cpsmusic

Summing Mixer Amp - Balanced or Unbalanced?
« on: October 11, 2020, 06:57:39 PM »
Hi Folks,

As I mentioned in another post, I'm currently putting together a summing mixer. The original design (from DIYRE) was balanced and passive. However, I thought the unit would be better if it included a make-up gain stage. The gain stages I've considered so far all take a single (unbalanced) input.

Am I right in thinking that if I want to keep the unit balanced-in-and-out, then for Left and Right channels I need to unbalance -> amplify -> balance?

This complicates the build quite a bit as it means that I need the four stages to handle the balancing. From what I can also see, these in turn require a mains PSU. Is that right?

Could I just feed the +ve balanced signal into the amp? I realise that this unbalances the inputs and that I'll lose the benefits of balancing, but will it work?

Cheers,

Chris


abbey road d enfer

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #1 on: October 12, 2020, 03:19:50 AM »
Hi Folks,

As I mentioned in another post, I'm currently putting together a summing mixer. The original design (from DIYRE) was balanced and passive. However, I thought the unit would be better if it included a make-up gain stage. The gain stages I've considered so far all take a single (unbalanced) input.

Am I right in thinking that if I want to keep the unit balanced-in-and-out, then for Left and Right channels I need to unbalance -> amplify -> balance?
You could duplicate the gain stages and use their outputs as a balanced signal.

Quote
This complicates the build quite a bit as it means that I need the four stages to handle the balancing.
What four stages? Give a description.

Quote
From what I can also see, these in turn require a mains PSU. Is that right?
Well, any active stage requires a PSU. Does it need to be "mains"? Batteries have their pros and cons, don't they?.

Quote
Could I just feed the +ve balanced signal into the amp? I realise that this unbalances the inputs and that I'll lose the benefits of balancing, but will it work?
Define "work". It would probably make some noise. Good noise or bad noise depends on your expectations. Balancing is necessary in presence of long lines, harsh EMI/RFI environment. Is it the case?
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

cpsmusic

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #2 on: October 12, 2020, 05:12:54 AM »
By four stages I meant two for the unbalancing and then two for rebalancing.

The only schematics I've been able to find online for these have required a mains PSU - are there any battery-powered versions out there?

I'm planning on using the mixer in a studio rack with short patch leads.

Cheers!

ruffrecords

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #3 on: October 12, 2020, 07:33:55 AM »
The common way to make a passive summing mixer is to do all the mixing balanced and use an external balanced input mic pre for the gain make up (this does the unbalancing, gain make up and balancing).

If you want to do this in the summing mixer itself then one option is to unbalance, amplify and then balance.

Another option is to use a comletely balanced amplifier, then there is no need to unblance and balance.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

JohnRoberts

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #4 on: October 12, 2020, 10:25:14 AM »
+1 to what (I think) Abbey said. Balanced interfaces are mostly useful for maintaining signal integrity over longer distances and inside harsh noise environments.

Inside mixers (even passive) the chassis can be an effective shield for unbalanced signal paths.

I have made a number of differential sum buses, but never a "balanced" sum bus. There should not be enough noise inside the mixer to benefit from being fully active balanced. A passive impedance balanced 0V bus could reduce the excessive component count, but making the 0V bus the same impedance as the signal bus to maintain common mode rejection ratio adds unnecessary Johnson noise. The 0V sum bus can use low impedance sum resistors and still maintain proper differential math.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

abbey road d enfer

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #5 on: October 12, 2020, 12:19:09 PM »
Find attached two (out of many) possibilities. The 1st one is the simplest, but relies on the equipment to which it is connected for providing good CMRR. Usually not an issue. I believe it's what Ian describes in his second suggestion. beware that it wouldn't be adequate for connecting to unbalanced equipment.
The 2nd one would be Ian's 1st suggestion; it makes sense only if you need to insert something in the signal path, like a fader, or if you think you may connect it to unspecified equipment.
And of course, as JR suggests you could make it plainly unbalanced, or differential.
The ultimate answer involves performance expectations, number of stems, equipment surrounding and working habits.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

john12ax7

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #6 on: October 12, 2020, 03:03:23 PM »
Do you like the sound of transformers? That would be a simple way to do the unbalancing  / balancing.

