Re: Balance to Un-Balance Converter

SSDIY · 2013-03-15 2:35 am

Re: Balance to Un-Balance Converter

Hi there,

Attached image is the balance to un-balance converter of my Alesis RA300 power amp.

I would like to know what is the difference of the performance wise if use this converter to convert balance signal to un-balance or just simple solder the pin 3 and pin 1 together inside the XLR cable.

Please advice. Thanks

gmphadte · 2013-03-15 6:14 am

If u have to use a long cable for interconnecting, then balanced is good as it cancels noise picked up by the cable, since it(noise) is common mode. If your connection is short, better use the Ji1. You will find no difference, but do not short 1 and 3 as you will get noise.

Gajanan Phadte

balerit · 2013-03-15 7:16 am

Connecting pin 1 to 3 is standard practice. Balanced lines are really only for low level signals like microphones.

SSDIY · 2013-03-15 8:40 am

gmphadte said:
If u have to use a long cable for interconnecting, then balanced is good as it cancels noise picked up by the cable, since it(noise) is common mode. If your connection is short, better use the Ji1. You will find no difference, but do not short 1 and 3 as you will get noise.

Gajanan Phadte

Hi Gajanan

Thank you for your reply.

I know the pros and cons of balanced connection. Personally I prefer to use balanced connection for my home stereo system because I always think XLR connectors and receptacles are better and stronger built than RCAs and a well made RCA connectors and sockets such as WBT cost a lot of money than a well made XLR connectors and receptacles such as Neutrik.

Recently, I am trying to change my system from RCA to XLR connection. The reason why I ask about the difference between the converter and solder pin 1and pin 3 togeter is because when I connect the signal source to the input of the XLR converter, the sound came out from the speakers are seriously distorted, loudly, foggy and lacking dynamics. However if I solder the pin 1 and pin 3 together and connect the XLR cable direct to the input of the power amp. The sound becomes normal.

Therefore, in this case, I would like to know what is the advantage to design and use a balanced to un-balanced converter if simple soldering pin 1 and pin 3 of a XLR cable together can do a better job.

SSDIY · 2013-03-15 8:43 am

balerit said:
Connecting pin 1 to 3 is standard practice. Balanced lines are really only for low level signals like microphones.

Hi balerit

I use the XLR cables to connect my CD player and power amps for my home stereo system. The outcome is positive and I feel happy with the connection.

balerit · 2013-03-15 11:43 am

SSDIY said:
Hi balerit

I use the XLR cables to connect my CD player and power amps for my home stereo system. The outcome is positive and I feel happy with the connection.

Great

AndrewT · 2013-03-15 12:07 pm

Connect Pin1 to chassis.
Do not connect Pin3 to Chassis.
When using the XLR to connect an unbalanced signal connect Pin3 to Signal Ground NOT to chassis.

Speedskater · 2013-03-16 1:25 am

Maybe I should repeat what Andrew just wrote.

XLR Pin1 is a shield and is only connected to the chassis with a very short wire.
XLR Pin1 is not circuit ground.

gmphadte · 2013-03-19 4:25 am

It should show no difference. Something is not correct.

Gajanan Phadte

SSDIY said:
Hi Gajanan

Thank you for your reply.

... dynamics. However if I solder the pin 1 and pin 3 together and connect the XLR cable direct to the input of the power amp. The sound becomes normal.

Therefore, in this case, I would like to know what is the advantage to design and use a balanced to un-balanced converter if simple soldering pin 1 and pin 3 of a XLR cable together can do a better job.

SSDIY · 2013-03-19 7:56 am

AndrewT said:
Connect Pin1 to chassis.
Do not connect Pin3 to Chassis.
When using the XLR to connect an unbalanced signal connect Pin3 to Signal Ground NOT to chassis.

Hi Andrew

Thank you for advice. Will do accordingly.

SSDIY · 2013-03-19 7:58 am

Speedskater said:
Maybe I should repeat what Andrew just wrote.

XLR Pin1 is a shield and is only connected to the chassis with a very short wire.
XLR Pin1 is not circuit ground.

Hi Kevin

Noted and thanks.

SSDIY · 2013-03-19 8:21 am

gmphadte said:
It should show no difference. Something is not correct.

Gajanan Phadte

Hi Gajnan

Thank you for posting again.
The problem was fixed. It was caused by mis-setting of the gain of the un-balance to balance converter. And I reset it from 20db to 26 db which is the gain of the original design then the problem is no longer exist.

Now, I have another question, hope this is the last one:

The output impedance of my pre-amp which is the New Frontier Balanced pre-amp designed by Mr. Erno Borberly. The pre-amp has an output impedance of 10K. I hooked it up with the crossover which is the Behringer CX3400. CX3400 has an input impedance of 50K (balanced).

Will the impedances between the output of the pre-amp and the input of the crossover cause any matching problem? Please advice.

AndrewT · 2013-03-19 8:57 am

SSDIY said:
................ Balanced pre-amp designed by Mr. Erno Borberly. The pre-amp has an output impedance of 10K. ............

You are making me angry.
There is no way Borbely's design has an output impedance of 10k.

SSDIY · 2013-03-19 10:09 am

AndrewT said:
You are making me angry.
There is no way Borbely's design has an output impedance of 10k.

Hi Andrew

Yes, he did. Below was Borbely descripted about the output impedance of his New Frontier Balanced Pre-amp:

"A much more important question is
whether these circuits can drive the
input impedance of a power amplifier.
The output impedance of the amps ex-
amined is basically equal to the drain resistor
of the amplifier. If RD = 10k, then
the output impedance is also close to
10k. But if the input impedance of the
power amp is also 10k, then you are certainly
in trouble. First, you lose 6dB of
gain by the voltage division between the
10k resistors; second, the 10k input will
most likely load the output and cause a
lot of THD. Even with 20k or 50k input
impedance, you might run into problems.
It is advisable to put an impedance
transformer at the output to avoid this.
Source followers to the rescue!"

Or take a look at the full description of the pre-amp I attached here:

gmphadte · 2013-03-19 10:11 am

Here is a link that explains the intricacies of impedance matching.

http://www.jaycar.com.au/images_uploaded/impmatch.pdf

Gajanan Phadte

gmphadte · 2013-03-19 10:39 am

Your post#14

I have found that a jFET input buffer works the best and raises the input impedance too
and have a Pedja Rogic buffer in my power amp.

Gajanan Phadte

AndrewT · 2013-03-19 12:16 pm

Who is going to tell SSD?
They won't let me tell him.

Michael Chua · 2013-03-19 12:55 pm

SSDIY said:
The output impedance of my pre-amp which is the New Frontier Balanced pre-amp designed by Mr. Erno Borberly. The pre-amp has an output impedance of 10K.

Is your pre-amp Fig 17 in Borbely's notes?

Regards
Mike

SSDIY · 2013-03-19 1:28 pm

Michael Chua said:
Is your pre-amp Fig 17 in Borbely's notes?

Regards
Mike

Hi Mike

Yes, figure 17 is the schematic of the pre-amp.

Michael Chua · 2013-03-19 1:52 pm

The output impedance is not 10K. It is very low (2.3 ohm), no problem driving a power amp with 10K input impedance.

I've attached an excerpt from pg 19. The Jfets, Q5, Q6 and Q7, Q8 are White Cathode Followers (from the days of vacuum tubes). They essentially buffer the outputs of the differential so that you can drive a power amp.

Re: Balance to Un-Balance Converter

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