The No.1 Website for Pro Audio
AES paper on capacitors for audio
Old 18th September 2020 | Show parent
  #31
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Quote:
Originally Posted by kludgeaudio ➡️
If it is, use a DC blocking cap that can handle the negative value, like a film cap or a bipolar electrolytic bypassed with a film cap if the value needed is too large to find a film cap off the shelf.
--scott
Thanks Scott. I am looking at avoiding/removing the bipolars where I can though. Fine with polarised El. Caps as an option.
Old 18th September 2020 | Show parent
  #32
Lives for gear
 
kludgeaudio's Avatar
 
Quote:
Originally Posted by YashN ➡️
Thanks Scott. I am looking at avoiding/removing the bipolars where I can though. Fine with polarised El. Caps as an option.
If you can't change the circuit design to eliminate the bipolar cap, you just have to live with it. But, bypassing it with a film cap of maybe 1/100th the value will make a huge difference in measured distortion in that kind of situation. Adding leak resistors to create a constant offset might be possible, but might not be.
--scott
Old 18th September 2020 | Show parent
  #33
Gear Guru
Quote:
Originally Posted by YashN ➡️
This is mine. Still don't know whether it counts as a 200 Delta (upper section Mixing module) or something like that or a Delta (rightmost end of hand-rest) 8...
I suppose I should check the internals of the Mixing module?
C5 and C105 need to be removed and reversed. Use a 220 or 470 uf/25V.
Old 18th September 2020 | Show parent
  #34
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Quote:
Originally Posted by Jim Williams ➡️
C5 and C105 need to be removed and reversed. Use a 220 or 470 uf/25V.
Thanks Jim, got it.

So after some more digging, turns out it's a Soundcraft 200 Delta I have.

Just checking Jim, this one already has the Mic pre-amps properly optimised, or there's room for improvement by rewiring here?
Old 19th September 2020
  #35
Gear Guru
Those parts are for the stereo mix sum stage outputs. They got it right in the inputs and groups.
Old 19th September 2020 | Show parent
  #36
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Quote:
Originally Posted by Jim Williams ➡️
Those parts are for the stereo mix sum stage outputs. They got it right in the inputs and groups.
Yep, I gathered for the caps info - had to use the Delta DLX schematics to reference them.

Awesome then, planning to do the cap modification for the Master Mix, and mic pres can stay the same.

Lovely.

Thanks Jim, and enjoy the week-end!
Old 20th September 2020
  #37
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Got the Master Module out and disassembled. Some work for tomorrow planned on it.

Is Grounding on the Delta 200 OK?

Last edited by YashN; 20th September 2020 at 02:01 AM..
Old 20th September 2020 | Show parent
  #38
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Quote:
Originally Posted by Jim Williams ➡️
Those parts are for the stereo mix sum stage outputs.
Job done last night before bedtime. Installed 470uF/25V reverse orientation. Went pretty well, except I had disassembled this PCB from the frame but this was unnecessary.

I notice that IC1 & IC2 relevant in this section in mine are TL072 instead of 5532 as in the Delta DLX schematics.

Is that OK or should I be worried?

Looks like all ICs on both PCBs have sockets - nice.

There's something very refreshing working on such a beautifully made modular system: dislodge module, unplug, release PCB, work, re-affix PCB, plug, test, re-mount modules. It all seems so clean and easy.

It was also refreshing to see TL072s and 5532s compared to the instrument sig paths which are bothering me these days and where I see BP caps and 4558s everywhere...

I'm not at the point of op amp rolling on the mixer yet, but I might do it one day, esp. for the Master section. Currently, I am looking at both cap and op amp rolling for the instrument sig paths though.
Attached Thumbnails
AES paper on capacitors for audio-mastersummingcaps.jpg  

Last edited by YashN; 20th September 2020 at 05:53 PM..
Old 20th September 2020 | Show parent
  #39
Here for the gear
 
🎧 5 years
Easiest way to start evaluating that is to see if the input pin one goes directly to chassis ground.

Quote:
Originally Posted by YashN ➡️
Got the Master Module out and disassembled. Some work for tomorrow planned on it.

Is Grounding on the Delta 200 OK?
Old 20th September 2020 | Show parent
  #40
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Quote:
Originally Posted by Riley Casey ➡️
Easiest way to start evaluating that is to see if the input pin one goes directly to chassis ground.
Reminds me I could test the XLR for the Pin 1 problem. Don't expect there to be an issue, but you never know.
Old 20th September 2020
  #41
Gear Guru
Delta console opamp mods require circuit changes. The 200 version also has a - 6 db level in the stereo sum stage. Then the fader jacks it up + 6 db and the balanced outs another +6 db. Therefore the stereo insert output levels are at - 12 dbu, too low for outboard insertion and way too much post sum make up gain.

