AlanP2008

[quote name='redstriper' post='734685' date='Feb 4 2010, 02:13 AM']I feel a bit daft posting this but.............. <snip> I have found a big difference and I've done it with different basses and different amps, there is a lot more deep fundamental and less harmonic overtone with the pup volume turned down. Is this normal and if so why have I only just found out? [/quote] I think you've discovered that as the source impedance of your bass increases (via the volume pot), the turnover frequency of the low-pass filter formed by the (increasing) source impedance and the capacitance of the guitar cable reduces, reducing top-end... A lot of guitars suffer from this too, and some guitars have a "bleed" capacitor fitted across the volume pot to prevent it from occurring.... In fact, it can be quite useful on a guitar - playing your chord stuff with the vol rolled off a bit for a softer sound - whack it up for lead parts, with a more agressive tone... ... I'm a bit surprised it is so noticable on a bass though - I have a Jazz, but it's an active, and I haven't tried it yet... I mostly use it with the vol pot right up (or knocked back only just a little) for this very reason...

Most cheap fans (and it *will* be a cheap fan) have plain/sleeve bearings - basically the shaft runs in a bush, and one or the other gets worn and starts to rattle - it often happens quite quickly too. Better fans have ballrace bearings. The fans in those amps are almost certainly a standard size - why would they go to the cost of a custom fan whilst China Inc is knocking them out for tuppence for PCs? You need to take the amp apart, check the size, check the supply it runs from (5V/12V/Mains...) and identify a decent replacement. The better/quietest fans are "DC brushless" types. The other variable is that some fans are intended to move lots of air, and some are intended to be as quiet as possible, and needless to say move a lot less air. I think it is possible to find fans for PCs that have temperature sensors with them, that speed up the fan as they sense a temperature rise (a "good thing" (tm)) Usual suspects - Maplins, Farnell, RS onliine etc... Hope this helps.

I'm not talking about the input impedance of the op-amp, it is the gain configuration that is important... If the Vref point were an effective ground, then the (non-inverting) gain of the opamp circuit would be set to (R6 + R4)/R4. However, Vref is not a particularly good ground - it is decoupled to actual ground by 0.22uF, so that capacitance appears in series with R4... At about 75Hz, that 0.22uF cap shows roughly 10k (the same as R4), which roughly halves the gain of the circuit (R6 + R4 +R4)/(R4 + R4) Ok, R1 and R2 also appear in parallel with C1 from an AC standpoint, which will make a bit of difference difference... but the principle stands... See my point?

[quote name='jensenmann' post='731751' date='Feb 1 2010, 02:28 PM']Finally I´d recommend a booster pedal, too. Snipping wires in your amp is not funny unless you´re expierienced in DIY-electronic. C1 is theoretically ok. I´d stay with a film cap for sound (less THD than electrolytics) reason but I´d make it as big as possible. Limit is money and space on the PCB. It´d probably be a Wima MKS-2 1uF/63V.[/quote] Unless I'm doing this wrong (and I'll admit that it has been a long time since I did this stuff professionally)... my back-of-a-fag-packet calculation of the -3dB point for a 10k resistor (R4) and a 0.22uF capacitor (C1) is about 75Hz... that's where the gain of the op-amp will start to roll off towards unity.... Not low enough I would think... 1uF would be about the smallest you would want - 0.22 is way too small...

