agedhorse

I thought I would let this play itself out, see what kind of armchair (or chesterfield) suggestions bubbled out of the primordial ooze. In the hundreds of these amps I have serviced and supported world wide (out of tens of thousands built), I have seen exactly 2 cold (dry) solder joints. Why is this? Because the flus chemistry and solder alloy used, combined with the double sided PCBs with plated holes, this is the most reliable way to build an amp, backed up by a matching history of less than 1 ppm wave solder joint failure. That’s probably the last place to look. Unless you are familiar with proper safety procedures, don’t go poking around with anything inside an amp. Now, when you say the noise in unaffected by the volume knob, WHICH volume knob… there are 2 channel volume controls and a master volume control. Does the noise change when you tap on the chassis? You can leave the cover on for this. dies the noise go away when you plug a 1/4” (6.35mm) plug into any of the 3 effects returns? by doing this, you can eliminate 1/4 of the amp at each step without even opening the amp up. Do not spray anything, anywhere in the amp, that just makes things more expensive down the road.

Great post Phil. I have read engineering articles about the use of bamboo alone and in conjunction with conventional wood in compression laminated beams of various cross sections. The results were promising, especially for longer spans. I don’t think the weight saving alone makes it a structurally beneficial material for a plywood substitute, but possible as a face lamination for its surface properties.

I looked at the "Natural fiber" promotion and immediately thought what a good advert campaign this would make for a laxitive... combine with heavy bass guitar and things are guaranteed to move right along

Agreed. Due to our size, we obviously have a significant system in place to track both the source and composition of the woods used in cabinet construction, in many cases this is not true and you get what you get (buyer beware). We use so much of these products that it's also in our interest to be sure that we are receiving what we are paying for. CNC grade materials have different composition tolerances, the core plies are more uniform and the face plies have a guaranteed minimum thickness. The plies are usually thinner and there are more of them too, resulting in less warp and twist. For high volume precision production, this is critical because the reference for the cutter is off of the top surface of the material and if the thickness varies, this affects the depths of dados and rabbits, plus any other joints (like lock-miters) the cabinet may employ. The cabinet shop can go through more than a hundred (4' x 8' equiv.) sheets of plywood in a single day, it's not practical to struggle with pieces that don't quite fit together. The advantage of CNC grades is uniformity (thickness, glue lines and lack of voids), the primary disadvantage is cost... but the end result is that it costs less to assemble and finish using CNC grade so in the end the cabinet is a much better product for not much more money. The accuracy for CNC parts milled in production is typically between +/- 1/64" and +/- 1/32" resulting in cabinets that have tight, square joints. As you can guess, for the finger joints used in some of our natural finish guitar cabinets, this is essential or the parts simply won't go together. Here's an video that shows cabinet production:

I've used a large amount (tens of thousands of board-feet) Italian Poplar (CNC grade mostly) for many years, haven't had any issues with softness or structural properties.

To be clear, most Italian Poplar is FSC certified: https://fsc.org/en/newsfeed/fsc-italy-publishes-national-forest-stewardship-standard

This is SOMETIMES done on pro audio amps specifically for bi-amp applications, it's important to recognize when this is done (it's always specified on the back panel legend around the jack) It's not a good idea for general bass guitar applications, a few manufacturers do stupid (non-conforming) things with pin 2+/-, and there are also (just) a couple of manufacturers that use NL2 jacks which will not accept an NL4 plug. The NL2 or NL4 splitter cable is the best solution for this with no downside (other than if you forget your cable)

I see a fair number of problems caused by knock-off Chinese SpeakOn plugs. Sometimes they can damage the mating jack, resulting in costly repairs.

Heavily weighted with lead perhaps?

Yup, and assuming that the comparison results using A weighting are "good enough" can result in incorrect, inaccurate (by a mile) conclusions. When somebody bases their opinions as "fact" because of meaningless data, yet they believe with all their hearts that it's uncontroversially true, that's getting awfully close to the definition of blind faith IME.

