Console signal flow, input cards, general discussion on API styled DIY mixer

[Tubemooley]

Hello again,
schem asks for 250uf @4v at the output of the op-amp.
I'm trying to source one and I found 
http://www.mouser.com/ProductDetail/Vishay-Sprague/715P22256JD3/?qs=sGAEpiMZZMvCt%252bwg%252braTuvW0YsKHLWlohro4WlUsabA%3d
an 'orange drop' cap 220pf 5% 500v, with a "load life" of 500 hours.

Few questions:
If I can't find a cap that meets the schema is it
1) always better to go with a higher value?
2) when calling for say, a 4v cap, is it ok to go with something higher? How high is too high?
3) What does 'load life' mean? is that cap life or hold charge life? 

And lastly if you want to recommend a better choice I am of course all ears.
I'm trying to use WIMA's where I can.

Thanks

ANSWERS -
1. Not always better but usually better. For signal coupling, the higher the capacitance, the lower the low-frequency cutoff point. So in this case, yes, larger is better.
2. Yes. Any cap you're trying to "replace", the new cap should have the same voltage rating or higher. Higher is always fine. If a 4v cap was used by a company in their product, any cap with voltage rating of 4v or higher is fine. For these signal coupling caps, 6.3v, 10v, 20v or higher is fine.
3. I'm not exactly sure what "load life" is. But 500 hours is not a long time.

Here's my take on this topic. You're looking for a 250uF capacitor. They don't make film caps that large. Well, they do. But they are huge in size and very expensive. The easiest cap to get in this size is electrolytic. I hate electrolytics but they can't be avoided. They dry out over time (5 years) and as they dry out, the bass response decreases. This is why some of us spend so much time re-capping our old gear. But even here in these console modules you're building, it's pretty hard to not use electrolytic caps. So use them. There are differences among the various electrolytics. Nichicon has fairly recently released a new Black Gate series. I believe they are very good. I also use Panasonic HE series. I think they're HE. I have to save notes on my PC's with which series of caps I use. There are a couple of Panasonic series which are recommended. And then ELNA makes some really good caps too. Within the last couple of years they released their Silmic series. Those are supposed to be very good. I want to get a few of those to try out.

I hope this helps. DANA.

 

[boji]

Thank you Dana, very helpful indeed.

 

[boji]

What size do you think this cap is? 33uf seems pertty big!

 

[Walrus]

Can't read that diagram. But there is certainly a 33uF cap in that area. Will check at work tomorrow.

 

[jsteiger]

It is 33uf. BTW, I use a 470uf/16V for the bastard 250uf/4V.

 

[fazer]

API's are not very sophisticated.   That filter is an add on 6 db/octave.   I don't use them much.    It's the micpre,   with the iron transformers that have some weight to the sound.  Only 2 2520 amps to the mix.   Its a great sound.   

I think there may be slightly more than 2 2520's to the mix, dependent on the desk. 2 for the 548 channel, 2 for the 550A EQ (no hard bypass, and always in circuit unless overpatched), 1 in the ACA and 1 in the master fader VCA, and then 1 in the Mix Booster output.
This is from memory so may be out by 1.... ;D

Walrus your right on the number of 2520s in the path to the Control room outputs.  What I was thinking about is the Amek Motzart at work has so many opamps in the signal chain of 1 channel,just to get in to the mix summing Buss amp.  That puts so many Caps in the path.    I also did not account for the 2 2520's in the 550 EQ. These will always be in circuit in a channel on an Older API unless you have a patch point to patch around. 

Boji    I think the Cap is 33uf .  I'll pull a 528 and check it tonight and post a value.

 

[fazer]

C20 is 33uf /6.3v.  I pulled the module and checked it.

 

[boji]

Thank you! You guys give me the confidence to keep plugging away at this.

 

[boji]

Concerning API 6db filters:

Fazer: API's [filters] are not very sophisticated....I don't use them much.

Circuit

ARD: Not very sophisticated according to current standards, that's why I've had some doubts.

Think I ought to leave them out?  For tracking I could use the Mic Pre's HPF. For playback I have plenty of plugins...

