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Old 6th August 2007, 07:27 PM   #41
anatech is offline anatech  Canada
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Hi fotios,
Quote:
Chris, do you know how many times i have seen this resistor of 10 which connect the gnd to earth (yet of fireproof type) burned?
I've seen that as well. You are thinking of a different location for the resistor. Still, the resistor from the main audio ground to case / mains ground should be used. It is a mis-connection that burns these out. So there are already problems that cause the damage. You can't blame it on that poor resistor. It is only like a canary in a coal mine.

I was suggesting that a small value resistor in series with one RCA ground will kill a ground loop, but you shouldn't have one to begin with.

-Chris
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Old 6th August 2007, 08:14 PM   #42
fotios is offline fotios  Greece
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Quote:
Originally posted by anatech
Hi fotios,
I have no problem with the NE5532. It is at it's best in lower impedance circuits whereas in higher impedance circuits, a FET input op amp usually will have lower noise and DC offset. So it's a case of "it depends" on what you are doing with it. The OP275 is a nice little dual op amp. Not expensive either.

In your conceptual diagram, you are presenting a nice view of a perfect world. Life isn't like that. Personally, I don't care too much for the RCA connection system. What might be better is something based on a shielded L, R and common conductors. The shields only connected to the source side. In this way you can have common signal grounds and proper shields. A new system for this type of signal flow would differentiate it from the more common RCA system. A five conductor or three conductor XLR plug would work. I find the five conductor DIN too light for most cables. The three conductor DIN is pretty much reserved for power connections (at least that is what I think when I see one).

In short, without changing the connector type, you are stuck with common grounds at each connection. That is the standard.

-Chris
As i understand you propose the use of a 3p XLR plug with a usual mic cable (2 conductors + shielding) for transporting the L & R channels commonly in the same cable. Indeed this is a practical and economical solution (how many costs a ready made microphone cable at last). But this is for me and a little number of other persons. Go to say this idea in the majority of others! Do you think the criticism that you will hear? This practice is used commonly in all profesional mixing desks. Also this preposes that the output of source must be also a simple 3p XLR or a stereo jack socket. I have not see yet a such output in any CD player etc.
And again the P.S. gnd node must be earthed only and only in one device of reproduction chain, or else the gnd loop will be formed again. When i worked as sound engineer remember well that i maked cutting of the shield in each XLR plug arrived in the mixing desk from the far located power amplifiers due to loud buzz caused from the big length of gnd loop created because as the mixing desk as the amplifiers they have earthed their grounds. So the earthing of gnd it taked place in the power amplifiers only. Some amplifiers have for accommodation a gnd lift switch. For the same reason the D.I. boxes have a same switch. I have seen also a such switch on some XLR plugs.
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Old 6th August 2007, 09:31 PM   #43
anatech is offline anatech  Canada
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Hi fotios,
No. The cable would contain: L channel shielded, right channel shielded, the common reference shielded. The originating end would require a for or five conductor connector.

Grounds are funny. I had an associate that went into a studio and soldered every XLR common to the chassis connection on every XLR jack on a 24 track tape machine. He called it "Euro-grounding". I called it stupid and disconnected all the shorting connections. The idiots had mounted the new tape machine directly on the other side of the unit 550 VAC transformer. Moving the machine solved the hum problem.

Anyway, I've worked in many recording studios, jingle studios, voice over, effects ..... Most have grounding issues of some sort. One I had to put back on -10 dBu RCA's due to loose interpretations on what a +4 dBm system is. That solved every problem they had. I'm also very familiar with large PA systems and telephone systems (interfacing as well) and very high end audio systems. As long as you stay on a reasonable system you should not have problems with ground loops.

-Chris
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Old 6th August 2007, 10:34 PM   #44
fotios is offline fotios  Greece
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Quote:
Originally posted by anatech
Hi fotios,
No. The cable would contain: L channel shielded, right channel shielded, the common reference shielded. The originating end would require a for or five conductor connector.

Grounds are funny. I had an associate that went into a studio and soldered every XLR common to the chassis connection on every XLR jack on a 24 track tape machine. He called it "Euro-grounding". I called it stupid and disconnected all the shorting connections. The idiots had mounted the new tape machine directly on the other side of the unit 550 VAC transformer. Moving the machine solved the hum problem.