I don't recommend it, the tuning is quite different on the Walkabout. If you do try it, de-rate the Subway driver to about 250-300 watts RMS or you could damage it.

Yes, and many of these parts are becoming difficult (or impossible) to source because the manufacturers are discontinuing them. 4 ohms is what I would recommend as a safe minimum load.

No, it’s real world performance definition specifications. The old way of defining Xmax would often result in THD numbers even greater. There are also speakers designed for increased THD numbers (and specific ~ratios of the harmonics) for coloration or texture purposes. This is seen sometimes in the bass world (think older Ampeg SVT 10” drivers) but also very often in the guitar world). Regarding amps, you might be surprised at the THD numbers that are generated within the preamps of many popular bass amps, 5% is common, and when overdrive effects are used, that number can quickly jump to over 20%. How an amp is used should go hand in hand with how it’s specified.

Very early on, they were ok at 2 ohms but we had a difficult time getting consistent MOSFETs and through 2 changes of manufacturer it became obvious that they were struggling with the process as well. This resulted in higher than acceptable failure rates into 2 ohms, so we discontinued the 2 ohm acceptable rating. Because these amps are quite expensive to repair (and difficult to get parts) , I would not recommend 2 ohm operation on any of the MOSFET amps. The Subway amps however, are fine with 2 ohms, using the 2 ohm mode switch on the back.

In a bass/guitar amp, depending on the player’s gain structure and intent, a great deal of design effort is placed on the non-line as aspects of the amplification. This means intentionally developing distortion components (spectrum of fundamental to the multiple harmonics), alterations to the dynamic response transfer function, and how entering into and out of these non-linear regions is handled by the design elements. This makes specifying power versus THD difficult because there are multiple curves overlapped that describe this behavior. Good designs sound good to players and delivers the required power under the conditions each player uses.

Some in fact do.

Marketing departments certainly like this, but apparently many players do feel that an amp's more powerful that way too. As players mature, they tend to grasp the benefit of linearizing the rotation and scaling of the range of the control though.

A simplistic explanation wouldn’t be accurate. It IS complicated.

Go with your gut then.

Yes, but for bass guitar especially, the mid characteristics and sensitivity are very important also. There is a tradeoff between raw power handling (including both thermal and mechanical) and sensitivity, mid extension, cost, and often there is a need for a larger enclosure size. With the number of players that would be ok with these tradeoffs being quite low, it's not really all that viable (IME anyway) for a commercial product. At this point, 400 watts RMS at low frequencies (say down to 40Hz) appears to be about the sweet spot. If you were to take such a driver and high pass the signal to 50Hz, than the same driver might be ok to 500W RMS, but that's a mighty bold assumption for a manufacturer responsible for warrantying their speaker to make with confidence that it won't come back to bite them in the butt (bum). Being wrong on such an assumption could result in extraordinarily high warranty costs.

I would add that your experience is quite unlucky compared with industry statistics.

There is no problem designing for 2 ohm operation with identical reliability to an amp with 4 ohm minimum load operation. In amps I have designed, the reliability statistics fully support this. There are many different protection schemes depending on the type and class of amp. These protection schemes include: - AC line over-voltage protection - AC line under-voltage protection - power amp thermal protection - power supply thermal protection -output stage over-current protection - output stage leading phase angle protection (illegal capacitve load) - DC offset protection - power supply over-current protection - excessive HF content protection - short cycle inrush current protection Some amps have many of these protections, some have just a few. There is substantial cost (and design effort) to these but when you can reduce the failure rates to almost zero by including them, in general it's a good choice.

Unfortunately, there’s little marketing value, but it does save massive costs to both the manufacturer and the player.

Most do have protection circuits, but it's important to recognize that protection circuits are not 100% effective against all faults and all fault conditions. Different designers and different companies place different amounts of importance on protection circuits since they add to the cost of the design while being almost impossible to market as a valuable feature to the majority of customers.

This may be your own personal experience with limited brands or models, but my experience is that this is not true in general.