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[Mike Bloomfield]

I'm not a newbie, but not pro either. I hope I posted this in the correct area...

I got a USED Trident S40 mic preamp and have been playing around with it. I really like it, but have a question about some buzz.

Quick background:

I'm hooked up to a Mac Pro using a Motu 2408 mk2 A/D converter/ interface. All equipment has a ground pin on their respective power cables and are all connected to the same metal rack bars so that should tie all their chassis' together. The wall jack does have ground going to the panel, but it is not a separate electrical panel. I have a Digimax D8 preamp (connected via analog outs and not the ADAT out) as well and it does not produce the same buzz.

Here's the scenario:

• Gating the signal at -63dB from within my DAW gets rid of the buzz.
• With NO input cables plugged in, if I turn the gain up it's relatively quiet (small amount of speaker static type noise). With the input gain over +45dB and the output gain at +5dB or more, the preamp begins to produce electrical noise, but I'm thinking that's fairly high gain.
• Plug the XLR cable in (no mic attached) and I get buzz (probably RF noise) at lower gain. Insert 48V phantom power and it gets a little worse.
• Attach a microphone to the XLR cable and the buzz significantly reduces, but is still noticeable with high gain settings.
• Using the instrument input (built-in DI) on the front panel produces the same as above.
  Hovering my hand centered and over the top of the amp increases the buzz significantly, but touching the amp chasis almost eliminates it completely.
• Adjusting the knobs increases the buzz and creates a frequency-sweep type hum when adjusting. I'm assuming this is due to the fact that the knobs are metal and transferring the voltage from my body (just a guess)??
• If I use my DI box and connect to the XLR input I can literally crank both input and output gain and the preamp is dead quiet.
• The buttons for EQ in, comp in, etc. all make very insignificant crackle when engaging/ disengaging, but I'm thinking this is fairly normal.

Do I have a grounding problem, does the preamp just need a good cleaning or is there some other problem? I shut off all my other equipment except my A/D converter and Mac, but it made no difference.

I have the output of the Trident connected to channel 3 of the Motu input. I used output #3 of the Motu to route previously recorded tracks into the Trident, but disconnected that 1/4" cable from the Trident before doing other tests. This routing cable was still connected to the Motu and left open-ended, but I had nothing from the DAW sending to that channel so I don't think it would have created any RF noise.

Any suggestions?

[Mac Kerr]

I'm not a newbie

Any suggestions?

Please go to your profile and change the "Name" field to your real full name as required by the posting rules clearly displayed in the header at the top of the section, and in the Site Rules and Suggestions in the Forum Announcements section.

Mac

[Mike Bloomfield]

Please go to your profile and change the "Name" field to your real full name as required by the posting rules clearly displayed in the header at the top of the section, and in the Site Rules and Suggestions in the Forum Announcements section.

Mac

Thanks for the tip. Done!

[John Roberts {JR}]

I'm not a newbie, but not pro either. I hope I posted this in the correct area...

I got a USED Trident S40 mic preamp and have been playing around with it. I really like it, but have a question about some buzz.

Quick background:

I'm hooked up to a Mac Pro using a Motu 2408 mk2 A/D converter/ interface. All equipment has a ground pin on their respective power cables and are all connected to the same metal rack bars so that should tie all their chassis' together. The wall jack does have ground going to the panel, but it is not a separate electrical panel. I have a Digimax D8 preamp (connected via analog outs and not the ADAT out) as well and it does not produce the same buzz.

Here's the scenario:

• Gating the signal at -63dB from within my DAW gets rid of the buzz.
• With NO input cables plugged in, if I turn the gain up it's relatively quiet (small amount of speaker static type noise). With the input gain over +45dB and the output gain at +5dB or more, the preamp begins to produce electrical noise, but I'm thinking that's fairly high gain.
• Plug the XLR cable in (no mic attached) and I get buzz (probably RF noise) at lower gain. Insert 48V phantom power and it gets a little worse.
• Attach a microphone to the XLR cable and the buzz significantly reduces, but is still noticeable with high gain settings.
• Using the instrument input (built-in DI) on the front panel produces the same as above.
  Hovering my hand centered and over the top of the amp increases the buzz significantly, but touching the amp chasis almost eliminates it completely.
• Adjusting the knobs increases the buzz and creates a frequency-sweep type hum when adjusting. I'm assuming this is due to the fact that the knobs are metal and transferring the voltage from my body (just a guess)??
• If I use my DI box and connect to the XLR input I can literally crank both input and output gain and the preamp is dead quiet.
• The buttons for EQ in, comp in, etc. all make very insignificant crackle when engaging/ disengaging, but I'm thinking this is fairly normal.

Do I have a grounding problem, does the preamp just need a good cleaning or is there some other problem? I shut off all my other equipment except my A/D converter and Mac, but it made no difference.

I have the output of the Trident connected to channel 3 of the Motu input. I used output #3 of the Motu to route previously recorded tracks into the Trident, but disconnected that 1/4" cable from the Trident before doing other tests. This routing cable was still connected to the Motu and left open-ended, but I had nothing from the DAW sending to that channel so I don't think it would have created any RF noise.

Any suggestions?

Hari kari,,, ?

