Console schematics for your consideration

Whew, after giving myself a straining tutorial on hotlinking and hosting and all that other stuff, this is a topic that was brought up in "the lab" regarding upgrading opamps in a console.


http://www.groupdiy.com/index.php?topic=5329

I was thinking of re-capping the master section of my soundtracs console, and maybe opamp upgrade also. As requested by Svart, i have scanned my schematics, and was wondering if anyone could offer any advice on possible upgrades, and if it'll evn be worth it? "if it aint broke...."

I see there are tl072 and 5534's everywhere, but I've been reading posts these past couple days saying those aren't bad at all...

well, enough talking, here's the schemos...


http://groupdiy.twin-x.com/albums/userpics/10028/Soundtracs_Solo_Midi_schemos.zip

:sam: I love this place!!

wow there is a lot to try here! First off I would change out the TL074s in your preamp areas to something like the opa404 maybe the opa4134(cheaper but i think it's being discontinued). unless the console design was especially bad(which I don't see anything out of the normal when i took a quick look) you probably won't hear too much difference without changing everything in the channel. looks to have a few extra caps in the audio path too.. you might be able to get rid of those if the DC offset between the stages isn't too high. If cost is a concern, plan to use the better opamps where they count the most, like in summing areas or in the mic pre area.

as for recapping, figure out what areas you can subtract caps from first, then get enough caps to do a pair of channels(same ones you just re-amped.) and compare them. chances are that you will hear a difference, especially if the caps previously used are old and cheap.(old doesn't mean bad, but cheap and old might..) compare to the unmodded channels and you should hear/see pretty quickly if the cost of redoing the board is worth it.

when i get some more time I'll have another look at the schemos. gotta get back to work for now though..

:thumb:

..to replace TL074's, the MC33079 is a pretty good little thing..

I agree with gyraf, I've only been using the mc33079 for my EQ sections since this is the only place i have quad opamps but I like it a lot!

mc33079? who makes those?

Svart, when you say subtrack caps, do you mean just take them out and replace with nothing, and my board will work?

yes, I would probably do the 8 buss channels and the master section first.

You mentioned doing the preamps? Would this make a difference if I'm only using a line level on these inputs? Just wondering, because that's all I use them for.


Thanks guys for taking time out of your day to at least look into this for me.

Digikey has the mc33079 for .84/1.24 a peice. they are made by a few different manufactuers, digikey has both ONsemi and ST parts.

when i say subtract i mean to take them out and place a jumper where they were. a lot of boards use coupling caps between the various stages when they expect a DC level difference. Usually they are there to keep pops and clicks from happening when you switch sections in/out. a lot of times when you don't *really* need them if you keep the stage either in/out when audio is passing through and only switch when pops/clicking can be tolerated. i saw a few instances in your various schemos i looked at. also you can increase these coupling cap's sizes since i saw a few that might be a little small and affect your low end response. without measuring, you can try substituting with nothing or with a higher value and see what happens. I see one between the preamp stage and the EQ stage that looks like it says .68uf. that to me seems low, most I've seen are around 47-100uf.

as for replacing the preamp IC's, it looks like your line input also goes through the preamp according to the schematic. I would go ahead and change it.

above all, once you get the ICs out of their places, replace them with a socket so you can try other types easily! sockets are cheap and make life a whole lot easier when doing this kind of thing.

I just happened to go check the other thread that this was started in, ( I moved this onbe here so as not to hijack the other guys thread), but there is a reply there regarding the schemos...

[quote author="pstamler"]Having looked at the schematics, there's no question in my mind that if you replace the TL07x's with different opamps, they must be FET-input units. They have direct-coupled fader sliders or high-value resistors on the inputs, and you'll make pots noisy or generate offset voltages if you use a bipolar-input amp.

Unfortunately, they're quad packages, so you can't use OPA2604s unless you wire up some header/socket combinations.

Peace,
Paul[/quote]


I went to OnSemi specs for the MC33079, and it appears to be Bipolar.

Will this work?

Just when I thought it was making sense, I'm lost again!!

I need a beer.

It will work in some of the areas, but not other it seems, I hadn't looked at the sections that the person looked at, but they are correct. look at the opa404. the opa4134 in DIP style is obsolete.

not many other choices from TI/BB for a quad.. the OPA404 is expensive unless you want to buy the OPA4134 in SOIC and use an adaptor to DIP.

another option is to insert capacitors between the faders and the opamp and use a BJT opamp... but that may be trouble too.

look around at Analog devices for a quad opamp with FET input and see what you find.

So would the MC33079 still work in the preamp sections?

I didn't see anything in the preamp section that would make me believe that it wouldn't, so give it a try.

:thumb:

Yes you can use opa2604 in smd on a special pcb that is not bigger than a dip14 , than you put 2 opa2604 on it or use a opa404 , the have a nice sound and headroom and rail to rail output.

If you would need the pcb , just give a pm and i will give you the pcb layout in gerber , double side pcb.

I always seem to be the one mentioning power supplies when a thread gets started about op amp "upgrades". Everyone else talks abou the op amps !!!

Make sure you have a really beefy PSU that is capable of delivering the goods before you consider modifying the desk too much. In my opinion this is the very first & the most important thing one should consider before any other modifications undertaken.

Check the current draw of the replacement opamps that you are using compared to the ones. This is because some of the "upgrade" op amps draw A LOT more current than TL07XX & 5534. When you replace a significant number of op amps this can sometimes overtax the original PSU.

Also upgrading a less than brilliant PSU can bring sonic improvements on its own.

good point Rob...

I think for now I am just going to do 2 channels with ti's tle2072 , supposed to be an updated "faster" than the tl072, to see how it sounds. I'll probably just stick with the 5532 for now, since I cannot seem to find Fet inputs.

Mind you dont throw the baby out with the bathwater here. Upgrade for a reason, I replaced 4558 with 5532 and HEARD a difference, cleaner and quieter for little money but when I tried other much more expensive chips instead of 5532 I could niether hear nor measure ANY improvement. Robs point about psu's is very valid, also watch individual "on chip" decoupling. I had a case where an upgrade worked but just didn't sound right, when I got round to scoping it there were oscillations everywhere, cured by caps soldered straight on the chips.
Steve

and to add.. sometimes you WANT something other than clean and clear. I had TOO much high end sizzle and wanted to smooth things out a bit. the 5532 to me has very good response but can be a little harsh in certain circumstances. i replaced them with opa2604s, got a little more detail and LESS sizzle. you could argue that they are superior or inferior for this reason but in my application it gave me exactly what i needed. same for the opa627's i used in place of 5534's and with dual adapters for the 5532s, they added a different flavor that is unique and much more pleasing than the flatness of the 5532.

beyond all other issues, the issue that is the most important but often gets left to the wayside when we start to over-analyze is that our ears must like it, even if it looks bad on paper.

:thumb:

give it a try for we could discuss if you should do it or not all day long and never get to a concensus. give it a try. if it oscillates, decouple it. if it sounds bad, try something else.

also remember that other components might sound differently after an "upgrade". caps that were decent before might now show their issues, same with old resistors, etc. So.. be prepared to do a pair of channels all the way to see what the ultimate outcome could be. compare to completely unmolested channels and see if it's really worth the money, or at least where the money should be spent. I found that the opamps made more difference than caps in my console when switched to something different.