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Pan potentiometrs on passive summing box
Old 28th October 2014
  #1
Gear Maniac
 
🎧 10 years
Pan potentiometrs on passive summing box

I want to install Pan potentiometers into my passive summing box. The passive summing box has 16 input channels. It is assembled with 10K resistors.
What nominal Pan potentiometers I should use optimal? I want to use ALPS pots.
Old 29th October 2014
  #2
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Assuming your passive mixer is balanced then you really need quad pots to do a balanced pan pot. For 10K bus resistors then 10K linear pots slugged with 4K7 would give you a reasonable mid point drop. The one problem with this is that the load presented by the pan pot is a little of 1K so your source needs to be able to drive this load.

Cheers

Ian
Old 29th October 2014
  #3
Gear Maniac
 
🎧 10 years
I plan to use vintage Neve 1272 for amp.
Old 29th October 2014
  #4
Lives for gear
 
🎧 15 years
Hi
Ian is referring to the SOURCE capability required not what follows the summing bus.
EVERY channel from DAW (or wherever the signals are from) could be loaded with as little as 1K Ohms in certain conditions and not all gear is 'happy' doing this.
Despite the apparent simplicity and perceived 'sonic advantages' of a 'passive' summing system, in reality there are a lot of compromises that to be accepted unless some very special components and possibly complicated circuit switching is used.
Matt S
Old 29th October 2014
  #5
Lives for gear
 
Geoff_T's Avatar
 
🎧 15 years
Hi

Actually, for a true 3dB down at centre you need 1.8Kohm resistors from wiper to top of the pots. This will present a load of around 1Kohm as Matt suggests, and you need a source that can drive that load.

You don't mention whether you would also use a level control in front of the pan pot as that pot would need to be a low impedance further lowering the impedance your passive mix applies to the source.

Neve monitor matrix panels on early consoles were passive but used an input transformer with 10Kohm input and 600 ohm secondary matching, and drove stepped level controls before driving the pan pot and bus and aux sends.

It worked, albeit not brilliantly, and shortly after they stuck an amplifier after the level control and before the pan pot and bus sends.

If you are making a totally passive mix, minus any transformers or buffer amplifiers, you need to do careful sums, including all the loads like the bus resistors, to see exactly what you are loading your source.

It's not as easy as it sounds once you start adding pots, etc.



PS I re-read the thread and took my ex-Neve hat off because it implied you are balanced mixing so pan pots get much more interesting... I think John's idea with a rotary switch is more practical but personally I would drop the pan idea unless you like making work for yourself!
Old 29th October 2014
  #6
Lives for gear
 
JohnRoberts's Avatar
 
🎧 10 years
If you can live with a little less resolution you could effect a simpler pan switch that gave you full Left, full Right, or mono... If you want a fine pan and level mix control why not use a real mixer?

JR
Old 29th October 2014
  #7
Lives for gear
 
🎧 15 years
Hi
There is a line in a song (whose name escapes me) 'even the simple things are all complicated'.
This is true when trying to achieve things like 'passive summing' and full feature monitoring. Yes you CAN do it in a simple (passive) way but there are many obstacles to 'high quality' such as level changes due to loading and so on.
Matt S
Old 29th October 2014
  #8
Lives for gear
 
Geoff_T's Avatar
 
🎧 15 years
Hi

Using a switch would still require a four pole, three position, rotary switch per channel. That would stump up the price considerably but the pot wiring would be even more complicated and expensive.

I have grounded the unused resistors in the sketch below, as it would be fed from an electronically balanced source (I believe) I guessed this was the best option.

I still think it not worth the bother....


Attached Thumbnails
Pan potentiometrs on passive summing box-balanced-pan.jpg  
Old 1st November 2014 | Show parent
  #9
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Quote:
Originally Posted by Matt Syson ➑️
Hi
There is a line in a song (whose name escapes me) 'even the simple things are all complicated'.
This is true when trying to achieve things like 'passive summing' and full feature monitoring. Yes you CAN do it in a simple (passive) way but there are many obstacles to 'high quality' such as level changes due to loading and so on.
Matt S
The Who, 'Substitute' - the simple things you see are all complicated, I look pretty young but I'm just back dated, yeah.

