Soundcraft TS12 restoration

[audiopete]

I am going to recap and clean a TS12 for a client and I am weighing the options for upgrading the channel strips. I've looked at all the info and threads I could find but one point never quite solidly addressed is current draw with new opamps. People have said they've gone to a modern opamp but no one says if the stock power supply can handle the extra draw. I am going to rebuild the PSU but I want to stay with it. If it can't handle the opamp upgrade then I won't do it.

I am going to replace the 1st pair transistors with 2SA1084 and I am thinking I'd like to replace the first 2 opamps TL072 in the mic pre as well.

Jim Williams, as always, has provided a wealth of info, but I understand its incomplete and that there is a lot more involved with his work. I don't want to redesign the circuit if possible, just plug and play new opamps that won't oscillate. I would like to do the minimum necessary upgrades and keep the budget contained as much as possible. Ideally the package is DIP8 to save the expense and labour of fitting SOIC to adapter boards.

I have my eye on AD8512 as a replacement because it has a Iq of 2mA per amp, 0.6mA more than the TL072. That's about as low as I can find - about 58mA extra draw per 24 channel. I looked at OPA2134 and LME49720 but they draw 5mA per amp. If I have to install 48 SOIC to boards I will but........

If anyone has advice for a better way, I would appreciate it. Cheers.

Soundcraft_TS12_Schems.pdf

[Jazz P Bass]

This console was made in 1987 or thereabouts.
Just my opinion but opamps alone are not going to make this unit 'sing'.

If anything will degrade with time it will be the electrolytic coupling caps.
A good cleaning, resolder, fader lubrication and an actual test of each circuit is the first items that I would address.
And yes, redo the power supply.

Old is old.
Can o worms is a can o worms.

[audiopete]

Hi sorry I did state that I am cleaning and recapping it. I realize a couple opamps are not going to make it into a new console, but if I can drop the noise any at the front end, it will pay dividends down the line x 24 channels for not a lot of money.

[Enzo]

All those noise figures are about potential noise. How much front end noise do you have NOW? Just because some newer part has a lower noise spec on the data sheet doesn't mean it will lower the noise in your circuit

[km6xz]

As Enzo suggested, there is just as likely to make something worse than better just swapping out different devices based on one of a hundred relevant parameters. Is there a noise problem now? The specs as published are for ideal conditions for test, not a working studio with all the noise sources, many of which did not exist in the 80s, such as as the high level of RF noise with computers, SMPS's, mismatching signal levels with interconnecting units designed for 4 different standards levels and termination impedance.
So the first step would be measuring noise figure in normal operation and isolate the sources. Grounds, magnetic fields, RF sources, termination mismatch in those descending noise source importance. Without careful reproducible base line measurements you can't tell where the noise is coming from and how to attack it without potentially doing more harm than good. It is a system, not a collection of independent devices. No two systems perform the same way and the ones that perform best are ones where a system approach optimized the system.

[audiopete]

There is hiss. You are telling me that a modern opamp today in the mic pre is not going to be quieter than a TL072 that has been in there for over 30 years? I researched as much as I could and Jim Williams has contributed good info on this. I don't want to rebuild Rome, I just wanted some info regarding the question I asked about a better opamp.

I am recapping the channels and if I can swap a few parts in the mic pre and get a lower noise floor then great. I am not trying to re-engineer this into a new console.

[Jazz P Bass]

Hey, I am all ears.
Try one channel & let us know.

[km6xz]

Actually new opamps will not generate that much less noise because the real noise sensitive gain is in the transistor diff amp input. Some famous large frame consoles that recorded very good sounding records in the late 70s and 80s used that lowly opamp with discrete front end. A lot of Grammy winners for example. Whitney Houston's first record that was a smash hit was recorded at 4 different studios with 4 different producers and they sound alike despite very different consoles. Large frame NEVE, SSL and Trident. The Trident TSM used those ICs on those song recorded in my studio.

Hiss is often improper stage gain structure or mixing I/O levels such as a system that is a mix of -10dbv, +4dbu and +4 or +8 dbm. How much level is going into the mic preamps? If you set everything at some nominal level like all the faders for channel, subs and master to 2/3rd level and terminate the mic preamp with its rated input z and dial in 20 gain, and normal all the aux and eq what level of noise are you measuring? Mute all the other strips expect for the one being tested.

[audiopete]

OK thanks I understand what you are saying and seeing the wisdom in it. I am hearing you and the message I'm getting is don't bother changing opamps. I also hear JAzz P Bass so I will do one channel for fun to A/B.

The whole story is the owner likes the console and does more personal recording with it, not so much a daily working studio. He does bring clients in from time to time but it's pretty casual. We discussed a new console and it really isn't worth decommissioning and moving adn doing the same thing with a new board. There isn't much resale value, so we decided to recap and clean it. I came across Jim Williams upgrade posts and it piqued my interest.

So you do recommend changing the stock 2N4403 pair to 2SA1084? This is the one transistor that I can find available that Jim Williams recommends.

[J M Fahey]

Was chiming in to say about the same.
Modern Op Amps are much better and can be used "straight" which way back then would have been unthinkable, and standard trick was to add a couple transistors, PNP by the way because they had noticeably less hiss , go figure, with at least 12 dB gain, so internal Op Amp hiss, by comparison, was 12dB "less important" .

The other option, of course, was to use an input transformer.

That said, Op Amps have advanced a lot but transistors were VERY good since the 70's, early 80's so suggested replacements may be better, no doubt, but probably not much more than 1 or 2 dB improvement.

