Measuring Amplifiers - Page 34 - AVS Forum
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post #991 of 1917 Old 05-24-2008, 07:09 PM
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input sensitivity 1.16v(+3.5dBu)
1800w 4ohms bridged mono
Turn off the filters and clip limiters?

Yep input sensitivity is 1.16v but we have to remember that our AVRs are all .75v or less (probably -10dBu), long running arguements from people that dont "hear" any difference but its a simple fact that we can not get full Watts from connecting the two together unless we use some sort of line shifters (ie. Art Cleanbox), well we can tweak the sub LFE output, etc and get close on some AVRs.

Check the fliters and clip limiters so many times because like you I thought hmmmm...it has 1800Watts bridged into my sub!!!! I shouldnt be able to turn the gain up to high at all without blowing my TC2K!! I wish it worked better

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post #992 of 1917 Old 05-24-2008, 07:23 PM
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There hasn't been a piece of consumer audio gear designed to operate at -10dBV for 20+ years.

Jack Hidley
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post #993 of 1917 Old 05-24-2008, 08:07 PM
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I couldn't hear any difference on my mains at -30dB but at -20dB, wow, I had to check to see if I'd left a sub plugged in! Using an HK525 AVR (70wpc) and hooked up the 260wpc RMX 1850 just for the mains and now thumpin' bass and drums! I did turn up the LR levels up +4 though. Never sounded like that before at any volume.
Can't hear the amp. It's in an enclosed 24U cabinet.
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post #994 of 1917 Old 05-24-2008, 08:15 PM
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Quote:
Originally Posted by penngray View Post

Yep input sensitivity is 1.16v but we have to remember that our AVRs are all .75v or less (probably -10dBu), long running arguements from people that dont "hear" any difference but its a simple fact that we can not get full Watts from connecting the two together unless we use some sort of line shifters (ie. Art Cleanbox), well we can tweak the sub LFE output, etc and get close on some AVRs.

Check the fliters and clip limiters so many times because like you I thought hmmmm...it has 1800Watts bridged into my sub!!!! I shouldnt be able to turn the gain up to high at all without blowing my TC2K!! I wish it worked better


Hi pennyray and bob7145,

This is what I get from thy,

RMX2450 = class H
[low rail = 55v, high rail = 110v]

RMX1850 = class H
[low rail = 44v, high rail = 88v]

RMX1450 = class AB
[78v rails]

RMX850 = class AB
[67v rails]

It's all the same design, just the output stage
rail voltage are different and the RMX850 has
six output transistor per channel vs. eight outputs
for the others.

BTW, specs say 1.8kW bridged into 4 ohms, 1kHz. Its 1.1kW bridged into 8 ohms, 20Hz-20kHz.
http://www.qscaudio.com/products/amps/rmx/rmx.htm

I'm running my CDP -> DCX2496-> 1850HD -> TH-112 (think my CDP level is 2+V or so, its modded), with the DCX sub ch outputs +6dB. Coincidentally just last night I was trying to re-create the kick of an event I just heard briefly, no problem overloading my SPL meter @ 130C (0.5m though, trying to remove the effect of the room) in bridged mode. Never tried longer though, it scared the hell out of me!
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post #995 of 1917 Old 05-24-2008, 08:18 PM
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Quote:
Originally Posted by Bob7145 View Post

Can't hear the amp. It's in an enclosed 24U cabinet.

Still waiting for a chance to drop by my local electronics centre to get some 24V 0.1 or 0.2A branded fans like NMB or Nidec or Sanyo, hope I can get some quiet ones. The OEM chinese fans (mine's red sun or something can't remember ) are quiet loud.
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post #996 of 1917 Old 05-24-2008, 08:26 PM
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Yeah, I replaced the loud 120v (120mm x 38mm) fans in the top of the cabinet with computer 12v (120 x 25) ones thru a fan controller plugged into the switched AVR outlet. Still need 1 more laying on top of the AVR.
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post #997 of 1917 Old 05-24-2008, 11:47 PM
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Yep input sensitivity is 1.16v but we have to remember that our AVRs are all .75v or less (probably -10dBu),

Where do you get that nonsense? Have you measured the max voltage of a sub output lately? All the ones I've measured will do several volts.

Dennis H
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post #998 of 1917 Old 05-25-2008, 12:01 AM
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''Yep input sensitivity is 1.16v but we have to remember that our AVRs are all .75v or less (probably -10dBu), long running arguements from people that dont "hear" any difference but its a simple fact that we can not get full Watts from connecting the two together unless we use some sort of line shifters"

It wasn't a fact the first time you said it and it still isn't.

It's true *sometimes* but not always.

Noah
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post #999 of 1917 Old 05-25-2008, 05:02 AM
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Quote:


Where do you get that nonsense? Have you measured the max voltage of a sub output lately? All the ones I've measured will do several volts.