[quote name='richrips' post='731127' date='Jan 31 2010, 09:56 PM']Am i correct in thinking that R6 is a variable resistor (i.e. a potentiometer or pot) on the diagram? i can't really see anything variable on the photographs. it looks like a fixed value standard resistor in the photos (i'm thinking its the one that sticks up rather than lying flat like R1, R2 etc). should i use a 100k resistor here? <snip> i'm trying to work out where in the signal path the circuit goes. will i see increased gain on the visual meter or will it just be louder with no change in the display level? cheers, rich[/quote] It is shown as a pot (variable resistor), but unless you have front-panel space for it, you could use what is known as a preset pot - which is a small device where you would set the resistance with a screw-driver... When the resistance is lowest, the gain will be lowest, and vice-versa. Alternatively, you could fit a 100k fixed resistor, and if it gives you too much gain, replace it with 47k or 33k (probably not too much point going lower than that....) You could hijack the instrument input, and put this amp right at the beginning, however, it might be a bit noisy in that location. Alternatively, you are likely to be able to break into the signal path in the region of the send/return or line-in jack. If you have an external power supply (even 2xPP3 batteries), you could insert the amp into the signal chain from outside the amp using the send/return point for testing (I recommend you do this)... On the subject of recommendations, if it were me (and I can buld this stuff myself, as you can imagine...) I'd be using some kind of stomp box to provide the amplification... The Danelectro Driive pedal is as cheap as chips, does nothing at all to the sound if you turn down the "drive" level, and has an output "level" control that will provide plenty of gain... Or a Boss CS-3 compression pedal... or an EQ pedal... Basically this approach is fool-proof, and avoids modding the amp itself... (On the amp modding subject, I'd be surprised if a single resistor change somewhere in the existing amp circuit wouldn't get the amp itself to give you the gain you want - if you have a schematic, I could figure out where... but then, why didn't Ashdown get the gain structure right to start with... everyone seems to complain about low gain on these amps...) Hope this helps. Alan edit: Just spotted I don't like the value of C1 - I'd put a much bigger cap in there 10uF like C4 would be fine - +ve end upwards.

[quote name='cheddatom' post='729719' date='Jan 30 2010, 02:47 PM']Basically, some wrotter who last moved my nice presonous pre-amp with PSU plugged in managed to pull the wires out of the plug a bit, shorting them, which I didn't notice before I plugged it in. No reaction from the pre-amp but the PSU stank and was very warm. I don't want to mess about trying to repair the PSU but I don't have anything else to provide that sort of power. Will the pre-amp be fine? If so, i'll buy a PSU.[/quote] I think you'd be very unlucky if the pre-amp was damaged during that event...

The circuit should work. The volume control will give a gain change from about unity gain to around x10 (20dB). The 10uF electrolytic should be 30V or more. It doesn't say, but the volts at K1 shoud be a good clean DC supply of +12V to say +32V or so, whatever is available in the amp. The issue about capacitor values is that the cap forms a high-pass filter with the resistance to ground that follows it. On the input side, that resistance is known, being effectively the 470k resistor... so 0.22uF is plenty big enough. On the output side, the load inpedance isn't known, as it will be whatever impedance presented by the thing the amp is driving, so it makes sense to make the coupling cap big enough to ensure a good bass response for any sensible low values of load resistance. Hope this helps. Alan

May I suggest that it isn't wise to simply solder odd wires to random tags that look like they might need them (although admittedly, it might work - in particular, that floating wire is a prime candidate for suspicion). If a wire *has* been connected to that tag, then there *will* be signs of it having been there - ie. solder, and evidence of broken strands... But the best approach woud be to: i) Identify each wire as to it's purpose - where is it connected (it can't be too hard - there are very few of them) ii) Deduce how each wire *should* be connected in order to achieve the desired result (connecting the battery circuit only when the jack is inserted). iii) Make it so... PS. Please be aware that if you manage to create a short circuit across the battery, and it is a nice new fresh battery, then it can potentially get hot enough to spoil your day...

[quote name='richrips' post='727531' date='Jan 28 2010, 01:19 PM']I just purchased an ashdown little giant and played my first gig last night. I found the both the pre-gain and master volume were both nearly maxxed and this was a jazz gig in a room barely bigger than a large living room. The LG 1000 has a rated output of 1000 watts in to 4 Ohms (and before i get jumped on, i know it is 2 seperate power amps and you would need 2 4 ohm cabs to get full power). i have 2 cabs rated at 8 Ohms. they contain kappalite 3012HO drivers with rms 400watts each. I'm guessing the power i should be getting in to 8 ohms would be between 250-350 watts per speaker (this depends on output voltage from the amp i believe??) Oddly, my previous amp, a crown xls 402 with peavey alpha valve preamp, kicks out 450watts per side in to 4 ohms- apparently less than the ashdown, but seems much much louder.... [url="http://www.crownaudio.com/amp_htm/xls.htm"]http://www.crownaudio.com/amp_htm/xls.htm[/url] is there something i have overlooked which makes the crown more powerful with my cabs than the ashdown? would it be worth swapping my kappalites for some 4 ohm 12's? tech help much appreciated! cheers, rich[/quote] Yes, I think you are confusing GAIN with POWER. In all probability, if these amps have the rep for being a bit low on gain, in order to extract the power you need more gain, which you should be able to get either by putting a pre-amp pedal between bass and amp, or in the effects loop (if it has one). Robustness of that product notwithstanding, you shouldn't be able to kill the amp by overdriving it - certainly not into 8 ohms anyway - it should be clipping well before it reaches any thermal limits, and it's internal protection should take care of all of that anyway... Those 3012 HO drivers are quite efficient - IMHO it should get very loud.