Anyway, I've worked in many recording studios, jingle studios, voice over, effects ..... Most have grounding issues of some sort. One I had to put back on -10 dBu RCA's due to loose interpretations on what a +4 dBm system is. That solved every problem they had. I'm also very familiar with large PA systems and telephone systems (interfacing as well) and very high end audio systems. As long as you stay on a reasonable system you should not have problems with ground loops.

-Chris
But yet your suggestion Chris seems to work fine with only one XLR or stereo jack as i think. I maked a rough draft and proved this. Of course under the condition of not shorted the gnd conductor with the metal case of the plugs or sockets (as maked your associate!!). As for the dBu, dBm, dBs, dBV etc. it is a crazy world. I have in my bookshelf for 15 years a nice book named: "Sound System Engineering" of Davis & Davis and when i have a query with the interpreting of such units in volts i solve it with the aid of this book. But in generally i am familliar with dBV because it is the simplest unit expressed directly as a voltage ratio (this "shickness" owed on a big part in Peavey). If it is permitted in the thread of other person can you tell me your opinion about MJE171-MJE181 and MJD44H11-MJD45H11? Have you engaged some time with these transistors? I will explain you later my aim with these devices.
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Old 7th August 2007, 02:58 AM   #45
anatech is offline anatech  Canada
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Hi fotios,
Quote:
But yet your suggestion Chris seems to work fine with only one XLR or stereo jack as i think.
Yes, exactly. It must be idiot proof and fool proof. I don't know how to make things know-it-all proof yet.

Quote:
If it is permitted in the thread of other person can you tell me your opinion about MJE171-MJE181 and MJD44H11-MJD45H11?
If this gets involved we can split it out. A little O.T. can be tolerated.
I like the MJE parts very much. I typically use higher voltage parts but these would work well as a headphone amplifier output. The MJD package I don't use. I try to stick with larger standard packages as much as possible. This to maximize cooling of the package and allow more possible substitutions if the need arises. The parts are reliable.

Quote:
As for the dBu, dBm, dBs, dBV etc. it is a crazy world.
Yes, too much confusion. We did need to differentiate between straight voltage ratios and those involving impedance (a power ratio really). Can you imagine having to do impedance corrections all the blinking time? Calibration would be a nightmare.

I haven't heard of dBs before. Do I want to know?

-Chris
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Old 9th August 2007, 12:27 AM   #46
fotios is offline fotios  Greece
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Default Re: Pre schematic

Quote:
Originally posted by Tex Houston
and the pre....
Hi Tex
At last, today i did get what this schematic remind to me. This arrangement with seperate IC in each input it is exactly as a dj mixing desk, with the difference that have removed the mixing and the crossfade sliders and in her places have mounted the input selection relays.
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Old 2nd July 2013, 10:37 AM   #47
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Default Buzzing Hum

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Originally Posted by Tex Houston View Post
It's a buzzing hum at low levels, pretty quiet mid turn and kindy hissy at full volume. Preamp and power supply are connected to star ground as is the volume pot through it's connection to the front panel. Layout OK?
First of all I would say that the auxillary part of the power supply must be very unstable as there only seems to be only a 1 uf capacitor (c11) to filter the ac ripple from the wire which is going to the collector and base of transistors (q1 and q3). What does this auxillary power supply power? audio circuits? I would recommend trying a bigger capacitor for c11 (1000 uf would be a good start). Other than this you should keep all of the signal wires short and well away from wires which carry high currents such as the power supply wires as they have a magnetic field around them. If neccessary shield the audio cables. Another thing to look into is RF instability does your circuit effectively filter out RF interference. Also keep your transformer well away from the audio circuitry especially as this is a preamplifier circuit. I would also use a lower value pot as a higher value pot can cause resistor noise as well as rolling off the high frequencies resulting a in a duller sound. The resistance of the pot and capacitance between the tracks and the contacts coupled with the input capacitance of the input circuit could create a low pass filter.

Last edited by AudioEngineer; 2nd July 2013 at 10:41 AM.
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