Another question... Unbalanced on a Balanced....

[Info-warrior]

Good warnings regarding shorting outputs. I've had no reason to test the robustness of my gear's balanced outputs under such conditions.

However, I thumbed through the manuals for a couple of my compressors and this is what they say, in summary, about balanced/unbalanced.

My Behringer Composer Pro's manual says that the compressor uses servo balanced inputs and outputs and can detect an unbalanced connection and make a level correction. That is if a 1/4 TS connector is used, which by definition will short one lead to ground, the servo will detect that and increase the gain on the other leg by 6dB. The wording of the manual treats inputs and outputs the same.

The manual for my Compellor 300 specifically tells us that tying one leg of the output to ground will transfer full voltage swing to the other leg. The manual states that the unit's inputs and outputs can be used just as if they were transformer based.

 

[mr_elbows]

short answer is that the console impedance will pull the output down to a very low level

 

[SFM-Ptgal]

short answer is that the console impedance will pull the output down to a very low level

yeap... for the cart machine (balanced) the fader is @ 8 and for the domestic cd player the fader is @ 12 (from 1 to 20)

Meanwhile regarding a question I posed a few weeks ago about joining 3 cart machine into the same fader, I was told outside this forum that I can join them in paralel without any problem because the impedances wil decrease. For example: 3 cart machines, 600 ohm output each. Joining 3 in paralell I'll get 600/3=200 ohms. The problem I can get is a decrease of audio level into the console from the 3 cart machines. True or not?

Well, I think I've created a nice topic... Quite instructive, not just for me

Pedro

 

[greg.hahn]

short answer is that the console impedance will pull the output down to a very low level

yeap... for the cart machine (balanced) the fader is @ 8 and for the domestic cd player the fader is @ 12 (from 1 to 20)

Meanwhile regarding a question I posed a few weeks ago about joining 3 cart machine into the same fader, I was told outside this forum that I can join them in paralel without any problem because the impedances wil decrease. For example: 3 cart machines, 600 ohm output each. Joining 3 in paralell I'll get 600/3=200 ohms. The problem I can get is a decrease of audio level into the console from the 3 cart machines. True or not?

Well, I think I've created a nice topic... Quite instructive, not just for me

Pedro

IF the output impedances are truly 600 ohms, then yes, you can "get away with it", though your cart machine isn't going to be all that happy driving a 200 ohm load. You'll have higher distortion and lower level.

MAny machines have an output WAY lower than 600 ohms, and shorting them all together will make something that is totally unusable.

You'd be far better off to use some build out resistors to keep the output amps happy. A 470 in series with the + lead, or a 220 in series with both the + and the - is the thing to do.

By the way...ya want to know the true output impedance? Feed a tone through it with a totally open circuit and measure the output. Put a pot, or decade box, or group of resistors across the output. Find the value of R that lowers the output by 6 dB. That value is your output impedance.

 

[speakerman]

I have driven a telco dry pair (not a POTS line) directly from a console output with no problems...one jerk engineer though (who thought he knew everything because he used to work for Pacific Bell as a cable man...big whoop) and works for a California group, argued with me that it needed eq and impedance matching...MAYBE back in the days of LONG cable connections and BC gear being 600 ohm transformer out....but in the modern world (post 1980s), that doesnt hold true...

I did the same thing with the stereo lines I had from the studio to the transmitter (pre-digital1979) of a station I engineered. I used McCurdy line amps (+32 capable) to directly drive the lines as constant voltage transmission drivers. I put a 1 watt 150 ohm resistor on each output and a low-voltage MOV across the line side of the resistors. I then used a small series fuse to each leg of the phone lines (lightning). It was really quiet and clean and never went down. I had 2 UREI 1/3 octave EQs at the transmitter end. The Bell guy assigned to my station freaked when I told him I was going to feed "pink noise" down his lines while we were working together on phone line problems. He called his supervisor which instilled a two day #issing match between the manager, me and the local Bell honcho. They claimed I would damage the lines and that fixed tones where the only way you could possibly measure the line response. They finally gave in once they learned was it was.
When testing, I always fed the lines from the studio out of polarity and adjusted the level balance and phase between the channels with a RTA hooked to the mono output of a Marantz tuner. Simply adjust for best mono cancellation across the range. It came close to the transfer function one might expect to the consumer through the audio chain and their equipment. I did TEF measurements during the same time period however found pink noise to work better for that application. TEF was better applied to room acoustics work and speaker/room tuning.

