Astonished...once again!

[dcl 3,158]

The old ALS Silver Mk IV s had lost all 6 subwoofer surrounds (literally all the way around) and one ribbon was buzzing. Ugh. In came the Polk SDA-SRSs hooked to M 1.0T amp, TFM-35 preamp and a Yamaha 5-disc changer.  A pair of Bose 901 Mk IVs sat on the sideline needing speaker replacements. A fortunate situation indeed but I sighed at the thought  of giving up the Darth Vaders in spite having the Big Coffins in their place. Luck enters the scene: I discover The Carver Site. Eureka! Following the forum discussions I ordered 6 woofers from Dynavox months ago, Over the weekend my wife and I replaced all the degenerate woofers. Needed to drill  new mounting screw holes, three of four for for each woofer, and make ugly solders that actually got better by the end. Holding our breathes the ALSs were plugged into a Denon multi-channel receiver that was powering Mirage Nanostat 5.1 speaker set-up. The surgery worked! Not as astonishing as I had remembered but a start. Today the M 1.0 T/TFM-35 combo was connected via a  Sunfire True Subwoofer Junior  line level high-pass output set to approx. 40 Hz. The room is 25 L x 12 W with ALS at one of the 12 wide sides and out three feet from the back wall.  At first, no sound whatsoever. The fault was Tape Monitor buttons pushed in whilst cleaning the TFM-35 face. One click and voilà! My mouth dropped open, my breath stopped. Oh my, my, my – this was astonishing! It was My Mourning Jacket's Evils Urges slamming sublimely . I had forgotten how astonishing music-at-home can be. There is a ribbon buzz and a subwoofer hum to sort out so back to the Forums for collective wisdom. My sincere appreciation goes out the Carver Site Forum members for their help. And my wife.

[Blues Pwr 765]

Welcome dcl to the forum, and congrats on your successful repair of the ALS Silver  MKIV's.

I'm sure others will be along shortly with questions and many helpful suggestions to help iron out the bugs in your system.......

[TNRabbit 370]

Listen up & down the ribbon for the EXACT location it's occuring, then go to the INNER screws on the back of the ribbon in that location. GENTLY tighten the screw on each side at that location about 1/8" turn & listen again. If still buzzing, try an additional 1/8" turn on those two & 1/8" on the ones top & bottom of those two. Try again. Let us know what you find.

[Nahash5150 9,952]

Welcome! Troubleshooting becomes fun here, so hang in there.

[weitrhino 1,425]

TNRabbit is dead on it. DON'T get too happy with those screws. When he says 1/8 of a turn he means it !!! Go slow!

[Guest blownrx7]

Congrats! Very nice setup btw. Are you planning anything else now that you had a taste???

[soulofsound 40]

Welcome dcl

You have a fine system going on.

The members here are friendly and helpful.

Think you will love this site as much as I do!

Some member or members will be glad to help you out.

Welcome again soulofsound|-|

 

[dcl 3,158]

Thank you for the warm welcome, that is very nice.  I will review the posts regarding ribbon buzz & selecting appropriate screws to minimally tighten, as well as humidity, although I think  it is a low humidity situation indoors this winter–but humid summers in Northern Virginia. We tend to keep the windows open spring through autumn. What would be the benefit, if any, to running a hair dryer set to low heat & low speed from a distance, not close,  over the buzzing area? Bad idea?    Not trying to shrink wrap the ribbons like the window insulation treatments I put up in winter. Future plans: perhaps introduce the second M1.0T into the system, both set mono, driving their own speaker. I have yet to top-out the M 1.0T LED lights, so would there be any real sonic benefit?  My guess is probably not. These, as I have learned here, are the non-inverting models so a flip of the switch on the back panel would precede a new hook-up. Still experimenting with the Sunfire True Subwoofer Jr. crossover level & volume. The ALS's bass is incredible, more so than in the past and I attribute that to room placement, having back and side walls walls not opening into another room or hallway.  I have set the crossover at 35 Hz and the volume rather low and the low end is very nice.  My wife said it is good to have Big Music (her words) again, meaning the sound & soundstage of the ALSs.  I will post an update as things proceed. And to correct a mistake, that is a CT-7 in the system, not TFM-35. Thank you once again for the cordial advice and hospitality. 

[zumbini 6,138]

Be aware that bridging provides more power but inevitably results in reduced sound stage.

Most people (myself included) find the loss of imaging to be an unaceptable trade off. 

