Sonic Impact Opened for mods--Help!

[sx881663]

Originally posted by D0Hbert
Is it ok to use 1% 1/4w metal resistors as replacement for feedback resistors r4 and r5? I can't source smd resistors locally. Thanks

In the past I have done this successfully. Just fold the leads under and clip them to fit. Be real careful of causing shorts and leave room so if they are touched and moved they won’t short out to anything nearby. Also be careful to not put any pressure on the pads or they might come loose from the board. If this does happen you might be able to save it with super glue or a liberal dose of contact cement. The contact cement is a good idea to strain relief it after you make sure it is working properly, lessens the chance of lifted pads.
Roger

[CambshireGordon]

Originally posted by sx881663


Gordon,
Yes a lot of effort went into doing all those pictures, a good job even if I don't agree with all he is doing. Much of it is too advanced for someone without proper skills or soldering equipment.
Roger

I could not agree more - reading about what others have done seems quite straight forward (particularly those others have been so generous to share their experiences - thank you to them). BUT openning up an SI is another prospect, especially seeing all of those SMD's and very small soldering points! AND reading how easy it is even for an experienced person, to lift a solder pad ... ...
I built many valve amplifiers and other pieces of electronic equipment in my (mis-spent?) youth when we used proper 'man-sized' components, but I have not wielded a soldering iron in agnst for many a year now and certainly not on something so small as the SI.
I recongised my limitations on openning up my first SI, hence my decision to ease myself back into the soldering fold by first building the Class-t-amp-2020 kit from Autocostruire - it uses those proper 'man-sized' components - see my post number 10 on the thread "For all t-amp tweakers". (For all T-amp tweakers)
My Autocostruire order has shipped and I eagerly await delivery - soldering iron is plugged-in ready. Maybe after a successful build will I advance with soldering iron onto the SI's.
CambshireGordon

[sx881663]

Working with these small components can be frustrating. Get out the 10X loupe and inspect the job, looks perfect but happens to be the wrong component or wrong place...
The other thing is that the SI boards are far from being high quality. The traces are super thin and pads can be easily destroyed. Just always remember to put only very low amounts of pressure on them and you should be ok. I drape a piece of solder wick across the whole component and that way heat and remove solder from both sides at once. While the whole thing is hot a small sideways pressure will usually loosen it. Find an old computer board to practice on first. I did this and recovered some parts that are hard to find.
On putting the new components on I put a dab of solder on only one pad first then while keeping it hot place the component down. You will find getting them positioned properly will take some practice, not so bad when only one side is soldered. On soldering the other side if you find you have left a big blob, not to worry as solder wick can suck up the excess with no problem. Larger multi lead components are best super glued into place first. This keeps a strain off of the component when you solder the leads down. I broke a couple of expensive opamps trying to line them up with one lead soldered. When you are done, use a high powered magnifier to carefully inspect every thing. Particularly look for solder bridges, real easy to do with this small close together stuff. Once again solder wick to the rescue!
Takes a steady hand and a fine soldering tip. You will find one of those large lighted magnifiers and a good pair of fine tip tweezers to be helpful if not essential.
Roger

[boarder]

Hi there,

could someone let me know the value of cap C12 ?

I scratched it away while I was cutting it out of its original case.

Many thanks,
boarder

[sx881663]

Originally posted by boarder
Hi there,

could someone let me know the value of cap C12 ?

I scratched it away while I was cutting it out of its original case.

Many thanks,
boarder

You are lucky, C12 is not critical in value as it is one of the power bypass caps. I would use from .47 up to 2 uf or so as long as they were rated at least 16 volts and are the same size. While you are at it you might as well upgrade both.
Roger