Aria Sinsonido preamp repair

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Re: Aria Sinsonido preamp repair

Post by Folderol »

@hugh
The tone control tests suggest that these mics are round about 1k. Even a 600ohm source means the control has less effect. 100ohm would give a -3dB point of 3.4kHz at maximum attenuation.

@Dave
That was my first thought, but they look like standard SM electrolytics, and the codes also suggest that. I'll be replacing the 0u47 ones with multilayer ceramics. They are not much bigger, more stable and much quieter.

I'm a bit concerned about the volume pot wiring, as it will have a frequency component, depending on it's position (as well as what's on the output). Near minimum the LF cutoff will be about 400Hz as only the 10ohm resistor will be relevant against the 33u cap, but at full volume it will be 4.8Hz. This could account of the apparent poor low end. So maybe it should be run as close to max as possible.

And finally a bit of bad news. My sig genny seems to have developed a fault on it's higher ranges and goes unstable when the gain is turned up :cry: and it's only about 45 years old.

I'd write a nasty letter to the manufacturer... only it was me :shh:
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Re: Aria Sinsonido preamp repair

Post by ef37a »

" My sig genny seems to have developed a fault on it's higher ranges and goes unstable when the gain is turned up"

Sounds like a duff decoupling CAPACITOR to me mate!

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Re: Aria Sinsonido preamp repair

Post by Folderol »

Job done now, and the beastie will soon be on its way home.

Latest drawing is here. Incidentally, I tend to post links to PDFs for drawings as they are much clearer than any bit-image. The changes are all indicated as you can see.

Aria Sinsonido Preamp final.jpg


Swapping the tone control caps for ceramic ones was a no-brainer. As well as being more stable, they are actually smaller than the originals!

From actual frequency response behaviour I've downgrade my guess at the original 'dry' caps to only 100nF.

Increasing the 33u caps to 47u and adding the 100ohm resistors, makes the worst-case LF -3dB point about 45Hz. That's with the volume control a sniff above zero. As the volume level increases that drops to to about 30Hz. This has one drawback in that the level will be lower in headphones. However, at the same time the battery life will be slightly better as the amplifiers won't be dumping power into a 10ohm resistor at low volume.

I added an extra resistor, rather than changing the value of the existing one partly because space was getting really tight, but also because it's quick and easy to revert if needed.
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Re: Aria Sinsonido preamp repair

Post by Martin Walker »

Folderol wrote:Job done now, and the beastie will soon be on its way home.


Bravo Folderol :clap:

- looking forward to hearing the end result in situ in the instrument :thumbup:

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Re: Aria Sinsonido preamp repair

Post by Dr R »

Yes, huge thanks again to Folderol for doing this. :clap:

Hope to have the board and bass reunited this weekend, though the football may have an impact on available time ;-)

I didn't record the original sound, but will definitely post recordings of the new improved sound.

Rich
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Re: Aria Sinsonido preamp repair

Post by Dr R »

Quick update:

"Real Life" has completely got in the way of reuniting the board and bass. :(

We've therefore booked a meeting room at work over lunch tomorrow and the plan is to bring in the gear to reconnect it and record it then. Fortunately the directors on our floor appreciate that most of the time we actually do useful and productive work:

http://dilbert.com/strip/1994-06-26

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Re: Aria Sinsonido preamp repair

Post by Folderol »

'Real Life' eh? Not sure I want one of those - sounds expensive :tongue:
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Re: Aria Sinsonido preamp repair

Post by blinddrew »

I think I saw one from a distance once, but I wanted no part of it... ;)
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Re: Aria Sinsonido preamp repair

Post by Dr R »

Still not done the soldering. There is a small, but at least non-zero, chance of it happening this weekend.

"Real Life" is on average a "good thing", but the peaks and troughs are unpredictable. Maybe there should be some sort of calibration system which allows for dynamics but didn't leave you totally exhausted at the end of two weeks?
LUFS = Life Units relative to a Fortnights' Sleep

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Re: Aria Sinsonido preamp repair

Post by blinddrew »

Dr R wrote:"Real Life" is on average a "good thing", but the peaks and troughs are unpredictable. Maybe there should be some sort of calibration system which allows for dynamics but didn't leave you totally exhausted at the end of two weeks?
LUFS = Life Units relative to a Fortnights' Sleep

Rich


Presumably the scale goes into the negative! :D
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Re: Aria Sinsonido preamp repair

Post by Dr R »

I was thinking more that if there were too many constant peaks at high amplitude it was unpleasant and grating. In which case negative units would imply something very strange that I can't quite think of an analogy for..
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Re: Aria Sinsonido preamp repair

Post by blinddrew »

Dead on your feet. ;)
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