Mottlefeeder

Some progress to report - I've breadboarded a non-inverting, unity gain buffer followed by a conventional volume control followed by a gain of 10 non-inverting stage, powered from a 12 V battery via a 240 Ohm resistor (dropping about 2 volts) and a 470mmF smoothing capacitor. It is stable, loud, and has a subdued click when switching off, and I can live with that if I make no further progress. Thanks to @Stub Mandrel for pointing me in the right direction I tried to use an LM317 to regulate the supply, but the audio circuit started motorboating - whether that was because I adjusted the voltage while it was live, I don't know. I'm also a bit short on headroom if you assume the minimum battery voltage to be 10.5 v and the regulator drops 2.5 volts. The next test is to see if I can add a variable HPF before the volume control, without it becoming unstable. David

You are right - there isn't a difference. The diagram I have shows the contact numbering going down on one pole and up on the other, like an integrated circuit. That numbering does give you a difference, but it looks like it is wrong. One lives and learns. David

I disagree. The supplier's connection table in my second post above shows that when the switch is in the central position, both poles connect to the same end, but with the switch not central, the two poles switch to opposite ends. If you turn the switch through 180 degrees your centre position will connect to a different set of contacts, so orientation is important. David

I can't tell from the photo whether it is notch up or notch down, but I also can't confirm that any two switch manufacturers do it the same way, so the only way to check it would be with a multimeter, or a battery, bulb and length of wire. You need to check whether 'switch in central position' connects the centre and upper contacts or centre and lower contacts in the original switches and then check that you have done the same. David

The switches are not symetrical in their operation - Toggle position vs contact position: P1 • 2-3, 5-6: ON P2 • 2-1, 5-6: ON P3 • 2-1, 5-4: ON If you have the switch wired upside down, then it will not switch the way the original did. That might be worth checking. David

I think that would make sense if the single coils need to be phase reversed to give you a scooped mids sound. David

We are on the same page, but your method would prevent a high output bass from causing clipping within the preamp. Thanks for that. David

It seemed like a good idea, but without a 'scope to find out what is going on, I'm minded to simplify rather than tweak. The pots are quite a distance from the pcb, and my use of screened cables to/from the volume and the variable hpf pots may be providing the capacitance giving the instability. It will be easier to stay conventional, scrap the variable hpf, mount the pcb on the input jack socket and take its output to a volume control then to the amp - the signal path stays on the pcb. David

A bass on its own does not deliver enough signal to drive the amp to clipping levels, so a unity follower would raise the input impedance to suit the passive bass, but not allow me to use the full capabilities of the amp. I think it would have to be non-inverting, with gain, and fed from a stabilised supply, feeding into a conventional volume control. David

Did a little bit of investigating, and the conclusions are not good. I had hoped to use an inverting op-amp configuration with a pot in the feedback loop to provide variable gain / volume, but it was unstable, as well as noisy on power down. I've disconnected the pot, and substituted a trimmer on the pcb, and a conventional volume control between the preamp and the main amp. It's still unstable and noisy on power-down, so the problem is elsewhere, possibly the 100 mm lengths of screened cable between the pcb and the HPF dual pot. So, I'm looking at a strip out and rebuild to get a stable preamp. I've stripped it out, and substituted a pedal eq unit instead. No instability, no hum, no noise on power down. In summary, I've now got a fixed 50Hz 12dB/Octave HPF in circuit within the amplifier module, and I'm wondering what I gain by rebuilding the preamp. Without a preamp, my active basses will drive the amp to something less than full power, and have their own eq, so my work around is to omit the preamp pedal for quieter gigs, and put it in circuit when needed for the volume boost, or the passive bass, or for rooms with odd acoustics. End of the road? David

Making slow progress, but getting there. 1. A plywood base plate 2. Amp and sockets fitted 3. Plate fitted to speaker cab. I still have to check whether the preamp clicks during switch-off with this amp, and fix it if it does. David

The specification for a speaker usually defines the range by the frequencies at which the volume has dropped to 50%. Going slightly below the specified low limit will result in even lower volumes, until you reach the point where the speaker+box no longer behave as designed, and the speaker movement becomes uncontrolled. This could cause speaker damage. Hypothetically, using a sub to reproduce the fundamental will put you in the audio spectrum used by the kick drum, and the result will be indistinct and muddy. David

That looks very similar to mine, which works on my Hohner B2v, so it should work if you can find one. Buying the adaptor brings in savings when you next want to change strings - you have more choices. David

I've just followed the link in your original post - no, don't go for that one. It's a replacement for everything beyond the nut, and may not fit the neck profile, or allow you access to your truss rod. Also, there are a couple of clamp-bars on the fretboard side, which pull the strings down onto the nut or zero fret, but do not clamp them enough to allow you to safely cut them. For that, each string has to be bent through 90 degrees and fed through a hole to be clamped by the screws on the end of the headstock. Roundwounds can bend like that, flatwounds tend to split and unravel. If you look at the clamping screws in the picture, you will se that they are 90 degrees round from where you might expect them to be. https://www.ebay.co.uk/itm/Black-4-String-Electric-Headless-Bass-Guitar-Locking-Nut-With-Screws-Hex-Key/284165012089?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20201210111314%26meid%3D33b30b56236349f5ab09652353c95d31%26pid%3D101195%26rk%3D1%26rkt%3D12%26mehot%3Dco%26sd%3D293146773871%26itm%3D284165012089%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseUnbiasedWeb%26brand%3DUnbranded&_trksid=p2047675.c101195.m1851 is the same part, but the pictures show it better. David

