agedhorse

The current in an electrical power circuit is generally considered to be continuous (there are a few exceptions, every region is slightly different) and the distances are much longer than what is being dealt with on a PCB or interconnection wiring. 50 amps of building power circuit would require at least 8 times the copper area as an audio circuit or internal power wiring for an audio device). This is because the audio circuits are designed around a minimum 12.5% duty cycle, and the voltage drop is based or wire cross-sectional area its length and the current in the wire. Power electrical current is based on 100% duty cycle (80% in the US for non-continuous loads).

Actually, it depends very much on the amp. Tube amps reflect the speaker’s impedance back through the output transformer to the plate circuit. This output matching transformer maintains the voltage (and current) ratio so that the high impedance plates transfer the energy effectively to the low impedance load. When the load is mis-matched to the plates, the voltages can increase to unsafe levels, especially when the output stage is overdriven. This effect is generally worse when the load is higher than the impedance tap is set for. some amps are more forgiving of mismatches than others, though the cost of being wrong can become awfully expensive.

Your wire size examples are for long runs of wire and based on a combination of voltage drop, temperature rise and continuous duty cycle. They are generally accepted sizes based on installed building applications with common insulation types. Components and component interconnections are sized differently for each application. For example I work with 50A transistors that have leads roughly equivalent to 2.5mm dia wire. It’s because the leads are short and the parts are used in <50% duty cycle applications.

The peak power of ANY 600 watt rms amp IS 1200 watts. It’s just two ways of describing exactly the same thing. It’s just a math conversion between units.

The Diesel is based on the tuning concepts in the TL cabinet, using the EVM-15L for the driver. The internal volume is pretty close to the stock EV recommendation (actually EV recommended a range of internal volumes, a range of porting versus internal volume and thus a range of tunings). In that box, the EVM-15L is good for right about 200 watts RMS down to ~60Hz and does so with very high sensitivity. These were calcs/plots that I did on the Diesel 115 w/ EVM-15L when designing the Subway speakers, in order to understand the legacy products and why they were as successful as they were. In this case, there was very little driver performance left on the table and because of the sensitivity (at the expense of power handling, it's only a 200 watt RMS driver regardless of the 400 watt numbers applied to the proline series), it will generally take about twice the power of most suggested "upgrade" drivers to achieve what this cabinet achieves with 200 watts. unfortunately both the driver and the box are very heavy which was a non-starter for the new product line.

Most of the Mesa Diesel 115 cabinets were loaded with EVM-15L drivers. This was specifically for the mid voicing. The EVM 15L/B drivers are good for about 200-250 watts RMS mechanically above 50Hz. The series 2 and proline drivers are mechanically the same, the only difference is a coating on the VC which helps bind the coil to the bobbin. The pro line drivers have pretty much the same mechanical power handling as the series 2, the way they were rated changed some.

Which also drops the mechanical power power handling on a driver with already limited power handling.

Because the vast majority of players are concerned with the ability to drive the lower impedance phones, something many headphone amps can not do well. We will look at updating the manuals at the next revision cycle to change this to include higher impedance phones too. I had to design a headphone amp for another product (guitar related) recently and the big issue was to be sure the new headphone amp could drive low impedance phones because more and more are going this direction. Many modern digital devices have limited voltage swing therefore can’t drive high impedance phones to more than a low volume.

Yes, the amp will drive 250 ohm headphones without any difficulty, but the vast majority of players use lower impedance phones and by far the greatest number of questions (and issues) is with the lower impedance phones. To refresh my memory, I checked the top 30 selling headphones and ~90% were 60 ohms and less. There were just a couple over 100 ohms. Just beware that there are quite a few high impedance phones that do not get as loud at low frequencies, the headphone out will drive some of them beyond their capability without them getting as loud as players expect.

To clarify, a first order filter is 6dB/octave and a second order filter is 12dB/octave.

