[jedi35]

Hey everybody,

I have the Crown VFX2A 2 channel external crossover in my system. It currently has six HA1-4741-5 op amps, and these are old and out of production. I have done some searches, called some places, and found out that I may be able to replace these older op amps with either the LM348N or the more expensive LM124AJ-ND. I don't know anything about op amps, and the places I've called, including DigiKey could not advise me on whether the replacements would be suitable for my purposes, or give me any audio advantages over the older design. There may be other replacement options yet, so I'd love the advice of you experts out there.

My current op amps in the Crown are still functional, but a buddy of mine suggested that I could get better sound if I updated them. He said that maybe there is an adapter that would allow me to use something more modern as well. Any help would be greatly appreciated.

Adrian

[Occam]

Adrian,

I'm hesitant to make a recommendation as I can't find a schematic for the Crown crossover. Given that, one is left in the position of proposing 'throwing crap up against the wall and seeing what sticks'. That said, I'll make some (educated) recommendations, but you should be aware that there is allways a possibility of your crossover going into oscillation and self destructing.

The opamps you've mentioned are basically quad amp versions of the 741 bipolar opamp. The safest bet would probably be the very good OPA4227PA quad opamp from Texas Instruments/ Burr Brown. Its specifications and speed are such that the swap should be straightforward. It 'sounds' good, too boot.

The quad bipolar 14 pin dip chip that I use in crossovers (no experience with Crowns) is the National Semiconductor LME49740MA. This is IMO a superb opamp, but it is substantially faster than the other chips mentioned and might make higher demands on the layout of the circuit specifically in the area of powersupply decoupling. This is a very well behaved chip, but because of its speed, it could be problematic. I've never had to use my oscilloscope to track down any misbehavior, but my preferred choice could be more problematic than the OPA4227.

Both the Ti/BB and the National opamps mentioned are available from digikey.

You might posit your question on boards (which I'm not familiar with) more oriented towards pro equipment where you're likely to find posters who've already addressed the issue.

FWIW,
Paul

[TomS]

Schematic for VFX2 on the last page here

http://www.crownaudio.com/pdf/legacy/s3p210-3.pdf

[jedi35]

Tom,

Thanks so much for the schematic. I actually didn't have the manual before now.

Paul,

OK, now that we have the manual, do you have any additional suggestions? I appreciate all the advice you've given so far. I'm not quite sure where the pro audio board is. Could it be Project Studio, or Digital Processing, or something else?

Adrian

[Occam]

Thanks Tom,

The schematic you referenced uses 5 dual RC4558 8 pin dual opamps, aka generic 'jelllybean' chips. Given what Adrian has said, I'd think the 'A' suffix a different implementation using quad opamps as he indicated. I looked for any additional schematics and couldn't find it.
Regardless, the schematic shows  minimal series pass regulators for the rails with nary a bit of rail decoupling at the opamps themselves. I'm assuming the 'A' version using the quad opamps isn't significantly different with regards to ps implementation.
If Adrian has the version using dual opamps, I'd suggest the dual versions of those chips I've already mentioned, the OPA2227PA and the LME49720NA/LM4562NA. The total lack of any rail decoupling shifts the preference towards the OPA chips because of their slower speeds.

Regards,
Paul

The 'Pro' boards I mentioned are out there somewhere on the web. I know they exist, duun where, and am certain they've folks who are just as opinionated as those you'll find here, but there you're far more likely to find folks with actual experience with the Crown crossover.

[jedi35]

Thanks Paul,

I should probably stay with quad opamps, since that's what's in there already, right? Is there anything to be gained by experimenting with duals? I'm certain that there are 6 chips in my Crown, so I guess that my unit is different. I'll search the web for pro audio boards, but I'm very interested in trying the OPA4227 chips.

Regards,
Adrian

[mjosef]

I used to frequent this pro site... http://srforums.prosoundweb.com/
You might also check the DIY site, some of the techies there have pro 'credentials', as well as the pro forum over at AA.

[jedi35]

mjosef,

I actually just finished registering at prosoundweb.com, and then saw your post. Cool!! What do you mean by AA?