Don't expect day-and-night

[audiopete]

Thanks J M. I won't expect dramatic results but I think a couple dB improvement across the board is worth the $4 or so per channel in transistors. Soundcraft changed away from the 2N4403 themselves, from what I've read. I'm going to change the opamps on one strip to listen to. My concern is the extra current draw x 24 channels and can the power supply handle it.

[dai h.]

some good reads:

https://www.gearslutz.com/board/geek...ound-same.html

Mic Preamp Improvements? (Soundcraft 800B) - Page 3 - diyAudio

very current thread:

http://groupdiy.com/index.php?topic=58382.0

interesting:

A few of the channels have Jim Williams class A mod's but I actually can't hear a difference between those channels and the normal ones.

SoundCraft « auxsend.net/consoles

JW is someone who does mods to make a living (in part apparently), so I think it might be smart to read his posts with that in mind.

[Jazz P Bass]

My concern is the extra current draw x 24 channels and can the power supply handle it.

And rightfully so.

There is nothing 'wrong' with a jfet input opamp like the TL072.

[audiopete]

Thanks everyone. I read through those threads (thank you very much - very helpful) and I have come away with the decision to skip the opamp change and replace the first transistors with 2SA1084. I'm going to recap the console and I am going to clean it from top to bottom including every contact in the signal chain from mic to cables, console XLRs, patchbay, internal connectors, pots, switches, faders and lift and clean all socket-ed ICs, off to the recorder and back to monitor world. I imagine lifting all grounds and cleaning them would also be a good idea.

Couple questions:

1. What is the best cleaner to use? Contact cleaner is pricey. Is Methyl Hydrate just as good, or is there something else cheap and not so toxic?

2. Should the transistor pair be matched to Hfe?

3. Should I bypass audio path electrolytics with, say, 0.1uF film caps?

4. By what factor can I (or should I) increase electrolytic values?

I think I might like to try a channel with a mic transformer. Is this a good idea? Any suggestions as to which one?

I really want to do just the best and necessary for my client. I am not interested in racking up the hours for the sake of getting paid. I want my clients to get best value for their money and I feel strongly about only doing things for good reasons. I can make those kinds of choices now thanks to all your input.

[km6xz]

Cleaners are cheap, deoxidizers are not as cheap. You have three chemicals to use, a cleaner for dirt and grime, pot/switch lubricant, and the one that will make the most difference in signal path, a good de-oxidizer. Don't skimp on the de-oxidizer, since it has the most positive impact.You use cleaners to remove dirt and film but keep it out of pots and in connectors since even those solvents labeled contract cleaner are too "dry" for low current electrical connections/contacts and it will cause faster oxidation. Applying a very little amount of Caig Laboratories, Cramolin, or CRC de-oxidizers is enough, if you can see it, was more than was needed. A lot of people use the spray deoxidizers as cleaners to wash away dirt but that is a waste of money since applying too much attracts dust and dirt because it is not intended to fully dry for a long time, further increasing the time between applications. Be sure to recondition the patch cords while you are at it. They all should be deoxidized about once every 6-12 months. If any are in doubt, replace it or rebuild it with new connectors or cable. Try hard not to get strong solvent cleaners on the shaft lube of the pots, faders and switches or else they will never feel smooth again, even if using Caig moving contact lubricant.

The most improvement in caps is the availabilty of more stable electrolytics and cheaper ones at higher temperature rating. 105C will last longer in units that are on all the time, particularly in the power supply.
Mic transformers are most effective when using mics that require a terminated load like dynamics. A ubiquitous SM-57 is the most popular mic in pro studios but amateurs think they are cheap stage mics. The difference in opinion is mostly based on what they were plugged into. Plugging into a high Z full diff amp preamp is going to result in a bit of ringing and "raggedness" in the upper mids and above. Loading it into a 150-600 ohm terminated impedance and it is like having a new mic. Studio condensers don't sound much different since they have a low output impedance buffer after the reactance conversion stage that isolates the signal generating circuit from the line driving circuit. Old tube mic do have transformers so they appreciate a terminated load. They work on a power domain, measured in dbm, and newer systems have low out z and high input z so work in the voltage domain and measured in dbv. You can experiment with various transformers without cutting up a channel, just put it in a well shielded box and connected directly to the channel I/O connectors. There is no reason it has to be mounted inside the console, just bond the grounds together.

Which brands/models? I like Jensen because they are not smoke and mirrors, just normal well made transformers without the really expensive fairy dust. Which, well 150 ohm input and whatever output Z ratio you want, 10k would be about as high as you would want. The JT-13K7-A model is good for 150<>3.5k and has very good specs. NF of 1db and 13db voltage gain. I have had good results with Lundahl Transformers also, take a look at their LL1538 model. Both are more than enough and under $100, barely. I would expect a big change when using modern condenser mics but dynamics, older condensers, or any type that are happier with a 150 ohm load, the sound difference of the mic itself will be worth the effort.

Added: I was just thinking of the original complaint about hiss. The new transistors should help a little but it might be a false victory lowering hiss since the big problem in most studios is too much level and head room. A large diaphragm condenser has a lot of output unless micing off some distance and and close mic set up will be testing the head room of the signal path a lot more than noise floor. Transformers can saturate, something to think of when micing amplified instruments or real belter singer so consider what type of music and which instruments are going to be recorded. There is a 13db gain that will help the noise floor but also might create a Headroom problem. But I assume the board has attenuators on each channel. Just in case, make sure there are some line attenuators in the studio if the engineer is going to be recording a kick drum with a large diameter mic.