I think that is a different discussion all together, have you measured the voltage sensitivity out of AVRs?


Quote:


It wasn't a fact the first time you said it and it still isn't.

It's true *sometimes* but not always.

So all those line shifter devices that have a -10 dBu connection and a +4 dBu connection are just myths?

I dont admit to be 100% accurate on those exact numbers but I do know that pro audio equipment and AVRs like Pioneers and Yahama have voltage sensitivity issues and I do know there are hundreds of threads talking aout and dealing with this issue. Okay, NOT ALL AVRs will have a noticeable problem, everyone happier?

Someone asked about the QSC1850 above and Im just saying in my home tests it doesnt even come close to rated power (compared to true comercial sub amps) unless I add a Art Cleanbox or similar device but those devices have subsonic filters and they amplify distortion (same goes for my EP2500). So to me the fact is in the evidence. Since that happened a couple years ago, I researched and found out that there is a voltage difference and sometimes people need to add a "line shifter".

I guess its pointless to debate it here, I guess those that have a issue dont need to come here for answers because its all a big myth and there is no connection problems whatsoever between AVRs and Pro amps because you guys said so.

I guess Thomas W instead of arguing that we are just crazy and the voltage issue is simply a myth, he points people to the help section to try and help them with their problem.

Quote:



Gotta match?

Occasionally people run into a situation where they have a pro-sound power amp requires a higher input drive level than that supplied by the output of their pre/pro or the BFD.

If you have the subwoofer output level turned all the way up, and the output from your sub is too low, you need to diagnose the problem. Start by looking at the input sensitivity spec for the power amp and the output voltage for the receiver of pre-pro. If there's a big difference between these two numbers you may need.....

Hey, atleast we are posting about it and for that one or two people that end up having the problem they will know what it is and not need to worry about being called crazy, there is good in every debate

It is not "open-minded" to reject knowledge - Bob Lee
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post #1000 of 1917 Old 05-25-2008, 05:13 AM
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Quote:
Originally Posted by TheEAR View Post

A little quick update on my crude testing of the XTi2000 and 4000 with TC Sounds TC3000 and LMS-Ultra(both in sealed 3cu ft cabinets).

Today I really pushed both amps driving these very capable sub drivers to the point clipping lights flashed!

The XTi2000 was driving one TC3000 15(one channel in use,no bridge),it gor seriously loud and the driver's cone was moving some serious air,the clipping lights came only on passages where bass in the 20-30HJz was making the cone move what was like 1.5-2inches of excursion! The amp was on a 30A line,not lack of current here.Keep in mind one channel was driven.

With the XTi4000 the clipping light never lit or flashed,it was very loud...again the driver's cone doing serious pumping. When it was time to let the LMS-Ultra work,I made the clip light flash faintly again when the cone was what looked like ~2-2.5inches of excursion.

For what these amps will be used,I will not even push them half as hard. So they pass my primitive test.


Your "crude testing" indicates that the pure sine wave testing method used in this thread is probably turning on current limiting of the switch mode power supply in the test amplifier, or the test unit is simply a bad unit.
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post #1001 of 1917 Old 05-25-2008, 06:22 AM
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Quote:


Your "crude testing" indicates that the pure sine wave testing method used in this thread is probably turning on current limiting of the switch mode power supply in the test amplifier, or the test unit is simply a bad unit.

Well, we haven't seen an XTi2K or 4K tested on the bench yet, right?
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post #1002 of 1917 Old 05-25-2008, 12:28 PM
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As far as levels go, I've never had a receiver that the Left was the same level as the Right. Usually one was slightly hotter and a +1 would even them out (if it was adjustable without going inside).
I got lucky and my combo works well, no hum with unbalanced rca to 1/4" (the pro amp is the only device with a ground on the power cable), extra power only obvious above -30dB, I like the dip switch filters (using 30hz + clip), But yeah I enjoy listening to 2 channel without subs again! In the winter I can turn on every amp but summertime the subs are unplugged unless it's important.
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post #1003 of 1917 Old 05-25-2008, 12:28 PM
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Another update worthy of a certified lab.

...

Today I let the XTi2000 and XTi4000 pound out the bass,both test tones and some Whack a Ton music used to demonstrate high SPL 150dB + car systems.


I will not attempt this again,my ears pulsate. The XTi2000 has enough juice in the trunk.XTi2000/4000 users should not worry too much about any lack of power.


Here for all the refined pseudo fragile audiophiles with low wattage tube amps I dedicate this track.Remember if you do not feel dizzy it is not loud enough.No deep bass just very high levers ~35-50Hz. http://www.imeem.com/people/jXjEgY/m...reet_beatsmp3/


Hmm only four 15's were used,and I have more bass I will ever use! Now time to continue the build...

