How do I convert two SE amps to a balanced amp?
Sep 14, 2009 at 8:57 AM Thread Starter Post #1 of 18

rshuck

Head-Fier
Joined
May 24, 2009
Posts
98
Likes
14
Hello again everyone, I'm back with another question.

I'm a bit indecisive at the moment. I have been contemplating building a Balanced B22 for a while now, but I also have a desire to build a balanced, transformer coupled all tube amp (as discussed in a previous thread). I am to the point now where I am trying to decide, and I have another question.

Someone mentioned that I could wire up two 2 channel amps to make a balanced amp. My question is - how do I do this?

What I am thinking I am supposed to do is wire L+ and R+ to Pin 2 and Pin 3 of one driver's XLR socket - but what happens to L- and R-?

I would of course do the same to the other (identical) amp for the other driver.

If that's all that's needed apart from changing the input, is this safe to perform on any amplifier, or will component changes be required as well?


I have a Heed CanAmp that I am in love with and I'm now also contemplating buying another and making a balanced amp out of the two.

Any help would be appreciated.

Ryan
 
Sep 14, 2009 at 3:36 PM Post #2 of 18

Steve Eddy

Member of the Trade: The Audio Guild
Aka: TempAccount555
Joined
Sep 28, 2003
Posts
6,609
Likes
543
Quote:

Originally Posted by rshuck /img/forum/go_quote.gif
Someone mentioned that I could wire up two 2 channel amps to make a balanced amp. My question is - how do I do this?


Vitamins.
atsmile.gif


Quote:

What I am thinking I am supposed to do is wire L+ and R+ to Pin 2 and Pin 3 of one driver's XLR socket - but what happens to L- and R-?


Nothing.

If you're using a two channel unbalanced amp, there should be no L- and R-. Just L, R and ground.

Quote:

If that's all that's needed apart from changing the input, is this safe to perform on any amplifier, or will component changes be required as well?


It's not safe to say "any amplifier." But generally speaking, yes, most amplifiers can be bridged this way. And "bridging" is really the more appropriate term here over "balanced."

k
 
Sep 14, 2009 at 3:51 PM Post #3 of 18

digger945

Headphoneus Supremus
Joined
Mar 31, 2008
Posts
2,917
Likes
14
Bridged can sometimes mean purpose built balanced. Purpose built boards for balanced in and out. They could be used with an unbalanced signal input, but just throwing two unbalanced amps together, one for left and one for right, isn't the same.
 
Sep 14, 2009 at 4:14 PM Post #4 of 18

Steve Eddy

Member of the Trade: The Audio Guild
Aka: TempAccount555
Joined
Sep 28, 2003
Posts
6,609
Likes
543
Quote:

Originally Posted by digger945 /img/forum/go_quote.gif
Bridged can sometimes mean purpose built balanced. Purpose built boards for balanced in and out.


In my opinion, a bridged amp should mean nothing more than a bridged amp. To call a bridged amp "balanced" creates a rather confusing corruption of what "balanced" has traditionally meant and what its primary purpose is (i.e. the rejection of common-mode noise). A bridged amp does not provide any common-mode noise rejection at all. In fact, a bridged amp will simply amplify any common mode noise along with the signal.

Bridged amps have been traditionally called bridged amps, whether in professional audio, home audio, and even car audio.

Quote:

They could be used with an unbalanced signal input, but just throwing two unbalanced amps together, one for left and one for right, isn't the same.


Yet that's precisely what most every "balanced" headphone amp out there does.

k
 
Sep 14, 2009 at 4:37 PM Post #6 of 18

Steve Eddy

Member of the Trade: The Audio Guild
Aka: TempAccount555
Joined
Sep 28, 2003
Posts
6,609
Likes
543
Quote:

Originally Posted by TimmyMac /img/forum/go_quote.gif
Let both ends of the transformer secondary tap float when driving the headphones.. presto - cheap 'balanced' output


Yes, if you're talking about a tube amp. Though the secondaries are typically grounded for safety purposes. Don't want any involuntary electroshock therapy.
atsmile.gif


And of course you can simply add an output transformer to a single-ended solid state headphone amp and pesto - also a cheap "balanced" output.
atsmile.gif


k
 
Sep 14, 2009 at 5:10 PM Post #7 of 18

glitch39

1000+ Head-Fier
Joined
Mar 28, 2008
Posts
1,368
Likes
26
if coming from a true balanced DAC, you can "technically" feed +R and -R to each channel of the first amp. You do same for the second amp by feeding -L and -L.

However, I must warn you that you can easily create ground loops as you can tying the grounds of two separate amps. As long as you know how to trace GND from your PSU all the way to your ouput, then it may be worth a shot. However, I see no real benefit in doing that as it will be more expensive overall.
 