Thanks,
Adrian

[Occam]

Thanks Paul,

I should probably stay with quad opamps, since that's what's in there already, right? Is there anything to be gained by experimenting with duals? I'm certain that there are 6 chips in my Crown, so I guess that my unit is different. I'll search the web for pro audio boards, but I'm very interested in trying the OPA4227 chips.

Regards,
Adrian

Adrian,

I'll preface my comment with the fact that if you ask a question of 2 diy audiophiles, you'll get 3 opinions....
Yes, duals will give you more flexibility in choices of opamps. Brown Dog has realeased an adapter board that will allow you to use 2 dual SO-8 smt monolithic opamps for a 14pin dip quad opamp -
http://cimarrontechnology.com/index.asp?PageAction=VIEWPROD&ProdID=36
This would greatly expand your choices, BUT, the reason to do so would be to use some of the newer opamps like the AD8499, but given that the major constraint, IMO, is the lack of ps decoupling, you're simply asking for trouble.

Unless you can find someone on the pro boards who have specific experience with upgrading the Crown unit, play it safe and use the OPA4227.

For some light reading, Tangent's website offers some excellent info -
http://tangentsoft.net/audio/
Read the articles under 'Op-Amps in Detail'

AA stands for AudioAsylum, another audioboard. Here is a link to their 'Pro' board, but be sure to put on your hipwaders  -
http://www.audioasylum.com/forums/pro/bbs.html

FWIW,
Paul

[jedi35]

Thanks again, Paul.

You've been quite helpful. Perhaps you could address another question I have. My Crown originally had all 1/4 " inputs and outputs, being fed by an Audible Illusions tube hybrid preamp when I first got it, which inverted phase. I have since switched to a Threshold preamp, which does not invert phase, and I've had the Crown modded with a level control for the bass outputs for amp matching, as well as RCAs so that I don't have to go through those awful adapters. However, the RCAs are installed on the previous connections I used with the tube preamp, which are labeled "inverted" high or low for each channel. When I switched to the Threshold, should I have switched to the normal, non-phase inverting connections on the Crown? If so, can it be simply corrected by switching the positive and negative at my speaker binding posts? As it stands, things sound very good right now, but I want to make sure that everything is correct.

Thanks,
Adrian

[jedi35]

Paul,

I have surfed to several pro audio and diy boards, and I have to say that your advice seems to be largely echoed on these other boards. The OPA4227 is highly regards for audio quality, low noise and low distortion. I also see raving comments about your favorite op amp, the National Semiconductor LME49740MA. I have come across one thread where someone doesn't seem to like the 4227, and claims that it's fast speed might make it an unsuitable choice for some circuit boards. What do you think about these comments?

http://www.diyaudio.com/forums/showthread.php?s=82f148796488d71a1d9f716091b535cb&postid=898177&highlight=#post898177

In this thread, someone is trying to find a replacement for the same op amps that are in my Crown xover, the older HA1-4741-5 quad chip.

Thanks,
Adrian

Here's another post where someone talks about replacing the old 741 chip:

"You almost certainly have chronic oscillation. This would be because of the change from the 741, which is very restricted in its bandwidth, to the NE5532, which is a much better device but needs special compensation to specifically prevent this problem. It is so much better in demanding applications that it is almost too good for a guitar preamp, which is a very undemanding task, (in the strictest electronic sense not the tonal one).

I would advise that, if someone who knows has told you to use a TL071 then get one. They are a direct replacement for your 741 and perform much better all round plus, they are cheap and plentiful. The TL072 is a dual version and the TL074 is a quad version of the same opamp. Maybe these would be easier to find locally?

I don't know where you are in the world but I can't imagine you would have a problem getting them. Just look on eBay and you may find a few. You could also try online suppliers like RS or Farnell who would have them but the postage adds on to the price unless you are making a bigger order.

If they had your address by PM, maybe someone you know here could post a couple on to you."

