Are API 550b Ballanced?

[borism]

Can someone tell me if API 550b are ballanced?
I'm getting a weird hum coming out my 550B , I have 2 of them and a 560 in the same Lunch box
The 560 is quiet as it can be, both 550s have this far, very low vollume hum sound (i really have to crank the monitor up to hear it, but now I know its there and paranoia starts to kick in)
Anyone have an comment maybe a similar experience?
thank you!

[borism]

Is this the right place to post this question?
anyone?

[borism]

Anyone?

[avedis]

Hi borism,

Here's a cut/paste of one of my older posts on a similar topic:

"550B, 550A, 550, 553, 525 = Unbalanced Input, Transformer Balanced Output

560, 560A*, 560B*, 554, 550A-1 = Electronically Balanced Input, Transformer Balanced Output

*Some 560A's and a few 560B's were transformerless and had unbalanced outputs. The transformer-balanced output versions were called 560AT and 560BT but the T was unnecessary when almost all of the 560's had transformer outputs anyway, so the T was routinely dropped in descriptions.

The 512c and the BAE 312A are both transformer balanced in & out.

Most of the time, modules with an unbalanced input don't present a problem when driven by something that has a transformer output, like a 512c or 312A or similar type module since you could unbalance a transformer and it won't freak out.

The loss of level is often due to interfacing gear that has an electronically balanced output stage to an unbalanced input, like the 550A or 550B. Some electronically balanced outputs can be designed to interface with unbalanced inputs without a problem but you'll have to give it a try and check yourself. Listen for a few things... first, is there a level loss? ... and if there is, how is the noise? It should be acceptable. Then, is the level loss frequency dependent?.... meaning, does the low end get obliterated?

I hope I haven't lost too many I'll try and answer questions if there are any on this topic."

Hope this helps,

Avedis

[borism]

Hey Thank you very much, you are the man himself
I look forward to try one of yournew E27 EQs, I belive I spoke directly to you on one ocation, mentioning this fact and that the E27 are fully ballanced , are they?
It is interesting what you are saying and might xplain this noise.
I just asumed the 550b is fully ballanced, you learn something every day
I dont think there is a loss in level
It just caught my attention that the Hum (very low lever however) came from both 550b and not from the 560 re issue, regardless of the slot of the unit in the Lunch box and I have to say the rest of the gear I own in the studio is dead quiet .
I'll keep xperimenting
Thank you again for your responce
Boris

[Reptil]

Ok, I bought a really old pair of API 550 A. I was planning on going the lunchbox route, but decided to rack these up myself in a 1ru box.

Now I also have a pair of Jensen line input transformers: JT-11P-5
I was told they are basically the same as the JT-11P-1
I want to hook these up on the 550A input with a simple 3 pole switch, so I can choose between the unbalanced, and transformer balanced inputs.
- Is this a good idea? Anything I have to take into account?
- Was there a specific reason for API not to balance these?

Then, should I remove the cover of the EQs? There will be better heat dissapation and the box will protect them, but I'm worried about interference from the PSU that will sit really close.

thank you
cheers,
Reptil

[nosebleedaudio]

One really good reason for kepping the path balanced is if your output device say a compressor is electronic balanced out and you feed that into a unbalanced input you loose 6db of level because you need to drop the - side of the output making it an unbalanced output. Otherwise the - side is driving into ground, not a good thing.
If the output was transformer coupled driving an unbalanced input it would not effect the level at all.

[Neve8128]

Hi Avedis,

could this be the reason why the 6 553's that I have installed on your 11 unit rack are crosstalking? For example, I send an audio signal to unit #1 and all others will also receive the same signal. I've been trying to figure this out for months without success and really appreciate your tips and suggestions.

Thanks,

Jay

Originally Posted by avedis

Hi borism,

Here's a cut/paste of one of my older posts on a similar topic:

"550B, 550A, 550, 553, 525 = Unbalanced Input, Transformer Balanced Output

560, 560A*, 560B*, 554, 550A-1 = Electronically Balanced Input, Transformer Balanced Output

*Some 560A's and a few 560B's were transformerless and had unbalanced outputs. The transformer-balanced output versions were called 560AT and 560BT but the T was unnecessary when almost all of the 560's had transformer outputs anyway, so the T was routinely dropped in descriptions.

The 512c and the BAE 312A are both transformer balanced in & out.

Most of the time, modules with an unbalanced input don't present a problem when driven by something that has a transformer output, like a 512c or 312A or similar type module since you could unbalance a transformer and it won't freak out.

The loss of level is often due to interfacing gear that has an electronically balanced output stage to an unbalanced input, like the 550A or 550B. Some electronically balanced outputs can be designed to interface with unbalanced inputs without a problem but you'll have to give it a try and check yourself. Listen for a few things... first, is there a level loss? ... and if there is, how is the noise? It should be acceptable. Then, is the level loss frequency dependent?.... meaning, does the low end get obliterated?

