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Balanced vs Unbalanced Pedals
Balanced vs Unbalanced Pedals
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Old 15th May 2019, 04:24 AM   #1
Kellaway is offline Kellaway  Australia
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Smile Balanced vs Unbalanced Pedals

Hi there,

I知 really new to electronics so forgive me if this question seems stupid.
I want to ask how one would convert a guitar pedal from an unbalanced signal to a balanced signal? Would it simply be a matter of using an xlr in and out or would you need two seperate circuits to make it work with a stereo signal? Is there a way to make a mono circuit stereo?
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Old 15th May 2019, 05:47 AM   #2
PRR is offline PRR  United States
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Not at all "stupid", since nobody is born knowing this stuff and much of it is not logical.

"XLR" is most often used for *mono* signals, one channel.

(I am about the only person I know who put stereo on XLR for a living.)

What are you really trying to do? Put a microphone through a pedal? Put a studio line signal through a pedal?
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Old 15th May 2019, 09:54 AM   #3
Kellaway is offline Kellaway  Australia
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Hey thanks PRR .

I知 wanting to put a microphone through some pedals but I guess I知 also wondering if there is some way to modify a pre existing circuit to be stereo. I see those TC Helicon things that are strictly for vocals and wonder what the difference is. I知 wanting to get into building guitar pedals but I知 also a singer and used to dream of having a as diverse a range of stomp boxes for vocals as with guitar. I realise I could just use a reamper to turn my Balanced microphone signal into a mono unbalanced signal. But I知 not sure if that is the best option. And I don稚 really like those Multi fx units.

Cheers
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Old 15th May 2019, 08:37 PM   #4
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Kellaway View Post
I知 also wondering if there is some way to modify a pre existing circuit to be stereo.
"Proper" stereo requires duplicate electronics - two microphones, two identical preamps, two identical power amps, two identical loudspeaker systems.

For vocals from a single singer, stereo doesn't gain you all that much - after all, there is only one single sound source, and a small one at that (the size of the singer's mouth!)

There are various ways to take a mono signal and make it sound fuller or richer, and one of those is to generate a sort of fake stereo, typically using a reverb pedal with stereo outputs. This type of reverb pedal takes in a mono signal, mixes it with lots of different slightly delayed and phase shifted copies of itself, and spits out two slightly different signals at it's two "stereo" outputs. This tricks the listener's ears and brain into hearing a bigger, more spread-out and "airier" sound.

Unbalanced vs balanced is something else entirely. Balanced signals are a way to reduce the amount of unwanted hum and noise that creeps into your signal. There is no connection between balanced signals and stereo; you can have unbalanced mono, unbalanced stereo, balanced mono, or balanced stereo!
Quote:
Originally Posted by Kellaway View Post
I realise I could just use a reamper to turn my balanced microphone signal into a mono unbalanced signal.
Ah. If that's what you want to do, there are mic preamps with both balanced and unbalanced outputs, so you can use whichever you like.

One of my favourites is the little ART Tube MP/C, which costs around $100 (USD), and packs a lot of really useful features into a little box, including a nice mic pre, a nice compressor / limiter that can be switched in or out, LED signal level metering, LED monitoring of the compressor, instrument or line level outputs, balanced and unbalanced inputs, and balanced and unbalanced outputs. If you believe in valve magic*, it also has a 12AX7 valve in it.

Here are a couple of links:

1) ART Tube MP/C Tube Preamp / Opto Compressor-Limiter / DI | Sweetwater

2) Tube MP/C – ART Pro Audio

I have found nothing like this product until you spend three to five times as much, so I consider it a rare gem in the usually overpriced and overhyped world of pro/ semi-pro audio.

*Valve magic - personally, I like what distorting valves do to my electric guitar sounds when they slather on 15% to 99% harmonic distortion. I am, however, deeply skeptical of claims that valves adding 0.1% harmonic distortion to pro-audio devices make everything sound better.

Whether or not the 12AX7 in the ART Tube MP/C is actually doing anything useful, though, there is no arguing the fact that this is a very nice little box, and very useful for vocals and bass guitar. I've even used it with some success on electro-acoustic guitars.


