Two 1/2 db and eight one db pads needed

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Two 1/2 db and eight one db pads needed

Postby Ski Spiggy » Sun Apr 29, 2018 9:31 am

Hi. I want to be able to step down the output of my buss compressor so to make it match the input level of my AD converter. Is anyone on this forum able to do make pads? Or do you know anyone who can make pads?

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Re: Two 1/2 db and eight one db pads needed

Postby chrisp » Sun Apr 29, 2018 4:53 pm

Pads are dead easy, you can build them into the cable plugs if you'd like. Balanced, or unbalanced, XLR or TRS for your connectors?

But, not sure why you need them. A bus compressor should be able to tame the input signal and dropping the makeup gain should address the returns to the AD. It sounds more like a gain staging solution to me rather than these relatively small db pads - a typical pad is more often 10 to 20db to drop, say, +4dbu to -10dbv, or to drop line level to mic level. Half or one db doesn't sound like it needs a pad solution. Perhaps describe more to us what your issue is and I'm sure the Trock family can help.
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Re: Two 1/2 db and eight one db pads needed

Postby Ski Spiggy » Tue May 01, 2018 8:50 am

The tone for this album is dialed and I'm using an api 2500 as the master buss comp. I changed AD converters and the new converter input gain is too hot. I have many 10db and 20db pads. I need 1/2db and 1 db pads.
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Re: Two 1/2 db and eight one db pads needed

Postby Text_Edifice » Tue May 01, 2018 6:06 pm

Hi James - just because building the pads is a fiddly exercise can I ask the dumb question: why don't you just pull down the output on your api makeup gain?

If you can't do that and don't have a master fader in your path there's really not that much difference between tracking your mix with peaks at -6dBFS and right up to the line. If you're mixing at 24Bit the difference is probably way down under the noise floor of the api anyway. So a 6dB pad would work fine.
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Re: Two 1/2 db and eight one db pads needed

Postby chrisp » Tue May 01, 2018 7:02 pm

OK. If it were me I'd look to tweak that manual Gain control if the output of the API is too hot, but if you're keen to look into pads ...

Great resource: http://www.uneeda-audio.com/pads/

Looking at the Balanced U configuration,

For a 1db Pad : k=10^(1/20) = 1.122, I'd be looking at Rshunt of 10K, so Rseries = 10K * (1.122 - 1) = 1220 ohms, divide by 2 (because in a U pad there are 2 series resistors) gives you 610 ohms, nearest real world value 620 ohms. Working backwards using 620 ohm series resistors, k = 1 + ((2 x 620)/10000) = 1.124, db pad value = 20 x log(k) = 1.015 db. So what you need in the U diagram is a 1% 1/2watt metal film resistors from Jaycar, 10K ohm for R2 and 620 ohm for each the R1/2.

Do the same for a 0.5db Pad and what you get (real world values) is 10000 ohm for R2 and 270 ohm for each the R1/2, giving a theorectical pad value of 0.46 db.

HOWEVER, please take the time to read the article because these values may not deliver what you want when dealing with tiny pad values in the real world. Note in particular the following extract -

Practically speaking, the absolute loss is determined by the parallel combination of the shunt resistor and the input impedance of the mike preamp. Since the preamp bridges the shunt resistor, the actual loss is slightly greater than calculated (less than 1dB). For loss values less than 20 dB, you may have to raise the value of the shunt resistor to make the series resistors large enough to not excessively load the source. In that case, the contribution of the preamp's input impedance to the attenuation error will increase.


In other words, the lower the pad db value, the more the resistor values become subject to the specifics of the equipment involved (the comp and the DA) and less predictable using theoretical formulae!

On the other hand, a pack of eight resistors from Jaycar is 55c, so you are looking at $1.65 plus soldering time to wire up a pad inside an XLR socket and see if it works (put the pad between pins 2 and 3).
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Re: Two 1/2 db and eight one db pads needed

Postby Ski Spiggy » Tue May 01, 2018 10:26 pm

Thanks guys. Yep, I get the question. Why not just turn the output down. I'm using the 2500 in old mode. That means the output directly effects the tone. The tone, set up with different converters, is superb.
I'm using a Lyra 2 now. And comprmising by running the signal through the mic pres with the pads engaged and at their lowest volume.
It sounds really good, but I'd far prefer to not go though the mic pre.

