posted 26 April 2003 23:18            

It seems to make even more sense to monitor the Capy's output in quad sound. But I haven't found any mixers with quad output. Ideally, I would like to just add two more monoblock amps and matchiing speakers, then use a mixer to direct the output to the amps. Any suggestions for brands or models?

Thanks,

posted 27 April 2003 04:52            

itīs extremely sure that you made something wrong with your adapters. pin 2 of the xlr should go to the tip of the rca, pin 3 *and* pin 1 *combined* should got to the shield of the rca. if youīre especially clever you combine pin1 and pin 3 in the rca directly at the input of the following device, then you get better shielding (use a symmetric microphone cable for that). and donīt connect the housing of the xlr to anything.

regarding the mixer it is most wise to use a mixer with subgroup outputs like the mackie 1604. connect subgroup 1-4 to your quad speaker setup and route your input channels to the appropiate outputs.

another alternative could be the new surround monitor controller by spl: http://www.soundperformancelab.com/smc/smc_E.html

posted 27 April 2003 10:10            

I believe the adapters supplied with the cappy are intended for use with the digital output to change AES/EBU to S/PDIF and visa versa and not as a balanced to unbalanced convertor for analogue signals. As you probably know its far better to use balanced connections in a studio where ever possible because the many different pieces of equipment have to all be connected together which makes the chances of an earth loop very high , unlike a home Hi-fi where everything is next to each other and not that many connections need to be made. Anyway, if you do have to convert from balanced to unbalanced there are some things to consider.
There are a few misconceptions about balanced/unbalanced lines based on history.

In the old days nearly every piece of equipment which had balanced outputs used a output transformer and as such if you wanted to connect this to an unbalanced input you would have to connect the cold pin to ground otherwise the transformer (which had a single winding between the hot and the cold) would only have one connection and you would get no signal.

Now days most balanced outputs are made of two driver opamps both giving there own out of phase signal relative to ground. Therefore if you short the cold to ground, you are simply shorting out a driver opamp and what will happen will depend on how the output stage was designed. If the output has a Hi resistance, then shorting this will do nothing but some designers (quite rightly) want to give you a lower output impedance. This can lead to a high current requirement on the equipments internal power supply which starts to comes out of regulation and passes ripple to the other (non shorted) opamp. This will sound like earth hum as well . This can also cause a high current (the same as the output signal) through the earth connection which can make all the other equipment get a bit of this signal and sounds like cross talk or bleed through (a lot of studios have this problem with time code which can be both balanced and unbalanced on different pro equipment).
Also on some pieces of equipment shorting the cold to ground can kill the opamp permanently (not mentioning the Fostex D20 T/C output).
So it is best to leave the could disconnected when going from bal to unbal, But you must short the cold and the ground together when going from unbal to bal, as a balanced input works on the difference between the hot and the cold. Sometimes leaving the ground disconnected in the XLR of the balanced input works, but not always.

So, If this doesn't cure the problem and you are simply getting an earth loop hum, (You would probably get almost the same hum when the cappy is switch off) then a mixer with balanced inputs should cure the problem . But if you don't want to buy a mixer then an audio transformer acting as an isolating transformer Should do the trick. You should first experiment with the cappy turned off and listen for the change in hum when you unplug the inputs , outputs, mains and anything else that's plugged into the cappy. You will probably find that it needs at least two things
plugged into the cappy to make the hum, so you have to find out which pairs cause cause it.

Note : Just to confuse the issue, Some ( but not many) pieces of new equipment have output opamp pairs that emulate transformers. These would need the cold and ground to be shorted
together when feeding unbalanced equipment.

Hope this helps

posted 27 April 2003 19:03            

Unbalanced Analog Audio Connections

Use an XLR-to-RCA adapter. This adapter allows for the use of standard RCA unshielded cables. The adapter connects XLR pin 2 to the RCA signal pin, and XLR pin 3 to the RCA shield.

For better results, use three conductor (one twisted pair plus a braided shield) audio cable with an XLR connector on one end and an RCA connector on the other. Connect XLR pin 1 to the cable shield, and connect XLR pins 2 and 3 to the twisted pair. On the other end, connect the RCA signal pin and shield to the twisted pair so that XLR pin 2 ends up connected to the RCA signal pin and XLR pin 3 is connected to the RCA shield.

posted 28 April 2003 07:22            

I'm a little confused here.

