Aux sends and returns in a mixer project- what's your opinion?

[abbey road d enfer]

At P&G, at least, tapers were  / are ( It was a while ago I was there)  trimmed manually on the production line - removing ink to get the taper within spec'.

Which made them awfully expensive; acceptable for faders in a £40+k mixer, but not for every pot in them.
In the meantime, silk-screen and ink technology have improved significantly.

 

[pahstah]

The pot is a Bourns 51CAN-D20-D10L, with is stated as audio taper

Paolo

 

[Newmarket]

Which made them awfully expensive; acceptable for faders in a £40+k mixer, but not for every pot in them.
In the meantime, silk-screen and ink technology have improved significantly.

Yes - I was thinking faders - which were the main thing.
Rotary CP 'pots' too but IIRC selling mainly to some 'high end' hifi outfits - Krell etc. - who wanted 'impressive' volume pots.
I recall it amused the MD how much they would pay for a large solid aluminium housing on the pot that didn't help in any technical sense.
They faders were indeed a 'premium' pricing option. Standard on high cost mixers becoming optional (vs ALPS ; TKD etc) as price reduced.
Technology wise I am talking mid to late 90s.
Then there is the issue of lubricating the guide rods whilst stopping the lubricant migrating to the tracks - cue Nyebar...

 

[boji]

Then there is the issue of lubricating the guide rods whilst stopping the lubricant migrating to the tracks - cue Nyebar...

What's your take on the CAIG stuff, Newmarket?

 

[boji]

The pot is a Bourns 51CAN-D20-D10L, with is stated as audio taper

Shoot, that's a nice cp pot, Paolo. Not too bad on cost either, but Mouser has a min qty order of 500.  I would have looked for those elsewhere had I not just the other day purchased some BK 1k/10k dual concentrics from CAPI.  I figured the 10k would be useful for returns panning down the road if returns-on-channel gets bothersome.

 

[boji]

I asked in the brewery about an oddity in the Jensen paper on tx's about polarity, and folk's answers were generous, but it still has me second-guessing myself.  I would not have figured it mattered before, but, since I'm inverting polarity with a ACA, reassure me there's nothing wrong with permanently flipping the secondaries to restore polarity? 

Thanks!

 

[abbey road d enfer]

, reassure me there's nothing wrong with permanently flipping the secondaries to restore polarity? 

Alternatively, you could  flip the primary! There may be a tiny (probably just barely measurable) difference in HF response, due to the different capacitive (stray) coupling.

 

[Newmarket]

What's your take on the CAIG stuff, Newmarket?

I should say that I wasn't involved with fader / pot manufacture myself as I was designing / developing electronics.
But I think the CAIG products you're showing there are applied to the tracks / wipers ?
I was referring to the application of 'damping grease' IIRC ROCOL Kilopoise to the guide rods. There is an issue of this migrating to the tracks (not good) hence use of a 'barrier' product - Nyebar - to inhibit this.

I haven't used the CAIG stuff for faders. But I do have a can of the general CAIG 'DeOxit' spray and I do find it works well for contacts / connectors etc.

 

[abbey road d enfer]

After having tried many things, I've found that using distilled water and soap is the best way to remove contaminants from fader tracks. Apply with a light brush or Q-tip and wipe. Let dry in warm air (foehn/hair dryer) before re-using.

 

[Newmarket]

http://www.coopersound.com/Application/cleanpg.htm

Better than what I can remember.
Essential what Abbey says. Note use of 'non-detergent' soap.
Note that it specifies Silicon Oil for the guide rod lubricant but indicates that may be better to leave unlubricated.
IIRC the application of the Nyebar was a bit of a process / dipping etc so not easy for DIY.

 

[boji]

Thanks for the advice guys. If the Deoxit is water soluble, I'll do a comparison test with a light touch.
Maybe F100L for the guides. Honestly the guides need replacing. They're from an early 80's Audioarts Wheatstone 32ch, so they got quite a bit of rock in the roll and dirt in the skirt.  :-*
Hopefully I can avoid using the most tired, as a few have noticeable abrasion grooves on the tracks.

 

[boji]

Anyone see a problem with three OPA's sharing two sets of power caps? You're welcome to tell me to stop being lazy and add a third if each need their own, and/or go smaller, etc. Thank you! (caps are 100uF)

 

[JohnRoberts]

Probably OK for electrolytics. I might consider separate HF ceramic discs by each, but those OA look pretty close together. You can always put holes in the PCB and not populate them unless needed. 

JR

 

[boji]

I might consider separate HF ceramic discs by each, but those OA look pretty close together. You can always put holes in the PCB and not populate them unless needed. 

That's a good idea!  Thanks JR.

 

[boji]

Looks easy enough.

 

[abbey road d enfer]

Anyone see a problem with three OPA's sharing two sets of power caps? You're welcome to tell me to stop being lazy and add a third if each need their own, and/or go smaller, etc. Thank you! (caps are 100uF)

The electrolytics can be put almost anywhere, not necessarily very close to the DOA's but I would put the ceramics as close as can be.
However you should ensure that the current that return from the loads are properly directed to where they belong.

 

[john12ax7]

Do the DOAs already have ceramic bypass caps on board?  I believe some do.

 

[boji]

However you should ensure that the current that return from the loads are properly directed to where they belong.

;D Yessir.  Workin' to it!

Do the DOAs already have ceramic bypass caps on board?  I believe some do.

Now that you mention it John12:ax, the GAR 2520's do.  Oh well. At least the pads are there in case of alternatives.

 

[boji]

Ok so mostly finished the Aux send card routing. 
I have quick question on the blank panel that sandwiches it:
I have put a pour across the whole blank PCB, does it matter if it's tied to acom or chassis?  I suspect you'll suggest acom since that just means more copper for the most important com, but I figure asking can't hurt as chassis would work well as a screen and I plan on using fat bus bars for audio.

 

[Newmarket]

Ok so mostly finished the Aux send card routing. 
I have quick question on the blank panel that sandwiches it:
I have put a pour across the whole blank PCB, does it matter if it's tied to acom or chassis?  I suspect you'll suggest acom since that just means more copper for the most important com, but I figure asking can't hurt as chassis would work well as a screen and I plan on using fat bus bars for audio.

How would / do the acom / chassis connect to the pcb.
I guess ACOM is on the edge connector ? or a busbar ?
Is there a 'Chassis' connection on that connector too or would it tie directly to the metalwork of the chassis ?