 

[Countrykev]

From Rane comes a must-have-on-your-bulletin-board chart on how to wire balanced, unbalanced, and interconnect and such.

http://www.rane.com/note110.html

 

[rbrucecarter5]

Alright... What If I connect an unbalanced domestic Sony cd player to a balanced 600 ohm input of the console? Should I take care with something?

Thanks!

A THS4131 EVM board from Texas Instruments will accomplish the conversion easily. It also is very low noise. You will have to supply power to the board somehow.

 

[SFM-Ptgal]

Just a quick note regarding a mod I made. Firstly I connected the CD player to a Tape input. As I stated b4 I got the result of having to turn the pot almost fully cw to add gain.

Yesterday I connected it to a Turntable input wich has a lower dbm input level. As a result: I have to use the variable output of the cd player and lower it so that it doesn't distort. I connected the pc soundcard SB-Live line output to the console to the same fader as the CD player and I got a gain decrease on the cd player (z-mismatch?). When I disconnect the pc cable the cd player recovers the audio level.

The console is an Harris Stereo 80:

http://s215.photobucket.com/albums/cc118/SFM-PTGAL/?action=view&current=DSCF7258.jpg

 

[Info-warrior]

Just a quick note regarding a mod I made. Firstly I connected the CD player to a Tape input. As I stated b4 I got the result of having to turn the pot almost fully cw to add gain.

Yesterday I connected it to a Turntable input wich has a lower dbm input level. As a result: I have to use the variable output of the cd player and lower it so that it doesn't distort. I connected the pc soundcard SB-Live line output to the console to the same fader as the CD player and I got a gain decrease on the cd player (z-mismatch?). When I disconnect the pc cable the cd player recovers the audio level.

The console is an Harris Stereo 80:

http://s215.photobucket.com/albums/cc118/SFM-PTGAL/?action=view&current=DSCF7258.jpg

If the input you were using is a true phono input, than it's not so much an impedance issue as it is a pure level issue. Phono cartridges are essentially microphones and require large amounts of preamplification to bring them up to line level--ie the level your CD player puts out. In addition to level correction, the phono preamp also applies de-emphasis and bass boost to restore the frequency response of the record. Records are recorded with pre-emphasis to mask surface noise and have the bass rolled off somewhat to keep the groove size down and to help reduce mistracking.

When you say the PC card was connected to the same input, I assume you just wired them both on so you can leave the fader up and just play either one without having to hit any other buttons or switches? If that's the case, than you're feeding your CD player's output to your soundcard's output and vice versa, not an Ideal situation as it could potentially cause damage. If you must put them on the same fader consider buying or building a simple selector box. If you want to use either without pushing additional buttons, you can always connect them up to a small submixer, though that adds another piece of gear.

 

[SFM-Ptgal]

Just a quick note regarding a mod I made. Firstly I connected the CD player to a Tape input. As I stated b4 I got the result of having to turn the pot almost fully cw to add gain.

Yesterday I connected it to a Turntable input wich has a lower dbm input level. As a result: I have to use the variable output of the cd player and lower it so that it doesn't distort. I connected the pc soundcard SB-Live line output to the console to the same fader as the CD player and I got a gain decrease on the cd player (z-mismatch?). When I disconnect the pc cable the cd player recovers the audio level.

The console is an Harris Stereo 80:

http://s215.photobucket.com/albums/cc118/SFM-PTGAL/?action=view&current=DSCF7258.jpg

If the input you were using is a true phono input, than it's not so much an impedance issue as it is a pure level issue. Phono cartridges are essentially microphones and require large amounts of preamplification to bring them up to line level--ie the level your CD player puts out. In addition to level correction, the phono preamp also applies de-emphasis and bass boost to restore the frequency response of the record. Records are recorded with pre-emphasis to mask surface noise and have the bass rolled off somewhat to keep the groove size down and to help reduce mistracking.

