Mottlefeeder

If you have the option of buying a pre-coated grill, I would seriously consider it. When you spray a grill, you spray from the front, and 70 % of your paint goes through to the newspaper behind. Then you spray at an angle so you don't miss the edges of the holes, and 70% of your paint goes through the holes... I reckon I spent £10-15 on paint for the last grill I painted. David

Another day of 3 steps forward and one back... Sorting out the wiring between the amp recess and the cab, one of my cable clips sprang off and disappeared. And where did it land - inside the speaker cab, between the speaker chassis and the speaker cone! I couldn't shake it out so I've had the grill off, and the speaker out, and while I was in there, I took out the acoustic wadding, then put everything back together again. The battery holder is now securely blocking that hole so it can't happen again, and I'm back to wiring up the amp and preamp plate. I've less room than I thought I would have, so it's getting a bit messy. David

That battery charger is fine for larger batteries, but I think it only goes down as far as 7Ahr. I use a CTEK charger for my audio gear - 2.3Ahr or 7Ahr, and only take the caravan battery for all day busking sessions using larger amps. Recessing the socket was easier than I thought it would be - I'm old school with regard to plastics, so it's back to model-makers plasticard for me. I bought a 2mm thick sheet to make the speaker cab vent. Hmmm, smell that solvent. David

I've heard it said that you should snap your fingers in side the enclosure to check whether it sounds too dead. Whoever suggested that was not building cabs this small, so I think I'll leave the wadding in until I finish the rest, then experiment after that. Moving on, my next problem is the power socket - Several years ago, I decided to standardise on Torberry connector for all my 12 v battery connections. Unfortunately, the panel-mount version leaves the plug protruding too far from the back panel, and likely to be broken, so I need to recess it somehow. David

Three steps forward, one step back... I was so engrossed in feeding battery and speaker cable through a small hole from the cab to the electronics that I forgot the speakers should be in parallel, and I wired them in series. Having fixed the speakers (8 screws) and the grill (6 screws), it all has to come off again to be rewired. On the bright side, I was able to use a 'normal 'amplifier to drive 10Hz though the 8 ohm load to run in the speakers. I've also fitted some sound absorbing polyester wadding in the front half of the speaker i.e. between the baffle and the brace, and also on the back wall. I can't see much reflection coming back from anywhere else. David

A bit more progress - the garage is about 3-4 degrees C at the moment, so metal bashing/drilling/filing occurs in short sessions. David

It makes perfect sense, but I hadn't thought it through other than for the bass frequencies. Thanks David

The longer term plan was to use an FDeck clone HPF giving a fixed 12dB/Octave at 35 Hz and a further 12dB/Octave filter, variable between 35 Hz and 140 Hz. Some form of limiter/soft clipping was also envisaged, although I have yet to hear a simple compressor circuit that I could live with. I also had plans for some fancy power switching to allow one socket on the back to be used for power-in or battery-charge, or not in circuit when the internal battery was in use. I've decided to start with some simpler options, and swap out bits if I need to: first on the list was the HPF. The first Win ISD graph shows the response with no filter (red), 35Hz 12 dB/Octave filter (Blue) and 40Hz 12 dB/octave filter (Green). As you would expect, neither filter has much effect on the response of this speaker enclosure, with its relatively high tuning. Having said that, the battery sits within the speaker enclosure, and I had concerns that the enclosure response would vary depending on whether you fit no / a small / a large battery. In reality, the difference between the larger battery and no battery increases the volume by 7% which reduces the tuning by 2Hz, which results in response changes of less than 1dB, so it is not an issue. The second WinISD graph shows the cone movement at maximum power, using the same colours, and this shows that an HPF is definitely having an effect. The horizontal red line is the limit for controlled cone movement, not the limit for coil damage, so I probably don't need an HPF for speaker protection, but using an HPF should give me better cone control and a tighter sound. An added advantage is that by suppressing the lowest frequencies, the battery will last longer. I already had a preamp from a previous combo amp design, which included a variable HPF, so I used that as the basis for this interim preamp. It contains three op-amps, and I configured them as a Hi-Z input buffer, a variable HPF, and a variable gain stage to provide both volume control and compensation for differing outputs from basses. The last image shows the 'finished' (cobbled together) preamp and a basic schematic. David

