4311B woofer constantly "flapping"

[BMWCCA]

I should have mentioned earlier that I have no idea what make this amp is. It's certainly not a high-end one. I got it at a yard sale, saw that the 4 rectifier diodes were blown, replaced them, and it worked. Replaced the 2 x 2200uf power supply caps, and tried adding a third cap also. There's nothing else in the power supply, and everything else in the amp is stereo - and as I mentioned if I disconnect the preamps from the power amps with no result.

Do mean no "change in the result"?

Gee, I'm not real smart but maybe it's time to try another amplifier known to produce a clean output before you condemn your 4311Bs???

[nee]

Do mean no "change in the result"?

Yes, no change in the result.

Gee, I'm not real smart but maybe it's time to try another amplifier known to produce a clean output before you condemn your 4311Bs???

Oh yes - this is not my main amp at all, just one I picked up along the way. My original post was just a general throwing out of curious symptoms in case anyone had a cure. My 4311Bs are fine everywhere else.

[herki the cat]

Many years ago I had an amp that oscillated with my JBL D140Fs, I did put a 20 ohm resistor in parallel with the speaker and this did dampen the oscillation, but did not stop it. You could try a Zobel network!
http://www.trueaudio.com/st_zobel.htm
The cure is a different amp!

I agree with member jcrobso, after reading all the posts related to this amp, it is time take it to the Good Will Store.

herki

[nee]

I agree with member jcrobso, after reading all the posts related to this amp, it is time take it to the Good Will Store.

herki

But that's where I got it from!

[herki the cat]

[quote= jcrobso, pyonc, SMKSoundPro/Scotty, BMWCCA:dont-know, 15 others, & me]
The cure is a different amp! ,
It is time to take yours to the Good Will Store![/quote]

But that's where I got it from!

Well, at least you are having fun, new member, neeWelcome to our museum! & BTW, do you have a cat?...& Maybe a motorcycle?

herki

[jcrobso]

After all of this I'm curious what it looks like!

[SMKSoundPro]

I am too! Please post pics of the offending amp, and it's internals if possible. It may be a simple fix, or it just may be trash! Let us help you decide.

Scotty.

[herki the cat]

I am too! Please post pics of the offending amp, and it's internals if possible. It may be a simple fix, or it just may be trash! Let us help you decide.Scotty.

Me too! and while you are at it, please trace out a schematic so we can have look at the forward gain/phase shift topology in terms of the negative feed back stability margin which probably would benefit from the Zobel Net Work recommended by jcrobso. He has been around the block a few times, Scotty also.

herki

[nee]

Yep, certainly having fun!

I have a cat, but no motorcycle.

I started tracing out the schematic but then gave up after a confusing half an hour - the amp cost me nothing, I fixed it with 4 diodes, it sounds fine, I won't use it with the 4311Bs and if I do I'll plug the ports. I'll try and get a photo of the guts though.

[herki the cat]

Yep, certainly having fun!

I have a cat, but no motorcycle.I started tracing out the schematic but then gave up after a confusing half an hour - the amp cost me nothing, I fixed it with 4 diodes, it sounds fine, I won't use it with the 4311Bs and if I do I'll plug the ports. I'll try and get a photo of the guts though.

Great, nevermind the schematic, but please do send the pictures of amplifier inside & outside. We will be looking for them.

Thanks very much, herki

[Mike Caldwell]

Thanks. Actually I don't turn on the Loudness button when I play CD or LP because of this issue...

Irregularities in record vinyl can cause sub low frequency output. A good high pass filter when using LP's is always a good idea. Play the silent sections at the beginning and end of a LP and watch the cone motions. It may not be flapping around but i bet it will be at least quivering/fluttering. with music playing you may not be able to directly see it but it will still be in the background.

[JBL 4645]

Maybe a video would help us see what is happening.

Flapping :dont-know

I want to see the video without excuses no later than today 6pm UK time. So chop, chop get to it and may the flapping be with you.

you now have "flipping" 28 minutes till 6:00pm UK time that's 18:00 hours for all those who can't tell time.

[herki the cat]

Irregularities in record vinyl can cause sub low frequency output... A good high pass filter is always a good idea. You can Play the silent sections at the beginning and end of an LP & see the cone quivering & fluttering which is still evident in the music play back.

Mike, the text of my two cents here certainly is old hat, :dont-know but it may nudge some creative person to come up with a few ideas to improve turntable technology simplicity that doesn't need to cost $10,000 to $125,000.

BTW... BMWCCA, where did you find this lovable :dont-know icon.

The "Well Tempered Arm Turntable" system iS a good example of very simple, clever, reliable, well designed system in all respects. To see the "Amadeus GT model," visit this link= http://www.welltemperedlab.net/welltemperedlab/

This problem of floppy records as you know is further aggravated by reinforced woofer feed-back energy coming up through the turntable plinth to the LP record. The usual fix consists of adding 50 to 75 pounds to the turntable platter and extremely complicate bearings plus another identical mass to the turntable plinth supported by a "highly damped spring" isolator system all of which collectively forms a low-pass filter tuned some where well below five Hz. This filtering is obviously necessary. Simplying product design always goes a long way.

Also, damping is required to manage the lateral and vertical resonance occurring some where in the spectrum of 6 to 12 Hz which is formed by the pickup stylus armature compliance and the pickup arm & cartridge mass reflected to the stylus point.

Record Master flatness requirements are addressed in the lacquer master cutting industry by use of a complicated " turntable platter-to-master disc" vacuum clamping system. The first mature Professional Quality Home LP Turntable Clamping System surfaced in the early 1980's in the "Canadian "Oracle Turntable Company" product featuring a slightly concaved platter top surface and a screw-down three-inch diameter record clamp machined out of Teflon to sort of squash the LP Record completely flat & locked down to the platter. This system is extremely effective.

There is an other interesting item regarding the sub-frequency spectrum of LP mastering where the mastering engineer struggles to achieve a minimum 17 minutes of program material on each side of the LP; this has to do with groove spacing and groove modulation amplitude of the cutting which becomes quite gruesome in the last half of the recording space because the groove diameter is reducing very fast towards the center of the record and the cutting wave front is fast becoming very steep.

The mastering engineer salvages stereo LP groove area by recording the spectrum below 100 Hz in monoral format there by sacrificing the vertical components of the bass spectrum in the stereo 45/45 two channel LP stereo recordings. This has always been the practice from day one in stereo LP recording which has misled nearly everyone to believe the myth saying there is no perceptable "natural stereo imaging" in the low frequency spectrum, which of course is what happens "man-made" in LP stereo recordings below 100 Hz to conserve LP groove area as described here.

This problem does not exist in digital CD recordings and sub bass stereo imaging does come in your CD's.

herki

[BMWCCA]

BTW... BMWCCA, where did you find this lovable :dont-know icon.

Apparently this list's owners knew there would be those (like me!) who would offer opinions based on their own experience without the technical training to back them up. I use it with full knowledge of my own limitations. It also comes in handy when a question is posed without giving enough information, as well. And it seems more gentile than the ubiquitous "WTF".

Now, if your question was literal rather than rhetorical, click on the "More" button in the "Smilies" window during a reply and open up a whole new world of emoticon expression. No substitute for human-to-human interface but it can help with some problems of electronic communication that strip emotion and nuance from the message.

[jcrobso]

http://www.youtube.com/watch?v=2L0nG...eature=related
This test at the low frequencies 5~10Hz reminds of what my D140F looked like on that one amp. The cone would just move back and fort at a very low frequency. Look at the motion about 20sec into the video.