agedhorse

Subway D-800 is 800 watts into 2 or 4 ohms, the aux input is suitable for using as a power amp input.

Recent tours with Primus had Les playing a Subway D-800 rig w/ Subway 112 cabinets, slaved for 1600 watts rms into 4 x 112's. I don't know what rig he is using for the new FFFB tour that's going out this spring.

Sometimes, sometimes not. It depends.

We’ve shipped a lot of these amps and haven’t seen any problems. I have no idea what the issue may be.

Probably a good example of two wrongs not making a right...

Sorry guys, that was a horrible typo. It should have been 2 ohm mode not 4 ohm.

Correct, set the amp to 2 ohm mode (NOT 4/8 ohm mode). This is covered in detail in the owner’s manual. This is why we put so much effort into the protection circuits. [edit for bad typo]

Just be sure that the shielding material is bonded to signal ground at the output jack, otherwise it can make things worse.

Does the position of the ground switch on the DI out make any difference? is the power source itself really earthed? This is by far the most common cause of noise. Just because the other amp was ok doesn’t rule this out because the internal architecture is different. Most IEC cables are molded assemblies, it’s easier to maintain safety certification under the components program.

Did you try both positions of the ground lift switch? I’m assuming that the monitor’s input is line level… is the monitor earthed? Is the amp earthed? This is important.

Since I have yet to see a bad DI in a ShuttleMax amp ever, let’s be sure it’s not something external to the amp. Set the DI to pre mode, line level, plug your bass in, be sure the mute switch is off. Check that your powered monitor is properly configured and you should have sound. No other controls on the amp will have an effect. In pre mode, the level may be a little lower than in post mode depending on how you have the amp’s controls set. Now, switch to post mode, set the eq to noon (flat), set the tone shaping filters off, select channel 1, bring the channel 1 volume control to 1:00 and slowly bring the channel 1 gain control up. You should have sound. If you don’t, can you confirm that you are using an XLR to XLR cable and that it’s properly wired? Is there a selector switch on the monitor between mic and line that might also switch the monitor’s inputs?

The position of the control is only one factor in the output power an amp delivers, but is interactive with everything else in the signal path. If you turn the bass volume down by 6dB and increase the amp’s master volume by 6dB, the amp delivers exactly the same power that it did before. This is an example of the position of the master not dictating the power that the amp delivers.

For clarification, a linear pot at 1/2 rotation is 1/2 the input voltage or 6dB of voltage attenuation which is 1/4 the power. Log pots are available in various taper rates or laws, this affects the output versus rotation curve and is part of the “user interface experience” (for lack of a better term).

Yeah, and I thought we got some rain... nothing like you guys!

Knob position has nothing to do with how much power is being delivered. This misunderstanding may be part of the problem. is the clip LED indicating input/preamp clipping or power amp clipping?

Cosmetic copy, features copy, intended to look like a Streamliner but an entirely different circuit.

Too much reading DIY service posts on the internet?

There is a line level aux in, no effects loop. The owner’s manual with block diagram is available on the website.

Since this came up on the TB forum also, let me provide the answer that I provided there. On the Pre-DI, there's a LOT more going on internally so the left to right signal flow matching the left to right feature architecture which makes more sense, otherwise every signal would have to cross over at least once and in some cases twice. This applies to both the jacks and the controls working together with the signal path rather than against it. As the gain increases (there's over 40dB of available gain), and as the number of amplification stages increases, the opportunities for noise and cross talk multiply exponentially. This is why ALL consoles and channel strips follow this format... the jacks in the same order as the controls and the controls in the same order as the signal flow for performance. This is a very quiet pedal compared with the average pedal. In another life, I designed pro audio consoles, and Genz Benz (Jeff's earlier company) started out as a pro audio company, and the designer of this product (Scott) is also a pro audio guy as well as an accomplished bass player. I was only responsible for most of the mechanical and PCB layout on this pedal. Since these are top mount jacks, it doesn't really matter from a wiring perspective as it does with side mount jacks (which I do not care for, especially) when there are more than 2 jacks).

I would suggest cleaning up the wiring and whatever crossover it’s supposed to have back to factory condition and listen to it before assuming anything. You might be pleasantly surprised.

Basic electrical engineering absolutely links voltage to power. Since (solid state) amps are generally considered an ideal voltage source, it’s also an ideal power source. While a speaker has a reactive component, when the capacitive and inductive regions are averaged out with the DCR of the speaker, the net result is an average or nominal impedance. The amp must provide voltage x current to drive this load which is power. In the inductive regions the current lags voltage and in the capacitive regions the current leads voltage. Regardless of phase angle, the amp must be able to deliver both voltage and current, this is something an experienced power amplifier designer has to deal with. A 500 watt, 4 ohm single driver compared to a 300 watt 8 ohm driver is likely to have a lower sensitivity, quite possibility 3dB lower, which would make the 8 ohm speaker (slightly) louder at 300 watts than the 4 ohm speaker at 500 watts.

Have you confirmed (beyond any doubt) that the problem is actually with the amp? I see a fair number of claimed problems end up being misdiagnosed as an amp problem when in fact it ended up being something else.

At a high enough voltage, wounds become self-cauterizing… The main tradeoff with bleeders is the loss of efficiency as voltage increases. This is an import consideration in small Switchmode power supplies meeting the EU’s eco-directive.

With the battery examples, the amount of current delivered to the load is a function of the open circuit voltage the internal resistance of the battery, and the resistance of the load (which in this case is 0 ohms). The 12V car battery has an internal resistance of about 0.02 ohms, the 9v battery has an internal resistance of ~5 ohm. It's not the capacity, but the internal resistance that limits the current. Generally, higher capacity batteries rated for higher discharge rates have lower internal resistance. The current delivered to the short circuited 12V battery would be 12V/.02 ohm = 600A The current delivered to the short circuited 9V battery would be 9V/5 ohm = 1.8A Some folks are more tolerant to getting shocked, but some are not tolerant at all. Because of this variability, the safety recommendations are absolutely valid and are also "best practice" in the service field. While bleeder resistors are required for all amps with an IEC60065 or IEC62368 safety rating, a wise and experienced service tech will ALWAYS verify that there is no voltage present before attempting service. Do you know what the biggest danger from shock is? It's either falling off of a ladder (in the power field) or getting knocked off your stool as the amp falls on you after you react to the shock. Once you have a tube amp fall on you, you may wish you were dead.

It's the voltage across the body resistance that causes the current to flow. 450 volts can easily cause enough current to flow through the body to kill (if you are moderately unlucky). The power supply has plenty of current available (>100mA) so yes, it is dangerous. Since this is a newer version (designed by Matt Wilkins, he worked under the VP of R&D at the time who was a good friend) which is safety approved to IEC 60065, there are bleeder resistors within the power supply that will safely discharge the power supply when power is removed regardless of the position of the standby switch (I verified this, it applies to all factory stock Fender Bassman 300's). This doesn't mean that the bleeders haven't been damaged, or some hack tech removed them because of some cool trick they heard about on the internet, so a professional tech will ALWAYS verify that the voltage has been discharged before doing any work. No, please don't do this, it's a common cause of additional damage to amplifiers. It's probably the quickest way to ruin a set of pots, and likely not the cause of the original problems anyway. When I was working for Fender, I saw the results of "magic cure-all spray" and is always cost the customers more (and if the amp was under warranty, this damage was not covered). The authorized service centers hated working on such amps because there was so much to clean up after.