Mottlefeeder

The bottom line is that acoustic instruments will feed back at relatively low volumes. In my experience, if you control the PA, stay acoustic: if someone else is controlling the PA, user a solid bodied bass. If you stay acoustic, you have a number of solutions, but A) As mentioned above, a notch filter will take out one offending frequency, but there may be other resonant frequencies almost as bad. B) A preamp with a phase switch in it will allow you to swap the phase to see which gives you more headroom - if your pickup is in phase with your speaker, it will feed back earlier. C) As mentioned above, plugging the sound hole(s) will give you more headroom, so if you are talking about something like an Ovation, 20mm lengths of rolled up foam pipe lagging in each hole will get you most of the way there. D) Using a variable high-pass filter can also reduce feedback problems, and can be used to take care of the lower of two resonances while a notch filter takes care of the upper one. I have a 5-string ABG and I use its notch filter and phase switch, a planet waves feedback buster, and a variable HPF. David

Depending on your definition of a Uke bass, there are three models in the Aquila Shortbass one range. Using a 23.5 inch scale and taking thundergut reds, the '60 has a bowl back and the '12 has a conventional body. The '14 has a 26 inch scale length. http://www.shortbassone.com/?cat=4&lang=en Bass Direct and Bass Centre prices seem to be around £400, but no one seems to have stock at the moment. I don't have one - I'm just an interested observer David

I've gone in a slightly different direction to get to the same place. We put the PA at the back of the band so we do not need to carry monitors - that means I stand between the PA speaker and the drummer and I can't hear my own rig. I started with a belt-mounted upmarket 'me/them' mixer like the Behringer P1, but I found that my budget in-ears did not keep out enough stage noise, so I sent that back and went for a small (cheaper) desktop mixer and an upgraded pair of in-ears. I now use the Shure SE215s, but I had to get the optional 'chistmas tree' type plugs to get good isolation. I take a feed from the nearest PA speaker through a resistive attenuator: a feed from my speaker output through a resistive attenuator; through the mixer and into my IEMs. Studiospares do a figure-of-8 twin microphone cable which gives me a 'bass to amp' feed on one side and a 'headphone left and right' on the other side. A belt-mounted plastic box holds the plug/socket adaptor to get from stereo jackplug to 3.5mm jack socket for the IEMs. The reason for taking a feed from the bass-speaker connection is that I want to know if it fails. David

Our band fund-raises for Cancer Research UK - £429,000 in 8 years and hoping to hit £500K by Christmas. Band diary said 7:00 so I got there for about 6:15. Bar staff didn't know what was going on. 6:50 and still no audience, or other band members - starting to get worried. The rest of the band turned up shortly after 7:00 and started phoning other venues with similar names (xxx conservative club) - the band leader started looking for the organiser's phone number. Eventually we got confirmation that we were in the right place, but not expected to play until 8:00. It was a charity event with little (if any) publicity. Got set up and ready to play - still no audience unless you count the 5 punters watching football at the other end of the room. Started playing at about 8:15 and the audience gradually built up over the next couple of hours. We stopped at just after 11:00 by which time the room held about 40 people, 5 of whom were interested and the rest treated us as wallpaper music. We got paid and we got half of the raffle money, all of which goes to Cancer Research UK, but it was hard work. David

I've taken out almost all notifications, just leaving in the 'automatically follow content' and I haven't had an error message so far, doing exactly what I have been doing in the past, so thanks to Ped - you probably have cracked it. David

For the last week or two Firefox has been giving me error messages saying that a web page is slowing down my browser, when the only web page I have open is Basschat. It appears to be caused by the 'Unread Content' page refreshing after I have viewed and then closed a thread. Right clicking and opening a thread in a new tab, then closing, does not produce the error message. Any thoughts on how I fix this? David

You've checked the cable, you've checked the speaker cab, Working back upstream, the chances of both speaker jack sockes developing the same fault is fairly remote, so my starting point would be inside the amp casing. The internal mains wiring and terminals should be insulated, but if you are not competent to work out whether that is true in your case, don't go there. a) There is a relay that does not connect the amplifier to the speakers until all the switch-on surges etc have been and gone. It may be inhibited by a fault, so listen for the click a second or so after you switch on. That will tell you if it is trying to connect, or not. If you do not hear a click, it could be due to (b) or (c) below. b) One of the fuses connecting power to the amplifier circuit may have blown, so check for blown fuses in holders on the pcb. If you find one, there is an obvious question to ask - why did it blow? c) You will find four or six transistors bolted to a heatsink that the fan is blowing air at/though. Check if the fan is working, and the fan grill and heatsink are clear of fluff/dead mice/etc. A clean heatsink and a working fan are good signs, but the fan may not operate until the temperature rises, so this is not a definite tick in the box. A well-designed amplifier should shut down undamaged if it overheats, but it is possible that yours doesn't, and a thermal fuse has blown. I've had two amplifiers with faulty outputs, and both were due to faulty output relays, so I'm slightly biased. David

