Amplifier Topology Question

allvinyl

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I have been investigating a issue I believe boils down to current delivery to my Viola Symphony amp. The class A/B VS can draw up to 1800 watts and I am concerned that the current power configuration for my system is choking current delivery to the amp. Hence, I am worried about clipping and damage to the drivers of my new GTA3R speakers. It has been suggested that other amplifiers (Pass class A) draw a consistent known number of watts thus avoiding current delivery issues.

Any comments and insights are appreciated.
 
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DonH50

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Class A means all the current all the time (and a lot more power wasted as heat). If you have power delivery problems with a class AB amplifier it will be on program peaks; with a class A amp, it will be a problem all of the time. The current draw is more consistent for a pure class A amplifier but that is not generally a reason to buy one.

The GTA3R is rated at 92 dB/W/m so with 400 W (into 4 ohms) from your amp that means about 111 dB at your ears from a pair 10' away in a completely dead room (*). That is very loud. I strongly suspect you are not clipping your amplifier unles you are much farther away and/or listening at dangerously loud levels.

IME/IMO/FWIWFM/etc. - Don


(*) See e.g. http://myhometheater.homestead.com/splcalculator.html
 

Folsom

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What is your power configuration?

Do you have an impedance graph for the GT speakers? That's a big question. Viola doesn't mention 2ohm stability, and planars from some other companies have been very cruel to amplifiers.

If the impedance drops too much you could be having all sorts of issues. But none of them are current per se. You can't stop current, that's a myth. What happens is voltage drops for some reason. Sometimes because so much current is used that the power supply capacitors have nothing left to give. There's also saturation.

What are the symptoms you have? Let's start there, not at an incorrect guess.


BTW class A run high bias with a constant current source configuration. That means that the power supply is using the same amount of current all the time. It produces A LOT of heat. Because you may have to spend 10w to get 1w, or even 30w to get 1w... they're not very efficient and for the given power are substantially more power hungry than your AB for the same wattage. But they do sound different, and the sound can be good.
 

microstrip

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Class A means all the current all the time (and a lot more power wasted as heat). If you have power delivery problems with a class AB amplifier it will be on program peaks; with a class A amp, it will be a problem all of the time. The current draw is more consistent for a pure class A amplifier but that is not generally a reason to buy one.

The GTA3R is rated at 92 dB/W/m so with 400 W (into 4 ohms) from your amp that means about 111 dB at your ears from a pair 10' away in a completely dead room (*). That is very loud. I strongly suspect you are not clipping your amplifier unles you are much farther away and/or listening at dangerously loud levels.

IME/IMO/FWIWFM/etc. - Don


(*) See e.g. http://myhometheater.homestead.com/splcalculator.html

Don,

Planar speakers ratings for efficiency should be taken with great care - the usual definitions apply to point like speakers in anechoic conditions. And IMHO this calculator should not be used with planar speakers that scale sound level versus distance very differently from point like common box speakers.
 

allvinyl

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Don, Folsom, Microstrip - I appreciate all of your insights and thoughts.

The symptom I noted was perceived clipping about 93 - 95 db when spinning vinyl. The room is essentially 18' x 36 x 7'2" with the speakers about 11.5' from the back wall and the listening position about the same distance from the speakers. I don't think I've ever had the new speakers over 100db. I keep the Rad Shack meter close and check frequently.

I don't have an impedance graph for the GT speakers but I believe Greg would address a request. I've had no success with Viola answering questions I asked about current delivery. Nor have I asked them about stability at 2ohms.

System component and power configuration: TT motor controller, Roadrunner TT strobe, Coincident line stage, Lino C phono (which runs off the internal battery once a signal is detected), Marantz tuner, Vitus CD, 2 Rhythmik subwoofer amps, Viola Symphony. Everything but one of the Rhythmik subwoofer amps is plugged into a Shunyata Hydra A/V and Typhon combo with the Hydra then plugged into a 30 amp circuit. The other subwoofer amp is on a different 20 amp circuit mostly by itself. My first thought to relieve the situation was to move the Symphony to the 20 amp circuit and put the subwoofer amp now on that circuit on the 30 amp circuit with the rest of the components.

I also received the suggestion of pulling a dedicated 240 line back to the same area behind the 2 racks and I could then leave most of the system on the 30 amp circuit and perhaps move the Symphony and Coincident to the 240 circuit.
 

microstrip

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(...) I've had no success with Viola answering questions I asked about current delivery. Nor have I asked them about stability at 2ohms.

(...)