Hopefully - upgrading components on double sided PCBs was not in the original project spec. David

One of the first things I noticed about your class D amp was the size of the inductors, which led me to the conclusion that this pcb was not going to deliver the power that the chip could deliver. So far I have not felt the cores getting warm. David

That's a new one for me - what's a TLRT? David

Some progress, but mainly cosmetic 3 coats of Tuffcab matt black, and an aluminium back panel - to be sprayed black when completed. David

I bought a Samsung TV that had no audio output sockets, and average rear-facing speakers. I ended up buying a USB D to A convertor so I could feed analogue audio into the Hifi. One thing I did find is that even with a sound bar and TV from the same manufacturer, the volume control for the TV cannot be used to control the volume of the sound bar. David

Sadly, being able to fix the problems I have found so far does not equate to having it all under control - but thanks for that vote of confidence. David

The manufacturer's data sheet for the chip states "The high efficiency of the TPA3130D2 allows it to do 2 × 15 W without external heat sink on a single layer PCB. The TPA3118D2 can even run 2 × 30 W / 8 Ω without heat sink on a dual layer PCB." Also, although the amp is rated as 40 W into 2 ohms with a supply of 13 volts, playing bass through it, I'm measuring a supply current peaking at 0.9 Amps - so probably averaging about 0.5 Amps. Assuming the amp is taking 13V * 0.5 A = 6.5W and it is 80-90% efficient, taking the worse case, 20% of 6.5W is slightly under 1.5 W. The amp will be vertical on the back of the cab, a 15 mm thick module mounted in the 35mm deep void between the cab back and the aluminium electronics cover, so I'm assuming that ventilation holes above and below the amp will provide enough airflow to keep it cool, Testing it flat on the bench, it might have been a few degrees above ambient, but not warm to the touch. David

A little more progress - Edges rounded off, front baffle painted with blackboard-paint, fitted with grill stand-offs, and off-cut of grill cut to size. I considered whether to stain and varnish the cab, but based on the tide marks I got staining a bass body, I decided to go with boring Tuff Cab black - now on order. Electronics space painted, component placement worked out and sheet aluminium on order - Near edge: battery fuse, amplifier fuse and external power/charger pigtail - likely to last longer than a fixed fragile plastic socket. Centre: 40 W Class D amplifier. Allegedly a TPA3116D2 containing two paralleled pairs of bridged amplifiers, capable of driving 100 W into 2 ohms. I doubt that this design would, and I'm not going anywhere near that. Blank area: EQ - most of my basses have active EQ, and for those that don't, I have an EQ /DI pedal. The function I use most is a variable HPF, so the space will have a home-built FDeck HPF pre, and possibly a gain stage to drive the amp. Top edge: instrument in, volume, HPF frequency, on/off switch and charge/external power switch. David

First bass, school project - blockwood body, teak neck, Formica fretboard, no intonation adjustment, no truss rod, string height adjustment by grinding metal off the bridge. It worked, just. Bought and sold: Yamaha BBN4: upgraded to a 5-string, then sold this one. Cort Curbow: 5-string (owned for about a week, didn't like the tone through my rig, exchanged for RBX 765) Yamaha RBX765: 5-string - still got this Warwick Corvette 4-string fretless - Bubinga body, Wenge neck, Ebony fingerboard. Tuned BEAD. First attempt at fretless, eventually upgraded to a 5-string Warwick Corvette 5-string fretless - Swamp-ash body, Ovankol neck. Neck heavy compared to 4-string: tried various fixes then sold it Steinberger CR5M: 5-string EUB - hands couldn't cope so sold it. Yamaha TRB1005: 5-string fretless - nice to play, but my playing did not make the progress I had hoped for - sold it. Ibanez EWB205: 5-string ABG -still got this 4-string headless bass kit: started as a Hohner Jack copy and then I clipped its wings so it's an asymmetric paddle - still got it, but not playing it. Countryman Bass ukulele: tried EADG, then BEAD then decided to stick with 5-string basses only. Sold it Hohner B2 V: 5-string headless - nice and small for playing under a gazebo in the rain (I'm a busker) Still got it. David

