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Old 28th October 2013, 10:41 AM   #11
Corpius is offline Corpius  Netherlands
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Yes, but I can not simply connect to ground to the negative input, right? With the buffer in between the buffer's negative output does not see ground or am I missing something here??
The negative output need to connect to ground, by means of a a multi-pole input selector or relay, while leaving the negative input open. But how does this effect the buffer if the output is shorted for a long time?
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Old 28th October 2013, 11:35 AM   #12
Corpius is offline Corpius  Netherlands
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Quote:
Originally Posted by tinitus View Post
hmm, not sure, maybe

I meant that a multipole input selector might do double function and simultaniously switch to SE convertion when selecting to those sources

but yeah, maybe a simple relay is easier

on second thought, maybe it would wise to cut ground input as well as signal input for all sources, so that only the active input is grounded
(might take care of possible chassis/ground loop issues)
I was typing a reply while you where posting, so ...

All input signals not used will be cut indeed, but I'm not sure if cutting their grounds is needed. It would make the input switching much more complex. Perhaps is connecting the negative output to ground the best solution. No op-amps/line drivers would be needed keeping the amount of parts in the signal path to a minimum.

What would happen if I connect the negative input to ground? Or would it be best to leave it open?
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Old 28th October 2013, 12:58 PM   #13
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Old 28th October 2013, 07:37 PM   #14
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The drawing in post #6 is far from a balanced circuit. A balanced circuit (input or output) needs to be symmetrical. All the circuit caps & resistors need to be matched to 1%. Not individual pots.

Also on a XLR connector the pin #1 is only connected to the chassis near the connector, it is not part of the circuit common or ground.
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Old 28th October 2013, 09:34 PM   #15
Corpius is offline Corpius  Netherlands
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pin #1 error solved.

Quote:
Originally Posted by Speedskater View Post
The drawing in post #6 is far from a balanced circuit. A balanced circuit (input or output) needs to be symmetrical. All the circuit caps & resistors need to be matched to 1%. Not individual pots..
There are no capacitors in the circuit path. The resistors are quite easy to match, but what do you suggest to attenuate the signal without using a pot? A logarithmic attenuator with resistors matched to 1% or even closer by using resistors from f.i. the RC55 series (0.1%) from Welwyn?
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Old 28th October 2013, 09:59 PM   #16
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Speedskater View Post
Also on a XLR connector the pin #1 is only connected to the chassis near the connector, it is not part of the circuit common or ground.
really ? I thought pin-1 was signal ground in a true balanced system ?

and chassis/earth would be a 'partly isolated system'
(you will find info on how to do that in Pass F5 and F5Turbo threads)

but I find it strange that there is so little solid info to find in general
or that the available info is so 'contradicting'
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Old 28th October 2013, 10:17 PM   #17
tinitus is offline tinitus  Europe
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Connecting unbalanced outputs (RCA or 1/4" Mono Jack) to balanced (XLR or 1/4" TRS)? - Powered by Kayako Help Desk Software

only problem using the cable itself to create the convertion ... the cable needs to be right

google search key ... RCA to XLR (and go to pictures in google menu)
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Old 28th October 2013, 10:29 PM   #18
tinitus is offline tinitus  Europe
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hmm, maybe leave out any RCA chassis connectors, and use only XLR on preamp input

use the cable to do the 'convertion'

proper input selector should be able to take care of the rest
(I would consider switch ground as well)
I guess a simple 3P4T/3pole-4way would do
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Old 28th October 2013, 10:39 PM   #19
sreten is offline sreten  United Kingdom
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Hi,

There are schemes commonly used in studios to take advantage
of a balanced input when connected to single ended outputs.

Presuming hot is driven by the SE output, the cold input though
carrying no signal level, is used to cancel any common mode
signal equally induced on both the hot and cold in the cable.

Covered by Douglas Self in his books, presumably also others.

rgds, sreten.
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Old 28th October 2013, 11:01 PM   #20
pooge is offline pooge  United States
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Quote:
Originally Posted by tinitus View Post
really ? I thought pin-1 was signal ground in a true balanced system ?

and chassis/earth would be a 'partly isolated system'
(you will find info on how to do that in Pass F5 and F5Turbo threads)

but I find it strange that there is so little solid info to find in general
or that the available info is so 'contradicting'
There is no "signal ground" in a balanced system. Each signal line has the same impedance to ground in a balanced system. The shield may be grounded, but it is not a signal carrying conductor.

http://jensentransformers.com/an/an003.pdf


http://jensentransformers.com/an/generic%20seminar.pdf

Last edited by pooge; 28th October 2013 at 11:06 PM.
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