Aria Sinsonido bass, control electronics/PCB AS690B

[sandy_r]

Around 2009, having got a blues/rock band together, i bought a second-hand fretted Aria Sinsonido bass and started to use it exclusively as my gigging instrument - great tone, easy action and soooo light!

 

...just one problem - the control electronics had a mind of their own and had to be left at the only setting which produced a musical sound

 

i searched online and found plenty of evidence for other owners with Sinsonido control PCB issues ...but no solutions offered, except trying to get another flaky PCB from Aria as replacement  

 

In 2014, when i started playing with an acoustic-oriented band, i had the Sinsonido converted to fretless, and i made a replacement PCB using a JFET to give me proper control of Volume and Tone. i posted the JFET preamp circuit at the other site, which had several Sinsonido threads (i hadn't found BC at that time!)

 

 

 

 

The circuit provides correct biasing of the Sinsonido electret mics, full control of Volume and Tone (12 o'clock=flat; 8 o'clock=max treble-cut; 4 o'clock=max bass-cut); battery drain is approx 2 mA; no headphone output provided

 

[FET pre, Tflat]

 

[FET pre, max treble-cut]

 

[FET pre, max bass-cut]

 

NB  i should emphasise that this circuit, and the 2 following, were created (or modded) to overcome faults occuring with the original Aria PCBs whilst keeping the full acoustic tones of the electret mic pickups in the original

 

Edited December 21, 2023 by sandy_r

[sandy_r]

Since then I've joined BC and found more reports of Sinsonido control woes, both here and at SoundOnSound (an excellent account by @Richard R of a team effort in 2018 to fix a Sinsonido with the control issue)

 

The SoS thread produced the first look at the Sinsonido PCB circuit, with all its weirdness - the control issues appeared to be due to a combination of aging electrolytic capacitors and non-standard design with additional filter components

 

i bought some used Sinsonido parts and tested the PCB in my own Aria bass - the Tone control had no effect, and the output was very low

 

i've re-created in part the SoS fix on that old Aria board, and i've also removed un-necessary components - the Aria PCB + fix is now operating acceptably (to the spec presumably intended by Aria): Volume is working correctly; Tone is working as a conventional 'Treble-cut' type control, as used in passive guitar controls; battery drain is slightly over 10mA; if you use a standard instrument jack-lead, as suggested by Aria, then you'll lose 1 channel from the 2 mic. pickup in the bridge (so the output will either favour the E string or the G). You would need a stereo-to-mono adaptor cable to produce a combined mix of the 2-channel output

 

 

[Aria PCB schematic by W.G., from SoS thread - annotated here for this fix]

(Tone electrolytic caps replaced with multilayer ceramics; un-necessary caps removed - all others replaced with Tantalum bead electrolytics)

 

[Aria PCB fix, Tflat, 2 channel mixed]

 

[Aria PCB fix, max treble-cut, 2 channel mixed]

 

Edited December 21, 2023 by sandy_r

[sandy_r]

As a 'halfway-house' solution between my JFET preamp (2 channel; full VT control; 2mA drain; no headphone out) and the Aria preamp + cap fix (1 channel; V + Treble-cut; 11mA drain, headphone out), i've drawn up and tested a circuit based on the Aria components

(2 channel, V + Treble-cut; 4mA drain, headphone out)

 

It keeps some aspects of the original intent by Aria, but hopefully improves some of the issues:

• it uses the same IC chip, LM386, which has low distortion and noise levels and can drive headphone output;
• it uses exactly the same electret biasing and Tone components, so the source sound is unchanged;
• the current consumption has been reduced to 50% of the original circuit, doubling the battery life;
• using a standard guitar/instrument jack cable (ie. mono) now keeps the signals from both electret mics in the bridge, instead of only one;
• the electrolytic capacitors (which dry out with time and have caused a variety of unmusical effects) have been replaced with either tantalum capacitors (much longer life and reliability at these low-power levels) or good quality non-polarised capacitors, where more appropriate;
• the headphone output feeds the stereo ¼" jack (as a mono signal, now, ie. same to both ears, rather than one mic signal to each ear)