As to me making the pads, I know my limitations. I make/build many things. But working out the math and engineering of making pads, is not me.
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Re: Two 1/2 db and eight one db pads needed

Postby Wiz » Wed May 02, 2018 7:51 am

Rob?
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Re: Two 1/2 db and eight one db pads needed

Postby Text_Edifice » Wed May 02, 2018 9:02 am

Hi James,

again, dumb question but why aren't you plugging the API into the line inputs?
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Re: Two 1/2 db and eight one db pads needed

Postby chrisp » Wed May 02, 2018 10:08 am

As to me making the pads, I know my limitations. I make/build many things. But working out the math and engineering of making pads, is not me.


Does this help?

small pads.png
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Re: Two 1/2 db and eight one db pads needed

Postby rob » Sun May 06, 2018 9:21 am

use the line inputs
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Re: Two 1/2 db and eight one db pads needed

Postby Ski Spiggy » Tue May 08, 2018 9:15 am

To Rob for the pads. You are awesome!!!!!!
To Rob and the others on using the line input. Ha. Without the full story, I can see I look like a noob.
Nah.

I went from a Lynx Aurora, to a Korg MR-2000, to the Prism for my final print. Each move was a step up in conversion quality. The input levels on the Aurora and the Korg were identical, and that was what the album was 'tuned to' with the api 2500.
I bought the Prism, and the input level was way too hot. I have measured about 3 1/2 db.

I contacted Prism to find out if there were pots inside the unit that I could adjust. They said no.
They sugested the only work around would be to plug into the mic pres instead of the line inputs, engage the pads, and turn them right down.

It is still too hot, but it's workable. I want to build the pads so I can use the line inputs again as obviously, going through the mic pre is not desirable.

Thanks again Rob. :)
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Re: Two 1/2 db and eight one db pads needed

Postby rob » Tue May 08, 2018 9:29 am

I reckon you want a variable pad to be sure you get things right

two pots in a box with XLR or TRS in and out
easy

shoot me an email if you want help
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Re: Two 1/2 db and eight one db pads needed

Postby Ski Spiggy » Tue May 08, 2018 9:41 am

Thanks heaps Rob. If I can get the input to a nice level using the pads, it means I can set and forget. Which is desireable. If it doesn't work out to be fine tuneable enough, I will shoot you an email.
Much appreciated.

:)
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Re: Two 1/2 db and eight one db pads needed

Postby Ski Spiggy » Sat May 12, 2018 10:41 am

Thanks to all who have responded and a huge thankyou to Chris. All sorted.
Clearly, making pads is really easy. It was just a case of messing around with ohm values to the get the right amount of attenuation.
It took a little time to get them spot on. But the end result is superb.
Last edited by Ski Spiggy on Sat May 12, 2018 10:55 am, edited 1 time in total.
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Re: Two 1/2 db and eight one db pads needed

Postby Ski Spiggy » Sat May 12, 2018 10:45 am

Message deleted.
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Re: Two 1/2 db and eight one db pads needed

Postby chrisp » Sat May 12, 2018 6:46 pm

Glad it worked out in the end. Awesome results is what we are about here.
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Re: Two 1/2 db and eight one db pads needed

Postby Ski Spiggy » Sun May 13, 2018 12:15 am

Also a big thanks to Rob who steered me in the right direction via email to avoid tiny value pads. My first go was using a 300 ohm pad, and then experimenting with 10, 11... 20ohm pads in series to get the right amount of attenuation. I achieved the desired attenuation but with a loss in tone.
Thanks to Rob's input, I messed around with using just one pad. And 390ohms was the winner giving a much clearer signal chosen in multiple double blind tests.
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