input attenuator for ua 1108? same as 1176...

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aryl

Active member
Joined
Sep 13, 2004
Messages
35
Location
portland, OR
i see alot of folks have been threading about attenuators for the 1176.

since the 1108 was the preamp section of the 1176, then all those threads should apply to my 1108 moduals?

i'll just start there.

its been a while since i've been on here. i sold my pair of ua's to a friend a couple years ago and recently bought them back.

i really don't want to go mucking with the curcuit(i may recap it soon, though). an input attenuator makes alo of sense. i do remember having some distortion issues when i was using it.

$50 for a three step attenuator from shure is rediculas.

if you have any thoughts, feel free to reply. i'm not against a stepped attenuator. thinking a -5 to -25 in 5db steps... it seems i can just move the mic to adjust within that range.

i mean, if you think that smaller incruments is crucial, say something.

i want to build something myself, but i must admit all the jargon and tech talk is still confusing.

david
 
you want something like the Shure circuit for mics, not a 600 ohm T. there's a ton of posts here about this.
 
I would expect you would want continuously variable, so you can dial in a level on the fly. It would just aggravate me to have to go move a mic to prevent clipping, especially since the clipping usually appears after you roll and the drummer gets excited and plays harder.

Variable%2020dB%20PAD.gif
 
...ok. a log pot and an audio taper pot are the same thing.

after a minor bit of reading am i to understand that the purpose of the duial pot is that is easier to make a log(or audio taper) pot out of two lineat pots than get the correct curve out of one?

david
 
...ok. a log pot and an audio taper pot are the same thing.

after a minor bit of reading am i to understand that the purpose of the duial pot is that is easier to make a log(or audio taper) pot out of two lineat pots than get the correct curve out of one?

david
 
There's a long drawn out back and forth between JLM and I about that attenuator.

http://www.groupdiy.com/index.php?topic=14888&start=15

David; the purpose of a dual pot is this is a variable U pad so you need two (variable here) series legs and one shunt.
 
It always seemed like a hack to me, but you are already hacking. With fixed gain modules, either you insert a volume control between two stages, or some combination of input output padding. There is always a noise penalty, and an impedance compromise that can affect mics sensitive to loading.

The other common solution is the pot after the input transformer, serving as both a resistive load and a voltage divider (volume pot). As seen here: http://jlmaudio.com/JLM1272simplemod.pdf

EDIT: Important to note the pot-on-secondary approach compromises signal to noise.
 
thoughts:
-one of the most appealing aspects of the attenuator is that i don't have to hack the curcuit.
-i'm wondering how they were setup originally. they must of had some way of regulating the input.
-has anyone ever heard one with the ldr?
 
People weren't loud back then; they needed all the gain, or they used a fixed pad up front. They fed a console fader, so there was the fine tuning. EVERYTHING used to be fixed gain blocks. I use ALMOST NOTHING BUT old fixed gain preamps with 20 db pads in front. It's just a different technical approach. I was about to mention the LDR version; haven't heard it. But that was what they suggested in this case. I'm sure the input transformer can be overloaded too, and needs an input pad up front in some cases. You can't get away from that one with a lot of old gear. Even a new Jensen mic input transformer will have a 0 dBm rating which a hot condenser will overdrive. A lot of modern recording technique with condensers really requires low gain line amps with phantom power, versus mic preamps with a lot of gain.
 
ok, the faders the old guys used were variable attenuators for the output and they just used fixed pads for the input if needed. i guess they relyed more on mic placement for proper levels.
currently i'm going to be using the pres through an audio interface into a laptop. the input controls will be my output attenuators.

at 45 or 50db gain it seems like a 20db pad will be more than what i need most of the time. i'm leaning back toward the stepped attenuator.

anything inbetween the mic and the transformer will be a "compromise". though, huh?

jlm, have you used an 1108 with this pad or known anyone who has?
that is more important than, "well, the way i understand the theory...."

thank you for your interest in this thread.
 
dig around here some more. this has been gone over a billion times. your questions have been addressed definitively already.
 
Here's an old thread I dredged up with good discussion of these tradeoffs:

http://www.groupdiy.com/index.php?topic=2192

Just plug "input output pad" into the search tool, and you will get a slew of threads.

EDIT: It also helps to search on member names like "PRR", "NewYorkDave", and "emrr". These guys have discussed extensively and you can benefit from their knowledge and experience.
 

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