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Everything posted by 6v6

  1. Great tip re template making, thanks! I spent an entire afternoon trying to make the body template from a cover template using different diameter straight bits and different size guide bushes, which works but is far more error prone than this approach I suspect.
  2. [quote name='Danuman' timestamp='1499033076' post='3328770'] My ideal travel/practice/mixer-upper package would be a regular LMIII with aux in/headphone out. [/quote] +1 and a built in tuner
  3. [quote name='Root45' timestamp='1493042700' post='3285107'] Nitro is available in aerosols, and is not difficult to do. [/quote] I've done a couple and it's definitely do-able, but I'd personally say it is quite difficult and very time consuming to get a good finish, particularly for refinishes where you invariably miss some tiny damage before laying down the primer and end up sanding it all off again (don't ask my how I know this, gah!) The materials are also quite expensive, and unless you have a spray-booth it's very weather dependent as you can't really spray in very cold or wet weather and get good results.
  4. Interesting, will be following this! I also have a cupboard full of tube amps and parts, been meaning to make a bass preamp for a while now so will be interested to see this thread develop
  5. I've found that an efficient 1x12 is adequate in a 4 piece blues/rock outfit, fwiw, obviously not all cabs are the same but there's plenty that claim good efficiency nowadays (mine is similar to the basschat v1 Diy design) If the cab starts to struggle (only happened a couple of times in 4 years) it invariably means the stage volume is too high, and in these circumstances audience members report that they can no longer hear the (normally not micd except kick) drums clearly. If the drums are micd in a bigger venue you can just Di the bass to get some extra projection through the pa, so you still don't really need a huge pile of speakers - the stage sound should remain pretty constant regardless of venue size, the pa just gets bigger (which would include more monitoring on big stages, but I just make do in pub gigs by putting my cab near the drummer so he can hear it clearly).
  6. [quote name='Passinwind' timestamp='1492766399' post='3282973'] I'll go out on a limb and guess that at least 90% of current production ones do not used starved plate mode. [/quote] That is my impression too, and I've been studying various guitar and bass amp schematics for years. Admittedly there aren't that many hybrid bass amp schematics available, particularly for the newer class D stuff, but think about it from an amp designers point of view - what's easier, copy/paste one of a few classic and well understood tube preamp circuits and specify one extra winding on your transformer, or mess around trying to make a tube circuit sound good running tubes outside their normal operating range? Unless you're running stuff on batteries it's a no-brainer IMO (yes, I'm an engineer, and yes I am lazy! ) The facts are out there in the schematics that are available, I've not found a any that show a mains powered amp running tubes at weirdly low "starved plate" voltages, but I'd be happy to study such a diagram if one exists.
  7. [quote name='sratas' timestamp='1492758276' post='3282881'] Thanks passinwind, but I don't want to begin to study the matter. I would like to obtain simple answers. For example: is there a solid reason to have a 300 v tube pre from a listener or player point of view? If the answer is yes, those reasons apply only if the pre is pushed or even if it is used clean? If not, there are examples of starved plate designs in so called all tube monsters, like the SVT, orange AD 200 etc.? Thanks for your attention [/quote] Respectfully, I feel like the whole starved plate thing is/was an unquantifiable tangent, there's a broad range of valid operating voltages for typical tubes, same as with most analog electronic components. And even so many (most?) bass/guitar amps are derived from the same circuits and run the tubes at what I would consider pretty normal voltages (as Passinwind has already alluded to, there are standard techniques to calculate the operating point of the tube, and there is no "full voltage" mode of operation). In battery powered pedals (and possibly a few amps, but I'm not aware of any) things get a little less clear - folks sometimes run tubes at abnormally low voltages, and IMHO this is mostly a marketing strategy (folks see a glowing tube and are prepared to pay more), but I'm sure there are a few examples of properly designed circuits deliberately using tubes outside of their normal operating range, it's just not a common thing, and none of the classic amps circuits I'm aware of do it.
  8. Fwiw my attempt at simplification is that plate voltage doesn't define the sound of a properly designed amp. Mostly it's about the combined frequency response of each stage of the amp, and in some cases how that response changes when pushed into saturation.
  9. [quote name='sratas' timestamp='1492356608' post='3279631'] Regarding high voltage and that tube driven mosfets in the WA back end, this is what the Mesa engineer "agedhorse" answered when I asked those features in a contemporary thread on Talkbass: "The B+ supply is somewhere around 300V. Power supply voltage is only a small factor as it is entirely possible to design a preamp operating at a lower voltage that sounds virtually identical. There are many other, more important factors involved. The second tube provides the direct gate drive of the mosfets. It's a combination PI/driver with voltage and current gain. It's a unique application of MOSFET technology." [/quote] That is interesting, in that the schematic shows the tube in the preamp is basically just a standard Fender style preamp stage, with some fixed resistors for the tone controls (EQ is then handled via an op-amp based stage after the preamp), and it seems to indicate they voiced the driver stage a particular way. So although "unique" is arguably questionable related to any aspect of amp design, it may well be this is an important and characteristic part of the amp topology, and it is a little different from the more typical approach of a Fender style tube preamp feeding an all solid state power-amp stage.
