Small Advent Woofer Problems

[bhqman]

Have a set of the Smaller Advents, having some low level distortion in one of the woofers and curious if the vast collective knowledge here has any leads as to the cause. I swapped the woofers and it is not the crossover. All wiring appears intact and correct.

Also, there is a 2mfc cap in there, I have never seen an mfc cap, any info on this would be great.

thanks,

[JKent]

This is kind of odd. Never having been inside the Smaller Advent maybe I shouldn’t weigh in on this, but you had my curiosity aroused.

My 1st thought was, “2mfc” must really be 2mfd—2 microfarads or 2uF. But when I looked for a schematic I found this, showing two 8uF caps

http://www.davidreaton.com/PDFs/Smaller_Advent_Crossover.pdf

then there’s this, showing an 8uF and a 4uF

http://www.sound-thinking.org/index.php?showtopic=772&st=15

then there’s this CSP thread

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=2816

it has a link to this site

http://macro.lsu.edu/russo/QuAdvent/QuAdvent_2.htm

that one also shows an 8uF and a 4uF. So I’m guessing the first link contained an error, but that still doesn’t solve your 2mfc question. Is it possible that cap was replaced and whoever replaced it used the wrong value? Also—are you sure the drivers are original? Maybe the tweeters were replaced and the different cap is a “correction.” I dunno....

Only "mfc" caps I find are multi-fiber ceramic caps like this:

http://liowgu.manufacturer.globalsources.com/si/6007000400395/LargeImage/450V-DC-MFC/product_id-1013447908/action-GetProduct.htm

Kent

[michiganpat]

in the smaller advent, the woofer runs full range. could you be more descriptive in the distortion, and is it heard all the time, or at loud volumes only?

have they been refoamed at all? is the foam surround intact, or are there potential holes, cuts or deteriorated portions?

if only at loud volumes, could it be air leaks from poorly sealed woofs, tweets, cabinet seams, or back plates?

[bhqman]

This is kind of odd. Never having been inside the Smaller Advent maybe I shouldn’t weigh in on this, but you had my curiosity aroused.

My 1st thought was, “2mfc” must really be 2mfd—2 microfarads or 2uF. But when I looked for a schematic I found this, showing two 8uF caps

http://www.davidreaton.com/PDFs/Smaller_Advent_Crossover.pdf

then there’s this, showing an 8uF and a 4uF

http://www.sound-thinking.org/index.php?showtopic=772&st=15

then there’s this CSP thread

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=2816

it has a link to this site

http://macro.lsu.edu/russo/QuAdvent/QuAdvent_2.htm

that one also shows an 8uF and a 4uF. So I’m guessing the first link contained an error, but that still doesn’t solve your 2mfc question. Is it possible that cap was replaced and whoever replaced it used the wrong value? Also—are you sure the drivers are original? Maybe the tweeters were replaced and the different cap is a “correction.” I dunno....

Only "mfc" caps I find are multi-fiber ceramic caps like this:

http://liowgu.manufacturer.globalsources.com/si/6007000400395/LargeImage/450V-DC-MFC/product_id-1013447908/action-GetProduct.htm

Kent

Thanks for the response, the drivers are definitely original, have had 3-4 pairs of these over the years, bought these with the intent to veneer them and keep. The MFC cap looks physically similar to the mfd, grey in color.

[bhqman]

in the smaller advent, the woofer runs full range. could you be more descriptive in the distortion, and is it heard all the time, or at loud volumes only?

have they been refoamed at all? is the foam surround intact, or are there potential holes, cuts or deteriorated portions?

if only at loud volumes, could it be air leaks from poorly sealed woofs, tweets, cabinet seams, or back plates?

Distortion is a low volume only, and only on certain material. almost like an amplifier hum. they have been refoamed and there is no rub on the voice coils. woofers have been sealed with plumbers putty and everything appears as it should. Thanks for the reply.

[michiganpat]

hmm....

IIRC mine, with untouched crossovers had an 8uf and 12uf temple brand cap in the crossover. I'd have to pull a woofer to verify (I didn't remove the old caps when I redid mine)...the woofer runs full range so the xover shouldn't impact it at all if the noise is truly coming from the woofer...

and the sound follows the woofer from cab to cab, and side to side? you've ruled out a source problem?

dunno what to say about that....

[dynaco_dan]

hmm....

IIRC mine, with untouched crossovers had an 8uf and 12uf temple brand cap in the crossover. I'd have to pull a woofer to verify (I didn't remove the old caps when I redid mine)...the woofer runs full range so the xover shouldn't impact it at all if the noise is truly coming from the woofer...

and the sound follows the woofer from cab to cab, and side to side? you've ruled out a source problem?

dunno what to say about that....

Hi there

If you remove the woofer from the enclosure, and each of my suggestions is with it out of the cabinet, and without disconnecting it or the wires from your

amplifier, use a very, very, low level sine wave or warbling signal from a test cd or record.

This is a very simple test method.

If you happen to have access to a signal generator, that would be even better.

With a signal in the 100 - 500 hz range and the woofer laying on it's magnet, facing upward, run at a very low volume

setting and you should be able to hear any rattles, buzzing or rubbing.

With there being no back pressure, be certain to do this at a very low volume level.

A 1 1/2 volt C-cell battery with the woofer disconnected from the cabinet wiring, will do for a back or forward movement only, but also worth a try.

Even gently pressing down with your hands, evenly centered on the cone, not the surround, will be another way of checking for voice coil rubbing.

Do not use a battery with the completely sealed speaker system, you would not do more than a back or forward woofer movement, the loading of the enclosure

would not necessarily help you.

Also if testing the completely sealed speaker system with a battery only, a woofer will make a sound or movement, hopefully, the midranges or tweeters are

blocked by the crossover network.

That also may work for you.

Good luck

Vern

dynaco_dan@hotmail.com