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      10-06-2012, 03:56 AM   #1
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Question Balanced inputs into 'normal' amplifier?

Anyone help with this? I'm tying myself in knots

With the base HU recoded to HiFi, the outputs are balanced, low level. However, very few amps claim to accept balanced signals, and the ones that do are relatively pricey.

So, assuming the coding is done:

1. What will happen if I just fit RCA plugs onto the end of the speaker wires and connect them to A.N.Other amp?
2. What would happen if I get something like the Autoleads PC1-601 Line Output Convertor which grounds the signal and connect that?

or

3. Do I need to suck up the cost and either buy the expensive amp, or buy a DSP and forget the HiFi coding?

Sigh.
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      10-06-2012, 05:03 AM   #2
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For my own, and anyone else's info, I found this article:

Quote:
This article explains the difference between balanced and unbalanced audio, when it is best to use which, and how to go about connecting a balanced output to an unbalanced input and vice versa.


Unbalanced Audio

Most domestic audio equipment has unbalanced audio inputs and outputs. This means that the audio output (left, right, or mono) appears on a single wire, and is referenced to "0V" or "Ground". Typical connectors used are RCA "phono" connectors, DIN plugs/sockets, and 0.25" (6.3mm) or 3.5mm jack plugs/sockets.
Unbalanced audio is fine for the domestic environment, and for line-level signals in a typical broadcast studio. Problems start to occur if the signals are being carried over long distances, especially if the source and destination have separate mains supplies.


Balanced Audio
A lot of professional equipment will have balanced audio inputs and outputs, usually on 3-pin "XLR" connectors. A balanced audio signal consists of a pair of wires carrying the audio signal in anti-phase with each other. Relative to 0V, if one wire carries a positive voltage, the other carries an equal and opposite negative voltage.
The 3 wires used in a typical XLR lead are often referred to as Ground, Live and Return, or Ground, Hot and Cold. "Live" and "Return" carry the "in-phase" and "out-of-phase" versions of the audio respectively. Calling the signals "Live" and "Return" makes it nice and easy to remember which goes on which pin of the XLR plug/socket:

X = Ground
L = Live
R = Return
The advantage of balanced audio over unbalanced audio is it's ability to reject external interference added as the signal is carried over the wire. The receiving equipment takes the voltage difference between the two wires as the input signal. Interference will usually get added to both wires equally, and so gets ignored by the receiving equipment.
Interconnections
Often, it is necessary to connect a balanced output to an unbalanced input, or vice-versa. The 100% correct and official way to do this is via a transformer or an electronic converter made from an op-amp. There are also some reasonably-priced ICs especially designed for the task - check out the SSM2141/2/3 from Analog Devices for example.
Assuming you are within the relatively benign surroundings of somewhere such as a radio studio however, there are simpler ways to connect balanced and unbalanced inputs and outputs. All result in unbalanced signals on the wires, so don't do this if you fear interference!

To connect an unbalanced output to a balanced input, simply connect the unbalanced signal to the "Live" side of the balanced input, and connect the Ground side of the output to both the "Return" and "Ground" of the input. Some unbalanced outputs assume they will be connected to a high-impedance input, so if your input is switchable between high-impedance and 600 Ohm, make sure it is set to high-impedance. If it is low-impedance only, you may be out of luck! If you're desparate to get a signal, try using the headphone output to feed the equipment - just make sure you turn the levels down to start with, and turn them up slowly until you get a reasonable level. The sound quality may not be brilliant, but you will get half-decent sound - better than trying to cope with the very low input level caused by feeding a high-impedance output into a low impedance input!

A word of warning. XLR inputs on mixers are also used for Microphone inputs. These assume an input level of somewhere in the region of -60 to -40dB. Feeding them with a 0dB input level is not recommended. Make sure that you use only line-level inputs, or that the input has been switched into line-level mode. If you only have a mic-level input, you can make do by using a resistive divider to reduce the input level. An attenuation of 60dB is a factor of 1000, so put a 10k resistor and a 10 ohm (or 100k and 100 ohm) resistor in series between the output and ground. Now connect the live and return pins of the input across the 10 ohm resistor.