  10. [quote name='sratas' timestamp='1491903283' post='3276253'] The walkabout has a 12ax7 in the gain stage and another one destined to drive the mosfets. Please do not expect I can give you detailed engineering data or explanations, but according to the Mesa people and the knowkedge available on other boards about the WA (mega thread on talkbass), it seems that the m-pulse technology was conceived this way to fill the behavioral gap between full tube and hybrid. I can testify they built something special with that proprietary circuit. [/quote] There are schematics available on the internet, nothing that special in there, it's a hybrid of tubes and cheap op amps in the preamp with a pretty standard solid state power amp. Not saying it's not a nice amp (I've played one and enjoyed it) but there's no proprietary magic in there imo, it's just one of the better (albeit overpriced in the UK) traditional hybrid amps.
  11. Like with a car, the cost depends on why are you getting a service and what needs to be done. Unlike a car, solid state amps at least have very few serviceable components, so I'd ensure you actually need work doing before handing over cash.
  12. [quote name='stevie' timestamp='1490950284' post='3269264'] I'll give it a go. I've just tried three other highly recommended drawing programs, but they're not as intuitive to use as Paint. I just need a copy-and-past feature so that I don't have to draw everything from scratch, and the ability to save text as text, so that I can edit rather than erasing and re-writing. [/quote] For simple diagrams I use Google draw: https://docs.google.com/drawings/ It doesn't have schematic symbols, but it works well for basic layout diagrams.
  13. I do a lot of Linux stuff in my day-job (although mostly on the development/architecture side not production level system administration) but feel free to PM and I'll do my best to help.
  14. I think this is pretty common, for example markbass sell the blackline 250 which is basically the same as a little mark 3 but the latter is twice the price for a different power amp and a yellow box. I'm not sure it's really justified by production costs, but entry level gear has to be cheap or it won't sell, and the more powerful models are generally what you need if you gig regularly so what do you do?
  15. The diagrams do look much clearer, thanks! One very minor observation - in the LF schematic there's only R1 shown not the parallel R1/R2 shown in the layout and parts list. I've been having a play spice modelling these in an effort to understand the frequency/phase response better (I'm a novice when it comes to crossover design but once studied the basic principles, many years ago!) Currently not quite sure the best way to model the electrical characteristics of the drivers (I assume an inductor/resistor but I'm unfamiliar with exactly how to approach specifying this). Modelling the LCR networks is simple enough though so I've started with that. Happy to share the results for discussion here if such reverse-engineering & analysis is OK by stevie
  16. I've got a Lm3 and never noticed any fan noise tbh, I do mostly use it in a band though. I can try to measure the volume in a home environment later.
  17. It's a real personal taste thing, but FWIW I'd perhaps go all gold on the tuners without any black, as there's already a lot of different wood colours etc going on, so I think it might look a bit cleaner and draw more attention to the wood?
  18. I'm interested and planning to build one of these, crossover details would be great as I've not had time to try modelling it (was planning to have a play in LTspice but an overview would be most helpful, my EE skills are rusty!). FWIW I think the question about combining Mk1 and Mk2 cabs was a good one, and I appreciate the clarification as I was wondering the same thing.
  19. Bad luck about the speaker, I guess it's worth trying to repair but given where the damage is I'd probably chalk it up to experience and find somewhere to re-cone it. The spacer looks saveable to me? Even if the holes are a bit oversized the tee nuts should end up squashed tight against the wood, you can screw them in with a screw and washer (to avoid damaging the speaker) then do them up tight (I'd use a drill/driver as it may be hard to do by hand). You could even put some sealant around each tee nut if you're still worried air will leak, and add some gasket tape between the speaker and the spacer to improve the seal? Good luck!
  20. Nice diagram and detailed design, great work folks, thanks! I think I'm going to have to build one of these to see how it compares to my current SM212 loaded cabinet My SM212 is from early 2013 - was there a spec change for newer drivers? I seem to recall something about that, so wondering if I'm better getting a new one for this build, or can I safely switch the existing driver between cabinets?
  21. My 70s Strat has the serial number under the logo on the headstock, and I can only think of one reason anyone would remove that...
  22. Honestly I think any of the jointing methods will be OK unless the cab is abused - I used biscuit joints on my build primarily because it makes it far easier to align the panels vs plain butt joints (although the cleats to reinforce the joint Phil suggests would also be a simple way to do that without any special tools). I agree dowels/biscuits on a lot of low-quality ply is a bad idea (the core is often full of voids and very weak), but if you make the effort to find good quality void-free birch ply it'll probably work fine with any of the methods mentioned, particularly when you consider the strength added by securely attaching (ideally glueing) the back of the cab and the baffle.
  23. Can you link the circuit diagram you're working from? Hard to comment on the component removal without seeing a schematic but it sounds like the capacitor was part of the tone stack, I'd expect to replace it with a different value vs just removing it.
  24. Interesting build! I think covering the cavities and making them airtight will be enough to fight feedback (thinking of an acoustic guitar soundhole bung which works by sealing the cavity not filling it) but I doubt foam inside would do any harm
  25. [quote name='T-Bay' timestamp='1484256062' post='3214172'] Sadly eBay is full of complete and utter morons these days. [/quote] This - I've given up selling anything on eBay because every other transaction turns into a fiasco like this. Good luck in resolving it!
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