Topic: ? about resisters

[rowjimmytour]

I made these patch cables for my R4 w/ built in -20dB pads and I was wondering if there is such thing as matching resisters.I bought my resisters at ratshack and one of the cables I have to add about 4-5 notches of gain to get the channels even. After listening to my matrix mix I can not tell any difference but was wondering if this is common w/ resisters. I used two 680 ohm 4% resisiters and one 150 ohm 4% resister and I have one 680>pin 1, 680>pin2, and 150>pin2>pin3. Really what I am wondering is should I leave it like it is or could I do better? I am going to buy some extension cables for SDB feed soon and plan on going rca(F)>rca(M) but if I could do better I would just go XLR(M) right>rca(M). Thanks in advance for any input.
PEace

[rowjimmytour]

It's good to have matched resistors in a balanced circuit, but a 4% tolerance shouldn't create a large difference in gain.  In fact, it shouldn't even be noticeable.  I would check to see if you swapped a 150 for a 680, or vice versa, in one of the cables.

I am 99.9% I did not swap a 150 for a 660 but I am not so sure if I installed the resisters all in the same direction w/ color code. If I did this would it make this much difference in the gain?
Peace

[Roving Sign]

No offense - but wouldn't the optimal cabling be a RCA > 1/4 TS? - The R4 is equipped to accept unbalanced line inputs

The XLR ins might be expecting to see a mic level signal - thus the need for the resistors....line level is too hot.

[rowjimmytour]

No offense - but wouldn't the optimal cabling be a RCA > 1/4 TS? - The R4 is equipped to accept unbalanced line inputs

The XLR ins might be expecting to see a mic level signal - thus the need for the resistors....line level is too hot.

I tried it w/ 1/4" line in and the signal was still hot and the reason I have the rca cable was my matrix on the fly w/ the UA5 I had before so I swapped one end rca w/ XLR and bubilt in pad.
Peace

[Patrick]

Cheaper resistors (like those bought at Radio Shack) have a much wider tolerance than other more expensive brands that are bought in wholesale by manufacturers.  This defintiely could account for a difference in gain, it sounds like you just picked two resistors that are at opposite ends of the "tolerance" spectrum, if that makes sense.  As long as you can match gain on the R4, and don't hear any sonic differences between the two channels, I'd say just roll with it.

[rowjimmytour]

Cheaper resistors (like those bought at Radio Shack) have a much wider tolerance than other more expensive brands that are bought in wholesale by manufacturers.  This defintiely could account for a difference in gain, it sounds like you just picked two resistors that are at opposite ends of the "tolerance" spectrum, if that makes sense.  As long as you can match gain on the R4, and don't hear any sonic differences between the two channels, I'd say just roll with it.

+t and thats what I thought but I was about to add 15' extension cords to my patch cables and was wondering if I should start over or just go rca(f)>rca(m) but like you say W/ gain I can match the channel and more important the signal is not hot and brick walling now.
Peace

[attheshow]

The way to get matched resistors is to buy the lowest tolerance (1% or 2%) you can find, buy extra, and measure the resistance with a multimeter. Use the ones that give the closest reading. Good luck!

[rowjimmytour]

I'm not sure exactly what you are trying with the XLR connector, is the 680 in series with pin 1?  That seems odd.  Anyway, the worst case scenario with a 680/150 L-pad and 4% tolerance would be about 1dB difference.  Worst case with 10% tolerance, which is very unusual to find these days, is about 3.5dB.  I don't know how much 4 or 5 notches of gain is, but I expect it's a lot more than that.  You have a wiring error or an incorrect resistor value somewhere.

-20dB pad wired in XLR connecter
Pin 1>680>Shield
Pin2>680>Blue(hot)
Pin2,3>150>White pin 3(neutral)
I think I am going to try again and match them more evenly even though I can't hear a difference now adjusting the gain more/less. I can tell the pad is working because the signal has cooled off big time.
Peace

[rowjimmytour]

2/nd time out last night they worked perfect and both channels were balanced perfectly. I think the fact the 1/st time I went out I ran out of R9(phonejack)>1/8"stereo>RCA>XLR>R4. Not sure why maybe but good news is my pads work perfect.
Peace

[DSatz]

A cuppla things--

If you have an unbalanced signal source and a choice to connect it to either a balanced or an unbalanced input, where the sensitivity and overload levels are equal in either case--then it's preferable to use the balanced input. Its common mode signal rejection will give you better immunity to noise from interference in the cable, PROVIDED that you use balanced cabling to make the connection.