Looking at the specifications of the Viola Symphony (class AB) I would expect it to be able to deliver a significant amount of current and be stable at 2 ohm - in bridge mode the amplifier is specified to deliver 800W on 4 ohms - I would expect it to easily deliver 400W in 2 ohm.
 

Folsom

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It's more likely you don't have enough overhang on your stylus to spindle than it is you're running out of power. That or not enough gain can cause it from a phono stage. Sometimes the answer is simple.

Does the clipping sound harsh? Can you describe it?

Have you tried without the Shunyatas? (not a fan personally, they might saturate sometimes, which will give a flatness in sound)
 

DonH50

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Don,

Planar speakers ratings for efficiency should be taken with great care - the usual definitions apply to point like speakers in anechoic conditions. And IMHO this calculator should not be used with planar speakers that scale sound level versus distance very differently from point like common box speakers.

I have a vague familiarity with planar speakers after living with them a few decades. I usually quote anechoic as it is the worst case and my room is actually heavily damped. The calculator does include 3/6 dB boost based upon near a wall or in a corner. It is a rough guide and has more options and more info than some of the other online calculators. Like any calculator, for anything, GIGO applies.

For those who aren't following our banter, the main difference with planars is they radiate in a figure-eight pattern to the front and back whilst conventional speakers radiate more or less equally in every direction from the front. Planar speakers (over roughly the midbass region depending upon panel size) do not radiate much to the sides or to the top and bottom -- it is a wave straight ahead and straight behind. This is a plus or minus depending upon how they are set up and how much you like room reflections contributing to the ambience. The back wave, if not damped, increases room ambience but also leads to comb filter effects that can mess up the image. I usually damp the back wave unless they are in a big room well away from the back wall (for any planar be it planar dynamic, ESL, or ribbon).

Microstrip's point (feel free to correct me, like you need an invite ;) ) is that due to this radiation pattern, the sound from planar speakers does not fall off like a normal speaker, anechoic chamber or not. There is less loss with distance than with conventional speakers, more like ~3 dB instead of ~6 dB for every doubling in distance. a rough guide would be to use the "near a wall" approximation to model the effective SPL boost from the radiation pattern.

Nit-picking aside, what matters here is that the 400+ W from the amplifier should provide even more SPL than my rough (and roughly worst-case) estimate. I am not sure where the distortion is from but strongly suspect it is not the amplifier, more likely something upstream or in the speakers themselves. I remember troubleshooting distortion at a customer's house ages ago and it turned out to be coupling from speakers to TT/cartridge -- that was somewhat a pain to fix; we finally physically moved the TT to a null point in the room and used a different suspension system.

Swapping the wall power point might help tell you if the amp is being current-starved but I am inclined to doubt it. Remember a 3 dB reduction in SPL means 1/2 the power needed from the amplifier. Average listening levels for most folks only requires a few watts. The peaks can easily hit 100+ W, however; long-ago studies showed peak to average levels in music are around 17 dB, a power ratio of 50:1. Movies tend to be even higher.

FWIWFM - Don
 

allvinyl

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It's more likely you don't have enough overhang on your stylus to spindle than it is you're running out of power. That or not enough gain can cause it from a phono stage. Sometimes the answer is simple.

Does the clipping sound harsh? Can you describe it?

Have you tried without the Shunyatas? (not a fan personally, they might saturate sometimes, which will give a flatness in sound)
Folsom - yes, it manifested as a harshness, actually an extreme stridency. It was so noticeable because the GTs are characteristically so smooth and grain free the anomaly jumped out at me. Interestingly enough, I am going to try a different PC on the Viola as I recently had success swapping PCs on the subwoofer amps. Your observation of the Shunyatas is not an isolated observance.

Additionally, I just took the cover off the Lino and set the gain up. The manual suggests the appropriate setting is such that its volume matches or is very close in volume to that of other sources and I felt, based on that guidance, the next gain setting is justified. I will check that out tomorrow when I listen to vinyl again.
 

Folsom

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Looking forward to reports on the simple change of just a gain increase.

There's no doubt power cords sound different. I find a lot of cables can add harshness, but sometimes I also think people that lose hearing might enjoy it.
 

allvinyl

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Apr 10, 2013
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I have a vague familiarity with planar speakers after living with them a few decades. I usually quote anechoic as it is the worst case and my room is actually heavily damped. The calculator does include 3/6 dB boost based upon near a wall or in a corner. It is a rough guide and has more options and more info than some of the other online calculators. Like any calculator, for anything, GIGO applies.

