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post #61 of 1370 Old 12-04-2014, 08:29 PM
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Quote:
Originally Posted by notnyt View Post
FR from amps, especially on the high end, will change based on the impedance of the load.
Not by very much at all in AB/G/H but will in many D depending upon topology, switching frequency and output filter design. I'd be more concerned about distortion at HF as feedback reduces. Besides most of the interest around here is in the LF FR which isn't affected by load. The only way FR can be affected at HF is if the Zout increases to a decent proportion of the load Z.
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post #62 of 1370 Old 12-04-2014, 09:37 PM
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Quote:
Originally Posted by notnyt View Post
FR from amps, especially on the high end, will change based on the impedance of the load.
That reminds me of a freq response test I did on time I think on an older clone amp and I got this bizarre curve. Other amps came out flat up top but this one and another old 800W dinosaur had similar weird things going on up top. The green trace is with 1000ohm load and the purple is with 8ohms. I never noticed too much of a difference in low end response rolloff with difference loads.

Do they list the input impedance on your interface? I dig everything about my soundcard but they don't list it's impedance and I didn't think about it until I realized that everything I tested (with an in to out loop) on it had more rolloff down low than other interfaces and cards. Came to find out that it's input impedance is around 4.4k which is unusually low.

I contacted Lab Gruppen's technical department years back and they told me that they don't use DC blocking caps in their inputs or outputs. I couldn't get the guy to spill the beans on what part of the design is responsible for it's low end rolloff.
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post #63 of 1370 Old 12-04-2014, 09:41 PM - Thread Starter
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post #64 of 1370 Old 12-04-2014, 09:53 PM
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Quote:
Originally Posted by Shreds View Post
I contacted Lab Gruppen's technical department years back and they told me that they don't use DC blocking caps in their inputs or outputs.
In almost every pro amp I've seen the schematic of, or had on my bench to be worked on, there is a DC blocking cap between the input stage and the poweramp stage itself. It's typically for a very pragmatic reason: there's lots of gain in amplifiers, and any DC will be amplified the same amount. If any DC is applied to the input and amplified at the output and could potentially damage speakers or greatly offset the voice coil in the gap, increasing distortion. The amp manufacturer will typically get the blame for the damage.

LG may use a DC servo to keep output DC at/near zero, but that just moves the location of the cap. Servos also have long time constants so are slow to respond to a fault condition and will only have a range of a few volts as they're typically implemented by opamps.
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post #65 of 1370 Old 12-04-2014, 10:02 PM
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I contributed to the group that came up with the Common Amplifier Format. http://www.cafgroup.org/
I don't agree with the way the "Tone" test is defined. They are trying to make it a single number, when what you really want is a curve; power versus time. You need to see the short term power, the long term power and whether it transitions smoothly in between.

My rule of thumb for hold time of a tone burst is minimum 40ms (sounds like a drum beat), 4 seconds (movie special effect, dub step "the drop", etc) and 4ever (long term power until thermal).

Watch out for strong temperature coefficient in the resistance of the heater elements. Have fun

Brian
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post #66 of 1370 Old 12-04-2014, 10:45 PM - Thread Starter
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Originally Posted by SpeakerPower View Post
I contributed to the group that came up with the Common Amplifier Format. http://www.cafgroup.org/
I don't agree with the way the "Tone" test is defined. They are trying to make it a single number, when what you really want is a curve; power versus time. You need to see the short term power, the long term power and whether it transitions smoothly in between.

My rule of thumb for hold time of a tone burst is minimum 40ms (sounds like a drum beat), 4 seconds (movie special effect, dub step "the drop", etc) and 4ever (long term power until thermal).

Watch out for strong temperature coefficient in the resistance of the heater elements. Have fun

Brian
I plan on starting with the bursts for the peak numbers. I'll examine output over longer durations as well, my scope has a good deal of memory.

Those bursts at 20hz are 5.5 cycles. It'll last 275ms.

I plan on heating up the elements to see what it does to impedance.