 

Soundstage is not an issue when driving subs but bridging still has a downside - less defined bass.

In my case (2 bridged M-500t's driving a pair of subs crossed at 120Hz) I found the loss to be minimal.

 

In either case there is certainly no harm in trying. Just let your ears be your guide. 

[weitrhino 1,425]

 

 

..... What would be the benefit, if any, to running a hair dryer set to low heat & low speed from a distance, not close,  over the buzzing area? Bad idea?    Not trying to shrink wrap the ribbons like the window insulation treatments I put up in winter. 

 

 

I've heard of that before but to me it doesn't seem like very sound reasoning.  If the issue actually is slightly loosened ribbon material it's the screws that are designed to apply, or reapply, the correct tension.  The hair dryer method would only make sense to me if the ribbon had become physically distorted somehow and the application of heat would cause it to return to normal.  I don't know about that.  It seems unlikely the ribbon would become physically distorted in a localized area.  I don't believe the Kapton material absorbs that much moisture either, and certainly not just in a particular area.  

 

Nevertheless, I don't see the harm in trying it if in a high humidity climate provided you're very careful not to apply too much heat.  You sure don't want to melt a hole in the thing.  If it works I wouldn't expect it to be very permanent, unlike adjusting a tension screw.

 

Technical information on Kapton can be found here:  http://www2.dupont.com/Kapton/en_US/assets/downloads/pdf/summaryofprop.pdf 

 

 

[B-Man 4,763]

 

 

Be aware that bridging provides more power but inevitably results in reduced sound stage.

Most people (myself included) find the loss of imaging to be an unaceptable trade off. 

 

Soundstage is not an issue when driving subs but bridging still has a downside - less defined bass.

In my case (2 bridged M-500t's driving a pair of subs crossed at 120Hz) I found the loss to be minimal.

 

In either case there is certainly no harm in trying. Just let your ears be your guide. 

Dom,

 

Would you please post a link or two that would help me understand this reduced sound stage and less defined base effect of bridging ?

 

Thanks !!

 

Brian 

[TNRabbit 370]

Hair dryer is fine. Results vary significantly with that approach, but it's free & worth a try.

 

If you never hit the top lights on the meters in your regular listening, PROBABLY wouldn't make a difference. HOWEVER, if you find the need for more "oomph", I highly suggest bi-amping versus bridging (run one amp channel to the ribbon on one speaker & the other amp channel to the woofer, after removing the tie-in plates on the back of the speakers. Then do the same on the other speaker/amp. This would require RCA Y-cables for each channel.

[zumbini 6,138]

Dom....Would you please post a link or two that would help me understand this reduced sound stage and less defined base effect of bridging ?....

The effect has been discussed many times, however, the process has not been well defined.

As I recall it has something to do with the change in signal path.

Rich and BoB P discussed it in a long thread that I can't seem to find.

Here are a few random quotes I did find:

RIch' date=' did you ever measure the M-500t Mk.II bridged?[/quote']

 

No, I"m not really interested in bridging stereo amps, so I haven't measured it;  IIRC, they usually measure twice 4W clipping rating, so the M-500t mk II should rate 980W into 8W.

 

pretty meaningless spec; I bet they'd perform like most bridged amps do; they may get louder but you'd lose bass integrity (then again, one M-1.0t mk II opt 002 owner is running two of them bridged into low sensitivity (something like 84dB/w/m) speakers and reports fantastic sound.........)

 

....I wouldn't bother with a bridging experiment, as all of the bridged 8R amps perform like ass into a 4R load, as the power supplies fare poorly.....they just weren't designed for it.

 

EDIT: I found this definition in the site "Glossary of Terms":

 

Bridge Tied Load
Using a stereo amplifier to drive a single channel loudspeaker, by strapping the load across the hot terminals of each channel(one channel is inverted in phase with respect to the other).  This results in a higher power output from the amplifier, with some caveats.

 

A standard stereo amplifier is a voltage amplification device, and normally supplies a voltage to two separate 'channels' of amplification.  In the illustration below, a stereo amplifier (capable of providing a 45V signal to each channel) will dissipate 250 watts per channel into a nominal 8 ohm load (P=E²/R).  Since current is the result of dividing voltage by resistance (I=E/R), the amplifier is able to source 5.5 amps per channel.

 

 

When a stereo amplifier is bridged, two things happen.  First, one of the channels is inverted with respect to the other (the two channels are now 180 degrees out of phase).  Second, the 'hot' terminals of each stereo channel are connected to one loudspeaker (the remaining two output terminals are unused).