A tweeter is typically about 10dB more sensitive than the low frequency section, so with the tweeter level control fully up (assuming that's the only attenuation), there will be a 10dB bump in the high end compared with the rest of the speaker's response.

Mid 90's. Be sure that you set your speaker to 8 ohm mode (assuming it's switchable between 4 and 8 ohms) I too would recommend a second speaker identical to your first.

Any electronics before the amp (pedals and active bass for instance) can contribute to a higher than ideal noise floor. If a speaker has a tweeter sensitivity that is significantly higher than the low frequency drivers, this can result in the perception of more hiss than you might otherwise expect. This is common with tweeters turned up to "bite your head off" level that happens with some cabinets. The brighter the tone, the more noise present.

This too is inaccurate and incorrect. Maybe a FEW models of wireless, but certainly not many or great many. Out of the hundreds I have set up, maybe one or two.

That’s not an active bass issue, it’s incompatible wiring/connection with that particular product. I’m not sure why they chose to use a TRS plug on the transmitter, but it’s unusual and maybe even unique. I have worked with hundreds of players, interfacing wireless systems (mostly at the professional level, with pro products by Shure, Sennheiser and Audio Technica) without any problems.

They do? I haven’t seen this to be the case, in 40+ years of being in the business.

Active basses can drive lower impedance loads. This includes long cables because the capacitance reduces impedance (via capacitive reactance) as the cable length grows (for bass guitar it’s typically not a big issue up to about 10M). Most wireless transmitters have an instrument input impedance of around 1M which is compatible with all pickups, active or passive.

Surrey Amps in the UK are qualified to troubleshoot and repair Genz Benz products, I can provide factory support and parts directly to them.

I never suggested he send the amp to the US, I did suggest that he find an experienced, qualified service tech to troubleshoot the actual cause. There’s a lot more than the switches involved in the filter switching. In this series of amp, I have seen maybe 1 or 2 bad in the last 10 years. I’m trying to help by providing good advice.

What is the primary current rating of the transformer? I'm about 99% sure it's well under 250mA full load at 230V, meaning that if there wasn't a problem with the transformer itself before powering it up with the higher value fuse and there was an issue in the circuitry downstream, you now have another problem in addition to the original fault. This is why DIY repairs, and repairs by techs who are under-qualified for the work they are attempting end up the way they do.

I already answered your question on Talkbass.

Did the tech check to be sure that the measured input current was less than the transformer's rated input current x0.65? This would confirm that the load was safe for the transformer.

First of all, that thermal protection isn't going to do much because it's on the outside of all of the wrappers so it will be measuring quite a bit less temperature than what's really present on the coil. The coil can overheat without the core overheating on a small part like that. Is the coil really overheating? Only a proper forensic evaluation (called a transformer "necropsy") will determine the true cause of the fault. The fuse should be slow blow (or time lag) and sized at a minimum of 1.25x the rated continuous primary current. For a toroid, it's possible that the inrush current (which is higher than for an EI transformer) might require an adjustment of this multiplier from 1.25 to 1.5, but this needs to be done after verifying that the transformer is not overloaded. There must be enough primary turns for the core material to prevent magnetic saturation, this design parameter is voltage and frequency dependent. If the transformer saturates, the primary current will be higher as will be the heating effect. Now for the real stuff... do you know what the input current is to the power supply. It looks like a FWB input capacitor filter. The transformer needs to be designed around the derating factor for this particular power supply topology. For this configuration, the rated current of the transformer multiplied by .65 is the usable current for the circuit being powered. It's possible that somebody forgot this when designing the power supply. There's more to solving this problem than replacing a part, you need to know what the maximum current of the circuit is and work backwards with all of the necessary design and derating factors to be sure you have a viable solution.

It's quite different from the ShuttleMax amps and about 1/3 the size. I would expect that you will start seeing Subway products in Europe in the next 3 months or so, we are finally digging ourselves out of backorders and parts sourcing issues. Crazy times we are living in.