agedhorse

Go watch Eurovision The Movie. It's silly, campy, in marginal taste, but funny and very well done.

It’s not gain or gain structure but limited maximum output level of many (not all) pedal preamps that’s responsible for not being able to drive a power amp to rated output. if a power amp has an input sensitivity of +4dBu (power amp sensitivity is measured with the input level control all the way up), the preamp must have a maximum output level capability of AT LEAST +4dBu (I recommend 6dB more if possible) in order to achieve rated power. The output impedance of the driving device (preamp) should be roughly 1/10th (or less) the value of the input impedance of the driven device (power amp). If not, there will be additional losses. In the case where the output impedance is 12k and the input impedance is 10k, there will be a ~6dB loss. Unfortunately, these specs are often omitted (or unknown/unmeasured) by manufacturers which makes matching a crapshoot. As an example of a pedal preamps that’s that can easily drive a power amp to rated output, the Genzler Magellan Pre-Di is one. It also includes all of the important, necessary specs to document the performance: Specifications DIMENSIONS: 6” (152mm) W x 4.3” (110mm ) D (w/ jacks) x 2.5” (63mm) H (w/ knobs and feet) WEIGHT: 1.1 lb (0.5kg) POWER SUPPLY: 9VDC-18VDC (low noise type), either polarity, 80mA POWER SUPPLY JACK: 2.1mm center pin with 5.5mm barrel (standard Boss pedal dimensions) INPUT IMPEDANCE: 1 Meg Ohm INPUT SENSITIVITY (nominal): -10dBu to -20dBu (instrument level) INPUT SENSITIVITY (maximum): >0dBu (9V supply), >+5dBu (12V supply), >+10dBu (18V supply) HIGH PASS Filter Range: 25Hz – 120hz, 18dB/oct variable EQ Filter Points: LOW: +/-15dB shelving below 75 Hz MID: +/-15dB peak-dip, between 150Hz – 2.8kHz HIGH: +/-15dB shelving above 6kHz PREAMP OUTPUT IMPEDANCE: 1k ohm (unbalanced), 2k ohm (balanced) PREAMP OUTPUT LEVEL (nominal): -10dBu to +4dBu (line level) PREAMP OUTPUT LEVEL (unbalanced maximum): +8dBu (9V supply) +12dBu (12V supply), +16dBu (18V supply) PREAMP OUTPUT LEVEL (balanced maximum): +14dBu (9V supply) +18dBu (12V supply), +22dBu (18V supply) DIRECT OUTPUT LEVEL (balanced nominal): -30dBu (mic level) DIRECT OUTPUT IMPEDANCE: 2k ohm (balanced) AUX INPUT IMPEDANCE: 10 K Ohm AUX INPUT LEVEL (nominal): -10dBu, stereo (sums to mono) AUX INPUT LEVEL (maximum): +10dBu, stereo (sums to mono) HEADPHONE OUTPUT: Drives headphones and IEM buds from 8 ohms -200 ohms, stereo output, mono signal path. (Higher impedance headphones, such as 600 ohms, will result in less output and headroom.)

That’s the reason for annealing and part of the reason for the dome shape (the other primary reason is to improve the HF radiation pattern). Work hardening and subsequent fatigue fracturing occurs when there is repeated flex in a material that is stiff in nature. As a practical example, JBL successfully perfected this process on their aluminum dust caps and high frequency diaphragms, they can last a lifetime if not abused.

My suggestion is to contact Surrey Amps, this is pro level service and Stan Lawrence is a highly qualified and experienced service engineer who is fully capable of taking care of Subway amps. I can support him at the factory level too. https://surreyamps.co.uk/contact-us

That's a cosmetic treatment, unrelated to the real thing except in looks. Proper aluminum dust caps are formed then annealed so that they resist cracking/fracture. This is no different than how (quality) high frequency diaphragms are manufactured.

It was around 2000-2001, the project was called "Indigo" (a dual concentric + sub music foreground/commercial audio product) and my job was to help them migrate the power amp from BASH technology (which went bankrupt) to ICEPower. This was long before Uli Behringer acquired them.

That's a short lived model that I never ran across. I didn't do anything with the studio side of the market, only the live/install side. It looks like yours is an aftermarket recone because that's not what the factory workmanship would be (based on my experience with the company). This looks to be a factory part:

I wonder if that was some kind of experimental application, doesn't look at all like a factory product. I did a fair amount of work for Tannoy many years ago, and at that time they were all about clean appearance and workmanship.

I can’t say that I have ever seen a Tannoy cone like that. Are you sure that’s a real Tannoy cone/product?

Things get super exciting when neutrons move...

The simplest and most well known example of off axis extension is the Duraluminum dust cap that attaches directly to the bobbin. It radiates the HF component of the signal like a 4” driver. The Duraluminum material is the same material that jBL developed for use in high frequency compression drivers. A wizzer cone is not a separate transducer, it’s just a specialized dust cap that attaches to the top lip of the bobbin just like the JBL aluminum dust cap. How well the HF energy coupled to the secondary radiation device determines in part the effectiveness. Decoupling the dust cap from the bobbin can be used to alter the response, as does the choice of materials.

There’s the basic premise of destructive interference due to the diameter of the driver versus the mid-high frequency wavelength, but this is modified by the size/shape of the dust cap and the geometry of the cone. With the right choices, the mid polar pattern can be altered more than an octave above what the basic predictions suggest. this can be taken to an even higher level by the use of a “wizzer cone” dust cap.

700 watts RMS is 1400 watts peak and 2800W peak-to-peak. You forgot the squared factor in the formula.

Yet there are several mechanisms that are used to improve off axis high frequency extension. This is why some 15” designs are better than others in this regard.

It could be any number of issues. If the OP is in the US then any QUALIFIED, Ampeg authorized service center should be capable of properly diagnosing the fault (the first step in any repair) and then repair the amp. If the OP is in the UK, Surrey Amps is qualified and capable of handling the diagnostics and repair.