Some time ago, FDeck (of HPF fame) suggested that if you knew what kind of sound you wanted, and didn't need a lot of fundamental (e.g. for DB) you could do your back a favour and use smaller cabs. This was one of the triggers for this design. I used the HPF of a Fishman Platinum Pro, and the HPF of a graphic EQ to identify how much bass loss was too much, and concluded that provided that the response got down to 70 Hz, it did not sound bass-lite (to me). Having identified the cutoff frequency, the next problem was what to do with the frequencies below the cutoff, where the speaker would be unloaded. After a few more evenings playing with WinISD, I found that a 12dB/Octave filter at about 55Hz would reduce the cone excursion below the resonance and keep it within Xmax, even with an input signal equivalent to 120W on the output. This WinISD screenshot shows the frequency response of a 25.5L box, with (red) and without (green) the filter, and two larger boxes for comparison - maximum bass extension (blue) and optimised by WinISD (grey). This WinISD screenshot shows the cone movement for a 120 W signal. Everything without the filter overloads above 40Hz. Given that a bass note is a mix of fundamental and harmonics, this may not be a problem, and I have played bass through these cabs without the filter, but I feel safer having the filter in circuit. Finally, this WinISD screenshot shows the power handling of the various cabs. the two 25.5 L cabs have identical traces, but the other two both have considerably worse power handling in the 50-100Hz region, where most of the energy of the note is likely to be. This prompted me to stay with the smaller volume cab with an HPF. I hope this image contains all the information required to build a cab. If not, please let me know. David

After the recent North West bass bash, lurksalot commented that I should start a build thread for my small battery powered amplifier in case anyone was contemplating a similar folly. Some of this has already been posted on another forum, but since photobucket has blanked out all the images, it seemed to make sense to start at the beginning with a new thread. I play a lot with acoustic guitarists, either busking, or at open mic nights, and my existing combo, a Hartke Kickback 10, was adequate, but rather heavy, and limiting because I had to sit by the power socket so as not to trail cables across the floor. My initial specification was based on the Hartke, with a bit of Phil Jones Briefcase thrown in - about 100W, one 10 inch speaker, one 7 AHr 12 volt battery and 2-3 hours of use per charge. I had already built a couple of Jack 10s. so I had a 10 inch speaker to hand - an Eminence basslite S2010, and for a small box, WinISD suggests a volume of 0.9 cu ft (25.5L)and a port tuned to 58Hz. Eminence offer similar figures on their website. The Mk I was a simple reflex box with the preamp, amp and battery mounted on a plywood plate that could be carried separately, or bolted onto the back of the cab. The amp is a Kenwood car stereo module, containing a switch-mode power supply to give positive and negative voltage rails, and a 60W @ 2ohms pair of class AB amplifiers, so it gives a genuine 120 W into 4 ohms bridged. It was unwieldy and cumbersome to carry when bolted together, and a pain to work with in a crowded room when loaded in in bits. Also, the battery life was OK for an acoustic evening, but for a day of busking I needed more power, so I had another think. The MkII had the same volume and porting, but incorporated the amp in a recess in the back, space for three 7 AHr batteries in the base, and a space for the preamp in the front. The woodwork suddenly became a bit more complicated - And the final result. This one was easier to carry, but the amp, which normally runs cool to the touch, now runs too hot due the lack of circulating air. At this point I started wondering whether I could find a class D amplifier module, and redesign the cab around that. The Mk III used a class D stereo amplifier chip on a ready made pcb - readily available from ebay. Just for a change, I made the cab smaller to accomodate the amp and speaker in the same volume as the Mk I speaker. Having recently aquired an Ashdown MyBass 550 in a trade, I was keen to be able to use it with this pair of speakers, so I added extra speakons and switches to the back of the cab so I could connect either the internal amp or the external amp to the speaker, or connect the internal amp to an external speaker. Almost inevitably, while setting up in a hurry on a dark stage, I managed to connect the output of the MyBass to the output of the battery amp - the MyBass won. At that point I decided that I should go modular, and have separate heads that clipped onto the top of the cab. No more switching options to get wrong, just clip the head on before you leave home and you're good to go. This is the Mk IV - the current version. The Mk III cab was butchered to convert it into a MK I style cab, and kitchen-cupboard kick-plate fasteners were fitted to anchor the clip-on amplifier modules The battery combo: The mains combo: This is the battery powered amp and battery with an earlier version of the preamp. I need to take some more photos before I post the next installment. David

Thanks for that - I'll check it out. David

Firstly, can I say that I too really enjoyed the day, and add my thanks to those who organised it. That amp has an HPF, and an LPF and no other EQ. The power stage is a 10W @ 8ohms or 20W @ 4ohms class D stereo amp available on ebay. With the internal 12V 2AHr battery (common in burglar alarms) and one cab, it will run all night at an acoustic open mic night, and with a 7AHr(scooter battery), it will run with two speakers for several hours, in a band with mic'd acoustic guitars and vocals and one or two conga players. I'm happy to share - but first I need to find a replacement for Photobucket - Am I right in thinking I can link to pictures in Dropbox?