[Occam]

Adrian,

Your understanding wrt the phase seems spot on.
Regarding opamps dunno what to say. I've recommended the slowest opamp for this line level application, with the least probability of acting out, that I find subjectively acceptable. I've listened to a lot of opamps, with varying ps quality, but there are many I've not evaluated. The OPAx227 is slightly faster than this 741 variant, the specifications are far better, and IMO certainly sound better than that drek.

As I said previously, ask 2 audiophiles for upgrade advice and you'll get 3 opinions. I'm not familiar with the specific posters in the diyaudio thread.

If that other guy thinks a TL07x might be your cuppa, be my guest. Personally, if the best I could get out of component was the sound of  TL07x s, I'd toss it in the trash.

FWIW,
Paul

PS - If necessary, its easy to replace your opamps with HA3-4741-5  s from Newark for $1.44ea, and it will be same as it ever was.... Its only obsolete in that it is a crappy 'jellybean' of an opamp.

[Speedskater]

It's the faster the op-amp the more it wants to oscillate! At work a million years ago, we manufactured a meter that used a 741, then after some years, the 741 use re-designed. The new 741 had much higher speed. All our new meters oscillated.
If you don't have a high-speed scope, odds are anything you do will oscillate.

[jedi35]

Thanks Paul and Speedskater,

Well, I think I need to try the OPA4227, and try to be prepared if it oscillates. If it does, what is the cure? After reading a bunch, it seems that soldering something like a cap or a resistor between certain pins should do the trick, right? That might be tricky work for something so small, and I have 6 of them to deal with. Digikey has these chips for almost $8 each, and I haven't found them cheaper anywhere else. I want to order a couple extra, and that put me at $61 before shipping. That's an expensive test. Any suggestions?

I swapped the speaker leads last night for correct phase, and things sound a lot better to me in general. Now there's so much bass energy that I'll need to tone things back a bit.

Regards,
Adrian

[Occam]

Adrian,

Sorry for the delayed response. Speedskater made a very good point. The circuits implemented 20+- years ago used lethargic opamps of the day, and most folks didn't realize the necessity for power rail decoupling, ps transient response, better feedback implementation, and the critical importance of good layout to minimize unwanted parasitics, as chips got faster. Its instructive to do a google search on the opamps discussed and from the PDF datasheets, look at the Global Bandwith (GBW) as well as slew rate.

As your Crown crossover is of unknown vintage, (but certainly retired) all I can suggest is calling Crown an getting a manual/schematic, as we don't know what it contains or how it is implemented. Or hopefully, you might run across someone credible who has specific experience with the unit.

I've recently upgraded the opamps of  a (first designed about 10yrs ago) crossover/controller that has allways used TL07x opamps. Nevertheless, the unit works like a charm with specific 20MHz+ unity gain bandwith opamps as it Incorporated minimal powersupply decoupling at each opamp package, as does my modded $150 Zhaolu dac. The designers/OEMs of both the crossover and DAC are, IMO, quite good, and have certainly benefitted from the efforts of those who trod their path earlier.

[jedi35]

Paul,

I have bookmarked the technical data on the opamps I want to buy, but don't really know what numbers are good when you're looking at GBW or slew rate. I'll try to contact Crown and see if I can get a response on this matter. Another issue has been brought to my attention. I've been told that it's very likely that my opamps are soldered to the board, and won't just pull out and plug back in. For that, I'm told that I'll need to have sockets installed that allow easy plugins. All this is getting a bit more involved than I thought.

Adrian

[TLSGuy]

I know this is an old thread.  But I have just restored my Crown VFX-2.  I have my original manual which contains the circuit and parts list.

I am a long time member and poster on the Audioholics forum.

I have posted full details of the restoration and a PDFs of the circuit and parts lists.

This thread is well to the top of the list researching this issue.  So I will post a link to my thread on Audioholics, which will answer the questions raised in this thread as well as providing the circuit details.

https://forums.audioholics.com/forums/threads/crown-vfx-2-repair-restoration-circuit-and-dual-op-amp-recommendation.112152/

I hope this will fill in any gaps should anyone else find this thread.