Last edited by notnyt; 12-04-2014 at 10:57 PM.
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post #67 of 1370 Old 12-04-2014, 11:40 PM
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Here is a 5hz CEA-2010 burst:

It's about time the REW generator went to 1hz anyways... Make it so # 1
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post #68 of 1370 Old 12-04-2014, 11:42 PM
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I plan on heating up the elements to see what it does to impedance.
A lot of people use ice in the bucket for extra cooling, you should check it under those cold conditions too.
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post #69 of 1370 Old 12-04-2014, 11:46 PM - Thread Starter
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post #70 of 1370 Old 12-05-2014, 02:19 AM
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I was able to force REW to do 1hz but you have to manually adjust it and restart the app. Mega pain in bum, but works.



There are many 2.0hz left axis keys and 10hz generator keys in the reg you need to mod.
HKEY_CURRENT_USER\Software\JavaSoft\Prefs\room eq wizard\

Couldn't get the left axis keys to persist, obviously overridden in the default run-time variables of the app; but the generators work (sort-of).

REW is totally capable of supporting this feature, it just needs to be activated in the code.
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post #71 of 1370 Old 12-05-2014, 05:32 AM
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I agree with what Brian mentioned about power versus time. That is really the best way to gauge the amplifiers strength. It can be graphed so they can be compared visually and overlaid. I've never seen anyone do this at different frequency bandwidths. I bet things would be quite a bit different at 20Hz versus 1kHz for some amps. 

Quote:
Originally Posted by A9X-308 View Post
Not by very much at all in AB/G/H but will in many D depending upon topology, switching frequency and output filter design. I'd be more concerned about distortion at HF as feedback reduces. Besides most of the interest around here is in the LF FR which isn't affected by load. The only way FR can be affected at HF is if the Zout increases to a decent proportion of the load Z.
True it may only be relevant for switching amps but if the amps are being tested it would be good info to have. It is also true that most will be looking for bass amps but I see that some people are trying to use the newer lightweight switching amps for full bandwidth reproduction as well.
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post #72 of 1370 Old 12-05-2014, 12:16 PM - Thread Starter
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post #73 of 1370 Old 12-05-2014, 01:05 PM
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Locked in for later reading..
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post #74 of 1370 Old 12-05-2014, 01:36 PM
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Quote:
Originally Posted by A9X-308 View Post
In almost every pro amp I've seen the schematic of, or had on my bench to be worked on, there is a DC blocking cap between the input stage and the poweramp stage itself. It's typically for a very pragmatic reason: there's lots of gain in amplifiers, and any DC will be amplified the same amount.
I hear ya Mr. Koolaid, but I tend to believe the guy in technical support who had a tech review the schematic and then told me that there are no DC blocking caps. Here is a snippet from a Lab Gruppen FP series manual about the amplifier's DC protection. Doesn't sound like AC coupling or a servo to me. I don't know how they handle protecting the amp from DC but LG has some seriously bada$$ engineers designing their stuff so who knows, maybe it's proprietary. Like I said, I couldn't get any specific info out of them about it.
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post #75 of 1370 Old 12-05-2014, 02:19 PM
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DC blocking and DC protection are two different things. The first I have already explained. For the second, lets say a fault condition shorts an output device to the rail and applies the rail voltage to the output, then the DC protection acts and opens the connection to the speaker eg UPC1237.
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post #76 of 1370 Old 12-05-2014, 04:49 PM
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Since it doesn't have DC blocking caps, it relies on DC protection then I guess.
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post #77 of 1370 Old 12-08-2014, 12:17 AM - Thread Starter
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Great success...

http://www.hometheatershack.com/foru...ml#post1009969

Quote:
Originally Posted by JohnM
I'll set the lower limit to 1.0 Hz for the sine, square wave and CEA-2010 generators in the next beta. Bear in mind that below 10 Hz there can be significant roll-off in soundcard inputs and outputs.
Also, I forgot to order some banana plug terminals so I could jumper it out to 2 and 8 ohm loads.

I'll only be able to test with both channels running in a 4 ohm config currently. Maybe I should add some more heater coils to my order ... I think I will. This testing rig is getting pricey, but should be fun.

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post #78 of 1370 Old 12-08-2014, 03:38 AM - Thread Starter
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revision 1... going to change this around some and add more heating elements... should have the parts in Wednesday.

