soundcraft 200b/400b/800b..etc..opamp upgrades/mods?

got a 400b and am going to try out some new opamps once i finish recapping it.

just wondering if anyone has swapped out the tl072s on their board for something newer and faster? how did you like it? any one ever upgraded the input transistors to something newer?

I am going to try to swap the opamps on few channels at first to see how it sounds. might go with the TLE2072 since it is a pretty close replacement with about the same current draw.

a friend changed the input transistors in his SC8000 with succes. He told me that noise improved. He´s been using some Japan stuff, don´t remember the type. Which transistor is in there right now?

The TL072 are not slow by any means. Who said they are?
They are not good in any application where they have to drive less than 2k load. For example the insert. The last opamp in the EQ section drives the insert IIRC. That being a TL072 driving oldschool stuff won´t be very happy with his job. In this place you could try an OPA2134. They were the best sounding OPs to drive the inserts of my TAC Matchless. Of course it may be different on your desk. Swap and listen! The TL072 did not sound bad at all. I prefered them over OPA2604 and OP275 in this application. I chose the OP2134 because it sounded very similar to the TL072 but having a better LF response and a little more clarity. The other two sounded really shite, seriously.
What helps is increasing the output coupling caps. SC always saved money by using small coupling caps. If you increase them you will get a way better LF response.

check Eddie Cilettie´s page about the 200B ground mod. This makes sense for the 400B, too. The grounding in these old SC desks is really poor.
Then you might want to tweak the HF filter cap to a higher frequency and the LF filter to a lower frequency. Those two stock values always sounded wrong to me.

jensenman, thanks for the reply.

the transistors in my 400b mic pres are the pn4355. it uses the similar preamp design as the 200b and alot of the out SC boards. if you could find out what transistors your friend used, that would be much appreciated.

i am going to bump up the values of the coupling caps before I even get started with trying to swap opamps. i was also considering swapping the values of the LF & HF, I will look into that. i am also going to do the star grounding mod as well. i'm sure that all these things will add up to make a big difference.

I'm not going to swap out the opamps without listening, I will definitely give the opa2134 a try. did you need to add .1uf caps to the power rails? what about a pf cap across the feedback resistor?

[quote author="outoftune"] did you need to add .1uf caps to the power rails? what about a pf cap across the feedback resistor?[/quote]


Neither one was necessary. All ICs were already bandwidth limited.
Could you send me the schematic? I only have the SC1600 schemos here. They might be pretty similar but who knows.

I´ll check which transistors he used but as a rough guess there are heaps of better transistors than the 2n4355 for this application. This is pretty much a standard type

got some great tips and help from jens....anyone else have some feedback?

In a 2400, the insert output will oscillate because the feedback is taken from the other side (output) of the output capacitor. This is a disaster waiting to happen if you have certain transformer-balanced inputs that are not terminated precisely. It can also cause oscillation if you have a long cable patched in. In my case, a Gates M6629 Solid Stateman limiter would do a low-frequency oscillation. Also, just about anything patched in would almost cause an oscillation in the insert output, and changing the op-amp to anything else - even a TLE2072 - caused a horrible mess. So I studied it and analyzed it in SPICE and figured out an easy fix...

I replaced the output capacitor with a 220uF electrolytic, moved the feedback point to before the capacitor, and put a 22pF capacitor from the op-amp output to the inverting input, but just in that one spot. I also looked through the rest of the design for the same problem and found that the schematic did have the same problem on the group cards, but the group cards were wired in the correct manner so I didn't have to make any changes. The schematic didn't follow the PC board, though.

I upgraded the power supply and used a lot of LM833 and NE5532's in there, along with TLE2071 and TLE2072's. I used thost new dual op-amps from National for the mix bus amps and that really cleared up the sound. Replacing all the capacitors got the bass consistent across the whole board, and replacing all of the ceramics cleaned up the HF response when the EQ was in use. I added extra rail decoupling only because the 5532 and LM833 require better decoupling. The only change I percieved with the 5532 or LM833's was a significant drop in hiss. The biggest op-amp improvement was in the mix bus amplifiers.

-Dale

Hi

I did an upgrade to my delta sr, which as very similar design. the biggest improvement I got by changing the output coupling caps in the Master, change NE5532 to lm 4562 makes a bit of a difference too ( you need to put 0.1mF caps from ground to each +- powersupply pin of the opamps. You got to change the powersupply, I got some condor linear ps cheap at ebay.
Another very helpful thing is to change the transistors in the mic pres to 2sa1084. changing the caps and OP in the EQ is also not a bad idea

nicholas

but start with the master

pn4355 PNPs are really not that bad. Soundcraft did switch to 2n4403
somewhere in the 2400/1600/800b days however if memory serves me.

Try a matched set of bc560c in a channel and AB the channels.
They do seem a bit better to my ears.

never tried the 2sa1084.. nicholas may have something there
so give them a try as well. :thumb:


GARY

I have a 400B and did some experimentation with op amps and caps. I agree with everyone about replacing the coupling caps with 220uf low Z Panasonics or Nichicons. This will extend the low frequency nicely and makes the single biggest improvement. Increase the cap on the mic pre as well to extend the low frequency at high gains. I just happen to have a pile of MAT03's laying around so I replaced the stock mic pre transistors with these. I haven't done any critical testing on that upgrade but I didn't notice any improvement as yet. This may well be a measurable improvement though. I socketed the op amps and I'm now using an LM4562 on the mic pre, an OP275 (or OPA2604, still deciding) for the EQ section and have tried both a OP604 and OPA134 for the fader buffer with good results. I replaced all the 100pf ceramic feedback caps with polystyrenes. I also experimented with replacing the EQ polyesters with BC polypropylenes. I expected to hear a big difference but didn't. As mentioned before make sure you upgrade your master section first since this console doesn't have direct outputs on the channels. While you've got the channels out go ahead and replace the power caps as well. You can mod one channel and compare opamp combinations without any power supply mods, but if you upgrade the others make sure you replace the power supply as Dale mentioned.

Jeff