Hi,
I have a mixing desk (Studiomaster 16:16:2) and I need some help identifying the capacitor types. I've attached a photo of a channel strip (not mine, from another thread). I can see electrolytics and ceramics on there but I don't know what the grey rectangular ones are.
https://www.diyaudio.com/community/attachments/100_4149-jpg.184679/
Thanks,
James
I have a mixing desk (Studiomaster 16:16:2) and I need some help identifying the capacitor types. I've attached a photo of a channel strip (not mine, from another thread). I can see electrolytics and ceramics on there but I don't know what the grey rectangular ones are.
https://www.diyaudio.com/community/attachments/100_4149-jpg.184679/
Thanks,
James
Not really, I think polycarbonate is pretty good, but unobtanium these days. You might want to replace the shattered opamp though(!)
Thanks. I've read about replacing the EQ caps with polypropylene improving the sound but I am of course sceptical!
That's not my photo but I have the same board minus the broken op-amp.
I like the mixer but I'd like to service it and make some upgrades if possible to make the sound cleaner and reduce noise. I'm planning on replacing all the pots and faders and electrolytics. I'm also thinking of adding decoupling capacitors, which it does not have, and implementing a star ground arrangement. I'm not sure what other things might be worthwhile. All the resistors are 5% carbon film so I wonder if putting in 1% metal film might be beneficial in some positions, perhaps in the mic preamp to give better CMRR.
That's not my photo but I have the same board minus the broken op-amp.
I like the mixer but I'd like to service it and make some upgrades if possible to make the sound cleaner and reduce noise. I'm planning on replacing all the pots and faders and electrolytics. I'm also thinking of adding decoupling capacitors, which it does not have, and implementing a star ground arrangement. I'm not sure what other things might be worthwhile. All the resistors are 5% carbon film so I wonder if putting in 1% metal film might be beneficial in some positions, perhaps in the mic preamp to give better CMRR.
That will be limited by the opamp choice and circuit design (resistor values), typically. But simply swapping opamps has various pitfalls, you have to know the schematic first really...
This type of construction is either polycarbonate (makrolon) for early types, and the blank coversheet is normally green.
Later types were less expensive and used PETP, with colorless blank sheets like these.
Petp caps are less expensive and have lower performance
Later types were less expensive and used PETP, with colorless blank sheets like these.
Petp caps are less expensive and have lower performance
I've tried to find the schematic but it seems unobtainable. I think I'm going to have to trace it out from the board. Once I've got that, it will be clearer if any worthwhile changes can be made, I think.
In terms of noise, it would be nice to reduce hiss but the main problem is mains hum. I'm hoping that this can be reduced by improving decoupling and grounding.
I would imagine that op amp substitutions on the channel strips would yield little advantage.
Elvee, if they are PETP, would there be any meaningful advantage in swapping them for polypropylene?
In terms of noise, it would be nice to reduce hiss but the main problem is mains hum. I'm hoping that this can be reduced by improving decoupling and grounding.
I would imagine that op amp substitutions on the channel strips would yield little advantage.
Elvee, if they are PETP, would there be any meaningful advantage in swapping them for polypropylene?
The Siemens stacked polycarbonates were very common at one point, I have a scattering of values still. If you have any datecodes from the chips on the channel strips that might indicate when the caps were made.
Those stacked caps might very well be polystyrene, in which case don't touch them. Any Mylar should be replaced with polypropylene Polycarbonate is only so-so for dissipation factor. Might gain a fraction of a dB on noise if you replace the carbon film resistors with metal film. Or not. I'd replace the electrolytics if they're old, going up one voltage range, which will usually reduce losses.
I don't think so: their losses are practically irrelevant in such an application, and the linearity isn't important either, because of the low excitation level.
In theory, PP or PS could be better, but in practice, looking at the construction and other components, it will not make the tiniest of difference. Make the safe choice and keep things as they are: less risks, less problems and SOTA quality without issues.
If it ain't broke don't fix it
My vote is also for PET/Polyester/Mylar: not good.
If you really want to be sure, remove one, heat and/or cool it while measuring the variation in capacitance. Most dielectrics have unique temperature coefficients, as show here.
With that being said, I wouldn't touch them either because: 1) In a mixing console, it's a lot of caps to replace 2) Unless it's a very high-end desk such as a Neve, there could be other factors that may mask the differences in the caps, i.e. circuit topology, choice of components, layout, and so on.
In short: not worth the trouble.
If you really want to be sure, remove one, heat and/or cool it while measuring the variation in capacitance. Most dielectrics have unique temperature coefficients, as show here.
With that being said, I wouldn't touch them either because: 1) In a mixing console, it's a lot of caps to replace 2) Unless it's a very high-end desk such as a Neve, there could be other factors that may mask the differences in the caps, i.e. circuit topology, choice of components, layout, and so on.
In short: not worth the trouble.
Thanks for the replies. The consensus seems to be that they're not worth replacing then. In terms of reducing noise/hum and possibly crosstalk, is there any merit to my idea of improving grounding and adding local decoupling, which is currently nonexistent?
I did replace all the electrolytics in the power supply recently which did lead to a noticeable reduction in hum so I wonder if it's worth doing all the electrolytics. The desk is from around 1980.
The pots and faders definitely need doing anyway, they're all beyond cleaning, so while I've got it pulled apart, the electrolytics wouldn't be much more work. I've got a vacuum desoldering station so replacing components is very quick on a single sided board like that.
I did replace all the electrolytics in the power supply recently which did lead to a noticeable reduction in hum so I wonder if it's worth doing all the electrolytics. The desk is from around 1980.
The pots and faders definitely need doing anyway, they're all beyond cleaning, so while I've got it pulled apart, the electrolytics wouldn't be much more work. I've got a vacuum desoldering station so replacing components is very quick on a single sided board like that.
Do it now, or you will be doing it later. There are NO decoupling capacitors on the board?
Can you post a photo of the foil side? Are those AB pots?
Can you post a photo of the foil side? Are those AB pots?
That's what we used in our telecom filters back in the early to mid 80's.
I always thought that they were stacked polyester.
I always thought that they were stacked polyester.
Yes: the clear ones are polyester (TM Hostaphan) and referenced as MKH, and the green ones are polycarbonate (TM Makrolon), referenced MKM
I've now taken some of the channel strips out to investigate further. It's actually only one channel that has those stacked capacitors, the rest are green mylar capacitors. Strange.
I've attached a photo of the board on both sides. There actually is some decoupling now I've looked closer, I didn't spot it before as it's just a single mylar between the rails on each op-amp (I was looking for ceramics and two per chip). There are no decoupling electrolytics where the power enters the board.
I'm going to start a new thread for this over in Instruments and Amps as that seems like the appropriate place for it.
Thanks,
James
I've attached a photo of the board on both sides. There actually is some decoupling now I've looked closer, I didn't spot it before as it's just a single mylar between the rails on each op-amp (I was looking for ceramics and two per chip). There are no decoupling electrolytics where the power enters the board.
I'm going to start a new thread for this over in Instruments and Amps as that seems like the appropriate place for it.
Thanks,
James