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What is up with the volume control? As far as I can find out: 250K logarithmic / audio. https://www.bassesbyleo.com/gl_bbe_wiring_diagrams.html. This thread might be useful https://www.basschat.co.uk/topic/309919-gl-spare-parts-looking-for-a-uk-supplier/ and this https://g-l-online-store.myshopify.com/products/split-shaft-potentiometer-tribute-series-bass. If it is not just the squirt of contact cleaner fix, I would desolder it and get the pot out to measure the shaft diameter and length. Useful hint: cover the body with card / cloth / masking tape, blobs of hot solder produce interesting results. No need to ask me how I know......

To encourage you, this, as built by my own bodging does not have neck dive, weighs in at 7.9lb (less now that the neck has a reduced profile) , 30.9" scale. Strap button is at about the 17th fret. It does have a 1Lb block of lead at the bridge end to stop neck dive. On the next one I am going to use an aluminium strap button extension bar behind the neck for the upper strap horn, rather than adding weight. A shorter scale length as @Jabba_the_gut uses in his builds would (obviously) help offset the increased machine head masses. Body elongation (as you hint at with reduced neck length) will also help. This bass has 13.5mm string spacing, playable with a plectrum, at the limit for me with fingerstyle. String spacing with 12 strings will be an interesting set of compromises.

Schmelzende Stompboxen - what a great name for a band

Rigel http://www.rigelinstruments.com/publish/abg.shtml and very nice they look and sound in the various youtube vids. I like db, I owned and played a db for about 20 years, I miss my db. I do not miss transporting it and now have an EUB. I can see the attraction of something in between e.g. http://www.claessenscustombasses.be/ or at the other end Rob Allen basses.

^ This. The heat and fumes are quite something even when done outside in the fresh air. This was just using CA to stop some small cracks in a domestic repair, not a major @Andyjr1515 type process.

I think we should be told, unless it is a matter of national security . Apols on thread derailment, however if I ever build a super extra long plus scale bass, the large body upper horn will show every finishing defect, so we need to know

Even when I take time, considerable care and effort then look, feel and think I have 'perfection', the gremlins intervene and create some new defects that require more work. I admire and envy those who have the skill and determination to get super high quality finishes. You know who you are

Try it for balance & weight. I have two, the bubinga bodied one is heavy (no surprise) and does not sit as comfortably as the ash bodied one. I suspect this is due to the chunky neck which the other does not have. Other than that, well made, stay in tune, they do the business. One is active, the pre amp is a bit neither here nor there.

You are quite correct, a boomer in US Navy slang is a ballistic missile submarine (SSBN). When the boomers are gone as suggested by @musicbassman, i.e. all the nukes have been used and WW3 is over, there will be little need for vintage guitars. In seriousness, having owned (in my youth, since I am a trailing edge boomer) what are now vintage guitars and comparing them to modern instruments, they are nice but I would not be putting my money into them. Modern (dirt cheap kit) is usually really outstanding value. Using a PA or 'stage volume' any subtlety or nuance of a really good vintage guitar is lost. It can be taken out without fear of loss or damage. A Robin Trower interview has stuck with me for many, many years, roughly summarised, he had vintage guitars and amps stolen, after that he chose to use modern kit that was replaceable in the same event.

Build and sell a few more basses of that quality. The bass amp of your dreams will then be yours

Inspirational! A great reminder of what can be achieved with chiselling skill.

Apologies to @Dom in Dorset, I had also misinterpreted the op and with hindsight (looking at the guitar quality) had stated the obvious that you will know. The extraction by drill hole was neat.

Assuming a dual action rod...... If it has come out from the headstock end (without any drama) then drive the new one in from the headstock end, unless I have missed something obvious. Prior to insertion check the welds on the new rod for any 'lumps' that might bind in the channel and grind them down. Round the edges of the fixed end to prevent 'digging in' and wax or PTFE spray the rod. Might be worthwhile getting the same into the channel somehow. Finally, I would give the new rod some hefty adjustments both ways. Better a duffer fails beforehand so be bold.

I am lost for words but am so glad to hear that you are alive and well (that is a relative term). Don't know what I can offer to help with from this distance. Can certainly give you a bass, though it will be long or medium scale.