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
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post #1004 of 1917 Old 05-26-2008, 11:13 AM
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Quote:
Originally Posted by penngray View Post

I think that is a different discussion all together, have you measured the voltage sensitivity out of AVRs?

If you mean the voltage of the sub output of an AVR, that's what I was talking about. All the ones I've measured put out several volts before they clip. There may be some AVRs without enough voltage to drive a pro amp but I haven't seen any personally.

Usually, in the threads, people having trouble driving pro amps are doing something like not turning the gain control all the way up on the amp because of confusing instructions in the AVR's manual. Turn it up all the way and the sensitivity of most pro amps isn't much different from most consumer amps.

The THX gain spec for power amps is 28dB (25v out for 1v in) while the QSC PLX series has a gain of 32dB (40v out for 1v in with the knob all the way up). You'd actually need more voltage from the AVR to get the same power from a THX-spec amp like an Outlaw as from the QSC pro amp.

Edit: okay I looked up some input sensitivities in the manuals to put the pro/consumer thing in perspective.

Outlaw 7900, 300 W at 8 ohms, 1.95 Volts for Full Rated Output
QSC PLX1602, 300 W at 8 ohms, 1.2 Volts for Full Rated Output
QSC PLX3402, 700 W at 8 ohms, 1.9 Volts for Full Rated Output

Dennis H
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post #1005 of 1917 Old 05-26-2008, 02:35 PM
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Dennis has gotta be right. I only have a Panasonic XR55 digital receiver, but with my gain control on full (or zero attenuation I suppose) I only need my LFE output to be set at 5 or 6 on a 0-20 scale.
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post #1006 of 1917 Old 06-01-2008, 11:10 AM - Thread Starter
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Here is a Velodyne SC-1250 subwoofer amplifier. penngray has kindly sent this amp to me for testing. there is a previous review of this amp from here: http://www.hometheaterhifi.com/volum...06-part-3.html.

Exterior view:


Interior view:


Continued
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post #1007 of 1917 Old 06-01-2008, 11:14 AM - Thread Starter
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Here are the measurements. I have only published at 50 Hz because it has essentially the same readings at any other useable frequency.



And here is a shot of the 96Khz oscillation that exists in this amplifier at all times.


Doesn't seem to hurt anything and it is noted in the other review, but it still seems very high. I knocked it down by 25 dB with a 30 Khz filter.

Chuck
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post #1008 of 1917 Old 06-01-2008, 11:26 AM
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finally, something that actually makes close to rated power.

Regards,
Dan
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post #1009 of 1917 Old 06-01-2008, 11:56 AM
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Thanks Chuck for the test!

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post #1010 of 1917 Old 06-01-2008, 12:39 PM
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I am quite surprised to see a toroidal transformer in there. I had the plate amp in my HGS-10 replaced from 2002 to 2007 design, it does NOT have this...

Both appear to have the same laminated transformer for the DSP (circuit on the right), which in the case of the HGS this is supplanted by an analog Servo/Crossover module.

I recognize the amp module, the metal box and caps, which looks 100% the same BTW.

I wonder how this extra toroid effects the output rating?

Any idea what percentage of the 5.79 THD is the 96khz?

I won't even ask about 2ohm
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post #1011 of 1917 Old 06-01-2008, 12:45 PM
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Quote:


I won't even ask about 2ohm

The SC-1250 will not do 2 ohms!! Its says so on the website, in the manual, etc.

Its actually the amp used with the SC class of passive subs from velodyne. Each SC sub is 8 ohms so you can wire one sub @ 8 ohms or wire two subs into it @ 4 ohms. That is what its designed for but I use two with my DIY subs (dont wire 2 4 ohm subs into it though!!!).

I like them because they have RCA connections with no voltage issues on my system (Please no more discussion), They look like they belong in a home theater room, they are silent, They have EQ and crossover functionality and they have a remote!!!!

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Velodyne uses Class D line switching amplifiers in powered systems. Line switching means that there is no power supply transformer, so no isolation from the AC line to the electronics inside the box. In a powered subwoofer, all of the electronics are inside the enclosure. The driver frame can be made of a nonconductive material and/or covered by wood. The bottom line is a number of steps can be taken to ensure that if there is a short in the amplifier, the user can never touch anything on the subwoofer that may have a dangerous voltage present on it. There is no way to get UL or CE safety approval with a line switching amplifier.

Since the amp that Chuck just tested is not embedded in a powered system, it uses a power supply transformer to ensure that the user can't be shocked if there is a fault in the amplifier.

