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Mic attenuator idea - someone should make this!
Old 1st January 2011
Originally Posted by emrr View Post
why own an OP-6 at all then?

it's not a realistic idea, for impedance matching reasons. it's cart before the horse. We need fewer tubes for less gain....different preamp. Use the OP-6 where appropriate, end of story. I put various OP-6 obvious mod ideas in the other thread; I consider them all to be BAD IDEAS because it destroys the monetary value of the unit. Use the right unit; no square pegs in round holes.
Yes, this is the (sad) conclusion I have reached - that I can only use my OP-6s, Ampex 350 and 400 in certain applications if I want to get the best tone from them. In-line pads will always change the sound.

This thread has been very educational for me. I appreciate it very much!

Old 1st January 2011
Lives for gear
emrr's Avatar
The only tempered reality I can offer is that in some cases I'd still rather live with the sound of a pad in a certain combo, because otherwise I'd have to change the combo, and it's proving to be the best combo. In that case, who cares what the pad does? It's still proving to be the best practical sound for the given moment. I live with a studio full of fixed gain antique preamps. They sound great, even though I have to use a pad 90% of the time. I mostly use them with dynamic mics, since condensers are way too hot to match with them. It works, I work.

Even a Sytek transformerless preamp which does a minimum gain of 12 dB will overload when set at minimum with something like an Earthworks condenser anywhere near a drum kit. The Earthworks, and many other modern condensers, need nearly no gain at all, just an input matching/buffering amp that provides phantom power.
Old 1st January 2011
Gear Maniac

Originally Posted by John Suitcase View Post
I realize this would change the sound somewhat, but what about replacing the input transformer altogether? Something with a 1:1 ratio, or even 2:1, rather than padding the input to the existing one? If I'm following the discussion, the OP-6 has an input transformer with some gain,correct?

This would be changing the vintage preamp into something more custom (and probably worth less, even if more functional!)

If the only mics available on earth all had output levels of hot condensers . . . then this is at least is going in the right direction. You still have to get good S/N numbers feeding the grid of a tube. Why lose a champion ribbon pre?
Old 2nd January 2011
Lives for gear
nosebleedaudio's Avatar

If it was me I would use the least amount of pad needed...Say 6dB to start..
Also i would want to know WHERE is it the input trans? The first tube stage?... ect...
If you are clipping at the input trans you have ONLY two choices, PAD the input, or use a different pre...
A pre with 90dB of was NOT designed for kick drum at 6"...
Old 3rd January 2011
Here for the gear

O pad is best

Hi all-

The reason one uses an O pad for a mic attenuator is to keep the impedence the same in both directions. Once pad is inserted, not only should the mic still see the same impedence (at 5k to 10k) as it did without pad, but the pre's input transformer must also still see the output impedence of the mic, approx. 200 ohms.

While a U pad can be built so that the mic and pre still see the the same value of impedence as before insertion, the U configuration is not as balanced as the O. This matter starts to get a bit metaphysical and so it is best to let the ears be the judge. The U pad is prevalent and may be part of the reason that pads generally "suck".

The more balanced or symetrical, the better. Both the O and U can work correctly mathmatically, but that does not mean they will sound the same.

It was while building a pad for an Ampex 350 that I found that the O sounds better, and still better with small caps in parallel with the series resistors.

Old 3rd January 2011
Lives for gear
John Suitcase's Avatar

Originally Posted by RHSuperfly View Post

It was while building a pad for an Ampex 350 that I found that the O sounds better, and still better with small caps in parallel with the series resistors.

What's the reasoning behind the bypass caps?
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