Running a stereo amp in parallel instead of bridged

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#61
stratus46 said:
BTL amps quadruple the power output. You double the Voltage which doubles the current.
Abracadabra ! A 4 Ohm load with a 14V supply gets you about 5 Watts but in bridge mode,
20 WATTS! That was a big deal. I built a BTL amp in my car back in '79 before it was popular.
I worked in a stereo repair shop and snagged a Marantz power amp module from E-Waste
(didn't call it that back then), repaired it, set the gain to -1, connected the Marantz input to
the normal speaker output in the Pioneer KP-500 and connected the speaker '-' to the
Marantz output. I was using 8 Ohm speakers so the Pioneer saw a 4 Ohm load as did the
Marantz, 10 Watts into 8 ohms was a massive improvement. It's exactly the same as balanced
line audio in XLR connectors, just at the final output end. Nothing shorts if done correctly
BUT YOU NEED TO BE CAREFUL DOING MEASUREMENTS. BOTH the speaker outs, + & - are
active and your dummy loads must be isolated AND the scope inputs. Easiest is 4 channel scope
with 1 probe on each output and add the signals with scope math.

G²
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Of course, but the question was: what is the advantage of attempting to series-connect amplifiers over bridging them? kodabmx already answered that: nothing if the amplifier can be bridged, which it can.
 
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#62
bremen nacht said:
"Ohm's law is not the only one at play here"

Ohm's law trumps all.
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#63
Bruce Gillingham said:
Tony,

I think that all of the members who have replied to your posts understand where you are coming from and some have provided very good explanations as to why you will not get the results that you desire. You seem to be, as yet, unconvinced. Let me see if I can help.

In your defense, if you are successful in coming up with a current sharing scheme for two (or more) amplifiers without incurring too much loss in the additional resistors, you may be able to eke out a small increase in speaker volume. This is because each amplifier will be supplying less current and its internal power supply rails will sag less under load. Thus, the amplifiers will be able to swing a somewhat higher output voltage which is necessary to supply additional current to the speaker. How much additional voltage swing can be obtained is dependent on how stiff the power supplies are. I suspect the increase would be inaudible.

The point that you seem to be missing is that you cannot pick which "laws" of physics that you want to apply. You must satisfy all at the same time. Ohms law (V = R*I) is, perhaps, the most fundamental equation in electrical engineering. In order to force additional current into a fixed resistive load, you must apply additional voltage across its terminals. There is no way around this.

I hope this helps,

Bruce
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In all honesty, paralleling amplifiers is not very common.... but here...

https://www.analog.com/en/technical-articles/paralleling-amplifiers-increases-output-drive.html

BTW, my background is in Physics.
 
#64
dreamth said:
Judging by the internal schematic of Parasound Z3, if I had 4 of them and no possibility to upgrade to a biamp system, I'd do a bold move : change the symmetrical supply to single supply(simply use 2 rectifier diodes of the bridge and no negative) , bias the amp's input at 1/2 v supply, change the input capacitors to nonpolar ones(that depends on the type of bridge type of drive) , probably dump the dc offset U101 or work around r219 refference .... and make it bridged .
That will get you almost the same theoretical output power, but better thermal management and transient power delivery in the low register, also colder amps mean less offset so less need for dc offset compensation. You could even make use of a higher bias approaching class A operation so less crossover distortions if carefully biased . Input stage slew rate doubles, but the final transistor Early effect worsens so you don't really get better speed unless you change the final transistors with faster ones ,but that's gonna be rather difficult to do as 2sa1047 with just 20Mhz ft actually has 120pF BC capacitance, 50pf less than 2sc5248...so the final stage is already pretty fast at lower supply voltages making it good for lower supply bridged operation.
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I got at least ten of them... I just couldn't help myself whenever I saw someone selling a "lot" of amps on HiFi Shark. I think I was paying about 75 bucks each by the time I stopped.

But no, I have no desire into breaking into them... I got stacks of other amps I could easily use.

One of these days I ought to put the NCore eval board into the Ghent case... that might fit into the Z-Rack., behind one of the Z-blanks...

Now, all I need is three pairs of NAD monitor handles.

You know, I even got a pair of DIY Aleph 60s and an F5 on a stack... plus more and more and more... I just figured this will be fun. However, before I wired it up I need to figure out how to mount the resistors on the back panel. Sure, I could pull the switch and go bridged... but where is the fun of doing that?
 
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#65
MarcelvdG said:
Of course, but the question was: what is the advantage of attempting to series-connect amplifiers over bridging them? kodabmx already answered that: nothing if the amplifier can be bridged, which it can.
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I wouldn't even attempt such a thing as nearly everything needs to float so the "ground" of the
"top" amp has ride on the output of the "bottom" amp. Nearly nobody would be able to service
it as it's pretty whacky. I expect it would be a LITTLE easier with an output transformer compared
to dierct coupled solid state amp. I don't think in terms of tubes since I abandoned then in the '60s.
Having serviced electronics for almost 50 years (longer before it was my paid job) I don't like things
that break or wear out. Tubes do those things in addition to being power hogs and space wasters.
Of course once you work that out, how about stacking 3 or 4 amps? What that defines is a variant
of class H with power supplies changing levels. BTL is FAR simpler and as I stated from my 1979 amp,
the "bridge" amp can be external to the original. If you look at the bridge switch of the Adcom GFA-555,
the second amp is just a gain of -1 (left channel) from the right channel.

G²
 
#66
stratus46 said:
Excellent analogy with the bulbs !

G²
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But, if you have more power in reserve because now you got two amplifiers in parallel they can drive a cruel impedance, huh? In essence they can hold the voltage even when more current is being drawn.