Some unbalanced equipment have there RCAs screwed directly onto the case and those that don't will always have the left connectors shield common to the right connectors shield.

Therefore if you connect up both left and right cappy outputs as you have said above, then pin 3 of the cappys left output will be shorted to pin 3 of the cappys right output. This means that the voltage on the shields of the unbalanced equipment, relative to the cappys internal 0 volts, will be determined by the protection resistors on the cappys output opamps.

Therefore if the cappy was sending out a 1k sine of 1 volt on the leftoutput and silence on the right , then shields of the unbalanced equipment would have a sine wave of 0.5 volts on it, relative to the 0 volts inside the Cappy . As pin 2 of the right hand output of the cappy will be giving out 0 volts relative to the Cappys internal 0 volts , the unbalanced equipment will receive a inverted sine wave of 0.5 volts on the right instead of silence.

The only thing that often stop this happening is the possible earth connection down one of the mains plugs, the earth connection through the wall and the earth connection up through the other mains plug. This is not the path you want one leg of your audio to take.

Of cause if the cappy output had transformers or transformer emulating opamp pairs this wouldn't happen but I didn't think this was the case with the cappy.

What am I missing here?

Pete.

posted 28 April 2003 08:13            

i believe most electronically balanced output stages nowadays simulate transformers.
i agree that shorting a non-transformer-balancing output to ground can cause a lot of problems. but i never had.

actually iīm pretty sure that capys outputs simulate a transformer output, true?

posted 28 April 2003 16:25            

actually ssm chips are nowadays heavily used throughout the whole audio world. this is one of the reasons why also analog audio electronic seems to sound pretty the same regardless which manufacturer. thatīs why i admire spl, theyīre really into developing new concepts of analog audio treatment. they designed eqs and mice preamps with +-60v power supply. what dynamic range!!!

happy tinkering!
- m

posted 28 April 2003 21:00            

I just went back and unscrewed the ends to assure that the proper connection was made for L and R. Pete, last week I went around my "studio" and turned off all fluorescent lamps, moved cables and power adapters away from signal cables, even tried running cables at right angles. I unplugged and plugged various accessories, tried different power strips for different components, tried using the same power strips for all components without any effect.

When I turn off the Capy, the hum from my preamp/headphone amp becomes louder. No, I haven't taken the cable shield and hooked it to the case of the preamp; I'm too chicken. I'm pretty sure I will simply go with a mixer to solve the bal/unbal problem, and to allow me to mix in other sources if I ever decide to use them.

So, just one person has suggested a mixer, the Mackie 1604. I won't be working with bands or making soundtracks for films, but I do want to take advantage of the quad output. Is the Mackie 1604 overkill if I will almost never use anything other than the Capy? What is everyone else using?

Thanks again,

posted 29 April 2003 08:01            

quote:

---

Originally posted by mrothstn:
No, I haven't taken the cable shield and hooked it to the case of the preamp;

---

ja, but what happens when you do connect the shield to the preamps case?
i connect my capy directly to a discrete surround amplifier for home use (yamaha) with the method i described above in my first post. works flawlessly. you donīt need a mixer to solve that problem. itīs a waste of money, believe me.

posted 29 April 2003 08:50            

Please ignore my last posting.

Anyway mark it looks like your doing all the right things so maybe there is a oddity in your setup that even the mixer might not cure. You might want to do some tests before you buy the mixer.

With the cappy turned off (But Connected) try temporarily shorting the tips to the shields and see what happens to the hum. Obviously never switch the cappy on in this state. Then try disconnecting bits from the
cappy one by one. If you end up with just one output connected and nothing else and it still hums then your should look at the housing (is it screwed into a rack with other equipment).

What makes the Hum stop?
What else is plugged into the pre amp?

As far as cheaper mixers go you might want to look at these
http://www.Behringer.com/02_products/prodindex.cfm?id=MXB1002&lang=eng
http://www.soundcraft.com/products/spirit_notepad.html

but you may want to poor glue in the phantom power button though.

Even if you went for a 128 Channel Neave you'd still end up wishing you'd gone for the bigger one.

Hope it helps

posted 30 April 2003 22:59            

Anyway mark it looks like your doing all the right things so maybe there is a oddity in your setup that even the mixer might not cure. You might want to do some tests before you buy the mixer.

