Crown VFX-2 Repair/Restoration Circuit and Dual Op-amp Recommendation

[TLS Guy]

I'm posting these details to make them generally available. The Crown VFX-2 filter/crossover is a well regarded and respected device, with working models still commanding prices around $200. There has been a lot of controversy on a number of forums, as the circuit has not been linked. There has been a lot of debate on how to approach the NLA OP-AMP ICs.

About 10 or so days ago I suddenly got a pretty loud hum and hiss from my left rear back speaker. The Crown VFX-2 was soon found to be the problem.

Now since I'm a hoarder, even though I purchased the unit in 1977 for long gone Margaritte's Music in Moorehead Minnesota, I still have the original owners manual. Back then a manual contained a full circuit and parts list. That is a practice that should never have been abandoned.

This is the unit in question. It is the fourth unit from the top. The black unit is the right most rack, fourth from the top,

Now my unit contained 10 NLA RT7412 dual op-amp ICs, one of which had failed.

After research I ordered a packet of 20, Texas Instrument PRC4558IP ICs from Mouser Electronics. Mouser Part Number: - 595-RC4558IP.

The price is $0.301 a piece. With shipping it cost me all of six dollars!

I checked the caps and all seemed fine, so not wanting to fix what was not broken, I left them alone. I changed all ten of the dual op-amp chips with the new ones. I did clean the switches and pots with electronics cleaner while I was inside.

The unit fired up right away and is now better than new. The old ICs, had a very slight hiss you could hear putting you ear up against a speaker. The unit is now totally quiet and back in service.

I have posted this in the hope it will show in an Internet search for anyone looking for advice on these fine units.
I can confidently recommend the TI PRC45581IP dual op-amp ICs as a replacement for the originals.

 

[sekess]

Those pots and switches seem to be sealed. How did you go about accessing the contact areas of the pots and switches in order to clean them?
Thanks

 

[TLS Guy]

Those pots and switches seem to be sealed. How did you go about accessing the contact areas of the pots and switches in order to clean them?
Thanks

I have not had trouble with the switches. The pots gave trouble early, so I replaced them all with higher quality ones, and I have had no trouble since.

 

[sekess]

Thanks for the fast reply.
I assume those triple-gang pots are not easy to come by.
Do you recall where you sourced replacement pots from?

 

[TLS Guy]

Thanks for the fast reply.
I assume those triple-gang pots are not easy to come by.
Do you recall where you sourced replacement pots from?

Yes, that is true. Analog pots are an endangered species. On my unit the pots gave trouble almost from the beginning. So we are talking about forty years ago now. I can not remember from whom I purchased them. I was living in ND then and I would not have bought them locally. There was no Internet then, so I assume it was from a mail order catalog source. It very well may have ordered them from Radio Spares in the UK, who sold excellent quality pots. They are long gone.

 

[highfigh]

I'm posting these details to make them generally available. The Crown VFX-2 filter/crossover is a well regarded and respected device, with working models still commanding prices around $200. There has been a lot of controversy on a number of forums, as the circuit has not been linked. There has been a lot of debate on how to approach the NLA OP-AMP ICs.

About 10 or so days ago I suddenly got a pretty loud hum and hiss from my left rear back speaker. The Crown VFX-2 was soon found to be the problem.

Now since I'm a hoarder, even though I purchased the unit in 1977 for long gone Margaritte's Music in Moorehead Minnesota, I still have the original owners manual. Back then a manual contained a full circuit and parts list. That is a practice that should never have been abandoned.

This is the unit in question. It is the fourth unit from the top. The black unit is the right most rack, fourth from the top,

Now my unit contained 10 NLA RT7412 dual op-amp ICs, one of which had failed.

After research I ordered a packet of 20, Texas Instrument PRC4558IP ICs from Mouser Electronics. Mouser Part Number: - 595-RC4558IP.

The price is $0.301 a piece. With shipping it cost me all of six dollars!

I checked the caps and all seemed fine, so not wanting to fix what was not broken, I left them alone. I changed all ten of the dual op-amp chips with the new ones. I did clean the switches and pots with electronics cleaner while I was inside.

The unit fired up right away and is now better than new. The old ICs, had a very slight hiss you could hear putting you ear up against a speaker. The unit is now totally quiet and back in service.

I have posted this in the hope it will show in an Internet search for anyone looking for advice on these fine units.
I can confidently recommend the TI PRC45581IP dual op-amp ICs as a replacement for the originals.

It's great to have a schematic, but this piece wasn't made for residential users and most of them wouldn't have known how to repair if it it had problems, anyway.

Mine had the silver face and it was a bit noisy, but not terribly.