To connect a balanced output to an unbalanced input, there are a couple of choices.In both cases, the "Live" side of the output is connected to the signal input.The other connection depends on whether the output is transformer isolated (in which case the "Return" side is connected to the input ground) or electronically balanced using ICs (in which case the Ground pin of the output may be connected to the input ground instead). The latter will result in a 6dB (i.e. factor of 2) loss of amplitude, and perhaps reduced signal-to-noise ratio.

Why have we got two possibilities? If you try to get a signal between a transformer balanced output and ground you will get nothing - the signal is not referenced to ground at all. On the other hand, if you connect the "Return" output of an electronically-balanced output to the input ground, you will be shorting that output to ground, and the chip may not like it. From an audio fidelity point-of-view, it is obviously better to use the "Return" output rather than the "Ground", so how do you know when it is safe to do so? If you're being professional, you could open-up the equipment, find-out which IC is being used and then go and read the datasheet. The more practical solution is to "suck it and see" - try it out and see if the audio sounds distorted or looks distorted on an oscilloscope - you're most unlikely to cause permanent damage to the chip as it will have built-in short-circuit protection.

If you regularly need to connect balanced outputs to unbalanced inputs, you may like to make up a lead with a switch in circuit to select whether the return or ground connection on the balanced output is connected to ground on the unbalanced input.


Nigel Dallard, Chief Engineer, Winchester Hospital Radio
9 October 1999
Now, obviously, car audio does not use 3-pin connectors, so the balanced outputs from the HiFi HU must be a +ve and -ve pair, rather than a +ve and 0V that you'd get from the base system.

I understand a lot of what that article says, and it looks like it's going to be a case of trial & error to get it right. Luckily I have an oscilloscope so it will be relatively scientific.

1. Fit RCA plugs to the speaker wires, and firstly see what the output is like without any modification of the signal. I don't expect that to work, because the amp will expect a 0V signal the the RCA sleeve, not an inverted copy of the +ve signal.

2. The article differentiates between tying either the -ve signal to input ground, or connecting the input ground to output ground. In car audio, everything is grounded to the chassis anyway so I'm hoping that it won't matter but I'll try it and see.
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Last edited by parapaul; 10-06-2012 at 05:31 AM.
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      10-06-2012, 07:35 AM   #3
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See my response in bold.

Quote:
Originally Posted by parapaul View Post

1. What will happen if I just fit RCA plugs onto the end of the speaker wires and connect them to A.N.Other amp?

You will get plenty of noise from the system output and on higher volumes the sound will be distorted.


2. What would happen if I get something like the Autoleads PC1-601 Line Output Convertor which grounds the signal and connect that?

Same response as for number 1
or

3. Do I need to suck up the cost and either buy the expensive amp, or buy a DSP and forget the HiFi coding?

DSP: waste of money in my opinion.
Hi-Fi coding: best bet for your money if you don't want DSP and want to start with clean base HU.

You do not need expensive amp (which accepts differential input). You would require something (LOC) which can convert differential signals into normal signals ---> Normal amp.

Wait for Mr. Singh to chime in and he may help you better TBH to find LOC which can convert differential balance signals to normal signals.

Sigh.
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      10-06-2012, 02:07 PM   #4
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makkan00, i take your point and agree that re-coding would be better than DSP, but a re-code cost a fortune by a dealer (and a lot still get i wrong) and trying to find an independent is near impossible whilst purchasing a DSP off ebay is easier on the wallet and arrives in the post.
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      10-06-2012, 03:18 PM   #5
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Quote:
Originally Posted by theg00se View Post
makkan00, i take your point and agree that re-coding would be better than DSP, but a re-code cost a fortune by a dealer (and a lot still get i wrong) and trying to find an independent is near impossible whilst purchasing a DSP off ebay is easier on the wallet and arrives in the post.

See coding sticky thread in the main UK thread and see who is closer to you.
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      10-06-2012, 03:26 PM   #6
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B.W I have used VEN4 LOC to convert differential balance input to normal paul.

I have recently sold it to forum fellow member.
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      10-06-2012, 05:21 PM   #7
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There are plenty of benefits of getting a DSP, de eq'ing is just one of them.