The feedback resistor is 3.9k, I change that to 8.25k. Then the inverting input to ground gain shunt resistor in the fader opamp is snipped out. That creates a unity gain buffer. Then the sum stage is at unity gain, the fader at unity gain and the outputs at their usual +6 db. Then the internal signal level is at -2 dbu, not -12 dbu.

For opamp replacement, a score of other changes are necessary.

Less noise, more signal, no change in max levels. Chassis ground is isolated via a 10 ohm resistor to avoid any looping.
Old 20th September 2020 | Show parent
  #42
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Quote:
Originally Posted by Jim Williams ➡️
Delta console opamp mods require circuit changes.
Thanks for all the tips, Jim. Definitely will prepare the terrain for stability if I op amp roll one day. As I have the PCBs out, might as well do that fb resistor change too.

Quote:
Then the inverting input to ground gain shunt resistor in the fader opamp is snipped out.
That would be [shorting Edit- Nope!] out R13, R113?

What are your thoughts on the TL072s near the caps I just replaced in in the hybrid sections while the Delta DLX shows 5532 there?

I suppose I can leave this as is?

I am wondering if the Delta 200 and the Delta DLX really have the exact same components.

Last edited by YashN; 22nd September 2020 at 04:40 PM..
Old 21st September 2020
  #43
Gear Guru
Delta 8 has the correct parts. It uses the 8.2k feedback resistor and the fader opamp is a voltage follower.
Old 21st September 2020 | Show parent
  #44
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Quote:
Originally Posted by Jim Williams ➡️
Delta 8 has the correct parts. It uses the 8.2k feedback resistor and the fader opamp is a voltage follower.
But the Sum stages aren't as optimised as the mic pre so that could be something to implement, right?

Saw some nearly unreadable schematics for the Delta 8 here.

Indeed, levels have been fixed.

Looks like NE5532 here as well for the Sum stages so I can only deduce that:

Soundcraft Delta 200 < Delta DLX < Delta 8.

This, or else the previous owner might have swapped op amps, a TL072 for an NE5532. Both are on my boards, but only TL072 in the L/R Sum stages though.

Haven't been able to find Delta 200-specific schematics.

Thanks again, Jim.
Old 26th September 2020 | Show parent
  #45
Gear Addict
 
YashN's Avatar
 
🎧 5 years
Quote:
Originally Posted by Jim Williams ➡️
Delta 8 has the correct parts. It uses the 8.2k feedback resistor and the fader opamp is a voltage follower.
Solid results for the mods including this one. Now my setup is usable.

Thanks Jim.
Old 29th March 2021 | Show parent
  #46
Here for the gear
Hi

may i ask something here ?

about the resistor to be "snipped out", is this remove them or replace by a wire ?

Benoit
Old 1st April 2021
  #47
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
I think people are forgetting some basic physics here. The total voltage across the coupling cap is not the sum of the dc bias and the signal. It is always just the dc bias. The signal waveform is the same on both side of the cap except for the dc bias. Hence the ac voltage across the cap is zero unless the frequency is low enough for its reactance to be a factor (which would be a poor design choice). You can swing the input as high as you like positive or negative, the ac voltage across the cap will be near zero.

Cheers

Ian
Old 1st April 2021 | Show parent
  #48
Gear Guru
 
tINY's Avatar
 
1 Review written
🎧 15 years
Quote:
Originally Posted by ruffrecords ➡️
I think people are forgetting some basic physics here. The total voltage across the coupling cap is not the sum of the dc bias and the signal. It is always just the dc bias. The signal waveform is the same on both side of the cap except for the dc bias. Hence the ac voltage across the cap is zero unless the frequency is low enough for its reactance to be a factor (which would be a poor design choice). You can swing the input as high as you like positive or negative, the ac voltage across the cap will be near zero.

Cheers

Ian

Well, physics doesn't typically separate steady-state from transient. If you do a time-based analysis, you'll find that the instantaneous voltage across the cap will be the "DC Bias" plus the instantaneous voltage from the signal.....



-tINY

Old 1st April 2021
  #49
Gear Guru
In a Wima film cap the AC rating is about 2/3 the DC rating. About 40 volts AC across a 63 volt DC rated cap.
Old 1st April 2021 | Show parent
  #50
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Quote:
Originally Posted by tINY ➡️

Well, physics doesn't typically separate steady-state from transient. If you do a time-based analysis, you'll find that the instantaneous voltage across the cap will be the "DC Bias" plus the instantaneous voltage from the signal.....



-tINY

Indeed it does not, but if you do a time based analysis you will find the voltage cross the capacitor varies very little. I am happy to provide a spice sim to illustrate. Basic physics tell us the voltage across a capacitor cannot change instantaneously. So when you raise the voltage on one plate, the other plate rises at the same time. It really is basic physics and it is how capacitors couple ac signals.

