Balancing card (2x unbal-to-bal & 2x bal-to-unbal) R vs G graph added

[guy_4]

Hello Audiox,
Do you have for sale PC boards for this summing amp ?
I would be much interested.
Thanks,
Guy

 

[audiox]

Do you have for sale PC boards for this summing amp ? I would be much interested.

You probably meant this project:
http://www.groupdiy.com/index.php?topic=29082.0

I don't sell anything related to my projects. But you can find pdf files for home etching in the first post. Gerber files are also available if someone wants to manufacture boards in larger scale.

 

[audiox]

Audiox, could you please explain the equations in the block diagram, I'm embarrassed to say not only do I not get them but I don't get them so thoroughly I don't even know what to google to figure it out for myself.

http://en.wikipedia.org/wiki/Logarithm

R=5k => G= -6dB, R=10k => G= 0dB, R=20k => G= +6dB

 

[audiox]

it's been a long time since high school math, what's the story with 20 log?

I think it would too cruel to send you back to high school. So I made a resistance vs gain graph to help you. X scale is linear to make it easier to determine the required resistance value.

http://docs.google.com/fileview?id=0B_XBYPfmG8pVNWQyYzgxOGEtMWNjYy00ZDJmLWI3YzMtOWRkZWIwZGZkZjRk&hl=en

 

[substitute]

Thank you so much, that graph really explains it, as far as the wikipedia entry goes, I'll need another cup of coffee before that starts to make sense. 

 

[conleycd]

Hey Audiox,

I'm wondering if this arrangement in the balanced to unbalanced allows for extended headroom because you would have the swing of each opamp?  Do you know what the clip point would be if I used say OPA2604s at +/- 24v?

Thanks.

CC

 

[audiox]

I'm wondering if this arrangement in the balanced to unbalanced allows for extended headroom because you would have the swing of each opamp?

No, since the overload level of the final (unbalanced) stage is what matters. You can always increase R1 and R2 to prevent overloading the op-amps if you have very high level balanced signal. But with unbalanced-to-balanced stage the output signal uses both sides of the voltage swing.

If your balanced input stage has gain of -6dB and balanced output stage gain of +6dB, the (system) overload level is 6dB higher compared with unity gain stages.

Do you know what the clip point would be if I used say OPA2604s at +/- 24v?

Subtract a few volts (depending on the op-amp used) from the voltage swing. Then convert to rms value to get the overload level.

 

[audiovisceral]

Does anyone make or sell these balancing/unbalancing cards?

 

[Kir_For_Pleasure]

Etched and built one card now for testing, but cant get any amplification of it...on the unbalanced in, i use a 3k resistor on r14 to calibrate the ne5532 for -10db..maybe i read the gain graph totally wrong.
.....so basic.. ???

 

[audiox]

maybe i read the gain graph totally wrong.

R14=3k gives you attenuation of 10 dB, not amplification.

 

[moamps]

Hi,

values for the R13 and R19 on the schematic and layout are 20k, but all calculation and
graph are made using 10k. ???

Regards,
Milan

 

[Kir_For_Pleasure]

If R13 is 20k and i want a amplification of 13
R14 must be 260k

 

[Kir_For_Pleasure]

now its working  i did it right all the time before i look at the graph but i changed the resistor on wrong channel 

 

[audiox]

values for the R13 and R19 on the schematic and layout are 20k,

Yes.

but all calculation and graph are made using 10k. ???

No. They are 20k in graph and equations too.

 

[AudioJohn]

One considerable advantage of using the DRV134 or SSM or THAT balanced line drivers is the cross coupling which give 'true transformer' output. This means that you can earth, or unbalance one leg (either) - and the output level stays the same.

Try unbalancing the -ve output (or XLR pin 3) of your balanced driver and see what happens.

Oh heck.......

 

[MrZpliff]

Should one worry bout DC on the output ? There are no output caps. Suppose they're not needed. Just wanna check :

 

[keefaz]

Is there an advantage in using both sides of dual opamps across the 2 channels rather than using one dual opamp for each channel in this balanced input design ?

Crosstalk wise, wouldn't it better to just use U1 for channel 1 and U2 for channel 2 ?

 

[audiox]

Should one worry bout DC on the output ? There are no output caps. Suppose they're not needed. Just wanna check :

Depends on your application. If connected e.g. to a relay or potentiometer it is a good idea to add the capacitor.

Is there an advantage in using both sides of dual opamps across the 2 channels rather than using one dual opamp for each channel in this balanced input design?
Crosstalk wise, wouldn't it better to just use U1 for channel 1 and U2 for channel 2 ?

Yes. However the excellent cross-talk of the op-amp makes it meaningless in practice. The PCB layout is much easier that way.

 

[Larsson]

Here´s a customversion of this pcb with eight channels of unbalanced to balanced.
I hope its ok for you Audiox that i customized your pcb!

https://www.dropbox.com/s/wjrwomyzt69f73i/300dpi8chbalancingcard.tif

 

[bsatriani]

Should one worry bout DC on the output ? There are no output caps. Suppose they're not needed. Just wanna check :

Depends on your application. If connected e.g. to a relay or potentiometer it is a good idea to add the capacitor.

Audiox, can you please indicate the output caps value?
Caps place would be beetwen R17 and "- BAL OUT3" for cold and R18 and "+ BAL OUT3" for hot? or elsewhere?