Pete,
Just to make sure I am not missing something basic, let me describe my setup. It isn't very sophisticated. The Capy analog outs are connected through homemade XLR to RCA connectors soldered according to SymSounds directions. The cable shields are connected to pin 1 of the XLR, but don't make any connection at the RCA end. The RCA ends are plugged into Aux 1.

The preamp is a Melos SHA-gold preamp/headphone amp I have used for years in my home stereo. One of my amplifier monoblocks is being repaired, so I am listening to the Capy through the headphone amplifier jack. The preamp just sits on my desk; it isn't attached to a rack.

With the cappy turned off (But Connected) try temporarily shorting the tips to the shields and see what happens to the hum. Obviously never switch the cappy on in this state. Then try disconnecting bits from the
cappy one by one. If you end up with just one output connected and nothing else and it still hums then your should look at the housing (is it screwed into a rack with other equipment).

I will try shorting the tips to the shields, but what do you mean by the tips? I can strip the braided wire cable sheaths on L and R so they are exposed, but then what do I connect them to? Do you mean connect the L and R shields together?

What makes the Hum stop?

Switching to another input like CD or aux 2. Muting also eliminates hum. I'll try a few other things and get back to you.

What else is plugged into the pre amp?
Nothing, though I tried listening to my CD player and there is no hum.

Even if you went for a 128 Channel Neave you'd still end up wishing you'd gone for the bigger one.

Yes, the grass is often greener.

Hope it helps

Pete.[/B][/QUOTE]

Thanks,

Mark

posted 01 May 2003 07:24            

Whay I ment by the tip was the signal pin, and if the back of the rca was unscrewed may be the contacts could be shorted there. But maybe we could aproch it a different way.

If the preamp is switch to aux 1 with nothing plugged in I asume that there is no hum (but try it out in any case).

If you plug the cd into aux1 and play it does it hum?

If you then unplug the CD and just plug one of the cappy cables with nothing on the other end into aux 1 does it hum?

If you then plug that one cable into the swithed off cappy with with no other connections on the cappy (no Mains cable no computer cable no midi cables) does it hum?

If you now connect just the mains cable to the cappy but still leave it switched off does it hum?

If you now connect the switch off computer to the cappy with the computers mains disconnected. does it hum?

Now if you connect the mains to the computer but still leave it switched off does it hum?

If you now boot the computer but leave the cappy switched off does it hum?

If you now shut down the computer and power up the cappy does it hum?

I'm sure you get the idea.

From there we can start to home in to the problem.

hope this helps.

posted 04 May 2003 22:24            

quote:

---

Originally posted by pete:

>>If the preamp is switch to aux 1 with nothing plugged in I asume that there is no hum (but try it out in any case).

Correct, no hum.

>>If you plug the cd into aux1 and play it does it hum?

No, nor does it hum in any other input.

>>If you then unplug the CD and just plug one of the cappy cables with nothing on the other end into aux 1 does it hum?

Yes! So simple, I should have tried this. When the RCA end is plugged into the preamp/headphone amp the hum is mild. Same hum with Aux 1, Aux 2, and CD inputs.

>>If you then plug that one cable into the swithed off cappy with with no other connections on the cappy (no Mains cable no computer cable no midi cables) does it hum?

Yes! The hum becomes much louder when the XLR end is plugged into the switched off Capy.

>>If you now connect just the mains cable to the cappy but still leave it switched off does it hum?

Yes, still an intense hum.

If I switch the Capy on, the hum drops down to the same low SPL and timbre as having just the RCA end plugged into the preamp.

So, it's time to revise the wiring for the cable, or buy premade adapters, or get a mixer. since I don't have a good way to attach the cable sheath to the chassis of the preamp, I will just disconnect the sheath from pin 1 of the XLR end. Duh.

Thanks for your help, I didn't want to experiment without guidance and mess up the outputs of the Capy.

Cheers,
Mark

Pete[/B]

---

posted 05 May 2003 18:51            

This allows you to use powered monitors directly conected to the controller, with full controll over panning volume down mix etc.
(No more loud pops when you compile an instruments)
You have several inserts, I/O and output options in the back.
When doing a surround mix you also get a stereo down mix on the same pass.