When you touch the chassis with your hand, you are grounding yourself to the same ground potential as the preamp chassis.. This may or may not actually be properly grounded. Apparently your mic cable and mic inputs are either not picking up common mode noise equally, or the preamp is not canceling it well. When you ground yourself you add some shielding and reduce the general noise level in the area.

This lack of noise rejection could be caused by one or more different faults.

You may want to start reading up on "pin one problem" for a general overview.

JR

[Mac Kerr]

Any suggestions?

If this is an old preamp from the same Trident that made the Trimix console, I am not surprised it has noise problems. My experience with the consoles has not been good. Not only did they have 3 different ground points to connect to house ground, but you were supposed to just try them each and use the one that was the quietest. Then you had to orient the external power supply correctly relative to the earth's magnetic field, I am not kidding, to further reduce the noise.

Since this is primarily a recording question, you may get better results in the R/E/P forums next door. Since you registered here on 1/10/11 you should already be registered there.

Mac

[Mike Bloomfield]

Can you bump this thread there or do I have to repost?

[Doug Fowler]

Can you bump this thread there or do I have to repost?

Repost.

[George Dougherty]

I'm not a newbie, but not pro either. I hope I posted this in the correct area...

I got a USED Trident S40 mic preamp and have been playing around with it. I really like it, but have a question about some buzz.

Quick background:

I'm hooked up to a Mac Pro using a Motu 2408 mk2 A/D converter/ interface. All equipment has a ground pin on their respective power cables and are all connected to the same metal rack bars so that should tie all their chassis' together. The wall jack does have ground going to the panel, but it is not a separate electrical panel. I have a Digimax D8 preamp (connected via analog outs and not the ADAT out) as well and it does not produce the same buzz.

Here's the scenario:

• Gating the signal at -63dB from within my DAW gets rid of the buzz.
• With NO input cables plugged in, if I turn the gain up it's relatively quiet (small amount of speaker static type noise). With the input gain over +45dB and the output gain at +5dB or more, the preamp begins to produce electrical noise, but I'm thinking that's fairly high gain.
• Plug the XLR cable in (no mic attached) and I get buzz (probably RF noise) at lower gain. Insert 48V phantom power and it gets a little worse.
• Attach a microphone to the XLR cable and the buzz significantly reduces, but is still noticeable with high gain settings.
• Using the instrument input (built-in DI) on the front panel produces the same as above.
  Hovering my hand centered and over the top of the amp increases the buzz significantly, but touching the amp chasis almost eliminates it completely.
• Adjusting the knobs increases the buzz and creates a frequency-sweep type hum when adjusting. I'm assuming this is due to the fact that the knobs are metal and transferring the voltage from my body (just a guess)??
• If I use my DI box and connect to the XLR input I can literally crank both input and output gain and the preamp is dead quiet.
• The buttons for EQ in, comp in, etc. all make very insignificant crackle when engaging/ disengaging, but I'm thinking this is fairly normal.

Do I have a grounding problem, does the preamp just need a good cleaning or is there some other problem? I shut off all my other equipment except my A/D converter and Mac, but it made no difference.

I have the output of the Trident connected to channel 3 of the Motu input. I used output #3 of the Motu to route previously recorded tracks into the Trident, but disconnected that 1/4" cable from the Trident before doing other tests. This routing cable was still connected to the Motu and left open-ended, but I had nothing from the DAW sending to that channel so I don't think it would have created any RF noise.

Any suggestions?

Since everything is already electrically grounded try this: for line level signals, disconnect the shield/drain/ground wire at the input make sure you leave it connected at the output.  Use rubber isolating pads to isolate the devices from each other and from rail to chassis contact.

This is the topology recommended to me by an old studio technician.  It isolates potential ground differentials between units in the signal chain and will typically eliminate ground differential hum.  Under no circumstance should you lift the ground on the electrical connections.  That is required for safety purposes.  There is no need to have grounds connected by signal lines for safety purposes as long as everything is grounded.  Anything that doesn't have a 3 prong grounded cord can be manually grounded if you'd like by tying to the chassis of the unit.

In my own experience, I had an amp rack of 4 QSC PLX2 amps that would hum on its own with nothing connected to the amplifier inputs.  All amplifiers were tied to the same electrical outlet and shared a common ground.  It may have been due to grounding between the chassis and the custom metal input panel I had installed, but snipping the shield on the signal lines connected to the amplifiers eliminated the hum.  Keep the shield intact at all other contact points though, such as the patch panel in my case.

[Mike Bloomfield]

Thanks for the suggestions. I've attempted every possible combination of ground/ no ground connection, balanced/ unbalanced cables, connected/ not connected, mic/ no mic and still get the buzz. I've sent the unit in for examination and hopefully repair.

If I use an XLR cable with the housing of the XLR jack grounded and I touch the XLR and the chassis of the preamp together at the input point, the buzz literally disappears. I think I end up acting as a capacitor in some way and that there may be a bad cap or caps in the unit. I'll let everyone know the outcome.

[John Roberts {JR}]

As is mentioned in my first response you may want to look into "pin one problem" . This may be an actual design problem in the original unit, but somebody will have figured out how to make it right by now.

JR

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