sfogg
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Posts posted by sfogg
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"I use MetCal stations on my bench at work and they are amazing...dunno how much they run for though."
I haven't touched my Weller since I bought my Metcal. I bought a MX500 used on ebay for about $200 and then acquired a bunch of different tips for it as needed.
For those that don't know Metcals big claim to fame is how fast their tips transfer heat. That means the joint is to temperature much quicker and you put less overall heat into the components being soldered. You can also use less temperature in the tip itself as you also don't get the temp. drop when you apply it to the components.
From cold on with any standard tip you can literally be soldering in about 5 seconds from turn on. I've held the ground rings for chassis mount RCA jacks in my fingers while soldering a string of them together with perfect solder joints and the rest of the ring hasn't even gotten warm in my fingers.
Just fantastic tools. I couldn't do the work I've been doing lately without one.
Shawn
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"As soon as you turn a screw, everything wants to rotate around that screw's axis. "
Yes, that is exactly what they do on the 902. When I did mine I left them fairly snug and then lightly tapped them into position around the body of the diaphragm. That way when tightened them down they didn't really move.
The 288s have adjustable locating pins that are seperate from the hold down screws which seems to prevent this. You use a paper spacer under the diaphragm to center it, lock in the locating pins then remove the diaphragm to take out the spacer and reinstall then tighten down the diaphragm hold in screws. Works well but isn't on the 902s.
Shawn
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" but because they were intended to be a two-way driver and go out to 20K,... the upper mids from this driver in a three-way configuration to my ear, are hard to beat at any reasonable price point ........."
If one is going to use them three way take advantage of the 902s bandwidth and push that crossover point up a bit to make life really easy for the tweeter. I always used the 902s two way but with the 288s I crossed them to 2404s at 8kHz. The 2404s sound better crossed up there.
Shawn
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"On the other hand, it wouldn't take much movement to mis-align. You never can tell with some of these shippers."
That
is very true. Also after aligning the diaphragm tightening it down can
change its position slightly too. They certainly do buzz when
misaligned with a VC rub, been there.It would be very interesting for someone that had buzzing at 500hz to try re-aligning the diaphragm to see if that helps or not.
Shawn -
"So I would expect Bill's process to be consistent with that. I'm even more puzzled."
Perhaps they got dropped in shipping and the alignment got thrown off? If you still have the 902s it might be worth testing alignment to see if that is the issue with yours. I know when I took the loading caps out of mine if I didn't align the diaphragm right it certainly buzzed from VC rub. Easy to fix that though.
"Yes
the phenolics are in good condition, at least they appear to be - visually they look good, and the voice coils measure fine."The only way to really tell their condition is to acoustically measure them. In some 288s I bought the diaphragm looked fine and they measured fine on the multimeter. They sounded horrible and had something like half the bandwidth they should have had. New diaphragms fixed that right up. I posted measurements of this on the forum a few years back. Can not see work hardening and the multimeter just shows that the VC isn't open.
Shawn
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"I remember reading Shawn's comments to Al, saying he crossed them at
500 1st order, played loudly with no problem, and Al replying that that might damage the drivers, and at the least, would not sound good."Actually
I crossed them at 400hz first order with Al's Universal Network. No
problems at all, sounded fine down there. That was with the lightweight
A type diaphragms in them without the loading caps.Altec rated them for 500hz crossovers running every day for 12+ hours a day in theater use.
Shawn -
Altec's test for diaphragm alignment on a 902 was 500hz tone played back at high volume to measure distortion and listen for buzzing.
Shawn
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"Make sure you get a Weller product, they are the best."
At least until you try something better.
Shawn
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"Average level is about 85dB at the listening position. Still THX reference level playback, just can't hit the peaks."
BTW, should point out that average level is based on movie playback where movies are mixed to be played back at reference level and mixed to preserve dynamic range. On any overly compressed music of today where louder=better the average playback level would be much higher but still limited by that 105dB maximum due to 0dBFS.
Shawn -
"There will be some receivers that no matter what they are connected to
will not produce the calibrated level 105dB reference level you insist
upon."It takes between about 3 to 10w or so to do this on a K'Horn in a home. How many receivers do you know of that can't put out that much power?
And I already stated that this isn't taking into account running out of power or power compression in the speaker itself. Even if the combo can't hit the peaks the average playback level will still be proper at THX Reference Level. Average level is about 85dB at the listening position. Still THX reference level playback, just can't hit the peaks.
"Hence, are you arguing that those receiver's manufacturers are being
deliberately deceptive; or willing to admit that 0dB on the receiver is
an entirely arbitrary point on a scale which is selected by the
manufacturer?"Neither.
There is nothing deceptive about that scale and it is also not entirely arbitrary. You do realize of course the speaker level trim is in essense a second individual volume control for each channel in the receiver don't you? Most have at least 20-30dB of range relative to the master volume control (the 0dB on the scale). The process of calibrating the receiver is using those speaker trims to dial in the levels properly which makes the master volume control calibrated and anything but arbitrary.
