Another Passive Mixer

Gentlemen,

I need a simple passive 3 channel mixer for experimenting with center microphone. I want to incorporate it into my tube pre. The 1st and 3rd channels are "main", and the center channel should be panned between them. The center should have independant volume control, but also, its out should be dependant on "main" volume. Here is what I came up with. Could you check if I did it right, and I'd appreciate if you check if resistor values are correct.

Spasibo bol'shoe!

Anyone? :sad:

Looks fine.

You don't want to add this mixer in front of two mic preamps, do you? This would be rather noisy with such resistor values. As a line level mixer after three pres, it is OK. I guess the three circles to the left are for a first gain stage?

Samuel

Ha! You must be a young'un. Those circles are tubes, my friend.

Marik, I have an idea for you. Give me a little time and I'll draw it up and post it.

[quote author="NewYorkDave"]Marik, I have an idea for you. Give me a little time and I'll draw it up and post it.[/quote]

That´s NYDave...

:thumb: :sam: :guinness:

With a spiced up avatar and all!

My old avatar has broken out of his box and is on a rampage in the streets...



...so his brother is filling in for him now.

Off topic, but is Steeplechase park and Coney Island the same? That guy?s face cracks me up! Where'd they come up with a logo like that? I assume he?s grinning from ear to ear cause he?s having so much fun at the park, right?

[quote author="NewYorkDave"]
Marik, I have an idea for you. Give me a little time and I'll draw it up and post it.[/quote]

:thumb: :thumb: :thumb: :guinness: :guinness:

My best friend lives on Cropsey and 26Av--just a couple stops from Coney Island. I love that place. Every time I am in NYC the first thing we go to a nearby sushi place and have "all you can eat" for $16. The best Albacore in town. Oysters are extra though-- three for a buck. Usually I have at least 15-20--if the world did not have oysters, why would we live then?

After all these fishes get tightly packed in our stomacks, we go home to have some rest and "wet the path"--to have some more Vodka, and then to Brighton Beach to swim, and then to a Russian restaurant for Soup Kcharcho, Pel'meny and Blinzes with sour cherries. Hmmmm.... Yumy :thumb:

It's hard to sum two channels without a lot of interaction between them, unless you're using expensive constant-impedance attenuators. Active mixing seems the way to go in this case. A single triode stage has enough open-loop gain to allow good two-channel summing.
24kB GIF

The panpot is my own variation on the popular dual-pot concept. It gives a good constant-power panning law throughout its range and has a fairly constant input impedance. This comes at a cost of a 6dB minimum insertion loss, though. Notice that the input and feedback resistors at the summing amplifiers are scaled to compensate for this loss, so that the output at the left and right main level controls is unity.

Tim,

I spent a long time writing a detailed reply to your questions, but my connection dropped while I was writing and when I tried to reconnect and post, all my text was blown away! I'm pretty upset about it, but I guess it's just as well since the whole subject was off-topic.

I'll just refer you to this fantastic book... Very good reading while you're staying warm at home this winter.
http://www.amazon.com/exec/obidos/tg/detail/-/1580084559/102-7606616-4993765?v=glance

[quote author="NewYorkDave"]It's hard to sum two channels without a lot of interaction between them, unless you're using expensive constant-impedance attenuators. Active mixing seems the way to go in this case. A single triode stage has enough open-loop gain to allow good two-channel summing.
24kB GIF

The panpot is my own variation on the popular dual-pot concept. It gives a good constant-power panning law throughout its range and has a fairly constant input impedance. This comes at a cost of a 6dB minimum insertion loss, though. Notice that the input and feedback resistors at the summing amplifiers are scaled to compensate for this loss, so that the output at the left and right main level controls is unity.[/quote]

Thank you NYDave!

The problem is that I have already built the pres on PCB, and because of lack of room, I cannot put in additional tube. Also, I should've posted schematics earlier. It is based on Kevin Carter's phono preamp (of course all EQ components are omitted):

http://www.kandkaudio.com/images/sephonopre.pdf

It has over 70db of gain, and I never use more than 50-55db, so losses are not that big of the problem. If I am using attenuator after a trafo, it should be even more expensive constant impedance H type. So wouldn't it be more practical just using more expensive constant imp. input attenuators?

[quote author="NewYorkDave"]Tim,

I spent a long time writing a detailed reply to your questions, but my connection dropped while I was writing and when I tried to reconnect and post, all my text was blown away![/quote]So that happens to you too? I wondered if I was the only one... :wink: Thanks for the effort, though. I'll check the book out. :thumb:

So, how many of these preamps are in your box? Can you use all of them for this three-mic stereo experiment?

[quote author="NewYorkDave"]So, how many of these preamps are in your box? Can you use all of them for this three-mic stereo experiment?[/quote]

Two complete ones, and one without output stage (only first half of the tube--already have 5 Lundahls there :shock: .)