[quote name='LauraBrokeTheBass' post='725754' date='Jan 26 2010, 09:13 PM']I'm in Scottish Borders, nearest major place is Edinburgh. ..... Painting the Bass with the Union Jack was one idea..[/quote] You have a death wish? Seriously?

[quote name='Hot Tub' post='725802' date='Jan 26 2010, 10:08 PM']You're not leaving the lead plugged in are you?[/quote] +1 *Normally* the act of plugging in the jack is what connects the battery - without the jack plugged in, the only way for the battery to discharge (as long as it is wired correctly to start with) is to self-discharge, and with decent batteries that should take years...

So is it fixed? Alan

[quote name='lemmywinks' post='722387' date='Jan 23 2010, 05:59 PM']Incidentally the socket i plug the amp into is right next to a TV ariel socket. None of the ariels in our house work apart from the front room one so could that have something to do with it?[/quote] Well, anything *could* be implicated... It might be that rewiring the house would sort it - in fact, that might be easier than actually trying to understand the mechanism (unless something specificly wrong is found with the existing wiring).... ... my point was that stuff (even radios) have to exhibit immunity from interference, as well as other stuff having to not radiate unnecessarily... The fact that you have two amps that seem to cause the same problem, is actually on your side - it is extremely unlikely that both amps have a similar fault... I'd assume that the Hartke has a standard "old fashioned" linear PSU. If so, there is nothing that is likely to be operating at RF in there... With the best will in the world it isn't easy to theorise a reason for the problem... Reasonable or not, at the end of the day, he's the one with the itch to scratch - Can't he get internet radio?

If you feel that there is something wrong with your house electrics, then you (or your landlord) should certainly get them checked by a qualified electrician - it's not rocket science... If the amp that you have has been type approved, it will have a CE mark (usually on the back or bottom, or somewhere like that). If it is older than a certain age (can't remember when) then CE marking wasn't a requirement (and there is no requirement to remove such non CE-marked products from use). These days it is illegal to place products on the market that are not CE marked, and that marking is the claim by the manufacturers that it complies with *all relevant European standards*, inlcuding those for Electromagnetic Compatibility, meaning that it meets the requirements for both emissions and susceptibility. Unless your neighbour can demonstrate your equipment is either illegal or (by measurement) that it is faulty, I think that is the end of it... Tough, but that's life - it is his problem.

If the buzzing stop or gets quieter when you touch the jack body, but the same doesn't happen when you touch the strings, then almost certainly your strings aren't earthed to the electrics - you can confirm this by checking the resistance between them with a multimeter - it should show 0 ohms or nearly so. There should be a good connection, usuallly from the back of a pot via a wire, often to the bridge somewhere... When the guitar is properly earthed, then your body plays an important part in screening RF interference from it, mainly around the back - but this can only happen if your body is grounded - usually via the strings. If it is not grounded, then your body will usually make the buzz worse, by actually re-radiating noise into the guitar... An alternative approach is a careful internal screening job usually using either adhesive copper foil or conductive paint - in each case that must be properly earthed too... Usually though, properly earthed strings achieve most of what you need... Lights with dimmers, and florescents, are usually worse than simple incandescent lights. Alan

Bought a 15" bass cab from James... Top fellow. Good deal. As described. Thanks Alan

[quote name='Mr. Foxen' post='707940' date='Jan 10 2010, 06:02 PM']Many handy models for winisd pro are [url="http://lowdownlowdown.com/greenboy/DL/WinISD/"]here[/url][/quote] Brilliant - thanks very much....

