thinman

In my job I get to see the mains voltages at various diverse locations in the UK and have seen the AC RMS voltage vary from 215v to 250v - that's a variation of 15%. Those levels can follow an expected time of day pattern, i.e. the voltage can drop during the ads in Corrie when everyone puts the kettle on and there are many short term effects, e.g. a nearby industrial user switching something on or off. So although the generated voltage may be well regulated, local cable lengths/capacities and usage can have a marked local effect. That variation in AC voltage can feed through to the power rails in your power amp as they are proportional based on the transformer. Say at full output into 8 ohms your amp outputs 50v (with 250v in ) (OK - I'm fudging this here as rail voltage is usually derived from the peak rather than RMS but the principle is the same). 50/8 = 6.25A, if the rail voltage is 15% lower (50*.85)/8 = 5.3A Power is I[sup]2[/sup]R then the difference in max power output = 225W vs 312W - probably noticeable as the overall gain would be lower. I've probably made some horrific error here but I'm sure someone will gleefully point it out!

[quote name='0175westwood29' timestamp='1349898987' post='1832081'] there seems to be quite a few around here, were you pushing the amp hard? or was it doing this at low volume? its just ive heard about ss class d power sections not liking being run at full, and no sound does sound like a output transformer, but it could just be a bad connection on the speakon connection? im sure some ppl will be along soon andy [/quote] Certainly not been run hard - my BFM cabs are very efficient - master no more than one quarter (but that's no real indication of output). I didn't want to tinker with it given it's very new and under warranty. The cutting out and back was very clean - no crackles or fading in/out - almost like some sort of overload protection was kicking in. I doubt it's anything else - I slot my other heads in-place with same bass, leads and cabs and all is well.

Are there many other EBS Reidmar owners on here? I bought one three weeks ago - love the sound but after one gig and two practices the output to the speakers started to cut out (cleanly) for 3 or 4 seconds at a time, then for longer and longer until nothing. Bit disappointed to be honest. So now I'm testing out Thomann's return service. Do they normally repair or simply exchange? Has anyone else had any problems with them?

[quote name='alexclaber' timestamp='1345204768' post='1774928'] I felt the same about my trusty Peavey combo! Phil, if you maintain (or increase) stiffness through bracing, whilst lowering mass, you raise the resonance of the panels to the point that they are no longer excited by pressure but instead excited by the backwave, and the backwave and the resulting panel emittance can be damped effectively, unlike pressure changes which you don't want to damp (as they excite the port). In the process you also reduce the backwave reflection which exits through the cone. Personally I consider panel resonance in a loudspeaker a horrible thing unless it's being used to cancel unwanted energy - the last thing I'd want is significant acoustic energy radiating from a panel, with particular consideration being given to how it screws up transient response. [/quote] I'm with Alex here - you could probably use 12mm birch or poplar ply but you will have the added complexity and marginal weight of the required bracing to eliminate any resonance. Bracing could be web-type braces and/or dowels across the height/width/depth of the cabinet. Probably still a gain over using 15mm or 18mm if done right. Just look at the construction of wooden aircraft for a bit of inspiration!

Well, finally fixed the thing. A can of freezer spray applied to the solder-side of the board showed up the problem having failed to find any component at fault. There was a solder joint to a small board at right-angles to the main board on which the preamp valve is mounted which was the culprit with output falling away when frozen. I had previously gone over these joints with the soldering iron to no avail so removed all the solder and re-did the joint. Problem gone. Still, the amp has been completely re-capped, a few IC pre-amps changed plus a failing gain pot changed. Hopefully good for a few more years as I love this amp. But then I'm contemplating getting an EBS Riedmar ...

[quote name='jackcoleby' timestamp='1339424506' post='1688215'] Oh no, I'm not pushing it hard at all. Never been past half vol. my current cab is a Marshall 410 with a max of 1200 watts. But it's 4 ohm and I want to change to 2 8ohms. Just wondering if it's safe to run with just one 8ohm for a month or so. [/quote] The position of your volume knob doesn't mean much in terms of what the amp is currently outputting - there's many factors that dictate that - the signal level out of the bass, the pre-amp gain, eq, speaker load etc.

