Hiwatt Output Stages, NFB

[loudthud]

At one time Eminence boasted that they had stopped using lead solder and were using conductive epoxy to connect voice coils. Could this be the problem? I have an Eminence 15 that has an open voice coil and no rub. Purchased a pair on ebay and one of them was DOA.

[J M Fahey]

Bea said:
My effort is still about understanding why my Mywatt killed an Eminence 2515 speaker which matches 350 W of thermal load - it worked like a charm during one reheasal and was dead when i switched on the amp again one week later.

JMF [b]immediately[/bI] said:
Somebody might have earned some extra ReichsMarks renting the studio while you were away.
Not kidding.

Bea said:
And the cause of a severe conflict with the band we share our rehearsal room.

Well, you should start screaming a little and kicking their drum set because ...............

Bea said:
And i would like to understand what happened. When did it melt - after swichting off the Amp? That would have meant that it was high before - but the last day i could use it i was definitely not louder as i usually am, rather less.

Dear Bea, you had it before your very eyes all the time, just hid very important data for some 30 posts sending us all in a wild chase.

Bea said:
The speaker did not show any problems - and it did survive that gig.
It died shortly later after having been used in our rehearsal room - with a smaller volume setting of the amp. The room has just 17 m^2, and our PA - one of my old 80W tube amp is not demanded in any way - its level meter nearly won't move when Verena sings.

Of course my first idea was that the guys sharing the room with us (young guys playing some kind of metal *really* loud who at that time had only a tiny bass combo) had abused my amp.

Bea said:
But these guy swear that they did not touch my amp - and i actually tend to believe them

Oh well, you definitely have a big warm heart

but don't waste time searching for alternative explanations

[pdf64]

In the past I've removed the fuse and fuse carrier from amps stored in a shared room.
And for low wattage speaker cabs, fitted a stereo socket with shorting contacts on the cab, with the hot to the ring, sleeve, tip and shorting contacts ground.
Of course it then needs a special lead and a spare.
More crap to forget / screw up when in a rush.

[Justin Thomas]

In the past I've removed the fuse and fuse carrier from amps stored in a shared room...

Same strategy I use... Luckily, my speaker cabs are so big for the seeming size of the room, everyone is afraid to use them! Apparently musicians think the physical bulk of the cab is what makes the power? :P But, whatever, their loss... No tone for the gutless. A Tele, chorus, & 12W thru a 100W 2x15" is pretty friggin' amazing.

Justin

[bea]

A Tele, chorus, & 12W thru a 100W 2x15" is pretty friggin' amazing.

And a bass, a modded 5 W Epiphone Valve Junior driving the Oberton 15L at the amps limit in a living room lets the neighbours four floors away ring within 3 minutes :-)
And it makes me curious running the tiny amp through 2 of these speakers.

but don't waste time searching for alternative explanations

It is always worth looking at possible own mistakes. Even if the result is excluding them it is a useful result.

Anyway, looking forward: what remains? If i take the Mywatt back into the rehearsal room it will be run on the same cab - now equipped with the 3015. The 3015 has a larger voice coil and will therefore take significantly more power - but the Mywatt should be able to kill it as well. Which means that without speaker protection i will not be able to use the amp any more. And that's the reason why i asked how to chose a light bulb as a speaker protection.

At present i am using an amp which is not so much a temptation for kids to play with - thats one of those beasts with 2 EL34 at 750 V - loud enough, good sound but really different from the Mywatt:

[g1]

In my experience, bulbs are only used for HF and horn protection, woofers always use fuses or circuit breakers. With tube amps this is not really an option as your number one priority is to maintain the load.
Even if your intent is only for the bulb to act as a dynamic limiter, it is likely to go open at high power levels. And when it is just limiting, it is unfortunately messing with the load impedance.

[bea]

At one time Eminence boasted that they had stopped using lead solder and were using conductive epoxy to connect voice coils. Could this be the problem?

Possibly, of course.

[bea]

Please let me continue this discussion:

Not always possible. Especially not with the 3015

Today i killed it. The 3015. Nominal 450/900 Watts, which i do not believe at least after the last discussion. The amp was not the Mywatt, but instead the G-2000 which drives 4 EL34 at 790 V. Nominal power 150 W at 1% THD at 1000 Hz. Actually a bit less due to old tubes and 230 V rail voltage going into a power supply set up for 240 V. It was the first day the amp cam back to life, and the preamp had been designed by me - so i was not silent - and the rehearsal room has recently been damped. The amp was far from audible clipping.

What happened? During Verena's solo (we did Child In Time) the loudness suddenly ceased, then quickly turned into scratchiness. I first thought one of the anode fuses of the G-2000 had failed, and the amp would run with reduced power. But when i noticed the "scratchiness" (which might well have been caused by the amp) i immediately stopped and switched off the amp. Attached my Valve Junior - again scratchiness. Desaster obvious...

I am really frustrated. An amp doing 130 W sustained and peaks of about 200 W kills a 450 W speaker... and the vintage 100 W Fane 12-100CT has nicely kept up with the 90 W of the smaller Dynacord ...

... i am still waiting for my 2nd Oberton...

[Mike Sulzer]

I am sorry to hear that Bea.

Please let me continue this discussion:



Today i killed it. The 3015. Nominal 450/900 Watts, which i do not believe at least after the last discussion. The amp was not the Mywatt, but instead the G-2000 which drives 4 EL34 at 790 V. Nominal power 150 W at 1% THD at 1000 Hz. Actually a bit less due to old tubes and 230 V rail voltage going into a power supply set up for 240 V. It was the first day the amp cam back to life, and the preamp had been designed by me - so i was not silent - and the rehearsal room has recently been damped. The amp was far from audible clipping.