 

The illustration below presents a bridge tied load configuration of a stereo amplifier.  The per-channel output voltage remains the same (45V), and the load remains the same (8 ohms).  What has changed, is that each stereo channel's 45V output is both out of phase with the other and tied to the same driver.  The result is a 90V differential across the load (double the stereo voltage).

 

 

Using P=E²/R from the previous example, the power dissipated by the load is now 1012W.

 

Using I=E/R from the previous example, the current required to sustain 1012W is now 11.25A.

 

This seems like a very good situation, and can provide more power to a speaker, provided you follow a simple guideline.

 

The relation I=E/R tells us that as output voltage doubles, so does required current.  Also, as driver impedance halves, required current will double.

 

An ideal current source amplifier (often called load invariant) will be able to source the required doubling of current as the load halves (from 8-4-2-1 ohm).  Not all amplifiers are load invariant (few are).

 

Using the above formulae for a 4 ohm driver would (ideally) provide 500W into a stereo 4 ohm load (requiring 11.25A per channel), and 2025W when bridging the amp (now requiring 22.5A).

 

The situation becomes harder for the amplifier to tolerate as the load impedance diminishes.  At some point, the amplifier can no longer source the current required to provide a doubled voltage level.

 

This is often experienced sonically as a very loud, but 'flabby' sound (especially in the bass).

 

For this reason, most stereo amplifiers that are bridgeable are rated into 8 ohm load drivers only.

 

<pet peeve>  It's often repeated that when bridged, each half of the stereo amplifier will 'see' half of the driver load.  This is untrue; the load is the load, and hasn't magically sprouted a center tap.  What has changed is the current sourcing demand placed on the amplifier due to the doubled output voltage across the load.

[mbskeam 1,725]

the hair dryer will work, but it may loosen up after a few months. I did a set that had a few buzzes

fixed them for the most part.

the other thing to try is apply a strip of felt on the back side of the ribbon, from top to bottom.

tape or contact cement will work.

also a note, on the latter ribbons on the inside, in the centers there was a small pc of foam that was

glued to the magnet, front and back.

on a ribbon that had a real buzzy/slappy area I did this and stopped the noises.

I can find the post I did on this if you need to go this route, just let us know......

[dcl 3,158]

I will apply delicate attention to the screws this weekend, thank you for the emphasis on minute turns. As things stand now the components hide out of sight behind the left speaker, the True Sub Jr. behind the right speaker. 

[zumbini 6,138]

That's a very stylish room dcl, and your system blends in perfectly.

[SteveFord 1,059]

If I may make one suggestion, give that amp a bit more breathing room. 

It'll last longer if it's running cooler.

[B-Man 4,763]

I agree - put the amp on top of the pre-amp... or in it's own "private" space.

[soulofsound 40]

I agree with Steve and B-man put the amp on top .

It will help keep it cooler and last longer!

And maybe some higher risers.

[dcl 3,158]

You fellows are sharp. Back to the second hand store for another wine rack. 

[soulofsound 40]

Man you have a great system going on.

Your amp needs room to breath and stay cool that,s all.

One hell of a system for a newbie !

You have been at this a while.

soulofsound

[dcl 3,158]

Regarding tightening slightly the screws at the level of buzz, may this be performed whilst music is playing or is it to be done with no audio signal. I have identified at least two, maybe three, buzz zones.

[weitrhino 1,425]

You can do it while music is playing. Use the minimum volume needed to hear the localized buzz. Visually inspect the driver for tears before making the adjustments. And above all, turn the screws very slowly and no more than 1/8 of a turn at a time.

 

Did I mention to do this v e r y slowly?

[dcl 3,158]

Thank you, makes sense, but being cautious comes with inexperience on my part. How far has any one particular screw been turned been by anyone doing this procedure? I've done 1/8 so far and not resolved the buzz sites. 1/4? 1/2? Proceeding with caution (jeez, you'd think I was doing touch-and-go brain surgery). Thank you for ongoing support.

[mbskeam 1,725]

you might try the hair dryer trick, but I dont think you will get all of it out.

also try running your hand from the back side covering the slots in the problem area.

if the buzz goes away, slap a pc of duct tape over this area. its not a real fix but it will help.

this worked on mine, and stopped ribbon slap in a few areas

as to the screws, maybe a bit more. but that would be it.