-Gnobuddy
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Old 16th May 2019, 02:13 AM   #5
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by Gnobuddy View Post
*Valve magic - personally, I like what distorting valves do to my electric guitar sounds when they slather on 15% to 99% harmonic distortion. I am, however, deeply skeptical of claims that valves adding 0.1% harmonic distortion to pro-audio devices make everything sound better.
What a valve in a mike preamp does is provide 20db of extra headroom before sounding awful.

As I've said before, Russel Hamm did all the measurements and maths back in '73

Hamm, R.O 1973 21(4) JAES "Tubes Versus Transistors-is there an Audible Difference"

For those in a hurry, go straight to the last paragraph
Quote:
Within the 15-20 dB "safe" overload range, the electrical output of the tube amplifier increases by only 2-4 dB, acting like a limiter. However, since the edge is increasing within this range, the subjective loudness remains uncompressed to the ear. This effect causes tube-amplified signals to have a high apparent level which is not indicated on a volume indicator (VU meter). Tubes sound louder and have a better signal-to-noise ratio because of this extra subjective head room that transistor amplifiers do not have. Tubes get punch from their naturally brassy overload characteristics. Since the loud signals can be recorded at higher levels, the softer signals are also louder, so they are not lost in tape hiss and they effectively give the tube sound greater clarity. The feeling of more bass response is directly related to the strong second and third harmonic components which reinforce the "natural" bass with "synthetic" bass [5]. In the context of a limited dynamic range system like the phonograph, recordings made with vacuum-tube preamplifiers will have more apparent level and a greater signal to system noise ratio than recordings made with transistors or operational amplifiers.
He defines "edge" or "bite" as being caused by the increase in harmonics above the seventh. (There's a large section on the impact of various harmonics)

What I've not yet read is a later paper which he co-authored which claims to provide "valve like" behaviour in a transistor pre-amp
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Old 16th May 2019, 04:17 AM   #6
Enzo is offline Enzo  United States
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I could be wrong, but I think the OP is confusing mono/stereo and balanced/unbalanced. The balanced signal from a microphone is not stereo. It is just balanced. I think he wants to connect the low-Z XLR mic to his 1/4" guitar pedals, and from the pedal back to the XLR for his mixer.
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Old 16th May 2019, 07:48 AM   #7
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Enzo View Post
I could be wrong, but I think the OP is confusing mono/stereo and balanced/unbalanced.
I came to the same conclusion, and I tried to address that misconception in my post above (#4).

The little ART preamp I mentioned can be used to convert a balanced mic signal into an unbalanced instrument level (or line level, switchable). Most guitar pedals should handle the instrument level unbalanced signal.

Also, most mixers I've seen have unbalanced line inputs, some with enough sensitivity to work with instrument-level signals, so a guitar pedal should be able to plug straight into the mixer. (I've done this often, playing my electric guitar through my mixer and small portable P.A. via a few FX pedals.)

So I think that ART preamp (or another similar device, if it exists) might solve the OP's dilemma.

-Gnobuddy
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Old 16th May 2019, 08:17 AM   #8
Bill Coltrane is offline Bill Coltrane  Netherlands
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Quote:
Originally Posted by Kellaway View Post
Hey thanks PRR .

I知 wanting to put a microphone through some pedals but I guess I知 also wondering if there is some way to modify a pre existing circuit to be stereo. I see those TC Helicon things that are strictly for vocals and wonder what the difference is. I知 wanting to get into building guitar pedals but I知 also a singer and used to dream of having a as diverse a range of stomp boxes for vocals as with guitar. I realise I could just use a reamper to turn my Balanced microphone signal into a mono unbalanced signal. But I知 not sure if that is the best option. And I don稚 really like those Multi fx units.

Cheers
There are pedals that output a stereo signal with just a mono input.
Examples are: Reverb, chorus and delay. All are very useful for vocals.
An other very useful effect for vocals is compression, this is not stereo.

So you can patch it up like this: Mic into compressor, into chorus (here it can be stereo), into delay, into reverb and out to amp. You can play with the order of efx, but this is kinda standard.