I hope I haven't lost too many I'll try and answer questions if there are any on this topic."

Hope this helps,

Avedis

[avedis]

Hi Jay,

To properly troubleshoot, I'd need to get some more info... but here's what I'm thinking your crosstalk problem may be:

Normally, the 553's unbalanced inputs should not present a problem with crosstalk because the combined impedance of the output of the driving module and the input of the 553 would be fairly low, making crosstalk in sheilded cables very unlikely to happen in shorter run cable...unless... you had a longer cable runs at the inputs to the 553's and the cables were part of a snake, bringing the cables closer, which could have a little inductance occuring the further you get away from the source driver. This adds some reactance at higher frequencies looking back from the 553's, so chances are that the crosstalk being heard is more abundant at the higher frequencies. And loosing 6 db's through interfacing isn't helping either.

First get it to crosstalk again with the exact same setup using the 11 space rack (nice unit made by BAE, not my company). Then, move the cables around and listen for crackling or changes in the crosstalk. Also try some changes with the cable and keep it away from the others and see if that makes a change.

This is just a theoretical best guess.

Avedis

Originally Posted by Neve8128

Hi Avedis,

could this be the reason why the 6 553's that I have installed on your 11 unit rack are crosstalking? For example, I send an audio signal to unit #1 and all others will also receive the same signal. I've been trying to figure this out for months without success and really appreciate your tips and suggestions.

Thanks,

Jay

[avedis]

Hi Boris,

Yes the E27 is fully transformer balanced. I like using Jensen's for this EQ.

Avedis

Originally Posted by borism

Hey Thank you very much, you are the man himself
I look forward to try one of yournew E27 EQs, I belive I spoke directly to you on one ocation, mentioning this fact and that the E27 are fully ballanced , are they?....
Thank you again for your responce
Boris

[Neve8128]

thanks for your reply. The wiring is mogami and there are three other racks of gear wired the same way and there's no noise, crackling going on anywhere.
The signal is equally splitting amongst all 11 slots it doesn't matter which input I use. It looks like when I insert the cards I can't remember which pin but I believe pin 1 or 3 short on all 6 xlr input on the rack. If I remove 5 out of the 6 cards then it doesn't happen.

Originally Posted by avedis

Hi Jay,

To properly troubleshoot, I'd need to get some more info... but here's what I'm thinking your crosstalk problem may be:

Normally, the 553's unbalanced inputs should not present a problem with crosstalk because the combined impedance of the output of the driving module and the input of the 553 would be fairly low, making crosstalk in sheilded cables very unlikely to happen in shorter run cable...unless... you had a longer cable runs at the inputs to the 553's and the cables were part of a snake, bringing the cables closer, which could have a little inductance occuring the further you get away from the source driver. This adds some reactance at higher frequencies looking back from the 553's, so chances are that the crosstalk being heard is more abundant at the higher frequencies. And loosing 6 db's through interfacing isn't helping either.

First get it to crosstalk again with the exact same setup using the 11 space rack (nice unit made by BAE, not my company). Then, move the cables around and listen for crackling or changes in the crosstalk. Also try some changes with the cable and keep it away from the others and see if that makes a change.

This is just a theoretical best guess.

Avedis

[avedis]

There hasn't been an opportunity for me to test 6 of them side by side; so I'm wondering if the crosstalk is happening from module to module due to something involving those two inductors. Some 553's just did not have covers... do yours have covers?

When you have signal in one channel, say channel 1, does the crosstalk get weaker as you move away from that channel? ... Does it decrease when you are in channel 3...4?

Get a croc-clip/alligator clip or any piece of conductive wire at least 20AWG, and attach one end a known ground.. some bare metal in the rack nearby, making sure you get an unpainted or unanodyzed area, and the other end just touch the metal chassis of the eq's and see if something changes in the crosstalk. Maybe the 11 spc chassis is not well connected to audio ground internally.

I know it's not your cables, but maybe the way the unbalancing is affecting the cable... so if it doesn't change, what would happen if you took another xlr cable and just went from a sound source, with no patch bay, into channel 1 and then listening to the other channels?
Pin 1 and 3 connect together at the input when something unbalanced in plugged in.

Avedis

[Steamy Williams]

Originally Posted by nosebleedaudio

One really good reason for kepping the path balanced is if your output device say a compressor is electronic balanced out and you feed that into a unbalanced input you loose 6db of level because you need to drop the - side of the output making it an unbalanced output. Otherwise the - side is driving into ground, not a good thing.
If the output was transformer coupled driving an unbalanced input it would not effect the level at all.

This is only the case with some electronically balanced outputs, as you can tie the cold to ground on quasi-floating electronically balanced outputs - which are quite common in high end audio equipment - and the unbalanced signal will not exhibit the 6dB drop in level. They function, to all intensive purposes, just like a transformer balanced output. There are other non-differential "balanced" outputs that behave similarly as well, at least as far as the user is concerned, such as ground compensated outputs.