Help Wiring a Replacement Potentiometer for Sonic T

[Lostcause]

Hi Steve, it's been a while since I played with one of these and I haven't had one of the MKII Sonic boards but...
If you have continuity from your power to the on-board cap and the LED is not lighting up then it does sound that a reversed polarity has knocked out the chip I'm afraid. Audio 1st's post shows the fuses that could have gone on the speakers... worth checking.
However.... there is one posibility which has happened to me in the past.
Check the cap that supplies pin 36 (CPUMP). If that has blown (continuity across it) then it just needs replacing.
Good luck

Oh yes, the parts you mention have no polarity.

[steve beltzer]

Thanks Lostcause!

After looking at Audio1st's post, I checked the fuses on Board 1, which got the spark and has the presumed bad chip. F81, F82 and F84 all had continuity across them. However, when I tested Board 2 which as far as I know should be pristine, with regard sparks at least, it registered the same. Interestingly, F83 is showing no continuity on either board.

I noticed that Panomaniac questioned whether they are fuses:

Post #101 Thanks for the photos, the board does look better. Are you sure those are fuses? Might they not be Ferrites for RF noise suppression?

Another thing, when I test the chip, pardon my ignorance, but how do I tell which side is up and which is down?


Steve

[Lostcause]

Hi Steve, yeah, Pano may be right, I've never had one of these boards so I can't check.....
Anyway, the picture is from the black resin side and you can see the dot in the top left corner.
Trace pin 36 until it meets a small cap and then test that for continuity.
EDIT:
OK just looked closer.. it's C9 right next to the pin.

Other than that it's not looking too good I'm afraid

[GR8FLPT]

Finally got mine yesterday... Ya I know I'm way behind the curve. It's the newer board. I have coils on mine to the speaker outputs. A ferrite doughnut with the speaker wires looped thru twice. I suppose it's a low pass filter for cutting upper frequency noise.

Anyone else do anything with those? I'm considering ditching the volume control all together. I had some 2uf Solens laying around & gonna bypass with a Sidereal .01 uf (yea old skool).

I've been digging around, I thought there were a few more mods besides the input caps & using a better supply (besides swapping hardware)? If anyone one can point me in a direction... I've already looked at M.Madis site. Unles I've missed something.

Thanks

[Buckapound]

Welcome to the cult, or whatever this is. Definitely good sound for cheap.

Volume control you either need or don't, so get rid of it if you don't need it.

The biggest other area of improvement is replacing the reservoir cap (C10?)m the biggest cap on the board. You should be able to at least double the value in the same footprint. Look for the "low ESR" or "low impedance" type. Panasonic FMs are often recommended, but Nichicon and others have lines of good grade caps too. There is room on the board to add even more capacitance, but as I recall from the discussions usefulness tops out at about 5-10,000 uf, and the closer to the chip the better.

I replaced the main output inductors, but didn't notice a dramatic effect. I don't think the ferrite rings can hurt anything. Some models have a small cap on the output (.1uf?), which also filters out HF hash.

Depending on your source device it might be worth changing the values of the feedback resistors, which changes the gain. I don't have the specifics, but I think the SI comes fairly low in gain, so if you're using an iPod, you might get a little louder sound by upping the gain. Then you can join the hi-wire world of unsoldering and soldering surface mount components.

Check back on the threads, There's a ton of discussion on the specifics.

Oh, and be aware that these things take a week or two of use to burn in and sound their best.

--Buckapound

[GR8FLPT]

"Depending on your source device it might be worth changing the values of the feedback resistors, which changes the gain. I don't have the specifics, but I think the SI comes fairly low in gain, so if you're using an iPod, you might get a little louder sound by upping the gain. Then you can join the hi-wire world of unsoldering and soldering surface mount components."

That ould be nice to up the gain a bit, anyone else try that mod?

As far as soldering SMT, I spent 5 years repairs computer motherboards under a microscope. The only issue is these tried old eyes can't do it without now... I use a magnifier & an Intel QX3 kids USB microscope to help locate the parts...

Ill definitely be changing out the big cap too. So you noticed no difference w/ w/o coils on outputs. Maybe I should put a scope on it to see if I notice anything.

I want this as clean & neutral as possible. you might say I have a bet going as to how far I can take it.

[GR8FLPT]

I found a old computer PS that I started to pull apart. Found some 470Uf & a couple of 2200 uf caps that could work. Nothing fancy, just using what I have hanging around in the garage.

I removed t form the case & replaced all the wires except ribbon cable with a higher grade of wire & gauge. Can't believe they are using 24 AWG wire on this. That stuff just about breaks off when trying to move things around.

Listened to it w/o the output caps, yep they definitely help on the hash. I have a PS from a old mobile audio display that I'm using. I adjusted it to 13V. That seems to give a bit more headroom.

Cap mod is next then PS caps next. I think I'll try the 470uf 1st & then maybe the 2200 uf after that. I have s couple of memory heat sinks I can put on the chip I may attach them to the ground plane (large pad under chip) I think that would draw more heat away than trying to attach to the plastic case.

[musicfreak]

Hello,

I managed to break the input pad and C62 on a rev. D board. Does anyone ha a diagram of this board or the value for this cap? Is the stealth mod going to bypass this cap too?

Thanks.
Regards.