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Post by Johnkenn on Nov 18, 2014 22:25:53 GMT -6
So - if I were to an additional one of my power amps and use them as mono blocks, would the extra power going to my monitors improve the tone or is it just gonna make it louder? I've got a chance to pick up another one and I can run them in bridge mode - one to each monitor. I would only be interested in doing it if I was going to achieve better sonic quality - no need for more volume...
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Post by tonycamphd on Nov 18, 2014 23:38:22 GMT -6
I would not consider myself an expert on this, i think smallbutfine would have great info here, but theoretically any time an amp is less stressed it runs cooler, giving it longer life, and should drive a single monitor more efficiently with more headroom than driving 2, also it should eliminate cross talk, so.... If it's good deal, why not give it a try? worst case you have a spare. Another thing to consider is sometimes certain amps sound worse when bridged to mono, i know the adcom gfa555(jw style) sounds insane in stereo, and crappy bridged so....again?
Theoretically though, letting one amp run one speaker should sound better.
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ericn
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Post by ericn on Nov 19, 2014 8:06:27 GMT -6
Some speakers need more power, some will say a smaller simpler amp is better, honestly it's what works for you.
Another thing to look at before you go and bridge a pair of amps is the current draw! So often in live studio and home use I have seen people up the available amp power BUT are tripping breakers when they start to draw that power because the inefficient amps don't have the raw current they need.
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Post by svart on Nov 19, 2014 8:54:14 GMT -6
I wrote a long and drawn out explanation of things and what I thought about it, and when I hit "post quick reply" the site had logged me out. Oh well.
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Post by Deleted on Nov 19, 2014 9:02:24 GMT -6
As said, sound quality of the bridge mode might not be the same as the sound quality in non-bridged stereo. Depends on the amp model you are using/amp architecture.
What you undoubtly reach by using mono blocks is somehow better channel separation (should be 100% :-)), this could result in a more precise stereo image.
That said, we use hi-end stereo amps non-bridged, ok, they are esoteric and very expensive. And there is nothing to miss in terms of stereo separation. The Superbeast DAC made much bigger difference for us...
We selected by ear. And we had a few fast and powerful amps to compare with from the beginning.
A Plinius power amp is our actual main amp. Price of a car, but incredible in class A mode.
The Array Audio amp we used before was pretty near. Resteks, too. But these are europe based manufacturers, i am pretty sure, there are excellent american manufacturers as well. Shipping costs of power amps is pretty expensive, they are heavy, so you mostly try to stay on the same continent....... ;-)
Adcom was a very good "budget" option...
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Post by svart on Nov 19, 2014 9:26:55 GMT -6
Ok, here's the long and short of it. (quicker and shorter version)
A "stereo" amp is nothing more than two mono amps in a single box.
Amps steer current into a reactive load (speaker). An ideal amp should reproduce exactly the same signal as the input signal, but with gain. Due to the circuitry in the amp, there are many places for the circuit to change the signal. This is worse with gain, typically.
Since lower frequencies take more current to reproduce and woofers take more time for excursion to move air, the amp spends a lot more energy and time on bass frequencies. The amount of time it takes to move from V+ to V- (slew rate) is important because it needs to be fast enough to also reproduce high frequencies at this same time. The higher the gain to the speaker, the worse this is. All this stuff changes through the crossovers and throughout the cycle. This is why overpowering an amp tends to help, it gives more current to overcome some of these issues by brute force alone.
Amp: Ok speaker, go OUT now!
Speaker: Going out, sir!
Amp: Speaker, come back, NOW!
Speaker: But sir, I'm still trying to go out!
Amp: NOW I SAY, DAMN YOU, NOW!
Speaker: GODDAMN IT, I can't, my kinetic energy has me moving OUT!
AMP: Fuck it, more current! (AMP pulls back on the leash as hard as possible and stops the speaker from going out)
Speaker: AGGGH! You're tearing me apart! (cone flex and distortion ensue)
This is the reason for bi/tri-amping. To drive each driver individually and tailor each amplifier to the driver it powers. This is also part of the reason for the new batches of studio monitors all being self-powered with amps for each driver.
The solution would be to use a stereo amp with L driving the tweeter crossover and the R driving the woofer crossover.
