Sharing a VU meter between several preamps possible?

I'm mounting 2 MP-2 and 2 EZ1290 in the same case. I have a bunch of nice vintage meters I'd like to put to use. I'v enever done this before so I'm not certain on what to do exactly.

I don't have room for more than 1 meter so I'm thinking of using a 5 position switch (OFF, pre1, pre2, pre3 and pre4) to switch one pre at a time to that 1 meter. Essentially sharing it.

Do I need a 1P5T or 2P5T? I guess break before make type right?

Last question. Can I get away by using 1 buffer between switch and meter? Would the wire from pre to switch cause any problems when not switched into buffer + meter?

jim

I dont think this would be a prob. Have A hi-z input buffer to da meter, and pick off your signl at a low z output type signal

Thanks shabtek. Just needed a small push.

I'm thinking I would need 2 section rotary switch to be able to isolate all the signals coming from each pre. + and - on their own section each. So I would need a 1P5T 2 section switch .

The buffer I will just either build using breadboard or buy JLM's.

jim

All the old broadcast meter panels you see are exactly that; a meter with a 5-10 position rotary switch and a terminal strip for hooking up different inputs. Hint: usually an 'off' position also. If you're going active/buffered then you don't need to worry about getting a 'proper' 3900 ohm Daven meter attenuator. Some old broadcast limiters also built in an external meter input for checking an external source.

Doug - Good to know its been done before. The OFF position is taken into account. The only thing I'm worried about is the wires from each preamp acting like antennae when they terminate at switch. They will be around 6 to 8 inches long. I guess if at worst they are well shielded it should not cause a problem.

jim

Exactly, Jim. I was worried about the loose wires to the output trafos too, but I checked with friends offline and both assured me it's not a prob. Yes, shielding would only help. I'm planning several projects with limited front panel space and need to share one meter with two channels, so I am doing the same you are. And as mentioned, it's normal way of doing things in older gear.

It's low impedance output, so it's less of a problem. Follow standard twisted and/or shielded wire protocol and you're done. High impedance spots like the secondary of an HA-100 are where you get into more problems with stray pickup and capacitive losses. You worry about length and need for shielding much more there.

the advantage of buffering each source would be less click or pop noise getting to an output, for the cost of an op amp and a few resistors per source(this can be nrea the source as well, eliminating the cable concerns, and the output loading remains constant).
I made a 12 stereo input sub mixer with multiple outputs and sub mixes, used a 1x24 rotary switch and a bank of small relays allowing metering of any input or output on one set of meters, it works great. I always use the SSL meter driver circuit, very easy to build and adjustable.....

You'll still need the 3900 ohm resistor, though; the ballistics of the meter are predicated on a 3900 ohm driving resistance.

Peace,
Paul

nielsk, are you saying to use a buffer for each preamp?

So preamp out -> buffer -> switch -> meter for each?

jim

yes