But, even though I got a spare set of Maggies (12), I am not gonna put those at risk.

Though Experiment time:

Let's think this through... forget about Ohm's Law here for just one second and think about the power supply's ability to provide power so the amplifier can hold a voltage into a load.

Let's say you crank the volume way up... to the point where a given amplifier ( single channel discussion here ) can not drive enough current into the load and the voltage starts to sag (or the amp starts to clip ). Let's assume the limitation here is in the amplifier circuit, not the power supply proper.

If now you add a second amplifier in parallel, now what happens is that the current load is shared by both channels. Meaning half the current is coming from each channel. So, now the end result is that as the volume is raised, the current drive capacity is double and voltage doesn't sag.

OK, let's return to Ohm Law... the derivative power equations now show that doubling the current into a given load will quadruple the power being delivered.

Got it.

I am not cheating out of Ohm's Law at all... It's a circuit implementation that allows more current drive when it gets to a volume of 11, that's all.
 
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#67
tonyEE said:
I got at least ten of them...

But no, I have no desire into breaking into them... I got stacks of other amps I could easily use.

You know, I even got a pair of DIY Aleph 60s and an F5 on a stack... plus more and more and more...

Sure, I could pull the switch and go bridged... but where is the fun of doing that?
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I hope you don't ask me about the fun when on a diy forum you just show off with 1 zillion amplifiers which you can't afford to diy...
 
#68
dreamth said:
I hope you don't ask me about the fun when on a diy forum you just show off with 1 zillion amplifiers which you can't afford to diy...
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One 3rd of my stuff... more than half of the very good stuff, is all DIY. Even if they all have blue LEDs on the front panel...

I have no real desire to DIY a bunch of cheap amps.

I honestly didn't expect the Spanish Inquisition... just how to calculate the output impedance based on the published damping factor.... AND a straightforward description of the sound difference between parallel and bridged operation... not opinions.
 
#69
ejp said:
Yep. I was assuming +/-14V rails. Shoulda noticed you were a car guy ;-)
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Audio and car stuff back then was for fun. Now just buy the premium sound package
and enjoy. I was actually a video guy and worked in commercial TV for 45+ years on
nearly everything analog - video and audio switchers, analog TV transmitters, studio
transmitter links, cameras, film to video and lots of VTR work from beginning 2" quad
to digital HD. Only thing I DIDN'T work on was the transmitting antenna.

G²
 
#70
tonyEE said:
But, if you have more power in reserve because now you got two amplifiers in parallel they can drive a cruel impedance, huh? In essence they can hold the voltage even when more current is being drawn.
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That's exactly what everybody has been telling you. Raise the voltage or lower the impedance. Otherwise no extra current.
 
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#71
ejp said:
That's exactly what everybody has been telling you. Raise the voltage or lower the impedance. Otherwise no extra current.
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Go back and read again.... read the Though Experiment.

You folks keeping analyzing this based on a DC signal circuit, I'm looking at this from a fluctuating signal going into the power limits and how the circuit behaves on such transients.
 
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#75
ejp said:
Ohm's law applies to AC as well as DC. Ye canna change the laws of physics. Sorry you don't get it.
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Think TRANSIENTS.... what happens when the gain of the circuit exceeds its ability to deliver power into a load.

For a given load and voltage, a given current will be delivered... this is determined by Ohm's Law... with a sin(t) component to allow for the signal.

The amplifier can only put out so much power... so when that power is exceeded it will compress the signal... ( most likely the voltage will sag as the signal will overshoot a bit and then settle...)... we think of this a clipping.

Now, in a parallel two amp set up, each amp is putting up only half the current into the load... so it can actually deliver the current and the voltage won't sag when a transient comes along that will exceed the available power from ONE of the amps. So, both amps can likely deliver the peak current.

The issue, IMHO, is that you keep thinking of a static DC situation, not on peak transients.

The voltage available from the power supply to the amplifier, and the amplifier itself, are capable of higher transient power delivery than the RMS rating. Recall that the rating of an amplifier is an engineering choice -OK, for stereo amps, not for HT multichannel stuff.

As I said, you are all taking a very simplistic look at this. Look at the behavior of the amplifier on high power transients... it is here where the parallel circuit's ability to deliver current that pays off. I think of it as a current amplifier... whereas the bridge configuration is a voltage amplifier.

And, please, I know physics, I spent years doing it. Don't insult my ability. Instead of engaging in ad hominem attacks, read what I describe and tell me if I am wrong. Otherwise, I will start giving you some neat equations and tell you that you just don't understand it.
 
#77
tonyEE said:
Don't insult my ability. Instead of engaging in ad hominem attacks
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Don't insult me by accusing me of things I haven't done. I have made no such attacks, and I will not tolerate being egregiously misrepresented.

As for 'static DC', if there was DC anywhere in this setup you would have a speaker fire. Possibly you mean 'steady AC', in which case I agree with what you are now saying. However you certainly started out, and persisted, with the bizarre claims that merely doubling the number of amplifiers would increase the power, and also that you were doubling the current and quadrupling the power. Indeed at one stage you claimed you were quadrupling the voltage. I don't see where you have acknowledged any of these mistakes.
 
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#79
Don't want to stir the embers but Accuphase (M-6000) did just that, employ a stereo amp, or two complete mono amps in parallel.
Also Nelson Pass' ACA is often run in parallel, yes, to achieve more power into lower loads and the power into 8 ohms stay the same, but let's not forget the ACA is a SE amp run on a single polarity PSU so it cannot easily double its power output.
Attaching Accuphase's brochure for those who might be interested.

Cheers
 

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