If not, then you also run into issues with the amps driving crossover networks and the distortion that all this causes.
OR you can just rock what you have and not worry about it..
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Post by jimwilliams on Nov 19, 2014 10:13:12 GMT -6
Depends on the quality of the amp. Some sound blah, some are revealing. I use Adcoms here, 535, 545, and 555 models. Yes, they are modified. I've put them up against $5000 power amps, all have been bested by the Adcoms.
A GFA555 run bridged mono mode (there is a convienient switch for that) will give you 500 watts per amp. Run a higher powered amp and you get more of the class A operation at normal listening levels.
I run single speaker runs with Kimber speaker cable with 16 seperate teflon/copper wires. All of the speakers here are passive using rebuilt crossovers with the finest components. I use InfiniCap, MIT and some silver foil/paper in oil crossover caps. I use Mills wirewound resistors and Alpha copper foil inductors. These parts cost as much as my speakers in some cases, but made them world class.
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Post by Johnkenn on Dec 18, 2014 17:39:08 GMT -6
So, I don't really feel like there was a consensus on this. I'm trying to decide to bid on this second Lexicon (which is re-branded Bryston 3bst). Think I'd be wasting my money?
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ericn
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Post by ericn on Dec 18, 2014 20:37:57 GMT -6
Shortest answer I can give you, unless your clipping. Feel like your dynamics are limited and have 40 amps so that these amps can deliver everything they can its a waste!
As the current owner of a 4b adcom 555 and multiple crests!
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Post by Johnkenn on Dec 18, 2014 20:40:01 GMT -6
Thanks, ericn...that calmed my gas... |
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ericn
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Post by ericn on Dec 18, 2014 21:00:51 GMT -6
Thanks, ericn...that calmed my gas... No problem, been there, in fact I was looking at the same amps on ebay till sanity kicked in! Also last night over way to much Moët Bolivard and Spotted Cow, the Electrician who lives down the hall and I were talking about how much more a system will deliver if you have the current so that an amp can deliver its rated power, if you want a couple of DB extra headroom and are handy Romex, and breakers are cheap! |
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Post by jimwilliams on Dec 19, 2014 10:03:39 GMT -6
Doubling the amp wattage will only get you a 3 db increase in volume.
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Post by ppa on Dec 20, 2014 16:58:25 GMT -6
Adcom GFA555 is a good amp, it was designed by Nelson Pass.
I have seen the schematic of this amp, it has a very short signal path, only four transistors.
Using a short signal path it's possible to have a simple THD structure. Moreover the costs are reduced since the circuit is simplier, BTW having even the advantage to have the chance to increase the quality of components since the reduced number of them.
The circuit it is optimized with a mid level of NFB. It has not the low level of NFB as some famous
power amplifiers (as some by Krell, Rowland, YBA, Electrocompaniet, Densen etc), but the reduced signal path is a very good point for Adcom that makes amps at a fraction of the cost of several famous amps.
Personally I like Adcom amps. I have designed some amps with reduced signal path.
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ericn
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Post by ericn on Dec 20, 2014 17:28:33 GMT -6
Adcom GFA555 is a good amp, it was designed by Nelson Pass. I have seen the schematic of this amp, it has a very short signal path, only four transistors. Using a short signal path it's possible to have a simple THD structure. Moreover the costs are reduced since the circuit is simplier, BTW having even the advantage to have the chance to increase the quality of components since the reduced number of them. The circuit it is optimized with a mid level of NFB. It has not the low level of NFB as some famous power amplifiers (as some by Krell, Rowland, YBA, Electrocompaniet, Densen etc), but the reduced signal path is a very good point for Adcom that makes amps at a fraction of the cost of several famous amps. Personally I like Adcom amps. I have designed some amps with reduced signal path. Can't dissagree with any of what you said, but JK was more looking for info on if he should grab another Lexicon 212 , AKA bryston 3b ST , and what he would gain. |
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Post by Johnkenn on Dec 20, 2014 17:48:56 GMT -6
Well, now I'm wondering whether I should grab a GFA555  |
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Post by ppa on Dec 20, 2014 17:56:37 GMT -6
Can't dissagree with any of what you said, but JK was more looking for info on if he should grab another Lexicon 212 , AKA bryston 3b ST , and what he would gain. I know the schematic of this amp and I council it very much. edit: I know the bryston, if the Lexicon is the same it is a very good deal (IHMO) |
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Post by ppa on Dec 20, 2014 17:59:18 GMT -6
Well, now I'm wondering whether I should grab a GFA555 bryston 3b St is a very good amp with an innovative out stage, I council it much more than 555 |
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Post by Johnkenn on Dec 20, 2014 20:38:41 GMT -6
So you guys think the Lexicon is exactly the same? I mean, it says Bryston 3B ST on the back...but why would companies do that? Always wondered. Is it truly exactly the same you think?
