Passive Monitor Controller: First ever design from rank n00b

[undertone]

Thanks Dave for this nice explicit schematic and explanations. I'm not an engineer, but I've been DIYing simple stuff for a long time and lately I've been putting together a passive attenuator box for my balanced active speakers. I have a couple of questions:

1. I'm not sure I understand the purpose of the decoupling networks connecting pin one/circuit ground to chassis. Why are these necessary? And won't they interfere with the ground reference used for the passive step attenuators?

2. Is it common practice to leave pin 1 ground disconnected at the input of a line level balanced device? Does this mean that pin one should not normally be connected to the shell when wiring XLR connectors?

Thanks for enlightening the unwashed

u

 

[moamps]

[quote author="NewYorkDave"]Corrected "equivalent circuits" PDF has been uploaded[/quote]

)

Vout/Vin=(Rsh//Rl)/((Rsh//Rl)+Rs+4.74k)
Att(dB)=20*log(Vout/Vin)

Regards,
Milan

 

[NewYorkDave]

Well, let's see:

If Vin = 10V and Rseries=5K, Rshunt=5K and Rload=10K,

(5K ||5K) / ((5K || 5K) + 5K +4.74K) =

2.5K / (2.5K + 5K +4.74K) = .204

Vout = Vin*.204 = 2.04V

Vout/Vin = 2.04/10 = .204

In other words, you're right :wink:

I have to fire my proofreader, he misses too many typos.

Oh well, I'll go take it down again now...

 

[undertone]

[quote author="undertone"]

1. I'm not sure I understand the purpose of the decoupling networks connecting pin one/circuit ground to chassis. Why are these necessary? And won't they interfere with the ground reference used for the passive step attenuators?

2. Is it common practice to leave pin 1 ground disconnected at the input of a line level balanced device? Does this mean that pin one should not normally be connected to the shell when wiring XLR connectors?

u[/quote]

For the record, answering my own questions:

http://www.rane.com/note151.html#fig3

http://www.vandenhul.com/artpap/wiring1.htm

http://svconline.com/news/avinstall_equipment_wiring_internal/index.html

http://www.engineeringharmonics.com/papers/papers.html#
Grounding and Shielding for Sound and Video

u