I could have posted this as a NAD, but it's probably not of interest to most of the members. I've now taken delivery of a Kenwood KAC-M1814. It is designed as a booster for poor car stereo systems, so it delivers 45 W x 4 into 4 ohms (or limited in some way to 45W x 4 into 2 ohms) / or bridged pairs to give 90W x 2 into 4 ohms. The first picture is the new amp compared with the 2-channel class AB amplifier that still gets dragged out occasionally. That one delivers 75W into 8 ohms or 150W into 4 ohms. That rig, with its 7AHr battery will run for about an hour, and I carry it as a back-up when we do generator-powered gigs etc. The KAC-M1814 has good and bad points: + it is small and powerful + it has a built-in variable HPF going down to 50Hz + it has a built-in low battery voltage cut-off + it has been designed and tested to operate in hostile environments + it is sold by a reputable company - the quiescent current is 800mA. so even at low volumes, it will only run for just under an hour or so on my smaller battery - the power output into 4 ohms x 2 is good, but into more conventional 8 ohm speakers it is only 45w per speaker when bridged. - mounted on the back of the speaker cab, it is functional rather than elegant. Just for comparison: Ashdown MyBass + mains invertor: Quiescent current 1.7A / average current 2A / peak current n/a Kenwood class AB: Quiescent current 440mA / average current 2.2A / peak current 5A Kenwood KAC-M1814: Quiescent current 800mA / average current 1.2A / peak current 2A So, with an amp in a metal box, and a requirement for a larger battery (the speaker cab is designed for up to 7AHr), my small rig is coming in at 9.6Kg, and should run for about 4 hours on the built-in battery. For an all-day busk, I would probably use the more efficient Basslite 10 inch speakers, and a large leisure battery. Back on track. David

I'm using one of these adaptors with flat-wound strings and have had no problems. The hole that you thread the string through is slightly dished, and the end of the locking screw is slightly convex, so it crimps the string outer against its inner, and so the string does not unravel if you remove it once it has been cut. David

Just checked the @upside downer link to the inventor's explanation - you are spot on. One lives and learns David

I can't see anything in shot that would provide that level of reverb/echo. If you ignore that, it's just a bowed banjo. Where's my hard hat? David

This is the pdf I saved from the Eminence site in 2012 Basslite_S2010.pdf

This is the graph from the Eminence web site - where did yours come from?

If they took one straight from the production line and tested it without running it in, would that account for the difference? David

Still thinking about my options, given that no amplifier other than the reject is small enough to fit the electronics bay, and I'm now thinking of just putting the preamp in the electronics bay, and making 'plate amplifiers' to bolt on the back of the cab. That would give me the versatility of connecting up an amp appropriate to the gig, but still give me the HPF I need to protect the speakers, Also, the rework on the electronics bay metalwork would only have to be done once. David

The problem with a mains amp and an invertor is the standing current of the power supplies. My 150 W and 300 W invertors have 0.5-1.0A quiescent current, and my Ashdown MyBass takes another 1.0-1.5 A (from the battery via the invertor). That's OK if we are busking all day and using a 110AHr leisure battery, but it's a third of my built-in battery capacity gone before I've amplified anything. Looking at car amplifiers, something like a Kenwood KAC-M1814 (two pairs of bridgeable amplifiers) would give 2 x 45 W @ 8 ohms / 90 W @ 4 ohms which would put me up in PJB territory for a twin speaker rig, and only have one set of PSU losses. My existing Kenwood class AB car amplifier - 2 x 60 W @ 4 ohms - has a quiescent current of 300mA, but takes more than class D when amplifying. Hopefully the class D unit will give the best of both worlds. I've considered lithium batteries, but the cost of new chargers, and a leisure battery capable of lasting all day, is more than I can justify. Also, the rest of band seem to have standardised on lead acid batteries and invertors, so there is merit in staying compatible with them. David

I seem to have walked into a dead-end here, so I'm having a rethink. The metalwork fits the existing amplifier module, but that appears to have quality issues, so I'm returning it and I'm loathe to replace it like for like. As @Chienmortbbcommented, the alternatives may also have quality issues, and it would cost me Import duties and processing charges to find out. The next option is to use a physically larger, and now obsolete class D module that I already have, and start again with the metal bashing. The first problem with that solution is that I then do not have that amp module available for its previous role. The second problem is that if/when that module dies, I'm back to square one. Option 3 is to fit the combo cab with a speakon socket and a power/charge socket (the battery is inside the cab), and to mount an amp module on a plate/power bulge on the back. This keeps the obsolete amp accessible to swap between old and new projects, and allows me to swap in a newer and/or more powerful amp if and when required. Option 4 is to go upmarket and buy an Ice or Hypex or equivalent module and a power supply to run it from 12 V. However, for the cost of doing that, I can get a car stereo Class D amplifier that is designed to do the job, and built to be robust enough for a car environment, and I can sell it on when I stop using it. At the moment I'm going with option 3. David

I have used this supplier for several cab grills and have been very happy with the results (he also offers a powder coating service) - http://www.speakergrills.co.uk David