Would it be best to approach the original question from the opposite direction? i.e. I want a better rig so I'll be completely open-minded about what's in the boxes. If you think about it logically, to decide on what size drivers you want first when really you're after a sound is rather limiting your options. It may also create you logistical problems such as transport.

Just an observation but I often see comments in threads such as this like "My XXX is putting out n Watts into my YYY cab" as though the amp's output is somehow a constant and is providing output even during silence rather than ranging from 0 Watts to whatever in proportion to the output signal. It may be the way I read some comments but on the other hand it may be a popular misconception!

Heater voltage is 6.2v and seems stable - doesn't seem much to go wrong there - it's got its own transformer winding with a pot across it. I'll double check it though. I think I'll replace the anode resistors next as they're a little difficult to get at when the valve is in to measure the voltage when powered-up. I'll try your soldering iron tip at some point too. Op-amps are NE5532 and TL08 - so very cheap.

Tried a signal into the FX return and that seems stable so that eliminates the power stage and a good chunk of the pre-amp. What would be the most likely component to be affected by temperature excluding the valve? Dry joint or resistor? There's a couple of IC op-amps in the circuit but would they behave as described? I tried measuring the anode voltage when the problem was present but a small bit of clumsiness with a probe meant I popped the 50mA fuse to the HT side so need to need to get a replacement. Knowing there's 300v knocking around there focuses the mind a little....

[quote name='BRANCINI' timestamp='1337215066' post='1657366'] I'm not familiar with this amp, but I'd start by monitoring the anode volts on the valve. Preferably while the fault is present ( pins 1 & 6 of its an ECC83 ) or as its old, even swapping the anode load resistors specially if theyre a bit discoloured. Always a good starting point, . Of course, thats assuming it is a pre amp fault. Have you tried feeding a signal into the effects return - if there is one - see if the faults still present ? [/quote] Thanks - I'll try an external pre-amp into the effects return. I have assumed it's a pre-amp problem primarily so maybe need to look wider now. I've checked the voltages across the resistors on the anodes and cathodes as the amp warmed up but didn't see them drift at all. It's difficult to tell for certain but it seems that the level drops off after hitting a note hard as though the power supply needs a bit of time to recover! However, there's no distortion or hum that I thought would go with the power supply filter caps going - just a real weakness to the sound for a bit. It's a pain to find because of the short window of time that there's a problem. I don't want to use the amp gigging because I've lost a bit of trust!

My Hughes & Kettner Bassbase 250 amp seems to be exhibiting strange behaviour after switch-on. After the initial warm-up of 20-30 seconds it seems to work OK for a couple of minutes, then has a period where the gain fluctuates considerably for a few minutes until it eventually stabilizes. At first I thought this was a fault (and it may still be) but I'm also wondering if it's just a quirk and that it needs to have warmed-up thoroughly to be stable. I've changed the valve and also all of the electrolytic caps (it must be around 20 years old), re-soldered most of the PCB joints but to no avail. I'm yet to go through the other components. Has anyone else experienced similar strange valve amp behaviour?

I had a similar problem which was down to the springy bit on the socket (that connects to the tip of the plug) being close against the cut-out in the body. This meant it had very limited distance to move making it more difficult to get the plug in and out and sometimes pushing the plug out a bit. The solution was to rotate it by about 90 degrees.

[quote name='stevie' timestamp='1336908153' post='1652539'] I'm not sure what context you're referring to. You quoted Bill Fitzmaurice as saying the results of mixing cabs are unpredictable. By the way, Bill Fitzmaurice is on record as saying you should never mix cabs *period*. [/quote] The context that in the real world most people are not going to be able to perform the tests/measurements that you claim are "child's play". Short of performing any measurements I'm purely taking the view that sticking to identical drivers will be more predictable than mixing when making choices on listening alone. I don't have a full history of everything Bill has ever said but obviously he has strong opinions, usually backed by sound reason. If you have specifics that you disagree with in his approaches then, keeping the personalities out of it, I'm interested to hear the technicalities in an attempt to understand the different points of view.

I'd say try and borrow anything you're considering and try before you buy. I don't disagree with any of the other comments but mics can be quite a personal choice in my experience.