Quick take on the 3012HO is good. Similarly low(ish) Fs at 51.5, very good Xmax and Xlim at 6.2mm (!) and 12.5mm, and excellent sensitivity at 100.5dB (that's worth amplifier money right there!)... Haven't found a supplier in the Uk though (Boo!) I'll try it out in WinISD (got to build the model first...) Thanks Alan

[quote name='Bill Fitzmaurice' post='707299' date='Jan 10 2010, 12:38 AM']Try the 3012HO. Xlim is moot, xmax is everything. The D12LF was state of the art ten years ago, rendered obsolete by the 3012HO, which is also a contender but really needs to be used with a six ought five midrange.[/quote] Thanks Bill, will do... (The D12LF now seems to be the D12LFA - the specs are different from the D12LF, although I'm sure it is just an improved version. - equally, WinISD Pro seems to only have models for the older types, DeltaLite rather then DeltaLite II, for example - I guess you have to update the specs yourself... that's what I did.) Re Xmax/Xlim: My understanding is that if you exceed Xmax, distortion will exceed some arbitrary value that the manufacturer uses to establish Xmax, whereas exceeding Xlim is likely to result in damage. If a bassist is rocking out, and it's all getting a bit noisy - he's unlikely to be concerned by a bit of increased distortion on peaks as he exceeds Xmax... (and anyway, some people like that kind of speaker compression). But he *will* be concerned if the voice coil starts hitting the stops, and/or he destroys his speakers! ... maybe I've got that all wrong?

[quote name='Bill Fitzmaurice' post='700798' date='Jan 4 2010, 07:00 PM']These specs in and of themselves reveal almost nothing about how the drivers work when loaded in a cabinet. That can only be determined using all the driver T/S parameters with speaker enclosure modeling software like WinISD Alpha Pro for the region of pistonic function, roughly up to 200 Hz, and the SPL charts from the manufacturer driver data sheets for above 200 Hz. And then there's the matter of being able to interpret the results. BTW, if one only had the above data as predictors the differences between the four drivers listed would be, for all practical purposes, inaudible.[/quote] Well I got hold of WinISD Pro and spent some time getting to grips with it. From the volume and the porting, the cab seems to be tuned to around 41Hz (which makes some sense I guess, given the likely resonance of te speakers). The speakers in the Mag 210 at the moment are Chinese made Eminence, without any id of the model number. Putting the models of the Emi Alpha in there (assuming the speaker is one of their cheaper designs...) it doesn't look too bad, but distinctly light on the bass end. There seems to be little point putting very high powered pairs of 10s in there, as speakers like the 2510 and S2010 (which looks a bit better in terms of response, but I haven't found anywhere in the UK that stocks them) end up displacement limited, and the bottom end still isn't that great. Putting just a single 10 in there improves the bass response immensely, but makes the displacement problem much much worse - you can't get more than about 120W out of it at 41Hz, or else the speaker in poling like crazy (Xmax is 4mm or so, but Xlim, where damage can occur is up around 8mm). I tried a lot of different things - no amount of tuning would make much diffference to the basic problems - poor bass response, and or displacement limited at quite low power. The best thing I found, was in trying a single Eminence Delta 12 LFA - a single 12", and it seems much better than a Deltalite 2512... It's Resonance is pretty low at 51Hz, and also being a single speaker in the cab gives an excellent bass response, but mainly, it has a massive Xlim at 13.5mm, which allows a lot of power to be used even with bottom strings. Ok, Xmax isn't so high, but it is good at 4.8mm. I know there is likely to be increased distortion if this is exceeded, but at least it won't be trashing the voicecoil... It isn't a brilliantly sensitive speaker at 94.6dB and I suppose that's the worst part - but at least you can get some power into it without trashing it... It's rated at 500W continuous. The main thing though, is that I got a convincing response curve (F3 at 42Hz), with the ability to get it powered up well... ... does this sound reasonable, or have I missed something (I haven't missed the point that this is all simulated...)?