Many people don't realize that a balanced input can give you noise immunity even if your signal source is unbalanced. But in order to get it, you MUST run a balanced cable from the signal source. To create this condition, find out the source impedance (output impedance) of the unbalanced device that's providing the signal, and then in your adapter from unbalanced to balanced (which MUST be at the "driving" end of the cable), provide that same impedance as precisely as you can between ground and the "cold" wire (the signal wire that you're not connecting to the output of your unbalanced device). Voila--much better noise immunity.

Secondly, the impedances of a symmetrical resistive pad become, in effect, part of the balanced input circuit of the preamp / recorder / mixer that you're coupling your signal into. It is for that reason that you want to match the values of the two series resistors in each pad to each other as closely as you can. Otherwise you throw off the balance of the circuit, and the common mode signal rejection of the input will be reduced--thus making the cable much more vulnerable to interference.

I would suggest matching the resistors of each pad to within a very few Ohms of each other if you can. It doesn't usually matter much if the two pads in a pair don't have absolutely identical loss; a fraction of a dB one way or the other can even be used to your advantage, to reduce the inequality of sensitivity which nearly any two microphones will have--even a "matched pair." For that matter the record level controls of most preamps are only approximate in their calibration, so the "35 dB gain" setting may well be +/- 1 or 2 dB.

--best regards

[jerryfreak]

dsatz, i have the unbalanced schoeps cmrs on the way, and wanted to be able to use them with a v2/v3 as well.
so youre saying that basically i could run balanced mic cable almost up to the mic bodies/battery box, then unground the -leg of the balanced connection to ground right near the mics via a resistor with the right 'impedance'. (I have to admit, i'm not an EE and i dont really understand the concept of impedance tho i know in some cases it can essentially be treated as 'resistance' as it becomes linear and also the units are in ohms, like resistance.). how do you measure the correct impedance.

specsheets say the following:

v3 input impedance: 3kohm
v3 Minimum Load Impedance 600 Ohms
cmr output impedance: 15 Ohms at 1 kHz

how to match?

A cuppla things--

If you have an unbalanced signal source and a choice to connect it to either a balanced or an unbalanced input, where the sensitivity and overload levels are equal in either case--then it's preferable to use the balanced input. Its common mode signal rejection will give you better immunity to noise from interference in the cable, PROVIDED that you use balanced cabling to make the connection.

Many people don't realize that a balanced input can give you noise immunity even if your signal source is unbalanced. But in order to get it, you MUST run a balanced cable from the signal source. To create this condition, find out the source impedance (output impedance) of the unbalanced device that's providing the signal, and then in your adapter from unbalanced to balanced (which MUST be at the "driving" end of the cable), provide that same impedance as precisely as you can between ground and the "cold" wire (the signal wire that you're not connecting to the output of your unbalanced device). Voila--much better noise immunity.

Secondly, the impedances of a symmetrical resistive pad become, in effect, part of the balanced input circuit of the preamp / recorder / mixer that you're coupling your signal into. It is for that reason that you want to match the values of the two series resistors in each pad to each other as closely as you can. Otherwise you throw off the balance of the circuit, and the common mode signal rejection of the input will be reduced--thus making the cable much more vulnerable to interference.

I would suggest matching the resistors of each pad to within a very few Ohms of each other if you can. It doesn't usually matter much if the two pads in a pair don't have absolutely identical loss; a fraction of a dB one way or the other can even be used to your advantage, to reduce the inequality of sensitivity which nearly any two microphones will have--even a "matched pair." For that matter the record level controls of most preamps are only approximate in their calibration, so the "35 dB gain" setting may well be +/- 1 or 2 dB.

--best regards

[Church-Audio]

dsatz, i have the unbalanced schoeps cmrs on the way, and wanted to be able to use them with a v2/v3 as well.
so youre saying that basically i could run balanced mic cable almost up to the mic bodies/battery box, then unground the -leg of the balanced connection to ground right near the mics via a resistor with the right 'impedance'. (I have to admit, i'm not an EE and i dont really understand the concept of impedance tho i know in some cases it can essentially be treated as 'resistance' as it becomes linear and also the units are in ohms, like resistance.). how do you measure the correct impedance.

specsheets say the following:

v3 input impedance: 3kohm
v3 Minimum Load Impedance 600 Ohms
cmr output impedance: 15 Ohms at 1 kHz

how to match?

