L2042 components

[Bill Sallak]

Hello—I have a few hundred US$ left in my end-of-year budget, so I plan to purchase some of the quantity parts I'll need for the L2042 restoration I'm beginning over the summer.

I know I'll need a few hundred Panasonic 22uF/25V electrolytic caps for recapping, as well as better op amps to replace all of the LM201's. (Anthony, I think you used OPA134 in the Wilma video—those still a good choice?)

If I'm able to do more than that, what are some other pin-for-pin replacements I can do for other IC's?

• The 470A also has an LF356 op amp. Can/should I use OPA 134 there too?

• Should I put in OPA134 for all the other op amps (LM301A, LM301AN, LF357, LF356N)?

• Can I use OPA2134 in place of the LM1458N twin op amps in 472 and 453?

• Is it more important to replace the tantalums at this point? Add decoupling caps? Etc.

Also, I'm thinking about socketing all of the IC's to make repairs down the road easier. Any reason not to?

Thanks always,

Bill

[Anthony Kuzub]

There are about 600 hours of Engineering services and Technologist troubleshooting

and 20k+ in test tools missing from your budget.

:-)

Anthony 

• Like.audio                                                

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[Bill Sallak]

Anthony et al.,

Thanks for your quick reply. Please let me be clear: I understand that I'm undertaking a significant task here, and neither my resources nor my experience compare with many of this group's members, least of all yours. I'm good with a soldering iron, I have a basic understanding of analog electronics and the value of quality analog gear, and I'm really interested in making this board the best thing it can be for me and my students.

If I'm in the wrong place to try to make that happen, I apologize for taking everyone's time. If recapping the board or doing some of these IC swaps is too big a thing for someone like me to undertake, I get it. I'll pull together the cash for a Behringer X32 and the WBS board can continue gathering dust under lock and key.

Since I joined the group, I’ve been asked for money in return for advice, then told that the group could walk me through almost anything, then agreed to video-document as much of the restoration as possible, which seemed amenable to everyone and now, well, this exchange.

I hope my confusion is at least understandable. Please advise me as to how to operate within the group more constructively, if that’s possible. Cheers,

Bill

[Charles Beauregard]

Bill,

I wouldn't replace the op-amps. The front end and the rest of the modules are clean as they are. You'll probably have plenty to do just by cleaning the switches and pots. If an op-amp becomes bad it's a good idea to put a dip socket. Not a bad idea to replace the tantalum but you can wait until they fail. If you replace the 22uf/25v replace them with 35v.  

If you insist on replacing the op amps, be careful to respect their max supply operation and don't mix single and dual op amps ! LM201 are not available anymore in dip casing. When needed, I usually replace them with TLE2141 (especially into M460 modules where some are supplied with +/-21vdc). 

To view this discussion on the web visit https://groups.google.com/d/msgid/WBSps/51c334b9-7719-4b3d-a631-ea9c2ec280c7n%40googlegroups.com.

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Charles Beauregard

Tel: 514-449-9904

[Anthony Kuzub]

Huge questions here sorry, I'm always short 

 Where are your schematic markups? 

Anthony 

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[Bill Sallak]

All of this makes sense, thanks. Let me clarify as best I can:

• Once I get the board in late May or early June, job #1 is to clean it. I believe I have the supplies for that.

• If it hasn't been cleaned in this long, it certainly hasn't been re-capped, and it's from 1987-ish. That should be job #2, it seems—new electrolytics on all modules and power supplies.

• I've spent a decent amount of time watching Anthony's Wilma videos on Youtube, and especially noted Anthony's statement that the high-frequency response of L-series consoles is slightly limited by the slew rate of the LM201 (and similar) op-amps chip, and that the OPA134 op amps and THAT line driver chips improve this noticeably ("cheesecloth/tweeters," etc.). If my understanding of this is wrong, please let me know. I'd like to do this if it'll help, though I take Charles' recommendation above seriously.

• I also noted the aux pot issue (it's on the agenda for sure, just need to know what kind of replacements are recommended), decoupling caps (unspecified in the video, but would like to do for my board; don't know if this is related to oscillations from the upgraded op amps or what), and stepped-gain sensitivity switches (don't have the skills to build these myself, but if the same craftsman has the desire to build 16 more, I'd be happy to buy them and install them).

• A number of discussions seem to revolve around "non-musical" Q-factors in various parametric EQ modules. Mine are stock M472's with switchable Q, I haven't heard them yet, but this may be something to do down the line if 

• I don't anticipate doing the kind of major signal-routing mods that were done to Wilma. It would be nice to have per-channel direct outs, and my understanding is that this is possible if I sacrifice the "B" mic input. It would also seem that I can just use the post-EQ insert send and return as a sort of direct out and return, but that's maybe not the best option.

I've got two big questions:

• Do I have a decent idea of the big picture? and

• I have to spend this money before I can get my hands on the console—I have to spend it blind-ish. If I spend it toward supplies for restoring this board, what's the best way to do that?

I totally get that these are big questions that perhaps haven't been quite spelled out. In addition to the documentation PDFs available here, I've got the original paperwork binder with schematics for the board in my office. Anthony, I'm happy to get you whatever markups would be helpful. Thanks again.

[Anthony Kuzub]

What you'll find when you overlay the replacement chips in the schematic, there are compensation circuits that bw limit the op amps... They are treated in a case by case basis.  The paperwork will set you free.  

Wilma is all 462b so I have no comment in the 472 

Decoupling caps in the VCC and vee lines are vital if you plan to extend the high end 

Anthony

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[Bill Sallak]

Sounds good. I'll buy the caps now and see where next steps lead after cleaning and re-capping. Thanks again!

B

[Ken McKim]

Hi Y'all,

Yes, this is just another opinion. But...

When my clients ask if it would be a good idea to change out the audio ICs in their vintage gear for something more contemporary, I usually try to discourage them. To be sure, there are ICs out there that will easily "outperform" ICs that were in vogue 40 years ago. BUT. Sometimes the magic in a particular unit is in the more modest specs inherent in the components employed. The 1458, for instance, has a slew rate of 1 volt/uSecond. Pretty slow by today's standards. The TLE2141 by contrast sports a slew rate of 27 volts/uSecond. It will track a transient (or a transformer aberration) without even breathing heavy. Could it be that the slower IC lends some sweetness to the overall sound? Hmm...

At very least, I would think you would want to change the components in one module and evaluate.

++Ken

Ken McKim

Owner, Trouble Report

trouble...@gmail.com

 

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[Anthony Kuzub]

Wise words Ken

I only did it because I was told to by the person paying me to do so, so I did. 

I'm not so subtly hinting at all the other repercussions to these decisions. 

Get it working - getting past all the mechanical things is enough to break some owners... 

I'm not hot-rodding is something the WBSps really can actively support... too many variables and options and opinions :-)

But we're all fans.   Sharing your journey will get you closer to the goal as a group.

Thanks and Regards

Anthony