Cheers

Ian
Old 1st November 2014
  #10
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
@Geoff,

The unused inputs need to be shorted together so they look like a zero impedance balanced source. They should not be connected to ground.

Cheers

Ian
Old 1st November 2014
  #11
Lives for gear
 
🎧 15 years
Hi Ian
Yes the unwanted signals to the bus must be terminated but whether they should 'float' or be taken to ground is debatable. Most of the 'commercial' applications as far as I remember that use this are taken to ground which will help achieve good HF crosstalk figures . I can think of a variety of 'for and against' scenarios and I think overall the 'ground them' wins.
Matt S
Old 1st November 2014 | Show parent
  #12
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Quote:
Originally Posted by Matt Syson ➑️
Hi Ian
Yes the unwanted signals to the bus must be terminated but whether they should 'float' or be taken to ground is debatable. Most of the 'commercial' applications as far as I remember that use this are taken to ground which will help achieve good HF crosstalk figures . I can think of a variety of 'for and against' scenarios and I think overall the 'ground them' wins.
Matt S
I think a lot of this comes from the confusion caused my modern electronically 'balanced' outputs where the two differential outputs are referenced to a common ground. In the good old Neve days, outputs were transformer balanced and floating. They were not referenced to any ground or zero volts. I am not aware of this causing any HF crosstalk problems. Connecting both the hot and the cold to the screen with all its common mode interference currents seems like bad news to me.


Cheers

Ian
Old 3rd November 2014 | Show parent
  #13
Lives for gear
 
Geoff_T's Avatar
 
🎧 15 years
Quote:
Originally Posted by ruffrecords ➑️
I think a lot of this comes from the confusion caused my modern electronically 'balanced' outputs where the two differential outputs are referenced to a common ground. In the good old Neve days, outputs were transformer balanced and floating. They were not referenced to any ground or zero volts. I am not aware of this causing any HF crosstalk problems. Connecting both the hot and the cold to the screen with all its common mode interference currents seems like bad news to me.


Cheers

Ian
Hi

I think it six of one and half-dozen of the t'other... based on the fact that it is a mess of sources and destinations, information for which is only partial.

If it were truly balanced and floating, coming from transformers and going to a transformer mix. I would agree that just shorting the top of the bus resistors together was all that was needed.

Back in the olde days at Neve you always shorted the unused (and unbalanced) contact of a bus feed to the same ground as the sending amplifier... invariably the chunky B- bus... so there was no difference in potential between the selected and deselected positions of the bus switch... and no associated click.

Here we have no clue what's feeding the bus resistors... it might be electronic balance and we don't know what tenuous connection those outputs might have to ground (if any). In an ideal world it would be nice to use the "ground" of the sending amp to terminate to but, as I had no clue whether that was even possible, I terminated them to ground.

Hopefully this might work... if it didn't... snip off the ground connection.

Also, hopefully, this will demonstrate to absolute beginners that there's more to a passive mix than an handful of resistors.

And reinforces my point that he should forgetaboutit!

Old 3rd November 2014
  #14
Lives for gear
 
🎧 15 years
Hi
Other companies took the 'spare engineers' from Neve, gave them a cold shower then made them do it properly!
Matt S
Old 4th November 2014
  #15
Lives for gear
 
🎧 15 years
balanced verses floating

The seasoned veterans posting here might want to explain to the newbies that balanced is never floating; and floating is seldom truly balanced. The common characteristic is differential mode signal. Balanced implies a potential relative to signal common/ground.
Old 4th November 2014
  #16
Lives for gear
 
🎧 15 years
Hi
Good point. Many of us who know this feel a bit reluctant to spell it out for the 'click and you will find', I have a yoootoob video on 'how to do brain surgery' set. Learning is doing, not watching a video about it.
Matt S
Old 4th November 2014 | Show parent
  #17
Lives for gear
 
ruffrecords's Avatar
 
🎧 10 years
Quote:
Originally Posted by cathode ➑️
The seasoned veterans posting here might want to explain to the newbies that balanced is never floating; and floating is seldom truly balanced. The common characteristic is differential mode signal. Balanced implies a potential relative to signal common/ground.

