48v, pad and phase kits for pre's?

cedric · Sep 21, 2005

48v, pad and phase kits for pre's?
i can only find this kit on the web.
it's in australia, and i kinda need some kits now

plus i'm not even sure how it works?

has anyone tried these? how can there be a wire out for the 48v phantom (ext. PSU?)?

http://www.jlmaudio.com/kits.htm

synthetic · Sep 21, 2005

I just follwed the Jensen mic input schematic.

http://www.jensentransformers.com/as/as016.pdf

I'm going to add the pad to my API pre, I already have +48V and Phase. Trust me, you need the pad on an API. I should have listened to the ones who tried to convince me...

alk509 · Sep 21, 2005

[quote author="cedric"]how can there be a wire out for the 48v phantom[/quote]

That's an in, not an out. I.e., You need a phantom PSU.

Peace,
Al.

JustinS · Sep 21, 2005

Hey Cedric,

I've used JLM's go between kits and power supplies & they're great... easy to put together & Joe's an awesome guy to deal with. Al is right, the go betweens are just switching units you'll still need a 48v power supply, Joe's are good - his 3 rail power supply (depending on transformer choice) can output up to +/-34v and a separate 48v rail. Where are you anyways?? Most of the shipping companies are pretty quick, my standard for small packages from the US is about 4 working days!!

Justin.

Sammas · Sep 22, 2005

Yeah... Joe's kits are second to none.

cedric · Sep 22, 2005

i guess what i've narrowed my search down to is a simple switch to give me a 20dB pad on the output of my pre's.

just a simple switch.
but i have no idea what kind of switch to look for... DPDT ?
and to get the correct 20dB pad i must know the output ohm of the pre's right?

soundguy · Sep 22, 2005

you can wire a pad onto a dpdt no problem.

Id suggest using an H pad and not a U pad, I foudn that they sound much better. I know this must sound absurd to some people but Ive built both over the years and the H pads always seem to sound more transparent than the U pads (which makes less sense as there are two more resistors, go figure).

dave

Family Hoof · Sep 22, 2005

With the H pad you can match impedances on both sides instead of just one so that nothing gets loaded down. I believe this is why they'd sound more transparent.

cedric · Sep 23, 2005

could someone please draw me up a nice "schematic"?

http://www.myonlineimages.com/Members/blindboyrecording/images/20dBpad%20DPDT%20switch.jpg

you only have to copy the picture, draw some lines, add some impedances (4 x 650 R1 and 250 R2 ohms?) and you've helped me a great deal.

Neeno · Sep 23, 2005

Here ya go...

Hope it helps...

NewYorkDave · Sep 23, 2005

[quote author="Family Hoof"]With the H pad you can match impedances on both... [/quote]

You can also do that with a U-pad. Remember, we're matching UNEQUAL impedances. With a mic, you generally want to reflect about 2K to the mic and 200 ohms to the preamp, and a properly-designed U-pad will do just this. If you use a "regular" (equal impedance) H-pad, you're either loading down your mic or reflecting too high of a source Z to the preamp. You can design an H-pad for unequal impedances; but if you want to present a high input impedance and a low output impedance, there's no point in having to use the extra resistors.

If you used a 150/150 (or 200/200) H-pad on a mic and thought it sounded more "transparent", it's likely that what you heard was the loading on the mic, attenuating the mids and lows.

There's no accounting for taste, but a pad like the one Neeno posted is technically the better one to use. I'd prefer to use 1K and 220 ohms (instead of 680 and 150), but it's a minor difference.

jeroddumas · Dec 28, 2005

How much attentuation does using 1K and 220 give?

rlaury · Dec 28, 2005

I still have these available.

http://www.groupdiy.com/index.php?topic=1402&highlight=rlaury

Whoops · Sep 16, 2009

jeroddumas said:
How much attentuation does using 1K and 220 give?

jdbakker · Sep 16, 2009

Whoops said:
jeroddumas said:

How much attentuation does using 1K and 220 give?

Click to expand...

Ask Mr. Ohm, he might know.

JDB.
[when math fails: build the pad, connect a 9V battery to the input, measure the output]

jsteiger · Sep 16, 2009

Mr. Ohm says...20db of attenuation

20*LOG(Shunt_R/(Shunt_R+(Series_R*2)))

Best, Jeff

Whoops · Sep 16, 2009

Thanks.

So what would be the benefits of using 1k and 220ohm compared to 680 ohms and 150ohms?

jdbakker · Sep 17, 2009

Whoops said:
So what would be the benefits of using 1k and 220ohm compared to 680 ohms and 150ohms?

http://www.groupdiy.com/index.php?topic=35433.0

JDB.

clintrubber · Sep 17, 2009

cedric said:
48v, pad and phase kits for pre's?
i can only find this kit on the web.
it's in australia, and i kinda need some kits now

FWIW, here's more from Australia:

http://sound.westhost.com/project96.htm

Has PCBs for sale.

Whoops · Sep 17, 2009

jdbakker said:
Whoops said:

So what would be the benefits of using 1k and 220ohm compared to 680 ohms and 150ohms?

Click to expand...

http://www.groupdiy.com/index.php?topic=35433.0

JDB.

Thanks a lot for the link JBD

emrr said:
1k/220r and 619r/169r 'U' pads arrive at same gain result.

1k/220r = crudely 2k22 load to mic and 220r source to preamp.

619r/169r = crudely 1k407 load to mic and 169r source to preamp.

Any mic and preamp combination may like one or the other better. One loads the mic a bit more heavily, both are reasonably speaking correct bridging relationships. With a transformer coupled preamp, the source presented to the input may be the more critical aspect with some transformers.

But I still don't know if I should one or the other.

Why some people preffer the 1K/220r ?
it's because of their mic and preamp combination that works better with those loads, or because it provides safer overall loads?

48v, pad and phase kits for pre's?

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