Mottlefeeder

I've had mixed results depending on the design of the cab. Some need to be tilted back, with support under the front, but others need support at the back if they are tilted back far enough to be useful. I also had one that was back- supported, and worked fine on the flat, but tipped upright again when used on a raked stage. It's worth checking if you haven't already done so. Staying with your design, if you have access to an angle grinder, (or a hacksaw?), you can remove part of the hinge casing to ensure that the handle travels past 90 degrees. As an alternative, you could screw 'captive nuts' https://www.screwfix.com/p/insert-nuts-type-d-m6-x-20mm-50-pack/61859 into the speaker cab base and bolt on a bracket when needed. David

Sanded the panel down, back to bare metal in places, then re-primed and re-top-coated it. Printed off another set of transfers and managed to apply them to the right parts of the panel, As they started to dry, they started to peel off - it seems that they don't stick to a matt paint finish. Dug out my time-expired dry transfers and applied a simplified set of control legends. They appear to be staying on, and now have two coats of lacquer to help them. Assuming no more problems here, I can start to reassemble it tomorrow. David

A short break and back to work. The back panel has been cleaned up, painted, and transfers applied. Unfortunately I followed the supplied instructions, which used a china mug as the recipient, and this resulted in too high a temperature for the transfers and paint I had used. Putting the transfer back under water did not make it come off (which bodes well for the future) but I now have to scrape off the bubbled transfer, probably respray the panel, and start again. David

A little more progress. The original plan was: input buffer -> HPF -> variable gain stage to provide a volume control, -> amplifier. That was simplified to: fixed gain buffer -> conventional volume control -> fixed gain (x10) -> amplifier, as in the previous post. Having discovered that my earth referencing was all wrong, and fixing that, I then decided to try and resurrect most of the original three stage design - buffer -> hpf -> conventional volume control -> boost -> amplifier. I discovered that all the extra capacitors I had in circuit meant that i could not fit that circuit onto the area of stripboard that I had, so I tried putting the gain in the buffer stage and removing the boost stage: buffer (x10) -> HPF -> conventional volume control -> amplifier. Unfortunately, the gain at which my passive bass can drive the amp to full power gives me clipping in the preamp with my active basses, so I do need some form of adjustable gain. The compromise is a Hi-Lo gain switch in the buffer stage. The current circuit looks like this. David

Finally, I've found the source of my problems (with this preamp). The pcb that I have been adapting came from a previous project that used positive and negative supply rails and the input and output were referenced to the zero volt line. In this battery system I've used a positive rail and a zero volt earth reference, so the input and output were referenced to the zero volt rail, while the bias resistors, feedback loops and volume control were still referenced to the mid-point rail - diagram (A). At low gains, it worked, but as I increased the gain, the circuit became progressively more unstable. I've now wired it so that the input, output and volume control are referenced to the zero volt rail, the bias resistors are referenced to the mid-point rail and the feedback loops are referenced to the zero volt rail by blocking capacitors - diagram (B). It now works as it should, with minimal hiss, no instability, and minimal switch-off click. David

Running it is not the problem. I'm trying to get rid of the loud click when you shut it down. David

Thanks for that. So far, the resistor/capacitor combination is working for me. If it works less well when I add another op-amp in circuit then I'll start looking at more complex solutions. The "plate amp" needs 200mV for full output, so about 600mv pk-pk. Assuming the preamp output voltage is supply rail - 1.5V, I could manage with a preamp supply of 4.5 to 5 V, assuming that the figures I have been given refer to sine wave measurements. However, my gut feel is that more headroom is better. David

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