When you say the PC card was connected to the same input, I assume you just wired them both on so you can leave the fader up and just play either one without having to hit any other buttons or switches? If that's the case, than you're feeding your CD player's output to your soundcard's output and vice versa, not an Ideal situation as it could potentially cause damage. If you must put them on the same fader consider buying or building a simple selector box. If you want to use either without pushing additional buttons, you can always connect them up to a small submixer, though that adds another piece of gear.

The TT inputs aren't phono-preamplified. They have a NIL of -20db while the tape ones have +4db.
5 devices can be addressed to the fader via Switchcraft lever switches. Each time I address a device to a fader it's level becomes lower. It's a console's feature ;D The PC and the CD player are on independent devices, not joined together.

 

[rrsounds]

Lots of good advice here.

In summation (!), in general you can connect multiple INPUTS together or short them to ground without a problem. To drive a balanced input from an unbalanced source, one side of the input can be (and usually must be) grounded.

But OUTPUTS are sources that have minimum load requirements, and need individual isolation in the form of resistance when connecting together (or to ground). The appropriate resistance depends upon the design.

Kind Regards,
David

 

[Info-warrior]

Just a quick note regarding a mod I made. Firstly I connected the CD player to a Tape input. As I stated b4 I got the result of having to turn the pot almost fully cw to add gain.


http://s215.photobucket.com/albums/cc118/SFM-PTGAL/?action=view&current=DSCF7258.jpg

If the input you were using is a true phono input, than it's not so much an impedance issue as it is a pure level issue. Phono cartridges are essentially microphones and require large amounts of preamplification to bring them up to line level--ie the level your CD player puts out. In addition to level correction, the phono preamp also applies de-emphasis and bass boost to restore the frequency response of the record. Records are recorded with pre-emphasis to mask surface noise and have the bass rolled off somewhat to keep the groove size down and to help reduce mistracking.

When you say the PC card was connected to the same input, I assume you just wired them both on so you can leave the fader up and just play either one without having to hit any other buttons or switches? If that's the case, than you're feeding your CD player's output to your soundcard's output and vice versa, not an Ideal situation as it could potentially cause damage. If you must put them on the same fader consider buying or building a simple selector box. If you want to use either without pushing additional buttons, you can always connect them up to a small submixer, though that adds another piece of gear.

The TT inputs aren't phono-preamplified. They have a NIL of -20db while the tape ones have +4db.
5 devices can be addressed to the fader via Switchcraft lever switches. Each time I address a device to a fader it's level becomes lower. It's a console's feature ;D The PC and the CD player are on independent devices, not joined together.

Sounds reasonable as most consumer gear is -10dBm and lately, it seems that CD and DVD players run hotter than that. I'm still not sure why, if the console has isolation switches on it, the level would drop when another device is added. Do you get any bleed through? That is if you select CD on the switch panel and play something from the PC, do you hear the PC soundcard at all, even if very muted?

If it's not a hassle, I'd try connecting both devices to another fader that accepts multiple sources just to see if the same condition exists.

 

[SFM-Ptgal]

Just a quick note regarding a mod I made. Firstly I connected the CD player to a Tape input. As I stated b4 I got the result of having to turn the pot almost fully cw to add gain.


http://s215.photobucket.com/albums/cc118/SFM-PTGAL/?action=view&current=DSCF7258.jpg

If the input you were using is a true phono input, than it's not so much an impedance issue as it is a pure level issue. Phono cartridges are essentially microphones and require large amounts of preamplification to bring them up to line level--ie the level your CD player puts out. In addition to level correction, the phono preamp also applies de-emphasis and bass boost to restore the frequency response of the record. Records are recorded with pre-emphasis to mask surface noise and have the bass rolled off somewhat to keep the groove size down and to help reduce mistracking.

