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Pad after mic pre (jts ma 123??)

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Pad after mic pre (jts ma 123??)

Postby Guitarking » Sat Sep 08, 2018 7:55 am

I've been experimenting with a Pre73 mic pre. I must say I find the difference between going straight into my RME babyface with my SM57 on a guitar cab and putting the PRE73 in between quite small. It think I will hear more difference when I crank the preamp, but than I overload my RME.
So I'd like to have some pad in between. I don't want to spend a lot of money as it' s only an experiment.
I found the JTS MA 123, an inline mic attenuator.

My questions are:
1. is it normal that the addition of the PRE73 doesn't yield a big change in sound?
2. is the JTS MA 123 a nice thing to buy to experiment with AFTER the preamp? I'm worried because it's advertised as a MIC attenuator. Does this mean putting it after the micpre will give problems, e.g. because of impedance issues?

Best regards!
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Re: Pad after mic pre (jts ma 123??)

Postby Hugh Robjohns » Sat Sep 08, 2018 8:58 am

Guitarking wrote:1. is it normal that the addition of the PRE73 doesn't yield a big change in sound?

Yes. The difference in sound between budget and high-end, or modern and vintage, preamps is often very subtle when used conservatively. (Read the SOS preamp shoot out from a few years back) Much of the character comes only when the preamp is driven quite hard.

2. is the JTS MA 123 a nice thing to buy to experiment with AFTER the preamp? I'm worried because it's advertised as a MIC attenuator. Does this mean putting it after the micpre will give problems, e.g. because of impedance issues?

Quite possibly. It presents an impedance of 1.6k to the preamp which is rather low and might result in a loss of treble and transient distortion.... although these might be effects you like! :-)

In cases where the preamp doesn't have an output fader I usually build a balanced passive attenuator with a few resistors, but if i want a variable pad i will plug in a nanopatch passive monitor controller. It's just a potentiometer in a box, but the impedances are right for line level devices.
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Re: Pad after mic pre (jts ma 123??)

Postby Guitarking » Sat Sep 08, 2018 9:41 am

Thank you Hugh!

Can you tell me how to build this passive attenuator to put behind the preamp? I do have some soldering skills, and if it's only a few resistors I might manage!
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Re: Pad after mic pre (jts ma 123??)

Postby ConcertinaChap » Sat Sep 08, 2018 2:19 pm

Hugh Robjohns wrote:but if i want a variable pad i will plug in a nanopatch passive monitor controller. It's just a potentiometer in a box, but the impedances are right for line level devices.

Of course! As soon as someone says it it's obvious. It's a neat idea and I'll remember it. Thanks.

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Re: Pad after mic pre (jts ma 123??)

Postby Guitarking » Sat Sep 08, 2018 3:54 pm

Hugh,

In addition to my previous question about how to make such a diy in line attenuator with resistors, i was wondering about the Shure a15as inline attenuator that i came across. It is advertized by being able to sit between mic and mic pre and mic pre and interface but i am puzzled. How can it cope with multiple impedances? Also its quite expensive considering one can make a diy.
Also, the diy you suggested is for mic pre to interface only, right? Is there also a diy for mic (condensers too) to mic pre?

Thanks again!!
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Re: Pad after mic pre (jts ma 123??)

Postby Hugh Robjohns » Sat Sep 08, 2018 5:04 pm

Guitarking wrote:In addition to my previous question about how to make such a diy in line attenuator with resistors, i was wondering about the Shure a15as inline attenuator that i came across. It is advertized by being able to sit between mic and mic pre and mic pre and interface but i am puzzled. How can it cope with multiple impedances?

I'm actually away on holiday right now, struggling to post from a phone... so writing a treatise on attenuators doesnt appeal... and anyway, there's plenty of stuff online for calculating all manner of balanced attenuators. Aim for 10 to 15dB (20dB is probably too much unless you plan to really cane the preamp).

The Shure attenuator has an input impedance of 1k. It can be used between pre and interface, just as your first suggestion can, but there is again the possibility of hf loss and transient distortion, depending on the design of the preamp's output.
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Re: Pad after mic pre (jts ma 123??)

Postby Kwackman » Sat Sep 08, 2018 5:16 pm

Hugh Robjohns wrote:I'm actually away on holiday right now, struggling to post from a phone...

I don't mean this to sound patronising, but....
You are on holiday, so give your brain a rest and stay away from the forums!
There must be bars/restaurants where you can spend lots of time not thinking about tech things?!
Enjoy the holiday, all this stuff will still be waiting for you when you return! :D
Here endeth the sermon.
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Re: Pad after mic pre (jts ma 123??)

Postby ConcertinaChap » Sat Sep 08, 2018 7:03 pm

Image

He's right, you know :)

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Re: Pad after mic pre (jts ma 123??)

Postby Hugh Robjohns » Sat Sep 08, 2018 8:18 pm

:lol: :beamup:
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Re: Pad after mic pre (jts ma 123??)

Postby Guitarking » Sat Sep 08, 2018 8:41 pm

Enjoy Hugh!!
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Re: Pad after mic pre (jts ma 123??)

Postby ef37a » Sat Sep 08, 2018 9:04 pm

Guitar King, if you want to PM me I can then email some circuits and tips to you.

And yes! Ditch the phone Hugh!

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Re: Pad after mic pre (jts ma 123??)

Postby Guitarking » Sun Sep 09, 2018 6:21 am

Thank you ef37a!!

Is it possible to use a mixer like Mackie vlz and use its insert as a line level attenuator?
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Re: Pad after mic pre (jts ma 123??)

Postby ef37a » Sun Sep 09, 2018 7:13 am

Guitarking wrote:Thank you ef37a!!

Is it possible to use a mixer like Mackie vlz and use its insert as a line level attenuator?

Well, unbalanced (single TRS) inserts come out at internal mixer level, often -2dBu (615mV) and taken just post the mic/line amplifier but pre channel fader so yes, if you mean a LINE signal into the mixer you would get attenuation by keeping the line gain low.

However, the through signal in the mixer would also be low and that might cause noise problems.

Got the PM btw, reply sent.

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