Would there ever be a time I would regret not having them? (You can tell how much exp I have with big desks) :-X

 

[jsteiger]

I use them. The couple of friends I know with API desk use them too. 60hz, 100hz and 200hz. Quite usable. It's very little investment in parts. I put them on my 812d cards.

 

[Tubemooley]

The guys already confirmed that C20 is 33uF. But even if they hadn't, that's the main coupling cap between the 2622 mic input trannie and the 2520. That's always going to be in the 22-50uF region. I think up to 100uF would be acceptable too. Go with the 33uF or bump it slightly to 47uF. DW.

 

[abechap024]

DANA:
There are differences among the various electrolytics. Nichicon has fairly recently released a new Black Gate series. I believe they are very good. I also use Panasonic HE series. I think they're HE. I have to save notes on my PC's with which series of caps I use. There are a couple of Panasonic series which are recommended.

Its hard to keep all of these cap types apart! If I didn't just recap my console I wouldn't know. Nichicon HE series are very recommend and I believe used a lot in recapping old API gear. Panasonic FC or FM are also good.

Good luck, Amazing project!
AC

 

[jsteiger]

For signal path, Vishay/BC axials are the way to go. They will get you closer to the original Philips caps than the others. Nothing wrong with HE's or FM's. The radials are much less expensive.

 

[cheApy]

right man same problem for me and at beginning i thank it was mic DI or cables that sucks

 

[boji]

Thank you guys. Seriously. The sharing of your knowledge and experience has been crucial to my progress.
I'll add the HP Jeff. As you said it's just a few caps and switches.

As usual, if you don't mind suffering a few more questions...

Would it be ok to have the leds and relays share ground with the 2520's 0v?

The schema recommends 5k pots for cue with 39k bus resistors, but I believe Jeff's beauties are going to use 10k and 47k throughout.
Curious if I ought to follow his lead here...

 

[fazer]

I think you would adjust the feedback resistor on the sum amp for the gain your after?  39k being input resistor to the summing bus per module send.    If you go with 10k it changes the gain of the sum amp.  Gain goes up.

 

[jsteiger]

The 10K boji was talking about was for the pots. I kept the 39K bus R's for Cue's and Echo's. 2-mix and subgroup bus R's remain 47K like the skiz shows.

I also made the Cue's switched pre/post fader. I made 2 of the Echo's switchable pre/post as well. The remaining 2 Echo's are post only.

It's been a while since I did all of that work so I forget exactly but, using 10K pots and the config I mentioned above, the signal path did not really change, under normal conditions, no matter how the those pots are switched. With all pots at max CW rotation, I remember the frequency response of the preamp section started to suffer. Same with the post fader amp section but only if all pots were set post and we were driving a 600ohm load with the direct out. All those pots a max level will never happen in a real world mix. The 2520 is a robust amp for sure.

For the pots, I used all Bourns 51 series 10K audio log. I have the spec sheet here. http://www.classicapi.com/catalog/images/gallery/pots/25K-CCW-AT/Bourns-51-53.pdf

The problem is, you will be cutting shafts unless you do a custom order. I have to! Literally 100's of them. E28 was the shortest shaft length I could find on hand. Like these http://mouser.com/ProductDetail/Bourns/51CAD-E28-D15L/?qs=sGAEpiMZZMtxdMMi52izyoIe1hIh3T%2fDyHzGP%2foFO%252bA%3d

I would recommend only getting what you need to proto a channel and make sure you are good with everything before proceeding. I will use the 51CAN when I do the 500 modules. I like the extra mounting brackets.

You are on a long road boji! Props to you and may the force be with you.  8)

Best, Jeff

 

[boji]

Thank you Obi Wan!

 

[jsteiger]

Thank you Obi Wan!

Oh no, no no. I am not worthy of that. I am just some schmuck who is lucky enough to have a great old API board and barely not-brain-dead enough to figure it out. 

 

[jsteiger]

Would it be ok to have the leds and relays share ground with the 2520's 0v?

boji,

API used a separate +24V supply for relays. The ground for this is kept separate in the console from the audio ground. They eventually do connect together using a Star ground scheme.

Cheers, Jeff