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post #79 of 1370 Old 12-08-2014, 04:41 AM
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Quote:
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I'll set the lower limit to 1.0 Hz for the sine, square wave and CEA-2010 generators in the next beta. Bear in mind that below 10 Hz there can be significant roll-off in soundcard inputs and outputs.
JohnM, take your time but hurry up.
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post #80 of 1370 Old 12-08-2014, 07:35 AM
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Quote:
Originally Posted by notnyt View Post
revision 1... going to change this around some and add more heating elements... should have the parts in Wednesday.
Not enough jiggowatts dissipation @ 2ohms x2 I assume?
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post #81 of 1370 Old 12-08-2014, 08:03 AM - Thread Starter
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Not enough jiggowatts dissipation @ 2ohms x2 I assume?
Each element is 12 ohms, no way to do 2ohms x 2 or 8ohms x 2, only 4 ohms x 2.
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post #82 of 1370 Old 12-08-2014, 08:13 AM
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Cool!

You are moving right along! At this pace you will be the amp testing king! Nice!

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post #83 of 1370 Old 12-08-2014, 08:14 AM
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Quote:
Originally Posted by Ricci View Post
I agree with what Brian mentioned about power versus time. That is really the best way to gauge the amplifiers strength.
+1
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post #84 of 1370 Old 12-08-2014, 09:30 AM
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I'm most interested is seeing what the amplifiers can maintain for 3-4 seconds continuously.

It's too bad you're so far away. I have a bunch of Crest CC2800/4000/5500 amps, speakerpower sp2-12k, pro lite 7.5, and the nu4-6000.
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post #85 of 1370 Old 12-08-2014, 09:32 AM - Thread Starter
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I'm most interested is seeing what the amplifiers can maintain for 3-4 seconds continuously.

It's too bad you're so far away. I have a bunch of Crest CC2800/4000/5500 amps, speakerpower sp2-12k, pro lite 7.5, and the nu4-6000.
If you want to ship em once I'm setup, I'll test em.

My scope has a good bit of memory, so I'll post full waveforms of the amplifiers power over time.
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post #86 of 1370 Old 12-08-2014, 10:45 AM
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The kind of input signal will greatly impact the output power over time. Settling on a few input signal types should lead to a few great discussions.

I will start... Does a square wave (and for how long) really represent well a maximum needed for LFE and music reproduction?

Does Don Keele's burst test work well to measure HT reproduction capability?
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post #87 of 1370 Old 12-08-2014, 01:11 PM
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Looking good Not.
If you can cram another 6 heater elements in that barrel or another barrel you can then wire for 2 ohm x 2 channels. Not sure how expensive that would be.

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The kind of input signal will greatly impact the output power over time. Settling on a few input signal types should lead to a few great discussions.

I will start... Does a square wave (and for how long) really represent well a maximum needed for LFE and music reproduction??
Personally I would say in no way, shape or form. Most people think their EDM, or dub, trance whatever music has a much more brutal crest factor than it actually does. Even in these forms of music there is a lot of breathing room for caps to recharge and heat to dissipate.

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Does Don Keele's burst test work well to measure HT reproduction capability?
I would say yes this is a good indicator of dynamic capability with a signal of useful duration.
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post #88 of 1370 Old 12-08-2014, 01:43 PM - Thread Starter
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Quote:
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Looking good Not.
If you can cram another 6 heater elements in that barrel or another barrel you can then wire for 2 ohm x 2 channels. Not sure how expensive that would be.



Personally I would say in no way, shape or form. Most people think their EDM, or dub, trance whatever music has a much more brutal crest factor than it actually does. Even in these forms of music there is a lot of breathing room for caps to recharge and heat to dissipate.



I would say yes this is a good indicator of dynamic capability with a signal of useful duration.
It was another $60, ordered already, they get here Wednesday. Going to go and get a new bucket top also.
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post #89 of 1370 Old 12-08-2014, 02:59 PM
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Make sure you get a label for the bucket, too.

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post #90 of 1370 Old 12-08-2014, 03:03 PM
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