 

The signals from the 2 electret mics are mixed equally into 1 channel now, using a pair of 47k ohm fixed resistors (these could be replaced by a single 100k trim pot, which would enable the balance between the 2 mic outputs to be adjusted/preset)

 

Since the circuit uses an LM386 IC in standard configuration, the core part of the circuit can be built using a generally-available PCB/kit for DIY construction, populated with the components shown here. The remainder of the circuit just adds the passive components for the electret biasing, the dual Tone control, and the outputs to the dual Volume control (a total of 6 fixed resistors, 4 capacitors and 2 dual 1k ohm potentiometers)

 

[photo of new DIY Sinso LM386 board]

 

Suitable LM386 kits can be found from all the usual suspects: for the prototype, I used one of the PCBs available for the Ruby Amp (chosen for its small size), but there are many general-purpose LM386-based audio kits which would be suitable

 

[1x LM386 pre, Tflat]

 

On my schematic for this new board I show an optional fixed-gain addition, between pins 1 & 8 - the original Aria board didn't use it, and I haven't found it necessary. If wanted, the default gain can be increased from the standard 20x anywhere up to 200x.  The LM386 datasheet contains the details (be advised, though, that increasing the gain will increase the noise floor, it could seriously overload your amp input, and adversely affect the battery life - you may also find that you need to 'customise' the kit PCB to accommodate both of these 2 extra-gain components)

 

Edited December 21, 2023 by sandy_r

[sandy_r]

Comparing audio clips of Sinsonidos owned by @Aalin, @GetFletch and me, it seems that there might be an additional issue with the Sinsonido electronics: the bridge pickup arrangement

 

The strings rest across the top of the pickup tube (which must have some amount of mute action). It appears that it is possible for the tube and content, under some conditions, to add unwanted 'buzz' or distortion to the required signal from the strings. The pickup designer has been contacted to ask for setup/adjustment guidance, but no info. received yet

 

Included in the used Sinsonido parts, which i bought, was a bridge pickup that i was able to inspect. The 2 electrets are inserted at each end of the tube, and there is some kind of internal baffle arrangement, which can be adjusted using 2 allen-screws through the top of the tube

 

I've been able to get electret mic. inserts (eb*y, etc) which are very close to the original size (approx 6.5mm diam., 5mm long, no-pin), which appear to have suitable specs. for the frequency range and operating voltage

 

[photo of rather grubby salvaged pickup tube, mic extracted, and possible replacement mic]

 

So, with replacement mics, and one of the replacement control circuits, it should be possible now to keep a Sinsonido in good working order, from an electronics PoV

 

Edited December 19, 2023 by sandy_r

[Aalin]

It's a huge job that you did Sandy for all the owners of Aria Sinsonido.
Speaking of the internal baffle arrangement, which can be adjusted using 2 allen-screws through the top of the tube,
Does trying to adjust the screws, turning them one side or the others could change the sound, to try to find the best position for the best sound possible ?
Thank’s for your answer
Alain

[sandy_r]

3 hours ago, Aalin said:

...
Speaking of the internal baffle arrangement, which can be adjusted using 2 allen-screws through the top of the tube,
Does trying to adjust the screws, turning them one side or the others could change the sound, to try to find the best position for the best sound possible ?
...

 

thanks Alain, i hoped that creating a reliable PCB would be the answer to all the audio issues with the Sinsonido, but i don't think we are any closer to the answer about the 'cranked' and 'muddy' sounds we get sometimes 🤔

 

i was hoping that we would get some answers about pickup adjustment from Soloette, but no news yet.  In the meantime, i'll try adjusting the Allen screws on the spare pickup first, and look for any visual change - then i can try adjusting one screw on my Sinso pickup whilst recording, maybe we can hear some effect?

 

à suivre (maybe on the other Sinso thread?)

 

Edited December 20, 2023 by sandy_r