A cuppla things--

If you have an unbalanced signal source and a choice to connect it to either a balanced or an unbalanced input, where the sensitivity and overload levels are equal in either case--then it's preferable to use the balanced input. Its common mode signal rejection will give you better immunity to noise from interference in the cable, PROVIDED that you use balanced cabling to make the connection.

Many people don't realize that a balanced input can give you noise immunity even if your signal source is unbalanced. But in order to get it, you MUST run a balanced cable from the signal source. To create this condition, find out the source impedance (output impedance) of the unbalanced device that's providing the signal, and then in your adapter from unbalanced to balanced (which MUST be at the "driving" end of the cable), provide that same impedance as precisely as you can between ground and the "cold" wire (the signal wire that you're not connecting to the output of your unbalanced device). Voila--much better noise immunity.

Secondly, the impedances of a symmetrical resistive pad become, in effect, part of the balanced input circuit of the preamp / recorder / mixer that you're coupling your signal into. It is for that reason that you want to match the values of the two series resistors in each pad to each other as closely as you can. Otherwise you throw off the balance of the circuit, and the common mode signal rejection of the input will be reduced--thus making the cable much more vulnerable to interference.

I would suggest matching the resistors of each pad to within a very few Ohms of each other if you can. It doesn't usually matter much if the two pads in a pair don't have absolutely identical loss; a fraction of a dB one way or the other can even be used to your advantage, to reduce the inequality of sensitivity which nearly any two microphones will have--even a "matched pair." For that matter the record level controls of most preamps are only approximate in their calibration, so the "35 dB gain" setting may well be +/- 1 or 2 dB.

--best regards

What dsatz is talking about is a twisted pair. But this only works in ideal conditions.. And its not a good idea for mic sources. If you had a preamp boosting the signal of the mics you could use a twisted pair on the output of the mic preamp * if it was balanced * and get the same results as balanced. But again this does not work for low level signals.. All your doing is connecting the + of the balanced line to the hot on the unbalanced signal and the - to ground on your device.. This method works for signals that have like impedance but not very well for high into low for example. This link talks about the subject that dSatz referred to. It also mentions the term LINE LEVEL meaning again this is not something you ever do with a mic level signal. It would be hard in most cases because you would need the ground for passing phantom anyway.

http://www.dplay.com/dv/files/fig2.pdf
Chris

[Church-Audio]

It's good to have matched resistors in a balanced circuit, but a 4% tolerance shouldn't create a large difference in gain.  In fact, it shouldn't even be noticeable.  I would check to see if you swapped a 150 for a 680, or vice versa, in one of the cables.

I am 99.9% I did not swap a 150 for a 660 but I am not so sure if I installed the resisters all in the same direction w/ color code. If I did this would it make this much difference in the gain?
Peace

You can buy metal film 1% resistors from digikey.. Metal film is important for audio as they tend to have less noise.. This is not so much an issue with a high gain source. But for anything of value its always best to spend a few extra bucks. Also if you get 1% resistors they will be ok to use with out having to match them but again if you have a meter why not match them.

[DSatz]

jerryfreak, yes, I'm saying that the "sooner" (in terms of the progression of the signals from microphones to your V2/V3 or whatever) you convert to balanced, the better. To be balanced doesn't require a signal on the wire--it's an impedance condition. Plenty of balanced microphones these days (all transformerless Neumanns, for example) are driven on only one wire.

--best regards

P.S.: I frankly don't understand Chris' (Church Audio's) objections, and suspect that he misunderstood something that I said. Of course the conductors in a balanced microphone cable are twisted--that is a much more effective way of resisting interference than even the shield is. ??

[aegert]

Dsatz is right on ... You must use 1% resistors and match all for both cables to ensure a consistent pad L vs R channel

For all here is a handy link for making pad circuits both Pi and T... I find its easier to put the pi circuit in a cable connector... The Pad should be on the end of the cable down stream...

http://my.athenet.net/~multiplx/cgi-bin/att_pad.main.cgi

A :-)