[quote name='stevie' timestamp='1336771099' post='1650991'] Bill Fitzmaurice is wrong. The results are perfectly predictable. They are quite easy to calculate, easy to measure (if you have the gear) and easy to predict if you have enough experience. Compared with calculating the performance of a modern stadium line array system, calculating the performance of a 1x15 and a 1x 12, or whatever combination of bass cabs you may care to mention, is child's play. [/quote] Child's play? Yes, we all do it every time we but a cab don't we? Technically, of course you are correct, but you've taken what I stated/quoted wildly out of context - I'm referring to the more common experience of putting cabs together and seeing what they sound like rather than treating it as a scientific exercise with the required knowledge and facilities.

Quite amused to find "mute" under the effects section! One for the purists...

[quote name='stevie' timestamp='1336760331' post='1650760'] That claim is normally made by people who have done it. It may not be the whole truth, but at least it's based on practical experience. On the other hand, those talking about dispersion, mixing drivers, matching motors etc. are generally parroting what they've heard. So why are Fender Twins better on their end? [/quote] Out of fairness to what I know Bill FItzmaurice has said, it is not that mixing drivers is guaranteed to be bad , it's that the results are [u]unpredictable[/u], i.e. it could, by luck and for some, yield good results, or at least results that the listener is happy with. On the other hand, if you're not lucky, it may not be as good with sticking with something that has some science behind it. I have a suspicion that in some cases where someone had, say a 2 x 10", and felt they needed something extra, that they don't often consider adding more of the same as intuition might imply that you're just going to get the same sound but louder, whereas something different like an 1 x 15" might add a new dimension. In reality more of the same can do that too but I wonder if all options were actually tried. Also, I suspect we hear most from those where their luck was in! Personally, I'm of the view that if the user is happy with it then that's good - but I like to attempt to understand some of the science too as it helps eliminate some unknowns and risk. Some on this forum have an excellent understanding of the science (the Bills and Alexes) , many more have a reasonable grasp of the basics too - I don't think too many just parrot it as there are rational explanations available - it's science, not religion.

This is where I saw the comment: [url="http://www.jamirotalk.net/interviews/paul.html"]http://www.jamirotalk.net/interviews/paul.html[/url]

Probably been asked already but I was reading an interview with Paul Turner (rather excellent Jamiroquai bassist) and he said that he didn't like 5 strings because he thought the tone of the E wasn't as good as on a 4-string. Is that a widely held view?

Would a stand be cheaper than another cab? A third cab seems like an expensive way of gaining a bit of height or angle.

[quote name='chris_b' timestamp='1336520613' post='1647083'] Just an observation; most of the rock and roll world has never heard of Bill Fitzmaurice, and is doing fine. [/quote] Miaow! Not sure what point you're trying to make here.

Just to complicate matters the cab rating won't guarantee that you'll know which will fart out first - the wattage is thermal rating, i.e. how much power before you melt the coil. It's other factors that determine when you get farting such as the cabinet design and the maximum excursion (i.e. how much range of movement back and forth it has) of the driver. It's quite possible that the higher-rated cab could break up sound-wise first depending on the driver and cab and this often happens at power levels way short of the driver maximum power rating. I remember seeing some testing and figures on Bill Fitzmaurice's site stating that it's not unusual for a cab with a 400W (thermal) rating could easily start farting at about 120W of input. So, go by your ears!

I thought I'd have a go at answering the original question... As previously pointed out if a speaker was producing a simple sine wave then the cone would move back and forth smoothly at the wave's frequency. If it is having to produce a complex wave, say the result of two sine waves of different frequencies, the form might look like the lower frequency but with ripples on it of the higher frequency. The cone will therefore follow the shape of that wave - in general moving back and forth at the lower frequency but rather than smoothly it will be making much smaller back and forth movements at the higher frequency. As I understand it that is what makes speakers imperfect (but not impracticably so) because the above behaviour introduces Doppler distortion. (The effect of a fire engine's horn apparently changing pitch as it passes you). Imagine the cone is the fire engine and its horn the higher frequency - the fact the higher frequency is being produced by something that is itself moving.

I suspect the preamp valve in my H&K is going - after switch-on there's a period when the amp behaves like someone is turning the gain up and down - the volume increases and decreases smoothly before eventually stabilizing. Has anyone experienced this - could it be something like the valve heaters failing? I read about valves going microphonic or noisy but not this. I've ordered a replacement anyway.