Talk me out of it! [Super Headless Bass Circuit Modification]

Hi all.

I have an all original, absolutely as-it-left-the-factory, Super Headless. It is the only instrument I own that has not been modded in some way, even down to the original strap buttons. I'll admit that the strings have been changed a few times (so I can't be a real bass player, right?   ). And I've owned this beauty since brand new back in the 80s. My daughters reckon it'll form part of my funeral pyre when they push my corpse into the middle of the local marina in a rowing boat and throw lighted matches at it.

My dilemma is this. Let's be honest - the active pre-amp in this thing is dreadful. The treble boost would peel paint, and the bass boost is too boomy. And it's either/or. There is no way to strike a tonal balance. Don't get me wrong. I adore this bass. It plays like a dream. Other big name basses have been and gone in my life through the years, but this is my constant companion for bringing the thunder.

Should I modify the pre-amp (and by modify, I mean bin it and fit my own - I'm an electronics engineer)? I've asked myself this question so many times over the years. Now I'm in lockdown due to the pandemic I have the time to take this on as a project. Feel free to flame me for my heresy. But should I do it?

If I do, it'll mean being able to ditch the graphic EQ on my pedal board. If I don't, it'll mean I'll probably ask this question again in a few years. 

Just hang onto the OEM bits and get stuck into it, mate - everything is reversible and if it makes you play the thing more, then how can it be bad?!?

Yes I 100% agree with Corsair on this - make it sound great but hang onto the original bits for resale value in the unlikely event that happens

Buy a decent bass amp...

Westbone wrote:Buy a decent bass amp...

I build my own. 

Corsair's advice is the best way to go. Life's too short to be unhappy with your gear!

Thanks guys.

Work starts this weekend. I've 18 volts to play with, so plenty of headroom. I want to leave the guitar cosmetically unchanged, so will probably look at building something that can sweep the mid range frequencies with the knob on the front and fit some presets to tweak (then forget) to be hidden inside the control cavity to tailor the rest of the spectrum.

Live the dream Sir and make that baby great again. I've dreamed about a super headless.....you are a blessed man. Will drink a cup of Yorshire Gold tea today to you. .

matsumokukuku wrote:...Yorshire Gold tea...

Very noice int it?

I can't get on with the taste of tea personally (tragic, I know) but I keep Yorkshire Gold in stock for my dad and my sis because they won't drink anything else. 

I've made a start on pulling this thing apart and now doing a bit of circuit tracing to see how that first toggle is wired for the stacked humbuckers. Until I can see how that switch is configured I can't decide whether it's a coil splitter or a series/parallel selector. Does anyone know the answer? There were no manuals or instructions when I bought this bass. I've always just fiddled with the switch to get the sound nearest to what I wanted. ;-)

Had a quick look on the website and also catalog scans and its simply listed as "Dual Tone Switch"

challpa wrote:Had a quick look on the website and also catalog scans and its simply listed as "Dual Tone Switch"

Thanks. That's what I'd found too. A bit vague. 

Having traced it through, it's a series/parallel switch - and thanks to Westbone for confirming this. 

I have updated the website entry.
Thanks fellers! 

Barry wrote:I have updated the website entry.
Thanks fellers! 

Life got in the way until this afternoon.
Built on breadboard and working nicely. It gives a decent amount of punch in the mid-range (around 400Hz) that I'm happy with.

All that I have to do now is remember where I put my oddments of Veroboard so I can get this thing soldered together and mounted up.

Once it's all in and working I can post a cleaned up version of my hand-drawn scribbles if anyone is interested.

Dragondreams wrote:... I can post a cleaned up version of my hand-drawn scribbles if anyone is interested.

Oh, heck yeah!

I agree with Barry... Any info and help pays off in a long way.... might need it if my 5 string 775 electronics konk out on me. .will toast  to you with more Yorkshire gold...

Thanks guys. :-)

I had more time on my hands over the weekend and pulled the "Mk1" (mid-boost) circuit out of the bass. It was okay, but having spent some time playing with it, it wasn't quite what I was after. I have a couple of Sire Marcus Miller Jazz Bass clones, and the pre-amps in those are awesome, which kind of set me a benchmark. "Mk2" is now a "proper" two-band EQ with around 15dB of cut and boost at two centre frequencies of 50Hz and 4KHz.

I've had to order a dual concentric pot for the treble and bass cut and boost because I don't want to make an extra hole in the body. The plan is that the volume and tone controls will move to occupy the current tone and boost control positions. What is now the volume control will become a pickup blend control. And the pickup selector switch will come out so I can drop the dual pot in there. This will also allow me to keep the overall "look" of the control layout pretty much as it is. I'm keeping the original parallel/series "tone" switch and the active/passive switch exactly the same.

Work on it has come to a halt until the dual pot arrives, but the circuit is built, tested, and mounted on the control cover in place of the original circuit ready.

I'll post some pics and the drawings for the two different pre-amp schematics once I've fed me and the cats (almost dinner time here in the UK).

I didn't bother drawing out the mid-boost circuit. To be honest, it's not really worth the effort.

The two-band is nothing revolutionary either. It's a simple Baxandall circuit round a dual op-amp. There are loads of similar examples all over the interwebs. I use pretty much the same circuit in one of the models of valve amp I build for customers.

I'm pleased it's coming together with a minimum of fuss, eh... and thank you for drawing out the circuit for us!!

I have added this info to the Restorations & Modifications section of our website: LINK

(I've also edited the post title so it can be found when searching the forum)

Thanks!

Hi All,

I have a Superheadless and often wondered about installing a different pre-amp (or even removing and using passive-only) as I found it gobbles batteries for fun.

Does the supply rail HAVE to be 18volts, or is it possible to have it at 9volts and have the batteries wired parallel to give longer life?   

Can this amp circuit be modified to have a 9v rail, or are there other designs out there?

Thanks

I know they make 18v mods these days. Especially for some of the fenders with coil tap. Also just for a little electrical expertise if you wire it in parallel you don't increase the voltage if you wire it in series you increase the voltage. Parallels great for keeping the voltage the same but increasing the life.

trying to identify this one no serial plywood body only markings are on back of neck base