agedhorse

It should be noted that different manufacturers might have different definitions of presence also, so what may be obvious on one amp bay not follow intuitively on all amps that label a control or switch "presence".

Tha bass guitar in the lowest octave produces less than 50% fundamental, the rest of the sound is harmonic series of the fundamental. Position of the pickup in relation to the bridge changes the percentages of the various harmonics (and the percentage of the fundamental in the total), as does the type of string, their material, the position of the strings with respect to the pole pieces (or magnetic fields), it goes on and on. A bass that just played fundamentals would sound very much like a sine wave generator (which is what it would be).

Be careful swapping fans to be sure the characteristics match what the designer intended. the is ESPECIALLY true on amps that have variable speed fan control circuitry. These circuits and the fans must track for the cooling to be the same.

This wouldn't be SOAR protection (in the classic or traditional sense of the approach), SOAR doesn't track temperature, the limits need to be calculated and designed around the design thermal limit. There are some unique thermal limiting circuits, a particularly effective (but very intrusive) one is a combination of SOAR with the addition of thermal feedback that operates on almost a cycle by cycle basis at low frequencies developed by National Semiconductor called SPiKe, (Self Peak Instantaneous Temperature Ke ), the Ke is an abbreviation for a thermal element in the equation algorithm. It was used on some integrated amplifier IC's. It is a way of decreasing the current limit as temperature of the die increases. It's purely a protection mechanism, it induces nasty current clipping into a reactive load. There are other approaches too, some of which feed back thermal information that lowers the threshold of a more conventional limiter circuit, and some that (in the case of an SMPS) feed back thermal information that will reduce the main supply rail voltages. The limiter approach is pretty common with class D amps, especially those using DSP because it can all be integrated in software. Another approach that many lateral MOSFET amps use is the natural behavior of the device itself, where as the current through the device (and the temperature of the device) increases, Vgs also increases which reduces the rated power that's possible. This is a VERY complicated subject with a LOT of highly technical details and math involved to make it work well. The simpler it appears, the more difficult it actually is in practice.

I was just pointing out WHY fan cooling often becomes the better choice if the size of the amp has anything to do with your choice for an amp.

The problem with passive cooling as the power levels increase is that the size of the amp will grow to accommodate the space needed for passive cooling compared with fan assisted cooling. I have designed amps with both types of cooling and I know firsthand the challenges involved.

Agreed, fans don't have to be loud to be effective.

Some players find the need to use an amp for multiple applications (including practicing alone).

There is always the chance that the AC mains could fail too, resulting in the amp stopping at a gig. Putting things like this in their proper perspective helps identify real problems versus perceived problems IME.

Virtually no difference IME.

As long as the noise from the fan is REASONABLE, but Paul, you know my feelings on what real world reasonable are. Everybody has a different take on what's reasonable.

You might be surprised

Beware that the fan's voltage, current, CFM and static pressure ratings need to be very close on any fan that uses feedback speed control. These parameters are an important part of how well the fan speed tracks temperature. It's possible to really screw things up by focusing on the quietest fan, resulting in an amp that will either shut down (if you are lucky) or fail (if you are unlucky).

As power levels increase and size decreases, fan cooling becomes more and more necessary. This is something that the pro audio industry has dealt with for decades. There are good implementations with fans and poor implementations with fans, noise level being the most objectionable issues. Fan cooled amps do not need to be noisy.

That's how that designer chooses to do it, in general it's the exception to the rule. It's no easier or harder to do it pre or post gain control, it's purely the designer's choice, which may relate to what else (voicing filters, effects loops, etc.) they may wish to include in the pre-eq signal path. I'm just suggesting that most choose to take the signal post input buffer and pre gain stage. If it's an issue to have the signal pre or post gain stage, it's good to know this before buying the amp.

It it's switchable, then in the pre-eq position it will almost always be BEFORE the gain control, not after.

Which one is this?

This is generally correct, gain is gain as far as gain before feedback is concerned.

For post-eq DI, that would be always after the preamp. For MOST pre eq-DI's it's before the gain stage. Of course there can be exceptions, but my experience it's about 95% give or take.

On most amps, this is unlikely to be much of an issue unless the gain is really low. Also, if you take the DI pre eq, most amps pick off the signal pre gain control, so this won't be an issue at all. This could only be an issue using a post eq DI out.

Probably not.

If you are hearing "fur" or distortion, then you are clipping something in the preamp. Turn the gain down a bit and you will be fine. Noise is independent of power amp topology or class. Designs (at least many) have gotten better in this regard.

It says the same thing about high impedance pickups running into low impedance inputs. Guitar/bass amps generally don't have low impedance inputs anyway - unless they have a line input which is typically only 20kohm or so. Both hi/lo level/sensitivity inputs on amps tend to be at least 500kohm (high impedance) or so, so there won't be a problem. Actually, this is only sometimes the case. Depending on the design, it's not uncommon for an active input to have a lower input impedance of say 50k while a passive input may have an input impedance of 1Meg. This is often the reason why many players view the active input as a "tone suck", not because of the lower sensitivity but because of the lower input impedance (especially an issue when using both with passive pickups).

Yes, the fans all in the Subway amps are MUCH quieter, almost silent.

Agreed. To this point, much effort was put into making the controls of the Subway line more intuitive.