Amek BC3 Op-Amp Sub (No, no, not like that!)

[amplexus]

I'm starting this off by saying I'm NOT op-amp rolling!

This is for my personal console, a 32ch framed BC3- a bunch of the channels (both stereo and mono) are in need of some love, and a few op amps are needing replacement. Most of them are bog standard 5532 and TL072, but the first stage amps and post-mute/pre-fader 'buffer inverter' are MC33078 which are well over $8 each in DIP format (and $1.20 in SOIC ) so hoping to find a suitable sub that's not gonna kill my refurbing budget for the month.

My candidates thus far are MCP6022 (Higher noise level, so not ideal for first stage, but lower dist), and the old 'classic' LM833 which has nearly identical performance specs. I suppose i could just knock a 5532 in there, noise is around the same and distortion about the same, but current is higher as is slew rate and I feel like there's probably a good reason why in a console full of 5532's Neve specified the 33078 for those positions (though I'm willing to be wrong about that)

Anywhodle, if anyone more thoroughly versed in console preamp design has comments or suggestions- i'm all ears!

(Schematic sections attached)

 

[pucho812]

why not just do dip to soic pcb's and put in the soic versions?

 

[amplexus]

By the time i buy the adaptor Pcbs and take up bench time building them, the cost gets pretty much up to buying the direct replacement in DIP.

why not just do dip to soic pcb's and put in the soic versions?

 

[Whoops]

By the time i buy the adaptor Pcbs and take up bench time building them, the cost gets pretty much up to buying the direct replacement in DIP.

But do you need to replace all the MC33078?

 

[Tubetec]

Colin at AML may have some spare modules for the BC3 ,might be worth sending an email .

 

[amplexus]

But do you need to replace all the MC33078?

No, but again, even if I had to do 4 or 5, if the cost was "buy a few adaptors and pay for shipping and make up new ones with SOIC chips" versus "drop in a replacement for $1.85", I'm gonna save my time and energy AND money. If it comes to it I'll just eat the cost of a few of the originals- obviously this isn't a case of not having any options, just trying to see if i can find one that keeps me A) working and B) laying out less money.

I'm going to be recapping the strips when they're out and replacing bad switches etc... a general service that it BADLY needed before I bought it. I worked out most of the demons during comissioning to get me up and running but I've got a bit of time now to give the whole thing a good refurb, would just like to be as efficient and economical as I can!

 

[amplexus]

Colin at AML may have some spare modules for the BC3 ,might be worth sending an email .

I've got a dozen or so spare mono strips and a few stereo as well (console came originally from a broadcast facility, so lots of spares), but most of them are in worse shape as I've already swapped them out over the last couple years for the best working ones. The whole console is in need a a refurb so buying 24+ strips isn't really a more economical option than just doing the service for want of saving a few bucks on the op amps.

 

[Tubetec]

Sorry when I said modules I meant the Neve designed sub boards .
I was lucky to pick up an ex broadcast BC3 that had been serviced , re-capped and had the P&G faders replaced by AML just prior to it being sold off .

 

[amplexus]

Sorry when I said modules I meant the Neve designed sub boards .
I was lucky to pick up an ex broadcast BC3 that had been serviced , re-capped and had the P&G faders replaced by AML just prior to it being sold off .

Ohhh like the balanced driver boards. Ya i get you now.

SO far those all seem fine (most of the places where i lose a leg or have signal dropouts are in other places, usually bad solder joints, dead caps or bad ICs) but ya Colin is a damn gem- sent me a #23 mute cap free out of the blue after a passing request in an order comment.

Mine came out of TVOntario’s mobile truck, likely the same place as my Otari MX5050. I was told that at least one Gordon Lightfoot show was tracked on this desk.

 

[Tubetec]

Mine is a different format ,with two 24 position bays and separate meter bridge , designed for drop through table mounting . Everything except the mic/line ins were on Edacs and I didnt get the patch bay so it took me a while to find the jack back panels , If you happen to have any of these to spare I might be interested .

Nice to have the Gordon Lightfoot connection .

 

[amplexus]

Mine is a different format ,with two 24 position bays and separate meter bridge , designed for drop through table mounting . Everything except the mic/line ins were on Edacs and I didnt get the patch bay so it took me a while to find the jack back panels , If you happen to have any of these to spare I might be interested .

Nice to have the Gordon Lightfoot connection .

Mine is also the EDAC insert version with pre AND post fader inserts fitted (TVO basically got every custom option available except the VCA’s and limiters). I was VERY lucky that mine came with all the EDAC snakes on Mogami brought out to TRS for the patchbays. I’ve done a lot of customizing in the last 4 years I’ve owned it so I know my way around my unit pretty well.

I never had any of the jack panels on the rear… probably because of the TVO installation every EDAC came out with a bundle of 2pr grey cables all individually numbered with a code corresponding to whatever patch point or tieline… which i’m betting were all hardwired at the terminating end.

Do you have the full service manual for yours?

 

[gyraf]

I was under the impression that the LM833 was just another name for the MC33078? I've always treated them like they were the same..

/Jakob E,

 

[abbey road d enfer]

I was under the impression that the LM833 was just another name for the MC33078? I've always treated them like they were the same..

