Some Questions Regarding Component Replacement On A Rare Vintage Console

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kineticsound

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Hello all. I am a longtime reader and fan of the forum, and a brand new member. I have some questions that are pretty rudimentary, and i have done some searching and found some information, but if I could get some specifics I would appreciate it. And since i just joined, i also thought it would be appropriate to begin with some info about myself as well as my questions.
My name is Ryan, I live in Michigan, I am a long time recording engineer (started out as a tinkerer/musician/huge geek for recording way back in the early 1990's. I play the drums and piano/keyboards/organ mainly, and can also play a little guitar, bass guitar, and other things. I went to school for recording/production back in 1997-98 and have been working professionally in all sorts of situations ever since. I built a modest home studio back in the 90's in the basement of my house and slowly worked towards expanding my knowledge, experience and equipment list while working with local clients doing all sorts of different types of music, but mainly rock/indie rock/emo/hardcore/punk and also electronic music of the house/techno/drum & bass and experimental/avant garde varieties. I built my first small commercial studio in 2004 out in Ypsilanti (where i was living at the time), in the rather large backrooms of a music store (CD's and vinyl record retail i mean) that was owned by a former boss of mine when i worked as a projectionist at a small movie theater in Bloomfield Hills several years before. Him and i had become good friends outside of work and he is a huge music fan; he had always wanted to own his own record store and had talked about getting into that sort of business back when we worked together at the theater...(why he would want to get into owning a record store at the very height of the whole Napster/Acquisition/online music sharing/stealing thing I have no idea, and in fact i had voiced my concerns regarding all of that to him at the time but he was not to be dissuaded from following his dream and i'm certainly not one to get down on someone for that!). So i had a nice little studio set up out in Ypsi for a little over a year; it was pretty cool in fact, I had a control room that was about 18'x15' with a large window already in place, all i had to do was beef it up with thicker glass and double up the walls for better isolation. Then directly next to the control room i had a similar sized room that i used as a drum booth/iso room, and then both of those rooms opened out onto a hallway that went towards the front of the building (where the record store was), and the hallway itself lead into a nice large live room that was about roughly 30'x45' with a rather high ceiling at about 20'. My former boss (who i would prefer to remain nameless for his own privacy reasons) would run the record store during the day from 9am until 8pm and i would come in usually around 6 or 7pm and do recording sessions from then until the wee hours of the morning. Our arrangement worked very well until about a year and a half later when my former boss sat me down and told me that he had to close up shop because he wasn't making any money. Gee, big surprise there right? So i had to tear down the studio and move out my equipment, some of which had to sit in storage (temp controlled of course) for several years until i could find myself another opportunity to build a studio somewhere where i could afford the rent which was the main reason why i was able to build the first one in the back of the record store (he only charged me a couple hundred bucks a month and i just don't have the means to pay thousands of dollars per month to set up a studio in a typical commercial space. I worked in the pro audio department at Guitar Center Canton for several years after tearing down the first studio, not because i like GC mind you, but because it was a great opportunity for me to use my employee discount to purchase all sorts of high-end gear at ridiculously cheap prices in preparation for the day when i could build another studio. In 2008 i found a place in Redford, MI that i could afford and in fact it had previously already been a recording studio (albeit a pretty crappy one with basic 2x4 framed walls with very little isolation, but the layout was sweet. It's a small space, smaller than my previous studio, but it does have nice high ceilings and several of the walls are non-parallel, so all i had to do was build additional walls right against the existing walls to double them up (with air gaps in between in all the places that was possible to do) and pull out the cheap thin window glass to replace it with 1/2" laminate glass and 3/8' lami separated by an 8" air gap. I also packed the walls that i build with owens-corning 704 (i think? or maybe 702, i cant remember now...) attic insulation which is 12" thick and not at all designed to be crammed into 2x4 wall framing, which was a pain in the butt but works pretty well, and lastly install double doors between the live room and control room, and also between the live room and the iso booth. I've been working out of this studio since 2009 and i love it even though it's not very big, but it gets the job done. And surprisingly the acoustics are not bad at all, partially because i spent a considerable amount of time and money doing everything possible to introduce absorption as much as possible where necessary and some amount of diffusion wherever i could.
Also I've been in and out of rock bands (playing drums usually) since the early 90's, and in about 2001 I began to get into DJ'ing both for my own entertainment and also semi-professionally at various clubs and venues in and around the Detroit Metro area. I've been a geek for electronics ever since i can remember, for example when i was very young my mother's friends used to bring things like household appliances, stereo equipment, etc. over to our house for me to have a look at and hopefully be able to fix. I can't say my success rate at age 9 was even close to 100%, however i did have quite a few successes, and that was before i really even had much of an idea what i was doing.
I began to take electronics much more seriously about a decade ago, and ever since then i have been studying, learning and experimenting with all sorts of recording gear as well as dabbling with building my own. I would by no means call myself an expert but i do know a few things i suppose. I also plan on starting a formal education in electronics at some point in the near future to add to my abilities as a recording engineer and i would love to design and build my own boutique recording gear at some point once i have the experience and abilities necessary.
And lastly i would like to say thank you to everyone on this forum for their kindness, helpfulness and VAST pool of knowledge. You all have definitely already helped me out on numerous occasions.

