Aria Pro II SB-1000 bass electronics restoration

[Apophenia Savant]

On 5/24/2021 at 7:56 PM, Prostheta said:

Sure thing. PM me here for my email.

The 80s circuit in the SB-1000 (passive/active) is problematic in that it requires dual value pots which are not really available commercially. I've always preferred the 70s active-only circuit. To my ears it sounds better, even though the only real difference is in the varitone filter.

How are the varitone filters different?

I have a Batwing in a black refinish, and I've finally started getting on with it. The first four settings seem to completely change the sound of my fret noise more than anything else; which is actually pretty cool if any fret clatter is part of your sound. (I feel like it's an underrated tonal element of a good bass sound personally)

I forget what the 5th setting sounds like, but the 6th is the dub monster when you roll off your treble. 

My re-attraction to the bass is mostly because I had a new nut cut and had it strung up as a B-E-A-D flatwound bass for about ten years. A couple weeks ago I decided to string it back up E-A-D-G, since I still had the G string from the 5string set that I bought, so they are the same identical strings. The weird thing is, the defined fret sound goes away when I string it back up as B-E-A-D, regardless of how I adjust the action or truss rod. Not that it doesn't have fret sound as a B-E-A-D bass, but for some reason when it's strung up proper the it feels like it there is a tonal pocket that it falls into now. I imagine it handles roundwound strings differently, but the flats are really underrated on this bass.

Are the pole pieces all identical? Or did they do something to finesse the sound of the individual strings?

[Prostheta]

The varitone is a stack of RC values that are used by the preamp to form an active LPF with a reasonable mid bump before the cutoff, hence why it changes the "character" of the sound differently to a passive LPF like the tone knob. I've played around with the idea of making an alternative varitone that is continuously variable as opposed to a selection of six RC values, partly because of the control but mostly because the rotary and fourteen components fabricobbled around it was just another example of Aria Pro II being slightly mad in the head. I didn't go too far down that rabbithole.

The "tonal pocket" you mention is why the SB-1000 is a recognised and desirable instrument....the weird neck taper, comparatively-larged cross section of the neck profile, Jacaranda fingerboard and neck laminations of quality wood that doesn't really come around any more combine to make it what it is. The 5th-7th positions have a very distinctive midrange which was common to the sister models such as the SB-700, etc. They were the same dimensionally, but different in terms of electronics and hardware configuration. That "honk" is what makes them stand out in pop recordings of the time....they sit differently in the mix to say, a Thunderbird or a P-bass. Maybe a bit more into J territory?

The polepieces in the MB-1E were all steel slugs of slightly differing lengths to match the string radius. They were built using two rotation mating ABS bobbins that look similar to a J pickup, but with evenly-spaced pole positions so generally a great big ceramic humbucker. Later pickups like the MB-II and MB-III used the same configuration, but half-loaded the bobbins with poles or rod magnets in a P-bass pattern.

Fret clatter is definitely underrated. I don't think Entwistle, Lee or Harris would have the same punch without it.

[Apophenia Savant]

3 hours ago, Prostheta said:

The varitone is a stack of RC values that are used by the preamp to form an active LPF with a reasonable mid bump before the cutoff, hence why it changes the "character" of the sound differently to a passive LPF like the tone knob. I've played around with the idea of making an alternative varitone that is continuously variable as opposed to a selection of six RC values, partly because of the control but mostly because the rotary and fourteen components fabricobbled around it was just another example of Aria Pro II being slightly mad in the head. I didn't go too far down that rabbithole.

Does the subsequent 80's varitone differ in terms of function, or just construction?

Thanks!

[Prostheta]

Not really, aside from a minor value change in one position. In the 80s circuit, the varitone is active all of the time and the switch controls active to the backup passive mode. In the 70s bass, the varitone can brought out of circuit using the switch, in which case a small value capacitor and resistor are left in circuit to keep the filter bleeding off RF frequencies.

Just look at how redundant that varitone is! Unfortunately there's not much simplification that I can do with the retrofit preamps. 22MOhm resistors aren't a common value, so it laying eight of them around there is silly talk.