Your range of strings is always going to be limited if you need double ball ends. If you buy/make an adaptor block to clamp standard strings at the neck end, you can then use standard strings that you already know that you like. David

Hi guys, I'll bring my two Bill Fitzmaurice Jack 10s, a couple of basic reflex 10s (almost Eminence-cab-design vanilla) all loaded with Eminence neo Basslite S2010s, my BEAD bass uke, my BEAD headless kit/homebrew, and a couple of fives. I'll also bring my combined HPF and LPF for anyone who was following the recent thumpinator/Fdeck thread. David

Oops, forgot to mention, having the mixer on the amp means that you need to get the headphone signal from it to you . I use a figure-of-8 twin microphone cable with the bass signal going down one side and the headphone signal coming back on the other. David

Assuming that your bass is active, and does not need a hi-Z input impedance on the amp, you could use a small mixer between the bass and the amp to give you a headphone-out facility (Bass to mixer 'line input', mixer 'main mix' output to amp input, mixer 'monitor output' to headphones). A Behringer Xenyx 502 at £30 would do it. If you use a passive bass, you could take the mixer feed from the line-out or effects-out of the amp (if it has one) or you could look for a mixer that has a Hi-Z instrument input, and connect it as above. A single-instrument-channel mixer like an Alesis multimix 4 at £85, or a soundcraft Notepad 5 at £85, would do it, or a Mackie 402 for £99 would give you two instrument channels - I use one of these as a 'me / them' monitor using a feed from the bass amp and a feed from the PA. David

A couple of years ago I couldn't find one, so I made one. As you say, a simple circuit will do the job. If you are into the DIY side of music/electronics, I can post the circuit, layout, etc. David

I rarely use the G on my 5, so when I bought a 4-string back-up bass I tuned it BEAD. I find it much easier to swap between basses when the strings I use most are where I expect them to be. David

The 'Overlord of Music' bridge and the pictured string locking set are commonly supplied with kit headless basses, and I have one. The problem with the string locking nut set is that the two visible allen screws clamp the string behind the zero fret, but the string is locked by bending it through 90 degrees and then clamping it, and thicker strings break when you do that. To use flat-wound strings, I ended up sawing off the existing clamp (at the bottom of the image) and fitting a separate clamping block so the strings pass straight through. If the remains of the original string locking nut set is angled in the right direction, the new block will not ride up when the strings are tensioned. David

One quick thing you might do is to check whether it is shutting down due to overheating - does it have a fan and is the fan running? If it has a fan which stays off permanently, that could be your problem. David

Walter Harley (of cafe Walter) put a short article on his website detailing a variable low pass fiter he used about 2000. Unfortunately I cannot find any references to it now, but I still have a paper copy. It works from 200Hz to 20KHz,with a 12dB/octave slope, but his stage gain was 1.16, which was considerably less than the 1.6 you would use for a Butterworth response, so the corner or knee of the graph is much smoother. I've built a couple and they sound good. I've emailed him to see if there is still an electronic version of the original article available, but if anyone can trawl through historical web pages, they might ba able to find it; Heading - Rackmount Bass preamp Subheading - Walter Harley September 2000

The 'series 3' of the FDeck HF Pre design has a 12dB/Octave fixed frequency (35Hz) HPF, followed by a variable frequency 12dB/Octave (35-140Hz) HPF so you will have 24dB/octave anywhere below 35Hz. https://sites.google.com/site/hpftechllc/home/hpf-pre Although a circuit diagram is not available for the series 3, adding a fixed frequency HPF to a variable frequency HPF would not be difficult for an average electronic DIY enthusiast. David

If you leave the eq flat, but turn down the volume on the bass, the disappearance of the problem would indicate a preamp overload - might be worth checking that out if you haven't already. David

The OP asks about protecting speakers "etc" so I do not think that excludes variable frequency high pass filters, which I agree only cut at 12dB/octave, but are much more versatile than a fixed frequency device cutting at 36dB/octave. In my case, my reflex cabs were designed using WinISD, and the ports are tuned in the low 50s, although I play a 5-string. According to WinISD, the speakers could be damaged by a strong 30Hz signal, but adding a 12dB/octave filter tuned to 40Hz removes that risk, so I use an FDeck clone for speaker protection, and where necessary, I increase the turnover frequency to get rid of boominess. In my experience, using a pair of Jack 10s, or a pair of reflex 10s, you can take out most of the bottom octave before the sound starts to get 'bass-lite'. David

I'm not sure that I agree with that - if your sound is boomy due to a hollow stage, and HPF can tame the boom, similarly if you want more punch and less mud, an HPF plus bass boost can fix that for you. In both cases you can hear the difference. David