On on to my questions.

So i have this old recording console built in the early 80's down in Texas (I believe) by a rather small company called Stevenson Interface Electronics that has long since gone out of business. I've owned it for about seven years now and have yet to do anything with it, partly because i have plenty of other equipment that i use at my studio and at home where i have a fairly extensive setup that i use for mixing, some overdubs and also for making my own electronic music which is something ive been doing for 20+ years now. Anyway, this console was originally designed (as far as i can tell) to be a monitor mix desk at some sort of live concert venue. It is pretty much hand-built, as were all of the Stevenson consoles, with somewhat shoddy silkscreening done on all of the channel modules as well as the back of the desk. It has 26 mono mic/line input channels (odd number, i know...), each with a Beyerdynamic transformer for the mic input, your standard compliment of phase reverse, -10 and -20dB pad, phantom power on/off, a three-band semi-parametric EQ w/sweepable high, mid and low, and a switch for wide/narrow Q on all three bands, as well as a 70Hz low-cut. It has 4 mono aux sends, 8 busses, a Direct Out switch on each channel, and all the other basics such as pan, channel on/off and a 10-LED bargraph channel meter. It does not have a tape-return path or a small fader section. It also has some sort of 8x8 monitor matrix section with VCA-groups which is partly what leads me to believe it was originally intended as some sort of monitor mix desk.
Looking at the guts, it was clearly built on a budget (and with late 70's/early 80's technology), with tons of TL071N op-amps as well as OP249's. I've never even seen OP249's before, i've seen plenty of other OPxxx(x) op-amps but not the 249 and I can't imagine it's specs are very good. now, i'm not one of those people that believes that swapping op-amps will give you all types of improved sound quality- in other words, i don't sit around talking about how "when i put OPA627's into my such-and-such piece of gear all of a sudden the string section became much more creamy and forward, and there was all sorts of new-found definition in the low end" and on and on... I am simply of the opinion that for example the TL071 is clearly an op-amp from yester-year and something like an NE5532 has basically been the cornerstone of a huge percentage of IC-based high quality pro audio equipment of all types for a long time now.
So my main question is this: all of the op-amps on the channel modules of this console are socketed (thank god), so it will be dead easy for me to replace them. What i would like to know is what would be an appropriate replacement for all of those TL071's (each channel has three of them) and OP249's (there are two of them)?
I am also going to re-cap the whole console, as i'm sure that the caps in there are the originals from the early 80's and they are clearly bleeding DC badly, but i think i can handle that job without needing to ask any questions here, although i certainly will if i run into any problems.

EDIT: I also have one other issue with this console, and it's not a small issue at all. In fact, it is probably the single most important reason why i have yet to do anything with it. It's something that i've never run into before in all of my years sitting at countless recording consoles, although i have a feeling that it might be something that isn't entirely unheard of. The problem is this: each of the 26 mic/line input channels has a channel on/off switch (rather than a mute switch), so depressing it turns the channel on. When i turn all 26 channels off, and introduce an input signal to every channel (1kHz test tone, actual modulating audio, whatever), and then begin to turn each channel on one by one, the output of the console on the stereo mixbuss gets lower and lower in level as each new channel is turned on. It's so bad that after turning on no more than about 8-10 channels the level on the mixbuss is down by roughly 12-14dB. And if i turn on all 26 channels, i end up with an output signal level so low that it's barely above the noise floor! What gives? As i said, i am no expert in electronics, and i've been trying to figure out what is going on ever since i got the thing years ago, and i have yet to be able to come up with any solutions or any sort of work-around. I'm guessing something is going on with the summing amps but I could very well be wrong. And just in case this helps at all, the console is fully modular, each input channel is a vertical card that plugs into it's associated 64-contact double-sided slot on a "motherboard" so to speak, which runs the length of the console and also has slots for the group-out/aux return cards (the 8 busses and the 4 mono aux return inputs are combined together on 4 modules- 2 busses and 1 aux return per) as well as the 8 monitor matrix modules (each of those has 8 inputs with rotary-style potentiometers from each of the 8 busses so that you can presumably group input channels together onto busses and then send varying amounts of signal from any of the 8 busses to any of the 8 matrix modules, which then has it's own output at the back of the console controlled by a VCA-assignable fader at the bottom of the module) and lastly at the far right hand side of the "motherboard" is the slot for the master module which of course contains the stereo mixbuss fader, talkback section including a built-in tiny little mic, a master LED indicating solo status, a pot for master solo level, a studio loudspeaker output and level control, and a few other typical master section things. And last but not least, in the interest of providing as much info as i can think of off of the top of my head in order to assist anyone who might be kind enough to read this and want to help me out, as far as i can tell, the console in general has standard balanced mic inputs on XLR's, balanced main outs on TRS and XLR's, 8 balanced buss outs on TRS's, but then it appears to have unbalanced line inputs on TS jacks for each input channel, unbalanced aux outs and aux returns on TS jacks, and inside the console on the far right hand side it has 8 very large input transformers made by Stancor that have clearly seen better days (and by that i mean that they aren't totally horrid looking, but they definitely look like what you'd expect for transformers that are more than 30 years old...) and i haven't yet figured out what they are for although i admittedly haven't really tried to investigate that particular aspect yet. All I know about them is that they are labeled on the top by Stancor as A-4350 Input transformers, and beneath that they say "Microphone or line-to-line" and then they give impedance ratings as follows: "Primary 500/333/200/125/50" and "Secondary 500/333/200/125/50".
I don't get it. Eight input transformers on a console that has 26 mic inputs w/Beyerdynamic input trafo's, one per input channel,  unbalanced line-level inputs on TS jacks, eight balanced buss outputs (but the Stancors are input trafos...) and eight of those weird mon matrix ouputs that i believe are balanced if i remember correctly, and 4 mono aux inputs that are unbalanced. What the heck would eight very large Stancor input trafo's be doing in there?