Coding is a good option though. Coding and a DSP is even better
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      10-07-2012, 03:40 AM   #8
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Makkan00, what a great sticky on coding, I had know idea there is that many member in the UK that can code.
I think I will be in the same position as Parapaul (post originator). Do you think adding a DSP (jl cleansweep) to a coded system will bring further benefits as mob17 suggest.
Mob17: have you added DSP to a coded system? If so can you identify the benefits because I have the DSP but I'm now think of coding as well.

I know a harness will simplify the fitting but will the harness need to be different if I code to hifi or leave as base and add a DSP. And how much do harnesses typically cost.
I have thought about making a harness but cannot find any wiring diagrams for a BMW 335D E90 2007, does anyone have these details

Sorry for the long post.
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      10-07-2012, 04:27 AM   #9
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What DSP do you have?
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      10-07-2012, 07:08 AM   #10
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its a JL Cleansweep.
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      10-07-2012, 07:21 AM   #11
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Quote:
Originally Posted by theg00se View Post
its a JL Cleansweep.
I read that earlier but am after exact model number.
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      10-07-2012, 07:27 AM   #12
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Sorry, Jl audio Cleansweep CL441DSP
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      10-07-2012, 01:52 PM   #13
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Quote:
Originally Posted by theg00se View Post
makkan00, i take your point and agree that re-coding would be better than DSP, but a re-code cost a fortune by a dealer (and a lot still get i wrong) and trying to find an independent is near impossible whilst purchasing a DSP off ebay is easier on the wallet and arrives in the post.
I've been quoted 100 for coding by an independent.

A Cleansweep or BitOne or MS8 are like hen's teeth on ebay, and to buy new they're upwards of 300.
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      10-07-2012, 02:56 PM   #14
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Quote:
Originally Posted by theg00se View Post
Sorry, Jl audio Cleansweep CL441DSP
That should do the job. All the best.
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      10-07-2012, 03:02 PM   #15
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Quote:
Originally Posted by parapaul View Post
I've been quoted 100 for coding by an independent.

A Cleansweep or BitOne or MS8 are like hen's teeth on ebay, and to buy new they're upwards of 300.
I'm surprised that you have not contacted coders in your region / near your area.
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      10-07-2012, 04:05 PM   #16
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None in my area, unless the thread's been updated in the last week or so.

The closest one is the Birmingham independent listed, and that was his quote.
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      10-07-2012, 04:40 PM   #17
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Quote:
Originally Posted by parapaul View Post
None in my area, unless the thread's been updated in the last week or so.

The closest one is the Birmingham independent listed, and that was his quote.
If you get one more person in your area for hi-fi coding, I can pass by your area on my return from Manchester trip.
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      10-07-2012, 04:54 PM   #18
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What is the input impedance of the power amp?

The cost of a balancing transformer (two required for stereo), is less than 10 each.

If high z input is available, it's a cheap solution.... if you can solder some wires to RCA's one side and what ever is required the other.

http://cpc.farnell.com/oep-oxford-el...2-2/dp/TF01454
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      10-08-2012, 12:33 AM   #19
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BigBanana, I'm listening... How would I connect the transformers?
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      10-08-2012, 04:42 AM   #20
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I remember fitting convertors for this 20 years ago whenh using a factory Ford Head unit (balance outputs) and connecting it to unbalanced input amps.

Something like this (2 needed): http://www.studiospares.com/di-boxes...FYXJtAodsigA0g
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      10-08-2012, 01:25 PM   #21
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Interestingly, I had a reply to a thread I started on Talk Audio. Someone suggested that the term 'balanced' on this situation doesn't actually mean balanced in the true audio sense, rather that it's just a flat EQ.

Going to do some testing with a scope and see what happens.
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      10-08-2012, 03:44 PM   #22
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Yes, Balanced in these terms has nothing to do with audio or EQ, its a term to describe the signalling layout.

Using a balanced or earth free signal for audio in a car (or any electrically noisy environment) is going to give better result as the chassis/ground is full of horrible electrical noise and is not going to improve matters if it forms half the audio circuit.
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