will need to find different amps with the same gain. Also if one amp is slow and the other fast, I don’t know how that will play out.
If one of the amps has a volume control, you can deal with the gain differences.
For all practical purposes, all amp have the same thru-put speed.

Freo-1

Re: Two stereo amps
« Reply #8 on: 7 Nov 2018, 10:20 pm »
In order to get optimum results for two amps, a active crossover is strongly recommended so the mid-treble amp is matched up to reproduce the intended frequency band.  Secondly, gain matching is crucial to get a flat response.  A small gain difference can make the playback sound off kilter. 

Speedskater

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Re: Two stereo amps
« Reply #9 on: 8 Nov 2018, 01:51 pm »
True an active crossover is a much better path, but it's an engineering challenge. There is more going on in a passive crossover than meets the eye.  You often can't just plug-in frequency and slope and get the same transfer function.

richidoo

Re: Two stereo amps
« Reply #10 on: 8 Nov 2018, 05:25 pm »
I could always hear the difference between the tube amp and SS amp in horizontal biamping. I find it distracting so I stopped trying. I wasn't happy with the treble sound of any of the AB amps of the time that I could afford so I used tube amps to get good treble tone. But a couple years ago I tried Modulus86 chip amp and found that it had treble as good or better than my tube amps. Then I needed more power so I tried ICE Edge and found it to be "the answer" (for me :) ) to perfect treble, low impedance and unlimited power, and it's cheap compared to ultra high end class AB amps that have good enough treble.

Edit:Be aware that most tube amps are AC coupled (input cap,) while most SS amps are DC coupled (no cap.) The cap rotates the phase by 90 degrees. If your SS amp is DC coupled then the input cap of the tube amp will cause a time misalignment between whatever bands are assigned to each amp. If tubes power treble only, you'll have a 1.5" time misalignment at xo freq of 2kHz which will ruin vertical directivity and tone. If tubes power mid and treble, then you'll hear a time misalignment of 12" at 300Hz between mid and bass. If your SS amp doesn't have an input cap you can add one if necessary, it can easily be added to the interconnect in the RCA plug. Some tube amps use cap coupling between multiple stages in the amplifier, each one rotates phase by 90 degrees. This is what determines whether an amp is "inverting" or not. Coupling caps can also be used in SS inputs or between SS stages.  The point is that the output signals must be aligned in time. This is why active speaker proponents like Linkwitz stress using the same amplifier on all drivers of the speaker. But you can work around it. A cheap little USB scope for your phone can display the phase difference between the amps. I don't think most audiophiles know about this and this is why horizontal biamping with tubes and SS often fails to sound as good as either one amplifying the whole speaker.

Another thing, commercial 3way speakers have dual input speaker posts that are wired one set to bass and the other set to mid/tweet.  So if you wanted one amp to drive bass and mid, while the other drives tweeter, you would need to rewire the speaker at the crossover board to move the mid driver crossover input from the upper post to the lower bass posts. But usually what people do in horizontal bi-amping is to use the tube amp on the upper posts to drive both the mid and tweeter together while a separate SS amp drives the bass only.
« Last Edit: 9 Nov 2018, 02:41 am by richidoo »

Speedskater

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Re: Two stereo amps
« Reply #11 on: 8 Nov 2018, 09:23 pm »
A coupling capacitor does not rotate the phase. But a cross-over cap does.

richidoo

Re: Two stereo amps
« Reply #12 on: 9 Nov 2018, 02:39 am »
A coupling capacitor does not rotate the phase. But a cross-over cap does.

Yes, thanks for the correction. :)

toocool4

Re: Two stereo amps
« Reply #13 on: 9 Nov 2018, 01:39 pm »

For all practical purposes, all amp have the same thru-put speed.

Maybe in theory, but in real life speed is different unless you have heard what I am taking about you will not know. I too was surprised the first time I heard it.

Speedskater

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Re: Two stereo amps
« Reply #14 on: 9 Nov 2018, 03:58 pm »
What differences you heard were not amplifier speed in any engineering meaning of the word.

* * * * * * * * *
Audiophiles have been mating solid state and tube amps together for decades without this 'speed' problem.

toocool4

Re: Two stereo amps
« Reply #15 on: 9 Nov 2018, 04:11 pm »
What differences you heard were not amplifier speed in any engineering meaning of the word.

* * * * * * * * *
Audiophiles have been mating solid state and tube amps together for decades without this 'speed' problem.

Maybe and maybe not. Comparing a Leben to a Spectral Audio we went from playing a record, switch from the Spectral Audio to the Leben we all thought we had started the record at the wrong speed. It’s like when you accidentally play a 45rpm at 33rpm, no kidding it was that dramatic.

mboxler

Re: Two stereo amps
« Reply #16 on: 9 Nov 2018, 04:13 pm »
A coupling capacitor does not rotate the phase. But a cross-over cap does.

Granted, I'm still learning, but I don't understand how this can be.

All capacitors introduce a 90 degree phase shift into a circuit.  However, when this phase shift is added to the phase shift of the load, the phase shift changes with frequency. 

Example, a 1uf capacitor in series with a 24K amplifier load will give you a 45 degree phase shift at 6.63 hz.  As the frequency doubles, the phase shift is halved, eventually approaching zero.   A capacitor in a crossover cannot behave any differently.


As far as amplifiers are concerned, is it not true that the output of some amplifiers is inverted and others not?  If you were to feed a non-inverting signal to the low pass and an inverting signal to the high pass, the summed voltages at the crossover point would tend cancel each other out.

What am I missing?

Mike

Steve

Re: Two stereo amps
« Reply #17 on: 9 Nov 2018, 10:54 pm »
What differences you heard were not amplifier speed in any engineering meaning of the word.


I think TooCool is talking about rise time. Many use this non scientific term, being knowledgeable in other fields.

Yes, TooCool, the ear perceives rise time differences of at least 5 us (microseconds), some claiming as low as 2 us.

cheers

steve

Speedskater

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Re: Two stereo amps
« Reply #18 on: 10 Nov 2018, 01:38 am »
I think TooCool is talking about rise time. Many use this non scientific term, being knowledgeable in other fields.
Yes, TooCool, the ear perceives rise time differences of at least 5 us (microseconds), some claiming as low as 2 us.
cheers
steve

The people that say that were confused by Kunchur. What you can hear is if one channel of a mid-range sound is suddenly delayed by 10 us, the sound will seem to move laterally a small amount.  It's about one channel time delay, nothing to do with rise time.

Speedskater

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Re: Two stereo amps
« Reply #19 on: 10 Nov 2018, 01:42 am »
Example, a 1uf capacitor in series with a 24K amplifier load will give you a 45 degree phase shift at 6.63 hz.  As the frequency doubles, the phase shift is halved, eventually approaching zero.   A capacitor in a crossover cannot behave any differently.
The same rules apply. But we have to look at the ratio of capacitor impedance and resistor impedance at cross-over frequency.
(they will both have the same impedance)