My usual rig is a pair of 10s powered by an Ashdown MiBass 500W amp, but I can also use one of the 10s with a small battery amp for acoustic nights and small gigs. Unfortunately, at 300 * 300 * 450 mm, even that is a little bit too big to be unobtrusive, so I started thinking about something as loud as my 10 inch battery rig, but somewhere between a Phil Jones briefcase and a Roland Bass Micro Cube in size. Obvious first question, why not just buy one of those? Answer, the PJB costs more than I wanted to spend for something that would be used occasionally, and I haven't been impressed with the Bass Micro Cubes I have tried, possibly because I play low-B 5 string basses. My small battery rig is a class D stereo amp producing 12 W @ 8 ohms / 20 W @ 4 ohms per channel, and according to WinISD, will produce 106 dB from 100 Hz upwards at max volume using one 8 ohm Eminence Basslite S2010. The -3dB point is 66 Hz. That is what I want to achieve in a smaller box. After a bit of searching, I found a 5 inch Faital Pro driver, available in a 4 ohm version, and two of those in a cab 350 * 350 * 170 mm will produce the same frequency response and the same volume. However, Hoffman's Iron law kicks in here, in that a speaker can go low, go loud, or be efficient, but only two of those at a time. These smaller speakers take 4 times the power of the single 10 inch speaker to reach the same volume. However, for a battery-powered pub session of 3-4 hours, I can do that on one battery charge. A few pictures of the build - 1 The basic shape - speakers at the front, vent in between them, electronics compartment recessed into the back face 2 The cab is sized to include the battery, which sits on a sledge which comes in through an airtight hatch in the back wall. 3 I'm not sure if this is 'you can never have too many clamps' or 'you can never have too much bracing' Bill Fitzmaurice seems to have standardised on 15 mm ply and a shelf brace every 200 mm, and I'm using 9 mm ply, so I'm bracing every 150 mm. 4 Have I missed anything before I glue the second side on? More to follow David

I made a U-shaped sleeve for my Ashdown MiBass Mk1, and added kitchen-cupboard kick-panel brackets to a speaker cab top and to a sleeve bottom so that I could clip it together to make a combo or a stand alone. This one is finished in TuffCab. David

As of today, I will no longer be monitoring this thread. If you want me to help, send me a pm David

Rod Elliott recommends using the 100 ohm resistors on the outputs to ensure stability, especially when connecting cables to those outputs, so if you dispense with the resistors it might be advisable to put a small capacitor in parallel with the feedback resistor to roll off the gain at high frequencies. David

I'm not a nerd, honestly, I just happened to be searching for components when I checked into Basschat for a break. Digikey stock a switch which looks similar, but we need to check whether the pin spacing, etc, is the same. If your unit is USA designed thirty years ago, it may be imperial, and most components these days are metric. ENG_CD_1825290_A3.pdf The switch drawing in squares C6-C7 is the type you need (I think) so can you check the dimensions of your switch against this drawing. The pin-spacing-grid width and length is important, as are the locating lugs on the corners. The length of the operating lever might also be important if you want it to work. David

OK that's a side-operated two-pole 3-way slide switch with a long actuating lever. The first problem will be finding a replacement of the right size. Failing that, have you got all the bits from the existing switch? I'm happy to do a bit of digging, but I make no promises - I'm based about 5 miles out from Altrincham. David

I'm using D'Addario Chromes and I can recommend them. Also, although it may be a minority interest, I'm using a 5-string acoustic, an Ibanez from their 'Exotic woods' series.

My string adaptor just sits on the end of the existing nut. The nut end face is angled slightly, so the string tension pulls the adaptor towards the back of the neck. Also worth checking is the 'Overlord of Music' nut and bridge set, sometimes sold individually. That nut will take standard strings, but it clamps them by bending them through 90 degrees, which some strings will not take. I don't know if it is a drop-in replacement for the existing nut assembly. David