Tip: Get a specialized vocal processor, I know you don't like them but they have everything you need and more.
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Old 16th May 2019, 10:45 AM   #9
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by Kellaway View Post
how one would convert a guitar pedal from an unbalanced signal to a balanced signal?
Then what you actually need is to build this signal chain:

1) Microphone which is weak "microphone level" (say ~10mV) balanced to stronger "instrument level" (say, ~100mV) unbalanced.
That is done at every PA mixer channel which provides Balanced Mic + Unbalanced Line inputs.
Mic goes into a typically 10/20X (20/26dB) gain, balanced input extra stage, which then continues into the main Preamp channel or, in your case, a "Guitar" pedal.
Practical example,you build just the upper preamp, make R5 and R6 10k each:

Click the image to open in full size.

2) the actual Effects Pedal, your choice.

3) its output will be now "guitar level" and unbalanced.
You may:

a) use it as is, feeding it into an unbalanced Line Input in a Mixer channel, Notebook/PC Line input or Audio-to-USB module, using an unbalanced Plug to Plug shielded cable , a.k.a. "a Guitar cable".
Fine within 4 to 6 meters distance.

b) IF longer distances are involved or your mixer has *only* Balanced XLR input, then you use a 2 Op Amp "Balanced Out" circuit, such as:

Click the image to open in full size.

popularly called "Direct Box", used to send regular Music Instruments straight to faraway Balanced Inputs.

Note: you are now running ~100mV signals instead of original ~10mV ones.
Personally Iエd use as-is; 99% of Balanced inputs handle that very well and you keep an improved S/N ratio advantage (the louder the Signal the lowe the induced noise ) BUT if you are plugging into a dated weak signal only "Vocal Amp" from the 70エs, you may attenuate signal again by 10X.
Mentioned just as a curio, doubt youエll need that.

Quote:
Is there a way to make a mono circuit stereo?
Splitting a Mono signal into 2 channels stays Mono, thereエs no new "Stereo information" added.
Now some pedals, as mentioned above, such as Chorus, Reverb or Phase may output 2 "different" signals which may be played back through a Stereo amplifier.
Then youエll need two output balancers, each feeding its own cable and Mixer channel, which the Mixer operator will pan Right and Left.
Quote:
I知 wanting to put a microphone through some pedals but I guess I知 also wondering if there is some way to modify a pre existing circuit to be stereo.
See above.

Quote:
I see those TC Helicon things that are strictly for vocals and wonder what the difference is.
They must be doing what I explain above.
Quote:
I知 wanting to get into building guitar pedals but I知 also a singer and used to dream of having a as diverse a range of stomp boxes for vocals as with guitar.
Cool
That said, acoustic feedback/howling is your enemy and some effects will drive you crazy. As in: avoid distortion ones which add a TON of Gain.

Quote:
I realise I could just use a reamper to turn my Balanced microphone signal into a mono unbalanced signal. But I知 not sure if that is the best option. And I don稚 really like those Multi fx units.
No need for a Reamper , just DIY some of what I suggested above.

Which by the way is relatively easy, may be built even on perfboard, and definitely inexpensive.

So now go plug your soldering iron and experiment
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Old 16th May 2019, 08:05 PM   #10
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by thoglette View Post
What a valve in a mike preamp does is provide 20db of extra headroom before sounding awful.
If you have 10 times the power supply voltage, sure, you get ten times the output headroom, i.e. 20 dB more. Valves at 300 to 350 V versus opamps at 30 volts.

I've always thought Hamm's paper basically boiled down to "If you have no idea how an op-amp works, don't know how to use a gain control, and are confused by the concept of input level padding, then use valve preamps."

For the purposes of this thread: I don't know what voltage the 12AX7 in the ART preamp runs at. The external power suppy is only 9V AC, but the preamp does provide +48V DC phantom power, so we know the internal power supply is doing some voltage-boosting tricks.

From ART's recommended usage, the 12AX7 is indeed supposed to provide the "bite" that Hamm likes so much, i.e., increasing levels of THD as signal levels go up. There is even a multi-segment LED meter to let you know how hard you're driving the valve.

I myself found negligible audible difference right up to the point when sudden and very audible (and quite unpleasant) triode clipping starts. This was just using solo vocals for testing. Perhaps pure sine-wave testing might reveal something more audible.

But, as I said before, valve or no valve, the little ART MP/C is a very useful little audio tool.

-Gnobuddy
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