For those who aren't following our banter, the main difference with planars is they radiate in a figure-eight pattern to the front and back whilst conventional speakers radiate more or less equally in every direction from the front. Planar speakers (over roughly the midbass region depending upon panel size) do not radiate much to the sides or to the top and bottom -- it is a wave straight ahead and straight behind. This is a plus or minus depending upon how they are set up and how much you like room reflections contributing to the ambience. The back wave, if not damped, increases room ambience but also leads to comb filter effects that can mess up the image. I usually damp the back wave unless they are in a big room well away from the back wall (for any planar be it planar dynamic, ESL, or ribbon).

Microstrip's point (feel free to correct me, like you need an invite ;) ) is that due to this radiation pattern, the sound from planar speakers does not fall off like a normal speaker, anechoic chamber or not. There is less loss with distance than with conventional speakers, more like ~3 dB instead of ~6 dB for every doubling in distance. a rough guide would be to use the "near a wall" approximation to model the effective SPL boost from the radiation pattern.

Nit-picking aside, what matters here is that the 400+ W from the amplifier should provide even more SPL than my rough (and roughly worst-case) estimate. I am not sure where the distortion is from but strongly suspect it is not the amplifier, more likely something upstream or in the speakers themselves. I remember troubleshooting distortion at a customer's house ages ago and it turned out to be coupling from speakers to TT/cartridge -- that was somewhat a pain to fix; we finally physically moved the TT to a null point in the room and used a different suspension system.

Swapping the wall power point might help tell you if the amp is being current-starved but I am inclined to doubt it. Remember a 3 dB reduction in SPL means 1/2 the power needed from the amplifier. Average listening levels for most folks only requires a few watts. The peaks can easily hit 100+ W, however; long-ago studies showed peak to average levels in music are around 17 dB, a power ratio of 50:1. Movies tend to be even higher.

FWIWFM - Don
Don - I was in the midst of typing my reply to Folsom when you posted this response. Swapping the PC on the Viola will let me test a couple of theories at once and also be the least expensive option. I can easily move the right channel subwoofer PC to the other circuit and put the Viola on the 20 amp circuit by itself. To accomplish this I'll be ordering a longer PC of the same provenance as those I'm now using on the subwoofer amps. They're working really well.

As I ran Acoustats from '79 to '09, I am intimately familiar with the effects of treating the back wave by fiddling with room treatments. It can make huge differences for the better if you can find the right balance.

Not to ignore Folsom's other suspect, the cartridge setup, I can say with a good degree of confidence with the Etna's setup done via SMARTractor for overhang, etc, and a microscope for SRA tracking exhibited no such anomalies through my previous speakers. To your point about the TT, I suppose it's possible the coupling of speakers to TT/arm/cart could be happening but it would be a first for this table. Testing this theory would be anything but convenient as it would mean having to move my main ESS rack. But, we do what we have to do. Right?

I'll let everyone know how tomorrow's listening goes. I won't be able to do the PC swap until next week hopefully before I leave for Axpona but that will depend on when the PC arrives.
 

Folsom

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I did say *if* the overhang isn't set right. For now I'd just increase the gain on the phono. Insufficient gain is a guarantee for bad, awful noises. And it's free to do.
 

DonH50

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It's possible your new speakers are exciting room issues not seen (heard) before and that is causing coupling not audible with your previous speakers. It's also possible a component in the electronics train is going bad. Lots of possibilities, hard to narrow down without "being there".

For a temporary trial, you could up a 10 AWG extension cord from Wal-Mart or some other "fine shopping establishment". I did that for one of my Rythmiks ages ago, never got around to replacing it, but I'm cheap and have ears of clay. I'm also no longer running my beloved Maggies, but my current speakers are almost as low in sensitivity, and overall a much worse load. They still sound pretty good (Revel Salon2's).
 

Folsom

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If it was room modes he'd need a room the size of a closet to excite modes in the frequency range that sounds harsh. Otherwise it'd be all bass and midbass, which sounds boomy/bloated, and over powers the stuff that can be hash.

It's not a question of current restriction from power cords unless they have a choke in them (Cardas makes one). The power conditioners can saturate though, which causes more of a flat sound, a dull sound. It's possible it could be the cable system that brings a hashness quality but that won't jump with volume. There's a pretty limited set of things that appear only with volume being cranked, and most all are on the electronic side. The one thing I'd say is a possible big exclusion, is speaker drivers that get screwed up and rub or something when playing too much excursion.
 

DonH50

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Only thing I have seen is when peaks excite the panels and cause distortion. You are right, though, that if room modes were an issue there would be plenty of pother symptoms.