Perhaps they would also like to explain that the screen is not a signal wire. Its function is simply to screen. It is not necessary for the signal to be transmitted from one unit to another.

Cheers

Ian
Old 4th November 2014 | Show parent
  #18
Lives for gear
 
nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by cathode ➑️
The seasoned veterans posting here might want to explain to the newbies that balanced is never floating; and floating is seldom truly balanced. The common characteristic is differential mode signal. Balanced implies a potential relative to signal common/ground.
Sounds like you really don't understand "Floating"
I would say 99.9999% of gear/Consoles ect the signal INSIDE the gear IS ground referenced..As some know...

Your post is not clear or correct...

Most people including me do NOT use GOOD transformers because they are $$$...They do things that can NOT be done with your typical electronic balanced Ins/Outs circuits...
Old 4th November 2014
  #19
Lives for gear
 
🎧 15 years
Hi
Many years ago where I was working there was a suggestion to design a transformerless mic input stage that had good common mode rejection and all the obvious qualities of a good input but also to be able to withstand being 'accidentally' attached to the mains (240 Volts). This was allowed to be 'common mode' and it did not have to 'work' as such under these conditions but when the overload was removed the circuit should then function correctly. After some considerable debate and ideas by some very clever people it was decided that a transformer would be a more practical idea as the just the size of possible input capacitors to withstand 400 Volts peak and still have low impedance at audio frequencies made the whole thing unworkable.
As an exercise yes but not commercially viable.
Matt S
Old 3 days ago
  #20
Gear Head
 
🎧 5 years
Hi,
I am a layman on the subject.
But I am looking to make a small mixer with 10 Audix 35104 modules.
I wanted to add the pan pot, and an auxiliary order.
In the master group, it would use only two output transformers (passive too).
What better solution for that?
pan = quadruple potentiometer?
I saw some routing modules being sold, but they are active, with IC.
I also found the Audix routing module, but they are old, lacking the transformers .. And there is no schematic diagram.
Some help will be appreciated.
Greetings from Brazil.
Old 3 days ago
  #21
Lives for gear
 
🎧 15 years
Hi
Well the 35104 modules use a single 24 volt supply and the internal operating level is -10dBu and originally fed into an auxiliary send/routing module which also had the fader make up amplifier (+10db), pan pot and two post pan amplifiers. ALL outputs after this had to have a proper 'line drive' amplifier to get from -10dbu up to 0dBu so as Audix used transformers wired for 6dB step up this had a line amplifier with 4dB of gain and was capable of feeding 150 Ohms load (600 ohms reflected back through 6dB step up).
There are 2 versions of 35104, one using a 5534 and the earlier version using transistors alone BC413 and BC415 types.
The 35104 by itself will not 'drive' a transformer wired for 6dB step up and you certainly cannot use a 'passive' panpot alone and get anything like a decent line level output. The clipping level is +18dBu and that is into a load of not less than about 2K Ohms.
The requirement was to be able to have +24dB 'headroom through the whole mixer relative to 0dBu hence the -10dBu internal operating level as although some stages could manage +18dBu, others might only manage +14 dBu.
Matt S
Old 3 days ago | Show parent
  #22
Gear Head
 
🎧 5 years
My 35104 comes with the D259 output drive. (I have some BA640 cards. I plan on using them in 04 audix)
I'm using 04 Marinair LO2567, 04 Sowter and 04 Carnhill, output transformers.
They have balanced outputs, with + 6db of gain, being with Marinair / marinair with + 4db or + 10db.
What do you suggest me? just a passive pan pot?
If I wanted a passive auxiliary warrant ... Was it also possible?
Thank you very much.
Sorry for so many questions.
I'm curious, but I don't know much about electronics.
I look for the information, then ask a technician to weld the parts for me.
Old 3 days ago | Show parent
  #23
Gear Head
 
🎧 5 years
veja fotos
Attached Thumbnails
Pan potentiometrs on passive summing box-screenshot_20201123-232416.jpg   Pan potentiometrs on passive summing box-whatsapp-image-2021-03-02-18.43.30.jpg  
Old 3 days ago | Show parent
  #24
Gear Head
 
