My original advice still applies.

Posted by TAFKA Steve on May 16, 1999 at 15:13:48

In Reply to: Re: Sorry, should have given more details. posted by EdS on May 16, 1999 at 06:19:25:

If your going to DIY, I still recommend sticking with the EVS as a model of how it should be done. The EVS units have no selector switch, because they only have one input (and you're only using one source, right?) and one output, and there are no switch contacts in the signal path, as the hot series resistor is fixed and the ELMA rotary switch only changes the shunt resistor values. As for a chassis, EVS says that a nonconductive chassis is better sounding than a metal one (Stan Warren was adamant about this) and so it is better to get a pair of small plastic chassis boxes, one for each channel, (Rat Shack will do) and connect the input and output grounds using high quality hard-wiring.

Shallco and ELMA switches are fine choices for this application. For a series resistor with your equipment choices (if you upgrade, the MSB Link does not offer particularly high voltage output or very low output impedance), I'd start with a 10 kohm Vishay S102 with one end soldered to the hot RCA input. After the signal passes through the series resistor, it connects to both the switched attenuator as well as the hot output RCA.

For each shunt resistor value calculations, use: dB attenuation = -20 log [R1/(R1 + R2)] where R1 = shunt resistor and R2 = 10 kohm. For example, to get 12 dB of attenuation, you need a shunt resistor of 3.33 kohm. This does not include the voltage loss of the series 10k, but since the CJ amp has a high input impedance, the extra loss is small. You can go with nearest value stock resistors for your steps, or you can custom order them to precisely (1% or less) the values you want (more expensive and it will take more time to get your order filled).

Again, Michael Percy sells attenuator kits, both switch types, Vishay and Caddock, and Holco resistors, high quality input and output RCAs, etc.

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Follow Ups Full Thread

Topic - How do you make a VERY GOOD passive pre - EdS 14:24:14 05/15/99 (15)

Thanks to everyone for the input (nt) - EdS 10:45:43 05/18/99 (0)

Re: How do you make a VERY GOOD passive pre - Thorsten 10:11:51 05/17/99 (3)

Re: How do you make a VERY GOOD passive pre - AlanC 19:01:23 05/17/99 (2)

Re: How do you make a VERY GOOD passive pre - Thorsten 05:11:16 05/18/99 (1)

Since when does +18 db = passive ??? (NT) - Sean 21:57:49 05/21/99 (0)

Re: Sorry, should have given more details. - EdS 06:19:25 05/16/99 (3)

My original advice still applies. - TAFKA Steve 05/16/9915:13:48 05/16/99 (2)

Hey TAFKA Steve! - EdS 18:30:26 05/16/99 (1)

Re: Hey TAFKA Steve! - TAFKA Steve 19:51:21 05/16/99 (0)

EVS Ultimate Attenuators - TAFKA Steve 01:28:23 05/16/99 (1)

Re: EVS Ultimate Attenuators - TAFKA Steve 01:37:23 05/16/99 (0)

Re: How do you make a VERY GOOD passive pre - Joe L. 20:26:25 05/15/99 (0)

Re: How do you make a VERY GOOD passive pre - Allan 17:04:03 05/15/99 (2)

Re: How do you make a VERY GOOD passive pre - Allan 20:23:54 05/15/99 (1)

Re: How do you make a VERY GOOD passive pre - Allan 23:13:15 05/15/99 (0)

Follow Ups

My original advice still applies. - TAFKA Steve 05/16/9915:13:48 05/16/99 (2)

Hey TAFKA Steve! - EdS 18:30:26 05/16/99 (1)

Re: Hey TAFKA Steve! - TAFKA Steve 19:51:21 05/16/99 (0)

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