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-   -   Need source for RCA attenuator feedthrus (http://www.diyaudio.com/forums/parts/94924-need-source-rca-attenuator-feedthrus.html)

tonyptony 23rd January 2007 11:28 PM

Need source for RCA attenuator feedthrus
 
I'd like to build my own special version of Rothwell style attenuators or Goldenjacks, but I'm having trouble finding the inetgrated M/F RCA "bodies" that you can build stuff into. Anyone know a US source for this device?

Listens2tubes 27th January 2007 11:31 PM

I'm also interested in this project. I found a simple 2 resistor attenuation scheme here: http://www.shoey.com/dat/xlr2rca.asp I am going to try the Eichmann Brass Bullet RCA's with a chassis mount female RCA jack in it's tail. It may be a bit tight depending in the female RCA jack's length. The + center post of the Bullet can be trimmed down as the hot side resistor lead can be pushed through the tip and soldered there. Which brings up the problem of how it all gets together. :eek: I would be interested in your schematic. Do you have the Rothwell spec's?

tonyptony 28th January 2007 12:41 AM

I don't have any specs for the Rothwell, other than to know they can be had in either 10dB or 14dB attenuation.

I actually was going to do the same thing you're suggesting, using Eichmanns and a female at the other end. The resistive divider scheme is simple enough; your link shows just about the only way to do it. I would just like very much to get these housings; it would make for a sturdier assembly than the method we seem both to be considering right now.

Chartal 28th January 2007 02:20 AM

Maybe this is what you looking for.
You just have to empty it and make your own.

Harrison Lab Rca In-line Attenuator / Crossover

fatmarley 28th January 2007 08:01 AM

I tried attenuating the signal in my pre amp, and the sound lost "bite". It cant be because of the type of resistors i used, because its the same ones i use throughout my system (vishay dale RN60's) . . I've also read a few threads where people tried those Rothwell jobs and didnt like them . . . Can one of you clever buggers explain why it does this?. . .

AndrewT 28th January 2007 11:38 AM

Hi,
the attenuator inserts a value of Rs that is higher than the unattenuated signal from the preamp.

The lower the attenuation the worse the added Rs becomes.

Choose the value of the resistors carefully to achieve good audio.

The problems are twofold.

The pre-amp/source must see an adequately large Zin at the receive end for the output circuits to work properly.

The power amp needs to see a source impedance for it's input filters to match the designers intended roll-off frequencies.

***If power amp Zin>=30k and DC blocking cap>=4.7uF and if Source can drive >=2k0, then it is usually possible to select resistors to suit.

eg. -20db attenuator for a Zin=50K would be series R=1k8, shunt R=200r giving Zin =2k0 and Rs=181r.
-10.2db series R=1k5, shunt R=680r, Zin=2k17, & Rs=499r
You can see that low attenuation gives a higher Rs as seen by the power amp. This value can be kept low if the pre-amp can drive a low Zin, in this case near 2k. If you increase Zin by selecting higher value resistors then Rs will increase as well and this will impact on the power amp filters. Even the values of Rs in the range 200r to 500r will roll off the treble a little early. Rs=1k could be quite severe treble cut.

If the pre & power conditions specified above *** cannot be met then attenuators will severely impact on the final response.


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