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agedhorse

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Everything posted by agedhorse

  1. This is accurate as far as transients are concerned, but ignores the fact that as you limit the peak amplitude, this allows for an increase in average power. For example, a reduction of 3dB of transients allows for a 3dB increase in average power. The ear perceives average power as loudness. This is one reason why tube amps appear to sound louder than their power might suggest, and also one reason why compression is so useful. With an increase in average power, the risk to the speaker transitions from mechanical to thermal assuming there is an effective HPF involved.
  2. Then why did you bother asking this question if you already knew the answer you wanted to believe? There’s a lot to learn from the answers and comments that were made my members here and on TB, it appears you have missed the essence of this information.
  3. IF the cabinet tuning resulted in the same curve shape (translated to filter terms this would be Q and slope) than the red trace has the potential to provide better performance with both tuned to slightly under critically damped. Now the elephant in the room is what the relative sensitivities are between those two drivers (which would be the gain term of the filter equation). Is the red driver significantly lower sensitivity than the green driver by chance?
  4. Have you looked at the comprehensive answers and information given to you over at your same thread at TB???
  5. Kind of yes and no. Whenever the conduction angle of each side of the push-pull pair is greater than 180 degrees, as some low level of signal one half will be sourcing current while the other half will be sinking current throughout the full waveform, and technically that's class A. BUT, often the distortion can be worse because the handoff from the positive to negative half may not have the identical curve shape so the distortion can actually increase where these curves overlap and under this condition it's possible for class B (if the ends of the curves just meet) can have "better" (lower) distortion characteristics. This is something that Doug Self did a lot of research on maybe 20-25 years ago. The challenge is that the bias point at 100Hz may be different than at 10kHz, therefore a happy medium must be arrived at, usually that ends up slightly over biased at low frequencies for adequate bias at higher frequencies. In practice though, this is of no consequence.
  6. Proper class B has almost no crossover distortion, but the challenge is to keep the bias conduction angle the same across the entire audio spectrum. At higher audio frequencies, sometimes additional bias is necessary to insure no crossover distortion which leads to more than enough bias at lower audio frequencies. This is an example of why often a single bias value is not adequate, and by biasing slightly into class AB at DC (and lower audio frequencies) to be sure that the operation at higher audio frequencies is adequate for at least class B operation.
  7. Both class G and Class H have multiple rails (can be either 2 or 3 tiers), both operate as class B/AB until approaching the rails at which point either the lower rail hands off to the higher rail or the signal hands modulated the higher rail into the lower rail. They can in fact have terrible distortion issues if the rail handoff (called commutation) is not done well. the terminology of class G and H are interchanged in definition depending on where in the world you are located. In the US, class H commutates the rails, class g commutates the signal tier. Class D amps do not have the distortion issues that you claim, you may not be happy with your class d amps, but not for the reasons you state because the distortion numbers are very close between good class d and good class AB/G/H.
  8. Perhaps I can help you understand why some designers choose to use a fan? Neither of the amps you listed are rated for 2 ohm operation, and neither are rated for as much power (RMS) either. When considering cooling strategies, my general goals (and others with similar philosophy) might choose to insure that their products are capable of operating at a higher duty cycle into a lower minimum impedance at higher ambient temperatures (I typically use 105 deg F) than other designers might choose to use. Also, the warranty offered often factor into the decision. The companies I have designed for over the years have offered longer than average, which predisposes me to a more conservative approach. I do work hard to minimize fan noise, but a small amount will always be present. If a fan bothers you enough, simply choose an amp without a fan and accept those compromises compared with the compromises of using a fan (noise)
  9. Assuming that no new damage is created. That's another topic, but I see folks try to do this kind of repair and damage otherwise perfectly good PCBs because they don't have the proper tools or experience to work on double sided PCBs (the norm now).
  10. Generally, IF THE POT HAS NOT BEEN CLEANED WITH "MIRACLE CURE-ALL" CLEANER, dust is not a problem with the rotary pots. What can be a problem is microscopic insulating layers of oxides and sulfides that are angstroms thick, just thick enough to inhibit reliable contact with the fingers of the pot's wiper element. DeOxit D-5 in particular is quite effective on this without damaging the conductive element (especially at the terminal rivets), but liberally applied will wash the lubricants from around the bushing onto the conductive track which will attract abrasive debris and grind the track and fingers into oblivion. Other substances can do this as well, but also damage the conductive surface, making it MUCH more vulnerable to wear. Some techs refer to such substances as "disaster in a can", because when they work on amps that have been serviced this way, they often can become disasters. A full set of pots on some amps can push the cost of repair beyond the realistic market value of the amp.
