JW

Passive monitor box. Pot question. De-balancing.
« on: June 25, 2020, 01:34:24 PM »
Please see attached schematic.

Hmmmm. How can I make this story short? Let's see. In an effort to provide volume attenuation between my converters (IZ Radar D>A, IC output. Very low impedance) and my monitor amp (Class D. Presonus S8 Sceptre's 10K input impedance) I rigged up two multideck switches that would ostensibly keep the signal balanced all the way to the amp. Long story short, one of the switches buzzes. They're identical. They're multideck, and bought off ebay . . . Let's just say, I know it is that switch but can't figure out why, and I have ditched this idea for the moment.

I decided to then try one of these Alpha Blue dual 10K pots that I had anyway, and they are supposed to have better matching than the usual dual pot . . .
EVEN though the run from my Radar (machine room) to the speakers/amps is about 40ft and this move would de-balance the run.

Much to my surprise, it's very quiet, I like the feel of the pot, and maybe I want to keep it this way. .

I wonder about what some of my experiments with grounding yielded though.

In my drawing, the dotted line is the negative lead from the Radar outputs. I've experimented with grounding this lead at the pot, and not. It does eliminate some very faint noise to ground it, and it also boosts the signal a bit. It also seems to have more high end than when left floating. So one would assume I think that it would be best to ground the dotted line in my drawing.

I noticed no difference in lifting the shields on either side of the pot, so left them as is, and I also didn't notice any difference when grounding the pin 2 "minus" lead of the Presonus amp.

Then I tried bypassing the pot all together on one channel, keeping it "balanced" and judging against the other channel that was going through the pot, debalanced. Much to my surprise, it's at the same level. What gives? Why not a -6dB due to the unbalancing?

Guess we'd have to take a look at the Presonus' amps input more carefully. But I can't find much. Just the manual. Seems according to the manual though that both TRS and XLR are "balanced" inputs. Presonus  just says to use a DI if not using a balanced run. They REALLY want me to balance this. But de balancing it sounds fine so far so why am I complaining?

Anyway, I've read the Rane documents and look at them all the time.

Just wondering if anyone can shed some light on my situation and look over the drawing.


scott2000

Re: Passive monitor box. Pot question. De-balancing.
« Reply #1 on: June 25, 2020, 01:55:47 PM »
Do you know what type of output the Radar is using? Some DACs  want you to leave pin 3 (or -) floating when feeding something unbalanced ...... There isn't any guessing or experimenting involved in regards to this I don't think....

JW

Re: Passive monitor box. Pot question. De-balancing.
« Reply #2 on: June 25, 2020, 03:52:03 PM »
According to gearslutz heresay, The Nyquists' used  AKM 4393 chip DAC's. https://www.digikey.com/product-detail/en/akm-semiconductor-inc/AK4393VF/974-1012-2-ND/2333361 I don't know how they're implemented though.

scott2000

Re: Passive monitor box. Pot question. De-balancing.
« Reply #3 on: June 25, 2020, 06:42:34 PM »

I remember this article being pretty informative.... I think it's the one with a trick to use to find out what type of output something is if you don't know.... I used it once and it worked well enough ...

https://www.prosoundweb.com/balanced-and-unbalanced-connections/


ruffrecords

Re: Passive monitor box. Pot question. De-balancing.
« Reply #4 on: June 26, 2020, 04:49:04 AM »
In a balanced connection the shield is not a signal carrying conductor. It is there simply to shield the other wires. The signal exists only between the hot and cold connections. All electronically balanced outputs however have outputs that are referenced to analogue 0V which also ends up being connected internally to the shield pin. This leads to all sorts of confusion with people thinking the shiled is a signal carrying conductor - it is not.

Bottom line is the shield should be connected end to end and to nothing else. Your pot should be connected across the hot and cold only.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

scott2000

Re: Passive monitor box. Pot question. De-balancing.
« Reply #5 on: June 26, 2020, 11:06:35 AM »
Guess I was confusing things with feeding an unbalanced destination.... :-[

« Last Edit: June 26, 2020, 11:12:17 AM by scott2000 »

abbey road d enfer

Re: Passive monitor box. Pot question. De-balancing.
« Reply #6 on: June 26, 2020, 01:55:52 PM »
Then I tried bypassing the pot all together on one channel, keeping it "balanced" and judging against the other channel that was going through the pot, debalanced. Much to my surprise, it's at the same level. What gives? Why not a -6dB due to the unbalancing?
Why would you loose 6dB? Floating outputs can be unbalanced without loosing a iota of level.
Now your problem is that you should not connect the shield to anything else than Pins 1.
Borh pins 3 connected together to the pot bottom. Pin 3 of source connected to pot top. Pin 3 of receiver (amp) to pot wiper.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

moamps

Re: Passive monitor box. Pot question. De-balancing.
« Reply #7 on: June 26, 2020, 03:26:40 PM »
Borh pins 3 connected together to the pot bottom. Pin 3 of source connected to pot top. Pin 3 of receiver (amp) to pot wiper.
Both pins 3 connected together to the pot bottom. Pin 2 of source connected to pot top. Pin 2 of receiver (amp) to pot wiper.

JW

Re: Passive monitor box. Pot question. De-balancing.
« Reply #8 on: June 26, 2020, 03:32:42 PM »
Thanks guys. I have it corrected now. When Ian posted, I was like duh. Why do I insist on connecting the shield to the pot? Right now, I have both (pin 3 minuses) on the pot bottom and the (+ input) on the pot input, and the (+ output) on the wiper. The shields just route through to the other side.

I'm pretty sure that's what you meant too Abbey? Typo for the last sentence?

I tried experimenting with either side's pin 3 lifted. But they both need to go to the bottom of the pot.

Interestingly, my sum to mono switch works better now. But that's another story. Thanks everybody. I like how this turned out, and I'm not hearing excessive noise from the unbalanced run. Seems very quiet so far.

abbey road d enfer

Re: Passive monitor box. Pot question. De-balancing.
« Reply #9 on: June 26, 2020, 04:44:38 PM »
Yes, typo. Not enough blood in my sugar.  :o
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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