200R Bridged T Pad Attenuator for Drip Ultra.47 PreAmplifier

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DonnieDarko

Well-known member
Joined
May 26, 2012
Messages
125
Hey guys,

I´m currently finishing up a  pair of Gregory´s Ultra.47 PreAmps.

For them, I purchased his  (insanely expensive) PCBs for a stepped Brigded-T-Pad-Attenuator:

https://vimeo.com/156996117

They have a BOM for setting them up as 600R, but for the PreAmp I need 200R Attenuators.

I wonder if someone round here has a excel sheet on the shelf from a previous build for a 24pos 200 R Bridged T Pad Attenuator with 2db steps?  I mean, in this universe, recently almost everything is possible, right?

Any help would be appreciated! :)
 
Can't open it at the moment, although seems like it is what you need. Send me pm and i will mail it to you. Drip should help people build what he sells, too many fall into this trap... Hope you have schematic because this site explains it well, it is good to understand:
http://www.uneeda-audio.com/pads/
Btw, it is possible to have nicely controled and properly functioned R47 with -20dB pad at the input and 6 position output pad. Even 1k pot works well ime, there are other options too. 

I never understood why would anyone search for 10K:200 instead of more common 30k:600 trafo, if both have the same ratio and should work the same. Trafo only reflects impedances, so it seems i don't get it at all, or somebody else doesn't. I'm thinking about it for some time, would someone please explain it?
 
I don't see why anyone would slavishly recreate a 200 ohm output just because the original was.  And.  The thing has no headroom anyway, there's no reason to attenuate the output.  You can squarewave it well before you clip a converter. 
 
Hey guys,

He is using the attenuator on the input, as described in this pdf:

https://ws.onehub.com/files/66fez4qy


 
Thanks for explanation Emrr, it is appreciated as always.
Donnie Darko; two pads at the input in series seem very strange, even if i don't go into details how they are designed (it is late here, both seem T pads, why series, etc...). This preamps works great with one ~ -20dB U pad at the input and like it was said, no output pad without troubles in everyday use.
We had lenghty discussions about impedance problems with lower than ~ -15dB pads at the mic inputs, although many companies go lower without complains from users.
On rare occassions -40dB input comes handy, although wouldn't really want to put it as a switch on front panel. Some people treat Redd.47 like magical machine when it is high quality mic amp for its time. Imo a lot of controls are needed on preamps/distortion boxes like Rude Tube designed by our members.
Some people want output pad on Redd.47 without really trying why, so i prefer soldering it into short cable, or use small plastic box with a piece of veroboard between two sides for Os, Ts, etc. Us that are mostly used can be soldered quite durable directly into connectors when using two resistors in // instead of one for series, shunt can be one, this makes it more durable when going this way. Of course it is still normal U pad, Rs in // are for durability...

Phaedrus Audio has small section about levels in this preamp, original EMI or Mr. Hinson's docs somewhere on the net too:
http://www.phaedrus-audio.com/Phab,%20Phame%20and%20PHI%20Manual_Issue1.1_June%202011_(mono).pdf

 
That is a terrible idea for mic use. 

Ok for line use. 

All reasons discussed and put to bed decades ago. 

DonnieDarko said:
Hey guys,

He is using the attenuator on the input, as described in this pdf:

https://ws.onehub.com/files/66fez4qy

 

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