  11. If it's the can that comes with the small removable tube that sticks directly into the nozzle it's not to bad, but the new style with the swivel is a real pain and you have to have just the right touch. Also, NEVER spray down the shaft (no matter what you might have seen on the internet). That's a quick way to ruin a complete set of pots as it washes the bushing lube everywhere it doesn't belong. I see units with spray residue all over the PCBs, and this attracts little conductive bits that then provide leakage paths. This is especially true on circuits with very high voltages and also very high impedances. Once this happens, the PCB must be removed and washed in an approved solvent to remove the oily residues. Then the usual production wash in a saponifier with a DI or distilled water rinse and mild temperature (like 120-130 deg F) bake dry. Pots and switches (and anything that can't be washed in production after wave soldering) must be protected. Different parts have different requirements, which is why I try to avoid this and when it happens it's costly to remedy because it takes a lot of time to do right. In my shop where I still service Genz Benz products, I know what parts are safe to wash and what aren't, but even then it adds between 30 minutes and an hour to a repair. It's one reason why I discourage DIY repairs, they are MUCH harder to correct and repair right. The other reason is that we have to examine the amp closely for any additional, hidden repairs that may jeopardize reliability in the future. Everything that goes through our shop carries a 90 day service warranty and I don't want to see any repairs back because I missed something. Generally I can keep it to one or less service re-work per year because of this policy. Hope this helps.
  12. Yes, often "not cheap" goes along with very good. A little bit goes a very long way.
  13. Use the TINIEST amount of cleaner, less is more in this case. In the US, DeOxit D-5 is the only substance that I have tested extensively with no long term (over 20 years) issues. I do see a lot of pots for units in for service that were cleaned with a variety of "miracle cure-all sprays" that have subsequently become ruined (either from the product, or from over-application which washes incompatible lubricants into places that causes additional damage). I do not know if there are equivalent products across the pond, but based on what I have seen acceptable products are few and far between.
  14. When using the FET channel, there should be a delay of about 3 - 4 seconds.
  15. I can pretty much guarantee that it has nothing whatsoever to do with capacitors (regardless of all the bad advice on the internet). In 12 years, I have never seen a bad cap on a ShuttleMax and I handle all the factory service/support for North America. By any chance do you have the amp set for the tube channel only, and you are waiting for the tube to warm up? That's about the right time for this to happen.
  16. For those wondering why all manufacturers are experiencing delays, here are a couple of good shipping industry articles that outline the specific issues being encountered, and why: https://www.hellenicshippingnews.com/will-container-shipping-reliability-come-back/ https://theloadstar.com/blanked-sailings-and-covid-19-bounce-back-bring-new-congestion-at-ports/ What we are seeing more shipments (both inbound to us outbound to Europe) being delayed for a variety of reasons, but primarily from canceled sailings where the shipping line simply eliminates a ship's trip and consolidates those containers on a later shipment. Since ships do not leave every day, and in fact they can leave every other week between some ports, resulting in accumulated delays if two trips get canceled back to back. This makes predicting anything related to delivery more and more difficult (and frustrating to everybody concerned, including us).
  17. Here's another review of the TT-800, comes from a player perspective: https://bassmusicianmagazine.com/2020/10/review-mesa-boogie-subway-tt-800-bass-amplifier/
  18. Steve - I'm sorry. I shouldn't have said "your" amp because there's no way for me to know which particular amp you might end up with. I should have said "amps destined for Europe". My appologies.
  19. This could certainly be part of it, though I have heard from players in the EU who have received their Subway amps (including a few TT's) so it's possible that a limited number of amps from earlier shipments were already sold. Just because a shipment enters the country doesn't mean that it hasn't been sold to another customer who was already waiting, I don't know how dealers manage waiting lists. I don't have this information, and it's not really my area. I am trying my best to be helpful and provide honest, transparent information. Obviously I am sometimes wrong or miss an important detail, but I can assure you that it's not intentional on any level. I do understand everybody's disappointment, really.
  20. I don't know what may have happened or why such delay, though there are constant shipping issues with inland freight at both ends, at the ports, on the water through customs and in destination transportation. I'm not making excuses, and I am truly sorry for your experience. I really do understand and appreciate your frustration.
  21. There are many ways to skin a cat, what is critical is understanding the difference between real performance and marketing performance. There are also plenty of companies/designers that did not understand how the ratings were derived and how the protection schemes were mapped to the various performance parameters, so in order to keep their products from shutting down (or failing), some chose to derate the modules in order to make them work. This is true of several of the modules, where there are different levels of performance depending on the amount of engineering that a company was willing to invest. Regarding the 250ASX2, there is a lot of hidden additional performance available provided the designer understands the intricacies of the part. I actually have a patent on some aspects of this as it relates to this part and it's based on close to 20 years of historical hands on design experience with IcePower products going back to some touring pro audio products I designed or consulted on. The more you know about a subject like this, the more you realize that you don't know... and the more interesting it becomes.
  22. Their implementation is different than most others IME. It's just how they chose to use that part. There is also a lot more to the IcePower specs than what's published, in fact most of the important information about the module resides between the lines, and requires a lot of experience to exploit safely, with high reliability.
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