James HE
Well-known member
I have a Soundcraft spirt sx 20 channel board. I opened it up a few weeks ago and gave it a pretty good cleaning. Got it used and it was pretty bad as far as dirt and grunge on the pots and sliders. I poked around to see what was up on the inside as far as chips and caps. Mostly smt componets. Tl072's on the channels and 5532's in the master section. So I had a bright idea :roll: .
(cue long story you might get a good laugh out of)
I have some OPA2604 soic's that I got by mistake instead of DIP - hmm what if I just swap out 4 of the TL072's for the 2604's? Sweet I'll try it. So I pack the board up and bring it to my house from my rehersal space. I forgot to bring the powersupply like a dumbass. So I have the board, the chips I want to swap in, all set up on my "bench" at home, but I cant really test it. Hmm I should just wait till tomorrow, but I was really looking forward to diving into it at the time. OK what ever I'll just swap them out anyways. Practiced my smt skills on an old PCI card, learned how to desolder and solder them, got confident enough to just go for it. I had to revome the HPF switch and a ceramic cap on each channel to have room to work. Took those out. swapped out the soic chips, put the switch and caps back in, closed up the board, went to bed. Took the mixer back to my rehersal space next day and tried out the channels.
no go, nothing coming out of those channels, except for some really bad sounds when I screamed into the mic and had the gain cranked. Aw shucks. I knew I was too much of a newbie to just pull this off, but I just wanted to learn anyway. And i love making rash, impulsive decisions!
A few days later I bring soldering station and all my tools to my space (and a light so I can actually see!) and started to figure out what the problem was. First thing I measured was the voltage going to the opamps. I measured a few different ones. Looks like the opamps work on somewhre around +/- 3 volts (it varied a lot depending on where I measured, from like 2.5 to 3.9). Should have measured that before! minimum voltage for the 2604's is +/- 4.5 V. Well that probably explains why the channels just did not work. I just assumed the board would be putting out more juice than that. Does this seem odd or wrong to anyone?
So I put the TLo72's back in. ONe channel at a time. The first channel I did came out perfect - or rather sounding as crappy as always. NOw here's where I knew I'd have some problems - cause I pretty much destroyed some of the ceramic caps when I pulled them out. I just wanted to get it back together, working somewhat, I can live without 4 channels, but I needed to have it back together as soon as possible and to confirm I didn't absolutly ruin it. I completly destroyed one of the caps (leg came off) I had some random ceramic caps from Radioshack and paralleld a few together to get near the right value of that cap. So instead of 680p I have like 640p but with some really crappy ceramic caps from Radio shack on one channel. That channel has twice as much gain and is reall really noisey. well, obviously I need to source some new caps, but I needed the thing back together so lets move on. The last two channels I redid work and sound ok but the gain is really low, not sure what the problem is there at all. As of right now I'm just not using those 3 bad channels. at least I got one back right!
Before I go back in I need a few caps - the ones I had to take out were 680pf ceramic. Honestly I don't know what they are for.. lol. It would be intresting to trace the board to figure out exactly the schematic, but I'd have to remove a ton of componets to really do that effectively - which I am not intrested in at all. I have a soundcraft 1600 schematic, (got it from here somewhere) and this looked similar, but it's not exactly the same. No problem I'll get some new caps.
Also I'm thinking I'll get new opamps. These have been unsoldered and resoldered now, all ham-fisted by me, and might be just fine, but I'd like to take the chance of one of them being damaged out of the equation. I could just put TLO72's back in, but that's no fun and makes all of this work absolutly pointless! So I need a replacement opamp. Something that will work with low votage (or upgrade the power supply - that might make the whole board better, but I'm not sure I want to undertake that - I'd rather just swap out some componets) I'm thinking about MC33078.
http://www.st.com/stonline/books/pdf/docs/2177.pdf
minimum voltage rating +-2.5V.
Is this fine? What other options do I have?
(cue long story you might get a good laugh out of)
I have some OPA2604 soic's that I got by mistake instead of DIP - hmm what if I just swap out 4 of the TL072's for the 2604's? Sweet I'll try it. So I pack the board up and bring it to my house from my rehersal space. I forgot to bring the powersupply like a dumbass. So I have the board, the chips I want to swap in, all set up on my "bench" at home, but I cant really test it. Hmm I should just wait till tomorrow, but I was really looking forward to diving into it at the time. OK what ever I'll just swap them out anyways. Practiced my smt skills on an old PCI card, learned how to desolder and solder them, got confident enough to just go for it. I had to revome the HPF switch and a ceramic cap on each channel to have room to work. Took those out. swapped out the soic chips, put the switch and caps back in, closed up the board, went to bed. Took the mixer back to my rehersal space next day and tried out the channels.
no go, nothing coming out of those channels, except for some really bad sounds when I screamed into the mic and had the gain cranked. Aw shucks. I knew I was too much of a newbie to just pull this off, but I just wanted to learn anyway. And i love making rash, impulsive decisions!
A few days later I bring soldering station and all my tools to my space (and a light so I can actually see!) and started to figure out what the problem was. First thing I measured was the voltage going to the opamps. I measured a few different ones. Looks like the opamps work on somewhre around +/- 3 volts (it varied a lot depending on where I measured, from like 2.5 to 3.9). Should have measured that before! minimum voltage for the 2604's is +/- 4.5 V. Well that probably explains why the channels just did not work. I just assumed the board would be putting out more juice than that. Does this seem odd or wrong to anyone?
So I put the TLo72's back in. ONe channel at a time. The first channel I did came out perfect - or rather sounding as crappy as always. NOw here's where I knew I'd have some problems - cause I pretty much destroyed some of the ceramic caps when I pulled them out. I just wanted to get it back together, working somewhat, I can live without 4 channels, but I needed to have it back together as soon as possible and to confirm I didn't absolutly ruin it. I completly destroyed one of the caps (leg came off) I had some random ceramic caps from Radioshack and paralleld a few together to get near the right value of that cap. So instead of 680p I have like 640p but with some really crappy ceramic caps from Radio shack on one channel. That channel has twice as much gain and is reall really noisey. well, obviously I need to source some new caps, but I needed the thing back together so lets move on. The last two channels I redid work and sound ok but the gain is really low, not sure what the problem is there at all. As of right now I'm just not using those 3 bad channels. at least I got one back right!
Before I go back in I need a few caps - the ones I had to take out were 680pf ceramic. Honestly I don't know what they are for.. lol. It would be intresting to trace the board to figure out exactly the schematic, but I'd have to remove a ton of componets to really do that effectively - which I am not intrested in at all. I have a soundcraft 1600 schematic, (got it from here somewhere) and this looked similar, but it's not exactly the same. No problem I'll get some new caps.
Also I'm thinking I'll get new opamps. These have been unsoldered and resoldered now, all ham-fisted by me, and might be just fine, but I'd like to take the chance of one of them being damaged out of the equation. I could just put TLO72's back in, but that's no fun and makes all of this work absolutly pointless! So I need a replacement opamp. Something that will work with low votage (or upgrade the power supply - that might make the whole board better, but I'm not sure I want to undertake that - I'd rather just swap out some componets) I'm thinking about MC33078.
http://www.st.com/stonline/books/pdf/docs/2177.pdf
minimum voltage rating +-2.5V.
Is this fine? What other options do I have?