When you say the PC card was connected to the same input, I assume you just wired them both on so you can leave the fader up and just play either one without having to hit any other buttons or switches? If that's the case, than you're feeding your CD player's output to your soundcard's output and vice versa, not an Ideal situation as it could potentially cause damage. If you must put them on the same fader consider buying or building a simple selector box. If you want to use either without pushing additional buttons, you can always connect them up to a small submixer, though that adds another piece of gear.

The TT inputs aren't phono-preamplified. They have a NIL of -20db while the tape ones have +4db.
5 devices can be addressed to the fader via Switchcraft lever switches. Each time I address a device to a fader it's level becomes lower. It's a console's feature ;D The PC and the CD player are on independent devices, not joined together.

Sounds reasonable as most consumer gear is -10dBm and lately, it seems that CD and DVD players run hotter than that. I'm still not sure why, if the console has isolation switches on it, the level would drop when another device is added. Do you get any bleed through? That is if you select CD on the switch panel and play something from the PC, do you hear the PC soundcard at all, even if very muted?

If it's not a hassle, I'd try connecting both devices to another fader that accepts multiple sources just to see if the same condition exists.

Yes, it still exists...
Tale a look at the transformers:
http://i215.photobucket.com/albums/cc118/SFM-PTGAL/Broadcast console/DSCF6128.jpg?t=1222065231

 

[SFM-Ptgal]

The real problem will be low level. Most unbalanced consumer devices have a nominal output level of -10 dbm. Professional balanced equipment is usually engineered for +4 dbm, a 14 db difference. If the console does not have enough gain, it may not be a happy marriage. Impedance matching may be another issue. You can usually go from a low impedance output to a high impedance input with no problem. Going from high to low creates distortion and usually a drastic roll-off of bass response. The wild card is not all balanced inputs are really low impedance. You'll just have to try it to see if it works OK. If not, there are a variety of matching devices out there. Henry Engineering, Peavey and a lot of others make -10 to +4 converter boxes.

Sorry to recover this old topic but I have a question:
Will the use of -10 to +4 converter boxes heal the roll-off of bass response or will just fix the level issue? The CD player causes a slight, the PC soundcard a notorious and the phono preamp a huge lack of medium to high frequency loss on any device addressed to same fader. The console is an Harris Stereo 80.

Pedro

 

[Chuck]

Sorry to recover this old topic but I have a question:
Will the use of -10 to +4 converter boxes heal the roll-off of bass response or will just fix the level issue? The CD player causes a slight, the PC soundcard a notorious and the phono preamp a huge lack of medium to high frequency loss on any device addressed to same fader. The console is an Harris Stereo 80.

Pedro

It sounds like your basic problem is a poor impedance match, and most active converter boxes will fix that. I don't really remember if the Gates console has 600 ohm transformer inputs or not, but I suspect it does. Back in it's day, it was considered normal to have "real" input transformers that presented a 600-ohm Load. If the output impedance of your source is higher than the impedance of the input it is trying to drive, then you will experience non-linear frequency response, which most noticeably rolls off the low end. Going from a relatively high output impedance to a low input impedance usually results in a very "thin" sound. Does that sound familiar?

As a rule of thumb, you can usually go from a low impedance source to a high impedance input with good results. Going from a high impedance source to a low impedance input is a recipe for disaster, or at least poor audio quality.

These days, most consoles use "bridging inputs" which are balanced, but present a relatively high impedance load (usually about 15 K Ohms). It keeps a lot of impedance matching problems from rearing their ugly heads. On older equipment like yours, it was common for the inputs to be very low impedance.

I think you will find that most of the converter boxes will help your problem. Just make sure that they are happy driving a 600-Ohm load.

You could also experiment with running your audio into the console by bypassing the input transformers. The secondary is usually much higher impedance than the primary (input). Of course doing this negates all the advantages of a balanced input, but since this appears to be a hobby studio in your home, you are probably not too concerned with getting RFI from a 50 KW transmitter into the input of your console. It might be worth a try.