/Jakob E,

No. The LM833 was supposed to be the 5532 killer, but it didn't catch on, probably because there was no 2nd-source, when the 5532 had many.

 

[abbey road d enfer]

the first stage amps and post-mute/pre-fader 'buffer inverter' are MC33078 which are well over $8 each in DIP format (and $1.20 in SOIC ) so hoping to find a suitable sub that's not gonna kill my refurbing budget for the month.

Ali Express has them dirt-cheap. Now you don't know if they're genuine or fake, but at 20 cents a piece, why not try them?

My candidates thus far are MCP6022 (Higher noise level, so not ideal for first stage, but lower dist),

I have absolutely zero experience with CMOS opamps in audio. The noise performance is not such a big issue in the mic preamp, since noise performance is dominated by the input transistors. Again I would suggest you try them and let us benefit from the experience.
EDIT: It seems these CMOS opamps are low voltage (<5.5V), so wont wuk.

and the old 'classic' LM833 which has nearly identical performance specs.

LM833 is available cheap there
https://www.reichelt.com/fr/fr/circuit-audio-vid-o-dil-8-lm833-lm-833-n-p10523.htmlI don't know if ordering in Europe is convenient for you.

I suppose i could just knock a 5532 in there, noise is around the same and distortion about the same, but current is higher as is slew rate and I feel like there's probably a good reason why in a console full of 5532's Neve specified the 33078 for those positions (though I'm willing to be wrong about that)

Yes, current draw is a big issue there. The rare opamps that have the same performance and low consumption are almost inevitably in SMD format.

 

[Tubetec]

I bought my BC3 in a live online auction when Meridian TV UK was liquidated .
I then had to travel to England to collect it , the manual hadnt been returned by AML after the previous service ,although Colin did have it , it was going to cost more money to buy it back . There was a very hulpfull Tech on site when I went to pick up the mixer and he was going to dig out the patchbay for me , unfortunately the security guy in charge of the collections became irate we me and my pal , I dont know if he thought we were trying to blow the place up or what , but he ended up saying the patchbay wasnt included in the sale and told us to get off the premesis or he'd call the cops.

 

[amplexus]

I bought my BC3 in a live online auction when Meridian TV UK was liquidated .
I then had to travel to England to collect it , the manual hadnt been returned by AML after the previous service ,although Colin did have it , it was going to cost more money to buy it back . There was a very hulpfull Tech on site when I went to pick up the mixer and he was going to dig out the patchbay for me , unfortunately the security guy in charge of the collections became irate we me and my pal , I dont know if he thought we were trying to blow the place up or what , but he ended up saying the patchbay wasnt included in the sale and told us to get off the premesis or he'd call the cops.

Damn! Thats an ordeal.

I only had to carry mine down from a 4th floor attic in a house with narrow stairs that turn back on themselves every like half-flight. On a very hot August day. Still though, the 3 of us made it down in under an hour without breaking anything

if you’d like, i’d be happy to scan my manual for you. I have the original binder with faxes from Amek in it detailing the modifications and customizations- quite faded. I’ve been meaning to digitize it anyway, if only to have it searchable and a backup of the paper!

 

[amplexus]

Ali Express has them dirt-cheap. Now you don't know if they're genuine or fake, but at 20 cents a piece, why not try them?

I have absolutely zero experience with CMOS opamps in audio. The noise performance is not such a big issue in the mic preamp, since noise performance is dominated by the input transistors. Again I would suggest you try them and let us benefit from the experience.
EDIT: It seems these CMOS opamps are low voltage (<5.5V), so wont wuk.

LM833 is available cheap there
https://www.reichelt.com/fr/fr/circuit-audio-vid-o-dil-8-lm833-lm-833-n-p10523.htmlI don't know if ordering in Europe is convenient for you.

Yes, current draw is a big issue there. The rare opamps that have the same performance and low consumption are almost inevitably in SMD format.

I’m in Canada, but Digikey has LM833 for basically the same price as 553x etc… less than $2… so i’ll order a handful and give em a shot and see.

In the stereo channels they use a pair of TL072 in the position that would be the 33078… tho they are line level only so theres that.

In theory I should have a fairly good amount of current headroom- the PSU audio rails are 15A, and I’m fairly sure I’m only pulling around 10 or 11A right now. But this console is a damn furnace so i’d rather not increase current anymore than needed!

 

[Khron]

NJM2068 anyone?

 

[amplexus]

NJM2068 anyone?

Oh shit, yea that looks like a good option. Slightly higher current draw, but not much. Better distortion spec, and almost identical noise and slew rate.

 

[Matt Syson]

I tested the prototype of the BC3 at the factory (because I worked there). The 33078 is a very good chip as are NE5532 but some attributes are slightly different. When pushed to give current (as an output particularly) the 5532 is a bit better than 33078. The 33078 is not as thirsty hence it was used except when on an output driver.
The TL072 could be usefully changed for TLE072 which is then a simple swap. Changing chips is a foolish idea unless you have full facilities to check what you have actually done
It MUST be recapped, as they do run hot, hence the fans in the armrest which MUST be running. They have a simple circuit to make them run slower that they would on full supply.
Matt S