Apr 24, 2010 at 5:59 AM Post #8 of 18

schawo

New Head-Fier
Joined
Mar 24, 2010
Posts
42
Likes
1
I have a true balanced DAC. I have 2 tube amps of the same type with matched tubes. Can I create a fully balanced system by connecting the R+ R- R(Gnd) to one amp and connecting L+ L- L(Gnd) to the second amp?

After that I would resolder the headphones to have L+ and L- outputs of the amp connected to the left driver and R+ R- to the right using a 4-wire cable.
Is it ok? Can I simply omit original grounds (R(Gnd) and L(Gnd))?
 
Apr 24, 2010 at 6:32 AM Post #9 of 18

FallenAngel

Headphoneus Supremus
Joined
Mar 7, 2006
Posts
9,627
Likes
72
Location
Toronto
Completely depends on the amp.

You can certainly run an amp in differential mode and have 2 amps together running in differential mode to create a bridged amp of sorts. Balanced implies the actual amp combines the channels to subtract the noise. Well, that's my "simple" understanding, I'm sure there's a much more correct answer out there.
tongue.gif
 
Apr 24, 2010 at 7:14 AM Post #10 of 18

schawo

New Head-Fier
Joined
Mar 24, 2010
Posts
42
Likes
1
In my understanding if you drive the driver coil in full balanced mode, than noise subtractions occurs at the driver itself, not at the amp.

My theory, plz correct me if I'm wrong:
You get a + and an inverted - signal from the DAC through the amp, and connect the + to one end, and - to the other end of the coil. In this case all the picked up noise will be canceled out, because noise has the same phase at both end of the driver coil without any voltage difference.

But this is only a side effect, the sketched system should have better stereo separation and other pleasing features.

If it can be carried out without burning the tubes or the can
smily_headphones1.gif


My question still stands: is this wiring ok?

fullybalanced.gif
 
Apr 24, 2010 at 7:34 AM Post #11 of 18

KingStyles

Headphoneus Supremus
Joined
Mar 4, 2009
Posts
2,716
Likes
46
You sell both and buy a real balanced amp.
tongue_smile.gif
 
Apr 24, 2010 at 1:06 PM Post #12 of 18

nikongod

DIY-ku
Joined
Jan 24, 2005
Posts
8,882
Likes
124
Quote:

Originally Posted by Steve Eddy /img/forum/go_quote.gif
A bridged amp does not provide any common-mode noise rejection at all. In fact, a bridged amp will simply amplify any common mode noise along with the signal.


If you measure across the load, how would you know? The error is common to both phases and cancels across the load.


Schwao:
That is the basic idea of making a 4 channel amp. Depending on your system things may go awry so be prepared to test everything.
Quote:

Originally Posted by KingStyles /img/forum/go_quote.gif
You sell both and buy a real balanced amp.
tongue_smile.gif



There are very few balanced headphone amps. The VAST majority are 4 channel amps.
 
Apr 24, 2010 at 2:45 PM Post #13 of 18

schawo

New Head-Fier
Joined
Mar 24, 2010
Posts
42
Likes
1
Quote:

Originally Posted by nikongod /img/forum/go_quote.gif

Schwao:
That is the basic idea of making a 4 channel amp. Depending on your system things may go awry so be prepared to test everything.



Every advice what to consider and what to pay attention for would be great!
 
Apr 25, 2010 at 12:07 PM Post #14 of 18

bidoux

100+ Head-Fier
Joined
Jul 10, 2008
Posts
419
Likes
12
Quote:

Originally Posted by nikongod /img/forum/go_quote.gif
There are very few balanced headphone amps. The VAST majority are 4 channel amps.


gilmore3_3.gif

Is this configuration considered as "balanced" ? A way to achieve balanced outputs with single ended input ?
 
Apr 25, 2010 at 3:28 PM Post #15 of 18

nikongod

DIY-ku
Joined
Jan 24, 2005
Posts
8,882
Likes
124
Quote:

Originally Posted by schawo /img/forum/go_quote.gif
Every advice what to consider and what to pay attention for would be great!


Just be careful with how you do or dont (heh) ground things. Thats always been the biggest stumbling block to my efforts at bridging amps.

Quote:

Originally Posted by bidoux /img/forum/go_quote.gif
Is this configuration considered as "balanced" ? A way to achieve balanced outputs with single ended input ?


Id include it
smily_headphones1.gif
Its a very neat circuit.

The article on head-wize doesn't say how to hook up the feedback to the circuit, or the DC servo for the second half but its still cool.

Another great balanced headphone amp design is j4cbo's M4 amp which was posted up a few months ago Here
 

Users who are viewing this thread

Top