What happened? During Verena's solo (we did Child In Time) the loudness suddenly ceased, then quickly turned into scratchiness. I first thought one of the anode fuses of the G-2000 had failed, and the amp would run with reduced power. But when i noticed the "scratchiness" (which might well have been caused by the amp) i immediately stopped and switched off the amp. Attached my Valve Junior - again scratchiness. Desaster obvious...

I am really frustrated. An amp doing 130 W sustained and peaks of about 200 W kills a 450 W speaker... and the vintage 100 W Fane 12-100CT has nicely kept up with the 90 W of the smaller Dynacord ...

... i am still waiting for my 2nd Oberton...

[bea]

I am sorry to hear that Bea.

Yes, and this seems to demonstrate the truth of the background discussed above the hard way.
But how do environments for such chassis be set up to operate safely?
Always with protection light bulb? Always with internal cooling fan or heat sinks (the latter would be hard to attach)?
What are the professionals doing with these chassis?

Despite of that i have severe doubts on the quality Eminence are delivering, at least with their Neo speakers.

And what would be the consequence? Build a 2x12 cab with 80-90 l and run it with two Beta-12 (i already own one...)?


And this brings back my question regarding the 2515: i switched it off after normal operation and a weak later it was dead. Sure the voice coil must have been hot - but that seems normal. Is there any physical possibility that a voice coils continues with its melt down shortly after the energy source is switched off?

[bea]

Please let me pick up this one:

Which is "differential thermal expansion".

How probable is this?

Obviously this will not explain the death of the 3015. But i need to understand what was going on there. Really just thermal overload? I was relatively loud but not loud enough that i needed to use ear protection (i own a pair of Elacins with 15dB filters) - a drummer playing moderately loud would have a lot of dynamic freedom.

Any things i should look for at the amp? A problem with the output transformer should not cause a problem for the speaker (but of course for the amp...), right?

Now i have two speakers available: an Eminence Beta-12 ("250 W") in a vented cab - already in the rehearsal room, and the Oberton 15L400 (needed at home, for playing the Mywatt or the G-2000), also in a vented cab. I do not know if the sounds of the two will merge nicely. I could use one of these or two, and i still tend to use the G-2000. Mhmm...

[J M Fahey]

Dear Bea, we deserve a little of your cool Music, care to link some?
My 25 y.o. Son saw your stage picture, and being a Bass player himself, was instantly intrigued about what Beyond Velvet (or is it Velvet Beyond)? would play.
If possible, of course, please don't feel obliged to anything

[bea]

Dear Bea, we deserve a little of your cool Music, care to link some?

The reason why i don't have any recordings in public has a name: GEMA. Having a recording online would cost us 170 € a year.

Despite of that it is very amateurish...

[J M Fahey]

Oh, we are all amateurs here

And it would definitely help understand what your speaker is being subject to.

The speaker cabinet visible in the picture looks quite small, ports look large (i.e. unloading speaker at the lowest frequencies, just where excursion is max.) , and I saw at least one of your bass guitars is a 5 string.

My personal experience is that Politically Correct Thiele tuned speaker cabinets:
a) don't really have much bass
b) often unload the speaker at some critical frequency.
So if you sweep one such cabinet down until F3 and stop there, cabinet works fine, as flat as can be, graph looks fine, etc. ... BUT if you send any frequency belown that, at stage levels ... speaker is as loaded as if it were on a table, naked, sitting on its back.

I bet they are the best *if* you calculate them, determine F3 (it's part of the process) ... and add a strong highpass filter (12 dB/oct or better) between preamp and poweramp.

As I see Thiele currently used is allowing owner to make a very small cabinet with specs that look good: "hey, I made a shoebox sized cabinet which still reaches 63 Hz flat" ... and then proceed to slam it with as low as 42 Hz, at full power ... or worse if a 5 string.

Personally, after wasting time for a couple years, and often smashing my head against the wall, I got back to the OLD fender formula: making larger cabinets and tuning them, no matter what, to 40/45 Hz , or plain making closed cabinets.

~40 Hz tuning not to "increase Bass" (speaker might be 12dB down by then) but to limit cone excursion at the lowest frequencies.

And despised closed cabinets usually have a high bass/low mids hump which to unsophisticated ears (general purpose public) passes as "bass" anyway

After all, World's most popular/envied Bass cabinet is Ampeg's "fridge" , which follows exactly what I am suggesting: **huge** and closed.
A large bump around 80 Hz and then it's falling like a brick .
Don't see many people complaining about that

Just curious, what is the red disk in front of the speaker center, attached to the grill?
Just for aesthetics or is it some kind of beam blocker?


EDIT:
1) *Loved* the Dynacord (Eminent 1?)
2) that Gibson Bass, with its house brick sized overwound Bass pickup is about the hardest Bass to amplify properly.

[Mike Sulzer]

The speaker cabinet visible in the picture looks quite small, ports look large (i.e. unloading speaker at the lowest frequencies, just where excursion is max.) , and I saw at least one of your bass guitars is a 5 string.

My personal experience is that Politically Correct Thiele tuned speaker cabinets:
a) don't really have much bass
b) often unload the speaker at some critical frequency.
So if you sweep one such cabinet down until F3 and stop there, cabinet works fine, as flat as can be, graph looks fine, etc. ... BUT if you send any frequency belown that, at stage levels ... speaker is as loaded as if it were on a table, naked, sitting on its back.

This was my concern, but I was hoping the pro would say something first. If the destruction is occurring from a combination of heating and excessive motion rather than heating alone, does this leave any evidence? That is, does the corpse have anything to say about the manner of death?