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post #1013 of 1917 Old 06-01-2008, 08:06 PM
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Yes, a true sub amp only, with a 1000 watts and a room Eq for a $1000.00 bucks. THD, noise floor, and steep roll off under 20Hz is probably acceptable for most of us.
Penngray, how well did the room eq work for you? Do you feel the FR is reasonably flat 20Hz to 100Hz?
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post #1014 of 1917 Old 06-01-2008, 08:21 PM
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Quote:


steep roll off under 20Hz is probably acceptable for most of us.

Why do you say that, it does not have a hard SFF

Quote:


Penngray, how well did the room eq work for you? Do you feel the FR is reasonably flat 20Hz to 100Hz?

I actually havent used the Eq on it yet because its all Auto, plug in the mic and press EQ, no way to tweak it, Sadly there is also no way to know what was set.

I guess I will once my room treatments are done.

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post #1015 of 1917 Old 06-01-2008, 09:01 PM
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I contacted Velodyne directly, let see what their support has to say about the toroidal transformer...

I just re-read the manual it doesn't say anything about an infrasonic filter starting point and oct/slope. I am fairly sure based on the DD series that it has one and is fixed to either 20 or 15hz... just not sure which.

Do not confuse the EQ in the SC-1250 with the SMS-1, there is no on-screen display.
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post #1016 of 1917 Old 06-01-2008, 09:10 PM
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[quote=penngray;13993018]Why do you say that, it does not have a hard SFF

Chucks Frequency response chart shows it down 4db at 15HZ and down 25db at 10Hz.
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post #1017 of 1917 Old 06-02-2008, 05:22 AM
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[quote=LINEARX;13993248]
Quote:
Originally Posted by penngray View Post

Why do you say that, it does not have a hard SFF

Chucks Frequency response chart shows it down 4db at 15HZ and down 25db at 10Hz.


Chuck's test is kind of invalid. The subsonic filter changes along with each preset.


"Each preset has its own characteristics with respect to subsonic filter, volume differential and a single equalizer (EQ) in order to optimize the listening mode for the preset."




Also, the subsonic filter and other things change along with selection of the specific matching subwoofer model that is set in memory. The SC-10 is the default subwoofer setting (rated at 24 Hz low end). It looks like the amplifier limits power / frequencies based on the subwoofer drivers capabilities.


"Your SC-1250 can control a variety of Velodyne SubContractor Series subwoofers as well as generic passive subwoofers. Special internal software settings are designed to maximize performance and reliability depending on the model of subwoofer being controlled, so it is important to match the SC-1250 amplifier with the subwoofer(s) it is controlling. The SC-1250 comes with a default setting for the SC-10 subwoofer. When the unit is first powered up, the model being controlled is displayed for 2 seconds on the numeric LED before the display reverts to the volume setting. The subwoofer to be controlled is shown as follows:

** - The generic subwoofer setting is for passive subwoofers not on the above list. CAUTION: there is no anticlipping or anti-distortion protection on this setting."
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post #1018 of 1917 Old 06-02-2008, 05:42 AM
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Quote:
Originally Posted by penngray View Post

The SC-1250 will not do 2 ohms!! Its says so on the website, in the manual, etc.

Its actually the amp used with the SC class of passive subs from velodyne. Each SC sub is 8 ohms so you can wire one sub @ 8 ohms or wire two subs into it @ 4 ohms. That is what its designed for but I use two with my DIY subs (dont wire 2 4 ohm subs into it though!!!).


What do you use for settings for your DIY subs? Default? Generic subwoofer?

You should do a True RTA sweep of the amplifier to see what the electrical FR looks like (AKA value/rolloff of the subsonic filter).
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post #1019 of 1917 Old 06-02-2008, 06:11 AM
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Quote:


Chucks Frequency response chart shows it down 4db at 15HZ and down 25db at 10Hz.

Quote:


Also, the subsonic filter and other things change along with selection of the specific matching subwoofer model that is set in memory. The SC-10 is the default subwoofer setting (rated at 24 Hz low end). It looks like the amplifier limits power / frequencies based on the subwoofer drivers capabilities.


"Your SC-1250 can control a variety of Velodyne SubContractor Series subwoofers as well as generic passive subwoofers. Special internal software settings are designed to maximize performance and reliability depending on the model of subwoofer being controlled, so it is important to match the SC-1250 amplifier with the subwoofer(s) it is controlling. The SC-1250 comes with a default setting for the SC-10 subwoofer. When the unit is first powered up, the model being controlled is displayed for 2 seconds on the numeric LED before the display reverts to the volume setting. The subwoofer to be controlled is shown as follows:

** - The generic subwoofer setting is for passive subwoofers not on the above list. CAUTION: there is no anticlipping or anti-distortion protection on this setting."

Hmmmm....I thought for sure I set the amp to GS (Generic Sub) before sending it too Chuck.

I didnt see Chucks Frequency response chart, was it posted?

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post #1020 of 1917 Old 06-02-2008, 06:14 AM
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Here is my current FR plot of my one DIY sub....


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