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Post by tonycamphd on Dec 20, 2014 20:51:31 GMT -6
Well, now I'm wondering whether I should grab a GFA555 IMO with the williams mods, this amp is likely impossible to beat for under $5k |
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ericn
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Post by ericn on Dec 20, 2014 20:57:12 GMT -6
When Harmon bought Lexicon They already had HK, Proceed and Mark Levinson in the Home Theater Market.
Lexicon didn't have an amp to sell as a system, The Levinson Dealers didn't want to let Lexicon dealers have the Levinson, Proceed amps.
Bryston AmPs can be found as OEM for the guys who do all the IMAX theaters as well.
I have seen 3b ST and NT212 side by Side with the cover off same amp, the fact that the Lexicon Badaged version can be had for original 3B money means we should shut up before others catch on!
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Post by jimwilliams on Dec 21, 2014 12:13:06 GMT -6
Adcom power amps, like many other designs are simple power opamps. They use a differential input and single-ended outputs. Feedback is global and consists of a 22k ohm feedback resistor with a 1k ohm gain/shunt resistor. They have a fixed gain of 26 db. The gain/shunt resistor is AC coupled but the rest of the signal path is direct coupled.
Each stage is a tutorial on the very best topology available for a bipolar power amp design. Component selection on later versions is also top-notch with every transistor optimized for it's stage. I've used/heard/installed a lot of pro audio power amps, so far none beats those 3 Adcoms I use here, 535, 545 and the later 555 models without the 2SC2240 transistors. Good power amps are easy, the rest of your audio decisions will be a lot tougher.
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Post by Johnkenn on Dec 21, 2014 13:30:37 GMT -6
dandeurloo tell us about your custom amp. I thought mine sounded good, but yours definitely had more bottom and was smoother on top when you brought it over. I think I remember you saying it was about $2k? That kind've put it out of my realm right now, but hey, when the ship comes in. Also, tonycamphd can you direct me to another used Adcom? I think it's cheap enough to go ahead and at least buy and have modded...then pick whichever is better.
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Post by tonycamphd on Dec 21, 2014 15:27:42 GMT -6
dandeurloo tell us about your custom amp. I thought mine sounded good, but yours definitely had more bottom and was smoother on top when you brought it over. I think I remember you saying it was about $2k? That kind've put it out of my realm right now, but hey, when the ship comes in. Also, tonycamphd can you direct me to another used Adcom? I think it's cheap enough to go ahead and at least buy and have modded...then pick whichever is better. i just checked ebay, didn't find much, you should search locally as well, look for "adcom GFA555" not "GFA555 ll" There is a gfa 545 on ebay for about $150 about to end, Jim likes that one as well, the 555 as more power...which is unnecessary for small monitors imo, i believe the 545 is 80 watts per channel? www.ebay.com/itm/Adcom-GFA-545-power-amplifier-two-channel-/331415693863 |
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Post by Johnkenn on Dec 21, 2014 15:51:08 GMT -6
I'll keep a search out for GFA555...thanks! What mods are necessary?
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Post by Deleted on Dec 21, 2014 23:27:09 GMT -6
I happend to be part of an amp shootout for some good very linear hifi speakers last week between several high priced amps and an Adcom GFA545. The other amps started at pricing range of 3,500-5,000 Euros, Array Audio, Restek, Plinius and the Adcom.
I picked one of the Resteks (that happened to be a really excellent flagship model type of amp) to be the optimal match, but i swear the Adcom was no. 2 in my choice. Unmodded!
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