I've been advised to bow out so I shall, don't really have anything else to add.
 

microstrip

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I have a vague familiarity with planar speakers after living with them a few decades. I usually quote anechoic as it is the worst case and my room is actually heavily damped. The calculator does include 3/6 dB boost based upon near a wall or in a corner. It is a rough guide and has more options and more info than some of the other online calculators. Like any calculator, for anything, GIGO applies.

For those who aren't following our banter, the main difference with planars is they radiate in a figure-eight pattern to the front and back whilst conventional speakers radiate more or less equally in every direction from the front. Planar speakers (over roughly the midbass region depending upon panel size) do not radiate much to the sides or to the top and bottom -- it is a wave straight ahead and straight behind. This is a plus or minus depending upon how they are set up and how much you like room reflections contributing to the ambience. The back wave, if not damped, increases room ambience but also leads to comb filter effects that can mess up the image. I usually damp the back wave unless they are in a big room well away from the back wall (for any planar be it planar dynamic, ESL, or ribbon).

Microstrip's point (feel free to correct me, like you need an invite ;) ) is that due to this radiation pattern, the sound from planar speakers does not fall off like a normal speaker, anechoic chamber or not. There is less loss with distance than with conventional speakers, more like ~3 dB instead of ~6 dB for every doubling in distance. a rough guide would be to use the "near a wall" approximation to model the effective SPL boost from the radiation pattern.

Nit-picking aside, what matters here is that the 400+ W from the amplifier should provide even more SPL than my rough (and roughly worst-case) estimate. I am not sure where the distortion is from but strongly suspect it is not the amplifier, more likely something upstream or in the speakers themselves. I remember troubleshooting distortion at a customer's house ages ago and it turned out to be coupling from speakers to TT/cartridge -- that was somewhat a pain to fix; we finally physically moved the TT to a null point in the room and used a different suspension system.

Swapping the wall power point might help tell you if the amp is being current-starved but I am inclined to doubt it. Remember a 3 dB reduction in SPL means 1/2 the power needed from the amplifier. Average listening levels for most folks only requires a few watts. The peaks can easily hit 100+ W, however; long-ago studies showed peak to average levels in music are around 17 dB, a power ratio of 50:1. Movies tend to be even higher.

FWIWFM - Don

Well, my main point was that we were making suppositions using a tool that IMHO is not adequate to this particular situation and will probably give users a wrong idea of their power needs, using non-reliable incomplete data about the situation. I also have long experience with several planar speakers and know how misleading are the efficiency specifications provided by planar manufacturers - they are not easily measurable. We debated this particular calculator in WBF long ago, and I still consider that although it is nice teaching/study tool it is useless for real life - and here I accept YMMV, as they say. As you referred 3dB means 1/2 power and 6dB 1/4 the power - what is the point of making estimations of power with an error of x4 or maybe x10?

Surely I agree with most of what you say in general - IMHO it only shows that we were mostly guessing and should move away from internet calculators. :)

BTW, one reason for the significantly different measurements on speaker efficiency published in different reviews is that although the value is quoted at dB/W at 1m its many times measured at a different distance and (inadequately) scaled according the rule of -6dB per doubling the distance.
 

allvinyl

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Only thing I have seen is when peaks excite the panels and cause distortion. You are right, though, that if room modes were an issue there would be plenty of pother symptoms.

I've been advised to bow out so I shall, don't really have anything else to add.
Nothing you've written or suggested has offended me. I welcome all contributions. Though I consider myself a long time audiophile and first a music lover, I am not an electrical engineer or anything close. I need subject matter expert advice.
 

Folsom

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Well, it's always possible the amplifier can't do it... But let's way for some more data like changing gain, or whatever he has planned.
 

allvinyl

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Apr 10, 2013
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Well, it's always possible the amplifier can't do it... But let's way for some more data like changing gain, or whatever he has planned.
Hi All,

Last few days have been really hectic hence the delayed report back.

I did change the gain inside the Lino C phono and it made a huge difference in the presentation. No strain now and I have plenty of gain on the volume pots of the Coincident. I'll be sending the Lino back to Channel D in the June timeframe for an update to the 2.0 version. Rob tells me that aside from changing the hardware to allow access to all the dip switches from outside the chassis (no more taking the cover off), the 2.0 Lino C has more gain. He tells me the 2.0's lowest gain setting will be equal to my 1.0 units middle gain setting. So likely an increase of about 6db which made all the difference when I changed my unit to the highest gain setting. This likely will translate to being able to use the middle setting on the 2.0 version.

I've not been able to swap the amplifiers on the 2 circuits yet but will get to that once I'm back from Axpona.
 

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