Balancer and De-Balancer on a TRS Jack to upgrade unsymmetrical gear

[Janus Audio]

Hi everybody,

I made SMD boards to balance inputs and outputs of some of my outboard gear, because I often hat hum problems with some devices. The boards are just some line receiver and line driver circuits based on LM4562s and can be fed from internal power supplies of the modded unit (as long it is a true bi-polar power supply). I tested them with up to 20dBu (which is all my DAC can do) and got THD less then 0.0012%

So far I upgraded my Quadraverb, Lexicon, LPX-1 and dbx 163A

Let me know, what you think!

Cheers, Sebastian

 

[TwentyTrees]

Great stuff, that's a very neat and compact solution to the problem. Nicely done.

 

[thomasdf]

Very clever design and neat build ! Bravo !

 

[Janus Audio]

Thank you!
I will test them with syngthesizers next. I sometimes get hum with some synths when they are connected via USB-MIDI

 

[Janus Audio]

Modding the Alesis Microverb II with symmetrical inputs and outputs

Checking the PSU where we can tap into the power rails:


Removing the old TS jacks:


Connect the sub-boards to the PSU V+ and V- taps and to the tip and sleeve solder pads of each TS jack:


Put the cover back in place:

 

[fazer]

Love it nice job.

You use to be able to buy these types of circuit kits from SparkFun for cheap. I wanted to make a hifi amp have a balanced input to work correctly with a balanced monitor controller and finally went to order the complete kits and they had discontinued them. Bummer.

 

[Janus Audio]

Love it nice job.

You use to be able to buy these types of circuit kits from SparkFun for cheap. I wanted to make a hifi amp have a balanced input to work correctly with a balanced monitor controller and finally went to order the complete kits and they had discontinued them. Bummer.

Thanks you!

I didn't know SparkFun yet - looks interesting! I don't see anything similar there though.
I will probably also sell the boards, if I manage to get a listing in the white board section.

 

[JohnRoberts]

these are called "bump boxes" and were popular last century back during the height of the -10 dBV bedroom recording gear boom, to step up/down signals between -10dBV unbal gear and balanced +4 dBu gear.

JR

 

[k brown]

Maybe I've just been insanely lucky, but in all my 40+ years mucking about with audio, I've not once encountered noise or interference from using unbalanced connections between line level gear.

 

[JohnRoberts]

Maybe I've just been insanely lucky, but all my 40+ years mucking about with audio, I've not once encountered noise or interference from using unbalanced connections between line level gear.

As you shouldn't using properly designed gear.

JR

 

[k brown]

As you shouldn't using properly designed gear.

JR

...and properly-made cables.

 

[fazer]

As you shouldn't using properly designed gear.

The controller is a presonus cs. It’s a passive design balance in out. It’s not noisy it’s just that it wants a full balanced connection to attenuate and work correctly. I build a balanced input using the circuit users in a genelec 1031 front end on a vector card and powered it off my Api power supply. It makes the controller work correctly. The Sparkfun kit was cool because the card set on the connector and mounted. Which would be great for the unbalanced amp mount in the chassis that powers my NS10 and aura tones. The mains are 1031’s. It works great because there are controls to attenuate tha ABC speaker outs to match output levels. They are pots that set across the hi lo balance lines. Everything work including the mono switches and dim with relays all passive. Everything turns to shxt when you connect unbalanced.

 

[RoadrunnerOZ]

Thank you!
I will test them with syngthesizers next. I sometimes get hum with some synths when they are connected via USB-MIDI

Problems with USB Audio/USB MIDI hum and also trackpad zipper noise I have noticed occurring with some laptops when using a USB Audio Interface and only occurring when the power supply is connected to the laptop - (also IIRC occurred with some all in one PC’s with external DC supplies) - without the supply connected there is no noise - weird problem as the power supplies are not even earthed to the mains - seems to be at its worst when the synths USB MIDI is connected to the laptop and the synth audio out connected to the interface inputs - any USB activity being heard as noise through the audio.

 

[Janus Audio]

Problems with USB Audio/USB MIDI hum and also trackpad zipper noise I have noticed occurring with some laptops when using a USB Audio Interface and only occurring when the power supply is connected to the laptop - (also IIRC occurred with some all in one PC’s with external DC supplies) - without the supply connected there is no noise - weird problem as the power supplies are not even earthed to the mains - seems to be at its worst when the synths USB MIDI is connected to the laptop and the synth audio out connected to the interface inputs - any USB activity being heard as noise through the audio.