Thanks so much for taking time to read my post and thank you all again for all of your wonderfully vast collective knowledge and experience!

Ryan Maslyn
Kinetic Sound
 

gyraf

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Hi Ryan,

Welcome on board - and your first post takes the prize for the longest yet this year.

Would you mind if I edited your post and put in some paragraphs/headlines? That would probably make it easier to extract needed information, and you'd be getting better answers..

For your main question - suitable replacement for TL071 - it would be extremely helpful if you posted a schematic. It's VERY hard to give qualified estimates without that. And seeing the schematic, there may be a handful of different modern opamps that suits different functions.

Jakob E.
 

mjrippe

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kineticsound said:
Thanks so much for taking time to read my post and thank you all again for all of your wonderfully vast collective knowledge and experience!

Ryan Maslyn
Kinetic Sound

Ryan, NOBODY is going to take the time to read your post.  We don't care where you went to kindergarten and what color your socks are today  ;)

With that said, if you need schematics for Stevenson Interface consoles I have posted them in the Technical Docs section.

Stancors are probably balanced bus out transformers ("line to line").  TL071 is the best replacement for TL071.
 

PRR

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The Oh-Yeah Question:

........output of the console ...gets lower and lower in level as each new channel is turned on. ....about 8-10 channels ...down by roughly 12-14dB.
Exact measurements, please.

You say "summing amps" but it is clear you do not know that. A passive mixer drops single-input gain as more inputs are connected; and that sounds like what you have (but numbers would be the proof). Passive mix networks have some advantages in PA work. (As number of open microphones goes up, the gain from each mike goes down, acoustic feedback margin stays fairly constant.)


The Other Question:

my main question is....
What i would like to know is....
what would be an appropriate replacement for all of those TL071's and OP249's?
____________________________________________

> the TL071 is clearly an op-amp from yester-year

So is the '990, the '5532, and the Gates 2-bottle preamps. The Fairchild 660 and the 1960s Neumann mikes are SO yester-year.

Yes, let's throw-out anything more than a year old, it's all junk.

IMHO-- driven from the hi-ratio Beyer input transformers and driving 10K pots, there is *nothing* wrong with TL07x. They are *extensively* used in high-class systems. Any complete studio-to-consumer path is riddled with TL07x.

> built on a budget

I dunno. Using TL071 singles is pretty extravagant for all that is in there (pre, EQ, etc). The duals were the same price and some layout economy.


> I've never even seen OP249's ... ... I can't imagine it's specs are very good.

Imagination not required. This is a *current* chip, the blurb-page and spec-sheet are easy to find.
http://www.analog.com/en/products/amplifiers/operational-amplifiers/jfet-input-amplifiers/op249.html#product-overview
    Fast slew rate: 22 V/µs typical
    Settling time (0.01%): 1.2 µs maximum
    High open-loop gain: 1000 V/mV minimum
    Low total harmonic distortion: 0.002% typical
http://www.analog.com/media/en/technical-documentation/data-sheets/OP249.pdf

It has a very high peak output current and 600 Ohm loading is addressed in the sheet.

FWIW-- Analog and Mouser are so proud of the OP249 that they ask Five Dollars for the PDIP ($6.54 if you want the Lead on it) (13 bux for Ceramic).


> input transformers made by Stancor that have clearly seen better days (and by that i mean that they aren't totally horrid looking, but they definitely look like what you'd expect for transformers that are more than 30 years old...)

Judge a book by its cover. You can't "see" a transformer's sound. If "aren't totally horrid looking" (how horrid is your horrid?) means they have rust on the cans, I would worry about damp and tarnish gotten into jacks and switches LONG before the transformers felt damp inside.
 

musika

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I never went to kindergarten, but I took a French class....

Ryan,

When you recap the console, make sure you go slowly making a few changes at a time and then test (and repeat).  You may find that your console sounds better after the recap (although those channel mutes are there for a reason !!!).  Also PM me as I am pretty sure I have some Stevenson Interface literature that I can send you.

~~ barely staying above water  "in this VAST pool of knowledge"
 

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