balanced to unbalanced converstion

hey, whay do you folks think is the best, truest way for me to go from the balanced output of my preamps to the unbalanced input of my recorder. i was thinking a 1:1 transformer might work well. how does quality factor in for this use? i'd build a small box with xlr and 1/4" connectors.

thanks for any information.

david

You can take the output from the XLR pin 2. If the output is floating, pin 3 must be grounded. If the pin 3 signal is made simply by an inverting op-amp stage, do not ground it. You may require an attennuator. That depends on output level of the balanced output and maximum input level of the unbalanced input.

If the cable run is very long, transformer could be a good idea.

the preamps are ua 1108. they have transformer output, so i dont think an op amp is involved. 50 db of gain out. going into the input of my tascam 424 4 track. i've been using my compressor with unbalanced outs (on bypass) for the conversion. the comp isn't true bypass. thought i'd simplify a bit.

http://www.rane.com/note110.html

will give you all the answers regarding your  question and more.

best

aryl said:

they have transformer output

Click to expand...

Alternative 1:
Connect XLR pin 2 to plug tip. Tie XLR pins 1 and 3 together and connect to plug sleeve.

Alternative 2:
Connect XLR pin 2 to plug tip. Connect XLR pin 3 to plug sleeve. This can be better alternative if you have problems with ground potentials.

aryl said:

50 db of gain out.

Click to expand...

No attennuator required. Just reduce gain.

I council you to use a op amp sbalancer, one 5534 or one OPA604 is good.

dont forget THAT 1200

Agreed, the THAT 1200 is an excellent chip

this a sbalancer using the Burr Brown opa604 op amp , if it's powered with + - 24V it can accept 24 dbu input and give 24 dbu on its output on 10K load.

with diodes protections

thanks. i appericiate the response. thats very interesting.

david

Hi Pier,

out of interest; its good point to use 0.1% tolerance resistors on the input,
but, what would you recommend for the caps on the input ?
any specific cap ?

thank you
kam

aryl said:

the preamps are ua 1108. they have transformer output, so i dont think an op amp is involved. 50 db of gain out. going into the input of my tascam 424 4 track. i've been using my compressor with unbalanced outs (on bypass) for the conversion. the comp isn't true bypass. thought i'd simplify a bit.

Click to expand...

Using a compressor with decent receiver and driver stages is not a bad way to de-balance and attenuate. Sometimes I use comps in bypass for gain staging like that.

Anyway, with xfrmr outputs on the pres, there's no need to add another xfrmr or a chip. Just read the Rane note that syn linked. Ground the low side of your preamps output xfrmr by connecting pin 3 to the shield of your TS plugs. Done. Yes, you sacrifice the benefit of balanced output, thus no rejection of anything picked up by the interconnecting cable. So what? Keep your cable runs short and don't live near a radio transmitter tower. 

If you want a passive attenuator there lots of good solutions posted on this forum. The 600 T-pad attenuators sold by Hairball Audio and classicapi.com are good (see The White Market), but a bit expensive. A 1k pot wired as rheostat or a voltage divider is acceptable. Good discussion of the drawbacks here: http://www.groupdiy.com/index.php?topic=2229.msg158702#msg158702

And here: http://www.groupdiy.com/index.php?topic=5779.msg71574#msg71574

kambo said:

Hi Pier,

out of interest; its good point to use 0.1% tolerance resistors on the input,
but, what would you recommend for the caps on the input ?
any specific cap ?

thank you
kam

Click to expand...

You don't have to buy 0.1% resistors (or capacitors for that matter)! What you do is take a bag of resistors and measure them with your Ohm meter.  Select a pair with the same value.  The exact value is not very important, what is important is balance and symmetry.

Speedskater said:

kambo said:

Hi Pier,

out of interest; its good point to use 0.1% tolerance resistors on the input,
but, what would you recommend for the caps on the input ?
any specific cap ?

thank you
kam

Click to expand...

You don't have to buy 0.1% resistors (or capacitors for that matter)! What you do is take a bag of resistors and measure them with your Ohm meter.  Select a pair with the same value.  The exact value is not very important, what is important is balance and symmetry.

Click to expand...

???
What about temperature drift......1% components drift less    .....when the temp rises.... your " balance and symmetry" is out the window

The thing important is these 4 resistors of 22k (r1,r2,r3,r4) have the values mached as well as possible:
r1 should be mached only with r2 , and r3 should be mached only with r4  
So the temperature drift isn't important if these 4 resistors of 22K are equal between them (r1 ----> r2 and r3 ----> r4) (same type, same manufacturer, etc..) , because they have the same resistor value vs temperature, they cange their value with the temperature at same manner.  
These resistor can be 5% of tollerance but selected with tollerance of 0.1% max.
The sbalancer's CMMR input depend by these tollerances. With 0.1% of tollerance the CMMR is of 60 dB at 1khz, and with 1% tollerance the CMMR is 40 dB.

Regarding the input caps (c1, c2, c3, c4), they could be oscon type (I council them), but they should be for audio or for switching power supply, even if the can be general purpose types but with low ESR.  
Their tollerance isn't so important forCMMR, because they assume an impedance value near to zero at audio signal frequencies, it's more important their ESR values than their tollerance. However, for best CMMR value at very low frequencies it's melior using 47uF value for these caps.

When I wrote "bag of resistors" I meant as received from your vendor. Most on-line shops sell a sealed bag of ten or one hundred 1% resistors for a reasonable price. Many capacitors come in 10 packs. Often 0.1% resistors are just selected from the production run and the rest are sold as 1% items.  Resistors (or capacitors) from a production run should have a very similar temperature drift.

yes, it insn't hard to find pairs of resistors with less then 0,1% of difference of resistance value. I remenber that in 50 resistors of the same pack I've selected 4 pairs.



regarding the sbalancers' schematics:

- c9 , c10  are NPO / COG type.

- c5, c6 are polyester type

- c7, c8 can be general purpose type, but low ESR type is better.

- r5, r6 are 5% or 1% 1/4W type

- r8 and r9 are 1% 1/4W type


if you have other questions, let me know , please.

If I read PPA's schematic correctly... does that circuit reverse the polarity of the signal? Worth keeping that in mind if you use it...

If the circuit is only ever going to be used with a true transformer balanced signal input, I guess you could swap XLR pins 2 and 3..?

-Mike C

yes, I've drawed this circuit with hurry so I've inverted pin 3 with pin 2, sorry.
However, I've simulated it and works fine before posting it. Thank you.