cpsmusic

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #7 on: October 12, 2020, 11:27:52 PM »
Transformers, yes, if I can find some that sound ok and are relatively cheap.


ruffrecords

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #8 on: October 13, 2020, 04:57:11 AM »
Transformers, yes, if I can find some that sound ok and are relatively cheap.
Those to factors tend to be mutually exclusive. A lot depends on what you consider to be 'reasonably cheap'.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #9 on: October 13, 2020, 05:49:50 AM »
Those to factors tend to be mutually exclusive. A lot depends on what you consider to be 'reasonably cheap'.

Cheers

Ian

To me EDCOR are the best if you don't want to spend that much and get a decent transformer, the other players like Jensen, Cinemag, Lundahl, Sowter, Carnhill, etc.. are in a whole different price range. OEP also makes good cheap transformers, however, I still prefer EDCOR. But of course, to me, the best transformer is no transformer, the THAT1200 series of line recievers are great


cpsmusic

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #10 on: October 14, 2020, 07:10:57 AM »
Those to factors tend to be mutually exclusive. A lot depends on what you consider to be 'reasonably cheap'.

Cheers

Ian

Yes, I know!

cpsmusic

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #11 on: October 14, 2020, 07:12:03 AM »
To me EDCOR are the best if you don't want to spend that much and get a decent transformer, the other players like Jensen, Cinemag, Lundahl, Sowter, Carnhill, etc.. are in a whole different price range. OEP also makes good cheap transformers, however, I still prefer EDCOR. But of course, to me, the best transformer is no transformer, the THAT1200 series of line recievers are great

Thanks for pointing out the THAT1200 series - they're another thing to consider.

abbey road d enfer

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #12 on: October 14, 2020, 10:12:21 AM »
Thanks for pointing out the THAT1200 series - they're another thing to consider.
The 1200 receivers are typical line level parts, not really the most adequate for a summing stage. More pertinent would be one of mic pre chips 1510/12.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #13 on: October 14, 2020, 11:06:22 AM »
The 1200 receivers are typical line level parts, not really the most adequate for a summing stage. More pertinent would be one of mic pre chips 1510/12.

I thought he was refering on how to unbalance the input stage, not to sum or amplify the output of the summing mixer.

ruffrecords

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #14 on: October 14, 2020, 05:01:44 PM »
I thought he was refering on how to unbalance the input stage, not to sum or amplify the output of the summing mixer.

If all the inputs are balanced , then you can just passive mix them balanced. This is the usual way yo make a passive summer. The resulting (low level) balanced mix is then usually unbalanced and amplified back up to line level. I think it was that aspect the Abbey was referring to.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

cpsmusic

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #15 on: October 17, 2020, 08:25:07 AM »
I wired up the mixer today - decided to go with four mono inputs, nine stereo inputs and one stereo output. I've given it a quick test just to make sure everything is connected right and so far it all seems to be ok. One thing I decided to add was a 4P2T switch that I plan to use to switch between balanced passive summing and some sort of makeup gain output which I'll add later.

Regarding the unbalancing, I meant unbalance the L/R inputs to the amplifier. I'm still undecided on what to use for the amplifier. I'd prefer something battery-powered but that limits things a bit.

Cheers,

Chris

cpsmusic

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #16 on: October 18, 2020, 11:11:47 PM »
For those interested, here's a picture of the summing mixer.

All the connections are working but I'm yet to try it out on a mix to see if it makes any difference sound-wise. Even if it doesn't it's still a handy thing to have.

Cheers!

cpsmusic

Re: Summing Mixer Amp - Balanced or Unbalanced?
« Reply #17 on: October 18, 2020, 11:13:14 PM »
It's point-to-point too so I guess that means I can charge double  ::)


 

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