Cheers

Ian
Old 2nd April 2021 | Show parent
  #51
Gear Guru
 
tINY's Avatar
 
1 Review written
🎧 15 years
Quote:
Originally Posted by ruffrecords ➡️
Indeed it does not, but if you do a time based analysis you will find the voltage cross the capacitor varies very little. I am happy to provide a spice sim to illustrate. Basic physics tell us the voltage across a capacitor cannot change instantaneously. So when you raise the voltage on one plate, the other plate rises at the same time. It really is basic physics and it is how capacitors couple ac signals.

Cheers

Ian

Ah, yes. impedance... So, the signal voltage is lessened and the signal current passes through.

Same issue with inductors in a switch-mode regulator.... except current and voltage are swapped.



-tINY

Old 2nd April 2021 | Show parent
  #52
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Quote:
Originally Posted by tINY ➡️

Ah, yes. impedance... So, the signal voltage is lessened and the signal current passes through.

Same issue with inductors in a switch-mode regulator.... except current and voltage are swapped.



-tINY

Exactly. The whole point of a coupling capacitor is to transfer as much of the output voltage as possible to the next stage which means you want the impedance of the cap to be as small as possible compared to the load impedance. By definition, this means the ac voltage across the cap is very small (except in poor designs). In Doug Self's excellent book on small signal audio design he goes into this in considerable detail. I think it should be required reading for all audio DIYers.

In an equaliser it is a whole different matter. Capacitors are used as frequency dependent impedances in pot dividers or LC resonant cicuits. In this case significant signal voltage will exist across the capacitor so the choice of dielectric is much more important.

Cheers

IAn
Old 2nd April 2021 | Show parent
  #53
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Quote:
Originally Posted by Jim Williams ➡️
In a Wima film cap the AC rating is about 2/3 the DC rating. About 40 volts AC across a 63 volt DC rated cap.
This applies to any capacitor. Again it is basic physics. What matters is the largest value of voltage across the plates of the capacitor. The rms value of a sine wave is about 70% of its peak value and it is the peak that matters.

Cheers

Ian
Old 2nd April 2021 | Show parent
  #54
Lives for gear
 
JohnRoberts's Avatar
 
🎧 10 years
Be careful about making broad sweeping generalities about "all" capacitors.

For the specific application of DC coupling capacitors the two capacitor terminals will generally follow each other up and down within their target frequency passband. Very low frequency signal can increase/decrease the terminal to terminal voltage.

Is that TMI yet?

JR
Old 3rd April 2021 | Show parent
  #55
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Quote:
Originally Posted by JohnRoberts ➡️
Is that TMI yet?

JR
TMI????

Cheers

Ian
Old 3rd April 2021 | Show parent
  #56
Lives for gear
 
JohnRoberts's Avatar
 
🎧 10 years
Quote:
Originally Posted by ruffrecords ➡️
TMI????

Cheers

Ian
TMI= Too much information...

In an audio DC blocking application the terminal voltage is relatively constant, but in filter circuits where one terminal is grounded the terminal to terminal voltage will clearly change with applied signal.

JR
Old 3rd April 2021 | Show parent
  #57
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Quote:
Originally Posted by JohnRoberts ➡️
TMI= Too much information...

In an audio DC blocking application the terminal voltage is relatively constant, but in filter circuits where one terminal is grounded the terminal to terminal voltage will clearly change with applied signal.

JR
Which is what I said in post #52

Cheers

Ian
Old 6th April 2021
  #58
Gear Guru
 
tINY's Avatar
 
1 Review written
🎧 15 years

Funny - I just was contemplating how to add an antenna for two-way radio to a classic Benz I have.... It has a window mount antenna block from an old cell phone - with no whip.

Turns out, a patch of window glass can be a dielectric - and end-fed dipoles present a high impedance. Same principal as a coupling cap in a tube amp....



-tINY

Old 7th April 2021 | Show parent
  #59
Lives for gear
 
JohnRoberts's Avatar
 
🎧 10 years
Quote:
Originally Posted by tINY ➡️

Funny - I just was contemplating how to add an antenna for two-way radio to a classic Benz I have.... It has a window mount antenna block from an old cell phone - with no whip.

Turns out, a patch of window glass can be a dielectric - and end-fed dipoles present a high impedance. Same principal as a coupling cap in a tube amp....



-tINY

And they said we would never use that book learning in real life. :-)

JR
Old 7th April 2021 | Show parent
  #60
Gear Guru
 
tINY's Avatar
 
1 Review written
🎧 15 years
Quote:
Originally Posted by JohnRoberts ➡️
And they said we would never use that book learning in real life. :-)

JR
Well, I don't really want to run the math or draw a Smith chart....
📝 Reply
Topic:
Post Reply

Welcome to the Gearspace Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…

Forum Jump
Forum Jump