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About Mottlefeeder

  • Birthday January 31

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  1. Rod Elliott recommends a connection to ground via a 10 ohm resistor bypassed with a 0.1 mfd capacitor. Covers most situations and doesn't not need a switch David
  2. One step down from a TRB and going for £160! I've had mine for 20 years and they are very good basses. GLWTS David
  3. I'm hoping for something modular so that I can fit the amp into the speaker casing, and power it from 12 Vdc when there is no supply available, or 230 Vac when there is. In the briefcase, PJ drops the mains down to 12 Vdc and feeds that, or the battery into a +/-X volt SMPS to power his class D amp. On 12 Vdc you have one voltage conversion, but on mains you have two in a row. It's inefficient having two conversions, but with mains power it is not that important. Looking at what is readily available, you can use a pure sine inverter with a 230 Vac rig, but that is one voltage conversion on mains, and two on battery, so it is inefficient and it is using up your battery power. As an example, my Ashdown MyBass Mk1 is Class D and with an inverter, it draws about an amp at 12 Vdc while idling, which is about a third of the capacity of an easy carry 7AHr battery. You can also use an automotive booster amp with an SMPS feeding a class AB amp, which has a lower quiescent current, but takes more on peaks. In summary, an automotive class D amp fed from a 12 Vdc SMPS would be the optimal solution. Unfortunately they don't do them in smaller power output units, and with a bigger unit you are back into the wasted power problem again. David
  4. Apologies for the slight thread diversion, but are any of you Class D module users aware of a 50-100W Class D module with a separate power supply, and a 12V dc SMPS to suit, to allow something like a PJ briefcase design to be built. The nearest I have got is a car stereo booster amp with a SMPS and a pair of bridged Class AB amps. Thanks David
  5. Lead acid batteries refer to the basic chemistry, in the same way that 'alkaline' or 'Lithium something or other' does. Lead acid technology is heavy, but also considerably cheaper than the other options. Within the family of lead acid batteries there are minor differences in design depending on what the battery is intended to be used for. Car starter batteries are intended to be kept fully charged unless they are cranking the engine but golf cart batteries are intended to be run down to 'empty' and then recharged. Batteries designed for discharge and recharge are known as deep cycle batteries. Using the wrong battery will not damage the rest of your gear, but it will result in the battery having a relatively short life. David
  6. I have an Ashdown MyBass mk1 500w amp, and I can run it from a 'modified sine wave' invertor rated at 300 W. The invertor has a continuous rating, and the amp is never used at full power, so it works. That setup draws about 2 Amps from a lead acid battery, so for a half-brick-sized 7AHr battery you can expect 2-3 hours of use before the voltage droops and the invertor shuts down. That type of invertor uses a very crude approximation to the mains waveform, and it is rich in harmonics, so it may cause a buzz through your gear, and it may invalidate your amp warranty if you have a problem. A better solution is a pure sine wave invertor, which does not generate a buzz, does not invalidate your amp warranty, but costs a bit more, £80 vs £30 for a modified sine wave invertor of comparable power. An alternative would be to buy a car stereo booster amp for about £50 and run that directly from the battery. Current designs from the reputable manufacturers will deliver 150 W into 4 ohms, or about 75 W into 8 ohms. An active bass will provide enough output to drive it directly (but not drive it to full power - for that you will need a booster, or an FX pedal with some gain). Something like https://www.caraudiocentre.co.uk/product_m-pioneer-gm-a3702_p-40132.htm would probably do (mine was a Kenwood, no longer in production), but you would need to check the maximum sensitivity was about 200mV. Anything complying with CES 2006 will specify RMS values, regardless of what the marketing department painted on the lid or put as a headline. David
  7. You also cut away some wood and added a plastic tube... David
  8. I was wondering why you had a two channel balanced feed circuit, and then I read this bit and it all made sense. Having said that, Rod Elliott has modified the DI output on his bass pre-amp design so that it could tolerate anyone accidentally applying phantom power to it - series resistors and zener clamps if I recall, to take care of the inrush. David
  9. The ASX pcb has 400mA fuses on the aux supplies, so you may be able to replace them (SMD fuses?), or short them out and make sure you have smaller value fuses downstream. David
  10. I'm showing my age - the last drive-in movie I went to was in the US in 1975. David
  11. My understanding is that the 2 m rule is for short duration exposures, and if you spend a long time with people, e.g. a rehearsal, 2 m spacing will not help you. As others have said, a drive in would be a safer option, but if you had to hang a speaker on your window, you could pick up infections from that, or if you leave your windows open, then you lose the 2 m when someone (drunken idiot) walks past. David
  12. Another couple of options would be to use a 230V ac fan, or a 12 v fan on a capacitive divider and bridge rectifier as here (shudder) David
  13. Have you checked that your preamp will not be affected by the fan EMF if you have a common supply. I put a fan on a 12 v battery powered system and found the preamp became unusable. I now have to use a pedal preamp fed from its own battery. David
  14. OK, A bit more information. It's two almost separate circuits - Firstly, I use a passive bass and long cables/not hi-z inputs, so it is a simple bass preamp, giving a hi-z input, an HPF, and an output to FOH or backline amp. That's two jack sockets on one side, (one in and one out) and a gain selector: 0dB or 10dB. Secondly, I usually create a headphone monitor mix with a small mixer on top of the back-line amp. I take a feed from the main PA, and a feed from my bass amp, and an ambience mic, and feed them back to me in stereo (acually two channel mono since I put me on the left and everything else on the right). With this box, I can select left only, right only or both and I mix them down to mono and feed them to the headphones. That's the other two jack sockets, (stereo in and headphones out) and the selector switch. Since I have the bass signal in the same box as the headphone mix, I added the switch in the battery compartment which gives me the option of substituting my live bass sound for the left monitor channel, so I can take a mono feed from the FOH mixer, or a stereo feed from a Zoom or Tascam recorder, and still control 'me or them' at my end of the cable. I use a 'figure of eight' twin microphone cable to connect my bass/IEM to my bass amp/monitor mixer. It's reasonably discrete and keeps the two sets of signals apart. The compromise is that it isn't an instrument cable, so I need the hi-z buffer - that was the starting point. David
  15. Four jack sockets, three switches, three opamps, two pots and one 9V battery in a box not much bigger than a tv remote. It's a: Hi-Z buffer with switched gain + 18dB/octave fixed frequency HPF + headphone driver + passive headphone monitor mixer with volume limiter, and I don't think all that would fit in the title box. The circuit evolved as I built it, so I have not got an accurate copy yet. If there's any interest, I can sort one out. David
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