Shawn -
115w 0dB
11.5w -10dB
1.15w -20dB
.115w -30dB
.0115w -40dB
.00575w -43dB
Shawn
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Roughly
3dB increase is 2x the power
10dB increase is 10x the power
Likewise 3dB decrease is 1/2 power
10dB decrease is 1/10 the power
Shawn
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"so any of these dB markings can not tell you a thing about how much
power the amp is putting out. It's not even relative. You can't say,
"the output is 20dB less than full power" because the input voltage has
no reference. So, the usefullness of putting a dB scale around the ring
of a volume control is pretty much limited to the "pizazz" factor, and
not much else. "Mark,
Shawn
If the dB markings are accurate (and they very well may not be on a
unit with a pot in it) those markings are still relative. If you turn
the volume from -20dB to -30dB you have decreased the average and peak
SPLs by 10dB. Likewise you also know the amp is putting out 1/10 the
power then it was before. What it does not tell you is an absolute
number for how loud the peaks could be or absolute metric for power
output. -
"that showed the approximate output at each detent level for the
nominal "test" load. Pre-out and main-in sensitivity is 700mV at
100k-ohms; nominal input into the pre is 130mV. Power RMS is rated 110
wpc, but I just had one of the 11000's rebuilt. According to the tech,
Warren Bendler (www.sansui.us), the amp tested out at 115 wpc + 0.05 watts into an 8 ohm load at 1khz (which is apparently the factory method of testing on the bench).Knowing
that... and not using any controls except the volume control, how do
you calculate the power that it would be producing for each detent?"You
Shawn
can't really tell this easily since it will depend upon what the input
voltage is and of course different analog sources may output differing
voltage levels. That is what is nice about digital inputs into
receivers/pre-pros... that max they can put out is the same for all
sources(0dBfs). It isn't as neat and clean in the analog domain. -
"if a receiver is not 'THX certified' then the
calibrated 0dB = 'THX Reference Level' argument falls to pieces "Not
in the least. If one calibrates the unit as I said above it makes no
difference if the receiver is THX certified or not. It will still be
calibrated such that 0dB on the volume control is THX Reference level.One
can calibrate *anything* to THX reference level, even a basic 2 channel
pre-amp. Simply play the -30dB channel balance noise and turn up the
volume until you measure 75 dB at the listening position. Mark that
position on the volume knob, that is THX Reference level. What you
loose doing this is the nice reference to how many dBs above or below
you are from reference level."unless
you're further arguing that regardless of the certification or not, all
receiver manufacturers are intending that 0dB on the display is to be
'THX reference Level'. "It
Shawn
is a reference, if one calibrates as stated above it results in THX
reference level. Before THX certification just about no receiver had volume
controls that became less negative as you turned up the volume. After THX
certification popularized the idea of reference level within a few years pretty much all of them did. -
"The decibel is simply a ratio, and on its own without a reference is meaningless."
That is why the system needs to be calibrated properly. That gives a reference to the 0dB settings on the receiver/pre-pro.
Shawn
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"Don't different receivers/amps produce different wattages of power? Therefore, at 0dB, different receivers/amps put out different amounts of power and that would mean they would produce different sound levels of loudness. As a result, I believe it would be hard to judge what 0dB really means considering the different receivers/amps out there. Am I right?"
No, not once the system is calibrated as I outlined above. When you calibrate the system it doesn't matter how much power you have, how efficient your speakers are, how big your room is or how far away from your speakers you sit. They will all play at the same level if calibrated properly, that is the whole point of calibrating your system.
Take a speaker 'A' that is 95dB/w/m and speaker 'B' that is 115dB/w/m. To make the math simple say we loose 10dB at the listening position from whatever the speaker is producing.
You set the volume to 0dB on the master volume control (or your receiver does this automatically when you go into the calibration section). Its built in test tones are typically -30dB. With a SPL meter you adjust each speakers output levels such that you read 75dB on the meter at the listening position.
Now you play a movie and have the volume at 0dB again. At the maximum possible output level (0dBFS) each speaker will produce 105dB at the listening position (115 at the speaker minus 10dB for distance). Speaker A is using 100w to do this, speaker B needs 1 w. The speaker trims calibrated for the differences in efficiency.
This is no different at all then having a surround system that has speakers of differing efficiencies, differing distances to the listeners and quite possibly differing amounts of power to the different speakers. Once you calibrate the speaker levels they all play at the same volume level no matter where you set the volume control.
And if you calibrated your system properly you will always know what the maximum possible SPL is per speaker at the listening position. That is what your volume control is telling you. 0dB on the volume control means Reference Level (THX came up with this, that is why it is THX Reference Level). Reference Level is 105dB per main speaker at the listening position, LFE can be 115dB. If you set your volume control to -10dB that means the maximum possible level is 10dB below reference level. So each main speaker could hit a peak of 95dB and the LFE could be 105. -20dB on the volume control means max peaks of 85dB and the LFE could be at 95dB.
Shawn
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"Who said anything about THX?"
The original poster, that is what Reference Level refers to.
Shawn
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"Absolutely not."
That is why it needs to be
calibrated. The way you calibrate it is to set the volume to 0dB and
then play a -30db or -20dB channel balance test noise and use the speaker
level controls. If you play a -30db tone you set all speakers to 75dB
at the listening position. If it is a -20dB tone you set all speakers
to 85dB at the listening position.That calibrates the
system so that the max output level per speaker at the listening
position is 105dB when the volume control is at 0dB on the
receiver/pre-pro.That is THX Reference Level.
Shawn -
Only if your system is calibrated properly.
Shawn
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Pulse code modulation.
Shawn
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"Remember, it all starts as analog and it all comes out as analog............. anything less is not true to the source!"
The problem with thinking like that is that analog is of course also an analog of the original.
Shawn
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You probably have a crossover setup in your pre-amp (L/R set to small) and that is being bypassed in direct mode.
Shawn
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"Did you get some K510's this year : )? "
Nope, I have had them for 2 years now. Time flies....
http://forums.klipsch.com/forums/p/84288/846295.aspx#846295
Shawn
altec 902-8t on khorn
in Technical/Restorations
Posted
Here is a 902 on a 511B...