🎧 5 years
next to that board, there are two or three BC413 and BC415 transistors
Attached Thumbnails
Pan potentiometrs on passive summing box-35104-output-stage-1.jpg   Pan potentiometrs on passive summing box-audix-35104-output.jpg  
Old 3 days ago | Show parent
  #25
Gear Head
 
🎧 5 years
See
Attached Thumbnails
Pan potentiometrs on passive summing box-audix-d259.jpg  
Old 3 days ago
  #26
Lives for gear
 
🎧 15 years
If you had the complete module that the line output stage came from it has 2 'preamplifiers' 9reasonable gain but low drive capability, and 2 of the line output stages as the schematic shows.
the 'quad' module had 2input transformers (intended for passive summing bus inputs but could be wired differently) then 2 'preamplifier circuits and 2 line output circuits. The output transformers (sowter)were installed in the desk chassis not in a module because they are too large,
Matt S
Old 3 days ago | Show parent
  #27
Gear Head
 
🎧 5 years
Quote:
Originally Posted by Matt Syson ➑️
If you had the complete module that the line output stage came from it has 2 'preamplifiers' 9reasonable gain but low drive capability, and 2 of the line output stages as the schematic shows.
the 'quad' module had 2input transformers (intended for passive summing bus inputs but could be wired differently) then 2 'preamplifier circuits and 2 line output circuits. The output transformers (sowter)were installed in the desk chassis not in a module because they are too large,
Matt S
Hi, Matt.
I don't have the "quad module".
The line-out stage I showed you already came on the Audix 35104, when I bought it. I just needed to install a 4700uF / 16v capacitor before the output transformer.
With this configuration, can I use the passive panpot? to make a small mixer.
Thank you for the informations.
Old 2 days ago
  #28
Lives for gear
 
🎧 15 years
Hi
Yes, you can.
I tested many tens of these modules in 1980 and the desks they went into.
The output of the mic/line module should be considered to be -10dBu and you will 'lose' 3dB in a 'usual' panpot and then the amplifier needs to give 4 dB at least and if you are having a 'fader' that might 'lose' more dB depending on how you want the scale to run. Then if you are making a passive mix you will lose a load more which is why in the original desks the 'low power' amplifier stage was used to regain the signal level as the passive buses were run at -35dBu.
Best
Matt S
Old 2 days ago | Show parent
  #29
Gear Head
 
🎧 5 years
Quote:
Originally Posted by Matt Syson ➑️
Hi
Yes, you can.
I tested many tens of these modules in 1980 and the desks they went into.
The output of the mic/line module should be considered to be -10dBu and you will 'lose' 3dB in a 'usual' panpot and then the amplifier needs to give 4 dB at least and if you are having a 'fader' that might 'lose' more dB depending on how you want the scale to run. Then if you are making a passive mix you will lose a load more which is why in the original desks the 'low power' amplifier stage was used to regain the signal level as the passive buses were run at -35dBu.
Best
Matt S
Understand.
Is the -10dBu output considering the module without the output drive and without the output transformer?
What do you think of this output drive D259 + the output transformer?
Have you tested the 35104 with the D259 card?
I also thought about replacing the D259 card with BA640. Maybe it would be better.
Thanks again
health
Old 2 days ago
  #30
Lives for gear
 
🎧 15 years
The BA640 would be a 'Neve imposter'. I cannot remember the schematic of the BA640 whether it is the class B design or class A, which was designed to run with significant DC current through the output transformer primary. The ratio was different too of course. Audix did not run any DC through transformer windings.
The 35104 followed by a line drive output amplifier such as contained on part of the D259 when connected to the Sowter transformer that Audix used with it's 1:2 ratio is a simplified path of what was used on that series of Audix desks.
The Neve Lo???? output transformer was designed with a 1:1.7 ratio and used a class A drive amplifier so although that would work, it may not achieve the originally required +24dBu output int 600 Ohms.
At least 6 of the people I worked with at Audix had previously worked at Neve as the two companies were separated by a few miles distance so exchanges of personnel were quite frequent.
Matt S
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