Exactly, with USB power there is often a lot of noise! And also all of the synthesizers I know have unbalanced outputs, even the very expensive ones. This means when you use MIDI over USB you are likely to get a ground loop and hum. Because contrary to pure MIDI the connection in an USB jack is not isolated with an opto coupler.

A quick fix can be just to use a traditional MIDI connections without USB or using DI boxes with a transformer inside. So you interrupt the ground loop and the line level side of the synth.
But as I wrote earlier, I want to upgrade all my synthesizers to symmetrical connections sooner or later - so I never have to worry about that stuff ever again

 

[thomasdf]

I have an Alesis 3630 which I love for what it does (or doesn't do well, actually) and I take it to venues for shows and etc but it's always a bitch because if has quite a low headroom ... A solution like yours with a -6 attenuation input and +6 on the output would be a game changer for sure. Do you plan to make them available ? Sorry if I missed the info here, I am drinking my first coffee of the day
Bravo again !

 

[JohnRoberts]

I have an Alesis 3630 which I love for what it does (or doesn't do well, actually) and I take it to venues for shows and etc but it's always a bitch because if has quite a low headroom ... A solution like yours with a -6 attenuation input and +6 on the output would be a game changer for sure. Do you plan to make them available ? Sorry if I missed the info here, I am drinking my first coffee of the day
Bravo again !

The typical gain structure for "bump boxes" was nominal +4 dBu balanced input to -10dBV single ended, and back.

Note there is a couple dB difference between 0 dBu and 0 dBV so the actual attenuation is less than 14 dB, closer to -12 dB. Of corse your specific needs may vary so dial it in for what you need.

JR

 

[Janus Audio]

I have an Alesis 3630 which I love for what it does (or doesn't do well, actually) and I take it to venues for shows and etc but it's always a bitch because if has quite a low headroom ... A solution like yours with a -6 attenuation input and +6 on the output would be a game changer for sure. Do you plan to make them available ? Sorry if I missed the info here, I am drinking my first coffee of the day
Bravo again !

Thank you!

The boards I made have a +6dB boost on the outputs, but no attenuation on the inputs so far. I might implement a -6dB attenuation for input boards in a future version.

And yes, I already sold some of my boards to a fellow studio owner here in Berlin and want to make the available. Working on a web shop at the moment.

 

[JohnRoberts]

Thank you!

The boards I made have a +6dB boost on the outputs, but no attenuation on the inputs so far. I might implement a -6dB attenuation for input boards in a future version.

FWIW I used to routinely run single ended signals around inside large consoles down 6 dB (nominally -2 dBu=0VU) to compensate for the +6dB of extra signal swing gained by driving both output legs in active balanced outputs. This way clipping occurred at the same level inside the console as outside.

JR

And yes, I already sold some of my boards to a fellow studio owner here in Berlin and want to make the available. Working on a web shop at the moment.

 

[Janus Audio]

That sound like a good way to do it inside a console!
For the unbalanced gear I modded so far I can say: it's all really far away from the 20dBu my D/A converters can deliver. Especially the digital reverbs don't like clipping obviously. But they all have an input gain controls, so it's fine. And on for the outputs it's definitely nice to have the extra 6dB of gain.

I also modded a dbx163A and it works really well with the 0dB input and 6dB output. The fixed threshold is still in the right place

 

[RoadrunnerOZ]

Exactly, with USB power there is often a lot of noise! And also all of the synthesizers I know have unbalanced outputs, even the very expensive ones. This means when you use MIDI over USB you are likely to get a ground loop and hum. Because contrary to pure MIDI the connection in an USB jack is not isolated with an opto coupler.

A quick fix can be just to use a traditional MIDI connections without USB or using DI boxes with a transformer inside. So you interrupt the ground loop and the line level side of the synth.
But as I wrote earlier, I want to upgrade all my synthesizers to symmetrical connections sooner or later - so I never have to worry about that stuff ever again

If you ground lift the balanced output from your mod boards from a synth this may solve the problem - but not necessarily always! Decoupling MIDI via optical seems to be the only cure in some cases - I have had this issue with synths that have balanced output, lifted the grounds and still got noise from the USB MIDI connection - (may have been on a Kurzweil PC3X IIRC). Using normal MIDI no issues. If the ground lift works for your synths you could always implement a ground lift DIP switch on the Jack board.