@Silvia Bluejayis on the money (pun intended). Feeling idle, rather than making my own, I looked into the same problem for a different make EUB that I own. The time involved will soon mount up for a one off luthier made bridge which makes the Gollihur offer a no brainer. I have used Gollihur for strings, made in France, sent to the USA, then back here and duty applied. Still cheaper than here

Missed that, however turning off unwanted peripherals: wifi, BT, lowering clock frequency and using a single core will have a substantial effect on current draw. some data here gives an indication: https://www.mischianti.org/2021/03/06/esp32-practical-power-saving-manage-wifi-and-cpu-1/. At 10Mhz cpu frequency (more than adequate to control leds and make sample voltage measurements) the current draw is about 13.2 mA. In reality it will be higher even before the LEDs and potential divider currents are factored in. These could be switched e.g. > 60hz with LEDs, battery sampled every 10 mins? 5 mins?

Late to the party gorgeous looking bass, natural no scratchplate or control plate, my favourite combo. Dimarzio j types might be one answer. I have a set that have moved over several basses, humbucking split coils, so virtually a p pickup in a straight line. Lol autocorrect put humouring split coils at the first go.

1x15 would be of considerable interest, I have a pair of 3015 kappalites awaiting use

That is a genius idea (and once mentioned is obvious). I like it I also like your UC choice, my time has also recently been focussed on ESP32 with WiFi and BT.

A good trip out . If you are going to use a microcontroller with the marker LEDs you could use a simple potential divider and a GPIO with ADC to determine low battery voltage. There are also various Arduino ready made voltage sensor modules available very cheaply.

From Middle English fetlen to shape, prepare; I did not know the origin of the word until I looked it up, it can also refer to a person's health - e.g. to be in fine fettle. In a more useful vein, the multi channel piezo pre amp https://www.bassparts.de/epages/61038859.sf/en_GB/?ObjectPath=/Shops/61038859/Products/PPX. They also make other interesting stuff at £££.

Fully understand the string balance issue, I have had to fettle several piezo guitars and basses to get reasonable results. I can see the appeal of Individual string outputs, particularly if you want to use midi. The last question probably has the easy answer, Individual string intonation gives better results than bar bridge types.

Adjustable bridge something like the one I made (and pretty generic) , this will give you height and radius adjustment and allows a simple rod or flexible piezo. You have the luxury of being able to print something fancy. You could sink it into the body, have a look at this https://www.liutaiomottola.com/instruments/libellula.htm. I have owned a fretless acoustic bass with a simple bar bridge since 1980. The original Roto Tru Bass strings lasted 40+ years, intonation has not been an issue. If you want individual string piezo amplification and are going down the diy route, in principle I would use two quad JFET op amps, with individual op amp buffering of each string in unity gain non inverting mode (you can get octal JFET op amps, however afaik these are surface mount so present a further complexity). These outputs would then feed into an inverting summing op amplifier to allow the individual string outputs to be equalised (through some variable resistor arrangement). Input capacitance, consequent high pass filtering, and setting the bias voltage, depending on what your proposed voltage supply is will need to be considered. There are plenty of good examples about to study e.g. https://www.analog.com/en/analog-dialogue/articles/avoiding-op-amp-instability-problems.html and this one. the title is so understated a mere 464 pages. https://web.mit.edu/6.101/www/reference/op_amps_everyone.pdf Hopefully more experienced Electronic engineers / designers will be along who know what they are doing, or someone knows the commercial product that will do what you want. I have seen a suitable commercial bass piezo pre amp that has individual string inputs but can't for the life of me remember what it is . Me, I would go simple in the first instance. If it does not work (i.e. strings too imbalanced) then look at mk3 bridge with the added complexity.

Onwards and upwards Battery indicators are a whole bundle of interesting electronics as you will discover. It made me think of a simple alternative. Dual battery compartment with a two way switch over in the event of one running down. My ex military Land Rover had dual fuel tanks which made me think about dual batteries. I can not imagine the cost of filling it, or running it, if I still owned it. This JFET pre-amp looks really useful (and small) and can be ordered with 10 MOhm inpout resistance for piezos. https://www.ebay.co.uk/itm/272951584025?hash=item3f8d2ea519:g:-CUAAOSwoFtfBGX8 They also make a version ready made with jack plug etc. In terms of bang per buck, I really rate the Joyo 504 / 505 preamps, however they are probably too big for Flo2.

All the above points are totally sensible and a means to using time effectively. I personally don't see the problem with reading music as you play - being at a certain age I can sometimes forget basic chord sequences of things I have played many times but have not played recently. Remembering the fills, passing notes, tricky bits does not seem affected. I do have a problem with people not putting the time in beforehand.