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

[Tubetec]

Thanks Amplex ,
A copy of the manual would be great to have , at any rate though no major rush on my side ,
in your own good time will be just fine .

Mine is the model without VCA's also ,which Im very glad about , as is the tradition in radio and TV in these parts faders were upside down , ie max at the lower end , most of the modules were easy to change over and I got rid of the overpress remote start at the same time , only the sub group modules needed and extra lenght of wire soldered in . I also disconnected and removed the d-sub remote connectors at the back of each module just to allow a little more air flow . The fans in mine never worked so I tend not to leave it on for prolonged periods of time ,so thats another job I must attend too , thanks once again Matt for the valuable insights , any info the fan mod would be appreciated .

 

[abbey road d enfer]

NJM2068 anyone?

Absolutely! Damn, I had forgotten about it. It was a favourite of mine.

 

[amplexus]

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

Not changing all the chips, just the bad ones. Have definitely run across a few in the past couple years and I know there are a few more in there. Again, not trying to do any kind of rolling, just trying to avoid paying inflated prices due to retiring DIPs

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

Caps are already ordered. 105c low impedance and low esr KEMETs. Thats been in the plan for a long time!

So… fun story… not only do i not have any fans in the armrests or anywhere else, there are no cutouts or wiring harnesses for them either.

guess I should put that on the project list too!

 

[amplexus]

Absolutely! Damn, I had forgotten about it. It was a favourite of mine.

It looks near identical to the original. Have ordered a dozen to have on hand, will report back.

 

[amplexus]

Thanks Amplex ,
A copy of the manual would be great to have , at any rate though no major rush on my side ,
in your own good time will be just fine .

Mine is the model without VCA's also ,which Im very glad about , as is the tradition in radio and TV in these parts faders were upside down , ie max at the lower end , most of the modules were easy to change over and I got rid of the overpress remote start at the same time , only the sub group modules needed and extra lenght of wire soldered in . I also disconnected and removed the d-sub remote connectors at the back of each module just to allow a little more air flow . The fans in mine never worked so I tend not to leave it on for prolonged periods of time ,so thats another job I must attend too , thanks once again Matt for the valuable insights , any info the fan mod would be appreciated .

Mine just has the Remote triggers, no overpress. I had a crap ton of cleanfeed modules too. I have ONE channel strip with a Lundahl on the input.. have considered doing it to the stereo channels (I have it configured as 16 mono/mic for tracking, and 8 Stereo returns for summing from DAW), but that's a lotta $$ for a very clean transformer.

Mine does get left on for long periods of time, and with no fans, I'm not shocked i'm seeing channels go wonkey over time. I guess that'll become an installation project during this overhaul too. I converted all my meter lighting to LEDs so I should have a TON of current headroom on the 12V Aux Rail. I'm running the 900 Series PSU in the equipment room behind me on it's own dedicated IG circuit. (I have a pair of them that can be run in parallel if i wanted to use the hacked together switchover box, but I never found the need for redundancy)

 

[Tubetec]

Mine came with a pair of 900 series SMPSU's , I only use a single 24 pos bay so its well within its capabillities , I have 17 mono mic/line ins, 4 stereo groups ,two with limiters ,master and monitor strips . Gets really hot towards the middle of the console ,where originally blanking panels were fitted , producers clip board must have sat there .

Incidently the pinouts of the edacs for the master/group/monitor section are of most interest to me , I got a bunch of the jack backpanels from Sahib a few years back so I more or less have the mic channels covered for direct out .

 

[Tubetec]

Problems with fitting transformers is your stuck with them in the signal path , for that reason off board transformers patched in as and when required makes better sense to me .

 

[amplexus]

Problems with fitting transformers is your stuck with them in the signal path , for that reason off board transformers patched in as and when required makes better sense to me .

And again- i get why neve spec’d the Lundahls. They’re clean af and built like tanks. I think the only reason they were given as an option was for situations where pure galvanic isolation was needed. Otherwise I believe he was aiming for as clean and quiet a preamp as could be done.

and that’s kinda why I wanted them. I have a sidecar full of tubes and transformers and lots of colour. I’ll reach for those 16ch when i want that. I want the BC3 preamps for clean and clear! Sticking any transformer on the input unnecessarily defeats that a bit imo.

That said where i’d love to fit the trannys is on the stereo returns I use for summing- but again, the lundahls are clena enough that if i were gonna do that i’d want to find a way to fit something a bit less clean

 

[Matt Syson]

The mic input on the BC3 is a copy of the mic input subcircuit that he designed for the AMEK Mozart MZ15 modules. Since the components used on many mic preamp designs are largely the same, 'simply a bit of rearrangement and a couple of (resistors and capacitors) extra apart from the low pass (anti RF) filtering that is ahead of the mic amp stage itself the cost to build it is not too different to any other. The transformers wer4e included in the design of the boards because some broadcasters (particularly) demanded galvanic isolation. Strictly speaking those transformers are 'incorrect' anyway as the winding resistance is a bit low but they also had to be able to handle +24dBu input levels which is rare for a true 'mic' transformer. For fun you could try to work out how loud you would have to sing/play to get +24 from a Shure (or any)mic.
You would have a pair of 900 supplies simply because broadcasters usually asked for a 'backup' in case of failure. Often wired in using diodes so that changeover required nothing more than switching the 'other' supply on. Auto changeover to backup supplies can be a fun project.
Matt S

 

[amplexus]

The mic input on the BC3 is a copy of the mic input subcircuit that he designed for the AMEK Mozart MZ15 modules. Since the components used on many mic preamp designs are largely the same, 'simply a bit of rearrangement and a couple of (resistors and capacitors) extra apart from the low pass (anti RF) filtering that is ahead of the mic amp stage itself the cost to build it is not too different to any other. The transformers wer4e included in the design of the boards because some broadcasters (particularly) demanded galvanic isolation. Strictly speaking those transformers are 'incorrect' anyway as the winding resistance is a bit low but they also had to be able to handle +24dBu input levels which is rare for a true 'mic' transformer. For fun you could try to work out how loud you would have to sing/play to get +24 from a Shure (or any)mic.
You would have a pair of 900 supplies simply because broadcasters usually asked for a 'backup' in case of failure. Often wired in using diodes so that changeover required nothing more than switching the 'other' supply on. Auto changeover to backup supplies can be a fun project.
Matt S

Yup. That’s all it was. A VERY hastily knocked up project box with a bunch of 30A FWBs screwed to a block of wood

Not the best wiring job ever, but it seemed to have worked for TVO for a couple decades or more so…. As I didn’t need the redundancy I just dismantled it and rewired the supply cleanly and relocated it to the equipment closet behind me. Ran some 10/5 SOOW and a big 6AWG ground conductor for the chassis under the floor