[Christian]

New to this forum and have enjoyed reading posts from y'all for quite awhile. I appreciate the seriousness you seem to have for purest audio sound and doing it yourself especially. I have a Ward Beck console that came from a TV station and I finally decided to overhaul the rest of the caps and replace the op-amps. Done power caps and cleaned the faders but have always stayed away from the audio path caps. They are all tantalums. Now I need to redo them. I figure after being on for over twenty years they could use a little help.

I want to have some channels all electrolytics of different brands and then leave a few channels tantalums. I thought it might be cool with slightly different sounding pre's. I have two sets of master modules so I felt I would do a set tantalum and then a set with electrolytics. I was wondering if someone could check out the schematics and give me idea's on what caps should be replaced with larger values and some good op-amp replacements. I have tried OPA604's and got a little oscillation, when the pan switch was engaged. I have had some Linear Technologies recommended by a tech, models LT1122 and LT1037. The op-amps needing replacement are LF356n and LM301an. You can look at the schematics at http://photobucket.com/albums/v215/cserig/

Thank you so much,
Chris

[SonsOfThunder]

I have a pair of M470 that I have been in the process of racking for far too long...

But at any rate, I replaced the opamps in one of them with OP176 with great success, no problems and sounds good...what little i got to listen to it.  If I remember, I had to remove C19 (4.7pF) to fix the same sort of problem you are facing.

HTH!  Let us know if that works for ya!
Charlie

[PRR]

> The op-amps needing replacement are LF356n and LM301an.

Beware the 301! It is very versatile and was used in several wonderful ways that do NOT match "modern" chips. In particular, several places use "feedforward compensation" (150pFd cap from -in to Comp) which makes the 301 incredibly fast, and very nearly single-stage. If a 301 has anything more than a 30pFd Comp cap, you need to re-think what Ward-Beck did. Or just leave it alone.

An issue: plans show +/-21V on LM301an. This is over the usual spec for 301 (36V max). There may be some special-spec versions rated 44V. I assume either it isn't really +/-21V or they got 44V rated parts, because 20 power-on years would have weeded-out the weaklings.

This business is clearly tacked-on, probably to control supersonics.


After you fix your oscillations (there is no such thing as "a little oscillation", oscillation is always bad and usually unpredictable), if you are going into modern recording gear you do not want this low-pass filter. (It reduced problems with old recorders that never expected to see anything over 20KHz.) Just do the red-line modification.

All caps look more than big enough to me, even over-sized for electrolytic distortion reduction. Bandwidth would extend to the geological, except the 70/100/150 high-pass seems to be 10Hz (12dB/Oct) when not-engaged. And that is 0.22 0.1 film caps, no gross distortion.

It is a pretty complicated path with a lot of push-pull emitter followers. Yet most of them work in Class A, and moreover are buffering BiFET amp chips which suck a lot less if buffered. And the "rude" way they bias the emitter follower forces the BiFETs into Class A. This isn't going to sound like the usual box of TL074s.

I suspect it will be the essential dead-clean 1980 console. Perhaps a little soul-less, but to "give it flavor" probably means messing it up. Go get an Altec Tube box for "color".

Sadly I do agree that the tantalums should probably all be replaced. They were hyped as "long life" but that has not turned out to be true.

[SonsOfThunder]

Ooo...  This is the first time I've seen the Master section.

Why would you bother to put the current boost trannys out there and then stick a opamp driven LPF afterward?  Strange...

Okay, I am looking at my M470.  I used OP176, deleted R39 and C16, deleted R46 and C19, and added a 100pF ceramic cap across R19!

Try the cap at R19 and see if that resolves your problem with the osc....  I remembered there being an oscillation and now I remember the strange fix.

HTH!!
Charlie

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